CW Single-Frequency Tunable, CW Multi-Watt Polycrystalline, and CW Hot-Pressed-Ceramic Cr 2+ :ZnSe Lasers Igor S. Moskalev, Vladimir V. Fedorov, and Sergey B. Mirov University of Alabama at Birmingham, COSS Center, 310 Campbell Hall, 1300 University Blvd., Birmingham, AL 35294 moskalev@uab.edu Abstract: We demonstrate CW ultrafast-tunable (4 μm/s), 150 mW, single-longitudinal-mode (120 MHz); and CW multi-watt (2.7 W at 2.5 μm), highly efficient (39% real efficiency) polycrystalline Cr 2+ :ZnSe lasers; and CW hot-pressed ceramic Cr 2+ :ZnSe laser. ©2007 Optical Society of America OCIS codes: (140.5680) Rare earth and transition metal solid-state lasers; (140.3380) Laser materials; (140.3570) Lasers, single-mode; (140.3070) Infrared and far-infrared lasers; (140.3580) Lasers, solid-state. 1. Single-frequency, fast-tunable, CW Cr 2+ :ZnSe laser The laser is based on a folded 10 cm Kogelnik/Littman scheme, Fig. 1. The Cr 2+ :ZnSe single crystal of the size 4x4x1 mm, which absorbs ~70% of pump at 1.55 μm, is mounted at Brewster angle into a thermoelectric cooling unit, providing temperature stabilization at 20±0.1°C. The radiation of 1.55 μm linearly polarized Er-fiber laser (IPG Photonics, ELM-10-LP) is focused into the crystal by a 50 mm lens. The output spectrum structure and laser linewidth are measured with a scanning FPI with a finesse of ~7.7. The output radiation has a linewidth of 120 MHz (measurement limit of the available FPI) over a 120 nm tuning range around 2.5 μm, and maximum output power is up to 150 mW at 5 W incident pump. The FPI-measured output spectrum of the laser is shown in Fig. 2. The output wavelength of the laser is scanned by tilting the mirror with a piezo-driven mirror shaker with a repetition rate of 220 Hz. This results in a complete wavelength scan over 9-nm range in 1/440 s (2.3 ms), which corresponds to about 4 μm/s tuning speed. Simultaneous monitoring of the output laser spectrum with a fixed-length FPI shows that the laser is operating in the single-longitudinal-mode (SLM) regime during the entire ultrafast 9-nm wavelength scan. 2. Multi-Watt-power, CW Cr 2+ :ZnSe laser Power scaling of the Cr 2+ :ZnSe lasers output to multi-watt level requires special geometry designed for maximum suppression of thermal effects [1],[2]. For obtaining multi-watt level of the output power in CW Cr 2+ :ZnSe, we utilize a gain element in the form of a thin and long, longitudinally-pumped parallelepiped which is cooled through two large unpolished facets. In this case, the Cr ions are concentrated in a very thin (~200 μm) layer near one of the large crystal facets and parallel to it. The crystal is fixed on a copper cold plate and cooled with a TEC. With this approach we have built the first to our knowledge multi-watt (2.7 W at 7.0 W incident pump), pure CW Cr 2+ :ZnSe laser, which is briefly described bellow. 1.55 μm Pump mirror Grating, 600 g/mm Cr 2+ :ZnSe Tuning mirror Output beam α d 1 d 3 d 2 d 4 Fig. 1. Cr 2+ :ZnSe tunable, single-frequency laser based on Kogelnik/Littman cavity. d1~25 mm, d2~25 mm, d3~20 mm, d4~30 mm. Fig. 2. Interference pattern of the SLM output spectrum from a 160 mm FPI. The spectral resolution is limited by the interferometer finesse of 7.7, which gives the upper limit on the laser linewidth of 120 MHz. a2359_1.pdf CTuN6.pdf