A 15 picosecond short wavelength laser probe for plasma diagnostics

Summary form only. The ultrashort laser pulse has been one of the most important tools for plasma physics diagnostics due to its capability to temporally freeze the plasma image and produce useful high temporal resolution characteristic information. Many plasma experiments, especially the high density laser plasma relevant to ICF require a laser probe with not only short-pulse duration, shorter wavelength, but also the precise time synchronization with the main laser beam hitting the target. In order to construct a practical laser probe for XG laser facility which is a high energy Nd:glass laser system especially for ICF experiments, we beam-split a small portion of the main targeting beam from the output of one of the pre-amplifiers, producing initially less than 100 mJ(800 ps/1054 nm) pulse. This pulse is the seed for the whole prober system and temporally synchronized with the main laser pulse with precise optical delay. Through fourth homonic generation and double stage Raman backward-scattering, pulses as short as 15 ps at 308 nm with 1 mJ energy are successfully obtained. The precise delay between the probe and the targeting beam can be easily adjusted when using a streak camera. A compact 1 Hz Q-switch Nd:YLF laser is routinely used for quick alignment for the following interferometry since the main targeting pulse can only be shot with several hours interval. This probe system also has the advantages of having the same wavelength as a XeCl excimer laser for further energy increase and be away from the homonic wavelength produced in the plasma to avoid severe interference in diagnostics.