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I am making a prototype where I need to direct the flow of the IR signal at some specific point. I found out that glass material doesn't work properly in combination with IR.

Is there any cheap lens which can do that with IR?

The main purpose is to not have wide range of the IR but directed one, like in laser, but wider.

It can be any LED which can work at 10m+- distance. But now I am having these: 5mm IR infrared 940nm LED And sensor which receives 38kHz - TSOP4838 IR Receiver Module

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  • \$\begingroup\$ Worth specifying which part of the IR spectrum, or providing a link to your IR source or sensor. \$\endgroup\$
    – user16324
    Commented Nov 14, 2014 at 12:50
  • \$\begingroup\$ Please check edit. \$\endgroup\$ Commented Nov 14, 2014 at 13:28
  • \$\begingroup\$ Yeah what wavlength? BK7 glass goes down to ~2um. Cheap soda lime glass is not so good. (guess how I know.) \$\endgroup\$ Commented Nov 14, 2014 at 13:30
  • \$\begingroup\$ I wish I could understand ... :D \$\endgroup\$ Commented Nov 14, 2014 at 14:47

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No need for pricey special filters at that wavelength, ordinary acrylic plastic (Plexiglas is one trademark) is quite transparent to 940nm IR, no problem (well, up to stupidly thick pieces anyway).

http://www.plexiglas.com/export/sites/plexiglas/.content/medias/downloads/sheet-docs/plexiglas-optical-and-transmission-characteristics.pdf

If you also want to filter out visible light, there is G 3142 or 1146 Plexiglas that absorbs visible light but transmits near-IR.

Should be available from plastic distributors in various thicknesses, and it's easily machined if you need a custom shape.

http://www.eplastics.com/Plexiglass_Acrylic_Sheet_Infrared_Transmitting

If you need an actual lens or prism rather than just a window, acrylic is a common material for making molded lenses- it's optically quite transparent at visible wavelengths too, and fairly hard (but brittle).

Edit:

Also, polycarbonate (one trade name is Lexan) is also fully transparent to near-IR.

So, pretty much any plastic optical component will be made out of acrylic (lenses, some sheet plastic) or polycarbonate (many light pipes, also available in sheet), and you can use it without problems at 940nm.

enter image description here

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Way back in the 1970s, I saw a thermal imaging camera made, I think, by EEV in Chelmsford. It had a lens made of germanium, which looked like a shiny metal lens. Totally opaque to visible light, of course. Sure enough our spectacles looked solid black in the thermal images produced, because it was working in IR wavelengths that glass cannot transmit.

I don't know if IR lenses are still made from germanium, nor do I know if such things could be made cheaply.

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  • \$\begingroup\$ Thank you for the answer, and dont you know if simple plastic would work? Since the LED is also covered by plastic... Or any other solution how to direct the signal? Maybe by putting it into tube? \$\endgroup\$ Commented Nov 14, 2014 at 15:36
  • \$\begingroup\$ @OndrejTokar There must be plastics that are IR-transparent, because as you say, LEDs are made out of them. But which plastics those are, I could not say. Sorry. \$\endgroup\$ Commented Nov 14, 2014 at 15:41
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    \$\begingroup\$ yes indeed, thermal IR sensors use Germanium as a lens material. Thermal IR being in the 10 - 14 um wavelength range. He is using less that 1 um wavelength light so this won't work. \$\endgroup\$ Commented Nov 14, 2014 at 16:45
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These aren't cheap: https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=7999

They're designed for mid infra red.

I suppose the price is relative to the cost of the prototype and how important it is

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I think AR coating on a BK7 glass lens will work for you. Thorlabs have those: https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=3280

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