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Why does light intensity decrease when light passes through a glass block?

  1. Mar 27, 2008 #1
    Hi Guys,

    I am new to this forum and have a "quick" question.

    Say you had a laser pointer and you directed the laser through a glass block and then to a LDR why would the light intensity recorded be lower than without the glass block? What is happening to the light when it is in the glass? And why does making the glass thicker make the light intensity decrease even more?

    Thanks a lot.

    Oli.
     
  2. jcsd
  3. Mar 27, 2008 #2

    dst

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    I'm guessing that the some of the particular photons will have energies corresponding to vibrational modes in the glass (lattice, electronic, molecular, etc). So each time that happens, some light is absorbed.
     
  4. Mar 27, 2008 #3
    So the glass actually absorbs some of the light?
     
  5. Mar 27, 2008 #4

    dst

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  6. Mar 27, 2008 #5
    Thank you very much, I will give this a good read.
     
  7. Mar 27, 2008 #6

    Claude Bile

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    Increasing the thickness of a glass layer would increase losses due to absorption and scattering since both are dependent on length.

    You also get Fresnel reflections, which is about 4% of the incident light reflected per interface for glass.

    Claude.
     
  8. Mar 28, 2008 #7

    Andy Resnick

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    the glass scatters light out of the beam direction. Unless you are working with optical-quality glass, glass is fairly heterogeneous.

    Even so, 'perfectly manufactured' glass is oh-so-slightly absorptive.

    Plot the intensity as a function of glass thickness- it should be exponential (Beer's law)
     
  9. Mar 30, 2008 #8

    Claude Bile

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    Indeed, the best glass for optical transmission (silica optical fibre) has losses of about 0.1 dB per km, most of which is due to absorption.

    Claude.
     
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