Single-Shot Coherent Brillouin Scattering for Gas Particle Velocimetry

Laser based diagnostic techniques are at the cutting edge of gas and plasma dynamics studies as they can perform direct probing of various thermodynamic parameters, i.e. temperature, density and flow velocity vector, of the gas or plasma flow. Among a multitude of techniques [1], coherent Rayleigh-Brillouin scattering (CRBS), a non-resonant four-wave mixing technique, is a notable example, as CRBS is an established method for direct diagnostics of the gas properties (i.e. translational temperature, number density, and flow velocity vector) of quiescent gas and gas flows (as those encountered e.g. in a wind tunnel) [2], [3]. This is a consequence of CRBS offering improved signal-to-noise ratio compared to other non-resonant methods, such as spontaneous Rayleigh Scattering [4] and filtered Rayleigh scattering [5], due to both the coherent nature of the signal [6] to the single-shot signal acquisition (order of ~200-300 ns), which is ideal for the study of fast dynamics [7]. The coherent signal is the result of a probe laser beam scattering off of an optical lattice, created by the interference of two counter-propagating pump beams that induce a dipole moment on the gas particles (atoms or molecules) forcing them to populate the high-field lattice nodes.