Broadly tunable near-and mid-infrared lasers are of interest for a variety of applications including high-resolution spectroscopy, metrology, pumping of nonlinear optical frequency converters such as optical parametric oscillators (OPOs) and standoff chemical sensing. Tunable laser sources in the 2-3 µm region include Cr 2+ -doped chalcogenide lasers; cryogenic systems, such as color center lasers; limited tunability devices, such as Tm and Ho lasers, gas or chemical lasers, and diode lasers; and nonlinear optical devices such as OPOs. Transition-metal-doped chalcogenide lasers are of high interest because of their high versatility, broad room-temperature wavelength tunability, high optical efficiencies, and their potential to be scaled to high powers via direct diode or fiber laser pumping. To date, continuouswave, gain-switched, Q-switched and mode-locked laser operation has been demonstrated. Material advantages include broad absorption and emission bands, high fluorescence quantum efficiencies at room temperature, high gain crosssections, and minimal loss mechanisms such as excited-state absorption or upconversion. Additionally, the materials can be produced by a variety of methods, including several direct growth techniques and diffusion doping. The principal material disadvantages include a relatively large change in refractive index with temperature (large dn/dT), which can induce thermal lensing, and a short, microseconds, energy storage time. In this paper we review fundamental material properties, the current state-of-the-art of continuous-wave and pulsed Cr 2+ doped chalcogenide lasers, and recent research results.

We have demonstrated 50 W of output power from a free-running Tm:YALO laser at 1940 nm. We have also obtained Q-switched operation with 7 mJ of output energy at a 5 kHz repetition rate. OCIS Codes: (140.3580) Lasers, solid-state; (140.3070) Infrared and far-infrared lasers.Tm:YALO lasers are useful pump laser sources for Ho:YAG lasers [1-4], 2 µm sources for laser radar applications, Cr:ZnSe lasers, which provide widely tunable output from 2.1 µm to 3 µm [5,6], and optical parametric oscillators (OPOs) [7]. Higher power and Q-switched Tm:YALO lasers are needed as better pump sources for higher power Ho:YAG and Cr:ZnSe lasers. In this paper, we report a 50 W free-running Tm:YALO laser and a 7 mJ laser Q-switched with a 5 kHz pulse repetition rate.The Tm:YALO laser cavity configuration is shown on the left of Fig. 1. The gain medium is a Tm:YALO laser rod with undoped YALO end caps that is dual end-pumped by 795 nm fiber coupled laser diodes. The laser resonator consists of a normal incidence high reflector, the 3% Tm doped YALO rod, two 45° angle-of-incidence dichroic fold mirrors, a Brewster cut TeO 2 acousto-optic modulator (AOM) for Q-switching, and an output coupler. Both the HR end mirror and the output coupler have radii of curvature of 10 cm. The laser output is polarized due to the natural birefringence of the Tm:YALO crystal. As seen in the photograph of the system on the right of Fig. 1, this is a self-contained, engineered laser system. The laser utilizes a watercooled base upon which are mounted the laser rod mount and inner enclosure (center). The pump diodes are hard mounted to a vertically oriented cooling plate. The entire assembly has dimensions of 31.5 cm W x 42 cm L x 16 cm H. Fig. 1. Schematic of the resonator (left) and photograph of the complete Tm:YALO laser (right).

A detailed investigation of frequency doubling of a transversely excited atmospheric CO2 laser operating at 9.55 microm with a CdGeAs2 crystal was carried out. The temperature of the crystal was varied between 80 and 295 K to maximize the frequency-doubled energy. The temporal shape of the generated beam at 4.775 microm was monitored to calculate its peak power. High values of midwave infrared pulse energy (16.65 mJ) and peak power (92 kW) were obtained, which can be of potential use in lidar systems.

We report on a Cr:ZnSe laser pump-tuned, intracavity CdSe optical parametric oscillator (OPO) with signal and idler tunable from 2.8 to 3.7 µm and 8.2 to 8.8 µm respectively and output power of 3 W.