| 2μm light wave has widely application in laser radar, medicine and remote sensing due to its strong absorption by water and safety for eyes. As a main working medium of solid lasers, Tm: YAlO3 (Tm: YAP) is a promising laser material which possesses some advantages such as high doping concentration, high growth speed, sufficient conversion efficiency, and significant structural anisotropy.Concentrated on the improvement of the growth parameters, growth defects and spectral properties, the growth process, coloration mechanism, and optical characteristics of Tm: YAP single crystals were studied through X-Ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM), Synchrotron Radiation White-Beam Topography (SRWBT), thermal expansion coefficient test, spectrophotometer and interference stripe measurement. The main results are listed blow:Based on the research on growth parameters and growth process, effect of seed orientation, pulling and rotation rates on the crystal quality was investigated. Crack-free and perfect Tm: YAP single crystals with the size ofφ(23～25)mm×(90～110)were successfully grown along the different crystalline axis by the Czochralski technique. The optimized pulling and rotation rates were proposed to be 1.0-1.5 mm/h and 15-25rpm, respectively.The as-grown crystals were analyzed by XRD method using its powder sample, which showed that only YAP phase existed and there was no TmAlO3 phase in the crystal. The X-ray rocking curve (XRC) of as-grown crystal showed a full-width at half-maximum (FWHM ) 31.5″, indicating the as-grown Tm: YAP crystal has the good perfection. Effective segregation coefficient of Tm3+ in YAP crystal was determined to be 0.88 by X-ray fluorescence spectroscopy, which is smaller than that in YAG crystal.The defects commonly contained in Tm: YAP crystals were investigated in detail. Thermal expansion coefficients along three main crystallographic axes were measured in the temperature range of 30～1350℃, and the results showed that they are 11.9458, 5.0012 and 10.5439×10-6 /K, respectively. Therefore, it is suggestive that the b-axis orientation as the growth direction is preferable in Czochralski method. Dislocations were observed by chemical etching method and optical microscope. It was found that there exist the areas with different dislocation etch-pit densities on the (010) plane of Tm: YAP crystal grown along b-axis. Such a distribution of pits could be attributed to the stress distribution during crystal growth. Twins were found only in the crystal grown along c-axis. The existence of main scattering centers in the crystals was confirmed by means of He-Ne laser beam and SEM technique. Meanwhile, the synchrotron radiation white-beam topography (SRWBT) was applied to study hidden defects of Tm: YAP crystals for the first time. The formation processes of defects were analyzed and the approaches to eliminate these defects were discussed.Investigation on annealing andγirradiation mechanism were carried out and discussed through absorption spectra. The results testified that the growth coloration is caused by deviation from the stoichiometric composition, the presence of uncontrolled impurities of the iron group, O–center, F+ center, and the complex of them. It is helpful to understand the coloration mechanism of YAP crystals doped with other rare earth elements.The polarized absorption spectra of Tm: YAP crystals were analyzed and the results suggest that the most interesting aspect is the intensive absorption peak at about 795nm, corresponding to the transition of Tm3+ from 3H6 state to the excited state 3H4. Absorption coefficient of Tm3+ ion in YAP crystal increases with increasing Tm3+ doping concentration. The strongest absorption peak for Tm: YAP crystal grown along a-axis is centered at 794nm and its absorption cross section is 8.64×10-21cm2. However, the peaks are both centered at about 793nm for crystals grown along b and c-axis, and their cross sections are 9.22×10-21cm2 and 6.80×10-21 cm2, respectively. These results showed that the anisotropic effect of optical characteristics exists in Tm: YAP crystal and b orientation is preferred.Investigation on the effect of polarized light on the absorption spectra of Tm: YAP crystal revealed that forπpolarization spectrum, the most intensive absorption at 794nm has a cross section 7.30×10-20cm2 and a 29nm FWHM, while forσpolarization spectrum, the most intensive absorption is situated at 793nm, with an absorption cross-section 18.30×10-20cm2 and FWHM≥25nm. Therefore, Tm: YAP crystal is suitable for LD pumping.Using a Ti sapphire laser that emits 795nm, the photoluminescence spectra were obtained. The strong emission peak is centered at about 1.86μm. The corresponding photoluminescence lifetime is about 4.8ms and emission cross-section is 4.5×10-21cm2. The results indicate that Tm: YAlO3 is a potential candidate for efficient mid-infrared lasers with laser diode pumping and the optimized Tm concentration is 4～6at% due to concentration quenching effect.Based on Judd-Ofelt approach, the intensity parametersΩt(t=2,4,6) of Tm: YAlO3 were calculated to beΩ2=0.93×10-20 cm2,Ω4=2.23×10-20 cm2, andΩ6=1.12×10-20 cm2. The spectral parameters such as experimental and theoretical oscillator strengths, radiative transition probability, radiative lifetime as well as the photoluminescence branching ratio were also obtained. The results showed that Tm: YAlO3 crystal has large emission cross-section and long radiative lifetime. Therefore Tm: YAlO3 crystal can be regarded as a high-efficient infrared laser material and favored for GaAlAs laser diode pumping.
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