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1J/5ns 187 MW Q-Switched YAG Laser!

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LAN_403

plazmatron

Fri Jul 03 2015, 01:12PM

Registered Member #1134 Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351

I havent posted here for a while, been away doing a CS Degree, but now the Summer is here it's time to ressurect dead projects!

I picked up off eBay what was described as a 'Tatoo laser handle' for 80 quid. These contain a small YAG laser head, and as it turns out a KTP crystal for second harmonic generation to 532nm (Bright Green)

A bit of google-ing revealed this is a watercooled unit capable of 1 Joule shots, with a 5ns pulse width, and a repetition frequancy of 1-6Hz (6W avg power, 187MW peak, yep Megawatts! )

The PSU's for these are quite expensive, and are supposed to 'Simmer' the lamp between shots, and are thyristor triggered.

I couldn't externally trigger the lamp, since the case is at ground, and the cavlity is suposed to be watercooled anyway. To avoid complexity I built a PSU using a series trigger for the lamp.

The PSU is a dead simple capacitor charging supply, that charges up a single 100uF 1400v capacitor using a circuit similar to the one described by Uzzors, and is designed to cut off at 1200v.

The tirigger circuit charges up a 11nF capacitor to around 8kV which discharges through a 4 turn primary of a hand wound transformer omn a ferrite ring. The secondary is 12 turns and is in series with the lamp circuit, providing the necessary start pulse.

When this laser was first fired, it became obvious why it was for sale, the beam quality was attrocious and the output was low!
It had probably been dropped, and wasnt helped much by poor engineering. Case in point was the rear mirror mount. After much faffing about, I got a little more output, but the mount itself is terribly designed, with four adjustment screws fighting one another!

I shimmed the cavity to the correct height, mounted the whole thing on a slab of aluminium, and removed the rear mirror mount, then replaced it with a proper kinematic mount.

(Above is an image of the Q-Switch (Cr:YAG)

Now this thing really sings! All I have to do no is source a small waterpump to water cool it, and I can have it pumping out 6W avg power!

As I mentioned earlier, this thing contains a KTP crytal, and it is huge! (6mmx6mmx4mm) Anyone who has built a dpss will appreciate the size!

If a short focus lens is attached to the laser, the pulse is so large it will break down the air at the focal point!

I only have one poor picture of this at the moment. I had to take video, and strip out the frame as a jpeg....

921

Experimentonomen

Fri Jul 03 2015, 05:14PM

Registered Member #941 Joined: Sun Aug 05 2007, 10:09AM
Location: in a swedish junk pile
Posts: 497

Get a computer cpu water cooling kit for cheap, should be enuf to keep this baby cool.

U just need to find a coolant that does not absorb too much of the light from the lamp, as well as not corroding the cavity as seen in photonicinduction's latest vid.

I'd guess a light oil is usually used to cool these rather than water.

plazmatron

Fri Jul 03 2015, 09:21PM

Registered Member #1134 Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351

De-Ionised water according to the specs, I have been running it with the cavity filled with water in anycase, to make sure I dont damage anything.
The lamp and rod are mounted quite close to each other, and the absorbtion of water is a mile away from the aborbtion peaks of Nd:YAG

Sure a CPU cooling setup would be ideal, I'm on the lookout for a cheap enough deal.

...

Fri Jul 03 2015, 09:50PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

Luckily that laser has the electrodes insulated from the cooling water, so just about anything will work as long as it is not too corrosive or absorptive at the 800nm absorption line of nd:yag. Water with normal clear pc cooling additive would be fine.

I wonder if these are going to become the new 'ssy1' of the hobbyist laser community, considering that they are pretty cheap new (just a few hundred bucks for the gun, even a whole brand new system can be had for under a thousand dollars) and have such short lifetimes that I imagine a lot of 'half dead' heads showing up on the usual surplus channels.

It would be interesting to meter the output energy, I am skeptical of their claims in terms of energy/pulse duration, would be interesting to see what the typical performance is for these systems.

Sigurthr

Sat Jul 04 2015, 12:26AM

Registered Member #4463 Joined: Wed Apr 18 2012, 08:08AM
Location: MI's Upper Peninsula
Posts: 597

Gorgeous performance, excellent decisions with redoing the mirror mounts, and fantastic summer project! Well done. I suggest you post this over at the laser forums too (LPF and PL) they'll love it.

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