Laserscope 800 / ALE YD4 Arc Lamp Power Supply

[dsli_jon]

...Molded, pressed PTFE reflectance material.....just thinking.

Hmm, interesting.. ie: http://www.berghof.com/en/products/p...nce-for-light/ ..However, I do-wonder if this had-been considered back-when, and discarded for either thermal, DI-water (long-term..) or long-term-performance properties, under-Kr-light-bombardment considerations, etc.. I don't have / know 'intra-cavity thermals' data, but.. Someone-must..

..In-particular, I'd be interested to see 'what would happen' to a PTFE cavity when, 'running hot' (40A) the water was suddenly jerk-stopped (mains power loss, etc..) - Which, btw - @ Draco, there, is a 'leading cause for Lamp-explosions'.. - and then re-started.. You know, 'abuse the cavity' a bit.. I'd suspect it would be 'fine' / stable, etc, but.. I'd wanna see a study performed to be 200% sure any-such 'severe stresses' could-not encourage any 'liberation' of any chem-component (..again, long-term..) of PTFE, as to forming 'deposits' in the closed-loop, there...
In-particular, 'build-up' on on the lamp / rod / flow-plates, etc.. ya know, sort of a 'wet-fog' at µm-levels even the double-team filtration-sys can't sack-out.. Certainly can't back these postulations w/ any data right now, but.. as you say, 'worth a think' / study..

..And, I've already got a great 'marketing tag-line' for such-cavities that You, in particular, should like: 'PTFE or Die'..

j

[planters]

Jon,
PTFE diffuse reflectance material is basically sintered Teflon. This material is EXTREMELY hydrophobic and should be one of the few materials compatible with DI water. Labsphere manufactures laser cavities with this material and has for some time. I believe that when the LS was designed, Labsphere was the only company around that manufactured this material (they have been around for decades and I have worked with them for this long). They charged a fortune. Now, there are at least three other companies that manufacture this material (that I know of) and the costs are lower.

I think that any water failure condition that threatened the chamber would threaten the lamps as well and should be covered in a fail safe shut down.

This material has the mechanical feel of a typical plastic such as Nylon or Delrin and can be self supporting, but apparently can be further enhanced with a highly reflective metal backing (private communication) because its light absorbance is negligible. Reflectances of 99.8% have been measured. We're talking cavity ring down.. a light capacitor. I'm replacing the BaSO4 reflectors on my pulsed dye with this material and plan to take advantage of the decreased losses to allow me to significantly reduce the dye cell diameter and retain efficient coupling. At these levels even the thin trigger wires become an issue and need to be redesigned.

The manufacturer says I should be fine, but I'll see if this gets fried.

[mixedgas]

CW arc lamps have a different electrode material then pulsed lamps. CW lamps really need to be designed for modulation parameters if they are going to be pulsed. The pressures are far different between a CW lamp and a Pulsed lamp as well.

There are some fundamental differences in the electrode aging that I can't get into details on the fourm, but suffice it to say a lamp should be designed for modulation if its used.

Steve

[planters]

Steve,
You are correct. Where I question the requirement is when the electrode never stops emitting as in a modulated ARC that simmers or say never dips below 16-17A between pulses. The reason I am questioning this is that obviously you can modulate the current on a standard LS even if only at the ridiculously slow rate of several HZ (manually). Also many pulsed (flash) lamps are operated in simmer mode between pulses. I see this as further blurring the line between these two regimes.

Another way to check this out is to get the parameters of the replacement lamps used on the GL models. I think they are doing this.

[mixedgas]

Steve,
You are correct. Where I question the requirement is when the electrode never stops emitting as in a modulated ARC that simmers or say never dips below 16-17A between pulses. The reason I am questioning this is that obviously you can modulate the current on a standard LS even if only at the ridiculously slow rate of several HZ (manually). Also many pulsed (flash) lamps are operated in simmer mode between pulses. I see this as further blurring the line between these two regimes.

Another way to check this out is to get the parameters of the replacement lamps used on the GL models. I think they are doing this.

There are some surface interactions on the electrode as you run the lamp, that form "needles" of emissive materials based on the local electric field. As you can guess, that forms a very nice field emission nano-cathode with very high emissivity. This creates a emissive hot spot that works much better then just the ordinary work function. However under some regimes these needles are destroyed.

"Seasoning" of new flashlamps and arc lamps is a well known but somewhat anecdotal thing among laser technicians. Flashlamp pumped lasers often need a reduction in lamp voltage after a week or two of high rep rate operation, the lamps become better then when processed at the factory.

Going into the mechanisms of Dispenser or "Phillips" cathodes is outside the scope of this thread and takes me into NDA Space.

Suffice it to say there is a discontinued application note and spreadsheet on ramping lamp currents that I really had to work hard to obtain. Some lamps can, some lamps can't. A VP of a very, very, very, large corporation that makes lamps ordered a forklift to a warehouse to recover a retired engineer's whole desk and filing cabinets from a very high perch. It was perched where no one would ever mess with the precious notes, that would NEVER be digitized. They then recopied the notes onto letterhead with the new company name and that WAS the application note. The notes were given to selected customers in the past, and one customer referenced it in a manual. Hence my finding it. My employer at the time was important enough (buying many, many, lamps) to warrant summoning the forklift. True Story)

Subtle differences in the lamp wall to electrode spacing also matter for various thermal and gas reserve reasons.

Short version: Verify the lamp cathode can operate in the regime used.

A brief section on Quasi CW operation is in the PE lamp catalog.

Steve



Steve

[dsli_jon]

I think that any water failure condition that threatened the chamber would threaten the lamps as well and should be covered in a fail safe shut down.

Sure, of course, any 'temp-critical' water-cooled sys should have some sort of 'dumb' pressure-based res / 'bladder tank' that would 'scrub' the cavity of heat / prevent lamp / rod damage, in-case of sudden mains / pump-failure, etc, but I'm talking about 'long-term fogging' / deposition effects on the glasses, from the thermals and/or DI.. Knowing, however, that 'Labsphere' has-had commercial PTFE laser cavities in-play for 'some time' is good data.. Sounds like you have a 'LS cavity-retrofit project' on your plate..

Cool-thinking; Will be keen to see "the Video"..
j

[planters]

Jon,
ANOTHER thing about this stuff is it is vacuum compatible and has a decomposition temperature above 400C...

http://www.labsphere.com/uploads/tec...d-coatings.pdf

However, I like the way my cavity does not leak and continues to run without a hiccup (knock on wood). I suspect the gain from this cavity material would be on the order of 10-20% (very uneducated guess). If the cavity was shot and a new one had to be bought/made then I would look at this material first.

Back to the spirit of the OP, I think the real gains would be realized with shallow modulation of the lamps, or...

I don't know if I told you this, posted it elsewhere or just mumbled it to someone. But, I thought of modifying a LS cavity to hold an additional lamp(s). This would be a true flash lamp, powered by an independent circuit that pulsed in conjunction with the Q switch. The main arc lamps would be unaffected and the pulse width would match the duration of the switching. The rod would be dumping energy as the flash provided more. The rod might experience lower thermal variations with time. Spontaneous emission from the rod which is wasted power between pulses would not rise with the added input. The attractive thing about this is it could be tested without modifying the underlying electrical system. The attractive thing about arc modulation is it does not require new hardware.

[mixedgas]

Planters,

Storage time of ND: YAG is 230-260 uS depending on doping and exact host composition. You'd pump the aux lamp 256* +/- 10 uS ahead of the Q-Qswitch opening. Except you'd have five possible issues. 1. The other plasma may adsorb part of the auxiliary light. 2. The rod may saturate. 3. You may end up with cavity optics damage. 4. The thermal lensing shall be interesting.

Besides the PSU to pulse a flashlamp at any rate over 30 Hz is going to be a monster. I'd be glad to send you contact info for a Lithuanian company that makes flashlamp PSUs, and its NOT whom you think it is. (Planters knows who I used to work for)

But at that point why not just go to two CW lamps. Its not like that is not already done on industrial lasers.

* Critical Number for a proper critically damped lamp driver.

Steve

[planters]

Steve,
That's what I wanted to hear, good reasons. These are ALL good reasons the flash lamp would prove squirrely, maybe fun, but squirrely.

The arc modulation is still attractive. That storage time implies that at a 10kHz rep rate (100us interval) that nearly 1/2 (unless this is a 1/2 life decay and then approx 25%) of the energy is lost waiting for the next pulse. Imagine if you were to run the lamp at 40 A continuously, but say 10 usec ahead of the Q switch you goosed it to 100A for 10usec. If the repetition rate was 10kHz then the duty cycle would be 10% and the average would be 46A. 2,3 and 4 might still apply, but you not be moving as far afield. Your thoughts?

Also, could you PM me that flash lamp PSU manufacturer? I'm running a lot of flash lamps now.