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12-14-2011, 05:47 AM #17
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Sigurthr
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Re: TEA Laser Build

If your diode is frying, it is probably because either the peak forward current (Ipf) is being exceeded (I think you said it was rated for 30mA) or the Peak Inverse Voltage (PIV) is being exceeded. More likely is that the Ipf is being exceeded because you said that there is no resistor being used.

Go down to your local electronics shop and grab the largest wattage resistors you can find in various resistance from a couple ohms to 1Mohm (1 million ohms), just put one in series with the HV Diode between the PSU and the Diode. Try to avoid "wire-wound" resistors as the added inductance would probably cause issues. You'll have to experiment with which reistance functions best. I have no idea how much current a TEA laser draws from the NST, so I can't give you a perfect value. I = V / R (remember it is in amps = volts over ohms, so don't forget to divide mA by 1000 for the amps or to multiply kV by 1000 for the volts). At 30kV a 1Mohm resistor will limit the current to 30mA, iirc.

I don't recommend adding a second diode, at least not in series, another one in parallel would not hurt but generally the rule for adding diodes in parallel is to never do it without a series resistor for each diode, since not having one can let all the current flow through only one of the diodes, frying it. So, I suggest you try with the resistor and see how it goes.

If you wanted to make it a bit less noisy you could form a Full Wave rectifier out of HV Diodes and use that in place of the single diode, this would double the pulse frequency of the laser as well. Full Wave Rectification takes 4 diodes, fyi, and is fairly simple to construct. Pull up a simple schematic on Wiki for you and you'll be all set.

Might I recommend trying various fluorescent materials as lasing targets instead of the white paper? Uranium "Vaseline" glass works rather well.

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12-14-2011, 09:05 AM #18
 Class 3R Laser Join Date: Aug 2009 Location: The Netherlands Posts: 1,482 Rep Power: 62
Bluefan
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Re: TEA Laser Build

Doubling the pulse frequency probably lowers the output:
Sam's Laser FAQ - Home-Built Nitrogen (N2) Laser
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12-14-2011, 07:17 PM #19
 Class 3B Laser Join Date: Dec 2011 Location: Michigan's U.P. Posts: 4,382 Rep Power: 873
Sigurthr
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Re: TEA Laser Build

It's been a few years since I had a chance to play with a TEA laser, thanks for posting that page Bluefan!

Aye, there is a limit on the pulse rate for homebrew TEA lasers. However, since a fullwave rectifier will charge the capacitor twice as fast it should balance out provided the lasing repitition rate limit has not been reached. As far as I know, homebrew units almost never reach the "speed limit".

Either way, if you've got the 4 diodes to try it, you might as well, imo. Once set up, it's easy enough to swap in or out the rectifier of a TEA laser for experimenting. The one comment I always heard from onlookers about this type of laser was "why is it so loud!".
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