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High Power Flashlamp Pumped YAG LASER

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LAN_403

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Sun Oct 21 2007, 10:46AM

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

sorry if the post is a little jumpy, it is 3am here

In any case, I finally got a hold of a pretty decent sized laser. It was designed for laser surgery, and used (more on that later) a Ho:YAG rod which was pumped by 2 flash lamps hooked up to a 3500v/70uf cap, and a 3kw SMPS charger.

In any case, I managed to get most of the important pieces to it (the cooling parts being the exception), so it should have been a pretty easy rebuild. And all things considered, it was a pretty easy build, heck I got the first signs of life within 10 hours of twiddling with it

But it did have its problems, mainly that the hv electrodes on the flash tubes are exposed to the cooling water... In theory, if you used ultrapure water that wouldn't be a problem, but lacking said water or the equipment to keep it that way, I had to improvise... So I decided to insulate the terminal with some silicone, and hope for the best.

But that is when things started to head south... As I was reassembling the laser brick assembly for the 5th time, I head a small crack, and got that sinking feeling in my gut, and sure enough, I had cracked the rod

And since this was a Ho:YAG rod, there isn't a real surplus of them around (since they are not used nearly as often as the Nd:YAG), so there was no chance of getting a new one for any reasonable price.

But I got over myself, and decided to hack in the rod out of one of my ssy-1 lasers

Of course the rod didn't quite fit, so I had to use a bit of 5 minute epoxy and cellophane tape (who woulda thought the missing ingredient to a $100k medical laser was a few mm of tape...) to hold it in place, but after a few hours of trying I finally got it all sealed up.

Then it was a simple matter of swapping the optics on the lasers (anyone interested in a HR/OC set for 2100nm?) and pumped a 150J into the flash lamps, and sure enough I got a nice flameball on the target (black piece of paper). So I did the happy dance and tuned him up until I got the pics you see below.

In theory, I should be able to do 10x 4J (output energy) shots a second, although I keep blowing the 15a breaker on my powerstrip if I do more than about .5/sec. In any case, I am getting about 1W of energy out as it is, and hopefully once I get the correct power supply working and hooked up into some big power I should be set for some major vaporising...

In any case, you are probably more interested in the pics of the beast, so here ya go...
the overall cavity

exploded view of the cavity

how the rod and flashlamps go together. They are all in glass tubes which force the cooling water up against the rod/tubes. There is also a silver plated copper cavity that goes around the whole mess

I don't know, but I am guessing there are <1000 people that have seen a Ho:YAG rod in person. For reference, there is a N131 ground into it

But that rod didn't last long (although long enough to do a bit of vaporising

), as it was soon cracked and replaced by the rod out of a ssy-1

Now before we get into the exploding stuff, here are a few other interesting shots...
why you never run a laser with impure water...

The flash tubes with the trigger pulse, but no charge on the main cap

The good stuff...

peter

Steve Conner

Sun Oct 21 2007, 12:10PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

That's impressive 0.o Did you get the power supply too?

ragnar

Sun Oct 21 2007, 12:17PM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

I've always admired your laser work Peter, sorry about snapping the rod -- that must have been painful. (Do I notice the gold plating flaking off in one of those pics?)

Have you got a photo showing some of the electronics, by any chance?

I can't wait to hear about the surgery stories...

Marko

Sun Oct 21 2007, 12:28PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Too bad for the rod, but at least some vaporised steel makes a showoff!

PS. I may be misreading your post, but did you crack the rod during assembly, or it was damaged in operation? (can that happen at all)? Painful in any case.

The thing looks much simpler as I first thought... although I never expected heating to be such a dire problem with pulsed lasers. Did you just give it too much continuous average power and overheated it..?

...

Sun Oct 21 2007, 05:25PM

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

Yes I do have the power supply, it is a really nice supply, and it really resembles something that Steve would have made

Unfortunantly, there is a db25 that does all of the control, and I have no clue as to what wires do what. However, I am pretty sure the manufacture will send me the data when I finally get arround to e-mailing them.

As to the rod, I was bolting the laser brick back together and I had an o-ring that wasn't seated properly that ultimately put some force on the rod and snapped it. Man, when I saw the rod if flet like I had dropped my 1st borne off a cliff or something

As to the electrodes, yes the gold plating is gone. The silicone over the hot electrode seems to be working for the moment, although I am pretty sure there is considerable current running through the water still. For now I am going to leave it there, and fix it if/when something bad happens.

BTW, on the brick, the small cooling lines you see in the first post are for cooling the optics, and the reason that they are in a separate line than the main cooling water is that the 2100nm light is absorbed by water, so something else had to be used. One of the first things I did was pull all of that cooling loop out

Some power supply pr0n:
the PFN:

The big grey thing with a big dent is the 70uf/3500v (500j XD ) main cap, the big black cube is the trigger transformer which induces about 30KV in series with the main cap to fire the tube (no external trigger wire for water cooled lasers), the round thing in the middle is the big inductor to keep the pulse the right length right, the grey rod in the upper left is the 150K 100W bleeder resistor, and PCB in the upper right is the controller for the trigger transformer.

The PS:

An overview of the PS. there is another complete system (filter caps, cores, heatsink, regulator board) under the aluminum plate that the top one is mounted to. The 2 halves are run in anitparallel.

The really high power section:

Notice how the series inductor is would with about 10awg (maybe 8awg) wire, and how the resonant caps are attached to the board with about 10 pieces of wire. Also, those cores are pretty huge (considering there are 4 of them), about 1/2" cross section.

The fets

The fets are irgpc56 600v/70A 'fast' (back with 10khz was fast), and the really weird looking diodes are 600v/25a Notice the extra components for the gate drive, presumable some type of active pulldown? I need to make a schematic of it some day...

Hazmatt_(The Underdog)

Sun Oct 21 2007, 07:30PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

Pretty sweet! Do you know who made the system? If it's Quantel or a different manufacturer? I'm curious because I have a power supply too but I've never seen the lasing unit.

...

Mon Oct 22 2007, 01:39AM

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

The laser is a Coherent VersaPulse model 2000, circa 1993.
The supply is made by converter power inc, presumably just an off the shelf charger used by coherent since they were only making a few hundred of these babies.

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