PROGRESS IN LASER FUSION 2.A Optical Fiducials for X-Ray Streak Cameras

A variety of techniques has been used to establish a timing fiducial for the x-ray emission. An x-ray fiducial can be obtained by coating the target with a thin layer of high-Z material whose characteristic x-ray emission is discriminated spectroscopi~aIly.~-3 The drawbacks of this technique are that the presence of the high-Z layer can alter the laserplasma interaction significantly and that the timing of the onset of the xray emission relative to the laser pulse is not well defined. An alternative is to use a secondary laser pulse of short duration to generate a plasma off an auxiliary target that consists of a different-Z materiaL4 The relative timing of the two laser pulses can be measured using an optical streak camera, and again, the x-ray signals are discriminated spectroscopically.