Abstract

Laser emission at wavelengths which are strongly absorbed in water is regarded as “eyesafe”. Tunable single-frequency lasers at these eyesafe wavelengths are required for a variety of applications from basic research to laser-based metrology. Prominent examples are in the field of LIDAR and coherent communication technology. Due to their high intrinsic intensity and frequency stability, nonplanar ring lasers (NPROs) ^[1] are especially attractive for these applications. Up to date, NPROs have been realized at 946 nm, 1 064 µm and 1.3 µm based on Nd:YAG as the active medium. With Tm:YAG as laser material, eyesafe NPROs at 2.02 µm were demonstrated with output powers up to 150 mW ^[2]. However, the quasi-three-level nature of this transition sets stringent requirements on the laser design like extremely small cavity dimensions. On the other hand, due to a natural coincidence of the 1 444 µm transition in Nd:YAG with an absorption peak in water (26 cm^–1), an eyesafe laser based on Nd:YAG seems to be a favorable replacement. In this contribution, we report the first demonstration of an NPRO with stable single-frequency operation at 1.444 µm

© 2000 IEEE