Studies On Growth And Performance Of Tm: YAP,ZnSe And Cr²⁺: ZnSe Laser Crystals

Tm3+ doped solid-state lasers in 2μm region, which can be directly pumped by commercially available laser diodes and possess high conversion efficiency due to the cross relaxation mechanism, have received much attention in recent years. Laser crystals have wide application in military, research and industry fields. In addition, broadly band tunable (2.0-3. 1μm) Cr2+:ZnSe laser also have gained much attention. Their extremely broad absorption band allows it to be pump by variety of sources. High quality Tm-doped YAlO3 (Tm:YAP) single crystal with 4 at% doping concentrations was grown by the Czochralski method. In this dissertation, a Tm:YAP laser was applied as a pump source for Cr2+:ZnSe,which lay a foundation for the study of laser properties of Cr2+ ZnSe laser crystal.In this thesis, after a brief summary of the development of the solid-state lasers, especially those Tm3+ doped solid-lasers in 2μm region, we investigated the growth, spectra and laser performance of Tm:YAP, ZnSe and Cr2+:ZnSe crystals. The main work includes two parts:1. Growth, spectra and laser performance of Tm:YAP crystalsTm:YAP with 4 at% doping concentration was successfully grown by Czochralski (Cz) method. Our research focuses on the improvement of the growth process and parameters. X-ray power diffraction studies confirm that the as-grown crystal is isostructural with the YAP crystal, the spectral properties of Tm:YAP were investigated. The absorption spectra study show that Tm:YAP crystal has strong absorption peaks of 688 and 794 nm, which are corresponding to the transition from the 3H6 ground state to the 3F3 and 3H4 excited state of Tm3+. The lifetime measurements show the decay time of 3F4 manifold is 5.82 ms. Laser experiments were demonstrated in 4 at% Tm:YAP. The best laser performance was achieved with the c-cut 4at% samples at 2.01μm Laser experiment results show continuous-wave output power of 5.16 W at 2.01μm was obtained under the absorbed pump power of 12.95 W, optical-to-optical conversion efficiency of 39% and the slope efficiency is 45.5%. Continuous tunable range from 1894 nm to 2066 nm is achieved with the maximum laser output power of 1.84 W at 2010 nm.2. Preparation and optical characterization of ZnSe and Cr2+:ZnSeLarge sized high quality ZnSe crystal was grown by the temperature gradient technique (TGT) method. The optical property and defects of the as-grown ZnSe crystal was studied. Chromium films were deposited at the surface of ZnSe crystal by a magnetron sputtering system, the mid-infrared Cr2+:ZnSe laser crystals were prepared by the method of the thermal diffusion. The spectral properties of Cr2+:ZnSe were investigated. The absorption spectra of Cr2+:ZnSe shows a strong broad absorption band with a peak at about 1800 nm is attributed to the 5T2â†'5E transition of the Cr2+ (3d4) ion substituted for the Zn2+ in the tetrahedral site. PL spectra measured at 77 K of Cr2+:ZnSe crystal shows broad band emission around centre wavelength at 2.2μm. This work may provide related reference data for the laser experiment of Cr2+:ZnSe.