TO-46 w/ window, heating and cooling

Package it in a low-humidity environment? That would let you move the entry window far away, down a plastic tube maybe, at room temp.

Fiber optics?

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

Right, they make a fiber option. Maybe that is the way to go. They also sell a package with a TEC inside the can. I think the price was well north of $1k.

Here's a silly idea,

It certainly has the uglies.

George H.

Liquid nitrogen is your friend. Boil it off steadily and you have a steam of cold and very dry nitrogen gas to keep you detector cool and keep damp air away from the window.

If you cool the detector with TEC, a second, even cooler TEC could dry the air close to the window by capturing any water vapor that did diffuse in.

If the vapour pressure of water in the air close to the window is low enough, nothing is going to condense on it ...

--
Bill Sloman, Sydney

As long as it works. I did something similar some 30 years ago. There was this large DIP IC in an existing product that would no longer work unless it was warmed up a bit, and a replacement was not available. So I glued a quarter-watt resistor on it and connected it to the unit's power supply. It worked like a charm.

I can do silly: epoxy a plastic rod, a light pipe, to the window of the spad. Its thermal conductivity would be such that the light-entry end is room temp and wouldn't have condensation. The details could be left to a physicist.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

Cementing a piece of plastic to the window might work. You don't want any air space, because water will diffuse into it eventually.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
https://hobbs-eo.com

Liquid nitrogen is your friend. Boil it off steadily and you have a stream of cold and very dry nitrogen gas to keep your detector cool and to keep damp air away from the window.

If you cool the detector with TEC, a second, even cooler TEC could dry the air close to the window by capturing any water vapor that did diffuse in.

If the vapour pressure of water in the air close to the window is low enough, nothing is going to condense on it ...

--
Bill Sloman, Sydney

One traditional way back in the old days of amateur cold film cameras was a suitably thick piece of perspex in front of the sensor and an attempt to dry the air nearby with a sacrificial colder getter (or a supply of dry nitrogen).

Thin nichrome or Raychem heater tape might do it.

--
Regards, 
Martin Brown

Hmm, similar to JL's idea. Why plastic and not glass? I know little about making good glass to glass/plastic bonds. I know there are special glues that match the index of refraction. (reflections are bad) When you look at people's setups for doing these correlation experiments, everything is AR coated.

George H.

ISTR Perspex was the material of choice for this sort of thing. It didn't object too much to being seriously cold and is water clear. This was for astronomy cooled film camera applications in the days before hermetically sealed dry nitrogen enclosures. ISTR a workable design is in SciAm Amateur Scientist which will give you some idea of the numbers.

Glass is too good a conductor of heat and would need to be too thick. ISTR about 1" thickness of perspex would support dry ice to ambient night air without being misted up on a good day.

--
Regards, 
Martin Brown

about

lues

you look

Thermal conductivity of plastic is about 10x lower than glass--about 0.1 W/ m/K vs 1.

Acrylic is great until some bright spark cleans it with IPA and it disinteg rates. I'd probably pick 1/8" polycarbonate as a start.

ARCs will reduce echoes from surface reflections that might put side lobes on your correlation peak.

Cheers

Thanks Martin, and others. So some rod of plastic, maybe I can get someone to put an AR coating on one end. I'm also fabing (making holes in) a hunk of copper clad.

1/2 floating R's with screw holes, for the stack up of; heater, to-46, cold plate. (A piece of plastic will most likely be better, but I can make this tomorrow.)

I should also get a quote on the fiber coupler, I have no idea, any guesses? The spad is $250 for one, I haven't asked for larger volumes.

I'm guessing ~$100.

George H.

perhaps try a place that makes picture frames, you can get anti reflective plexiglass and polycarbonate for those

Dry ice! I was wondering what happens if you cool these things down even more. All the data I've seen stops at ~ -25C, the max of the two stage TEC. (or something) I could stick a finger of copper into LN2, and measure to whatever temperature where my amp failed, or some other connection.

I'm going to want the ARC centered near 800 nm. stuff for visible may not be so good.

George H.