Tetravalent chromium laser crystal operates at communications wavelengths

Tetravalent chromium laser crystal operates at communications wavelengths

The Solid-State Laser Group at City College of New York (New York, NY), headed by Robert Alfano and Vladimir Petricevic, has demonstrated room-temperature lasing of Cr4+:Ca2GeO4, a new tunable tetravalent chromium laser crystal for near-infrared wavelengths. Dubbed "cunyite," its development follows that of Cr:forsterite (Cr4+:Mg2SiO4), which was the first crystal to use Cr4+ as the lasing ion; however, forsterite only lases between 1.15 and 1.35 µm. According to Alfano, the much higher dopant level in the new material permits even a thin crystal to lase. He claims potential tunable operation over 1.3 to 1.6 µm, which includes communications (1.3 and 1.5 µm) and eye-safe (beyond 1.45 µm) wavelengths.

The cunyite crystal "works better," says Alfano, "because the chromium fits better in the germanium site and doesn`t go into the calcium site" as would Cr3+ impurity ions in Cr:forsterite. Free-running laser output is centered at 1.4 µm, and the lasing threshold is as low as 1 mJ of absorbed 1064-nm energy in a nonoptimized cavity. The crystals were grown by a top-seeded solution method that combines vertical pull (Czochralski) and solution (flux) growth techniques.