CROSS-SECTION OF SUPERCOOLED (UF6)-U-238 IN MULTIPHOTON ABSORPTION INDUCED BY 16 MICROMETER RAMAN-LASER RADIATION

Measurements of multiphoton absorption of 16 mu m Raman-laser radiatio n in supercooled (UF6)-U-238 at 90 K were performed by using a pulsed Laval nozzle with an optical path length of 50 cm. The laser fluence w as varied between 50 and 500 mJ/cm(2) for four frequencies in the rang e from 625 to 629 cm(-1). The energy absorbed by (UF6)-U-238 molecules was investigated as a function of laser frequency or fluence, and hig hly accurate results were obtained with the use of the nozzle whose op tical path length is much greater than that of nozzles used before. Th e results indicated that the absorption cross section at the peak abso rption frequency (627.8cm(-1)) was proportional to the -1/3 power of t he fluence.