10.6-μm Laser Scattering from Cyclotron-Harmonic Waves in a Plasma

We report the scattering of C${\mathrm{O}}_2$-laser light from driven cyclotron-harmonic waves in a collisionless plasma of density 4 × ${10}^{10}$ ${\mathrm{cm}}^{-3\mathrm{}}$. Using light-mixing spectroscopy, we observe scattering from waves with frequencies of several hundred megahertz, wavelengths from 2.0 to 0.75 mm, and associated fractional electron-density modulations as small as ${10}^{-5\mathrm{}}$.