In situ dye laser calibration for Thomson scattering diagnostics

The standard laser Thomson scattering calibration technique involves the convolving of density and wavelength response calibrations. This usually includes an in situ Rayleigh scattering from neutral gas for an absolute density calibration at the laser wavelength. In addition, a spectral calibration (i.e., a National Bureau of Standards traceable lamp and white reflective plate) is required to determine the relative wavelength channel responses for the combination of collection optics, spectrometers, and associated detectors. This technique involves a considerable amount of time and effort in two-dimensional scattering systems because of the number of spectrometers/detectors and the large range of scattering and collection angles. An alternative technique employing a nominal 40-mJ, small-divergence tunable dye laser substituted into the Thomson scattering laser beam path is proposed. Rayleigh scattering (from ∼10-Torr H2) measurements are made at a high repetition rate (1–10 Hz) while the dye laser output wavelength is scanned. This includes in one step the in situ density and channel response calibrations.