Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Quantum angle selectivity of polirizers filter

  1. May 8, 2007 #1
    given that light can be polirized at any plane while the polirized
    filter has only a precise orientation, I assume there is a range of
    angles of polirizzation that go though the polirized filter others are cut out.
    how large is the angle selectivity of the polirized filters ???
    how is this selectivity taken into account in the formalism ?????

    The same for electronic spin: how selective is the Gerlach apparatus on
    the spin angle ???
    Is the intensity of the magnet tuned up to the kinetic energy of the electron ???

    thanks of any help,

    best regards

    beda pietanza
     
  2. jcsd
  3. May 10, 2007 #2

    Meir Achuz

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    The intensity of the transmitted light is I=I_0 cos^2\theta. (Malus law)
    There is also a cos^2 dependence to the up-down deflection in Stern-Gerlach.
     
  4. May 11, 2007 #3
    I assume some polarisers (say birefringent materials) effectively make perfect quantum measurements (the outcome being one of two pure states). However, the stereotypical polariser (a series of parallel lines) seems potentially very inefficient because (even aside from whether it blocks half the beam that is correctly polarised) it would be expected to permit some light with polarisation deviating by a small angle (in the limit where the lines are widely spaced, the polariser will have no polarising effect on blue light). Do such polarisers really produce a mixture of quantum states?
     
  5. May 11, 2007 #4
    OK, thanks,
    the intensity of the transmitted light should depend also from the "angle selectivity" of the polirizing filter used and should also depend on the specific frequency of light, how these variable comes into play?????

    Same for Stern-Gerlach magnet how the speed of the electrons and the intensity of the magnet are taken into account ?????

    I=I_0 cos^2\theta doesn't containes all varables involved

    best regards

    beda pietanza
     
  6. May 11, 2007 #5

    Meir Achuz

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    It doesn't need to. That law just comes from a vector dot product.
     
  7. May 12, 2007 #6
    I'm not a physicist nor a matematician, so please making a example: if we have solar light going through the filter , the various components of the spectrum, how are they attenuated????

    If I use a different filter with different caratteristics how do you calculate the outcome???

    best regards

    beda pietanza
     
  8. May 12, 2007 #7

    Meir Achuz

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    It only depends on cosine^2 of the angle between P and polarizer.
    It's that simple.
     
  9. May 13, 2007 #8
    I'am not convinced, I still think there are the "angle selectivity" and the “band width” of the filter that affect the intensity of the light coming out.

    EI. using a filter box (containing 3 identical filters in a row) you don’t know the content of the filter box, if you still use your formula without knowing the characteristics of the filter box I suppose your results would be incorrect.

    best regards

    beda pietanza
     
  10. May 16, 2007 #9

    Meir Achuz

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Other effects, unrelated to polarization, can affect the intensity.
     
  11. May 16, 2007 #10

    DrChinese

    User Avatar
    Science Advisor
    Gold Member

    The term "angle selectivity" is not one usually associated with a filter. A polarization filter does have a range of wavelengths that it is rated for. Within that range, it is basically going to be the COS^2(theta) relationship which applies.
     
  12. May 24, 2007 #11
    Sorry if I should start a new thread on this: I raised a query about the polarization of light under Classical Physics, and Claude Bile suggested I ask it under QM.

    I've read about the use of polarization filters in series, where two at 90 degrees cut out all the light whilst introducing a third intermediate filter lets some through. But I can't quite get the picture, even classically. Can you tell me whether a single photon can be considered to be linearly polarised? Or all photons always considered to have some element of circular polarization and hence are left or right cicular or elliptical? Sorry to be a little naive, my QM is weak.
     
  13. May 24, 2007 #12

    DrChinese

    User Avatar
    Science Advisor
    Gold Member

    I personally see this situation as one which demonstrates the quantum nature of light. Specifically, you witness the effect of an observation (i.e. the observer) on the photon . The polarizer causes the photon's state function to collapse into one in which it is either aligned with the polarizer or orthogonal (90 degrees offset) to the polarizer.

    The actual transmission function - cos^2(theta) - was discovered nearly 200 years ago by Malus. This was prior to the advent of quantum theory, which is why it is often characterized as being part of the classical picture.
     
  14. May 24, 2007 #13
    Thanks Dr Chinese. I've had a Google® and have printed a few things out to read offline, including Classical and Quantum Malus' Law by Krzysztof Wodkiewicz. If there's anything else you could suggest I'd be grateful.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Quantum angle selectivity of polirizers filter
Loading...