Refractive index measurements of solid parahydrogen

Solid para-H2 is a promising gain medium for stimulated Raman scattering, due to its high number density and narrow Raman linewidth. In preparation for the design of a cw solid hydrogen Raman laser, we have made the first measurements, to our knowledge, of the index of refraction of a solid para-H2 crystal, in the wavelength range of 430–1100nm. For a crystal stabilized at 4:4K, this refractive index is measured to be np−H2 1:130 0:001 at 514nm. A slight, but significant, dependence on the final crystal-growth temperature is observed, with higher np−H2 at higher crystal-growth temperatures. Once a crystal is grown, it can be heated up to 10K with no change in np−H2. The refractive index varies only slightly over the observed wavelength range, and no significant birefringence was observed. © 2011 Optical Society of America OCIS codes: 290.3030, 120.4530, 260.1180, 160.4760, 290.5910. Molecular hydrogen has long been considered a particu-larly useful gain medium for stimulated Raman scatter-ing, because of its large vibrational frequency. As early as 1986, sequential Stokes conversion in a multipass cell of gaseous H2 was used to convert a pulsed dye laser int