Vacuum UV high-performance spectrophotometric setup for use in the 105-200-nm wavelength range

A high-performance spectrophotometric system designed for both reflectance and transmittance measurements in the 105-200 nm spectral range under a wide range of thermodynamic conditions is presented. The basic principle of the system is that of a classical double-beam fixed configuration with the reference signal given either by reflection on the front surface of the optical cell window or the faces of an additional plane parallel window. Specific components include a continuous discharge in D2 or H2 as the VUV source, an asymmetric monochromator with a holographic grating, double-beam section optics, and electronics for data acquisition which memorizes both the ratio between the two signals and the reference signal. Absolute scaling for the system requires the comparison of measurements with and without absorbent in the cell. Drifts of 0.7 percent per day at ambient temperatures and absolute reflectances as low as 0.5 percent have been measured, illustrating the high performance of the system. The apparatus is especially suited for long cycles of low-temperature, high-pressure experiments.