How does LIGO measure gravitational waves

[AamsterC2]

I'm aware that the LIGO system uses interferometry but I'm confused how it works in this case. Do they test both beams of light? Or do they use one beam to test the wavelength of the other and see the difference? Also it is sensitive up to 10 e-18 meters, is that for the change in wavelength or change in the length of the beam?

 

[jedishrfu]

This may help. It talks about how interferometers are used to make interference patterns:

http://www.kavlifoundation.org/how-ligo-works

 

[stefan r]

I'm aware that the LIGO system uses interferometry but I'm confused how it works in this case. Do they test both beams of light? Or do they use one beam to test the wavelength of the other and see the difference? Also it is sensitive up to 10 e-18 meters, is that for the change in wavelength or change in the length of the beam?

It is one beam of light. It gets split. The wavelength of light does not change. Interference changes the amplitude measured not the frequency.

Check these two ideas:

Beam Splitter.
Destructive interference.

 

[Alfred Cann]

I'm puzzled that the stretching of space by a gravitational wave stretches the LIGO arm but not the light within it. Because we are told that the red shift of a distant galaxy is caused by light being stretched by the expansion of space (the universe).