0
$\begingroup$

I have already researched into this and I am left slightly confused still. I have gathered that the use of a quarter wavelength is to turn a linearly polarised wave into a circularly polarised wave. But why? I appreciate any feedback.

$\endgroup$
  • 2
    $\begingroup$ One-quarter of the wavelength is just an estimate because the frequency or wavelength isn't sharply determined for a signal. But the reason why LIGO is highly sensitive when $L=\lambda / 4$ is exactly analogous to the reason why the electric dipole antenna is best at $L=\lambda / 2$. $\endgroup$ – Luboš Motl May 26 '16 at 14:47
  • 2
    $\begingroup$ Can you be more specific? Is there some image or text where they specifically mention the use of a quarter wavelength at LIGO? If you mean quarter waveplates, they are used in any large optics experiment. Note that at LIGO, you would find these typically on a laser bench, but it is not a key component in the interferometer itself. $\endgroup$ – Bas Swinckels May 31 '16 at 16:11
0
$\begingroup$

I believe you mean "quarter wave plate" rather than quarter wave length: https://en.wikipedia.org/wiki/Waveplate

Quarter wave plates are sometimes used after polarized beam splitters (PBS). Suppose you have a PBS illuminated by a source. One polarization (say linear horizontal) goes one way and the other (linear vertical) goes the other way. Now suppose you want to split the linear vertical light a second time. If you put it through another PBS then the light won't be split; all the light will come out in the vertically polarized direction. So you insert a quarter wave plate, which turns the linear vertical light into circular, after which the second PBS splits the light in half once more.

To get a more specific answer, give us a link to a picture of the interferometer setup you are are trying to understand and we can answer what specific purpose it plays there.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.