The following specifications have been checked by Chris Chagaris and should be fairly accurate:
(The following 3 photos provided courtesy of: Roger Vernon (rvernon@ienvision.com).)
This is the Hughes M-60 Tank rangefinder assembly that has been turning on the surplus market for anywhere from $50 to $300.
(The following 5 photos provided courtesy of: Dave (Ws407c@aol.com).)
(The following 2 photos and description provided courtesy of Wes Ellison (ellison@falcon.cc.ukans.edu).)
(The following 9 photos and description provided courtesy of Wes Ellison (ellison@falcon.cc.ukans.edu).)
Except for the rangefinder assembly (similar to what is shown in the other photos, above, everything is home-built.
Note that to get this working required replacing the OC that came with the rangefinder with the OC from a Korad ruby laser and put in a fixed first surface mirror in place of the Q-switch. The original OC looks like a piece of transparent glass where one would expect to see it reflect strongly at deep red wavelengths. The claim is that it resonates sharply at 694.3 nm - but this is undetectable visually and unsupported by its behavior - which is not to want to laser using that optic.
With the real OC, it will punch a hole in a Styrofoam cup, both sides! Now to work on that blasted Q-switch. :)
The best I can figure is that in the original application, they were using more pump energy than what I was using. The PFN that came with it is 150 uF at 1,500 VDC maximum. That would be about 168.75 Joules. I am using 666 uF at 1,200 VDC or about 480 Joules. But the inductor is what determines the pulse width. My 10 uH coil will give it about 250 us peak flash time. I haven't a clue as to what that white PFN has in it. Also, I would assume that the mechanical Q-switch is running all the time. So, the prism on the Q-switch, the HR prism and that resonant (transparent) OC all have to work together to get an output. I haven't run into anyone yet that has gotten one to work with that resonant OC though.
(From: Sam)
I suspect that in the original application, the Q-switch was running all the time and you won't get it to work with that optic unless you use the Q-switch and have it perfectly timed! How about the monostable and pot approach?
(From: Wes)
Hehehehe.....tried that, along with an op-amp to pick up that magnetic sensor to fire it. Oh it fired just nicely, just didn't lase. That's the problem with that motorized job (UGH!) I am looking for either a Kerr cell or AO type of Q-switch for it now.
(From: Sam)
How did you adjust it? I would probably have replaced the energy storage cap back with a tiny cap so the flash lamp would work like a strobe and then set it by eye. :)
(From: Wes)
Ummm....never thought about that. Strobe the rotating prism. The problem is that the sensor has to pick up the pulse with the prism in the exact spot so that the rod will spoil before it makes 1/4 turn to align the cavity. The speed on the side of the motor says 30,000 RPM which equates to 500 revs per second (2 milliseconds/rev). Divide by 4 and you get 500 microseconds. The pulse width is 250 us so timing become very critical. The pulse has to occur in that 500 us span. Myself, I think the Q-switch on this thing would make a nice sinker for 30 pound test line and a nice hook to catch bass. :)
The laser assembly is sitting on top of a metal box. The metal box contains the high voltage trigger circuit. Looking to the far right of the box on top, you can see that rotating Q-switch prism. The small pin on the bottom of the shaft is the magnetic pickup. When the pin aligns with the Hall effect sensor, it will produce a pulse that is amplified and delayed by the proper amount to trigger the flashlamp firing SCR so that the prism will be in the optimal position to unspoil the cavity just after the end of the flashlamp flash. Once the prism rotates to the correct position with the HR and OC in alignment with the cavity....POW ! A super pulse. No easy task considering that you are dealing with a mechanical motor and I plan on doing away with it for now.
(From: Sam.)
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.
The fan turns on when a thermistor sitting just to the bottom and left of the hole reaches 115 degrees cavity temp. This I designed so it would shut the charging bank off until the cavity cooled.
(The following photos and description courtesy of: Curt Graber (cgraber@fwi.com).)
The pictures show a bank of (6) 2,900 uF, 400 V electrolytic capacitors. Three of these units (as the picture is shown) are wired in series for a net 966 uF, 1,200 V; six of them would provide 1933 uF; or if you require a different power density ratio, wire them in series groups of four caps for 725 uF, 1,600 V, and parallel two of these groups for 1,500 uF, 1,600 V. The white box in the picture is the original 150 uF, 1,250 V cap (not used).
The charging system for the above bank of caps is a 1,000 W microwave oven transformer. These units are available surplus or cheaper :-) and are way capable - a typical rating being: 3 KV at .5 A!! This potential is rectified through a homemade bridge made with microwave HV diodes (12-15 KV). You also may use just one as a half wave rectifier.
DOUBLE WARNING: These transformers can be quite lethal, and when built into the power supply capacitor bank, you have just built your own electric chair should your body fall conductive to it's potential.
(Note: I would most definitely recommend - require - bleeder resistors with a visible indication of non-zero charge on *each* of the lethal caps --- Sam).
The rep rate is based on the power supply charge limits and not the cooling capability of the cavity. The unit was fired at a rep rate of once every 5 to 6 seconds for better than 5 minutes in one instance with no perceived change in power and or damage to flashlamp or rod (I have both a ruby and a Nd:YAG rod that I can interchange in 10 min.) Will the bulb take 2,500+ Joules of input? No - the limits of the EG-G FX-103 flashlamp are 1,550 Joules explosion energy and when you work up your power supply, the maximum input is calculated from: repetition rate, cooling type, and percentage of explosion energy versus lifetime (# of shots). The original flashlamp lasted through many months of play with power ranging from the rod's threshold of approximately 640 VDC up to the 1,200 VDC master pulse.
Output power? who knows. I just recently obtained a power meter and haven't played with it yet and also need a new lamp as the original one expired in a final glorious pulse. The power output is amazing even without the Q-switch. I can't imagine what this unit would do with the Q-switch timed and functioning. I also have a Hughes Q-Switch Driver but I don't have the pinout and as soon as I figure it out the Q-switch will be re-installed.
Several flashlamp manufacturer's have replacement bulbs for this unit with larger tube diameter's allowing even higher input energies. ILC has one that is still 3" arc length but 9 mm outside dia instead of the 5 mm of the original. That unit will take a 2,500+ Joule input and live. I've also thought of gold plating the cavity to optimize for the YAG rod. However, I've been told that the ruby will not likely even reach threshold in the gold cavity - the YAG would improve by 8 to 12%.
