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How to measure the speed of light with this setup

  1. Mar 18, 2014 #1
    This is an experiment I'll be undertaking for labs.

    Given the following equipment:
    - laser with modulation input
    - lenses and mirrors
    - function generator
    - high-speed photo detectors
    - oscilloscope

    and the setup as shown in the picture (the function generator is connected to the laser power, the laser power's connected to the laser, the laser sends a beam of light towards a mirror, the mirror reflects the beam of light, the beam of light then goes through a lens and into the photodiode, which is hooked up to the oscilloscope via a variable resistor), how would you measure the speed of light?

    From this source* (looks like a similar experiment, though I'm struggling to understand it), the function generator would be turning the laser on and off, so it'll be arriving at the detector in pulses.
    I'm not sure how the oscilloscope is used in this - if each pulse creates a peak then the wavelength would just be related to the frequency at of the function generator, though I'm not sure how that comes in either.


    Attached Files:

  2. jcsd
  3. Mar 18, 2014 #2


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    Homework Helper

    Hi Chip,
    Good thing you are trying to prepare as much as you can before sitting down in front of the thing. And yes, Mak and Yip's abstract gives away what is being measured, right? Namely the phase difference between input to the laser and photodiode signal. They even give a hint at what to do exactly (i.e. move the mirror).
    I didn't buy the article, but I can imagine several ways to go about. Imperial college mentions a few.
    Good luck and have fun!
  4. Mar 19, 2014 #3
    Thanks BvU - the stuff from Imperial College helped a lot. got the gist of it enough to know what were supposed to be doing.
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