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I am curious to know a way that will make infrared pass through metals. Metals are good reflectors of infrared,can we manipulate the wave in order to make them pass through metals?.

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    $\begingroup$ If you concentrate a powerful enough light on a small enough spot, you may be able to cut a hole in the metal, and then infrared light could go through the hole. $\endgroup$ – The Photon Jun 14 '18 at 5:10
  • $\begingroup$ Can i use an intense infrared wave resonant with molecules vibrational frequency to cut a hole in it? $\endgroup$ – user197535 Jun 14 '18 at 5:26
  • $\begingroup$ You cannot pas a coherent infrared beam through a metal. You can heat the metal with an infrared beam and make it radiate infrared, since these are the frequencies of heat waves. $\endgroup$ – anna v Jun 14 '18 at 5:30
  • $\begingroup$ Can't pass an infrared beam through any metal I know of because the plasma frequencies of the metals are all too high. I suppose if one had some hypothetical metal with a low enough of a carrier density that its plasma frequency was below 1.5 eV then it would be transparent to at least some infrared light. Don't know of any metal that goes that low, though. The lowest I know of is cesium, with a plasma frequency of 2.8 eV. $\endgroup$ – user93237 Jun 14 '18 at 5:39
  • $\begingroup$ Why vibrational resonance doesn't work for metals? $\endgroup$ – user197535 Jun 14 '18 at 6:17
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If you have a metal that is thin enough (i.e. thinner than the infrared skin depth), then you can pass infrared light straight through. Keep in mind this would be metals with thicknesses of the order of tens to hundreds of nanometers depending on the metal. One way this could be easily achieved is careful sputtering of a metal film onto glass. Transparent conducting films somewhat fall under this type of category (though they work quite differently).

Alternatively, you can easily pass infrared light through some doped semiconductors (e.g. Silicon). These aren't as good as usual metals at conducting electricity, but can do the job in some situations.

If the idea is to take any random chunk of metal and try to pass infrared light through it, the best you can do is to drill a hole for a line-of-sight application, or fill that hole with an optical fiber when line-of-sight won't work.

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A metal sheet will transmit up to about 50% of infra red incident on it, but there is a time delay and a condition:

  • Assume you have a thin metal sheet (easier to imagine for purposes here), hanging in a vacuum (to do away with convection and conduction).
  • Colour the metal surface black.
  • Choose an infrared heating lamp with characteristics (e.g. infrared wavelength) so as to maximise heat absorption by your metal plate.
  • Heat up the surface of the metal sheet from one side with the infra red lamp, so that the heated area is approximately the same as the total area of the sheet.

Gradually, the amount of infrared radiation emitted by the sheet on the none-heated side will increase. The temperature of the sheet will reach a plateau when, per unit time, the total incident infrared radiation energy equals the total emitted infrared radiation energy. This temperature depends on the power of the infrared heating lamp. At that point in time, about 50% of the infrared energy absorbed by the sheet is effectively being transmitted through the sheet.

In other words, that heat energy-saturated metal sheet is 'passing' infra red radiation through it.

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    $\begingroup$ This is not the same as transmission. The answer is incorrect. $\endgroup$ – my2cts Aug 13 '19 at 17:09
  • $\begingroup$ @my2cts go ahead, enlighten us with your answer. $\endgroup$ – Dlamini Aug 19 '19 at 0:36
  • $\begingroup$ Heat conduction followed by thermal emission is not the same as radiation transmission. The incoming spectrum and wave direction is very different from the outgoing one. This answer is incorrect. The correct answer is the one by @KFGauss. $\endgroup$ – my2cts Aug 19 '19 at 7:05

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