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High and low energy photon absorption

  1. May 9, 2015 #1
    Hi All,

    Kindly find here 2 questions, i was wondering about:

    1) Will (helium cooled) Mono C-silicon be able to absorb a high intensity laser of about 900-1100 nm ?

    2) How can Ultra-violet and visible light cause rise in material temperatures.

    Thanks.
     
  2. jcsd
  3. May 9, 2015 #2

    Simon Bridge

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    1. That would be IR so it would be surprising if some was not abdorbed.
    2. Same way any light increases temperature.
     
  4. May 17, 2015 #3
    Silicon is quite transparent at photon energies below the indirect band gap of Eg=1.1 eV at room temperature.
    It is an amazing experience to look straight trough a wafer with night vision.
    There is absorption below Eg because the valence band is not fully occupied due to thermal effects.
    Above Eg phonon assisted transitions occur.
    At very low T it is the larger direct bandgap that determines absorption.
    Anything at or below red light passes through.
    See http://en.wikipedia.org/wiki/Direct_and_indirect_band_gaps#Implications_for_light_absorption
    See also
    http://refractiveindex.info/?shelf=main&book=Si&page=Vuye-20C
     
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