Principles of Millimeter-Wave Collective Scattering
The principles behind millimeter-wave collective scattering are illustrated in Fig. 1 below. Electromagnetic radiation (ki, ¦Øi) incident on a density fluctuation or grating (k, ¦Ø) in the plasma results in a small portion of this power in a scattered beam (ks, ¦Øs) whose frequency ¦Øs and wavenumber ks must be matched. The amplitude of this scattered signal is proportional to the amplitude of the density grating (Ps =1/4ro2|ne/neo|2li2L2Pi for the coherent density fluctuation case), and thus provides a means of monitoring such fluctuations in a nonperturbative manner.
Fig. 1. Illustration of wavenumber matching in the collective scattering process.