The Big Green Thread (I'm gonna regret posting this in the morning)

[badger1666]

Straight through the middle not on any of the four edges

[steve-o]

LOL dude --
I was kinda hoping for some info on the angles of incidence (yes, on the flat side, but which one(s), polarization, and maybe if I'm lucky, a diagram of a pumping scheme for an MCA . Any help is appreciated muchly !! Thank you all !!!!!

[mixedgas]

Thx Badger, yeh I kind of figured to pump the vanadate .. but where exactly , on any of the 4 flat surfaces (i think it may matter) and polarization etc ..
Steve, I'm not trying to derail this thread.. just adding info from another perspective .. may help .. may not .. too much info never hurts .. :]

The trick is clamping the MCA so it does not crack. My guess is this. REPEAT GUESS! Get a fairly thick piece of copper, say 1/8th or 1/4". Thats your heat sink. Its to not be much larger then you MCA, maybe a mm or two. Copper is a PITA to work with. You may have to heat treat it to work harden it. Copper tooling is ran at VERY high sppeds.

The copper needs symmetrical cooling, at the edges, back, etc.

Drill a hole in it about twice the diameter of the focused pump beam. Lap it on a piece of glass using 600 and 1200 sandpaper, and maybe some 1 u cerium abrasive, wet. If you can see tool marks on your copper, and its not getting very flat, you need to change your technique.

Indium sticks to the copper and crystal when compressed. If done correctly, it allows for the crystal to expand. It WILL expand.
If clamped too tightly, it will crack the MCA.

So this is where it gets tricky. I'd use two polished copper plates, one side gets the indium, the other is copper so it will slide. The indium goes on the hot side. The Asians glue them with a low outgassing, alumina ceramic loaded epoxy after pressing on the Indium with a press. Glue is the issue. You might burn this one, and want to move it over. So I've used nylon screws that "give" and allow for stress. But thats tricky, you have to get a feel for the correct torque on the screws. You also need a even number of screws, at equal angles around the crystal, so the forces are even. Some people would use indium on BOTH sides, including myself.

The MCA needs to expand in thickness, and radially outward. A strong spring, but not too strong, could press a plate on the MCA.

Or the output side could be a nylon or delrin block, etc... I'm not a mechanical engineer. I'd buy two or three MCAs and try a scheme and see if get cracking.

Gettin 4 watts (That Much? Are you Sure???) heat out of the MCA is tricky. The copper transfers the heat to the heatsinks, TE cooler, water, whatever.

I'd call V-Loc or whatever and ask how THEY specify the clamping/gluing, etc.

The other scheme is to press the MCA against a Sapphire disk that is heat sinked into copper.

Releasing Indium often requires heat, after its under pressure a while.

GOOD LUCK, your in a undefined region here, until you practice a bit.

How much do you control the temp of a thin MCA?

On my cheap MCA based laser modules (I've bought em as modules), I end up varying the amount of heatsink to find a optimal pump diode temp. Usually by sliding the laser tube in and out of the heatsink.

The one way you can start is focusing the pump diode and running it at low power, but high enough to threshold the MCA.
Then you back the MCA into the focus. Then you find the bounds and pick the middle. Your also going to need to spin the crystal around its axis if polarization matters. You may also need to let the crystal get a bit warm. Too much focus is bad, too.

Welcome to "ONE SHOT AT IT" laser design. There is art in it, besides science.
Its a thinking game. The above is suggested advice, and worth a pitcher of warm spit.

If these were rectangular crystals, I'd have better advice.

Steve

[steve-o]

Thanks Steve,
I was thinking of using spring-loaded heat sinks to allow for expansion. Would that do ?

[mixedgas]

Thanks Steve,
I was thinking of using spring-loaded heat sinks to allow for expansion. Would that do ?

Spring on OUTPUT side, yes. But oh whatta spring. You need to play with a piece of Indium foil. Not too much force, but not too little either.
Dont totally squish out the indium. It needs to stay a bit thick so it provides "give" around the crystal.

A big spring may do more harm then good.

Dang, that was about as scientific as the Flintstones. I just dont know how to express "FEEL" in prototype making.
I know the correct indium compression when I see it. That is hard to express.

This is why I like 4-40 nylon screws.

Sizing the copper block for a 3x3x5 KTP with Indium 100% around the crystal is easy. That I know how to do. This is hard to express.
Its easy to clamp/glue one of these MCAs at half a watt of pump. Not so easy at WATTS of pump.

We now return to the thick crystal high power thread, where the mechanics are actually easier.


Steve

[steve-o]

Yes, a "spring" as in, a piece of light guage aluminum flange on only *one* side of the heat
sink of the non-critical side of the crystal, so as not to affect the alignment, of course
Yes, definitely--now back to the serious matter of the project-at-hand -- ;]
Thx 4 the info --
Peace--
--S

[mixedgas]

A very wide 1/16 thick piece of 2024 ( Soft Al, has give, but bad hysteresis as a sping) with all four corners secured with 4-40 nylon is possibilty. Not my prime choice, but doable. Practice on a cut down piece of microscope slide or cover slip. You may need a nylon or mylar pad some place.

Make both sides hard, stiff copper, clamped with give.

I just took a closer look at your new toy.

What you have is called "END PUMPED", because its pumped into the broad face.

I wonder if they use a fat pump and use more of the crystal area instead of a focal tiny spot.

It is optically contacted, but I have no idea what the clear stuff is. I'd hope for clear, undoped vandate, or sapphire.

Many mysteries here.

Steve

[steve-o]

Thx again Steve, once I find a suitable 808 diode and lens I'll prolly jest play around with it an' see what I can get .. thx again .. cheer-i-o-o ..

[mixedgas]

Sorry, but you can only have good quality compound on the copper, but at least 3-4 mm from any optic. Any of that stuff gets on the optic, it will scratch it when you clean the optic. If you need compound, other then on the pump diode, I'd rethink things a bit. Only God and the factory chemists will know if it outgasses.

BTW, handle these in such a way that you should NEVER have to clean it. Clean/Scrub everything except the MCA, lens, and pump diode with acetone and alcohol before assembly. Photography places have cheap cotton gloves by the bag, I'd avoid rubber gloves like the plague.

If this goes further, lets pop open a cool "MCA" thread and copy these posts over.

Makes it cleaner to read/search

Half inch end mills with four flutes and flat cutting ends work OK in drill presses. 1/2" Copper rod is on Ebay. I've used this to press copper studs and steel ball bearings into THICK aluminum blocks. In other words, with practice, you can make a interference fit on a drill press. You drill the half inch hole undersize and then ream it to a -0/+.001 fit with the end mill spinning in the drill press. Drill the copper on a lathe so the pump hole is centered. Now that I have access to a mill I dont do it any more. But I did do it when I was kid. It requires a inexpensive machinists vice to do this.


Steve

[planters]

Steve-o,

This was the point of the OP, so no problem at all. I agree with Steve R.'s advise except I do not like the nylon screws as much. Don't get me wrong they do work,but as they tighten they can bind and get a little sticky so it can get hard to tell if you are tightening them down or just twisting the plastic. I prefer belleville washers. They are available in various degrees of stiffness and I like the stiffer ones in any given screw size for this purpose. They also work well for TECs.

http://www.mcmaster.com/#belleville-...prings/=k3wa6c

Also, if you do get to an operating laser and you reach threshold, then as you adjust the focus of the diode and/or increase power watch the divergent beam ( use a weak lens or better view a retro-reflection for a LONG beam path). It will be easier to see if things get a little funky; hopefully before anything breaks.