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OT: polyethylene infrared window source

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  • OT: polyethylene infrared window source

    I need a small (20mm) window through which I can take infrared (heat) images. After a bit of googling I found out that a thin sheet of polyethylene would do very well indeed, but I need some help in finding a household source I can use to test the concept.
    Clear soda bottles etc. would probably work well and have roughly the stiffness I want, but they are curved and I'm not sure adhesive will keep it flat.
    Would anyone know a better source to harvest a small, flat and optically "fair" piece?

    I'd also be grateful for any adhesive suggestions to bond it to steel :-)

    Thanks,
    Igor

  • #2
    What wavelength? Typically true mid to far IR thermal imaging cameras use sapphire, germanium, or Zinc Selenide windows. Silicon is also somewhat transparent.

    The problem with polyethylene is getting something optically clear like you mentioned.

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    • #3
      Hard to say exactly what wavelength, it's a thermopile array so it depends on the windows used in the device (which is not mentioned on the datasheet). However it seems there are commercial polymer windows available for imaging applications, so it's not too far fetched.
      Now I'm second guessing whether a soda bottle will work as it's PET, not PE...... Milk jugs seem to be PE, but are usually frosted.

      Igor

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      • #4
        How big do you need? I have a couple small sapphire windows somewhere around here.

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        • #5
          That's very kind, but sapphire blocks everything from 6um which might be a problem. The polymer windows have a much wider passband.
          I'll have to check with the manufacturer what type of window is in the device itself. If they use sapphire as well it would be the best solution.

          Igor

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          • #6
            If it didn't need to be "rigid" I'd use "Saran Wrap" (reg trade mark) or equal.
            We used that on a 6" window back in about 1960 or so for a long wave scanning
            system. (human temp against ambient background)
            Does that date me? :-)
            ...lew...

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            • #7
              Anchor Optics is the source for all such things at very reasonable prices. It is the scratch and dent sale arm of Edmond Optical Supply, one of the oldest names in the business and one of my all time favorite suppliers.

              http://www.anchoroptics.com/

              What you are looking for is a "warm window" rather than a "hot window". Let us know how that array works as I have been considering buying one myself.
              Last edited by Evan; 08-29-2012, 08:59 AM.
              Free software for calculating bolt circles and similar: Click Here

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              • #8
                Here is the perfect item for $8.50. Longpass window, 2"x2", ADC thermoset and blocks all visible light. Extremely favourable IR transmission at 10 microns. Excellent mechanical properties and resistant to scratches and chemicals.

                http://www.anchoroptics.com/catalog/product.cfm?id=363

                Or slightly more at Edmond Scientific:

                http://www.edmundoptics.com/optics/o...s-filters/1918



                I forgot to mention if you need something right now a piece of exposed colour film (the black part) is basically the same characteristics.
                Last edited by Evan; 08-29-2012, 09:44 AM.
                Free software for calculating bolt circles and similar: Click Here

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                • #9
                  How about polycarbonate instead of polyethytlene?

                  Supposedly polycarbonate will pass most IR wavelengths: http://en.wikipedia.org/wiki/File:Po...ansmission.png

                  You should be able to find a thin, flat, rectangular, clear piece of polycarbonate measuring 2" by 4.25" at a welding supply store for a dollar or two. They are sold as disposable protectors for the glass filter used in a welding helmet.

                  A couple of examples:

                  http://www.amazon.com/US-Forge-Weldi.../dp/B0000DD6J7


                  http://www.harborfreight.com/pack-of...ers-95950.html


                  (OK, so they don't have Harbor Freight stores or use dollars in the Netherlands, but I'm willing to bet that they do have welding supply stores.)
                  Last edited by doorknob; 08-29-2012, 10:02 AM.

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                  • #10
                    Edmund operates everywhere including Europe. The closest distributor is at Unit 1, Opus Avenue, Nether Poppleton, York, YO26 6BL, UK
                    Free software for calculating bolt circles and similar: Click Here

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                    • #11
                      Thanks guys, I also had a look earlier today at Edmund and they also have a rather cheap plastic window material:
                      http://www.edmundoptics.com/optics/u...l-windows/2043
                      It's a bit unclear to me what the spectrum performance is for the cast windows, it doesn't seem to show specs for the ADC cast windows at either Anchor or Edmund.....
                      I'm hesitant to use polycarbonate as it will be in contact with transmission oil, I'm not sure it'll like that or whether the spectrum is satisfactory.
                      No answer yet from the device manufacturer, I'll give them a call later.

                      Off to bed now,
                      Igor

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                      • #12
                        The spectrum above is for the ADC cast window at Edmund.
                        Free software for calculating bolt circles and similar: Click Here

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                        • #13
                          Just got word from the manufacturer; it uses a silicon window and the relevant band is 4-14um. That makes the ADC window not an option as it stops at 2.3um.
                          So it's either using the plastic window with this mediocre spectrum


                          Or take a silicon window and glue that on or machine it to size. Any tips on speeds and feeds for silicon?

                          Igor

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                          • #14
                            I can send you a 3" disk of silicon 0.5mm thick. However, while it has an optical finish on one side the other side is matte finish. If it is placed directly against the face of the array that shouldn't matter. The primary problem is figuring out how to send it. It is much more fragile than glass.




                            The passband of silicon is directly related to thickness and the loss increases rapidly with thickness. Silicon is decent at 0.5mm but a thickness able to resist mechanical damage will be at least as bad as the plastic. To be thick enough to resist breakage from even minor impact will require at least several millimetres. Quartz falls off steeply at 4 microns from 70% to almost zero at 5microns. Plastic will be the best bet for reason of ruggedness.

                            You don't machine crystalline silicon. Score with a diamond and snap. It can be cut with a water jet.
                            Last edited by Evan; 08-30-2012, 10:56 AM.
                            Free software for calculating bolt circles and similar: Click Here

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                            • #15
                              That's very generous Evan, but it's looking like I will have some company budget to spend on this. I'll go order some plastic and silicon windows at Edmund.

                              Yeah, I was kidding about the speeds and feeds
                              Igor

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