Interferometric characterization of cryogenic targets in a laser- fusion target chamber

Current cryogenic targets for laser fusion experiments consist of glass Microshell® pellets with deuterium-tritium fuel frozen inside. The fuel forms a uniform layer in the optimum configuration. Until very sophisticated injection systems are developed, these targets must be prepared in the experimental target chamber. This situation imposes re-straints upon any technique used to characterize the quality of the targets before they are irradiated by the high power laser. This paper describes a wavefront- shearing interferome-ter for characterizing cryogenic targets in situ. The interferometer, which is based on the Saunder's shearing cube, is easy to adjust and is very stable in the presence of mechanical vibration; it produces fringes of high contrast without sacrificing intensity. The interferometer has been used with a low power pulsed laser to measure both the effect of amplified spontaneous emission, produced by the high power laser, and the effect of room-temperature thermal radiation on cryogenic targets