[sleavey]

Cavities. We trade off bandwidth for peak sensitivity by sending the same light back and forth between mirrors in the arms of the interferometer hundreds of times. As the gravitational wave passes, the same light samples it over and over and picks up additional phase shift, enhancing the signal. The downside is that we can't see gravitational waves at signals far above the cavity pole frequencies at a few 10s of kHz, but the most promising sources we aimed at when the detectors were designed were considered to be below that.

We also use techniques called power and signal recycling to enhance this bandwidth-sensitivity tradeoff even more. Combined these techniques give you what remains between your 1/1000th wavelength and the actual sensitivity of LIGO and Virgo.

[magicalhippo]

In addition they've been using squeezed light[1] since 2019 to help increase the sensitivity.

[1]: https://www.optica-opn.org/home/newsroom/2019/december/squee...

[mycall]

I wonder if twisting light is similar to this (now useful in fiber optics) or if this would be another dimension to explore.

[colanderman]

That sounds like a block & tackle [1] for light.

[1] https://en.wikipedia.org/wiki/Block_and_tackle

[jjoonathan]

Cool! Thanks for the explanation, it makes sense!