A dual-color, frequency-agile, single-shot CRBS laser system for the measurement of neutral species velocity distribution function in weakly ionized plasmas

Resolving the velocity distribution function (VDF) of neutral species in weakly ionized plasmas can expand our understanding of physical interactions between charged and neutral particles. Towards this goal, we present a custom built, dual-color, frequency-agile, single-shot coherent Rayleigh-Brillouin scattering (CRBS) laser system, which is designed specifically to obtain remote, direct measurements of the VDF of neutral particles [1]. CRBS is a four-wave mixing technique in which the interference of two pump beams in a medium generates a moving optical lattice. A third probe beam is Bragg-scattered from the lattice, generating a fourth CRBS signal beam. By scanning the velocity of the lattice within a single laser pulse [2], single-shot CRBS can restore the VDF of neutral particles from the variation of the signal intensity per velocity component. The system is designed to maximize signal-to-noise level in a low-pressure plasma environment, being capable of measuring the VDF at pressures as low as 0.1 Torr. To achieve this, we adopt a three dimensional and two-color phase-matching scheme, details of which and of laser system will be presented in this work. [1] Gerakis, A., Bak, J., and Randolph, R., ``A frequency agile, high intensity, two color laser system for single-shot coherent Rayleigh-Brillouin scattering,''Manuscript in Preparation,2020. [2] Gerakis, A., Shneider, M. N., and Barker, P. F., ``Single-shot coherent Rayleigh-Brillouin scattering using a chirped optical lattice,''Opt. Lett., Vol. 38, No. 21, Nov 2013, pp. 4449--4452.