MHz-rate Nonlinear Spectroscopy and Imaging Platform for Transient and Nonequilibrium Flows

The goal of the proposed work is to demonstrate 100 kHz to MHz rate nonlinear spectroscopy for measurements of molecular energy distributions, energy transfer, major species, and temperature in transient combusting and nonequilibrium flows. This will be accomplished, in part, by extending burst-mode laser technology to the fs/ps regime for three-orders of magnitude higher probe-pulse energy at MHz repetition rates. This laser architecture will also ensure precise synchronization of transform-limited fs and ps pulses for efficient coherent excitation of multi-photon transitions while minimizing interferences such as nonresonant background and collisions. During the Phase I, we investigated the optimal laser architecture for fs/ps burst-mode laser spectroscopy and demonstrated potential spectroscopic and imaging systems using high-speed ps coherent anti-Stokes Raman scattering (CARS) as a test platform. A model was developed and shows that the prototype design planned for the Phase II will achieve the desired goals. The Phase II will result in a prototype 100 kHz to MHz rate nonlinear spectroscopy system and demonstration in Air Force relevant conditions. This research program will result in commercial laser spectroscopy and imaging systems that will address critical research needs in areas such as advanced propulsion, munitions, space vehicles, and related industries.