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Old 05-05-2010, 11:35 PM #1
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Default Pulsing C-W Co2 tubes

I've been thinking about running C-W Co2 lasers with a capacitor
and a PFN with current limiting. I'm understand that overdriving a
tube won't get more power, it will just saturate and stop lasing.

What I thought was that a 2mA PSU for charging is far
more simple and allows battery power to be used for a
longer time.

The capacitor would be charged to the ignition voltage of
the tube, and supply power from say 22Kv to 16Kv as it discharges.

The PFN would lengthen the pulse and the current limiting
would stop the tube saturating.

I'm going to the largest hamfest in my state (No I don't own it,
I just reside in it) and I'm looking for devices that lase.

I hope to find a Co2 tube there, but a C-W HV PSU is beyond my
construction skills.

If anyone is interested, or will be there, it's the Morrabbin hamfest.

I'd like to know if I'm a raging lunatic or not, and if the idea has any
merit.

Regards

Lachlan


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Old 05-06-2010, 12:56 AM #2
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Default Re: Pulsing C-W Co2 tubes

CW tube pressures are different from pulse tube pressures. Its easy to saturate the tube with a high power pulse, and when you saturate it , lasing will cease. In other words the response is NOt linear to current at the pressures used for cw. So if your cap was low in energy and you were at say less then 2 to 5 times the same average power as the CW mode, you would possibly get a burst of lasing. But if your at overdrive, it would lase briefly and go out.

CW power supplies are easy, a neon transformer and a string on 1n4007 diodes (about 20-30 of them) plus a small filter cap and some ballast resistors are cheap and easy at a hamfest. Co2 ballast resistors are often 20K, and a few watts to ten watts. Find a variac while you are there. Put a 100K, 3 watt resistor across each diode in the series string, this equalizes the voltage across the diodes so they are less stressed. furnace transformers might work just as well as neon transformers for the very small tubes. Remember a neon transformer has a center tapped secondary for safety, so for a single anode co2 tube, you need to float the transformer in a thick plastic box to avoid shorts.

Be very careful both with HV and caps. The Scientific American magazine article on how to build your own Co2 covers this very well, as does one lame book I NEVER thought I'd reccomend, "Lasers, Phasors, and Ion ray Guns" is often found in some public libraries, its pretty much lame, and inaccurate, but its Co2 power supply is simple and actually works.


Steve
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