Z-Fold 532 nm Cavity YouTube Video

[Laser57]

I found this green wavelength DPSS cavity interesting, anyone ever see one of these specific laser cavities before? Curious what it might be out of.


https://www.youtube.com/watch?v=GvKyKeSZIaU

[mixedgas]

Not what I thought it was, as its DPSS...

Was thinking Laserscope AURA, but has DPSS instead of lamp pumped.

Sorry.

[buffo]

The company that bought out Laserscope (was it AMS?) released a diode-pumped, q-switched YAG that was quite a bit more powerful than those old flashlamp-pumped units. Dan Briggs had one at the UKLEM. This arrangement looks similar (albeit with a simplified optical path); I wonder if this is one of the early DPSS units from AMS? (Briggs would probably know...)

Adam

[Laser57]

I wrote Daniel Beam on is YT laser channel, by that name, no answer regarding what this came out of. I'd love to have an old Laserscope whether flashlamp or diode pumped, but they are too heavy to ship to me in Qatar, plus I won't be here forever, maybe returning to USA this year.

[buffo]

Yeah, I saw that. Not sure if "Daniel Beam" is actually Dan Briggs or not, but I suspect it's someone else. Still, if that guy replies to you, that would be cool too.

You can find the later versions of the DPSS medical units from AMS on the surplus market for crazy cheap, but that's because without the encrypted cards that come with the fiber package, you can't get the computer to do anything. (And without the computer, running the pump diode driver in manual almost always results in a blown YAG rod after just a few minutes of operation.)

I heard that someone here in the USA figured out a work-around, but I don't know the details - or even where to start looking for info. Maybe this "Daniel Beam" has some info...

Adam

[Laser57]

Manual control of? Just the current? If you had a current limiting driver, that shouldn't happen, especially if tied to a temperature sensor but maybe the guy twisting the knob might have been sloppy.

[buffo]

I'm not clear on the details, as this is well beyond my experience, but as it was described to me, the IR pump diode on the AMS units is capable of producing close to 700 watts. This translates to nearly 200 watts of green (average power of course; since it's Q-switched, the peak output is in the 10's of KW).

The key is that the YAG rod is end-pumped. If you hit a YAG rod with 700 watts of IR at the nominal absorption wavelength, the rod basically shatters at the face where the pump energy first enters. Obviously this is not good.

To get around this, the computer adjusts the output wavelength of the pump diode by very carefully adjusting the temperature of the diode, such that it's output wavelength is "detuned" away from the peak absorption band of 808 nm. Thus, the absorption is less efficient and the pump energy can penetrate deeper into the rod before being absorbed. This prevents the rod from shattering while also ensuring that the entire length of the rod is fully excited. This wavelength adjustment is not a static thing either - the computer is constantly making adjustments to the pump diode.

That's why if you try to bypass the computer (because you don't have one of the encrypted cards that would otherwise enable the computer to function), you will quickly destroy the YAG rod, because you don't have a way to accurately detune the pump diode's wavelength. I've been told that without the computer, these lasers will only operate for a minute or two at full power before destroying themselves.

I suppose if someone really understood the physics going on, they might be able to come up with their own diode driver and TEC module that would accomplish the same feat as the original computer, but to the best of my knowledge, no one has managed to do this. (Although there is a rumor that someone here in the USA figured out some sort of work-around; likely related to spoofing the encryption cards, if I had to guess.) That's why these units turn up on the surplus medical market for next to nothing. They're essentially worthless if you don't have the cards to unlock the encryption (and the cards are single-use only, and are fantastically expensive, or at least they were back when they were still available).

Again, this is my understanding after listening to others describe how these things work, so I could be off on some of the details. Please post back here if you are able to learn anything from "Daniel Beam".

Adam

[Laser57]

I'd be happy to run at one quarter the full power it was designed for Appreciate the insights. If he responds to my question, will post.

[mixedgas]

That would be Kevin @ Starlight... He didn't crack it, he designed a whole new controller. But I fear he's not doing that project any more.

Steve

[Laser57]

I know Kevin, thanks!