Refractive index dispersion and anisotropy in Cr4+: Mg2SiO4

Abstract

Room-temperature refractive index dispersion and anisotropy were measured in the orthorhombic Cr4+:Mg2SiO4 (Cr4+:forsterite) single crystal between 300 and 2000 nm. Use was made of bireflection in an oriented single crystal prism and of birefringence modulation in an oriented plane-parallel sample for obtaining accurate measurements of the anisotropy. Minimum-deviation measurement in an oriented prism provided the refractive index dispersion for one of the axes, whence for the other two axes as well. The crystal is biaxial, and its dielectric principal axes X, Y, and Z, coincide with the crystallographic b, a, and c axes, respectively. Taking 632.8 nm (the HeNe laser line) as a representative wavelength of the visible range, the refractive indices would be na = 1.6505 ± 0.0005, nb = 1.6365 ± 0.0006, and nc = 1.6685 ± 0.0006. The dispersion curves were fitted to different Sellemeier functions. Our results would be very useful for the design of compensating elements of group-velocity dispersion in Cr4+:Mg2SiO4 short-pulse laser cavities. © 2002 Elsevier Science B.V. All rights reserved.