A pulsed-laser calibration system for the laser backscatter diagnostics at the Omega laser

A calibration system has been developed that allows a direct determination of the sensitivity of the laser backscatter diagnostics at the Omega laser. A motorized mirror at the target location redirects individual pulses of a millijoule-class laser onto the diagnostic to allow the in situ measurement of the local point response of the backscatter diagnostics. Featuring dual wavelength capability at the second and third harmonics of the Nd:YAG laser, both spectral channels of the backscatter diagnostics can be directly calibrated. In addition, channel cross-talk and polarization sensitivity can be determined. The calibration system has been employed repeatedly over the last two years and has enabled precise backscatter measurements of both stimulated Brillouin scattering and stimulated Raman scattering in gas-filled Hohlraum targets that emulate conditions relevant to those in inertial confinement fusion targets.