Experimental setup for Fourier transform infrared spectroscopy studies in condensed matter at high pressure and low temperatures

An experimental setup for Fourier transform infrared (FTIR) studies in condensed matter at high pressure and low temperatures is described. We have adapted a close-cycle cryostat (T=20-300 K) to the sample compartment, which is used as a cryo chamber, of a FTIR spectrometer (frequency range 10-15 000 cm(-1)). A Cassegrain-type beam condenser is assembled to measure infrared absorptions of samples contained in a membrane diamond anvil cell (P up to 100 GPa). The tuning of the pressure and the cell alignment is performed from outside the evacuated instrument. An additional Light path allows visual observation and it? situ pressure calibration. The advantages of this system, demonstrated by its application to CH4 and Ar-(H-2)(2) crystals, are high radiation throughput, long time stability, visual observation of the sample, remote measurement and variation of the local pressure, and remote alignment of the cell with the IR beam. (C) 1997 American Institute of Physics.