Multiplex H_2 coherent anti-Stokes Raman scattering thermometry with a modeless laser

The use of a modeless laser as the Stokes source for multiplex coherent anti-Stokes Raman scattering in molecular hydrogen is reported. The elimination of noise associated with mode competition in conventional standing wave lasers is shown to result in reliable and accurate single-shot thermometry of H(2) in a microwave-assisted diamond chemical vapor deposition plasma reactor. Single-shot temperatures are recorded with a precision of 7.3%. Possible improvements to this precision are discussed and applications of the technique for on-line process monitoring are briefly presented.