Narrowing a laser beam's linewidth by a factor of over ten thousand using Raman scattering of light from vibrating diamond crystals

https://www.eurekalert.org/news-releases/1091068

linewidth measures beam's frequency/ color purity, narrower = more monochromatic/ spectrally pure... tested deliberately noisy input Brillouin laser beam with linewidth >10 MHz... hitting mm-scale diamond crystal in carefully designed cavity, Raman scattering narrowed output beam to 1 kHz limiting detection... Raman technique transfers timing irregularities into diamond crystal vibrations, dissipated, leaving behind narrow waves... quantum computing, atomic clocks, gravitational wave detection"

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https://www.eurekalert.org/news-releases/1119602