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Group delay measurement using Michelson Interferometer

  1. Jun 2, 2009 #1
    For my undergraduate project, I have been tasked to measure group delay of dielectric mirrors. I have found only papers that point mainly to use a Michelson interferometer using white light interferometry. I have googled and found how to construct a standard Michelson interferometer. However I am having trouble in finding resources on how to modify it to measure group delay. In addition, how can I measure the group delay from the interferogram that is produced from the interferometer?
    Any books and resources on group delay measurement is highly appreciated. :smile:
  2. jcsd
  3. Jun 2, 2009 #2
    Why dielectric mirrors? Do you mean "back surface" silvered dielectric mirrors, as opposed to "front surface" mirrors? How accurate will your measurements be? Are you just doing a mirror comparison, or trying to measure the aether effect better?
  4. Jun 2, 2009 #3
    Hi Bob, the aim of the project is to characterize dispersive properties of mirrors. I have a mirror that was coated with SiO2 and Si3N4 as thin film on Si substrate. So one side is side is reflective the other side isnt. In the interferometer I will use a standard reference mirror in one arm and the dispersive mirror in the other. I wish to be able to get group delay from the interference pattern by that is produced.
  5. Jun 2, 2009 #4
    If you are using a white light interferometer, you should be measuring the group delay without any adjustment to your setup. Phase delay only applies to a single wavelength light source, and you have a multiple wavelength (broadband) light source. When you take your measurement, you will be measuring the group velocity, the velocity of the wave packet. This is opposed to measuring the phase velocity, which is the velocity of the light itself.
  6. Jun 2, 2009 #5
    Look here for a brief introduction to group delay and a couple of references to papers including one for measuring group delay using a white light interferometer.

  7. Jun 3, 2009 #6
    I am using a white light interferometer to do the measurement. I seen from the papers that there are many variations to the experiment that confuses me. (Some have used Fourier transform, some used tunable filter etc)

    What would be a good way to measure the group delay from the interference patter? Assuming I have the interferometer setup using a white light source and the interference pattern is projected to a wall or captured with a CCD camera.
    The main hurdle I am facing now is given the pattern, how am I going to use it to get group delay. I have not come across any books that can give a description on that.
  8. Jun 3, 2009 #7
    Thanks for the link :smile: I have been though the place and looked at the reference papers. The paper describes what modification they did to the experiment and the results, but there wasnt much mentioned about how they actually did the experiment and processed the data from the interferogram. That is the missing jig saw puzzle in my confused mind. :confused:
  9. Jun 3, 2009 #8
    If you have access to an FTIR (Fourier Transform Infrared Spectrometer, i.e. a Michelson interferometer with a movable arm that can measure spectra from the near-IR to the far-IR), I would think that would make your measurement that much easier. Basically, I think you could simply measure the broadband transmission spectrum of your sample, and do some post-processing to extract out the information you need. Someone in your materials science department is guaranteed to have one, especially if they have some sort of shared facility.
  10. Jun 4, 2009 #9
    Thanks for the insights, I will need to go read up how FTIR works and see how can I apply it to measure group delay. Hopefully I can find one at the material science department.
  11. Dec 12, 2009 #10
    Hi I need help on a project of graphene photo detector by using FTIR spectrometer but I'm not sure how to set up equipments. I wonder if someone can help me.

  12. Dec 12, 2009 #11
    welcome to PF.

    You can start a new post in the appropriate forum ( for your question this'd be Atomic-Solid State section) to get a better response.
  13. Dec 13, 2009 #12
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