Abstract

While Tm: YAG lasers with their attractive wide gain profile in the infrared are available since some time, they have so far only been operating as multi-mode devices. We demonstrate a miniaturized Tm:YAG laser emitting single transverse mode radiation tunable between 1940 nm and 2030 nm. Only two controlled longitudinal modes are emitting at frequencies separated by the free spectral range of the laser resonator of 1 GHz. Each frequency is stable to better then 1 MHz. With 700 mW of pump power at 786 nm we achieve up to 80 mW dual frequency output using a longitudinal pump geometry (see figure below). We extend a simple standing wave resonator design which previously has been shown to work for Titanium Sapphire lasers [1]. This Z-shaped resonator is comprised of two plane mirrors and two curved mirrors which produce a tight focus in the center of the cavity where the Tm:YAG crystal is placed on a water cooled copper mount (see figure below). Dual frequency operation is achieved by a 150 μm thin infrasil etalon. A second etalon of 163 μm thickness allows for coarse tuning exploiting the 100 nm frequency separation between the coincidences of transmission maxima for both etalons. Fine tuning is obtained by a tunable 6 mm thick etalon which is formed by the plane outcoupler and a 4% reflector placed outside the resonator. The entire setup uses miniature flex mount mirror adjustments and is mounted on a 20 * 10 cm² base plate forming a compact and rigid structure. With the possibility of employing diode pumping our system becomes a versatile and economic precision device which may proof useful even in difficult environments.

© 2000 IEEE