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Old 20-07-2013, 10:43 AM
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Material to transmit LWIR?

I am experimenting with a long wavelength IR sensor (5,000 - 14,000 nm), and am looking for some material to protect the sensor when I install it outside. Apparently most common materials (glass & plastics) do not transmit LWIR. I have not tried the dark-coloured material used on security camera housings, but expect that it wouldn't work, since these cameras use NIR (700 - 1100 nm).

Does anyone have any ideas?

Cheers
Chris
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Old 20-07-2013, 02:47 PM
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rcheshire (Rowland)
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http://www.google.com/search?client=...r+transmission

Chris. A Google search with a number of interesting articles discussing the problems you mentioned with LWIR transmission. I suspect you have read them anyway.
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Old 21-07-2013, 07:34 AM
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Thanks Rowland. I had browsed a number of articles but found one more good one via your link. It does seem that the field is quite limited, and to mainly exotic (or at least - less common) materials.

Now I'll have to start hunting for a small 'sample' of one of them.

Chris
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Old 22-07-2013, 12:13 AM
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looks like polyethylene film works OK if it is not too thick - need to strike a balance between transmission and protection though. If it is thin, will have no optical aberration effect at these wavelengths
http://www.google.com.au/imgres?imgu...9QEwAg&dur=265
has to be the right material though - other plastics can be opaque, even in thin films - I think the current glad wrap is polyethylene.
http://journals.ametsoc.org/doi/pdf/...F%3E2.0.CO%3B2

to improve mechanical strength over a large area, could use flywire to support the film and put up with some additional loss due to shading effect.

Last edited by Shiraz; 22-07-2013 at 11:46 AM.
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Old 22-07-2013, 08:06 AM
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5ash (Philip)
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Cling wrap??
Philip
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Old 22-07-2013, 09:35 AM
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I wonder if anyone told the military that!
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Old 22-07-2013, 11:07 AM
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recent example of transmissive plastic http://www.popsci.com.au/technology/...-boston-bomber - optically opaque material strong enough to use as a boat cover was still fairly transparent in thermal IR and allowed imaging through it.

also seems that bubble wrap may be worth a try http://climateandstuff.blogspot.com....in-camera.html

cellophane? http://www.coloss.org/beebook/I/physiology/5/2/2/4

Tupperware possibly?? might be worth getting an IR non-contact thermometer and doing some tests around the kitchen.

maybe http://www.edmundoptics.com/optics/w...lated-products (this has a polyethylene spectrum)

or just buy a cheap PIR intrusion sensor and use the window from it

Last edited by Shiraz; 22-07-2013 at 04:49 PM.
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Old 22-07-2013, 11:34 PM
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Ray, thanks for all of those suggestions. I will try the IR temperature gun through a few of those and see how they go.
Chris
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