Growth And Properties Of RE（RE=Nd，Ho，Tm）:LiYF₄ Laser Crystal

With the development of Science and Technology, laser technology has been widely used in the high-tech application, and has drawn great attention around the world. It has gradually become one of the key research and development programs of Optoelectron industry in this new century, and significant social and economic benefits were brought.Laser has characteristics of good atmospheric transmission, strong penetrability confidentiality, good in security, and eye-safe, etc. in the wavelength range of 1-2μm. It has a wide application prospect in the field of military, medical and environmental monitoring and so on. LiYF4 is a kind of optimum matrix material for laser and optical materialsafter YAG. RE(RE=Nd,Ho,Tm):LiYF4 crystals, with characteristics of low melting point, wide transmission range and low phonon energy, are important solid laser materials for lasers at wavelength of 1-2μm.Resistance heating Czochralski technique was adopted to grow LiYF4 laser crystals. Crystal structures and spectroscopic properties were systematically studied by X-ray diffraction, thermal expansion, absorption spectra and fluorescence spectra. The laser output of RE(RE=Nd,Ho,Tm):LiYF4 crystal was realized by laser diode(LD) pumped. The research and main results are as follows:1.The fluorination, purification and dehydration of raw materials were realized by using high-temperature fluorination method. Through a lot of experiments, the optimal ratio 1.06:0.94 of LiF and YF3 was found, high quality polycrystalline were synthesized.2.The rule of temperature distribution, heat transfer and the shape of solid-liquid interface, etc. were analyzed in the crystal growth process, which provides a theoretical foundation for adjusting and improving crystal growth technology. The temperature field was designed by molybdenum as the outer layer and graphite as inner layer for the first time. In this temperature field, the high quality RE(RE=Nd,Ho,Tm):LiYF4 crystals was grown.3.By changing the growth atmosphere, from using pure CF4 gradually to the decreasing proportion of CF4, the final mixed atmosphere 10% CF4 and 90% Ar was confirmed and good results was achieved.4.The common defects of crystals were discussed in the crystal growth process, the effects of crystal growth rate, crystal rotation rate, thermal effects, crystal orientation, crystal size, etc.were studied.5.Physical properties of RE(RE=Nd,Ho,Tm):LiYF4 crystals were studied, the problem of the crystal cracks due to the different thermal expansion coefficient was solved by using a series of special optical processing.6.The absorption spectra and fluorescence spectra of crystals were tested. For Nd:LiYF4, Tm:LiYF4, Ho:LiYF4 and Tm,Ho: LiYF4 crystal,the strongest absorption peaks were located near 808 nm, 790 nm, 1908 nm, 779 nmrespectively and fluorescence output were1.053μm, 1.94μm, 2.06μm correspondingly.7.The laser output performance of Nd:LiYF4 crystal, Tm:LiYF4 crystal, Ho:LiYF4 crystal and Tm:Ho:LiYF4 crystal were tested. By testing the 3×3×10mm3 Nd:LiYF4 crystal laser performance at 808 nm diode-pumped laser and at 20.5W pump power, output laser wavelength of 1053 nm, the maximum output power of 8.5W, light-light conversion efficiency of 41.5% and slope efficiency of 52.6% were obtained. By testing 1.5×6×60mm3 Tm:LiYF4 crystal laser performance at 792 nm laser diode-pumped laser and at 25 W pump power, the output wavelength of 1907.8nm, the maximum output power of 10.5W, lightlight conversion efficiency of 42% and slope efficiency of 50.6% were obtained. By testing Φ5mm×32mm Ho: LiYF4 crystal laser performance at 1910 nm center wavelength and at 23.3W pump power, the output wavelength of 2065.56 nm, the maximum output power of 10.1W, light- light conversion efficiency of 43.3% and slope efficiency of 56.5% were obtained. By Testing the 4×4×15mm3 Tm:Ho:laser performance LiYF4 crystals at 792 nm central wavelength and at 7.0W pump power, the output wavelength of 2064.56 nm, the maximum output power of 875 mW, light-light conversion efficiency of 12.5% and slope efficiency of 24.9% were obtained.