Cryogenic diodes

[jnrpop]

Hi
i recently purchases some cryogenic pulsed or cw 618-635nm red/orange diodes from chris ( Herrc )
I need to get a suitable enviroment of around -20C to -40C for a CW red output or a Pulsed orange 620nm output

Would anyone have any ideas how i would achieve this temp, is it even possible with using a TEC/Heatsink/Fan setup.
I have a Kovar box with built in tec, i can run it around 2a which should be about around 30W, is that efficient enough for this amount of cooling? Ive got to worry about condensation also.
Any input would be greatly appreciated, Thanks

[shrad]

hi,

the TEC has to be outside of the box, and I imagine the kovar box has the peltier inside of it which is not what you want

to reach -20, you'll need to stack several peltier devices to achieve a delta T of several times what a single peltier can do

to avoid condensation inside the box, you'll have to flush the air inside with a weak vacuum, then fill the box with a neutral gas (food grade CO2 like the one used for cream syphons will do) and then seal the box

the main problem is, if your box has its inside at -20 to -40, it will be covered with ice in less than a minute if it is not insulated well enough

even if it would be insulated enough, there's still the question about the insulated window and how to avoid frost over it

[jnrpop]

Thanks very much for the info, yer its going to be a challenge, Dry ice is the other option but i dont think getting to -20C is the problem, its cooling the diode to that temp without having its output frosted or subject to condesation, i think the diode is open-can, allowing me to create a dry-ice box setup with the open-can side sticking out of the super cooled heatsink, allowing me to collimate the output seperate to the diodes....but i do have co2 on hand, just need to insulate and seal this kovar box, its either figure something out or run it pulsed at -1C to 2C...Should be fun.

[shrad]

if your diode's body is at -20°C, condensation will form on the diode chip also, especially if they are in plain air

your diodes must be mounted in a block which will be refrigerated, but the whole setup needs to be enclosed, so the collimation setup will also reside in the cold area, and you must find a way for the beam to exit the enclosure without being totally messed up with ice on the external side of the window

[wolfblue]

You might want the diode in nitrogen for the moisture, and then heat the output window. If you were clever, you could even heat the window with same TEC stack that cools the diode.

--John

[shrad]

actually CO2 is the same for moisture, I had a talk with the people at work about neutral gases to fill enclosures with (I was trying to get a bottle of N2 for that purpose, but that was lab grade gas in 200bar bottle, quite expensive and dangerous)

they told me any CO2 or even N2O cartridge would prevent moisture as any N2 filling, with a much, much lower price

[jnrpop]

Thanks for the info, does anyone know what a cold-finger is? Chris recommended using this setup for the diode! I wonder what unit these doides actually came out of, would have to be a extensive expensive setup!

[ledfreak3d]

lol this is not going to work

[jnrpop]

What are your thoughts ledfreak3d? Im unsure about the whole thing to, so you now what a cold-finger is?

[sugeek]

What are your thoughts ledfreak3d? Im unsure about the whole thing to, so you now what a cold-finger is?

http://astro.ai-software.com/article.../quickcam.html

This is a different application but it will get your point across. The diode would be attached at the end of a thin piece of aluminum as a cold finger which then in turn is attached to the peltier device.

An example from the link above:


-Adam