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 430–1100 nm. For a crystal stabilized at 4:4K, this refractive index is measured to be np−H2 = 1.130 ±0.001 at 514 nm. 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 10 K with no change in np−H2. The refractive index varies only slightly over the observed wavelength range, and no significant birefringence was observed.


Astrophysics and Astronomy