| Orthogonally polarized solid-state lasers at 2μm band can output linearly polarized lasers with mutually perpendicular polarization states,it is in the atmospheric window and the human eye safety band.It has an important application background in the field of laser radar detection.Especially in a single longitudinal mode orthogonally polarized laser source,when two orthogonal linear polarization modes switches alternately,the delayed polarization switching dynamics directly affects the operation stability of the system.Moreover,the time synchronization and energy balance of output pulses in two orthogonal polarization modes are important fundamental issues in practical technology.In the thesis we focus on resonantly-pumped Ho3+:LiLuF4(Ho:LLF)orthogonal polarization solid-state laser at 2 μm band.The delayed polarization switching dynamics,the pulse synchronization and alternate switching characteristics in single longitudinal mode orthogonally polarized lasers are studied theoretically.The delayed polarization switching dynamics of a single longitudinal mode Ho:LLF laser under continuous wave operation is studied.Considering the optical anisotropy of laser crystals,a semi-classical vector laser dynamic model is given.The delayed responses of orthogonal polarization switching caused by transiently or gradually switching the pump polarization are analyzed.The influence of physical parameters on delay time is discussed.In the gradient switching of pump polarization,serious polarization mode competition can be found in the dynamics during laser polarization switching.The seed injection method is proposed to reduce the delay time of polarization switching.Meanwhile,the seed injection method can suppress and even eliminate the effect of polarization mode competition during the polarization switching process.The characteristics of orthogonal polarization pulse output are studied for a Cr:ZnS passively Q-switched single longitudinal mode Ho:LLF laser.Considering the optical anisotropy and crystal birefringence in laser cavity,a semi-classical Q-switched vector laser dynamics model is given.Under varous pump polarization angles,the characteristics of two orthogonal polarizations and pulse delays caused by transiently switching the pump polarization are analyzed.When the pump polarization switching occurs at different times within the pulse interval,distinct phenomena and behaviors of output pulse can exhibit.Under gradually switching the pump polarization,the coupling effect of two orthogonal polarization modes can be found in pulse delay dynamic process.The physical scheme is provided for obtaining alternate orghogonal polarization pulse output in single longitudinal mode laser.The pulse synchronization and alternating polarization output characteristics in Cr:ZnS passively Q-switched single longitudinal mode Ho:LLF laser are studied.Based on the semi-classical Q-switched vector laser dynamics model,the problems of pulse synchronization and alternating output in time for two orthogonal polarization modes are discussed.Here two different cutting manners of Cr:ZnS saturable absorber are taken into account,with considering the different orientation between the Cr:ZnS crystal axises and the cavity eigen axises.The Cr:ZnS crystal cut at a specific orientation keeps the crystal axis of at 45° angle to the cavity eigen axis.When the pump polarization is at 45° angle or circularly polarized incidence,a pulse sequence of orthogonal polarization modes can produce a time synchronized output.While the pump polarization is at other angles,the orthogonally polarized pulse sequences generally have alternating polarization output behavior in time.The regulation method of energy ratio and time interval for the alternating polarization output pulses is discussed,which provides a feasible solution for practical applications.The results of the thesis provide a physical basis and technical guidance for the design and development of a single-mode orthogonal-polarized pulsed laser source at 2 μm band. |
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