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IIRC laser beam divergence is often specified in mrad.

"Like all electromagnetic beams, lasers are subject to divergence, which is measured in milliradians (mrad) or degrees."

http://www.parallax-tech.com/fluorine.htm

only $2450 for 3 gallons..... it wouldn't be exotic if the liquid was cheap.

Heh, looks like my recollection on the pricing is a bit off: 250ml for 555.35USD at one retailer and 3Gal for 2,450USD from another.

Oil IS an accepted dielectric fluid! Highly refined mineral oils are widely used for cooling and insulating electrical equipment (like the transformer that feeds power to your house), and relatively cheap, even given current petroleum prices.

Specialty fluids like Fluorinert are less messy when you need to work on the submerged parts, but that stuff is EXPENSIVE. How about over $300 per LITER?

http://www.parallax-tech.com/fluorine.htm

I forgot to mention 3M Fluorinert:
http://products3.3m.com/catalog/us/en001/oil_gas/s pecialty_materials/node_HX0DNRHXKWge/root_GST1T4S9 TCgv/vroot_G1F6DNZDBVge/theme_us_oilgas_3_0/comman d_AbcPageHandler/output_html

http://products3.3m.com/catalog/us/en001/oil_gas/s pecialty_materials/node_L98WR0Q8WQbe/root_GST1T4S9 TCgv/vroot_G1F6DNZDBVge/gvel_M2C4BHRN70gl/theme_us _oilgas_3_0/command_AbcPageHandler/output_html

http://www.parallax-tech.com/fluorine.htm
"1 liter bottle Fluorinert-77 ~ 4 lbs = $240 plus shipping."

I should call 3M and see if they can find me a non-conductive, inert, non-volitale chemical to submerge a PC in. I'm sure they make one.

You should. But I'll save you the trouble.

It's called 3M Fluorinert, and now that it's come up in two separate discussions in two days, I now know more about the stuff than I ever wanted to. (Great use of company time, eh?)

This is the 3M page about it, they make a bunch of different varieties for various purposes. I believe what you'd want to use on a computer is the '77' variety. (I'm told that's what the Cray II used.) 3M Fluorinert
Some people who will sell it to you in small quantities (3M wants you to buy 11 lbs.)
And here's the obligatory Wikipedia entry: http://en.wikipedia.org/wiki/Fluorinert

I just did some research...my un-implemented idea about submerging a mobo in oil was a while ago, and at the time I was never able to find any supporting information on it. It seems now though that a lot of people had the same idea, and a few of them have even gotten it to work.

Also, I found the name of the material used in the Cray II's submersion cooling system. It's called Fluorinert FC-77, and it's made by 3M. Electrically inert, not toxic to the touch (unlike PCB based transformer oils), great heat transfer properties ... too bad it's ridiculously expensive. The cheapest place that sells it in small quantities (3M wants you to buy 11 lbs.!) has it for $240 a liter. Apparently it's used in the cooling systems of some lasers.
http://www.parallax-tech.com/fluorine.htm

However there are people who have successfully cooled systems by submerging them in vegetable and sunflower oil:
http://www.hwspirit.com/reviews.php?read=16 Sunflower Oil
http://www.markusleonhardt.de/en/oelbilder.html German, Vegetable Oil (?), even submerges the PS

I can't find a picture of a mineral oil cooled one (although there are references to a Slashdot story), but I think if I were going to do it, I'd definitely go for some sort of inorganic or synthetic liquid. Having a rancid vat of vegetable oil on my desk just doesn't appeal to me at all.
These guys will sell you a 5gal jug of "odorless, tasteless, crystal clear, technical grade white mineral oil" for $54.45 (and they have 55gal drums available, if you want to go into business). They have a bunch of viscosities available, I just looked at the lowest one.
http://www.steoil.com/catalog.asp?productgroup=70t

May I recommend Fluorinert FC-70?

For new customers, 1 liter bottle ~ 4 lbs = $240 plus shipping. Existing customers pay $220 for 1 liter.
http://www.parallax-tech.com/fluorine.htm

100W is plenty for a couple hundred kilobits from Mars with a 1.3m dish (as evidenced by Mars Odyssey). This corresponds to about 2 degrees of beamwidth.

A cheap industrial CO2 laser has a beam divergence of about 2 miliradians; this is about .12 degrees. Assuming you do this on only one side of the connection, you get about 24dB of additional gain. In other words, putting a 100W output power laser on a Mars orbiter gives you a EIRP equivalent of 24kW into a 1.3m dish, while saving a bunch of mass and volume occupied by the dish.

You can buy Fluorinert it in 250cc or 1L bottles here:

http://www.parallax-tech.com/fluorine.htm

I saw on a website onetime where a guy had his whole computer in (IRC) mineral sprits. In the web site he recommened the use of FC-77 as mineral spritis is flameable; but the site noted that FC-77 price was quite high. A quick google search reveles that one site has FC-77 for a little over $200 a litter. Maybe buying a window AC unit and hacking it into computer case may be cheaper?

Uhmmm, unless the lasers are considerably cheaper than this, I think that you are going to be hard pressed to put one together for a grand.