Diode-pumped Cr:LiSAF ring laser generates 43 mW
A tunable, diode-pumped, chromium-doped lithium strontium aluminum fluoride (Cr:LiSAF) ring laser produces as much as 43 mW of output power at 849 nm in a single longitudinal mode, according to scientists at Schwartz Electro-Optics Research Division (Concord, MA). With the addition of a birefringent filter, the laser is tunable from 810 to 860 nm. Frequency stability of the unenclosed system is better than 15 MHz over the 10-s measurement accumulation time. A 2 ¥ 3 ¥ 5-mm Brewster-cut Cr:LiSAF crystal (Lightning Optical, Tarpon Springs, FL) is mounted on an uncooled copper block and end-pumped at 670 nm by two 500-mW indium gallium aluminum phosphide (InGaAlP) diode lasers (Uniphase, San Jose, CA).
The four-mirror cavity forces the beam into a figure-eight optical path. A spherical lens collimates the output of the pump laser along the diffraction-limited axis, and a 12X cylindrical telescope expands it along the nondiffraction-limited axis. The collimated, expanded beams are focused onto the gain medium by a spherical lens. To ensure unidirectionality, a Brewster-cut terbium gallium garnet rhomb and a crystalline quartz plate were inserted into the cavity. Lidar is one possible system application. "We may look at the ring laser for injection seeding oscillators to narrow the bandwidth for lidar applications," says group leader Henry Zenzie. "We also could seed pulsed Cr:LiSAF or pulsed Ti:sapphire lasers with this system," he adds.