Abstract

A single-frequency Ti:Al₂O₃ ring laser containing electro-optic birefringent filters and etalons could be switched from one frequency to another in 60 µs over a 1000 cm^–1 range. By using three tuners—one coarse and two fine—the laser was able to access any frequency of the cavity except those frequencies corresponding to weak atmospheric absorptions. Near those frequencies the low-frequency selectivity between adjacent cavity modes caused the laser to operate one longitudinal mode away from the absorption. The single-frequency access time was measured to be inversely proportional to the frequency selectivity of the combined tuning elements. Good agreement with calculations was obtained. The excellent thermal properties of sapphire at low temperatures permit high-power operation of the Ti:Al₂O₃ laser. During a 160 µs pump laser pulse, a Ti:Al₂O₃ laser generated 400 W of diffraction-limited output at 77 K. With a spot size of 400 µm in the Ti:Al₂O₃ crystal, thermal steady state in the pumped region is achieved in 30 µs, a time that is short compared to the pulse duration. These results indicate that a liquid-nitrogen- cooled Ti:Al₂O₃ laser can be expected to generate 400 W of cw output. At higher operating temperatures, the laser turned off before the end of the pump pulse as a consequence of the increased optical aberrations associated with lower thermal conductivity and higher dn/dT. The results were consistent with theory.

© 1990 Optical Society of America