Retroreflecting multipass cell for Raman scattering.

A retroreflecting multipass cell consisting of two lenses and both on-axis and off-axis retroreflecting mirror assemblies has been constructed and tested. A gain in Raman scattered signal intensity of 20 has been attained in a focal volume 1.1 mm x 0.3 mm x 0.3 mm. A system employing off-axis paraboloids should provide somewhat higher gain and a diffraction limited focal volume. These systems are applicable to Raman diagnostics of various gas dynamic processes, including flame gases, or the characterization of the gas mixing process in gas-dynamic or chemical laser nozzle arrays.