MEASUREMENTS OF DIRECT-DRIVE LASER IMPRINT IN THIN FOILS BY RADIOGRAPHY USING AN X-RAY LASER BACKLIGHTER

In direct drive inertial confinement fusion, the residual speckle patt ern remaining after beam smoothing plays an important role in the seed ing of instabilities at the ablation front. An x-ray laser is used as an extreme ultraviolet backlighter to characterize the imprinted modul ation in thin foils for smoothing by random phase plate and by spectra l dispersion for both 0.35 and 0.53 mu m irradiation, and by induced s patial incoherence for 0.53 mu m irradiation. Measurements of the impr inted modulation due to a single optical mode generated by two beam in terference, and modification of the imprint with a superposed smooth i rradiation to study time dependence of the imprinting process are demo nstrated. (C) 1997 American Institute of Physics.