For current production lasers, the manufacturers' Web sites often provide basic specifications. For older lasers, it's often difficult to obtain detailed specs so estimates based on physical size, and then testing may be the only option.
The sections in this chapter are arranged approximately in alphabetical order by manufacturer.
Red (632.8 nm):
Rated Melles Griot Coherent Model Power Length Model Number ----------------------------------------------- 31-2017-000 0.8 mW 7.00" 05-LHR-601 31-2010-000 0.8 mW 7.00" 05-LHP-601 31-2033-000 2 mW 12.40" 05-LHR-321 31-2025-000 2 mW 12.40" 05-LHP-321 31-2058-000 4 mW 15.50" 05-LHR-151 31-2041-000 4 mW 15.50" 05-LHP-151 31-2074-000 7 mW 18.00" 05-LHR-171 31-2066-000 7 mW 18.00" 05-LHP-171 31-2090-000 10 mW 19.05" 05-LHR-991 31-2082-000 10 mW 19.05" 05-LHP-991 31-2108-000 17 mW 25.07" 05-LHP-925 31-2196-000 17 mW 25.07" 05-LHR-925 31-2140-000 35 mW 40.60" 05-LHP-928 *
* Cynlindrical head in rectangular case.
Green (543.5 nm):
Rated Melles Griot Coherent Model Power Length Model Number ----------------------------------------------- 31-2264-000 0.3 mW 12.40" 05-LGR-321 31-2298-000 1.0 mW 20.09" 05-LGP-293? 31-2772-000 2.0 mW 20.09" 05-LGR-393
Yellow (594.1 nm):
Rated Melles Griot Coherent Model Power Length Model Number ----------------------------------------------- 31-2230-000 2.0 mW 17.95" 05-LYR-173
Orange (611.9 nm):
Rated Melles Griot Coherent Model Power Length Model Number ----------------------------------------------- 31-2207-000 2.0 mW 15.60" 05-LOR-151
I have tested three specific Coherent models:
Rated CDRH New Melles Griot Coherent Model Wavelength Power Power Power Length Model Number ------------------------------------------------------------------------------- 21-2090-000 632.8 nm (Red) 10 mW 30 mW 17 mW 19.05" 05-LHR-991 31-2772-000 543.5 nm (Green) 2.0 mW 5 mW 2.7 mW 20.09" 05-LGR-393 31-2230-000 594.1 nm (Yellow) 2.0 mW 10 mW 4.8 mW 17.95" 05-LYR-173
The "CDRH Power" is what is listed on the safety sticker. The "New Power" was the average power measured on samples of these laser heads I tested that appear to have never been used, or have seen very little use.
All Melles Griot HeNe laser tubes are hard-sealed with essentially unlimited shelf life - 12 years is quoted but for all practical purposes, it is infinite. Most standard tubes have a planar HR mirror with a concave OC mirror with its curvature selected for maximum stability. This long radius hemispherical cavity configuration puts the beam waist at the HR with a slightly diverging beam from the OC. But a compensating curvature on the outer surface of the OC mirror of most laser tubes that are sold as or in standard products results in a positive lens and the beam that exits the laser is quite well collimated. (Specific applications like barcode scanning may call for a divergence other than the minimum possible to avoid the need for an additional external lens.)
And in the "I always wondered about that" department, the correct way to pronouce Melles Griot is
MEL-liss (emphasis on the first syllable).
GREE-o (emphasis on the first syllable).
This was confirmed both by someone who knew Jan Melles and Richard Griot personally, and from a VP at Melles Griot. But apparently, some of their employees don't even get it right. :)
The following data came from a variety of sources including an old Melles Griot brochure, the 1999 catalog, and the Melles Griot Web site. Go to "Product Info", "Lasers", "HeNe" or more directly to Melles Griot Lasers, "Helium-Neon (HeNe)". Then click on any location.
This is not a complete list but probably includes most of those you're likely to come across.
Red (632.8 nm):
Minimum e/2 c/2L Supply Nominal (1) Output Beam Diver- Mode Opr/Strt Tube Tube Size Model Power Diam gence Spacing (Rb=75K) Current Diam/Lgth 05-LHR/P- ------------------------------------------------------------------------------ .4 mW .34 mm 2.40 mR 1360 MHz 1.22/5 kV 3.2 mA 23/118 mm 007 .5 mW .46 mm 1.70 mR 1272 MHz 1.18/8 kV 4.5 mA 25/127 mm 640 .5 mW .47 mm 1.70 mR 1200 MHz 1.29/5 kV 3.3 mA 19/135 mm 002(2) .5 mW .46 mm 1.77 mR 1063 MHz 1.32/5 kV 4.0 mA 25/150 mm 213 .5 mW .49 mm 1.70 mR 1040 MHz 1.25/5 kV 4.5 mA 29/152 mm 700 .5 mW .50 mm 1.61 mR 1039 MHz 1.29/5 kV 4.5 mA 37/152 mm 604 .6 mW .47 mm 1.70 mR 1078 MHz 1.43/5 kV 4.0 mA 25/146 mm 004 .6 mW .85 mm 0.95 mR 787 MHz 1.29/5 kV 4.5 mA 37/200 mm 410 .8 mW .47 mm 1.70 mR 1078 MHz 1.33/5 kV 3.0 mA 25/149 mm 006 .8 mW .46 mm 1.77 mR 1063 MHz 1.32/5 kV 4.0 mA 25/150 mm 211 .9 mW .47 mm 1.70 mR 1078 MHz 1.38/5 kV 3.3 mA 25/147 mm 049 .9 mW .48 mm 1.70 mR 1100 MHz 1.20/5 kV 4.0 mA 25/146 mm 704 .9 mW .48 mm 8.00 mR 1078 MHz 1.31/5 kV 3.5 mA 25/145 mm 041 .9 mW .65 mm 1.24 mR 862 MHz 1.05/5 kV 4.0 mA 28/183 mm 041 1.0 mW .53 mm 1.50 mR 883 MHz 1.47/8 kV 4.5 mA 29/178 mm 900 1.0 mW .59 mm 1.35 mR 687 MHz 1.79/8 kV 6.5 mA 37/226 mm 110 1.0 mW .66 mm 1.25 mR 683 MHz 1.10/8 kV 3.5 mA 28/227 mm 101 1.5 mW .53 mm 1.50 mR 889 MHz 1.71/8 kV 4.5 mA 25/178 mm 008 1.5 mW .58 mm 1.39 mR 793 MHz 1.66/8 kV 5.0 mA 37/228 mm 130 2.0 mW .49 mm 1.65 mR 638 MHz 1.45/10 kV 3.7 mA 29/243 mm 038 2.0 mW .55 mm 1.47 mR 822 MHz 1.94/10 kV 4.5 mA 25/191 mm 009 2.0 mW .59 mm 1.35 mR 687 MHz 1.77/10 kV 6.5 mA 37/226 mm 219 2.0 mW .59 mm 1.35 mR 687 MHz 1.79/10 kV 6.5 mA 37/228 mm 120 2.0 mW .63 mm 1.40 mR 641 MHz 1.82/10 kV 4.5 mA 29/241 mm 088 2.0 mW .72 mm 1.10 mR 612 MHz 1.85/10 kV 6.5 mA 29/255 mm 080 2.0 mW .76 mm 1.06 mR 638 MHz 1.57/10 kV 4.5 mA 29/243 mm 097 2.0 mW .76 mm 1.06 mR 636 MHz 1.71/10 kV 5.0 mA 30/250 mm 073 2.0 mW .79 mm 1.00 mR 574 MHz 1.81/10 kV 6.5 mA 37/270 mm 320 2.5 mW .52 mm 1.53 mR 822 MHz 1.77/10 kV 4.5 mA 25/198 mm 690 2.7 mW .58 mm 1.41 mR 694 MHz 1.81/10 kV 4.5 mA 28/226 mm 082 4.0 mW .80 mm 1.00 mR 438 MHz 2.29/10 kV 6.5 mA 37/353 mm 140 5.0 mW .80 mm 1.00 mR 438 MHz 2.29/10 kV 6.5 mA 37/353 mm 164 5.0 mW .80 mm 1.00 mR 438 MHz 2.08/10 kV 6.5 mA 37/353 mm 150 7.0 mW 1.75 mm 2.05 mR NA-MM 1.90/10 kV 6.5 mA 37/353 mm 160 7.0 mW 1.02 mm .79 mR 373 MHz 2.65/10 kV 6.5 mA 37/410 mm 170 10 mW .65 mm 1.24 mR 341 MHz 2.64/10 kV 6.5 mA 37/440 mm 991 12 mW 1.20 mm 3.40 mR NA-MM 2.09/10 kV 6.5 mA 37/350 mm 185(3) 16 mW 1.47 mm 1.40 mR NA-MM 2.48/10 kV 7.0 mA 37/464 mm 981(3) 17 mW .96 mm .83 mR 267 MHz 3.70/12 kV 7.0 mA 37/600 mm 825 17 mW .96 mm .83 mR 267 MHz 3.70/12 kV 7.0 mA 37/600 mm 925 25 mW 1.23 mm .66 mR 165 MHz 5.10/15 kV 8.0 mA 42/930 mm 827 25 mW 1.42 mm 2.40 mR NA-MM 3.20/10 kV 7.0 mA 42/590 mm 831 35 mW 1.23 mm .66 mR 165 MHz 5.10/15 kV 8.0 mA 42/930 mm 927 35 mW 1.23 mm .66 mR 165 MHz 5.10/15 kV 8.0 mA 42/930 mm 928(4)
LHR models are random polarized; LHP models are linearly polarized. Not all model numbers have both versions. Barcode scanning tubes are nearly all only available random polarized.
For lower power lasers, models ending in an even number are often (but not always) a bare tube, with the corresponding head being the same number incremented by (or ORed with) 1. For high power lasers, the laser head number is listed.
The operating voltage across the tube itself can be found by subtracting the voltage drop across the ballast resistor (I*Rb), from the value listed in the table. Actual starting voltages are typically 3 to 5 times the tube operating voltage (though the specifications may be higher). Note that I've assumed a 75K ballast resistance for all tubes. The actual manufacturer recomendation may differ slightly but 75K should be acceptable for most.
Both random (LHR) and linearly polarized (LHP) models are available for most of the lasers listed above. The only other difference in specifications for red HeNe lasers between these is their price - about 10 to 15 percent higher for a complete polarized laser. So you can imagine the difference in the tube cost alone since everything else is identical. (The output power of "other-color" linearly polarized HeNe lasers compared to similar size random polarized models, particularly for yellow and green which have very low gain, tends to be much less since the losses through the internal Brewster plate become more significant.)
And speaking of prices, if you have to ask, you can't afford a new HeNe laser! But since you asked, prices (Summer 2002) from Melles Griot vary from around $300 for a 0.5 mW laser head to over $4,000 for one rated at 35 mW (power supply sold separately)! Prices in Summer 2005 haven't changed that much but only complete systems can be ordered on-line. Prices: $587.83 (0.5 mW) to $4,532.88 (35 mW). Fortunately, surplus prices tend to be much more reasonable - typically between 5 and 20 percent of these depending on actual age and condition as well as many other factors including your luck in finding a good deal. :)
Green (543.5 nm), random polarization:
Minimum e/2 c/2L Supply Nominal Output Beam Diver- Mode Opr/Strt Tube Tube Size Model Power Diam gence Spacing (Rb=75K) Current Diam/Lgth 05-LGR- ----------------------------------------------------------------------------- .08 mW .88 mm 2.35 mR NA-MM .88/8 kV 3.7 mA 25/149 mm 004 .2 mW .63 mm 1.26 mR 732 MHz 1.56/8 kV 4.5 mA 29/215 mm 025 .2 mW .75 mm .92 mR 373 MHz 2.62/10 kV 6.5 mA 37/410 mm 171 .3 mW .81 mm .99 mR 574 MHz 2.20/10 kV 6.5 mA 37/269 mm 321 .5 mW .80 mm 1.01 mR 438 MHz 2.39/10 kV 6.5 mA 37/351 mm 141 .5 mW .80 mm 1.01 mR 438 MHz 2.39/10 kV 6.5 mA 37/351 mm 151 .5 mW 1.35 mm 1.10 mR NA-MM 1.94/10 kV 6.5 mA 37/351 mm 252 .8 mW .89 mm .92 mR 373 MHz 2.62/10 kV 6.5 mA 37/410 mm 173 1.0 mW 1.3 mm 1.00 mR NA-MM 1.87/10 kV 6.5 mA 37/351 mm 161 1.0 mW .80 mm .86 mR 328 MHz 2.75/10 kV 6.5 mA 37/475 mm 293 1.5 mW .86 mm .81 mR 328 MHz 2.75/10 kV 6.5 mA 37/475 mm 193 2.0 mW .86 mm .81 mR 328 MHz 2.75/10 kV 6.5 mA 37/475 mm 393
Green (543.5 nm), linear polarization:
Minimum e/2 c/2L Supply Nominal Output Beam Diver- Mode Opr/Strt Tube Tube Size Model Power Diam gence Spacing (Rb=75K) Current Diam/Lgth 05-LGP- ----------------------------------------------------------------------------- .2 mW .75 mm .92 mR 373 MHz 2.62/10 kV 6.5 mA 37/410 mm 171 .2 mW .77 mm .90 mR 438 MHz 2.39/10 kV 6.5 mA 37/351 mm 141 .3 mW .77 mm .90 mR 438 MHz 2.39/10 kV 6.5 mA 37/351 mm 151 .3 mW .86 mm .89 mR 373 MHz 2.62/10 kV 6.5 mA 37/410 mm 173 1.0 mW .86 mm .81 mR 328 MHz 2.75/10 kV 6.5 mA 37/475 mm 193 1.0 mW .86 mm .81 mR 328 MHz 2.75/10 kV 6.5 mA 37/475 mm 293
Yellow (594.1 nm), random polarization:
Minimum e/2 c/2L Supply Nominal Output Beam Diver- Mode Opr/Strt Tube Tube Size Model Power Diam gence Spacing (Rb=75K) Current Diam/Lgth 05-LYR- ----------------------------------------------------------------------------- .?? mW ??? mm ?.?? mR NA-MM .??/5 kV 3.? mA 25/149 mm 006 .35 mW .63 mm 1.26 mR 732 MHz 1.62/8 kV 4.5 mA 29/215 mm 025 .35 mW .69 mm 1.09 mR 574 MHz 1.95/10 kV 6.5 mA 37/269 mm 320 .75 mW .80 mm 1.01 mR 438 MHz 2.43/10 kV 6.5 mA 37/351 mm 151 1.0 mW .75 mm .92 mR 373 MHz 2.59/10 kV 6.5 mA 37/410 mm 171 2.0 mW .75 mm .92 mR 373 MHz 2.59/10 kV 6.5 mA 37/410 mm 173 2.0 mW 1.17 mm 1.00 mR NA-MM 2.09/10 kV 6.5 mA 37/351 mm 161
Yellow (594.1 nm), linear polarization:
Minimum e/2 c/2L Supply Nominal Output Beam Diver- Mode Opr/Strt Tube Tube Size Model Power Diam gence Spacing (Rb=75K) Current Diam/Lgth 05-LYP- ----------------------------------------------------------------------------- 1.0 mW .75 mm .92 mR 373 MHz 2.59/10 kV 6.5 mA 37/410 mm 173
Orange (611.9 nm), random polarization:
Minimum e/2 c/2L Supply Nominal Output Beam Diver- Mode Opr/Strt Tube Tube Size Model Power Diam gence Spacing (Rb=75K) Current Diam/Lgth 05-LOR- ----------------------------------------------------------------------------- .5 mW .63 mm 1.26 mR 732 MHz 1.66/8 kV 4.5 mA 29/215 mm 025 2.0 mW .80 mm 1.01 mR 438 MHz 2.49/10 kV 6.5 mA 37/351 mm 151 4.0 mW 1.17 mm 1.00 mR NA-MM 2.07/10 kV 6.5 mA 37/351 mm 161
Infra-Red (1,523 nm), random polarization:
Minimum e/2 c/2L Supply Nominal Output Beam Diver- Mode Opr/Strt Tube Tube Size Model Power Diam gence Spacing (Rb=75K) Current Diam/Lgth 05-LIR- ----------------------------------------------------------------------------- 0.5 mW 1.26 mm 1.59 mR 438 MHz 2.49/10 kV 6.5 mA 37/351 mm 151 1.0 mW 1.33 mm 1.48 mR 373 MHz 2.97/10 kV 6.0 mA 37/410 mm 171
Infra-Red (1,523 nm), linear polarization:
Minimum e/2 c/2L Supply Nominal Output Beam Diver- Mode Opr/Strt Tube Tube Size Model Power Diam gence Spacing (Rb=75K) Current Diam/Lgth 05-LIP- ----------------------------------------------------------------------------- 0.4 mW 1.26 mm 1.59 mR 438 MHz 2.49/10 kV 6.5 mA 37/351 mm 151 0.8 mW 1.33 mm 1.48 mR 373 MHz 2.97/10 kV 6.0 mA 37/410 mm 171
Infra-Red (3,391 nm), random polarization:
Minimum e/2 c/2L Supply Nominal Output Beam Diver- Mode Opr/Strt Tube Tube Size Model Power Diam gence Spacing (Rb=75K) Current Diam/Lgth 05-LFR- ----------------------------------------------------------------------------- 1.0 mW .83 mm 1.60 mR 438 MHz 2.50/10 kV 6.0 mA 37/351 mm 151
Infra-Red (3,391 nm), linear polarization:
Minimum e/2 c/2L Supply Nominal Output Beam Diver- Mode Opr/Strt Tube Tube Size Model Power Diam gence Spacing (Rb=75K) Current Diam/Lgth 05-LFP- ----------------------------------------------------------------------------- 1.0 mW .83 mm 1.60 mR 438 MHz 2.50/10 kV 6.0 mA 37/351 mm 151
Note: Some of the listed values for divergence in particular appear to be questionable. For example, for the same beam diameter, diffraction limited divergence should be proportional to wavelength. The discrepency for the 3,391 nm IR tube is particularly striking. Either the divergence or beam diameter are almost certainly incorrect. It probably doesn't matter much though because the 3,391 nm model is no longer manufactured. I also suspect the output power rating for the 05-LGR-171 may be a bit higher than listed in the source for this information.
Brewster angle window HeNe tubes:
Minimum Supply Supply Nominal Number Output Voltage Voltage Tube Tube Size Model of Power Tube Only Rb=68K Current Diam/Lgth 05-LHB- Windows ------------------------------------------------------------------- 1.0 mW 1,430 V 1,870 V 6.5 mA 37/222 mm 270 1 1.0 mW 1,460 V 1,900 V 6.5 mA 37/253 mm 290 2 3.5 mW 1,080 V 1,520 V 6.5 mA 37/265 mm 370 1 4.0 mW 1,030 V 1,470 V 6.5 mA 37/265 mm 570 1 ??? mW 1,??? V 1,??? V 6.5 mA 37/265 mm 580 1 6.0 mW 1,430 V 1,870 V 6.5 mA 37/351 mm 670 1
The most common application for one-Brewster HeNe tubes was probably for particle counting since by using an external high quality HR mirror, the intracavity flux can be several watts which makes a speck of anything stand out! (Some large one-Brewster HeNe tubes can do as much as 100 W intracavity, not these!). Passing the air/gas/whatever flow through the cavity of a one-Brewster HeNe laser is similar to passing it through the output beam of a high power laser - at a fraction of the cost (and it's much safer as well since if anything macroscopic in size (like an eyeball or piece of paper) were to block the intracavity beam, lasing simply stops with no damage to vision and no risk of fire!
The LHB models all have HR mirrors that are probably optimal for 632.8 nm (red) though newer versions, at least, may be quite broadband and better than 99.9 percent from 590 to 680 nm so operation at some of the non-632.8 nm wavelengths may be possible. However, older versions may not have such nice HRs.
Other variations on these tubes are also produced (though they may be special order). I was given an 05-LGB-580 which has an HR optimized for 543.5 nm (green). With an external green HR, the behavior is very similar to the red version but with loads of circulating green photons instead of red ones. :) I was told that this tube may have been made for the sole purpose of confirming the quality of the mirrors to be used in normal internal mirror HeNe laser tubes. So, I doubt you could buy 1. Maybe 1,000, but not just 1! Applications for such a tube would be very limited due to the low gain as it stops lasing entirely in a few minutes after cleaning the optics just due to dust settling on the B-window.
The 05-LHB-370, 05-LHB-570, 05-LHB-670, and 05-LHB-580 have wide bores and generally operate with multiple transverse modes to achieve maximum intracavity power in particle counting applications. The 05-LHB-270 and 05-LHB-290 have narrow bores like most conventional HeNe tubes. (The 05-LHB-270 appears physically similar to an 05-LHR-120 except for the Brewster window at one end.) The model 05-LHB-570 is the one-Brewster HeNe tube used in the CLIMET 9048 one-Brewster laser head described in the section: A One-Brewster HeNe Laser Tube. You can't tell from the model numbers but both Melles Griot and Hughes style designs may be used. For example, the 05-LHB-570 looks like a normal Melles Griot tube but with a Brewster angle window frit sealed to the metal end-cap instead of an OC mirror. The 05-LHB-580 looks like a Hughes style tube, but with an optically contacted Brewster window instead of an OC mirror (though some Hughes style polarized HeNe tubes are just one-Brewster tubes with an OC mirror attached to a glass tube that slips over the Brewster stem and is itself glued in place). Thus, the 05-LHB-580 is actually a much higher quality (and more expensive) tube than the 05-LHB-570 but you can't tell this from the catalog listing! Here are diagrams of each type:
One possible explanation of why the Hughes style design is used for the high quality tubes with optically contacted Brewster windows is that since Hughes already produced HeNe tubes with a glass Brewster stem (as noted above), when Melles Griot took over the Hughes HeNe laser product line, making the modifications for the graded seal to accommodate the fused silica Brewster stem (needed to match the expansion coefficient of the fused silica window) was probably easier than starting with a metal end-cap.
Zero degree AR coated window HeNe tubes:
Minimum Supply Supply Nominal Number Output Voltage Voltage Tube Tube Size Model of Power Tube Only Rb=68K Current Diam/Lgth 05-WHR- Windows ------------------------------------------------------------------- 4.0 mW 1,030 V 1,470 V 6.5 mA 37/269 mm 570 1 6.0 mW 1,670 V 2,110 V 6.5 mA 37/351 mm 252 2 8.0 mW 1,670 V 2,110 V 6.5 mA 37/351 mm 183 1
Rather than mirrors, one or both ends of these HeNe tubes have optical flats with very high quality AR coatings to permit the use of external mirrors. One advantage of this arrangement is that external optics can be used to control polarization (the output beam of Brewster tubes is always linearly polarized and can't be changed).
The 05-WHR-252 and 05-WHR-183 appear to be identical except for the number of windows - and the loss of 2 mW with the two window version!
Red (632.8 nm):
Output Size Model Power (LxWxH) Applications Price -------------------------------------------------------------------------- ML800 0.8 239x72x74 Student use deomonstrations $389.00 ML810 0.8 239x72x74 Student use demonstrations $399.00 ML811 0.5 181x33x47 Pointer, CE approved $399.00 ML855 5.0 540x72x74 Lecture demos, research, holography $899.00 ML868 0.8 328x72x74 Modulated, lecture demos, communication $489.00 ML869 1.5 328x72x74 Modulated, lecture demos, communication $499.00
Green (543.5 nm):
Output Size Model Power (LxWxH) Applications Price -------------------------------------------------------------------------- ML815 0.08 181x33x47 CE approved $719.00
The actual markings on a typical unit are:
METROLOGIC INSTRUMENTS, INC. DAAA09-86-C-0834 PN 11746797-2 TUBE,LASER,PLASMA,HELIUM-NEON NSN 6920-01-148-4713 WARRANTY FOR 24 MONTHS WARRANTY EXPIRES: FEBRUARY 1989 SERIAL NUMBER: 703-045
There is no doubt this is a military laser. It is a machined stainless steel cylinder about 1.75 inches in diameter by 14 inches in length, with a precision welded flange at the connector-end. (See the photo on the H&R Web site.) It weighs in at over 3 pounds! The tube is potted in a rubbery material which completely fills the entire length of the cylinder with the HV connections via a pair of female contacts. There is no physical difference between the anode and cathode terminals but they are labeled "P1+" and "P2", respectively.
So, you'd think that this laser has to be at least 5 mW, right? Wrong! What's inside appears to be a 9 or 10 inch tube rated at about 1 mW with a TEM00, random polarized beam. The tube is long enough that polarization variations due to mode cycling are relatively small. The sample I have produces about 1.4 mW. It runs best on about 5 mA at 1,250 V, but remains stable down to about 2 mA. The internal ballast resistor is at least 90K ohms (might be a bit larger). So, almost any HeNe laser power supply designed for a 1 to 2 mW laser should be suitable. H&R recomends their model G7-001 but their much cheaper TM91LSR1495 works fine, and the typical barcode scanner brick would probably be adequate as well even though the current is generally lower (3 to 3.5 mA).
I don't know if the tube is simply a barcode scanner tube in a fancy expensive package, or one of Metrologic's "hard seal steel ceramic tubes" that were introduced around 1980. Those seem to have had a rather short life cycle since the higher cost might only be justified in, well, military applications. :) And, much cheaper glass tubes with frit-seals - what we know and love today - came along about the same time. By 1987, modern tube construction we well developed and soft seals had faded into history for most HeNe lasers. Someone I know tried a medical X-ray machine on the head cylinder without success. Gouging out all the potting material and ruining the magnificent packaging would hardly be justified to simply find a common barcode scanner tube inside! With the laser powered (to provide internal illumination), I tried looking in the output-end through a dielectric filter that blocked 633 nm and I think there was glass visible inside but it was hard to tell. The side of the mirror looks somewhat strange but maybe that's just because it is coated with the rubber potting compound.
On the H&R Web site, this laser is listed as a "Ruggedized HeNe Laser Head" used for some sort of weapons training/sighting application. It would also make a decent hammer. If there is a steel ceramic Metrologic tube inside, hammering nails probably wouldn't affect its lasing performance at all. I'd love to know how much one of these beauties cost the American taxpayer. :-)
Here are some specifications for two REO tunable lasers. Both of these models were listed in their 1992 catalog though only the LSTP-1010 shows up in a recent listing. As expected, both are linearly polarized (500:1) since they use a Littrow tuning prism external to the laser tube:
Note the line at 604.6 nm (orange/yellow) which is almost never seen in other other-color HeNe lasers (at least it isn't supposed to be there). :) A new LSTP-1010 with careful cleaning and alignment may actually produce more than 3 times the spec'd power for 543.5 nm, 594.1 nm, and 604.6 nm.
One or more of the other visible HeNe wavelengths may also be present in some samples. I've seen one with a small amount of 629.4 nm and heard of another that produces almost 1 mW or 640.1 nm. These are just not guaranteed in the specifications but may result from subtle variations in the mirror coating wavelength reflectivity functions for the Littrow prism and OC.
There was also an LSTP-0050 which should have similar wavelength specs but the output powers are unknown.
And for only $4,050.00 plus shipping and handling, you can now buy your very own LSTP-1010 through Edmund Industrial Optics and elsewhere. :)
These lasers show up on eBay from time-to-time but are almost invariably dead or dying, though I know of one instance where such a laser turned out to work on all lines at near rated power after some tender loving care. (Apparently, its power supply had died so the laser was put on the shelf for who knows how long, but the tube recovered after being run for many hours.) A PMS tunable laser from 1984 is physically similar to the REO version sold today (2007). However, the Littrow prism has been improved and the heater on the OC mirror has been eliminated. Installing a new tube in an old case is possible but will probably not result in quite the same performance as a new laser. The output power for all lines will not be as high as with a new prism and the green line in particular could be down right whimpy. :) Even so, the laser may still exceed the LSTP-1010 specifications (at least initially), though possibly just barely for the green line. However, there may be surprises like some 640.1 nm or 629.4 nm due to differences in the coatings. Of course, since it's likely that a new tube will likely be almost as expensive as a new laser, a tube swap is not going to be cost effective.
Some photos (from Dave):
(From: Lynn Strickland (firstname.lastname@example.org).)
The five lines are 543.5, 594.1, 604.6, 611.9, and the common (red) 632.8 nm. You might see a flash at 629.4 nm and at 640.1 nm, but nothing to write home about. The 629 and 640 nm lines are so weak, and so close to 633 that they're sometimes hard to distinguish. There should be nothing at the IR lines (1,153, 1,523 or 3,391 nm).
As originally designed, these lasers used a Brewster window tube with a Littrow prism as the wavelength selection mechanism. The tube's internal mirror was a broad band output coupler. Don't know if it's changed, but I doubt it. (Same in 2007. --- Sam.)
The fundamental design issue is that the optimum Bore-to-Mode Ratio (BMR) for green is much higher than for red. (BMR is the ratio of limiting aperture size to mode radius. To get TEM00 operation for green, the optimal number is about 4.2, for red it's about 3.5.) If you know the wavelength, mirror curvature, and spacing, you can calculate the mode radius at any point in the cavity. The capillary bore serves as the limiting aperture, so adjusting bore length and bore diameter sets the BMR, which in turn determines transverse mode purity.
Thus, if you optimize the BMR for green power (which you have to do), the red is under-apertured, and has something like 50% off-axis modes. It's getting close to a doughnut-mode.
REO builds some of the highest 'Q' Brewster tubes in the world (probably THE highest), exclusively for the company, Particle Measuring Systems (PMS). REO and PMS used to be one in the same, but the owner sold off the particle counter biz a few years back, for something like $75 million. They now have some sort of supply agreement. The REO tubes aren't the most robust or mechanically stable, but if you get them packaged right, probably some of the highest power you can get from a given tube length. This is mostly due to coatings (all Ion Beam Sputtered), and a super-polishing process they have for substrates. As they say, it's all done with mirrors. ;)
A green Brewster tube IS a bitch! The original REO (PMS) tube was a 5 mW size - about 15" long. They did a soft-seal on the B-window; because it's fused silica. Don't know if they've gone to optical contacting/graded seal now - I'd hope so.
I think REO added a 7 mW, maybe even a 10 mW size for power. I recall seeing some longer ones at a trade show. As for cavity power, I've seen an REO B-tube with 2 HRs do almost 45 Watts of intra-cavity circulating power. They're probably higher than that now. These puppies are like $1,700 each in volume and only sold to PMS - pretty hard to come by.
There is a weak line at 635.2 nm which could also show up as its gain is higher than that of the 594.1 nm and 604.6 nm lines. 640.1 nm is actually quite strong - next in line after 632.8 nm. See the section: Instant HeNe Laser Theory for a listing. But it's probably killed by the mirror coating selectivity.
Here is a photo of the PMS One-Brewster HeNe Laser Tube and a closeup of the Littrow Prism Tuning Assembly from PMS Tunable HeNe Laser showing its proximity to the one-Brewster tube's Brewster window. There are adjustments for wavelength and transverse (alignment). The Littrow prism is the shiny thing at the far left. The Brewster window is next to it. There is normally a tight fitting metal cover to keep out dust which has been removed to take the photo. Except for the high quality internal OC mirror and window, the HeNe tube itself isn't that much different from the common variety, though the metal envelope - typical of PMS/REO tubes - may help stability. It does have a heater coil on the OC mirror mount. According to a PMS patent (4,740,988: Laser Device Having Mirror Heating), this is to eliminate color centers that may develop in the mirror coatings from exposure to UV in the bore light. (These heaters are on some but not all older PMS HeNe laser tubes.) The resistance is around 31 ohms and it runs on 9 VAC from a small transformer. I've never really seen any definitive improvement in anything when running the heater. New tubes don't need it. The rest of this laser is unremarkable - a brick power supply and case. :)
CAUTION: The Brewster-end of the tube is all glass and fragile. The high voltage is also exposed in that area. So, if you have removed the cover of the laser, take care. It would be a darn shame if a reflex response to contact with the HV resulted in broken glass. :(
CAUTION: DO NOT attempt to remove or even loosen the screws at the bottom of the rear plate. The adjustable Littrow prism mount is directly attached to the rear plate and this is joined to the Brewster stem of the tube via an O-ring-sealed box with a removable cover. Removing the rear plate without observing exactly how this affects the relationship of the Littrow prism mount to the tube's Brewster stem and taking appropriate precautions may also break the tube.
CAUTION: DO NOT turn the micrometer adjustments further than necessary, especially in the tighten direction. I believe there should be enough clearance between the Littrow prism and Brewster window such that contact is not possible, but you really don't want to find out this isn't the case. The total useful range of the Color knob is less than 1 full turn and perhaps 1/4 turn for the Transverse knob. You won't find a blue line by turning the Color knob past green! :)
If the laser needs to be opened, take out the screws ONLY at the top at each end and lift the lid straight up. DO NOT remove or even loosen the screws at the bottom of the rear plate. Note that since the resonator is formed by all parts of the laser case, removing the lid will likely change alignment enough to matter. Thus, it is best done with the laser lasing red so adjustments can be made. Of course, if the laser doesn't work, the alignment won't matter much.
Of course, if the laser was obtained on eBay, then the non-lasing state is normal. :) :)
One problem that limits power in the REO tunable HeNe laser are losses through the Brewster window of the 1-B tube. The Brewster angle is only correct at a single wavelength so there will still be some Fresnel (reflection) at all the others. And, even super polished fused silica isn't perfect so there will still be some scatter. In addition, matching the orientation of the prism and the Brewster window of the tube is also critical to maximize power. If these issues could be eliminated, the available power at all wavelengths would increase, but this would be especially dramatic for the very weak 543.5 nm (green) and 594.1 (yellow). So, what I suggest is to place the tuning prism inside the tube envelope mounted on a two-axis bearing. Coupling through the glass can be via a pair of magnets to adjust tuning (pitch) and transverse mirror alignment (yaw). This is quite simple mechanically. Even simpler would be to attach the tuning prism assembly (also inside the tube) via a flexible metal bellows adjusted via an external mount similar to the one in the present LSTP tuanble laser. In either design, 2 of 3 Brewster surfaces are eliminated from the intracavity beam path. The 3rd one is for the Littrow prism which unfortunately cannot be eliminated unless a high efficiency grating could substitute for the prism. Dust collecting on the optics is also, of course, no longer a problem. :) And, a glass-to-metal or frit seal could be used in place of the soft seal or optically contacted seal presently used to minimize stresses in the Brewster window.
An older Siemens HeNe laser catalog may be found at Vintage Lasers and Accessories.
Legend for Type: SM=Single mode, TEM00; MM=Multimode, P=Linearly polarized.
Red (632.8 nm):
Model Number Power Type Head Tube ------------------------------------------------ 0.5 mW SM LGR-7656 0.5 mW SM P LGK-7650 LGR-7650 0.5 mW SM LGR-7651 0.5 mW SM LGR-7651A 0.6 mW SM LGK-7655 LGR-7655 0.75 mW SM LGK-7639 0.75-1.0 mW SM LGK-7657 0.8-1.4 mW SM LGR-7655-N 1.0 mW SM LGK-7655-S LGR-7655-S 1.0 mW SM LGK-7641-S 1.2 mW SM LGK-7632 LGR-7632 1.5 mW SM LGR-7649 2.0 mW SM LGR-7621S 2.0 mW SM LGK-7672 2.0 mW SM P LGK-7634 LGR-7634 2.2-3.2 mW SM P LGK-7634 5.0 mW SM LGK-7627 LGR-7627 5.0 mW SM P LGK-7628 LGR-7628 5.0 mW MM LGK-7621-MM LGR-7621-MM 5.2 mW SM P LGK-7628-1 LGR-7628-1 5.5-7.5 mW SM P LGK-7628-L 7.0 mW SM LGK-7627-M 10.0 mW SM LGK-7653-8 10.0 mW SM P LGK-7654-8 10.0 mW MM LGK-7627-MM LGR-7627-MM 12.0 mW? SM LGK-7638 15.0 mW? ?? ? LGK-7654-15 15.0 mW SM LGK-7665 15.0 mW SM P LGK-7665-P 18.0 mW SM LGK-7665-18 18.0 mW SM P LGK-7665-P18 20.0 mW SM LGK-7665-20 20.0 mW MM LGK-7658-7 25.0 mW SM P LGK-7626-L 25.0 mW SM P LGK-7626 25.0 mW SM P LGK-7676-L 28.0 mW SM P LGK-7676 30.0 mW SM P LGK-7626-S 30.0 mW SM P LGK-7676-S
Green (543.5 nm):
Model Number Power Type Head Tube --------------------------------------------------- 0.5 mW SM LGK-7770 LGR-7770 0.5 mW SM P LGK-7774 0.5 mW SM P LGK-7786-P50 0.75 mW SM P LGK-7786-P75 1.0 mW SM LGK-7770-S 1.0 mW SM LGK-7785-P100 1.0 mW SM P LGK-7786-P100 1.05 mW SM P LGK-7786-P 1.2 mW SM LGK-7785-P120 1.5 mW SM LGK-7785-P150 1.5 mW SM P LGK-7786-P150 2.0 mW SM LGK-7785-P200 2.5 mW SM LGK-7785-P250 (on request)
Yellow (594.1 nm):
Power Type Model ------------------------------------- 1.5 mW SM LGK-7511 2.0 mW SM LGK-7512 P
Orange (611.9 nm):
Power Type Model ------------------------------------ 2.0 mW SM LGK-7411
More complete specifications are available at the LASOS Web site.
The LGR-7638 laser tube is generally unremarkable except for the reasonably precise three-screw mirror adjuster at the cathode end. There is enough range that as long as you don't lose the beam entirely, it should be low risk to tweak mirror alignment on this laser. In all other respects, the tube looks like a stretch version of shorter Siemens/LASOS bare tubes with two spider bore supports and one square getter.
The following are based on physical measurements of an intact LGK-7638 laser head and my tests of a two samples of somewhat less than pristine samples of the LGR-7638 tube alone. Only one of these came close to new specs with a maximum output power of about 13 mW. Thus the electrical measurements are not likely to be exact, as operating voltage and optimal current may change with use.
The measurements and healthier of the tube samples were provided by Alan Scrimgeour in response to a posting on alt.lasers.
The LGK-7676 resonator consists of 4 full length 5/8 inch diameter rods joined by 10 thick plates. The tube is secured to these plates using sets of 4 screws with padded tips going in from all four sides at most locations. Some sets are adjustable for bore centering and optimizing straightness. The end-plates hold the mirror mounts. Coarse mirror adjustment is via some thinner rods attached to the ends of the main support rods, with pairs of nuts but no springs. This should permit the mirror mounts to be removed and replaced for cleaning of the optics without requiring coarse realignment. Fine mirror alignment uses Allen's head screws to press on rods which slightly warp the aluminum to which the actual mirror cell is attached. It works reasonably well with good sensitivity and repeatability except that the two adjustments at each end aren't quite independent. Note that with this scheme, walking of the mirrors requires turning the screws at the two ends in opposite directions. The fine adjustments are similar to those in the SP-907 but the coarse adjustments for that laser are three spring loaded nuts which means that removing the mirror mounts requires complete realignment (unless you are *really* good at counting turns!).
The entire resonator assembly is mounted on a thick piece of machined L-shaped aluminum fastened with screws at only two locations. However, under about half the thick plates (see above) on both sides of the "L" are adjustment screws to provide some sort of additional support.
The LGK-7676 uses a coaxial tube with about half of its bore exposed (as opposed to the side-arm tube with totally exposed bore used in Spectra-Physics lasers). While this does result in a more compact package (overall dimensions under 3"x3"x39"), there is less space for IR suppression magnets. In fact, the LGK-7676 only has two sets of magnets (in proximity to less than 25 percent of the bore) for this purpose but could definitely use more. Adding moderate strength magnets (greater than refrigerator strength but much less than rare-earth disk drive strength) almost anywhere along the bore - even outside the large gas reservoir - resulted in a noticeable increase in output power - about 1 percent for a single magnet. I would guess that with enough magnets, a 10 to 20 percent boost would be possible.
There are both anode and cathode ballast resistors of 81K and 27K, respectively. The power supply connector has 3 pins - anode, cathode, and Earth ground. But note that this pinout is not the same as on the physically similar connector on Spectra-Physics lasers. Thus, a Spectra-Physics power supply cannot be used on a Siemens/LASOS laser or vice-versa without modification or bad things will happen to the laser head and/or power supply. Check the power supply and laser head wiring to be sure they are compatible if not originally mated!
The sample I tested is an LGK-7676S with a spec'd output power of at least 30 mW. Of course, since I like to spend as little as possible to acquire these things, mine is a high mileage tube which apparently served hard duty in some sort of high speed printer since there was toner all over it. These are turning up on eBay (and possibly from surplus outfits directly), probably being replaced when their output power drops below a certain value by tiny diode lasers. :)
I was able to run it on my SP-255 exciter only by reducing the anode ballast resistor to 60K and removing the cathode ballast resistor entirely. Prior to this surgery, even with the input voltage to the SP-255 at 140 VAC (the upper limit of my Variac), it would only run for a minute or two (and only if it felt like it) and then cut out, not to restart for several minutes. With the modifications, it will now run all day at 120 VAC input, though restarting was sometimes still a bit of a problem until I added circuitry in an external pod to the SP-255 to boost its starting voltage. (Note that this may not be needed for LGK-7676, SP-907/107/127, and similar size lasers with lower mileage tubes.) See the section: Enhancements to SP-255.) The SP-207 should be able to drive this laser without problems but I don't happen to have one of those.
After bore straightening and mirror adjustments, I was able to squeeze more than 19 mW out of the laser at a somewhat reduced operating current (10 mA instead of the spec'd 11.5 +/- 0.5 mA). (I'm using the lower current only so I can look forward to increased power by a simple tweak in the future.) It would exceed 20 mW if when fully warmed up, the laser was shut off for 30 seconds and then restarted. But the output power would drop back to its previous level over the course of a minute or so once the "good" gas had time to migrate back out of the bore or something. :)
Regrettably, Spectra-Physics no longer manufactures any HeNe laser tubes. They appear to sell selected complete HeNe laser systems from Research Electro-Optics, Inc. (REO) and the SP-117A stabilized HeNe laser - but even that uses a Melles Griot tube!
Here is a chart of some older Spectra-Physics HeNe lasers. Most of these are from a 1988 catalog (along with 1988 prices). Not all information was available, thus the "???" in places. You can go to the Spectra-Physics (now Newport) Web site for current models (which are now quite limited, possibly to the SP-117A frequency/intensity stabilized laser only). But the hobbyist and experimenter is much more likely to acquire the classic ones below (unless very well endowed!). Typical output power when new may have been 50 percent or more greater than the value listed.
Scans of original Spectra-Physics brochures and catalogs which include some of these lasers can be found at Vintage Lasers and Accessories.
Minimum Laser Wave- Mirrors Output Exciter Original Model length Int/Ext Power Model Price Description/Comments ------------------------------------------------------------------------------- 107 632.8 nm E 30 mW? 207 $ ?,??? Similar to 127 (1) 112 632.8 nm E 10-30 mW 200 $ 6,000 RF excited 115 632.8 nm E 3-6 mW 200 $ 4,650 RF excited, 24" resntr. 116 632.8 nm E 25 mW 250 $ 13,250 " " tuning prism 120 632.8 nm E 6 mW 256 $ 1,980 Small lab laser (2) -01 1,152 nm E 1 mW " $ 2,800 " " -02 3,391 nm E 1.25 mW " $ 2,800 " " 122 632.8 nm E 5 mW? 253A $ ?,??? Short version of 124 (3) 123 632.8 nm E 10 mW? I $ ?,??? Between 120 and 124 124B 632.8 nm E 15 mW 255 $ 4,900 Popular lab laser (3) -01 1,152 nm E 2 mW " $ 5,500 " " -02 3,391 nm E 5 mW " $ 5,500 " " 125A 632.8 nm E 50 mW 261A $ 16,000 Huge-head >125 lbs. (4) -01 1,152 nm E 10 mW " $ 17,500 more than 6 feet long. -02 3,391 nm E 10 mW " $ 17,500 " " 127 632.8 nm E 35 mW I $ ??,??? 39 inch resonator (1) 130 632.8 nm E 0.6 mW I $ 1,525 Self contained (5) 130B 632.8 nm E 1.5 mW I $ 1,225 " " 130C 632.8 nm E 1.5 mW I $ ?,??? " " 131 632.8 nm E 1.0 mW 251 $ 2,350 632.8 nm E 1.0 mW 252 $ 2,825 132 632.8 nm I 2 mW I $ ??? Self contained (6) 132P 632.8 nm I 1.8 mW I $ ??? Self contained (6) 132M 632.8 nm I 3.5 mW I $ ??? " " 133 632.8 nm I 2 mW 233 $ ??? Separate rect. head (5) 133M 632.8 nm I 3.5 mW 233 $ ??? " " 133P 632.8 nm I 1.8 mW 233 $ ??? " " 134 632.8 nm I 3-5 mW I $ ??? Self contained 135 632.8 nm I 3-5 mW 235 $ ??? Separate rect. head (5) 136 632.8 nm I 2 mW 236 $ ??? Cyl. head, rand. pol. (8) 136P 632.8 nm I 2 mW 236 $ ??? Cyl. head, lin. pol. (8) 137 632.8 nm I 2 mW 236 $ ??? Cyl. head, rand. pol. (8) 137P 632.8 nm I 2 mW 236 $ ??? Cyl. head, lin. pol. (8) 138 632.8 nm I 2 mW 236 $ ??? Cyl. head, rand. pol. (8) 138P 632.8 nm I 2 mW 236 $ ??? Cyl. head, lin. pol. (8) 142 632.8 nm I 2 mW 248 $ ??? Separate rect. head (5) 142P 632.8 nm I 1.5 mW 248 $ ??? " " 143 632.8 nm I 4 mW 247 $ ??? " " 143P 632.8 nm I 3.5 mW 247 $ ??? " " 144 632.8 nm I 5 mW 247 $ ??? " " 144P 632.8 nm I 4.5 mW 247 $ ??? " " 145 632.8 nm I 2 mW 248 $ ??? Separate cyl. head 145P 632.8 nm I 1.5 mW 248 $ ??? " " 146 632.8 nm I 4 mW 247 $ ??? " " 146P 632.8 nm I 3.5 mW 247 $ ??? " " 147 632.8 nm I 5 mW 247 $ ??? " " 147P 632.8 nm I 4.5 mW 247 $ ??? " " 155 632.8 nm I 0.5 mW I $ 310 Educational laser (6) 156 632.8 nm I ??? mW I $ ??? " " 157 632.8 nm I 3 mW I $ 525 Self contained 159 632.8 nm I 5 mW I $ 630 " " 102R 632.8 nm I 2 mW 212 $ 610 Cyl. head, rand. pol. 102P 632.8 nm I 1.5 mW " $ ??? Cyl. head, lin. pol. 105R 632.8 nm I 5 mW 215 $ ??? Cyl. head, rand. pol. 105P 632.8 nm I 5 mW " $ ??? Cyl. head, lin. pol. 117 632.8 nm I 1 mW ???? $ ??? Stabilized (7) 117A 632.8 nm I 1 mW 217A $ 3,500 " " " 117C 632.8 nm I 1 mW I $ ??? " " " 118A 632.8 nm I 1 mW 218A $ ?,??? " " " 119 632.8 nm I 0.07 mW 259 $ 5,775 " " "
For more details on the popular large-frame Spectra-Physics HeNe lasers, see the next section.
It should be possible to possible to obtain orange (611.9 nm), yellow (593.9 nm), and green (543.5 nm) output with similar modifications (at least for the longer lasers), though the gain of these lines is only a fraction of that for the red or IR lines (1152.3 nm and 3391.3 nm) so output power will be lower.
Some photos of these lasers can be found in the Laser Equipment Gallery under "Spectra-Physics Helium-Neon Lasers". Old brochures can be found at Vintage Lasers and Accessories.
Spectra-Physics Laser: SP-120 (1) SP-124B (2) SP-125A ------------------------------------------------------------------------------- OUTPUT Wavelength (nm): 632.8 632.8 1152.3 3391.3 632.8 1152.3 3391.3 Minimum Power (mW): 5.0 15 2.5 5.0 50 10 10 BEAM CHARACTERISTICS Beam Diameter (mm): .65 1.1 1.4 2.5 1.8 2.4 4.1 Beam divergence (mR): 1.7 .75 1.0 1.8 .6 .8 1.4 RESONATOR CHARACTERISTICS Transverse Mode: TEM00 Degree of Polarization: 1000:1 Angle of Polarization: Vertical (+/-5 Degrees except SP-120, +/-20 Deg.) Resonator Configuration: Long Radius Resonator Length (cm): 39 70.1 177.0 Longitudinal Mode Spacing: 385 MHz 214 MHz 85 MHz PLASMA TUBE Plasma Excitation: +3.7 kV, 6 mA +5 kV, 11 mA -6 kV at 30 to 35 mA (RF Opt: 15 W at 46 MHz) Starting Method: ~8 kV ~12 kV Trigger pulse on isolated (Direct from Exciter) bar adjacent to tube. AMPLITUDE STABILITY Beam Amplitude Noise: <.3% RMS <.3% RMS <2% RMS (RF: <.5%) Beam Amplitude Ripple: <.5% RMS <.2% RMS <.5% RMS (RF: <.6%) Long Term Power Drift: <5% over 8 hours and 10 °C Warmup Time: 30 Minutes 30 Minutes 1 Hour ENVIRONMENTAL CAPABILITY Operating Temperature: 10 to 40 °C Operating Altitude: Sea Level to 3,000 m (10,000 ft.) Operating Humidity: Below Dew Point POWER REQUIREMENTS Power Supply: 115/230 VAC, 50/60 Hz, +/-10% Exciter Model (DC): SP-256 (1) SP-255 (2) SP-261A Input Power: 50 W 125 W 456 W PHYSICAL CHARACTERISTICS Laser Head Size: 3.26" (W) x 3.26" (W) x ??? (W) x 3.66" (H) x 3.66" (H) x ??? (H) x 18.48" (L) 32.00" (L) ??? (L) Laser Head Weight: 7.5 lb 25 lb 100 lb Power Supply Size: 7.25" (W) x 7.25" (W) x 13" (W) x 3.72" (H) x 3.72" (H) x 6" (H) x 9.88" (D) 9.88" (D) 18" (D) Power Supply Weight: 7.5 lb 7.5 lb 30 lb
The 1974 brochure for the SP-124A lists 611.8 nm (orange) as an optional wavelength, power not specificed. The 594.1 nm (yellow, 11 mW) and 543.5 nm (green, 5 mW) wavelengths were also mentioned in a paper but although mirror sets for yellow at least were available, it's not known if they were from SP or an official SP product. The green may have required changes to gas pressure/fill ratio and operating current as well.
Actual power from these lasers may be much more than their ratings would indicate, especially when new: greater than 35 mW for the SP-124B and up to 200 mW (!!) for the SP-125A with optimal mirrors, 150 mW with a tuning prism. (However, I don't know how likely such 'hot' samples, especially of the SP-125A, really were.)
There is also a model 127 (OEM versions: SP-107 and SP-907) with the following partial specifications (632.8 nm). Beam diameter: 1.25 mm, divergence 0.66 mrad, length 38.75", height and width: about 4", power requirements: 5 kV, 11.5 mA, starting voltage: 12 kV + 6 kV pulse. This appears to be the only large-frame Spectra-Physics HeNe laser in current production. See the next section.
Mirror sets for green (543.5 nm), yellow (594.1 nm), and orange (611.9 nm) were available for the longer lasers. (The SP-120 and SP-122 may be too short for the low gain green line.) There were also tunable versions of the SP-125 and possibly others. The SP-116 was a tunable version of the RF excited SP-115. These used a Littrow prism in place of the HR mirror.
See the following sections for more information on these Spectra-Physics lasers.
Even without powering up the laser there are two things that can be inspected to get a rough idea of the tube's health (beyond the overall condition and that it isn't in a million pieces):
The actual plasma tube in these is the SP-082 with various -dash numbers after probably related to the actual output power. I believe higher -dash numbers mean a higher output power tube (at least when new). These laser heads may sometimes be listed based on the tube number but they are the same thing since you really can't buy a tube by itself unless someone was bored and decided to totally disassemble one!
The SP-107/907 resonator is over 38 inches long and of the "Stabilite" design similar to that of the SP-122 and SP-124 but the mirror mounts differ. There is an internal L-shaped structure and outer thinner metal skin. There are two versions, differing the design of their mirror mounts:
In addition to mirror alignment, there are a pair of bore centering brackets about 1/2 and 3/4 of the way relative to the cathode-end of the laser. These have an effect on both output power and beam shape. Carefully tweaking for maximum output power should done in conjunction with mirror alignment.
The bare resonators have no beam centering adjustments and I don't see any on the packaged SP-127.
The tube has a side-mounted cathode chamber like other SP lasers but it is quite oversize - about twice the typical diameter. The ballast resistors (2 at the anode-end, 1 at the cathode-end, all 27K ohms) are mounted externally in glass tubes sealed with rubber and heat-shrink tubing. The power supply connector has 3 pins - cathode, anode, and Earth ground. But note that this pinout is not the same as on the physically similar connector on Siemens/LASOS lasers. Thus, a Spectra-Physics power supply cannot be used on a Siemens/LASOS laser or vice-versa without modification or bad things will happen to the laser head and/or power supply. Check the power supply and laser head wiring to be sure they are compatible if not originally mated!
IR suppression magnets are placed at every available location on two sides of the bore. Thin rubber boots seal the space between the Brewster windows and mirrors but these can be pushed back to permit cleaning of the windows and mirrors in-place (barely and not recommended unless the resonator has been previously disassembled as the optics stay quite clean). Some of these lasers include a metal cover and electrical heaters to decrease the warmup time required to achieve rated power and stability. CAUTION: The part of the rubber boots surrounding the tube are easily torn if the boots are removed since they tend to stick to the tube.
Depending on specific model, the SP-107/127/907 has a minimum output power of 25 or 35 mW but may do much more when new. The following is from a Spectra-Physics datasheet. Only the specs for the red version are shown but any of the other HeNe lasing wavelengths (except possibly 3.391 nm which may require a wider bore tube and removal of the IR suppression magnets) should be possible by substituting appropriate optics. A yellow or green version would be nice. :)
Spectra-Physics Laser: SP-107B ----------------------------------------------------------------- OUTPUT Wavelength (nm): 632.8 Minimum Power (mW): 25 or 35 BEAM CHARACTERISTICS Beam Diameter (mm): 1.25 Beam divergence (mR): 0.66 RESONATOR CHARACTERISTICS Transverse Mode: TEM00 Degree of Polarization: 500:1 Angle of Polarization: Horizontal (+/-5 Degrees) Resonator Configuration: Long Radius Beam Waist Location: Outer surface of output mirror Resonator Length (cm): 95 Longitudinal Mode Spacing: 161 MHz PLASMA TUBE Type: Hard-seal (later versions), cathode in side-arm Operating Voltage: 5 (+/- 0.4) kV, 11.5 (+/- 0.5) mA Starting Voltage: ~15 kV Lifetime: Greater than 20,000 hours AMPLITUDE STABILITY Beam Amplitude Noise: <1% RMS Beam Amplitude Ripple: <1% RMS Warmup Time: 20 Minutes (95% power) ENVIRONMENTAL CAPABILITY Operating Temperature: 10 to 50 °C Operating Humidity: 5-90% non-condensing POWER REQUIREMENTS Power Supply: SP-207A (110/220 VAC +/- 10%) SP-207A-1 (100/200 VAC +/- 10%) SP-207B (90-130 VAC or 180-260 VAC) PHYSICAL CHARACTERISTICS Laser Head Size: 3.7" (W) x 3.7" (H) x 38.75" (L) Laser Head Weight: 23 lb Power Supply Size: 2.4" (W) x 1.4" (H) x 10" (L) Power Supply Weight: 3 lb
Complete specifications for the SP-107B can be found at Vintage Lasers and Accessories Brochures.
It is possible to run these lasers on the smaller linear SP-255 exciter but starting may be erratic or not work at all (at least for non-pristine tubes) unless the AC line voltage is increased to 125 VAC for starting (it can then be backed off somewhat while operating). A bleeder resistor of 200M ohms or so rated for 15 kV can be installed to discharge the power supply capacitors after shutdown as starting of the longer SP-107/127/907 tube apparently requires the voltage to rise from close to 0 V to start reliably on the SP-255's whimpy starter. An alternative and better solution is to add a passive boost circuit to the starting multiplier of the SP-255. This can be in an external pod requiring no modifications to the exciter itself. Note that the added starting voltage may not be needed for LGK-7676, SP-907/107/127, and similar size lasers with lower mileage tubes. If your laser starts reliably, don't worry about it. Otherwise, see the section: Enhancements to SP-255.) Make sure the laser head frame is securely connected to the power supply (and earth) ground. Since the operating voltage and current are well within the capabilities of the SP-255, the laser and power supply should both be happy once started (though the AC line voltage may still need to be slightly above 115 VAC to minimize drop out/restarts if there are line dips, expecially for a high mileage tube which may have increased operating voltage). Changing the jumpers to use one of the lower line voltage taps on the SP-255's power transformer would probably help in a marginal case (low line voltage, or a laser with a higher HeNe tube voltage or higher ballast resistance) where regulation can't be maintained with adequate current without using a Variac to boost line voltage.
The laser tube is about 20 inches long with separate bore and gas chambers side-by-side. The bore uses rather thin glass tubing and is a very large diameter for a HeNe laser - about 3 to 4 mm ID - consistent with early HeNe laser technology. The laser head is nicely mounted with lots of fine machined hardware. It has no IR suppression magnets. There are two RF connectors on the side for the Spectra-Physics model 200 RF-type power supply. One of the connectors is for the actual RF signal; the other is for starting. There is an impedance matching network located under the "tube deck". This consists of a series LC circuit (C is adjustable for peaking the tuning) between the RF input and case with the output taken from the junction of the L and C. The RF drives a dozen or so electrodes with alternating polarities in close proximity to the tube bore. The start connection goes to the input of a potted transformer which produces a several kV pulse when the "Start button" on the exciter is pressed. The starting pulse goes to a separate small electrode clamped near the center of the tube bore.
The laser has external adjustable mirrors mounted on the very solid precision milled black anodized aluminum box support structure. Both mirrors have screw adjustments for coarse alignment not accessible from outside the case without removing the end-plates. The front mirror also has external fine adjustments in X and Y via two precision Lufkin micrometers and the rear mirror is mounted on a precision slide with an external micrometer adjustment for mirror separation (try to find that on any modern laser!). I don't know if the intent of this axial adjustment (over 1/2" of travel) was to fine tune the longitudinal or transverse modes or both. Since the resonator frame would experience little if any heating (and expansion), the micrometer could be used to center a longitudinal mode and maximize output for this low gain laser. In addition, the larger movement could possibly be used to select a particular transverse mode pattern, though actually achieving TEM00 operation in such a wide bore laser might not be possible.
The power supply for the SP-115 is a high quality 15 to 25 watt 40.68 MHz RF source consisting of a crystal controlled oscillator and a power amplifier using a 4x150 tube. All active elements are tubes, of course, but out of character for the era, the oscillator and driver are built on a printed circuit board. Overall, the system looks like something straight out of the ARRL Handbook (which is probably where the design came from!).
Not surprisingly, on the sample I have, the tube has leaked and only produces a weak purple glow when the RF is turned on. The getter has the "white cloud of death" syndrome and without an aluminum can cathode, there is no possibility of getter action anywhere else. (Not that a tube this far gone would have any chance of revival in any case. The tube would make an ideal candidate for refilling since the vacuum could be breeched by cutting the exhaust nipples at either end of the gas ballast without contaminating the Brewster windows.) The SP-200 does do a nice job of lighting 20 W fluorescent lamps and most likely screwing up radio reception in the neighborhood. :)
There was also a Spectra-Physics model 116 laser which appears similar but has a tuning prism to enable wavelength selection. It goes without saying that a working sample of an SP-116 would be a real prize. :)
Photos of a SP-120 laser head and the SP-120 resonator and tube can be found in the Laser Equipment Gallery (version 1.85 or higher) under "Spectra-Physics Helium-Neon Lasers". One thing the photos don't show because it had probably been removed, is the "starter helper" electrode, clamped to the bore near the side-arm. This is connected to the positive (anode) supply via a 100 pF HV capacitor. So, the initial rise in voltage produces a pulse on that electrode which helps to ionize the gas. Given the whimpy starter of the SP-256, it probably is worthwhile insurance. But I can understand why it was removed - getting the tube out for replacement or Brewster window cleaning is very difficult with that assembly in place.
The complete user manual for the SP-120 laser with SP-256 exciter can be found at Spectra-Physics Model 120 Laser with 256 Exciter Operation Manual. On the one sample of the SP-256 exciter that I've seen, the current was set for 7.2 mA. However, I don't know if this is the default optimum setting for the SP-120 laser or whether it had been tweaked. (The specs list 7 mA at 3.7 kV. But less than 6 mA will work on a healthy tube.)
There is also an SP-120S. The "S" stands for "Shutter" and indeed, these have a plastic shutter lever to block the beam. They also have really cheapo plastic end-covers which block access to the screws and thus make it impossible to do any adjustment without removing them entirely. Perhaps that's a good thing. :)
There are also IR versions indicated by additional numbers after the model: A 120-1 is 1,152 nm and a 120-2 is 1,523 nm, output power not known but probably not much. So, if you obtained an SP-120 on eBay that has a tube with a nice shiny getter and good discharge color but no beam, check the dash number! Some versions might have a black VIS-blocking filter in front of the output mirror, so that would be another clue. It's hard to pass red light through a black filter. :)
The resonator uses three-screw adjustable mirror mounts for coarse alignment (tweaking these is a true pain!). Fine alignment is done via a pair of recessed hex screw adjustments at each end which actually shifts the tube position at each end without affecting the mirror alignment. Each screw moves the end of the tube diagonally ( \ , / ) along a line intersecting the center of the mirror. So, use opposing pairs to walk the alignment. The adjustment screws are accessible via a pair of holes visible once the circular bezel/optics mount is unscrewed. It is possible to replace the tube in about 5 minutes without requiring major mirror re-alignment (no need to touch the coarse adjustments, only the tube centering).
The resonator is constructed from 3 pieces of thick very nicely machined aluminum stock - an L-channel and 2 end-plates bolted together to form a very rigid structure. It is supported at only three points and essentially floats inside the outer case (the "Stabilite" name as discussed for the SP-124 laser, below) which isolates the resonator from external stress (or so it is claimed). So, the clunking you hear when changing the position of the laser head is normal.
CAUTION: Unless the tube has been removed, there should be no need to clean the optics. Since there is no way to clean the Brewster windows with the tube in place and no way to clean the mirrors without removing them, it is a royal pain to be avoided. Remove, clean, install, test and tweak, repeat until output power comes back to what it was before attempting this stunt. :)
The one I obtained also used the strange SP-253A exciter - a switchmode power supply which sends medium voltage AC to a voltage multiplier/boost module in the laser head. See the end of the next section for more on this. There is also an SP-123 which appears similar but with an internal power supply. (Not sure why the large difrerence in output power in the table, above, though. Another reference to these lasers also shows a large difference of 3 and 7 mW for the SP-122 and SP-123, respectively.)
The SP-124 laser head is a box about 76 mm (H) x 76 mm (W) x 813 mm (L) (3" x 3" x 32"), nicely massive for its size. There are threaded beam apertures at both ends though the HR is backed by a solid aluminum plate so I don't think much light would ever get through that even if there was leakage through the mirror!
This is one of SP's "Stabilite" series lasers. This approach to frequency stabilization is based on a mounting system that employs optimally located pivots in an attempt to minimize the coupling of gravitational and vibrational torques and other distorting forces to the resonator cavity itself. In the SP-124, most of the mass of the laser head is in such an optimally mounted heavy solid frame with roughly an L cross section that runs nearly the full distance between the mirror mounts and attached to each of them at three points.
Adjustments accessible externally at each end of the laser allow the beam alignment (X and Y) to be tweaked very accurately by moving the entire optics chassis relative to the head mounting studs (which accept 6-32 screws or rubber feet). The adjustment scheme is sort of interesting (to me, at least): A V-shaped block (bolted to the rosonator and case) sits between a pair of wedges (part of the mounting stud assembly) that can be moved up and down via a pair of screws (call them A and B) and retained in position by a stiff spring. Rotating both A and B equally in the same direction moves the beam in Y; rotating A and B equally in opposite directions moves it in X. The setting may then be locked.
The external mirror HeNe tube is clamped in rubber mounts at its ends and also stabilized at the 1/3 and 2/3 (approximately) positions. Metal bellows join the tube mount brackets to the mirror mounts and, in conjunction with the rubber seals, prevent dust and dirt from getting on the inside surfaces of the mirrors and on the Brewster windows. The mirror mounts have hex head bolts for adjustments with set screws to prevent their settings from changing over time. An additional metal bellows joins the OC to the treaded output aperture.
The HeNe tube itself is a bare capillary about 7 mm OD with a 1.1 mm ID (no, I didn't measure it - just trust the specs!). The cathode, getter assembly, and HeNe gas reservoir is in a side-arm at the output-end of the laser bent to run parallel to the bore. It is about 32 mm x 178 mm (1-1/4" x 7") with the 'can' electrode nearly filling the glass envelope. The anode is (naturally) at the other end of the bore along with the three 9.8K ohm (5 W at least) ballast resistors also in a parallel side-arm inside the gas envelope as apparently is the case with other Spectra-Physics lasers of this era. Interesting, they are just ordinary Ohmite power resistors. I guess this approach does reduce problems with high voltage insulation breakdown but it would be a shame if the laser went bad because a $.50 resistor failed and could not be easily replaced! The total value of about 30K ohms would seem to be rather low but might have been selected to match the needs of the SP-253A exciter (see below) or additional external ballast resistors may be required. The SP-124B version of this laser may use a more normal 81K ballast resistance.
A series of relatively weak (e.g., refrigerator note holder strength) ceramic magnets 14 mm (W) x 22 mm (L) x 6 mm (H) (9/16" x 7/8" x 5/16") are mounted in close proximity under (15 magnets) and on one side (24 magnets) all along the length of the bore wherever they fit. (See the section: Magnets in High Power or Precision HeNe Laser Heads for an explanation of their purpose.) The approximate arrangement is shown below. I may have the poles backwards (which is of course irrelevant). A cheap pocket compass came in handy to determine the pole configuration!: The magnets were positioned with their broad faces about 2 mm from the bore.
Magnets N_S_N_S_N_S_N_S_N_S S_N_S_N_S_N_S_N N_S_N_S_N_S_N_S_N on side |_|_|_|_|_|_|_|_|_| |_|_|_|_|_|_|_| |_|_|_|_|_|_|_|_| (24) ------------------------------------------------------------- HR end ============================================================= OC end of bore ------------------------------------------------------------- of bore Magnets N_S_N S_N_S N_S N_S S_N S_N S_N S_N S_N S_N_S N_S_N below |_|_| |_|_| |_| |_| |_| |_| |_| |_| |_| |_|_| |_|_| (15) N_S_N +-----+-----+ Where: |_|_| = 2 adjacent ceramic magnets: |N S|S N| +-----+-----+I assume that the only reason there aren't 24 magnets below the tube is that the holes in the Stabilite frame got in the way.
Apparently, there must have been a couple of power supply options for the SP-124. Most of these lasers appear to use the Spectra-Physics Model 255 Exciter (SP-255). This is a traditional HeNe power supply providing operating and start voltage through a high voltage BNC connector. However, the laser I have apparently is supposed to use an SP-253A Exciter, a model for which no one (including Spectra-Physics) seems to have any information or even acknowledge exists though I have since found out that the SP-122 laser, a model slightly shorter than the SP-120 but built more along the lines of an SP-124, may have also used the SP-253A (possibly a slightly different version or at least different jumper options). For more information on what I have found out so far about the exciter, see the section: Spectra-Physics Model 253A Exciter (SP-253A).
Unfortunately, on the system I obtained, the boost/start module (which is what I assume was supposed to be inside the head to attach to the exciter) had been ripped out with the cable just chopped off and thus I can't even determine what was there originally. So, I removed the multiconductor cable and replaced it with a HV coax (terminated with a standard Alden connector) and wired it directly to the tube anode terminal and chassis ground (recall that the ballast resistors are inside the tube. Yes, I know, the 30K ballast resistance may be too low for use with the SP-255!)
Using my SP-255 to power the head, I get a nice pink glow in the bore (more red than orange indicating a rise in pressure from slow leakage over the years) but as expected, no coherent light. The low ballast resistance is fine as far as maintaining a stable discharge (I don't know if this would still be the case if the gas pressure in the tube were correct). Maybe someday in the far distant future after that hot place freezes over AND those pigs start flying, I will get around to regassing the tube! :)
The SP-125A tube has a common cathode in the middle of the tube with two anodes, one at each end. The dual discharges are driven from its SP-261A Exciter which provides 6 kV at up to 35 mA. The SP-250 Exciter is also compatible with this laser.
With a bit of rewiring of the laser head, one could feed the anodes separately reducing the individual current requirements so that a pair of power supplies similar to the SP-255 could be used. With this sort of scheme, it should also be possible to selectively power only one of the discharge paths for reduced beam output if desired. Yes, I know, why would you ever want *less* power? :)
Two sets of ballast resistors in the laser head totaling 87K ohms (75K+12K) provide the operating voltage to each of the anodes of the dual discharge tube. They are located between the anodes and chassis ground (The SP-261A's output is negative with respect to ground. Thus, ground is the positive supply voltage). The HeNe tube's single cathode is attached directly to the negative output of the SP-261A.
The starter operates in a manner similar to that of the method of triggering the xenon flashlamp in a typical electronic flash unit or solid state laser power supply - by pulsing an external electrode in close proximity to the HeNe tube bore. The whole tube is supported by metal rods which are insulated from the cavity structure by nylon disks. One of the rods is the trigger electrode. The starter runs off a voltage from the 75K/12K ohm taps of both ballast resistors ORed together so that it repeatedly generates a trigger pulse until BOTH discharges have been successfully initiated.
The SP-261A also has a low power RF output (this isn't the same as the RF power supply option mentioned below) which drives a pair of plates in proximity to the HeNe tube. The RF is supposed to stabilize the laser power (presumably by some sort of discharge dithering process). However, the RF apparently also results in interference with local radio stations. :(
An RF power supply option is/was also available. (Possibly some version of the SP-200 though the specs don't quite match for the one I have. See the section: Spectra-Physics Model 200 Exciter (SP-200).) This would replace theSP-261A and starter entirely by driving the tube directly with radio frequency energy - 15 W at 46 MHz. Note the greatly reduced power to the tube compared to the 150 to 210 W for the DC discharge! The drive is applied via coax from a BNC connector on the back of the laser to a resonant circuit about midway in the laser head. The two phases of the output of the resonant circuit connect to a pair of 0.1 inch diameter bars running the length of the tube about 0.6 inches from the centerline suspended from insulators.
Unfortunately, many SP-125s that appear as surplus are not good for more than long boat anchors (or as a parts unit for salvage of the optics and frame). Unless the tube has been replaced relatively recently, being soft-seal, it has likely leaked to the point at which the getter can no longer clean up the contamination. Refilling is the only option and that cost would make what you paid for the laser look like pocket change. And, refilling a HeNe tube is generally not a realistic basement activity. So, if you come across an SP-125 at a low price, unless it is guaranteed to lase, buyer beware. An SP-125 sold "as-is" almost certainly means the seller couldn't get it to work (not that everything possible wasn't tried) since they likely know it is worth 10 times as much in operating condition!
Also see the section: SP-120, 124, and 125 HeNe Laser Specifications and Spectra-Physics Model 261A Exciter (SP-261A).
(From: Marco Lauschmann (email@example.com).)
The SP125A is absolutely beautiful with much chrome and a metallic blue cover! It is nearly 2 meters long and looks like an older large-frame argon ion laser. A Spectra-Physica scientist noticed that this device will deliver twice the rated power with no problems. Others have claimed as much as 200 mW for the red (632.8 nm) model!
The tube assembly used in the SP-127 is the same as the SP-107B described above, with the side-arm plasma tube itself typically labelled "082-2 (25 mW), 082-3 (35 mW), or 082- (either). It has optically contacted Brewster windows rather than Epoxy seals, so it should have essentially unlimited shelf life. A brick power supply provides the required 11 to 12 mA at 5 kV, switchable between 115/230 VAC. The case is similar to those used for SP's ion lasers except that the SP-127 has slots on top to view the cheery glow of the bore discharge. :) Mirrors are relatively easily removable and replaceable without requiring major realignment, and swappable to change wavelengths. I'm not sure of all the wavelengths besides red (632.8 nm) that were supported by Spectra-Physics, but orange (604.6 nm and 611.9 nm), yellow (594.1 nm), and the near-IR lines (1,152 nm and 1,523 nm) would likely be possible without also replacing the tube. However, green (543.5 nm) might require a different gas-fill and the mid-IR line (3,391 nm) might require a larger bore to get any sort of reasonable power.
Unfortunately, SP has stopped manufacturing the SP-127 and sold off their parts inventory to Cambridge Lasers Laboratories, Inc., who will still rebuild these (and other SP HeNe lasers) - for a price. :)
The only readily available HeNe lasers with similar output power now are the internal mirror Melles Griot 05-LHR/P-927/928. The newer versions of these are traditional HeNe cylindrical laser heads mounted in a rectangular case, presumably for added thermal stability - or so they look simlar to the SP-127!
The tube inside the lasers in the photos is the typical small Spectra-Physics side-arm type (like those in the SP-155 and other similar lasers also shown on the Web page above) but with Brewster windows instead of mirrors. However, earlier versions may look a bit different with a side-arm for the anode as well and really early versions (SP-130, no B) actually used a heated filament for the cathode (though for some reason, the schematic of the SP130 with the heated filament is dated slightly later than the schematic of the SP130B with the cold cathode design).
Based on the length of the tube, I would have expected its output power to be in the 2 to 5 mW range. However, from the specifications in the manual, it turns out to be only 0.75 mW when used with the hemispherical mirror configuration (planar and 30 cm radius of curvature), but capable of a TEM00 beam despite its wide bore (2.5 mm). With a confocal configuration using a pair of 30 cm mirrors, the beam is multimode (non-TEM00) and output power may be as much as 1.5 mW.
When I obtained the first of these lasers (the one in the top two photos), the tube actually still lit up but there was no output beam. At first I thought it might even have a chance of working since the discharge color looked sort of reasonable, though somewhat less intense than I would have expected. Fiddling with the optics didn't yield any positive results. And then, when I wasn't looking, the discharge went out! As best I can tell, a crack must have opened somewhere in the tube and it is now at much higher pressure or up to air - bummer! I can find no visible damage or any evidence of this except that it won't start even on a much larger HeNe power supply and shows no signs of a glow from an RF source. So far, the getter hasn't changed color.
I don't think this laser was ever really alive - the tube was probably gasy or helium deficient or something but I still can't explain what happened. The only place it could have leaked that I can't see is under the anode connection which is kind of potted but there shouldn't have been any heat there to cause such a problem.
And to compound my disappointment, I dinged the OC removing the tube. Enough of it may be left to still work but the optics appear to be soft-coated as the AR coating came off totally by just barely touching it. However, that still hurts. Sometimes, you just have one of those days. :(
The laser in the third photo was DOA with an up-to-air tube, seriously damaged mirrors (coatings mostly gone), and evidence of prior dissection attempts (cut wires, etc.). The tube in that one is probably one of the earliest non-heated filament types with a small cathode and separate side-arm for the anode.
However, I have since obtained a third SP-130B which originally had a red/blue discharge. But while running for a few hours, the color gradually changed to a mostly correct white-ish red-orange. And, with an optics cleaning and alignment, this SP-130B actually lases. The output power is not up to spec - about 0.25 mW at maximum current (it's rated at 0.75 mW) - but that's still a bit amazing considering its age. See the section: Reviving a Spectra-Physics Model 130B Antique Laser for details. I've had it for over 5 years now (since 2000) and it's output hasn't changed noticeably. I run it for a few seconds almost daily just to let it know that it's loved and that seems to keep it happy.
The internal power supply accounts for much of the weight and most of the height of the box and consists of:
There is no actual starter - the open circuit voltage of the power supply is about 5,000 VDC but drops to around 1,500 VDC under load.
For more info and schematics, see the section: Spectra-Physics Model 130 HeNe Laser Power Supply (SP-130).
Now, the question becomes: Do I leave the dead ones intact as examples of antique lasers or replace their tube and optics with modern 3 mW barcode scanner tubes (about the largest that would fit height-wise, a 1 inch diameter tube) to have working lasers? I guess there's nothing special about 3 mW HeNe lasers so leaving them intact would be the best option. And, it would be a shame to only have 3 mW when the power supply is easily capable of driving at least a 5 mW tube. In order to do a test with an SP098-2 barcode scanner tube (actual output: 2.8 mW), I had to add 500K ohms of ballast resistance in addition to what is built into the power supply to get the current low enough so the adjustment would include the optimum current setting. (I can hear the antique connoisseurs breathing a collective sigh of relief!) Who knows, maybe someone will drop replacement tubes and mirrors in my lap someday! Hint, hint. :)
There is also an SP-130C laser which is virtually identical in construction and function, except for the lack of an external current adjust pot.
Photos of a typical SP-155 can be found in the Laser Equipment Gallery under "Spectra-Physics Helium-Neon Lasers".
The HeNe laser tube is the classic Spectra-Physics side-arm design but with the anode electrode mounted about halfway along the length of the bore. The same tube with the anode mounted at the end would produce around 4 to 5 mW. In fact, the Spectra-Physics 157 (3 mW) and 159 (4 mW) lasers are virtually identical except for the tube's anode location and the use of a larger power supply. (The SP-156 may be similar but I haven't seen one to confirm.)
The power supply for the SP-155 is a basic transformer/doubler/multiplier design with a single transistor current regulator. The power supply on later versions of the SP-157 and SP-159 lasers may be a potted brick instead of a discrete PCB but all of the SP-155 lasers appear to retain the older quaint power supply design. :)
Note that other manufacturers sell (or have sold) lasers identical in appearance to the SP-155. For example, there is a Uniphase model 115ASL-1 and a Liconix L-388 (even though it is made by Uniphase). However, these use a hard-seal Uniphase barcode scanner HeNe tube (similar to a model 098 with a tiny collimating lens attached to its OC to reduce divergence) rather than the fancy Spectra-Physics side-arm tube we know and love. But their power supplies are similar or identical to that used in the SP-155. (There is also a Spectra-Physics model 155ASL which is physically identical to the Uniphase and Liconix lasers except for the name on the front. I assume it has the same construction though I haven't seen the insides of one up close and personal.)
Also see the section: Spectra-Physics Model 155 HeNe Laser Power Supply (SP-155).
The RMM355 is multi-transverse mode laser, which in itself is a novelty. This sample has an output power of about 40 mW 8.3 mA. (Yes, that's 40 mW.) The beam is generally circular with what is basically a top-hat profile (more or less flat with ripples), has a divergence of about 2.7 mR, and is random polarized. The model number does include "R" and "MM". :) The RMM355 (which is an earlier model, not listed on the Spectral Web site) is rated at 35 mW minimum output power and typically does 40 to 44 mW after warmup. The current version is the RMM355L which is rated at 42 mW minimum at 10 mA, and typically does 48 mW after warmup. Spectral actually has an even larger model which has a minimum output power of 60 mW!!. Wow, darn, I want one! :)
The laser head is a rectangular aluminum extrusion, capped at both ends with what look like black Plexiglas plates apparently attached with adhesive which has so far resisted my best efforts to remove them. The head is about 2-3/16x2-3/16x34-3/4 inches but the actual tube length is not known. There are no screws or mounting holes anywhere. However, based on the spec'd longitudinal mode spacing of 175 MHz, the tube in the RMM355L has a mirror spacing of about 33 inches - nearly the length of the laser head. I measured the operating voltage on the RMM355 and it is about 3,380 VDC, within the tolerance limits of the spec'd value for the RMM355L of 3,300 V, so the tube length is probably the same. The HeNe laser tube has internal mirrors and is probably of relatively conventional design, but with a wide bore. There is a simple hole in the output cap for the beam to pass (no shutter) and a hole in the rear plate for the Alden cable. I'm sure I could get more power by aligning the mirrors but it doesn't look like there is any easy non-destructive way of getting inside at either end. They seem to be glued all too well. What's the fun without tweakability! :)
Thankfully, regardless of the looks of the power supply box, the actual power supply is a Laser Drive brick, 2900 V at 7.8 to 8.3 mA, adjustable. It was set all the way up on my sample. 40 mW at 8.3 mA isn't too shabby but I tested the laser head using an SP-255 on a Variac and the it produces about 43 mW at 10 mA and 44 mW at 10.5 mA. I have since acquired a power supply that is adjustable via an external pot and goes up to 12 mA (which is apparently acceptable for this laser, at least for a short while). With that, I can get 48 mW at 12 mA. :)
Except as noted, these are all cylindrical laser heads with lab-style power supplies. Note that the divergence values for multimode (non-TEM00) lasers, and even whether some are TEM00 or multimode, may not be correct due to errors in both the on-line and printed datasheets I've seen.
I have two sets of specifications here. The first were mostly from the JDSU Web site as of 2006 but a few may be from other sources:
Red (632.8 nm):
Minimum e/2 c/2L Nominal <------ Model -------> Output Beam Diver- Mode Operating Tube Laser Power Power Diam gence Spacing Voltage Current Head Supply System ------------------------------------------------------------------------------- .5 mW .48 mm 1.70 mR 1090 MHz 1.35 kV 4.0 mA 1108/P 1205 1308/P .8 mW .48 mm 1.70 mR 1090 MHz 1.35 kV 4.0 mA 1107/P 1205 1307/P 1.5 mW .63 mm 1.30 mR 730 MHz 1.70 kV 4.9 mA 1101/P 1201 1301/P 2.0 mW .63 mm 1.30 mR 730 MHz 1.70 kV 4.9 mA 1103/P 1201 1303/P 2.0 mW .63 mm 1.30 mR 730 MHz 1.80 kV 6.5 mA 1122/P 1206 1322/P 5.0 mW .81 mm 1.00 mR 435 MHz 2.35 kV 6-6.5 mA 1125/P 1202 1325/P 7.0 mW .81 mm 1.00 mR 435 MHz 2.45 kV 6-6.5 mA 1137/P 1202 1337/P 10 mW .68 mm 1.30 mR 320 MHz 3.10 kV 6.5 mA 1135/P 1216 1335/P 17 mW .70 mm 1.16 mR 257 MHz 4.10 kV 6.5 mA 1144/P 1218 1344/P 22 mW .70 mm 1.16 mR 257 MHz 4.10 kV 6.5 mA 1145P 1218 1345P 25 mW .70 mm 1.16 mR 257 MHz 4.10 kV 6.5 mA 1145 1218 1345
The models 1508/P and 1507/P are self-contained "Novette" lasers that run from DC wall adapters but have identical specifications to the 1308/P and 1307/P, respectively.
Green (543.5 nm):
Minimum e/2 c/2L Nominal <------ Model -------> Output Beam Diver- Mode Operating Tube Laser Power Power Diam gence Spacing Voltage Current Head Supply System ------------------------------------------------------------------------------- .25 mW .70 mm .98 mR 441 MHz 2.25 kV 5.5 mA 1652/P 1207 1352/P .50 mW .70 mm .98 mR 441 MHz 2.25 kV 5.5 mA 1653 1207 1353 .50 mW .80 mm .86 mR 325 MHz 2.70 kV 5.0 mA 1673P 1208 1373P .75 mW .70 mm .98 mR 441 MHz 2.25 kV 5.5 mA 1654 1207 1354 1.00 mW 2.50 mm ?.?? mR NA-MM 2.25 kV 5.5 mA 1654M 1207 1354M .75 mW .80 mm .86 mR 325 MHz 2.70 kV 5.0 mA 1674P 1208 1374P 1.00 mW .80 mm .86 mR 325 MHz 2.70 kV 5.0 mA 1675 1208 1375 1.50 mW .80 mm .86 mR 325 MHz 2.70 kV 5.0 mA 1676 1208 1376 1.60 mW 2.70 mm ?.?? mR 325 MHz 2.70 kV 5.0 mA 1676M 1208 1376M
Yellow (594.1 nm):
Minimum e/2 c/2L Nominal <------ Model -------> Output Beam Diver- Mode Operating Tube Laser Power Power Diam gence Spacing Voltage Current Head Supply System ------------------------------------------------------------------------------- 1.00 mW .73 mm 1.00 mR ?? MHz 2.25 kV 5.5 mA 1677 1207 1377 1.50 mW 2.50 mm 1.00 mR NA-MM 2.25 kV 5.5 mA 1678 1207 1378
Orange (611.9 nm):
Minimum e/2 c/2L Nominal <------ Model -------> Output Beam Diver- Mode Operating Tube Laser Power Power Diam gence Spacing Voltage Current Head Supply System ------------------------------------------------------------------------------- 3.00 mW .74 mm 1.10 mR ?? MHz 2.25 kV 5.5 mA 1679 1207 1379
The "M" versions for the above lasers are apparently multimode but with incomplete specifications. (The "M" here is apparently not the same as for the ones listed below.)
The next set is what are currently found in the .pdf on the JDSU Web site in 2010. Most of the specifications are the same except for operating voltage (maybe JDSU calibrated their HV probes!) but a few models are no longer present:
Red (632.8 nm):
Minimum e/2 c/2L Nominal <------ Model -------> Output Beam Diver- Mode Operating Tube Laser Power Power Diam gence Spacing Voltage Current Head Supply System ------------------------------------------------------------------------------- .5 mW .48 mm 1.80 mR 1090 MHz 1.25 kV 4.0 mA 1108/P 1205 1308/P .8 mW .48 mm 1.70 mR 1090 MHz 1.25 kV 4.0 mA 1107/P 1205 1307/P 1.5 mW .63 mm 1.30 mR 730 MHz 1.70 kV 4.9 mA 1101/P 1201 1301/P 2.0 mW .63 mm 1.30 mR 730 MHz 1.70 kV 4.9 mA 1103/P 1201 1303/P 2.0 mW .63 mm 1.30 mR 730 MHz 1.80 kV 6.5 mA 1122/P 1206 1322/P 5.0 mW .81 mm 1.00 mR 435 MHz 2.30 kV 6.0 mA 1125/P 1202 1325/P 7.0 mW .81 mm 1.00 mR 435 MHz 2.30 kV 6.0 mA 1137/P 1202 1337/P 10 mW .68 mm 1.30 mR 320 MHz 3.10 kV 6.5 mA 1135/P 1216 1335/P 17 mW .70 mm 1.15 mR 257 MHz 3.80 kV 6.5 mA 1144/P 1218 1344/P 22 mW .70 mm 1.15 mR 257 MHz 3.80 kV 6.5 mA 1145P 1218 1345P 25 mW .70 mm 1.15 mR 257 MHz 3.80 kV 6.5 mA 1145 1218 1345
The models 1508/P and 1507/P are self-contained "Novette" lasers that run from DC wall adapters but have identical specifications to the 1308/P and 1307/P, respectively.
Green (543.5 nm):
Minimum e/2 c/2L Nominal <------ Model -------> Output Beam Diver- Mode Operating Tube Laser Power Power Diam gence Spacing Voltage Current Head Supply System ------------------------------------------------------------------------------- .25 mW .70 mm .98 mR 441 MHz 2.25 kV 5.5 mA 1652/P 1207 1352/P .50 mW .70 mm .98 mR 441 MHz 2.25 kV 5.5 mA 1653 1207 1353 .50 mW .80 mm .86 mR 325 MHz 2.70 kV 5.0 mA 1673P 1208 1373P .75 mW .70 mm .98 mR 441 MHz 2.25 kV 5.5 mA 1654 1207 1354 .75 mW .80 mm .86 mR 325 MHz 2.70 kV 5.0 mA 1674P 1208 1374P
Yellow (594.1 nm):
Minimum e/2 c/2L Nominal <------ Model -------> Output Beam Diver- Mode Operating Tube Laser Power Power Diam gence Spacing Voltage Current Head Supply System ------------------------------------------------------------------------------- 1.00 mW .73 mm 1.00 mR ?? MHz 2.25 kV 5.5 mA 1677 1207 1377
Orange (611.9 nm):
Minimum e/2 c/2L Nominal <------ Model -------> Output Beam Diver- Mode Operating Tube Laser Power Power Diam gence Spacing Voltage Current Head Supply System ------------------------------------------------------------------------------- 3.00 mW .74 mm 1.10 mR ?? MHz 2.25 kV 5.5 mA 1679 1207 1379
Some of these laser heads have an "M" version (or only come in an "M" version) which have 2 inch diameter mounting rings permanently attached.