| The mid-infrared laser in the region of 2.7?3 ?m has wide applications in the fields of biomedicine,nonlinear optics,space scientific research,LIDAR,remote sensing detection,environmental pollution monitoring,material processing,etc.Among all the methods to obtain lasers in this waveband,the Er3+-doped solid-state laser has attracted extensive attention,and a high laser efficiency beyond the Stokes limit can be realized through high power?970 nm laser diode(LD)pumping and cooperative up-conversion between Er3+.The Er:YAP crystal has many advantages,such as high thermal conductivity,lower phonon energy,natural birefringence,and linearly polarization laser output,and so on.Thus it possesses unique superiority in the field of high power mid-infrared lasers.However,there is no research report on improving the mid-infrared laser.performance of Er:YAP crystal by optimizing the doping concentration of Er3+and co-doping the deactivated ion Pr3+.There are few studies focus on achieving high efficiency mid-infrared laser output by using LD pumped Er:YAP crystal.In this dissertation,in order to further improve the laser performance of Er:YAP crystal and obtain a high-power and high-efficiency mid-infrared laser,the pumping mode,crystal orientation and doping concentration were optimized.And then the laser pulse width is decreased and peak power is further enhanced by electro-optic Q-switching technology.The specific research contents are as follows:1.High optical quality Er:YAP and Er,Pr:YAP crystals with different doped concentrations are grown successfully by Czochralski method.The crystal structure and quality are characterized.The absorption and fluorescence spectra,fluorescence lifetimes are measured,and the factors affecting the spectral performance and the mid-infrared fluorescence emission mechanism of Er3+are analyzed by comparing the energy level diagram of Er3+ and Pr3+.2.Laser performance of xenon lamp pumped,LD end-pumped and LD side-pumped 10 at%Er:YAP crystal are investigated,the advantages and drawbacks of three pump methods are analyzed systematically.In general,a high-power and high-efficiency quasi-continuous laser can be obtained by the LD side pumping,which is a relatively ideal pumping method.3.The polarization characteristic and optical anisotropy of Er:YAP crystal are studied.It indicates that the crystal has the characteristics of polarization absorption,polarization output and multi-wavelength laser output.The linearly polarized laser can be used as pump source to enhance the absorption efficiency of the crystal to the pump light,which is beneficial to improve the laser efficiency.The absorption coefficient and laser performance of different axial crystals possess a certain difference with each other.Under a lower pump power,the a-axis crystal with higher absorption coefficient at 973 nm has better laser performance.However,under a higher pump power,b-axis crystal exhibits better performance due to the higher thermal conductivity and smaller thermal expansion coefficient.4.The laser performances of Er:YAP and Er,Pr:YAP crystals doped with different concentrations are studied comparatively.The main factors affecting the laser properties are analyzed,which can provide guidance and basis for the further optimization of the laser performance.The results indicate that 15 at%Er:YAP crystal possesses better performance.The maximum average powers of 23.5 and 11.1 W are achieved at 250 Hz and 1000 Hz,respectively,which are improved to 26.75 and 13.18 W by using the laser crystal rods with concave end-faces.The maximum output power and slope efficiency of Er,Pr:YAP crystal are lower,but it is suitable for Q-switched lasers.5.The Q-switched laser performance of xenon-lamp pumped and LD side-pumped Er,Pr:YAP crystal are studied by using LGS crystal as electro-optic Q-switching,which has a high damage threshold and low dielectric constant.The Q-switched pulsed lasers are obtained with 5 Hz,40 ns,1.59 MW and 150 Hz,61.2 ns,0.33 MW,respectively.The main innovations of this dissertation are as follow:1.Two solutions of high doping concentration of Er3+to enhance the cooperative up-conversion process and co-doping deactivating ion of Pr3+ to reduce the lifetime of the lower energy level are proposed to overcome the self-termination effect of Er3+ laser,and then improve the laser efficiency.2.The LD side-and end-pumping methods are used to achieve high power and good beam quality mid-infrared laser,respectively.3.The laser performance of Er:YAP crystal are improved further by using concave end-faces to compensate the thermal lens effort during the laser operation.4.Using LGS crystal with high damage threshold as Q-switched device,the Q-switched laser experiment setup is designed.The Q-switched lasers with high peak power and short pulse width are obtained on the Xenon lamp pumped and LD side-pumped Er,Pr:YAP crystal,respectively.The research work in this dissertation provides an important reference for the performance optimization of mid-infrared solid-state laser and the preparation of crystal materials,and that lays a solid foundation for the practical application of high-efficiency,high-power and high-frequency mid-infrared Er3+laser. |
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