TRANSFER IN MATERIALS

UTILIZING TECHNIQUES DEVELOPED EXTENSIVELY IN THE NATIONAL LASER FUSION PROGRAM, WE PROPOSE TO MEASURE THE TIME DEPENDENT CHANGE IN CRYSTAL X-RAY REFLECTIVITY BROUGHT ABOUT WHEN A CRYSTAL IS HEATED TO THE MELTING POINT ON A PICOSECOND TIME SCALE. THIS EXPERIMENT WILL OBTAIN DATA ON RADIATION-LATTICE DYNAMICS ON A TIME SCALE 2-3 ORDERS OF MAGNITUDE FASTER THAN PREVIOUSLY OBTAINED WITH X-RAY TECHNIQUES. WE WILL PROBE DIRECTLY THROUGH THE USE OF X-RAYS THE TRANSFER OF ENERGY BETWEEN THE LASER EXCITED ELECTRON-HOLE PLASMA OF A CRYSTAL AND THE PHONON EXCITATIONS OF THE LATTICE; THE POORLY UNDERSTOOD MECHANISMS BY WHICH HIGH ENERGY DENSITY LASERS TRANSFER THEIR ENERGY TO THE CRYSTALLINE TARGET LATTICE ON EXTREMELY SHORT TIME SCALES ( APPROX < 100 PS) WILL BE STUDIED BY ANALYSIS AND MODELING OF THE EXPERIMENTAL RESULTS.