Sweeping through infrared frequencies

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ahmedswift
 
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Sweeping through infrared frequencies

Post by ahmedswift »

Hello, I am working on a spectrometry project with the NoIR camera. I need to be able to emit different IR wavelengths in synch with the image capture. Do you carry (or can you suggest) an IR source that can be controlled to sweep through IR frequencies? I don't need a fast sweep or anything in very high frequencies. Thanks

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adafruit_support_mike
 
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Re: Sweeping through infrared frequencies

Post by adafruit_support_mike »

I don't know of anything pre-made off the top of my head, but you should be able to build a black-box emitter without too much trouble. The general idea is to make a heated box inside a layer of insulation.

All objects absorb and emit photons at a rate that's determined by the temperature of the material, and the peak frequency is a function of the temperature. If you heat a box to a given temperature, the photons emitted from the inside surface can't leave the box, so the have to be re-absorbed by some other part of the inside surface. If the temperature of the box is constant, the frequency of the photons inside the box will settle to the frequency where they're absorbed at the same rate they're emitted. If you cut a small hole into the side of the box, you get a stream of photons at that frequency.

Black-box chambers are usually made from graphite, which is conveniently close to being black and is stable at high temperatures, but for the IR spectrum just about anything will do. The peak black-body frequency crosses into the visual spectrum at about 500C, so you should be able to get the temperatures you need using the heating element from a cheap soldering iron.

For the sake of speed, you can make the box from copper or aluminum tubing with endcaps. Those metals transmit heat well, so you won't have to wait very long for the temperature of the box to stabilize. Put a thermistor or thermocouple hanging free inside the tube to measure the equilibrium temperature of the photons inside the tube, and wrap the whole thing in an inch or so of rock-wool insulation to keep it from losing too much heat to the air.

Add a piece of 1/4" tubing from the emission port to the outside of the box, and you should have a fairly good controllable IR source.

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ahmedswift
 
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Re: Sweeping through infrared frequencies

Post by ahmedswift »

Thank you, I had not considered a heatbox in my question. My bad, I should have set the context. I am looking for something that will, for lack of a better term, "shine" IR light on an external target and use the NoIR camera to gauge the strongest response.

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zener
 
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Re: Sweeping through infrared frequencies

Post by zener »

You could put a hole in the heat box and focus the IR with something like this:

https://www.edmundoptics.com/optics/opt ... el-lenses/

Or confine/direct the emissions with a tube that has very low emissivity (highly reflective), like aluminum foil which has an emissivity of 0.03.

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adafruit_support_mike
 
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Re: Sweeping through infrared frequencies

Post by adafruit_support_mike »

The only other thing I know of that would allow you to sweep IR frequencies would be an array of dye lasers, which would be an expensive proposition.

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ahmedswift
 
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Re: Sweeping through infrared frequencies

Post by ahmedswift »

Thank you for the responses. I will post when I get this built

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