LASER DO TIPO Nd-YAG Q-Switched modelo SSY1 utilizado no M1 Abrams

SSY-1 laser is a compact flash lamp-pumped Nd:YAG laser with passive q-switch. This type of
laser generates pulses of 1064nm light with duration measured in nanosecond scale. The laser
assembly is a part of a rangefinder from the U.S. military. Some useful and interesting information
about the SSY-1 laser assembly can be found at the Sam's Laser FAQ: link.

Figura 1: SSY-1 Assembly

The Nd:YAG rod is side-pumped by a regular flashlight tube, as it is shown in Fig. 2. A passive q-
switch installed in the laser, at the HR end of the resonator, is made of Cr3+:YAG. The resonator is
actually a plano/plano type which means that the mirror surfaces are completely flat (not like it is
drawn in the Fig. 2). The laser rod and flash lamp can be easily taken out of the resonant cavity to
access the internal components of the laser (e.g. remove the q-switch). The resonator is therefore
permanently aligned and it's not necessary to re-align it after accessing the interior of the
laser. Figures 3 to 6 show the laser taken apart.
Since this laser is flash lamp-pumped it uses the same electric circuitry as every flash lamp: it is
basically a capacitor charged to a few hundred volts and some kind of triggering circuit. Originally,
the flash of SSY-1 laser is powered by 36uF capacitor charged to 900V which gives about 15 joules
of stored energy. To power my laser unit I built a very simple power supply running directly off
230V mains (dangerous!). Fig. 7 shows a schematic of my power supply.

Emissor

Receptor

This setup allowed me to measure what is the laser behavior at different capacitor energy and also
with and without q-switch. Figures 14 to 17 show some charts with experiment results. Top line
(yellow) is the flash tube current, the middle (blue) is flash light and the bottom (purple) is laser
output. The vertical axis of the charts is not scaled in any units.

Figura 2: too low pump energy, no laser pulse

Figura 3: 16J pump energy, nice laser pulse
detected

Figura 4: 32J pump energy (too much), series of

pulses at the output

Figura 5: 32J pump energy, q-switch removed

The chart presented in Fig. 15 shows the proper setting of the laser. Pumping energy is high enough
to reach the q-switch threshold and we get a nice single laser shot. In Fig. 16 the energy is way too
high. The q-switch is triggered and the energy stored in the YAG rod lases out, but then the rod
instantly gets pumped again by the same flash of pumping light and the lasers shots again and again,
five times in total. In such situation the peak power of the laser beam is not getting higher. Instead,
we just have a series of laser pulses. In Fig. 17 a long and relatively flat laser pulse is shown. This is
because q-switch was not present in the laser cavity. Without q-switch nothing stops the lasing
process and the energy from YAG rod is being constantly lased out during the pumping light pulse.
Notice the delay between the laser pulse and the pump light pulse, this is the time for energy stored
in the YAG rod to reach lasing threshold (optical amplification of the rod has to exceed the cavity
losses).

A Small Nd:YAG Laser - SSY1

Description and Specifications
SSY1 is a small Nd:YAG laser head that was used in the rangefinder for the M-1 tank. It includes a
flashlamp with external trigger, YAG rod, passive Q-switch, and mirrors, all in a package about
25x25x105 mm (not including mounting feet). See SSY1 Laser Head Assembly for a photo which
includes a U.S. Quarter for size comparison. See Major Components of SSY1 Nd:YAG Laser
Head for the individual parts. (This photo courtesy of Meredith Instruments. Another SSY1 laser
head is shown in SSY1 Laser Head Assembly Zapping. (Photo courtesy of Chad Andersen.) The
inset shows the SSY1 firing at a black plastic box without any focusing. The maximum flashlamp
energy input from the matching pulse forming network, PFN1, is about 20 J.
(Note that there is a unit showing up on eBay with labels showing "MILES US ARMY" and
"LASER TRANSMITTER ASSY M16A1" that looks like it might contain an SSY1 head. However,
this device is used for battle simulations or war games and only has a pulsed 904 nm laser diode.)
The SSY1 laser head used to be available from Meredith 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 (though that would probably
have suffered as well). (For reference, the output is from the end with the red wire. The ends look
identical.)
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:
•Beam characteristics.
•Wavelength: 1,064 nm.
•Divergence: A few mR (not yet measured).
•Quality: A simple positive lens will focus the beam to a microscopic spot.
•Output energy: Estimated between 10 and 50 mJ. It is at least equal to "1 Alcoa". :)
The laser will punch a hole in kitchen-strength aluminum foil when focused (but
doesn't do razor blades using the 15 J PFN). Over 100 mJ is possible on "lively" units
up at 900 V on the PFN1. However, repeated operation at these energy levels tend to
destroy the Q-switch and adjacent rod AR coating.
•Lasing medium.
•Type: Nd:YAG rod, AR coated ends.
•Rod diameter: about 4 mm.
•Rod length: about 50 mm.
•Lasing threshold: less than 7.5 J (100 us pulse duration).
•Flashlamp - This looks similar to an ordinary photographic variety, perhaps somewhat
higher quality, but not the very high quality EG&G FXQ style lamp. It may be a FXQG-
264-1.4 or FXQSL-559-1.4. See the section: Shawn's High Energy Experiments with the
SSY1 Laser Head. Applied Photon Technology, Fenix Technology, EXCELITAS, and others
may have exact replacements.
•Arc length: 35 mm (about 1.4 inches).
•Outside diameter: 5 mm.
•Inside diameter: 3 mm.
•Overall length: 75 mm.
 •Ko impedance parameter: 16 ohms-amp0.5 (estimated).
•Flashlamp envelope: quartz.
•Electrodes: machined solid tungsten.
•Minimum voltage: less than 300 V.
•Maximum voltage: greater than 1,000 V.
•Maximum energy input at 100 us pulse duration: 25 J (guessed!).
•Recommended energy input at 100 us pulse duration: 15 J at 900 V.
•Maximum average power input: 7 W (estimated).
•Trigger: External trigger electrode (white wire).
•Manufacturer: Probably either EG&G or ILC (likely available from both
companies) but I haven't been able to locate the specific model on their Web site - it
is not one of EG&G's 1300 series but may be an FXQG-264-1.4 (see below).
•Optics - Mounted at each end of the SSY1 assembly against machined flat posts - no
adjustment possible or needed for basic operation. However, it seems as though the
alignment on these is is not generally anywhere near perfect. And, some samples are quite
poor. It's quite possible that this is the main reason for differences in output energy on
undamaged units. It would be interesting to install one of the mirrors on an adjustable mount
and determine if any significant improvement is possible.
•Flow tube: Dual chamber for flashlamp and rod, slightly yellow tinted glass. Since
this is an air-cooled laser, the term "flow tube" is used only because that's what it
would be in a liquid-cooled laser. :)
•Cavity reflector: A thick white powder coating the outside of the flow tube and itself
covered with plastic. I don't know whether the powder is toxic but wouldn't
recommend removing it in any case since it is very effective.
•Cavity length: 9.3 cm (3-5/8").
•High Reflector (HR): 12 mm diameter x 5 mm thick. Exterior surface appears
slightly bluish (but may vary with coating run). The HR is normally at the Q-switch
end (black and white leads of flashlamp).
•Output Coupler (OC): 12 mm diameter x 5 mm thick. Exterior surface appears
slightly greenish (but may vary with coating run). The OC is normally at the non-Q-
switch end (red lead of flashlamp).
•Passive Q-switch: There is a third element adjacent to the HR-end of the rod. Its
surfaces appear coated and slightly gold-ish in color. This is a the passive Q-switch.
It uses a dye that is bleached (turns clear) once the light intensity in the cavity
exceeds a specific value. The Q-switch is tack-glued into position and can be
removed intact by carefully drilling out two glue plugs on either side. It is a chamber
about 7 mm in diameter with optical flats on either end and some sort of dye material
in between.
•Physical configuration - Overall dimensions (excluding mounting feet) are 25x25x105 mm.
 •Outer casting: This holds the cavity assembly in position between the fixed
(precisely aligned) HR and OC mirrors and provides a pair of bolt holes for
mounting of the overall laser head assembly.
•Cavity assembly - The reflector and trigger electrode are part of an inner assembly
which includes the rod fastened at one end and the Q-switch at the other, with the
flashlamp adjacent to rod. Actually, there is no highly reflective reflector. :) The rod
and lamp sit inside a glass (probably or perhaps, quartz) tube with a double bore.
This is surrounded by a layer of some very white stuff which sort of looks like
plaster or drywall compound. An outer wrap of tough plastic keeps the white stuff in
place. The white material does reflect most of the light into the rod and diffuses it at
the same time. So, energy distribution into the rod is probably quite uniform.
However, some light is wasted as the white stuff is not totally opaque - the flash of
the flashlamp can be seen through its surface. Plastic caps glued to the ends of the
double bore thing are what actually hold the parts in position.
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.
•Electrical connections: Approximately 6 inch long flexible wire leads for flashlamp
anode (red), flashlamp cathode (black), and external trigger (white). CAUTION:
Don't apply excessive force to the red and black wires as they attach directly to the
terminals of the flashlamp. Also, don't twist the white one as it can come loose from
its glue and break the fine trigger wire inside.
•Power Supply - I built a line powered capacitor charger and trigger using PFN1. See the
section: Sam's Power Supply for a Small Nd:YAG Laser Head (SG-SP1).
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).
Variations in Performance of SSY1s
Depending on how much use or abuse any given SSY1 has had in a past life, there could indeed be
significant differences in output energy for the same input energy. I don't know to what extent this
may happen for samples that appear to be in perfect condition but it should be possible to identify
obvious problem areas. Inspect the Q-switch dye cell, flashlamp, rod ends, and optics for dust, dirt,
discoloration, mottling, and physical damage. If the dye cell appears anything but perfect, it
probably should be removed as its condition will only deteriorate with use. Discoloration of the
flashlamp will reduce the amount of light to the rod but unless it is very severe, won't prevent the
unit from working but will just increase the lasing threshold slightly. Unlike a HeNe laser with its
low gain, a spec of dust won't kill lasing but a careful cleaning probably won't hurt. For anything
beyond light dusting, use proper laser mirror cleaning procedures to avoid damaging the optics.
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.

Comments on the SSY1 Nd:YAG Laser

(From: Moses Clark (itek@sybercom.net).)
1.I have fired the laser using a 120 uF, 900 V homemade PSU.
2.I could generate smoke from carbon paper (what a benchmark!).
3.The manufacturer of the cavity is Kigre Laser (according to Jeff Myers who works there).
They supplied it to Hughes aircraft. The laser is a Huges Aircraft M-1. It was originally used
on the M-1 Tank and was later integrated into some hand-held laser rangefinders. The
Nd:YAG rangefinder on the M-1 is now being replaced with a 1.54 um Er:Glass eye-safe
rangefinder made by Litton Laser Systems.
4.Kigre also sells a passive Q-switch, a dye filled saturable absorber cell) as an add-on to the
cavity for $150.00. (This or one similar to it is part of SSY1. --- Sam.)
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.)

Patrick's SSY1 Experiments

(From: Patrick Jankowiak.)
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.
Shawn's High Energy Experiments with the SSY1 Laser Head
WARNING: The passive Q-switch will not survive the abuse inflicted by high energy operation for
very long - it is a high failure item even under normal conditions. The mirrors apparently tolerate it
better but these also may degrade after awhile. And, even if the flashlamp doesn't explode, the pulse
repetition rate must be very low so as not to exceed its average power ratings and to limit heating of
the rod and the entire assembly. Using PFN1 (36 uF, 900 V), MTBF may be in the 100K shots
range; this may drop by several orders of magnitude with ultra-high energy operation!
(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:
1.I'ms not sure if the entire SSY1 output beam was hitting the carbon disk a foot away. The
disk is about 6 mm in diameter and the beam at the output coupler is about 4mm.20
2.When smoke came from the disk (as indicated by a * above), I'ms not sure how much
energy was actually being lost due to vaporizing some of the surface of the sensor.
3.I'ms just guessing that the absorption of the 805 nm laser diode is about the same as the
1.06 um SSY1.
I'ms looking for a larger diameter piece of carbon so that I can expand the beam without vaporizing
spots on the surface.
(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:
•d is the mean diameter in inches.
•t is the number of turns.
•b is the length in inches.
So, here are some options for 820 uH:
•68 turns, 6 inches in diameter (110 feet of wire).
•48 turns, 12 inches in diameter (150 feet of wire).
•34 turns, 24 inches in diameter? (210 feet of wire).
You can see why the inductor from parts express was so attractive.
(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.
Other High Energy Experiments with the SSY1 Laser Head
(From: Jay Byler (rjaby@aol.com).)
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.

Pspice Program for SSY1

(From: Shawn West (west007@libcom.com).)
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 main program is lasflsh.cir.
•The schematic file is lasflsh.sch.

Frequency Doubling SSY1

It is possible to produce pulsed green (532 nm) output from SSY1 without too much difficulty. In
fact, it is trivial if your SSY1 has its Q-switch in place and in good condition..
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:
•First, I tried an SSY1 head which had had its Q-switch removed. Although it lased and
would burn holes in Zapit paper when roughly focused (and from previous experiments, in
aluminum foil), I could not get any detectable green from my KTP even after very carefully
adjusting its position and orientation on my block of wood.
•Next, I used an SSY1 head with its Q-switch in place. This produced green on the first shot,
even just above threshold (700 V or about 8 J into the flashlamp). Adjusting the angle of the
KTP had some effect but not anything as dramatic as results with a CW DPSS laser.
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.

High Power SLM Green from SSY1

Bill Jensen, from the Holography Forum has modified the SSY1 and PFN with some interesting
results. He replaced the original passive Q-switch which could not handle high peak power with a
new Cr4+:YAG passive Q-switch and add an intracavity etalon in an attempt to obtain a single
longitudinal mode. He also, made a new PFN using much higher uF caps and a custom inductor.
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.

Using SSY1 to Make Holograms

(From: Adam.)
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:
•First Holo Made YAGna Laser.
•Description and Photos. (May not work from USA.)
YouTube Links (from above):
•Crystals YouTube Video.
•Cat and Coins YouTube Video.
•Flower Pulsed Hologram YouTube Video.
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....
Other SSY1 Tidbits
(From: Wayne Verish (wverish@aol.com).)
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!