Preparation Of 2.79 Pm Erbium-Doped Scandium Gallium Garnet Single Crystal Fibers And Investigation Of Cascade Laser Technology

Mid-infrared laser,especially in the 2.7-3 μm waveband,has been widely used in biomedical,space science,laser remote sensing and environmental monitoring due to its special spectrum.Among the many ways to obtain this band laser,Er3+-doped solidstate lasers can be directly pumped by commercial～970 nm laser diodes(LD)and directly generate a radiation wavelength of 2.7-3 μm through the transition between the 4I11/2 and 4I13/2 energy levels.Erbium-doped garnet oxide crystals have important applications in the laser field due to their high symmetry,high chemical stability and excellent thermal properties.However,the thermal effect of the laser crystal element and the self-termination effect of Er3+ seriously hinder the further improvement of its laser performance.Therefore,in order to further improve the thermal effect and self-termination effect of crystal,this dissertation will focus on the optimization of single crystal fiber laser matrix crystal,the preparation of single crystal fiber,laser performance,radiation resistance and Er:YSGG crystal cascade characteristics.The specific research contents are as follows:1.Six kinds of laser host crystals with high optical quality YAG,GGG,YSGG,GSGG,GYSGG and CaMgZr:GGG were successfully grown by the Czochralski method.The physical properties such as thermal properties,transmission spectra,refractive index and phonon energy of the six crystals were compared,and the annealing process can reduce the thermal expansion coefficient of crystal heat.The YSGG with low phonon energy and high thermal conductivity,and GYSGG host crystals with excellent radiation resistance were selected as the research objects of this dissertation.2.High-quality Er:YSGG SCF with a size of Φ 0.85 mm × 85 mm and Er,Pr:GYSGG SCF with a size of Φ 0.75 mm × 70 mm were prepared by crystal posttreatment process.The diameter fluctuations are ±2%and ±3.5%,respectively,indicating that SCFs possesses excellent diameter homogeneity.The thermal distribution of SCF and bulk crystal in laser operation is simulated and compared by finite element analysis.The results show that the former has a better heat dissipation effect.The laser output with high beam quality(Mx2/My2=1.28/1.29)was obtained by an LD end-pumped Er:YSGG SCF laser experiment,indicating that the SCF is suitable for the seed source of mid-infrared laser amplifier.3.Er,Pr:GYSGG single crystal with high optical quality was successfully prepared by the Czochralski method,and its phase structure,crystal quality and optical uniformity were characterized.The thermal properties,mechanical properties and refractive index of the crystal were tested in detail,which provided a reference basis for the subsequent research on Er,Pr:GYSGG SCF.4.The effects of y-ray irradiation on the transmission loss and laser performance of the Er,Pr:GYSGG SCF were compared and analyzed.The results show that the transmission loss coefficients of the fiber before and after irradiation are 0.07 dB cm-1 and 0.09 dB cm-1,respectively.The maximum output power and slope efficiency of the single crystal fiber after irradiation are only reduced by 2.5%.The laser beam quality of the irradiated SCF is Mx2/My2=1.11/1.13,indicating that it possesses excellent antiirradiation performance.The SCF is a mid-infrared laser amplifier seed source that can be used in space environment.5.An LD end-pumped 1 at.%Er:YSGG cascaded pulsed laser experimental setup was designed.The characteristic wavelength of the cascade laser was determined at 1645 nm at room temperature,which confirmed the existence of the cascade characteristics.Compared with the non-cascade case,the slope efficiency of the cascaded mid-infrared laser is increased by 121%.In addition,the Stokes sub-level transitions corresponding to the four emission peaks were identified.The above results show that the cascaded laser is helpful to further improve the performance of Er:YSGG mid-infrared laser.The innovations of this dissertation are as follows:(1)It is proposed to use single crystal fiber to enhance the thermal management of laser gain medium.For the first time,the Er:YSGG and Er,Pr:GYSGG SCFs with high quality,large aspect ratio and excellent diameter uniformity were successfully prepared by crystal post-treatment process.(2)A combination of thermal simulation and laser experiments is proposed to explore the advantages in thermal dissipation capability.At finally,the 2.79 μm laser output with high beam quality(Mx2/My2=1.28/1.29)was achieved in an LD endpumped Er:YSGG SCF.(3)The cascade laser output characteristics of Er:YSGG crystal at room temperature were explored for the first time.The characteristic wavelength of the cascade laser was determined at 1645 nm,which confirms its cascade characteristics at room temperature.The results show that the cascaded laser helps to improve the midinfrared laser output performance.And the Stokes sub-level transitions corresponding to the four emission peaks were identified.The research work of this dissertation provides an important reference for the improvement of thermal and self-termination effects in mid-infrared Fr3+-doped solidstate lasers,and lays a solid foundation for the practical application of high beam quality 2.7-3 μm erbium lasers.