TO-46 w/ window, heating and cooling

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So now I need to cool down my spad.  It's in a to-46 pac,  

https://www.dropbox.com/s/zwnnh54jmxp3cgf/TO-46.JPG?dl=0

Unfortunately cooling it will mean I get condensation on the window.  
So I want to try heating around the window area and cooling the rest.  
(with TEC.)  How to do it?  The case is magnetic so there is a good chance
the thermal conductivity is not all that great.  I guess the first thing I  
will try is making a little donut shaped heater, and try sticking that to  
the front face.  

But I'd love to hear other ideas!  

Any favorite heater wires? I've got this Phosphur bronze wire,
http://www.calfinewire.com/datasheets/100164-phbronze5cda510a.html
but it takes a lot to make a few ohms.  

George H.    

Re: TO-46 w/ window, heating and cooling
On Tue, 22 May 2018 07:40:30 -0700 (PDT), George Herold

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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  


Re: TO-46 w/ window, heating and cooling
On Tuesday, May 22, 2018 at 10:53:13 AM UTC-4, John Larkin wrote:
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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,
https://www.dropbox.com/s/tk7uga8ytj2d714/heater.JPG?dl=0
It certainly has the uglies.  

George H.  
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Re: TO-46 w/ window, heating and cooling
On 5/22/2018 8:48 PM, George Herold wrote:
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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.

Re: TO-46 w/ window, heating and cooling
On Tue, 22 May 2018 08:18:41 -0700 (PDT), George Herold

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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  


Re: TO-46 w/ window, heating and cooling
On 05/22/2018 11:18 AM, George Herold wrote:
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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
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Re: TO-46 w/ window, heating and cooling
On Tuesday, May 22, 2018 at 12:08:23 PM UTC-4, Phil Hobbs wrote:
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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.    
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Re: TO-46 w/ window, heating and cooling
On 22/05/2018 18:58, George Herold wrote:
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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

Re: TO-46 w/ window, heating and cooling
On Tuesday, May 22, 2018 at 2:06:51 PM UTC-4, Martin Brown wrote:
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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.  

Re: TO-46 w/ window, heating and cooling
onsdag den 23. maj 2018 kl. 02.31.23 UTC+2 skrev George Herold:
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perhaps try a place that makes picture frames, you can get anti reflective
plexiglass and polycarbonate for those




Re: TO-46 w/ window, heating and cooling
On Tuesday, May 22, 2018 at 8:42:38 PM UTC-4, Lasse Langwadt Christensen wrote:
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I'm going to want the ARC centered near 800 nm.  
stuff for visible may not be so good.  

George H.  

Re: TO-46 w/ window, heating and cooling
On Tuesday, May 22, 2018 at 2:06:51 PM UTC-4, Martin Brown wrote:
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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.    

Re: TO-46 w/ window, heating and cooling

about  

lues  

 you look  
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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



Re: TO-46 w/ window, heating and cooling
On Wednesday, May 23, 2018 at 12:40:35 AM UTC+10, George Herold wrote:
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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


Re: TO-46 w/ window, heating and cooling
On Wednesday, May 23, 2018 at 12:40:35 AM UTC+10, George Herold wrote:
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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


Re: TO-46 w/ window, heating and cooling
On 22/05/2018 15:40, George Herold wrote:
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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).
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Thin nichrome or Raychem heater tape might do it.

--  
Regards,
Martin Brown

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