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 storage 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, many types of experiments have been done there. In the present article, after a description of the optics of BL6A1 and of the time-resolved infrared spectrum of the source, I discuss the use of that beamline for spectroscopy with diamond anvil cells (DAC) in the far-infrared region. 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 with respect to conventional sources. In the former type of experiment, the bulk TO phonon spectra of alkali halide thin films have been measured in order to observe the change in the phonon spectrum due to the phase transition under pressure. The transmission spectrum on the surface phonon state of CuBr microcrystals has also been measured in order to study the response of the surface phonon state to a pressure up to 20 GPa, The reflectivity spectra under pressure have been done instead on a single crystal of KCI, where a change in the rest-strahlen band of KCl due to the phase transition has been observed. Through these measurements one has confirmed that infrared synchrotron radiation is a powerful light source, particularly for those experiments where the acceptance angle of the sample surface with respect to the incident light beam is very small. This is indeed the case of spectroscopy under high pressure in a diamond anvil cell. Finally, a proposal is presented for realizing an even more intense infrared radiation source on a storage ring, with particular regard to the spectroscopic investigation of solid specimens.