Multipassing a Cryogenic Sample: Use of a White-Type Cell with 8 Passes for Studying Solid Hydrogen

The use of a White-type multipass arrangement external to the optical head of a cryostat for Fourier transform spectroscopy of solid H2 was explored in previous work from our laboratory [1, 2]. The present measurements were made by extending from 4 to 8 passes through the cell within the liquid-He vaporization cryostat (Janis Research Inc., Model 10 DT) [3]. This multireflection system was mounted inside the sample chamber of the Bruker IFS 120 HR interferometer as shown in Fig. 1. Water absorptions were minimized by evacuating the whole spectrometer. All six windows of the cryostat and of the sample cell were equipped with an antireflection coating which was optimized for the spectral range 7500 - 9000 cm-1.