The laser head consists of the flashlamp and YAG rod in a sealed box, the KTP doubling crystal (outside the cavity), servo controlled apertures (variable slits) for X and Y spot size, and a servo controlled attenuator to adjust pulse energy. Note that this attenuator approach is much simpler and more consistent than alternatives using adjustable capacitor voltage or pulse duration control.
The YAG rod is probably about 50 mm long by 3 or 4 mm in diameter, AR coated both ends. The mirrors are glued to the cavity box (non-adjustable). The servos are the types used for RC models but work fine in this application. :) Optics are glued to precision X-Y adjustable mounts. A fiber optic light pipe cable introduces a targeting beam for viewing the dimensions of the laser spot into the light path via a 45 degree mirrors which is transparent to the laser beam but reflects an adequate portion of the white light beam.
Energy into the flashlamp is about 28 joules (66 uF at 850 V provided by three 200 uF photoflash capacitors in series). Triggering is via an SCR and EG&G trigger transformer to an external electrode on the flashlamp. I don't know what the exact maximum output energy is but for this application, less than a mJ is adequate once the beam is focused to a spot of a few um.
The controller consists of analog knobs for X and Y aperture and laser power (operating those RC servos, all with digital readout), single shot or 1 pulse/second select, and a knob for the targeting light source brightness via a phase control dimmer. Nothing particularly high tech!
Although the output of the YAG rod is clearly dangerous (it is probably a few 10s of mJ) and the final green output may even be hazardous to vision, the system has a Class I rating (unconditionally safe) because everything is fully enclosed under normal operation. There are two head interlocks: A magnet on the cover and dual reed switches on the optics chassis prevent operation if the cover is removed and a tilt sensor prevents operation if the head isn't within 20 or 30 degrees of vertical. There is also an interlock connector on the rear of the power supply and the firing control is a momentary SPDT (foot) switch. The interlocks interrupt primary power to the high voltage transformer (the rest of the system continues to function) but the firing switch controls logic inputs.
The following specifications have been confirmed by Chris Chagaris (pyro@grolen.com) and amended by Dr. Ed Edmondson (EE0035jr@aol.com). However, there could be other variations with slightly different part values so double checking what you have would not be a bad idea! And, of course, if you replace the PFN with one of higher energy, the values for output pulse energy will be greater (unless the flashlamp explodes). (Refer to Photos of Hughes Range Finder and Home-Built Pulsed Lasers.)
Where "test data" is listed, it's for a sample of this unit I have which included a test data sheet.
These AN/ Numbers are related to the following equipment. AN/VVS-1 is used on the M60A2 Tank, AN/VVS-2 is used on the M60A3 Tank, and the AN/VVS-3 is used on the M1 Tank. (Note: Only the AN/VVS-1 is definitely a laser rangefinder. The AN/VVS-2 seems to be a night vision system. I do not know about the AN/VVS-3. --- Sam.)
The major contracting firm even made a version designated LAV-105 (Light Assault Vehicle) which was used on a US Marine APC's (Armoured Personel Carrier).
These laser rangefinders were replaced with eye-safe versions using erbium:glass at 1,540 nm and YAG-KTP-OPO at 1,580 nm. This older non-eye-safe version of this assembly is being sold on the Internet by several different surplus companies and individuals on eBay and elsewhere.
Test data: 50 mJ at a PFN voltage of 1,095 VDC.
Test data: 1.4 mW based on 50 mJ pulse energy divided by 35 ns pulse duration.
The top part of the cavity reflector may be taken off by removing the one obvious screw and carefully wiggling the cover loose (if necessary). Take care not to smash the flashlamp in the process. DO NOT TOUCH any of the interior surfaces, especially of the flashlamp! Fingerprint oil may cause it to explode after a few flashes (so they say). The flashlamp does not actually touch any part of the reflector assembly but mounts via its end-caps into a grounded block at the cathode-end and an insulated nylon block at the anode-end The rod is clamped in place in the bottom part of the cavity reflector, possibly cushioned by a layer of indium or other soft heat conductive material.
In normal operation, the motor is spun up on demand just prior to the laser firing. It would be a good idea to implement this feature in any home-built power supply designs to prolong the life of the motor.
Test data: Spinup time at normal operating voltage (?) should be less than 200 ms, 40 ms typical, 70 ms on this unit.
The spec'd maximum voltage is 1,250 VDC and the operating voltage (50 mJ output energy) on the test data was 1,095 VDC.
References:
With the long fluorescence lifetime of ruby - about 3 ms - timing of the Q-switch is not as critical as it is for Nd:YAG with its much shorter fluorescence lifetime (230 us). The Q-switch motor spins at 30,000 rpm or 500 rps for a period of 2 ms. So, if the flash duration is resaonably short compared to 2 ms, there will be a high probability of a decent output energy even if the flashlamp was triggered at random relative to the Q-switch position! Even if the flash duration is as long as 3 ms, half the time, more than 50 percent of the available energy will have been transferred to the rod when the Q-switch is triggered. This is probably the main reason that faulty Q-switch trigger circuits seemed to produce successful results, though I bet the variation in energy due to the timing not always being optimal remained a mystery and was probably attributed to other causes. However, with a proper design, the pulse energy should be quite consistent.
(From: Doug Little (dmlittle@btinternet.com).)
The pulse generated by the Q-switch's magnetic pickup looks a little like this:
/\
___/ \ ___
\ /
\/
If you build your trigger circuit carefully and make sure you connect the magnetic pickup the right way around (rising or falling edge) you can minimize any unwanted delay between pickup and trigger. You can then of course introduce an artificial and adjustable delay of your own for optimization purposes. A suitable circuit is shown in Q-Switch Trigger Circuit for Hughes MS-60 Ruby Laser and described in the section: Doug's Q-Switch Triggering Circuit for Hughes MS-60 Ruby Laser (DL-ST1).
There are some important things to realize when you try to set up your own timing circuit:
There are two ways around the second problem. One is to run the motor backwards, giving you a whole rotational period of about 2 ms to play with. Being a mechanical motor, this is a lot of time to wait before discharging the lamp without expecting some sort of speed fluctuation. The longer the delay, the less accurate the prism's final (flash) position becomes in terms of motor speed!!! I have strobed the prism with a super-bright LED using a very short on-time of several us and I can say that a 2 ms delay results in a slightly wobbly prism, instead of a preferred rock-solid one. The second solution involves the motor/Q-switch mounting platform. If you loosen the hex bolts you can rotate the whole unit about 5 to 10 degrees in either direction. This affects timing quite a bit and gives you the opportunity to buy back a few 10s of us.
WARNING! Adjusting the Q-switch platform may kill your laser's alignment and you will have to go through the whole horrible process of adjusting the optics with a reference laser and it can take hours. I know because I did it myself. If your laser is already aligned, you may want to think very hard before you go adjusting those hex bolts!
(From: Randy Smith (randysmith@adelphia.net).)
I too have one of these ruby laser units that I am trying to get running. To start off with, there needed to be some sort of timing control unit to synchronize the flashlamp with the spinning mirror. I built such a device using an 87C552 micro, with a 4 digit thumb switch control to allow for an arbitrary offset from TDC (top dead center), entered in degrees. The jury is still out as to the functionality of this unit, but it does look good on a scope and also, when used to drive a small laser diode, it can be used to view the instantaneous position of the mirror. I will find out for sure this coming weekend, when I test it in operation with the laser.
(From: John Grebas (kerravon@bellsouth.net).)
The original PFN produces a 250 us pulse. If the lamp is fired immediately when the magnetic sensor picks up the pulse, approximately 300 us later you will have a beam. You have to have the motor running forward (red motor wire on positive) and the speed set so the period of the magnetic pickup is 1.6 ms.
But I also used a bank of 12, 470 uF, 400 V caps, and a 200 mH inductor, at 979 V to get a 1 ms pulse. I run the motor in reverse with a period of 2.5 ms, I delayed the magnetic pickup pulse by 1.5 ms (between 1.4 ms and 1.5 ms). So with the motor running in reverse with a 2.5 ms period between pulses and a 1 ms pulse from the PFN, and a 1.5 ms delay, you will get your beam (2.5 ms = 1 ms + 1.5 ms). If you follow that you should be OK. So I could run my motor (backward) with a 2 ms period, with my 1 ms pulse I would set the delay to 1 ms (2 ms = 1 ms + 1 ms). Basically your delay + your PFN's pulse time should equal the period of the pulses from the magnetic pickup (controlled by the speed of the motor. Say you have a 700 us pulse from the PFN you could run the motor with a 2 ms period with the 800 us pulse, you would set your delay to 1.2 ms.
I finally got the thing to work but I had to step up the power input to the flash lamp. I simply added a second 150 uf cap in parallel with the other to get a total input of about 216 joules. I charged both up to 1,200 volts. I used the Doug Little's Q-Switch Trigger Circuit for Hughes MS-60 Ruby Laser to synchronize the flash lamp discharge with the Q-switch (See the section: Notes on the Hughes Q-Switch. I ran the motor CCW at 36,000 RPM and adjusted the Q-switch prism to be about 1/8th turn past the pickup when the lamp fires. This seems to give the best results. It blows the ink off a page. Next, I'ms going to see what it will do metal. :)
I figure that with only the original 150 uF or so cap producing at most 126 joules, at 1,300 volts max, it is probably just barely at the lasing threshold with an optimally timed and aligned Q-switch. The military techs had a device for this unit that tuned the Q-switch without firing the flash lamp. If one had that device then you could probably get it to work with just one cap. Also if it had a real OC instead of just a clear optical medium I think that would help a lot.
(From: Sam.)
Yes, we know that the use of a dielectric OC reduces the lasing threshold significantly. Wes Ellison actually got the laser operating without the Q-switch using an OC from some other ruby laser.
The problem with the resonant optic is that there is no way of knowing if it is any good by inspection or by any easy tests. The location of the reflective wavelength peaks depend on the spacings of the surfaces in a multiple plate etalon. For these low reflectivity surfaces, the response function results in very broad peaks and multiple peaks will fit within the gain bandwidth of ruby so they don't have to be positioned precisely as long as they match. The thickness of the two plates is what determines the peak location for them and they are presumably matched. However, reflections between the plates with a distance determined by the spacer will also affect the overall response. It is not known (though could be calculated) what the exact effect will be. If someone (before you of course!) was curious and disassembled it, even if all the parts were put back together in the correct order, some change in performance is possible, though it's not known how serious this is likely to be. But, even a speck of dust trapped between one of the plates and the spacer could be significant when dealing with wavelengths of light. Given the general difficulty in getting this laser working with the resonant OC at all, replacing it with a dielectric OC with a known reflectance may be worthwhile especially if there is any uncertainty in the resonant OC's condition. And as noted, this could result in a lower threshold as well.
I first tested one of these with a red laser (though not at 694.3 nm, probably a 650 nm diode). The reflectivities of the surfaces are consistent with uncoated glass. I doubt anything has degraded in storage. For it to work as an OC, you don't need much reflectivity, maybe 15 or 20 percent at 694.3 nm. So, presumably, what is required is that two of the dips in the Fabry-Perot resonance of the two plates should (coincide so the attenuation) adds and be within the gain-bandwidth of the ruby crystal (about 0.5 nm). I don't know how they can guarantee that. Perhaps the thicknesses are controllable to the required degree. Or, maybe the thickness of the two plates is not quite the same so that there is a series of dips with slightly different spacing, assuring that one set of them lines up under the ruby gain curve.
Here are some more comprehensive test results using an HP-5501A HeNe laser tube at 632.8 nm. The difference between 632.8 nm and 694.3 nm really should not affect the maximum/minimum reflectivity as an etalon, only the location of the peaks and valleys. This tube has a built-in high quality beam expander and is also quite stable even without being installed in the HP-5501A laser head. The horizontal angle of the OC was adjusted to produce minimum and maximum readings at as close to normal incidence as possible.
The output power of the laser increased slightly as the tube warmed up. So, these sets of measurements were taken a few minutes apart:
Parameter Test 1 Test 2 Test 3
-----------------------------------------------------
Laser power 382 uW 409 uW 414 uW
Minimum power (T) 221 uW 237 uW 238 uW
Transmission % 57.8% 57.9% 57.5%
Reflection % 42.2% 42.1% 42.5%
Maximum power (T) 362 uW 388 uW 392 uW
Transmission % 94.8% 94.9% 94.7%
Reflection % 5.2% 5.1% 5.3%
Ratio Max/Min T 1.64 1.64 1.65
Ratio Max/Min R 8.12 8.25 8.02
Note: The reflection (R) values were computed from transmission data since actually measuring the reflected beam at the small angles where the etalon effects are significant would be almost impossible. So, the actual reflected power may be slightly lower due to losses, but probably not by that much for this low-finesse etalon. The maximum reflection of about 42 percent is much more than enough to function as an OC. So, I'm not sure why some people apparently are unable to get this to work. Perhaps they are giving up too easily, assuming it was a lost cause.
"I purchased one of the Hughes rangefinders (two, actually, if I can find the other one...), and have been looking at what might optimize the output. It appears that simmer pulse operation, with 600 V square wave pulses with a duty cycle such that one pumps for the length of a rotational period without killing the tube would do the trick. IGBTs would do the switching - the question is how to trigger the tube without a serial transformer in the existing cavity. The best idea I have would be to use an insulated wire externally as the trigger - has anyone tried this and made it work?"
(From: Chris Chagaris (pyro@grolen.com).)
How exactly do you intend to "optimize the output"? I get the impression that you wish to optimize repetition rate by utilizing a pseudo-simmer mode circuit. You must realize that this laser was designed to operate at a low repetition rate and must do so for a number of reasons. The original flashlamp contained in this laser is an EG&G, FX-103C-3 which is the predecessor of their FXQ-1302-3. With the design of this cavity employing only convection cooling of this original lamp, the maximum average power is rated at only 20 watts. At an input energy to the lamp of let's say 100 joules (somewhat above minimum for laser operation) your pulse repetition rate would be limited to one pulse every five seconds. With such a slow repetition rate I cannot see the justification for employing a simmer mode of operation. Since there are no active means of cooling the ruby rod, this could also present a problem, as ruby does not dissipate heat very well and the likelihood of damage from over-temperature is great if this system were to be operated much above its design limitations. With the configuration of this particular laser cavity (semi ellipse) the use of an external trigger wire for successful firing would be highly unlikely. The flashlamp is in intimate contact with the grounded aluminum base of this reflector to aid in the cooling of the lamp. A wire of any kind would interfere with this contact and of course would serve no purpose as the current would just flow to ground. A wire with enough insulation to protect against the very high voltage pulse (10 kV or more) would be very impractical.
(From: Sam.)
I agree with Chris 100% that boosting the repetition rate isn't really viable. As far as triggering, an alternative to series triggering is parallel triggering which can easily be extended to multiple trigger sources. See the section: Basic Structure and Characteristics of SS Laser Power Supplies. EG&G (now Perkin Elmer) has info on simmer mode and much more on their Web site. Go to Perkin Elmer Optoelectronics and then to "White Papers". The title is: "Design Considerations for Triggering of Flashlamps".
(From: Chris.)
In more detail, there are two points to consider in answering this question:
P(avg) = E x f
Where:
The flashlamps that one may find in the MS-60 rangefinder ruby lasers are either the original EG&G lamp, FX-103C-3 or the replacement EG&G flashlamp, FXQ-1302-3. Since this ruby laser's cavity is not actively cooled (merely convection cooled) the maximum average power rating for these lamps are 20 watts and 150 watts respectively. Consider an input of 100 joules to this first lamp. This would limit repetition rate to one pulse every five seconds. This same input to the replacement lamp rated at 150 watts would give you a safe maximum pulse rate of 1.5 pulses per second. Of course an increase in pump energy to the lamp would decrease the maximum safe repetition rate.
Ruby was never meant to be pulsed at a great repetition rate. Another problem that one would face at high repetition rates is the overheating of the ruby rod, which does not dissipate heat too well (unlike YAG). This can permanently damage the ruby crystal.
The SSY1 laser head used to be available from Meredith Instruments along with a matched pulse forming network (see the section: Pulse Forming Network 1. (Meredith had also been auctioning these and other items on eBay.) SSY1s frequently show up on eBay from various sellers. The going price is in the $100 to $200 range for the laser head. New SSY1s and parts may also be available from Anderson Lasers, Inc. and elsewhere. I constructed a capacitor charger and external trigger circuit. See the section: Sam's AC Line Power Supply for SSY1 (SG-SP1). An alternative design which runs from low voltage DC is described in the section: Sam's Inverter Power Supply for SSY1 (SG-SI1).
For initial testing, figuring it would be real effort to get it lasing, I used my trusty IR remote control tester for detecting the beam. Big mistake. :( The first shot sent the photodiode off to photodiode heaven (or wherever faithful photodiodes go when they die). Its output just stayed on! I should have used the IR detector card available from Radio Shack (and elsewhere).
OK, so go to plan B. :)
I placed a piece of black coated paper in front of the laser and fired off a few shots. No effect except for a bright blotch of white light from the flashlamp. (Maybe I didn't examine it closely enough.)
Next, I tried a small lens approximately focused on a piece of black coated paper. To make sure any effect wasn't just due to spill from the flashlamp, these were positioned about a foot from the laser head. Immediate gratification! The moderately focused output beam easily obliterated the black coating on the paper. This was accompanied by a very nice 'snapping' sound and white or yellow incandescent plume when hitting the black coating, and a more muted sound after the black stuff had vaporized. When carefully focused, it will make nice tiny holes in aluminum foil (the incandescent plume is green-blue in this case) and other thin materials, and mini-craters on thicker objects. I've heard of people driving this laser with much higher energies to blasting holes in razor blades (see below). However, it is all too easy to blow up the laser components when doing this - the flashlamp and Q-switch are most susceptible to damage or destruction.
I don't have any way of actually measuring the energy of the beam but let's just say it is definitely not something to be taken casually, as far as eye safety is concerned! My wild off-the-top-of-the-head guestimate would be at least 10 mJ, probably 20 or 30 mJ, though it may be as high as 50 to 100 mJ. Hopefully, someone will eventually measure the output pulse energy! The Nd:YAG rod is probably capable of much greater energies but that flashlamp doesn't look all that sturdy so I'ms not about to push my luck, at least not yet. :)
The lasing threshold is about 7.5 J - less than the energy of the electronic flash in a typical pocket camera! This low value is no doubt due to both the cavity and optics design - and the optimal pulse length from the PFN. Thus, using one of those cheap flash units (or just its power supply) directly probably wouldn't work at all as the duration of the flash pulse would be way too long with insufficient peak intensity. (The unit described in the section: Micro Laser Rangefinder Using Disposable Flash Pumped Nd:YAG and OPO is based on a much smaller Nd:YAG rod - about 1/8th the volume.)
Here are the specifications, as best I can determine:
The white flashlamp trigger lead is connected to a fine wire that runs the length of the inside of the bore where the flashlamp lives.
The cavity assembly may be detached from the outer casting by removing 4 screws providing access to the inner surfaces of the HR and OC, and the rod ends for cleaning. The flashlamp may then be removed by unscrewing a nylon fastener at the anode/OC-end and carefully straightening the cathode lead. CAUTION: Avoid touching the flashlamp envelope. If you do so by accident, clean it thoroughly to remove all traces of skin oils.
The maximum energy input using this power supply is 15 J (36 uF capacitor charged to 900 V. Nearly 100 percent of the energy in the capacitor is transferred to the flashlamp. An energy of 15 J may not sound like much but it is more than adequate (actually twice the threshold) for pumping the 50 mm rod with the optimal 100 us pulse duration and well designed cavity
Note: The dimensions are from my memory or lack thereof - I haven't measured them since getting SSY1 to lase, corrections welcome.
WARNING: Despite its small size, this is a Class IV laser. While SSY1 probably won't set anything on fire unless you fire it at an explosive or have a natural gas leak, this laser is quite capable of doing serious damage to vision. Treat it with respect! Cover the HR mirror aperture (I used black electrical tape) since there may be some leakage from there which is invisible and enclose the output beam path so that backscatter can't hit anything of importance (like your eyes).
I've now tested 3 of these babies - 2 that appear to be in original condition and another with the Q-switch removed and the AR coating gone from one end of the rod. (I've also used the mirrors from an SSY1 to construct the resonator for another YAG cavity, see the section: Mini YAG Laser using SSY1 Optics and SG-SP1.) The two intact units produce about the same output energy. The other one lases but probably at slightly lower energy. It still smokes black tape (possibly better than the other ones) but won't penetrate aluminum foil. The sound it makes when focused on a target is also softer. However, I don't know to what extent these differences are due to the lack of a Q-switch versus the missing AR coating It's probably a combination of both but the reduced effect on thermally conductive aluminum foil and softer sound would be consistent with the longer, lower peak power pulse produced without a Q-switch. Perhaps at some point in the future, I will swap rods with an original SSY1 to separate out the effects of the missing Q-switch and AR coating.
CAUTION: Although the capacitor in the PFN that comes with SSY1 is rated for around 35 uF at 900 VDC, running at this energy may destroy the Q-switch dye cell and possibly the AR coating on the YAG rod adjacent to it after not too many shots. Some samples may survive almost indefinitely but others could succumb in less than 100 shots. I would recommend limiting the voltage for repetitive use to 700 or at most 750 VDC.
I am trying to build a laser rangefinder using this laser.
(From: Ivan (sinebar@bellsouth.net).)
I got my small YAG laser working using the PFN from Meradith Instruments and a power supply based on the SG-SP1 schematic. Even without a lens it will burn a spot on a black target.
(From: Rick (rick@skyko.com).)
I got bored this afternoon and figured I would dig out the SSY1 I bought a few months ago on ebay from Meredith. If that is not the easiest laser to get lasing, I don't know what is. I think it is easier than modifying a green pointer! :-)
I started with two plain old 330 uF, 400 V electrolytic caps in series from my junk box (I have some 1,500 uF 450 Cornell Dublier electrolytics, but I didn't want to take out the Q-switch yet). I then dug out a smallish 12 VDC-powered hene supply (for like a 1 to 2 mW tube and wired that up to the caps through ten 100K 1/2 watt resistors wired in series (for 1M at 5 W). I found a dented old auto ignition coil transformer deep in my junk boxes and I wired up a 4:1 divider using 1M 1/2 resistors off the caps to charge a small 2.2 uF 250 V capacitor. To fire the laser, I turn on the HeNe laser power supply, watch the voltage across the main caps charge (about 20 V per second or so) and then when it is at the desired voltage, I short the 2.2 uF cap across the input terminals of the auto ignition transformer, whose coil is hooked up to the trigger wire of the SSY1. I then took a note from Sam's experience and wound about 55 turns of 14 gauge plain old solid copper wire with thin plastic insulation around an used up plastic speaker wire container bobbin. I measure the inductance of the completed coil with my LC meter and found it to be 199.5 uH. Not bad! Overall though I would say it is the crudest SSY1 power supply yet! :-)
For the very first shot I was not absolutely sure which end was the output, lol, so I put a black electrical tape target about 2 inches from each end. I let the main caps get to 450 V total and then shorted the 2.2 uF cap to the transformer. A nice satisfying flash! and a perfect 3-4 mm white spot on the electrical tape on the end with the red wire (ah, the output end, heh heh).
I then found a 1.5" FL lens and proceeded to de-anodize some aluminum. The thing is loud when it is focused. I am actually adjusting the focal length as I type (while waiting for the cool down of the SSY1 lamp (what is the duty cycle on these things anyway? (Figure about 10 W average power into the lamp. --- Sam ) I am giving it about 3 to 5 minutes between pulses). I think I may be able to make some small craters in the black anodized aluminum, but maybe not until I swap out the series 330 uF caps for the series or paralleled 1,500 uF ones (after removing the Q-switch).
Not a bad little laser for $125. It really deserves a better supply though. :-)
(A day passes.)
I just fired a shot from my SSY1 with 165 uF caps (two 330 uF caps in series) charged to 550 V (so about 25 joules) into a Molectron J25LP-0686 sensor head with a responsivity of 5.0 V/joule at 1064 nm. I measured a 620 mV pulse on my oscilloscope.
This would mean the output power from the SSY1 at 25 joules to the flashlamp is 124 mJ.
Is that even remotely possible?
(From: Sam.)
Might be a bit high, but not out of the question.
(From: Rick.)
It does punch a hole through aluminum foil at this power level, and also it pits a stainless steel razor blade (but does not punch through).
It also left a 4 mm mark on the carbon looking sensor head... whoops. :-(
While making some more power measurements from my SSY1, I heard an increasing snapping sound as I went up in pump joules. Since I have the power sensor head well past the focal point of a positive lens (normally I would hear this snapping sound when I focused the spot on a piece of electrical tape or aluminum foil) I was wondering where it was coming from. I then covered the SSY1 with a piece of cardboard to mask the flashlamp light spillage and fired it up at 165 uF, 700 V (40 J). I saw a bright pinpoint flash of light at 1.5 inches from the lens in mid air! Very very cool (first time I have seen this phenomenon, though I have heard of it). I guess this gives another data point to the output power level... Air sparks at 200 to 400 mJ? :)
I am going to try and capture this on video and stick it on my Web site.
(From: Sam.)
Use a shorter focal length lens and the light show will be even more spectacular and/or occur at lower energy.
(From: Mike Poulton (mpoulton@mtptech.com).)
You can push them really hard. I ran about 1 kW average input power for 5 seconds at a time, letting it cool about two minutes between bursts. I had a small fan pointed at it, but no real forced air. It didn't like this, but I did it quite a few times and it still works fine. The yellowish plastic around the cavity is discolored brown from the heat - it was probably close to 400 °F and it didn't fail.
(From: Sam.)
On another note, the laser described below is the modern version of SSY1 which is similar, perhaps even a bit smaller:
(From: Erbium1535 (erbium1535@aol.com).)
The South Carolina State Museum in Columbia uses a Nd:YAG laser to pop a balloon inside a balloon in their Townes exhibit. (C.H. Townes was born in Greenville, South Carolina.) The laser, manufactured by Kigre, Inc. in Hilton Head, SC is a Q-switched MK-367 unit and is described on the Kigre MK-367 Nd:YAG Laser System Page. The actual laser is approximately 0.6 x 0.8" x 4" in size and emits a 17 mJ pulse pulse with s duration of less than 4 ns. They also offer a frequency doubled green version. The MK-367 was originally developed for the ophthalmic surgical market, specifically as a photo disrupter for posterior capsulotomy. The power supply is approximately 4" x 4" x 1.5" and operates from 12 VDC.
The laser is somewhat unique in that it is permanently aligned, utilizes a ceramic exoskeleton for stability, and a positive branch confocal resonator design for high beam brightness. Kigre has sold more than a thousand of these miniature lasers for various applications including medical, industrial, rangefinding, and pyrotechnic ignition. The MK product line has been around for more than 15 years, so these lasers sometimes find their way to the used laser discounters. New ones are still available and cost about $3,600. If you do come across one of these, be very careful as it is a very powerful Class IV laser! (Yes, but the SSY1 is potentially an even more powerful Class IV laser! --- Sam.)
I have some news about what I have done with the SSY1. The Q-switch is retained. I used two lab power supplies (ye olde tube-type monsters) to charge the stock PFN to 800 VDC, and used the trigger pulse from a small photoflash unit to fire the flashlamp. The discharge resistor made a convenient current limiter for the charging. I first tried it with the photoflash unit to charge PFN1 but my SSY1 would not fire at the photoflash-supplied 400 V on the lamp.
I had no carbon paper so I took a small white cardboard box and a black 'Sharpie' pen and painted a square made of 5 layers of ink, allowing the ink to dry between layers. I was gratified to see the laser work the first time and ablate the ink nicely. The ink method may be better than carbon paper for some purposes. I took pictures and videos which I hope will be interesting. The Kodak P850 camera is ideal since it does 30 fps video at 640x480 resolution. It also allows one to edit the video in-camera as well as extract individual frames to create images. OK, this is not a Kodak Ad, just saying what gave me good and easy results without having to buy editing software. One thing that surfaced is the apparent TEM02 mode of the laser. This appeared in the ablation marks in the ink. They were very hard to see by eye but the camera picked them up. The mode marks seemed to remain the same from pulse to pulse, so I believe it is genuine. I hope you enjoy the pictures and videos. Some are quite large, but I made also an animated GIF where I increased the brightness and reduced the speed and you can really see the smoke.
Here is the page: Patrick's SSY1 Laser Page.
(From: Sam.)
Well, I have to say, that's the BIGGEST SSY1 capacitor charging power supply I've ever seen. Heck, a 6 VDC input HeNe laser power supply can easily charge PFN1. :)
As far as the TEM02 mode pattern. I think that's just the tip of the iceberg. The diameter of the SSY1 rod with the plane-plane resonator is much too large to assure a TEM00 mode, probably by at least a factor of 2. So the actual mode pattern may be much more complex than what is appearing in the smoked ink.
(From: Shawn West (west007@libcom.com).)
I've taken a different approach than the others and am pumping it with a long pulse, about 2.5 ms. With my long pulse I have put a 0.020 inch diameter hole in a 0.004 inch thick razor blade. I've punched holes through aluminum foil of different thicknesses too. I've back calculated the energy required to punch the holes in the razor blade and the two aluminum foil experiments. The calculations show that it would have taken 1.7 to 1.8 joules to melt and vaporize the metal in each case (if I did my calculations right). When I hit the razor blade with 800 volts on the capacitor (360 joules) I was able to punch a 0.024 inch diameter hole in the 0.004 inch thick blade. My calculations, which again could be wrong, show that it would have taken about 2.5 joules to do this. These calculations do not include the amount of reflected energy or the energy conducted away from the material. I have also sparked the air using a short focal length (about 1.5 cm) lens. I'ms using a 1,120 uf capacitor with approximately a 0.15 ohm ESR.
My inductor is 820 uH with a resistance of about 0.15 ohms. It is from Parts Express (part #266-760, about $23). The inductor is wound with an effective 12 gauge copper foil and has an air core. I'ms using a piezo-electric igniter from a gas grill to flash the tube.
I have also used a 270 uF capacitor and a 80 uH inductor (ESR of 8 or 9 milliohms). However, the longer pulse PFN put out more energy (more destruction to the target) than the short PFN when the caps were charged with the same energy. This could have been due to the ESR differences of the two capacitors or the higher current density with the shorter pulse PFN exciting the shorter wavelengths of the xenon (i.e. not exciting the 800 nm hues as well to mate with the Nd absorption). I'ms trying to keep the current density in the flashlamp below 4,000 A/cm2 to favor the 800 nm absorption band of the Nd:YAG crystal. I also wanted to pump out a lot of energy. This forced me into a long pump pulse.
I spoke to Jim McMann (sp?) from Perkin Elmer (EG&G) about the flashlamp in mid-December, 1999. His phone number is 1-800-950-3441. At that time, he thought the flashlamp was an FXQG-264-1.4. From what I have found out since then, there are two EG&G flashlamps that could have been used for the SSY1. The first is the FXQG-264-1.4. This flashlamp is made from titanium doped quartz that cuts off UV wavelengths below about 225 nm. The second is the FXQSL-559-1.4. This flashlamp is made from cerium doped quartz that cuts off UV wavelengths below about 320 nm. I don't know which one was originally used.
Both of these have a 1.4 or 1.5 inch arc length, and are probably xenon filled to 500 Torr (though I have not been able to verify the fill pressure). The ID was 3 mm and the OD was 5 mm. If you calculate Ko with a 1.4 inch arc length, you get:
1.28 * (1.4 * 25.4) 500
Ko = --------------------- * (---------)0.2 = 15.5
3 450
Using a 1.5 inch arc length results in a Ko of 16.6 which is what I measured
it to be.
For the more conservative arc length of 1.4 inches with a 3 mm bore, the explosion energy for the flashlamp = time.5 * 90 * arc length in inches * bore in mm = 378 * time.5. (Time is in milliseconds.)
I designed this to run from 300 volts (50 joules) to 800 volts (360 joules). My damping factor (alpha) ranged from 1.03 at 300 volts to 0.8 at 500 volts to 0.63 at 800 volts. I think at about 560 volts the current density in the flashlamp was about 4,000 A/cm2. The explosion energy with a 2.5 ms pulse is about 590 joules and at 800 volts I was running at about 60% of the explosion energy. I normally run at about 560 volts where alpha = 0.76, at 30% of the explosion energy (about 177 joules), and the current density is about 4,000 A/cm2 in the flashtube (the approximate maximum current density for which the 800 nm line is strongly excited). When I was hitting the razor blade and the aluminum foil the capacitor was charged to 700 volts (274 joules - about 46% of the explosion energy). The maximum pulse rate is about once every 45 seconds. Right now my charger is running from 120 Vac but I plan to make this portable and run from 12 volts with a pulse rate capability of about once every 30 to 40 seconds.
I have not removed the Q-switch to see the effect yet.
(From: Sam.)
Well, that's certainly impressive!
I assume that with the Q-switch, you are actually getting a series of short pulses of a few dozen mJ each. My quick off the top of my head calculation for output energy using the Q-switch would be 25 to 50 times 20 or 30 mJ which is in the .5 to 1.5 J range so your calculations of output energy may not be far off. This laser would probably also do nicely with an arc lamp if you could cool it somehow. :)
(From: Shawn.)
My scope is getting calibrated now, but when I get it back I'll check the reflected light to see I am getting a bunch of pulses or a long continuous pulse with a steep front end (maybe even a spike on the front end of the pulse). Does this Q-switch have a self terminating bleaching effect independent of incident power or does it remain bleached as long as the power is above a certain threshold?
(From: Sam.)
I don't know for sure but assume that it returns to its non-bleached state immediately after the laser pulse and until the spontaneous emission (not the incident flashlamp power) exceeds the threshold again. Not knowing the exact composition of the dye used here, I can't say what the exact time is. For the rangefinder, the likely objective would be one intense pulse for each firing of the flashlamp so there would be no need to select one that recovered quickly but they do exist.
(From: Greatest Prime (FishyBill@mediaone.net).)
The nickel complex BDN in toluene has a recovery time of about 1 ns. (Actually, you can make it in a number of ways. One is to dissolve BDN in methyl methacrylate and polymerize it. You have to watch out the active catalysts do not destroy the dye.) This allows for multiple pulsing. Other dyes and solvents tend to shorten the recovery time. That is what makes mode locking possible at a pulse repetition rates of more than 100 MHz. However, repetitive operation of dye Q-switched lasers is more complicated than merely considering recovery time of the dye. There usually are long term thermal effects of considerable importance.
(From: Sam.)
It might be possible to test the SSY1 laser for multiple pulsed operation by firing the flashlamp with a longer than normal pulse. Once the first Q-switched output pulse depletes the upper energy state, the Q-switch should revert to its non-bleached condition. If the flashlamp is still on, the cycle should repeat. Doubling the flashlamp pulse duration from 100 to 200 ns while maintaining approximately the same flashlamp light intensity should be enough and this can probably be done safely (for the flashlamp and dye cell at least for a few shots to perform the test) by doubling the values of the PFN capacitor and inductor. I've heard of rangefinder lasers similar to the SSY1 failing in a way that results in multiple output pulses - this may be a way to experiment with this mode! Diode pumped solid state lasers take advantage of this effect to generate a series of very short pulses with very consistent energy between pulses and a rate determine by the pump input.
One way to determine the pulse shape or pattern would be to fire the focused laser beam at a rotating disk with a piece of black paper or carbon paper glued to its front surface. The shape of the burn mark or pattern of spots should reveal whether it is lasing CW for the duration of the input pulse or pulsing at a regular rate as would be expected if the Q-switch were active the entire time. A 75 mm diameter disk rotating at 3,600 rpm would result in a linear velocity of about 1.4 mm/100 us for this laser oscilloscope. :)
(From: Shawn.)
I noticed that my divergence is significantly greater with the long pulse (2.5 ms) versus the short pulse (approximately 400 us). Do you have any thoughts on why this could be happening? How much more energy do you think I could get out if I removed the Q-switch?
When I was using the short pulse PFN I could discolor a black piece of cardboard about 2.5 feet away with the spot size only growing slightly (perhaps a few mm in diameter). However, with the long pulse PFN, I placed a piece of black cardboard about 3 inches from the output coupler (and hit it) and then moved it back 4 inches (about 7 inches from the output coupler) and the diameter grew by about 2 mm. At about 1 foot from the output coupler I can't discolor the black cardboard with the long pulse PFN.
(From: Sam.)
That's interesting and could indicate that the dye does remain bleached after the initial pulse. Or, the dye bleaches from the center out which would restrict the area of lasing when Q-switched.
(From: Shawn.)
Are you thinking that if the dye bleaches from the center out in combination with the applied pulse duration, then the Q-switch will effectively clip the higher order modes letting only TEM00 to oscillate. However, with a long pulse, the dye possibly remains bleached over the whole rod diameter which permits the higher order modes to oscillate creating the high divergence. Maybe I should pull the Q-switch and insert an aperture into the cavity to clip the higher order modes?
(From: Sam.)
As far as total energy, if the Q-switch is not participating after the initial pulse, than it won't make much difference. However, if the dye bleaches and recovers quickly, then perhaps it could be significant.
(From: Shawn.)
I use a cheap 660nm laser pointer to bore sight the laser. When I get the laser pointer lined up I can see the "orbit" reflections that seem to surround the fundamental spot. However I thought with a plano-plano cavity the reflected spots tend to follow a line from the fundamental or follow a slight curve (i.e., not surround the fundamental spot). Could this cavity be a near hemispherical or a plano-plano cavity? If this is a near hemispherical cavity could that explain why the center of the q-switch would bleach first?
(From: Sam.)
I thought it was a plano-plano cavity but didn't check carefully. Just look at the reflections from the optics of something distant and see if they look flat. :)
Shining a laser pointer into it you also have reflections from the rod ends and the Q-switch to confuse things. I'll have to check...
I just went and used a HeNe laser reflected off the mirrors with a piece of paper to block the reflections from the rod ends and Q-switch (so they wouldn't confuse things). The mirrors appear to be planar as far as I can tell but this still isn't conclusive since I was just kind of holding the thing steady and trying to view the reflected spots.
It does look as if the rod ends and/or Q-switch is ground on a slight angle because without the paper, there is a distinct far off-axis spot.
(From: Shawn.)
I noticed that far off axis spot too when I'ms bore sighting it with the laser pointer. Do you think it would be worth it to put an aperture in the cavity and how big of an aperture do you think would be good to use? What is confusing me is that the output of the side of the rod closest to the flashlamp seems to put out more energy and I am trying to envision the optimal location for the aperture (i.e., should the aperture be placed off centerline toward the flashlamp side).
(From: Sam.)
The fact that you get more energy off-center suggests (at least to me) that the cavity is indeed planar. A cavity with curved mirrors would tend to homogenize the distribution I would think.
What are you hoping to accomplish with an aperture? Obtain a TEM00 beam? That may not be possible from such a short cavity. There's a magic number for a given cavity configuration to determine if a TEM00 beam will be produced (sorry, I don't have the equation or the value for this laser) but I bet it would require a rather narrow beam.
(From: Shawn.)
I was just hoping/dreaming to be able to project the unmanipulated beam further. I think you are right again about the planar cavity. A near hemispherical cavity should have more energy in the center.
(From: Sam.)
Well, you can still expand/collimate it and that will help but if you were after HeNe-like beam quality, not likely. :)
(From: Shawn.)
I fixed my divergence problem. I remember when I got the laser, I illuminated the bore and noticed a slight star-burst pattern that seem to be coming from the Q-switch. Yesterday, I noticed the star-burst getting more pronounced. I guess my higher energy pulse must have aggravated the existing imperfection. So, I removed the Q-switch. My divergence problem has gone away. I'ms assuming that the imperfection in the Q-switch was dampening the oscillations in the center of the laser rod. The beam now grows about 0.1 to 0.15 inches in diameter over a 3 foot distance.
Before, when I charged my capacitor up to 700 volts (about 275 joules) I could only put about a 0.020 inch diameter hole in a 0.004 inch thick razor blade. Now, without the Q-switch I can put a 0.033 inch diameter hole through the same razor blade. If you just ratio the changes in volume the output energy has increased by over 2.5 times.
(From: Sam.)
Yes, I've heard that the dye based passive Q-switch is one of the items that fails most often (the other being the flashlamp). So, it may have been slightly bad to begin with but your super power pulses might have really done it in!
For those who haven't yet begun to abuse SSY1, it is probably best to remove the Q-switch dye cell before attempting to run at much higher energy input than the 15 J max of PFN1. To do this, detach the rod/flashlamp assembly from the resonator frame (make a note of the direction in which it is installed). At one end you can see an AR coated end of the YAG rod (I think there is a screw at that end which holds the rod in place). At the other end is the Q-switch dye cell (slightly larger diameter than the rod) which is held in secured with some tan or brown adhesive which has to be removed to free it. There is a tiny fill hole where some adhesive was forced in on the side - using a drill bit in your hand to remove what's in there may also be needed. Take care to avoid scratching or breaking the dye cell - you may want to replace it at some point in the future (and that dye cell originally cost something like $200!).
Without the Q-switch, the output will not be as short a pulse but may actually result in more total energy (though less peak power).
(Several months pass.)
I have now built everything into a portable self contained unit (including the laser pointer target designator) that could operate from a 12 VDC source. A pushbutton must be held in to charge the caps but there is an overvoltage cutoff to prevent accidental overcharging. There is an LCD readout for capacitor voltage. Of course, the most important part of this rig is my pair of 1,064 nm laser safety goggles!
I've fired well over 2,000 shots with my SSY1 setup and there appears to be no decrease in output power (based on the diameter of hole through a razor blade). The Q-switch has long since died and was removed about 2,000 shots ago. :) My max pulse rate is about 1 shot every 45 seconds. EG&G says that I am driving the flashlamp properly. I bought a couple extra flashlamps just in case.
I've made a sort of hodgepodge laser power meter. I sliced a piece of carbon from a carbon zinc battery anode. The slice is 0.239" diameter (6.071 mm) by 0.065" thick (1.651 mm). I epoxied a thin piece of plastic to the back of the carbon disk to act as an electrical insulator for a Fluke k-thermocouple junction. The thermocouple junction was epoxied perpendicular to the flat surface of the disk. I used an 805 nm laser diode to "calibrate" the disk. The laser diode is calibrated. I set the laser diode to put out 1 watt. I put the carbon disk in front of the laser diode aperture and turned on the laser for different durations as measured by an oscilloscope. I took several measurements while measuring the delta T and time duration for each exposure to the laser diode. Approximately 2 minutes elapsed between each measurement. My data is shown below:
Test Tinitial Tfinal Delta T Pulse Duration MC calculated
# (Deg C) (Deg C) (Deg C) (seconds) (Joules / C)
----------------------------------------------------------------------
1 23.8 30.0 6.2 1.56 0.252
2 24.1 31.2 7.1 1.67 0.235
3 24.2 27.8 3.6 0.92 0.256
4 23.8 28.2 4.4 1.11 0.252
5 23.7 26.1 2.4 0.58 0.242
6 23.5 34.1 10.6 2.50 0.236
Energy into the sensor in joules = time duration in seconds since the power
input is 1 W. The average MC comes out to be 0.246 J per Deg C.
It took about 10 seconds for the temperature to stabilize. I guess that the thermocouple wires were not bleeding away the heat too fast.
I charged up the capacitor for the SSY1 to different voltages and fired it into the sensor which was about 1 foot away. I have a laser pointer with a cross hair diffractive lens that bore sights the laser and is aligned to perhaps 1 to 2 mm. The following are the test results:
Vcap Tinitial Tfinal Delta T Calc Eout Flashlamp Energy Efficiency (Volts) (Deg C) (Deg C) (Deg C) (Joules) (Joules, from Pspice) (%) ----------------------------------------------------------------------------- 350 24.4 27.0 2.6 0.64 57.1 1.1 400 23.7 28.3 4.6 1.13 73.6 1.5 450 23.9 29.9 6.0 1.48* 91.9 1.6 500 23.9 31.7 7.8 1.92* 112.0 1.7 500 24.0 31.3 7.3 1.80* 112.0 1.6 550 24.0 32.2 8.2 2.02* 133.8 1.5 600 23.8 33.6 9.8 2.41* 157.3 1.5* Smoke came from the sensor during these measurements!
The flashlamp energy was calculated by the Pspice simulation. The following are some of the things that were not considered in the measurements:
(From: Sam.)
Cut, file, or grind one of your carbon rods to create some slices length-wise. Sand them smooth and butt the long edges together to form a larger surface area. Yes, I know this will be messy!
You're getting me interested in trying this stunt. I have a pair of 1,800 uF, 450 V computer grade electrolytic caps. Yes, I know, not laser caps, but at with relatively discharge pulse, might survive. With the caps in series, at 800 V, they would provide about 288 J; at 900 V, about 360 J. Or, better yet, I should run them in parallel which would be slightly less efficient but would eliminate any issues of voltage balancing, reduce the stress on the flashlamp, and the air-core inductor would only need to be about 200 uH. I have plenty of thick wire to wind it.
I would remove the Q-switch before the first shot so that it would live to pulse another day. :) I also have some other mirrors with cosmetic defects which I might substitute as well. The same capacitor charger I used originally with SSY1 would work fine here though I might have to beef up the current limiting resistor's wattage a bit. :)
As I mentioned, the air core inductor I used was from parts express. It was about 2.5 inches in diameter and about 2 inches long. It was wound with copper foil 2 inches wide and used insulation between each layer. However, here is a formula for the inductance of a coil whose length is greater than 0.4 times its diameter:
d2 * t2
L (Inductance in uH) = ---------------------
(18 * d) + (40 * b)
Where:
(From: Sam.)
Nah, that's cheating. :) I found a 3 inch diameter form during a walk in the park - from a Hallmark(tm) party ribbon or something - perfect. Extrapolating from the tables above, a 200 uH inductor would require about 50 turns. I actually wound 55 turns in 5 layers using #14 insulated solid building wire. This isn't exactly magnet wire but the insulation is still rather thin so it packs nicely. The 55 turns should yield a bit more inductance - perhaps 250 uH - resulting in a slightly longer pulse. So much the better - it will be easier on the flashlamp.
I located the pair of 1,800 uF, 450 V caps and confirmed that their ESR is still unmeasurable (0.0 ohms) but I will probably need to reform them since they are quite old. I even have a preliminary power supply design. See the section: Sam's High Energy AC Line Power Supply for SSY1 (SG-SP3) and stay tuned for exciting developments.
I successfully fired the SSY1 with a cap bank at 64 uF at 985 V. It made a very clean hole through a razor blade in one pulse with the aid of a focusing lens. I understand that this is running the tube pretty hard at input of around 31 J. I could not find out how long the tube would last under such stress.
(From: Sam.)
That's very impressive since the energy input is significantly lower than that discussed above! I do assume you removed the Q-switch dye cell as it probably wouldn't last long under this abuse. As far as lamp life, it is running 3X or 4X of the energy normally used in the rangefinder application. So, life will be reduced but it would be necessary to calculate the expected life based on the lamp's specifications.
I put together a OrCad (formerly Microsim) Pspice simulation that accurately models the flashtube characteristics (with a given Ko) that agrees with measured results.
Based on the simulation, the amount of energy that actually makes it to the flashlamp terminals is about 75% of the capacitor stored energy for my PFN setup. So for my previous % of explosion energy numbers you can multiply by 0.75 to get the real % explosion values. So, for worst case (800 volt = 360 joules stored on the capacitor) only about 270 joules make it to the flashlamp which gives a % explosion energy of 270 / 590 = 45% rather than the theoretical maximum of 60% as previously stated.
The Pspice files (ASCII text) for the flashtube follow. You can change Rctrl from 1u to put the reverse diodes in the circuit or a 1M resistor to take the diodes out to see if you would be getting any negative ringing current. Resr is the ESR for the capacitor and Rind is the resistance of the inductor. You can set the capacitance, inductance, Ko, and the initial capacitor's voltage in the PARAMETERS box. You can use Rsense to display the flashtube current. Vtube is the voltage across the flashtube. The energy line integrates the tube voltage x tube current to arrive at the energy that makes it to the flashtube to gauge the efficiency of your circuit. For the energy line 1 volt equals 1 joule. The key for proper simulation is to know the proper C, L, Rind, and especially Resr.
The peak power of SSY1 is something like 16 mJ/4 ns which is 4 MW. I'd expect order of 1 mJ of green without any optics - just put the KTP in the beam and adjust its orientation for maximum green output. The green beam will be almost coaxial with the IR beam with a walk-off of only about 4.5 mR. One problem though is that the beam from SSY-1 is not polarized so you will lose some efficiency there. I don't know how much. But if the KTP is aligned properly, there should definitely be some green photons produced. First try this simple approach to the determine if the green pulse energy and consistancy are acceptable. There is no space inside the SSY1 resonator for a Brewster plate with the Q-switch in place so one of the mirrors would have to be re-mounted externally.
CAUTION: I recommend using an aperture to make sure the IR beam hits only the clear central part of the KTP as at high enough power/energy, it could conceivably damage or destroy the KTP if it hits something that absorbs significantly. (However, as I found out, this is probably critial with SSY1 driven from PFN1. See below.)
Adding optics to concentrate the 1,064 nm beam would boost the energy density significantly. However, this is tricky because the peak power is so high and damage to the KTP is all too likely if the beam waist becomes too narrow inside the KTP even if it is all through the center.
I finally did some very basic experiments.
Using SG-SP1 as the power supply (adjustable from 0 to 900 V, 36 uF capacitor in PFN1, 0 to 15 J, 100 us pulse duration at maximum output) and a 2x2x5 mm piece of flux grown KTP similar to what's available from CASIX and Roithner for use in small to medium power DPSS green lasers. For a mount, I simply placed the KTP on a block of, wood shimmed so the KTP was approximately centered in the beam (very precise!). Here are the results:
The reason of course for the difference in behavior between the two lasers is that although the total energy may be similar with and without a Q-switch, the peak power without the Q-switch is on the order of 1,000 to 10,000 or more times lower (a pulse duration of 100 us as opposed to 4 ns). Since the frequency conversion process is non-linear, it is the peak power which ultimately determines the amount of doubled output.
I would estimate the green output to be in the 1 mJ range (give or take a factor of 5) but have no real way of measuring it precisely - only eyeballs that haven't been calibrated in a few years. :) The consistency from shot-to-shot was fairly good, again as determined by eye. The green version of the Kigre MK-367 puts out about 4 mJ.
Increasing the input to the flashlamp to its maximum value of around 15 J did increase the brightness of the green flashes but not dramatically.
I didn't take any special precautions to protect the edges of the KTP and no damage could be detected after the experiments anywhere on the KTP. So, at these power/energy levels, this concern would seem to be unfounded for a few dozen shots at least. However, your mileage may vary.
So, get out your SSY1s and chunks of KTP and fire away. :)
WARNING: Take care with respect to reflected invisible IR and visible green beams. The KTP and any other external optics should either be fully enclosed or covered with a material that doesn't pass significant radiation at 1,064 nm. Green scatter should be identified and blocked as well.
After the beam goes through an IR-blocking filter, he is getting 160 mJ of green with 50 J into the flashlamp. The lamp needs to cool for at least 1 minute between shots. After some nay-sayers said the laser couldn't take being pumped like that, he set up a PIC microcontroller that fired the laser once a minute for over 2,000 shots. The green output from the laser did not go down.
I've made some pulsed holograms using SSY1-based DIY "YAGna" laser. I'm following Bill Jensen's experiments. For now It's a single SSY1 (no amplifiers yet) equipped with a Brewster window (there is enough space for a window in a cavity). I'm putting 6.5 J into the flashlamp (just above the lasing threshold). I'm getting 30 to 36 mJ of 1064 nm and 10 to 15 mJ of 532 nm after conversion in a 5x5x5mm KTP crystal.
Here are some links:
YouTube Links (from above):
SSY1 is unmodified (except for the Brewster window). There is no intracavity etalon, yet the coherence length is at least 18 cm (depth of one of my transmission holos). Is it possible that the passive Q-switch acts as an etalon?
(From: Sam.)
Very interesting......
I would have expected not only the issue of coherence length due to the large number of longitudinal modes, but also multi-spatial mode operation. While the coherence cycle is the length of the cavity, the wide gain badwidth of Nd:YAG permits many many longitudinal modes to oscillate.
I suppose it's possible the Q-switch is acting as an etalon, expecially if its AR coatings aren't perfect (especially if damaged!). This might cut down the number of longitudinal modes somewhat.
There's still a lot about SSY1 we really don't understand....
Just when I thought I had run out of things to point my little Yag laser at I decided to try a tuft of steel wool (no soap please!). The result was surprising! With the voltage cranked up to 900 volts, and the output focused through a simple hand lens the shot ignited a small portion of the steel wool, which then rapidly proceeded to consume the entire pad! This will be interesting to capture on video or digital camera.
Tired of smoking carbon paper with your SSY1? Try steel wool if you dare. Also a great way to blast holes in those pesky free CD rom disks you get in the mail!
Photos of a Quantronix 114 (in slightly better condition) can be found in the Laser Equipment Gallery (Version 1.71 or higher) under "Quantronix YAG Lasers".
Here is a general description though specifications are somewhat sparse:
It looks as though you have got the makings of a nice project. A 'bashed up' laser is better than no laser at all. :-) At least the most important components survived. If you could provide me with the number on the arc lamp, perhaps I could uncover what it actually is. Typically a krypton arc lamp of 70 mm arc length and a 5 mm bore (EG&G, FK-125-C2.75) filled to 2 atmospheres would operate at 100 volts at 30 amps. With this typical input power of 3 kW, coolant flow rate should be at least 120 cm3/s.
The conical and heimspherical electrodes are common. The pointed cathode is to help maintain arc stability.
There is a similar EG&G Krypton arc lamp (FK-111-C3) which has a 7 mm bore with a 75 mm arc length rated at 6,000 W with liquid cooling. Electrical characteristics are 112 VDC at a whopping 56 A. Wall loading is 145 W/cm2 as opposed to the smaller 5 mm bore lamp of 110 W/cm2. However, average lamp life is only 40 to 60 hours, whereas the FK-125-C2.75 should last from 400 to 600 hours with proper cooling.
Sam, where's your sense of adventure? :-) I think an attempt to refurbish this laser as an arc lamp-pumped CW type would be fascinating. Consider the cost of a new flashlamp, the likely necessity to install a new OC of a lesser reflectivity for successful pulsed operation, and the need of a PFN, as opposed to the challenge of building a phase-controlled arc lamp power supply. The design and construction of a PSU such as this strikes me as something that would be right up your alley. I have recently acquired a 6 inch arc length, krypton-filled arc lamp and have considered the construction of such a supply myself. Of course, the lamp that I have will require about 40 amps at 150 VDC! I've got a 10 kW isolation transformer. So there's a start. :-)
Interesting that the OC reflects green. I would tend to agree with you that this laser was not likely doubled. The OC for SHG would normally reflect close to 100% of the fundamental wavelength and transmit about 100% of the harmonic. This being the case, I would doubt such an optic would appear to reflect green.
(From: Sam.)
Geez I dislike even working on the power supplies for little air-cooled argon ion lasers with their current-hog requirements let alone 40 A at 150 V!! :)
It is definitely not a green YAG and I don't even know if intra-cavity doubling had been introduced in those days.
(From: Chris.)
As far as the Q-switch is concerned, I would expect that it was not a simple mechanical system like the one on the Hughes MS-60 ruby laser. I would tend to doubt that a rotating prism Q-switch would be used in-line. Usually if a mechanical Q-switch was going to be used in-line, it would be a rotating HR mirror at one end of the resonator. A roof prism is most often the rotating element in such a system because of its retro-reflecting properties, which assures alignment in one direction, while the rotation of the prism brings in alignment in the other direction.
Mechanical Q-switches tend to be rather slow as compared to electrooptical and acousto-optical Q-switches and judging from the rated pulse width achieved by this laser, I doubt that a mechanical Q-switch would be able to achieve that 50 ns pulse duration.
The power supply/heat exchanger on my 116 requires 208VAC 3 phase to crank the silly thing up. Admittedly, Quantronix did over design the power supply for worldwide use, so the transformers and control circuitry are a bit over-kill. The important point, however, is the fact that a lot of juice gets sucked up generating a clean initial pulse to jump start the krypton lamp and then maintain the 25-35 Amps DC to keep it going. Also, the water for the cooling needs to be kept VERY clean (as you may already know). The micron and de-ionizing filters basically make de-ionized water from store bought steam-distilled, ozonated water. Any particulates in the water stream when the lamp is running is a sure guarantee that the flowtubes and the lamp jacket are going to get coated and cooked!
Be careful YAG rod assembly. Some of the original flowtubes were uranium doped quartz to stabilize the UV into visible wavelengths. Just a word of caution.
The endplates you describe as "polished gold plated brass caps" are now gold plated nickel, since brass has a tendency to contaminate the DI-coolant and turn stuff green. Not good for the flowtubes or the lamp and crystal.
The Q-switch on my 116 is an 25 W RF driven Acousto-Optical model from IntraAction Corp. My guess is the 114 was probably driven the same way.
Anything in the DI-coolant stream should be nylon or stainless steel. No brass, bronze or anything else. The DI-water will pull "tons" of metal ions out of the fittings and put them into the coolant. Also (and this one is a real stretch), under no circumstances should the DI-water be consumed internally! It would literally take the calcium out of your blood-stream and in enough quantities could kill. Sounds strange, doesn't it: Ultra pure water will kill you! Takes the elemental ions right out of your system, or so I've been told. We'll have to leave that experiment untried!
The label reads:
NSN: 6660-01-344-4006
P/N 34860ASSY39097821
Contract No: F04606-96-C-0108
Varo Inc., Optical Systems Division
Garland, Texas, U.S., FSCM No. 27777
The actual manufacturer may be Litton as that's the name on the warranty stickers. :)
The unit I have is probably just the laser head and transmitter/receiver electronics. I assume whatever calculates the distance is in a separate box. The warranty seals say "Litton" so I assume they are the actual manufacturer of the laser.
Inside the outer aluminum cover are several modules: Laser,
Photos of this unit can be found in the Laser Equipment Gallery (Version 1.95 or higher) under "Varo Rangefinder Erbium Laser".
(From: Peter Gottlieb (nerd@verizon.net).)
I have some further info for you regarding the Varo erbium laser module. This module is part of the portable AN/GMQ-33 "Cloud Height Set." This meteorological instrument is used to determine ceiling height from 100 to 3,000 feet AGL. It runs on a 24 Volt NiCd or LiSO2 battery and is 12" x 14" x 13" and weighs 32 pounds. Operation is as follows: Level set; turn on; do self-test; hold switch away from set; press once to start laser charging cycle; when ready light comes on, making sure not to look into lens, press switch again and laser will fire. Display will indicate ceiling.
I just picked one of these up from a government sale. It passes self test and I opened it up (except for the sealed laser module) and checked for loose hardware and other problems (none seen) and am charging the batteries tonight and will test it out tomorrow. Seems like a cool item.
Of course, it there are serious problems, I don't think I could possibly afford to get mine fixed if it doesn't run. The acquisition cost for this instrument is $97,879.00!!
These pin numbers are for J1, the dual row 16 pin connector. The external connector for everything except the high speed rangefinder pulses is one of those expensive mil-style round types. Since I don't have a mate, don't intend to find a mate, and expect that few others would either (unless the cable comes with these units), I'm not even intending to provide those pin numbers.
Pin numbering assumes pin 1 is the second row in on the right, facing the board with the component side up. This is the standard IDC pin designation.
15 o o o o o o o o 1
16 o o o o o o o o 2 Top of PCB
------------------------------------- Edge of PCB
Pin Description
------------------------------------------------------------------------------
1 Power ground
2 Voltage monitor for LM139/HV inverter.
3 Analog/digital ground
4 Status output?
5 High voltage monitor (through 15M/150K voltage divider to HV).
6 -Va monitor (around -16 VDC)
7 Drive with +5 VDC to enable +/-Va supply after main power is applied.
8 +Va monitor (around +16 VDC)
9 Power input - probably around +24 VDC at 3 or 4 A.
10 Ready to fire status output? Goes high once capacitor is charged.
11 Ground to enable digital supply.
12 NC
13 Laser and Q-switch trigger. Input high TTL level to initiate firing
sequence. This may be left tied to external +5 VDC if desired.
Laser will then automatically start Q-switch motor once the HV
reaches approximately +600 VDC and trigger the flashlamp once the
motor is up to speed.
14 NC
15 NC
16 NC
HV capacitor and trigger connector (J2):
Pin Description ---------------------------------------------------------------------- 1 Ground 2 Pulse to trigger flashlamp 3 NC 4 NC 5 High voltage out to flashlamp capacitor (charges to 600 +VDC)
WARNING: If interlock/bleeder board is removed, the flashlamp capacitor will hold its charge for a long time. The only discharge path is through a pair of 15M resistors. For testing, I added a bleeder resistor of 40K, 10 W across the capacitor.
LOG connector (J3):
Pin Description --------------------------------- 1 +15 2 -15 3 Ground
RCVR connector (J4):
Pin Description --------------------------------- 1 +15 2 -15 (Not used) 3 Ground
MON connector (J5):
Pin Description --------------------------------- 1 +15 2 -15 3 Ground 4
MD connector (J6):
Pin Description --------------------------------- 1 Request trigger 2 Pulse to trigger flashlamp 3 Vin to analog power supply 4 Ground 5 Motor power (from power input via inductor and diode)
The power input of 24 VDC was estimated based on how high it had to be before the +/-Va voltages started regulating - about 20 VDC. It's possible that the normal input would be 28 VDC since that might be more standard.
The Motor Driver Board (MDB) connects to the Power Supply Board (PSB) and to the Q-switch motor and position sensor and nothing else. The motor is just a high speed permanent magnet DC motor. The sensor is an LED/PD pair. There are signals from the power supply to both turn the motor on and off and to request a firing pulse. There are a couple of flip flops on the driver board (74HC74) and some other "stuff" in addition to the power enable transistors.
Thus, the firing pulse actually originates from the MDB and get passed through the PSB to the SCR that triggers the flashlamp.
The following is based on my partial reverse engineering of the PSB and MDB and will fire the laser:
If pin 13 is tied to pin 10 or TTL high, laser firing sequence will commence automatically after step (2).
The laser does not fire if the steps 1 and 2 are performed out of order, and then all power has to be removed to reset.
However, permanently connecting the TTL high derived from the zener circuit described above to pin 7 appears to work. Then, it's just a matter of applying +24 VDC, giving the capacitor time to charge, and then pulsing pin 13 high to initiate the firing sequence. Or, if pin 13 is tied high or to pin 10, the laser will fire automatically once the capacitor has charged. So, apply power and after after a few seconds, the laser fires and shuts down.
WARNING: Make sure the laser output is directed to a safe place! It might be more or less eyesafe with the original optics in place but you probably ripped them out a long time ago exposing the raw beam with is narrow and nasty. :)
These procedures fire the laser exactly once. Then power has to be removed and the sequence repeated to fire it again. The capacitor is virtually totally discharged after firing so the PFN works really well. It doesn't recharge automatically but don't bet your life on it!!! I don't know if this is the normal behavior or whether something is broken or there is a reset signal that needs to be applied to get it to recycle without removing power.
I also really don't know if the way I've got it to work has any relation to how it's supposed to work! This laser does not output a beam because there is damage to the end of the rod facing the OC mirror. This apparently will happen if there is the rod-ends are not absolutely and perfectly clean due to the high peak intracavity power during the Q-switched pulse. It goes through all the motions and I have no reason to expect there is an electronics problem at this point. However, if it's detecting a fault (there is an unidentified signal from the MON module - perhaps that's its function) then a fully functional laser might not shut down after firing but will recharge automatically ready for the next shot.
WARNING: Disable interlock/enable bleeder when not actually using laser!
So, in summary for simplest operation: Build a zener circuit to produce a TTL high level from the input supply and connect it to pins 7 and 13. Connect the zener and input supply ground to pins 1 and 3. Enable interlock to disable bleeder and apply power to pin 9. A few seconds later, the Q-switch motor will spin up, the flashlamp will fire, and the motor will shut down. Remove input power and reapply to fire another shot. Disable interlock if done with the laser.
Single
Frequency Complexity
Manufacturer Model Robustness Optics Electronics Elegance
------------------------------------------------------------------
Coherent Compass-M 3 4 5 4
Coherent 532 5 3 4 4
Lightwave NPRO 142 5 5 3 5
Uniphase uGreen 3 1 2 3
It consists of a power supply unit which attaches to the laser head via a cable with an 8 pin plug, but there are only 6 separate connections as the main power feed is doubled up with two pins for +5 VDC and return. That leaves 4 remaining signals, 2 of which are fat wires and the other two are the same color. These are almost certainly for the TEC drive. Indeed, the resistance across the two fat wires is close to 0 ohms. And although one of the wires to the connector is green (it's not ground!), a tell-tail fat red wire can be seen spliced to it snaking into the bowels of the laser head, approximately where the TEC would be. So, it's almost certain that the laser diode driver is entirely within the laser head powered solely by 5 VDC, but the TEC driver is in the power supply box.
The unit I'm testing is a model DPY305c, no output power rating listed. The laser head itself has quite a bit of circuitry in its squarish rear section, along with a heatsink and cooling fan. The laser/optics are in a cylinder protruding out the front. Unfortunately, gaining access to the laser/optics appears to be a major undertaking, requiring extensive disassembly. The circuitry inside the laser head is on two small PCBs, one above the other, attached via wiring and components with additional parts sandwiched between them. From the similarity in some of the electronic components that are used, it's possible that the same designers worked on the Adlas 300 prior to developing the DPY315M and what later became the other Compass-M lasers. But none of the spiff and polish of the Compass-M construction is evident anywhere in this laser head and some of the soldering is absolutely dreadful. It looks like getting to the laser optics platform may be near impossible without extensive disassembly and unsoldering of wires or worse.
The laser powers up but is extremely unstable with wild and continuous output power fluctuations between less than 1 mW and perhaps 50 mW, though the 5 VDC power is rock stable. The actual rated output power is not known but it has been suggested by a Web search that some versions of the Adlas 300 at least are rated up to 250 mW. (The CDRH sticker lists 300 mW for 532 nm so that can't be the rated output power. Not surprisingly, these stickers are identical to those used on the Compass-M lasers!) Given the difficulty of access and the relative rarity of these lasers, I'm not sure how far I will go. If anyone has additional information on these lasers, please contact me via the Sci.Electronics.Repair FAQ Email Links Page.
These lasers were originally developed by a company named Adlas (Advanced Design Lasers) in Germany. Adlas was bought by Coherent but only the newer models have the Coherent part number. They all appear to still be manufactured in Germany. Older C315Ms have a DPY315M model number but except possibly for minor revision differences of the head PCB which are mostly artwork related, they appear functionally identical. There were a number of earlier Adlas models with a similar basic design but quite different construction and packaging. The third generation Adlas laser designs which includes the C215M, C315M, and C415M, were a "major" upgrade and so Coherent than just bought Adlas to solve the problem of their lack of a high quality low to medium power green laser, or something along those lines. :) The Ads for the Adlas DPY 315M only ran for a couple months and then they came out as Coherent.
According to information that used to be on the Coherent Web site, the C215M and C315M are supposed to be single frequency (single longitudinal mode) lasers and as such, the coherence length should be extremely long and ideal for holography and interferometry. The only reference still present there that confirms this is the "Comparison Chart for Continuous Wave (CW) Solid State Diode Pumped Laser Systems" at the bottom of the "CW DPSS Lasers" page, above. The Coherent Web site has been flip-flopping on this over the years since acquiring the technology in the late 1990s. Unlike the Coherent 532 green DPSS laser, these do not use a ring cavity but a more conventional Fabry-Perot (linear) cavity, though it would support single longitudinal mode operation if the birefringence of the KTP were used in conjunction with the Brewster plate to create a birefringent filter or if the KTP had surfaces coated (or uncoated) to act like an etalon. Both of these appear likely. (See the cavity descriptions, below, and the section: Birefringence or Etalon Effect Used for Mode Selection in C315M?.) Since the spec is no longer present, I wonder if they are indeed guaranteed to be single mode. One current specification in support of single mode operation is the optical noise - less than 0.25 p