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.
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 1.18/5 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 .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 .48 mm 8.00 mR 1078 MHz 1.31/5 kV 3.5 mA 25/145 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 111 1.0 mW .66 mm 1.25 mR 683 MHz 1.10/8 kV 3.5 mA 28/227 mm 101 2.0 mW .49 mm 1.65 mR 638 MHz 1.45/10 kV 3.7 mA 29/243 mm 038 2.0 mW .59 mm 1.35 mR 687 MHz 1.79/10 kV 6.5 mA 37/228 mm 121 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 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 321 2.5 mW .52 mm 1.53 mR 822 MHz 1.77/10 kV 4.5 mA 25/198 mm 691 4.0 mW .80 mm 1.00 mR 435 MHz 2.35/10 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 151 7.0 mW 1.02 mm .79 mR 373 MHz 2.65/10 kV 6.5 mA 37/410 mm 171 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)
Notes:
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.
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 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!
Here are the optical and stabilization specifications for the 05-STP-901 (from Melles Griot):
Optical Specifications ---------------------------------------------- Output Wavelength: 633 nm Output Power: 1 mW M2: <1.1 Beam Diameter (1/e2): 0.5 mm Far-Field Divergence (1/e2): 1.60 mrad Polarization: Linear, >1000 Mode: TEM00 Stabilization Characteristics - Frequency Stabilized Mode ------------------------------------------------------------- Frequency Stability (1 min/1 hr/8 hr): +/-0.5/2.0/2.0 MHz Power Stability (1 min/1 hr/8 hr): 1.0% rms Frequency Offset: +/-150 MHz Temperature Dependence: 0.5 MHz/°C Stabilization Characteristics - Intensity Stabilized Mode -------------------------------------------------------------- Frequency Stability (1 min/1 hr/8 hr): +/-3.0/5.0/5.0 MHz Power Stability (1 min/1 hr/8 hr): +/-0.1/0.2/0.2% rms Frequency Offset: +/-50 MHz Stabilization Characteristics - General --------------------------------------------------------------- Noise: 0.05% rms Lock Temperature Range: 10 °C to 30 °C Time to Lock: <30 minutes
The specifications for the SP-117A should be similar.
The unit I acquired is of relatively recent manufacture (as these things go) - 1996. The only major problem I found with it was a dead HeNe laser power supply brick - a Laser Drive unit rated 4.5 mA at 1,600 V, similar to the one in the SP-117. It appears to be a standard model except for a hand-printed label with "0.03 percent noise". So, it's either built with better filtering or is specially selected for this application from standard units. Using an external HeNe laser power supply temporarily allowed the controller to be tested. However, it appears to be much more finicky than the original SP-117 in Frequency Mode and would only stabilize with one of my SP-117-compatible laser heads. It basically ignored one that had a slightly leaky photodiode and my home-built clone, simply turning on the "Locked" LED but not actually doing anything. All three of these laser heads stabilize reliably on the much older SP-117 controller. I suspect that an adjustment of the gain of the photodiode preamps would take care of this - probably just turning it up all the way. So, perhaps I shouldn't be so hard on it. :)
Switching to Intensity Mode at first resulted in the heater simply turning on. The offset pot had to be adjusted to get the mode signals to be in the required range for the locking circuitry to operate, but then it would lock in either mode, with perhaps 30 seconds required to settle down.
Switching from Frequency to Intensity Mode or back caused the Locked LED to flash and the Locked relay to chatter for a few seconds. I'm not sure if this is normal behavior, but it doesn't seem to affect anything functionally. (The Locked relay provides a set of SPDT contacts that can be used to control auxiliary equipment, though there is no external connector for it. But a cable could be wired to the PCB pads and snaked out through the ventilation slots on the bottom of the case.)
Monitoring the heater drive signal on an oscilloscope shows how sensitive this feedback scheme really is. Even playing music at a moderate level evoked a detectable response. Tapping on the concrete floor resulted in an oscillation that took a few seconds to die out.
The electronic design of the SP-117A and 05-STP-901 clearly has it roots in that of the SP-117 (no A) but in addition to the added circuitry for the intensity mode, the frequency control loop has been upgraded to a pure integrator (with a few additional op-amp stages). The PCB layout is completely new and TL084s have replaced LF347s. But much of it looks like it is unchanged from the SP-117 design. The heater drive is a crude pulse width modulator rather than linear pass transistor. Considering the care with which the PCB is laid out with separate analog and digital grounds and linear everything else, it seems strange to have this source of high level digital noise. The input is +12 VDC from a linear power supply. +9 VDC is provided by a LM317 linear regulator. A 555 timer generates the PWM clock and also the -9 VDC power via a charge pump. Timing delays are implemented using several CMOS monostables.
Also see the sections starting with: Description of the SP-117 and SP-117A Stabilized Single Frequency HeNe Laser for more details of the electronics including complete schematics for both the SP-117 and SP-117A/05-STP-901.
For best performance, the controller should be adjusted to match a the specific laser head. There are only three pots inside, so this isn't that complex a procedure!
Adjustments for MG-05-STP-901 and SP-117A:
Pots R9 and R10 (500K ohms) set photodiode preamp gain while R13 (50K ohms) sets balance in INTENSITY mode. All measurements should be made with respect to AGnd (TP7). An oscilloscope is desirable for the INTENSITY mode adjustments but not essential.
It's possible that an earlier PCB revision of the MG-05-STP-901 or SP-117A may have different parts designations. In particular, the SP-117 - no "A" - has other part numbers but it should be obvious which pots and test points to use.
FREQUENCY mode:
The LOCKED LED should not be on at this point (even if it was before the adjustments were made). If one of the pots is fully CW but the signals can't be made equal, reduce
The system is basically working at this point but for the final adjustments, let it remain this way for at least another to give everything time to warmup fully.
INTENSITY mode:
Adjustments for SP-117:
The SP-117 only has FREQUENCY mode, which is functionally identical to FREQUENCY mode of the SP-117A. There are also 3 pots. R11 and R13 (the two 500K pots) are equivalent to R9 and R10 of the SP-117A with R12 (the 50K pot) adjusting the position on the gain curve. I do not know why a similar function to this last pot isn't included in the SP-117A. Or, perhaps it is and my schematics have errors. Errors? Nah. :)
The LOCKED LED should not be on at this point (even if it was before the adjustments were made).
The system is basically working at this point but for the final adjustments, let it remain this way for at least another hour so to give everything time to warmup fully.
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
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107 632.8 nm E 30 mW? 207 $ ?,??? Similar to 127 (1)
115 632.8 nm E 5 mW? 200 $ ?,??? RF excited, 24" resntr.
116 632.8 nm E 5 mW? 200? $ ?,??? " " 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 $ ?,??? " "
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.
117A 632.8 nm I 1 mW 217A $ 3,500 Stabilized (7)
118A 632.8 nm I 1 mW 218A $ ?,??? " " "
119 632.8 nm I 0.2 mW 259 $ 5,775 " " "
Notes:
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
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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
Notes:
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. :)
This system is still in production and has a sticker price of just under $5,000. It consists of a cylindrical laser head and power supply/controller. Go to Spectra-Physics/Newport and search for "117A".
The 05-STP-901 from Melles Griot appears to be the same system as the SP-117A except for the front panel decor and color scheme as it has the same specifications, controls, indicators, and connectors - including the strange three-pin Spectra-Physics HV connector not found on any other Melles Griot lasers. In fact, the PCB inside the 05-STP-901 case has the Spectra-Physics logo on it and "Fab" and "Assy" numbers that begin with "117"! As if this is not enough, the 640 MHz mode spacing of the 05-STP-901 listed in the Melles Griot catalog is the same as the Spectra-Physics 088-2 HeNe laser tube used in the SP-117. And, Melles Griot *does* have an 05-LHR-088 tube which matches the 088 physically and has a mode spacing of 641 MHz. Coincidence? I don't think so. :) (However, inquiries to Melles Griot have not indicated any acknowledgement of this, nor the option to actually buy such a tube without the attached laser.) Thus, a new SP-117A would probably have a Melles Griot tube inside since Spectra-Physics has been out of the HeNe laser tube business for some time. See the section: Melles Griot Stabilized HeNe Lasers. However, at least some of these tubes have an AR coating on the HR mirror (likely in addition to being wedged) as well as on the OC mirror. The purpose would be to futhre minimize backreflections and to get the most power from the waste beam since that's used for the mode sampling photodiode pickup. So, an AR coating on the HR is one way of determining that the tube you have is from or for a SP-117/A or 05-STP-901 stabilized laser, rather than a barcode scanner. Common non-stabilized HeNe lasers - even very expensive ones - do not have this.
A search of the Spectra-Physics Web site used to return a link to a model 117 with some confusing text about the model 117, 117A, and 117B, but that 117 isn't the same as the original SP-117 or SP-117A described below, and the page seems to have disappeared. It even mentioned Brewster windows but none of these lasers ever had Brewster windows! The SP-117B was probably an OEM version of the SP-117A, possibly superseeded by the SP-117C, covered later. There may also have been an SP-117D, similar to the SP-117/A, also for OEM applications.
The following description applies to both the SP-117 and SP-117A (and MG 05-STP-901) unless otherwise noted. The laser head I dissected was an SP-117, though I expect the newer ones to be very similar. A typical SP-117 is shown in Spectra-Physics Model 117 Stabilized HeNe Laser System. The SP-117A is in an similar package with the Frequency/Intensity mode keylock switch and Locked LED added. The PCB is a completely new layout to accomodate the added circuitry for Intensity mode but everything else is similar. Why change a good thing?
The HeNe laser head is powered from a HeNe laser power supply brick (approximately 1,700 V at 4.5 mA) via the usual strange Spectra-Physics screw-lock HV connector, with a separate cable with a DB9 connector for the photodiode signals and heater power. The only thing non-standard about the brick may be a lower p-p ripple and noise specification but there is no special external regulation of this power supply. However, for it to turn on requires that the interlock plug be present on the back of the controller, that the microswitch inside the HV connector be depressed by a plastic pin in the HV plug, and that pins 2 and 7 on the signal connector be jumpered.
The cylindrical laser head contains the tube, output optics, and beam sampling assembly. A view of the parts after disassembly is shown in Spectra-Physics Model 117 Stabilized HeNe Laser Head Components. Sampling is from the waste beam at the HR-end - simply a polarizing beamsplitter (inside the black cylinder, upper left) feeding a pair of solar cells/photodiodes (glued to the metal bracket attached to it). Since this is at the HR-end of the tube, it doesn't reduce the output power. The entire guts can be pulled out by loosening a bunch of setscrews. Disassembly to the state of affairs in the photo took about 10 minutes, all completely reversible except for cutting small blobs of black RTV silicone holding the laser tube in place in the cut out aluminum cylinder at the top of the photo..
The HeNe laser tube itself looks like it is some version of a Spectra-Physics model 88 - the same type that used to be found in barcode scanners. However, note that the version used in the SP-117/A has cathode-end output, unlike the anode-end output of the barcode scanner tube. A sample I have produces over 3 mW, so it's probably a higher power version, perhaps an 088-2. As noted, those of more recent manufacture may use the Melles Griot 05-LHR-088. I have no idea if the tube is special in any other way, like having been selected for no more than two longitudinal modes or filled with isotopically pure gases or blessed by the Laser Gods. :) There were no markings of any kind on this one and at this point, I rather think that the only special requirement is that the tube not be a "flipper" - one where the polarization state of the modes switches abruptly rather than remaining fixed. In fact, I rebuilt an SP-117 laser head with a surplus 088-2 tube and it would seem to work fine. See the section: Transplant Surgery for Two Sick Spectra-Physics Model 117 Stabilized HeNe Laser Heads.
The HeNe laser tube has the multiple layer aluminum foil covering Spectra-Physics is so fond of. There may even be more layers than normal, covering a larger portion of the tube than normal. A thin film heater (copper-colored cylinder) is wrapped much of the way around the tube on top of the aluminum foil, and glued in place. Finally, here is an application where the aluminum foil actually might make sense to distribute the heat uniformly. :) The short black cylinder on the right holds a (PBS) Polarizing BeamSplitter (with the reflected output blocked) to select one of the two orthogonally polarized modes of the laser, possibly optional since it was not present on one of the SP-117 laser heads, or an SP-117A laser head that I've seen. So, either, whoever originally had these things salvaged the PBS as the only remaining useful part before selling them, or that is an option not present on all units. On the SP-117, it's a normal PBS cube mounted such that the laser guts have to be slid out of the laser head cylinder to access the set-screw holding it in place. On the SP-117A, it's a PBS that has a rhombus cross-section - a slightly distorted cube - presumably to minimize backreflections. And on the SP-117A, the PBS is secured by two screws accessible from the front once the bezel is removed
Prior to assembly at the factory, the tube must be tested to determine the best orientation for maximum signal change of the two polarized modes since there is no adjustment for this once the tube is mounted with RTV silicone. The specific orientation is determined by slight asymmetries in the tube construction - random factors like mirror coatings and alignment - but should not change with age or use.
After an initial warmup period where the heater is run continuously, the controller enables the feedback loop which monitors the two outputs of the beam sampler and maintains cavity length using the heater so that one of the orthogonally polarized longitudinal modes is on a slope of the gain curve (frequency stabilized) or where one mode is closer to the center of the gain curve (amplitude stabilized). Although I haven't measured it, there are probably around 75 complete mode cycles before locking.
The user controls on the SP-117A consist of a switch for power and a switch to select between frequency and amplitude stabilization. There are indicators for AC power and Stabilized. (The SP-117 is physically identical but lacks the mode select switch.) After a warmup period of about 15 to 20 minutes for the laser head to reach operating temperature, the Stabilized indicator will come on and may flash for a few seconds, and after that should remain solidly on. This really indicates only that the stabilization feedback loop is active, NOT that the laser is actually stabilized and meets specs - that may require another minute or so. For the SP-117A and MG 05-STP-901, the behavior is similar in Frequency or Intensity mode. (The SP-117 has no Intensity mode.) In fact, the way they are designed, everything is identical in both modes until the Stabilized indicator comes on, then it switches to the Intensity signal for locking. If power is cycled, the delay to Stabilized is much shorter, so no actual counter delay is involved, just some circuit watching for the mode changes to slow down below some threshold. Indeed, if the photodiodes are disconnected, Stabilized will come on in under a minute even though the modes are varying wildly. Stupid electronics. :)
The internal circuitry of the controller box is relatively simple and includes some CMOS logic including several monostables (!!) for timing the warmup period, multiple op-amps and comparators, a 555 timer, voltage regulator, and switching transistor for the heater - all standard stuff. A linear power supply feeds the HeNe laser power supply and the control electronics,
Here is the pinout of the DB9 control connector as determined by my measurements. There may be errors.
Pins Function Comments ---------------------------------------------------------------- 1,6 Heater ~19 ohms, 12 V source on pin 6. 2,7 Interlock Shorted. 3 Ground May not be connected on some versions. 4,5 Photodiode 1 Anode is pin 4. 8,9 Photodiode 2 Anode is pin 8.
Although, it's very likely that any reasonably healthy SP-117/A laser head will lock on any SP-117/A controller, adjusting the controller for optimal mode signal swing will result in best stability and permit the location of the two orthogonal modes on the neon gain curve to be fine tuned. If anyone has information on the official internal adjustment procedure for the SP-117 or SP-117A controller and/or a service manual or schematics, please contact me via the Sci.Electronics.Repair FAQ Email Links Page.
There are three sheets:
The PWM ramp generator ends up on the analog page only because it is actually in the same chip as the amplifiers.
There are three sheets:
Some of the circuitry of the SP-117 and SP-117A is similar and the designer of the SP-117A clearly had access to the SP-117 schematics. However, substantial portions have been totally redesigned rather than simply tacking on the amplitude stabilization and modulation input as a minor addition. The low voltage power supply including the on-board regulation, the heater driver, the HeNe laser power supply, and at least some of the logic/timing circuitry are very similar. But in the SP-117A, the negative voltage source is provided by an a 555 rather than an ICL7660, different op-amps types are used in the analog sections, and the basic design of the control loop has also changed. Of most significance in terms of performance, unlike in the SP-117A, there appears to be no pure integrator stage in the analog chain of the SP-117. Note how much simpler the control loop (analog schematics pages) is for the SP-117 compared to the SP-117A! So there will always be an offset due to the finite and relatively modest gain between the photodiodes and heater response. This means that the exact position of the locked lasing line on the neon gain curve will have a dependency on ambient temperature and initial conditions when the SP-117 is turned on or restarted. And, it will drift somewhat until thermal equilibrium is achieved, which may take considerable time after the Locked indicator comes on. Exactly this behavior has been observed with the SP-117 and wouldn't make sense had the design been similar to that of the SP-117A with a full PID control loop. These anomolies were bothering me and in fact were the original reason I decided to trace the SP-117 circuit. My confusion was your gain. :)
This laser seems to be interesting in another respect: While for the typical ordinary HeNe laser, the modes roughly follow the profile of the gain curve as they traverse it, with this tube, the mode on one side will tend to disappear and reappear on the other side of the gain curve relatively abruptly. I don't know whether this behavior is a peculiarity or a feature but it seems like it could be beneficial. ;-)
The laser is a single unit mounted on a solid baseplate (with exposed high voltage!). It is designed to install in a cabinet painted with the decorator colors of your choice. :) See Spectra-Physics Model 117 OEM Stabilized HeNe Laser Assembly. There was a separate box with a +/-12 VDC switchmode power supply and lighted power switch as the only user control. The SP-117C has no output polarizer so that must be supplied by the user. Its operational behavior is similar to the other SP-117s, though the warmup is faster - under 10 minutes. Locking is then abrupt with no overshoot or ringing. Locking following a power interruption of a few seconds occurs in under 1 minute. When to switch from warmup to lock mode is probably detected by a complete mode cycle taking more than around 15 seconds.
The HeNe laser tube looks like the same 088 used in the other systems. It's probably from Melles Griot by its relatively thin-walled construction. The 12 VDC input HeNe laser power supply brick is hidden underneath. The PCB generally resembles the one in the SP-117A and 05-STP-901 controllers with many of the same part numbers, though there are also many differences and it has clearly been substantially redesigned. The timing is now done using 12 bit binary counters instead of multiple monostables. The majority of the discrete resistors have been replaced with resistor packs. There is also a pair of resistor packs in sockets for reasons unknown. The input is +/-12 VDC (rather than just +12 VDC), supposedly being regulated to +/-9 VDC on-board according to the test point labeling. But the resistor that sets the voltage on the sample I have has been selected to produce +/-8 VDC instead of +/-9 VDC and that works fine. There is no 555 oscillator to generate the negative voltage of the SP-117 and SP-117A controllers, so the associated PWM clock must be produced in some other way. There are pads for four large series diodes with jumpers in their place. These would be used to reduce the DC voltage to the HeNe laser power supply if more than 12 VDC were used for the positive power supply. Small MOSFETs are used to control the Enable line of the HeNe laser power supply and the Locked signal, as well as some internal signals. And, in case you're wondering, I have absolutely no intention of reverse engineering this unit the way I did the SP-117A! But I have determined most of the external connections to the 14 pin header visible in the upper left corner of the above photo based on how it is wired and the obvious PCB traces:
Pin Function --------------------------------------------------------------------------- 1 +Va - Positive analog power, +12 to +15 VDC. 2 +Va? 3 Mode control?? Input to NOR gate, pulled high. 4 Analog Ground 5 Locked Status (+Va V: unlocked, 0 V: locked, will sink 0.6 A). 6 -Va? 7 -Va - Negative analog power, -12 to -15 VDC. 8 -Va 9 Digital Ground 10 Digital Ground 11 Digital Ground 12 Digital Ground 13 NC 14 +Vd - Digital power, +12 VDC (+15 VDC with all diodes installed).
The Locked signal originates from an IRFD210 MOSFET which can sink 0.6 A, more than enough current to drive an LED - or a bank of them. :) The +/-12 VDC for the unit I have comes from a small switchmode power supply in a separate box. The analog and digital positive voltages (+Va and +Vd) are the same. I added a Locked LED there and will install a switch if the unidentified control signal does something useful.
I am in need of a user manual for the SP-117C including info to confirm what I have on the 14 pin header is correct and to determine the function of the unidentified control signal. (Grounding it either during operation or prior to power-on has no obvious effect.) If you have any info, please contact me via the Sci.Electronics.Repair FAQ Email Links Page.
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: Spectra-Physics 120, 124, and 125 HeNe Laser Specifications and Spectra-Physics Model 261A Exciter (SP-261A).
(From: Marco Lauschmann (mla@sbk-ks.de).)
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 o