HIGH-PRESSURE SOLID-STATE SPECTROSCOPY AT UVSOR BY INFRARED SYNCHROTRON-RADIATION

Solid-state spectroscopy by infrared synchrotron radiation (IRSR) has been in use since 1985 at the beamline BL6A1 of UVSOR, the electron st orage ring facility of the Institute for Molecular Science at Okazaki in Japan. The wavelength region covered by BL6A1 extends from the near -infrared to the millimeter wave region (1 mu m to 3 mm). Up to now, m any types of experiments have been done there. In the present article, after a description of the optics of BL6A1 and of the time-resolved i nfrared spectrum of the source, I discuss the use of that beamline for spectroscopy with diamond anvil cells (DAC) in the far-infrared regio n. Spectroscopy under high pressure, based either on transmission and on reflection measurements, has been carried out in order to show the advantage of the utilization of the infrared synchrotron radiation wit h respect to conventional sources. In the former type of experiment, t he bulk TO phonon spectra of alkali halide thin films have been measur ed in order to observe the change in the phonon spectrum due to the ph ase transition under pressure. The transmission spectrum on the surfac e phonon state of CuBr microcrystals has also been measured in order t o study the response of the surface phonon state to a pressure up to 2 0 GPa, The reflectivity spectra under pressure have been done instead on a single crystal of KCI, where a change in the rest-strahlen band o f KCl due to the phase transition has been observed. Through these mea surements one has confirmed that infrared synchrotron radiation is a p owerful light source, particularly for those experiments where the acc eptance angle of the sample surface with respect to the incident light beam is very small. This is indeed the case of spectroscopy under hig h pressure in a diamond anvil cell. Finally, a proposal is presented f or realizing an even more intense infrared radiation source on a stora ge ring, with particular regard to the spectroscopic investigation of solid specimens.