My question has always been, how does the LIGO receiver take energy from the incident gravitational wave? I understand how a radio receiver matched in impedance absorbs energy from a radio wave, but how does the LIGO absorb energy? What is the equivalent of impedance matching?
How does the LIGO absorb energy?
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I’m guessing. My background is microwave engineering so I understand amplitude detection and phase measurement.
But light is just very, very high frequency electromagnetic energy propagating through space at the speed of light. Same as microwave energy. So the same principles apply.
In the microwave case you would add an adjustable phase shift element to one side of interferometer and then form the sum and difference of the signals from the two legs. The you just adjust the variable phase element to null the difference and maximize the sum and use a detector to make an amplitude measurement. Phase information is obtained from the reading of the variable phase element.
The above works fine for a single sinusoid in the microwave world. The gravity wave detection problem is much more complex since you are looking for a relatively low frequency perturbation of a light wave bouncing around in the LIGO system. And that perturbation has a finite bandwidth. It is not, I assume, a simple sinusoid.
But the basic principle for detection still must apply. You are using detectors that measure the magnitude of LIGO lasers signal amplitudes in both arms and, I’m betting, lots of computing power to add in the equivalent of my microwave phase shifter across the frequency range of the gravitational wave.
Or something like that.