Tunable solid-state lasers allow the user to customize the source to the application. An integral part of this light source is the laser medium. Laser crystals, based on tetravalent chromium (Cr4+) ion operate in the technologically important near infrared (1-2 μm) spectral region.
The 1-2 μm spectral range, includes wavelengths at 1.3 and 1.5 μm, both important for optical communications, and the eye-safe wavelength range beyond 1.45 μm. Possible uses include optical communications, eye-safe ranging and remote sensing, and biomedical and scientific applications.
A series of Cr4+-doped crystals is being developed for the 1.2-1.7 μm region. These materials have desirable characteristics - high emission cross sections, wide tuning range, and an absence of parasitic centers. Prime candidates are silicates and germanates such as Cr4+:CaMgSiO4 and Cr4+:Ca2GeO4 (Cunyite).
Large laser-quality crystals of highly-doped Cr4+:Ca2GeO4 have been grown by a top-seeded solution growth method, which is a combination of vertical pull (Czochralski) and solution (flux) growth techniques. These crystals were used in the first successful tunable laser operation of the Cr4+:Ca2GeO4 laser crystal.