I shone a green laser light(~532 nm) through a glass slab and what I saw inside was that the light beam was now red. Imagine a regular refraction diagram but color the beam outside green and that on the inside red.

As frequency doesn't change upon entering another medium, effective light velocity in a medium becomes directly proportional to that of wavelength. So, as speed decreases shouldn't wavelength also do so? But in this case, it increases. Or is this logic wrong?

Also, it can't be due to light losing energy.

What is happening in here?

  • $\begingroup$ What color is it after it exits the back side of the glass? $\endgroup$ – garyp Apr 1 '16 at 16:11
  • $\begingroup$ But it's green when it comes out... And also it is not because the light is being seen through the slab... I kept the slab above the green beam, and looked from above- it was still green. Conclusion: it only occurs when beam PASSES THROUGH the slab. $\endgroup$ – Adam Karlson Apr 1 '16 at 16:11
  • $\begingroup$ What the eye sees outside the glass slab as green, is the scattered light on molecules of air. What the eye sees when the beam goes through the slab is the scattered light on molecules of glass. As you say that the beam looks again green coming out of the slab, the frequency of the scattered light does not change in the air, an elastic scatter. My first guess is that the scatter in the glass is inelastic and the red color appears ( which could be a perception of red by the retina en.wikipedia.org/wiki/Color_vision ). i am waiting for an optics expert $\endgroup$ – anna v Apr 1 '16 at 17:21
  • $\begingroup$ Um...Anna. I have also tried looking at the beam through a glass and I can see green. Shouldn't any part of that light going through the glass interact in the same way, thus producing red every time? It's a beam WHICH PASSES THROUGH THE SLAB WHICH IS REDDENED not one being looked at. I hope I am clear, (wish I could explain better) $\endgroup$ – Adam Karlson Apr 1 '16 at 18:47
  • $\begingroup$ Please describe the glass in detail -- what is its composition? Is it a standard optical glass, like BK7? Also what is the power of the laser beam? Some glasses can fluoresce, which could give your red color; if the laser fluence is high enough the glass may fluoresce. Also what type of laser goggles are you wearing; these can alter color perception. $\endgroup$ – Peter Diehr Apr 1 '16 at 21:21

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