Research On Output Characteristics Of Orthogonal-polarization And Self-mode-locked 2?m Laser

Diode-pumped orthogonal-polarization and mode-locked lasers operating in the 2 ?m eye-safe wavelength range and atmospheric transmission window have many important applications in coherent Doppler wind liadrs,differential absorption lidars,photo-medicine,material processing,precision laser spectroscopy and frequency conversion.In this thesis,by using Tm,Ho:LLF crystal as the gain medium,the orthogonal-polarization and self-mode-locked Tm,Ho:LLF lasers are investigated in theory and experiment respectively,and the simulated and experimental results are discussed in detail as well.The orthogonally polarized Tm,Ho:LLF laser is realized by adopting the a-cut and c-cut Tm,Ho:LLF crystals as the gain media,respectively.Furthermore,the self-mode-locked Tm,Ho:LLF laser is also realized with an a-cut Tm,Ho:LLF crystal.First,by analyzing the absorption and emission spectra of Tm,Ho:LLF crystal,the gain spectra for ?-polarization(E//c)and ?-polarization(E?c)states of Tm,Ho:LLF crystal for several inversion ratios are calculated.Based on the energy transfer process of Tm,Ho:LLF crystal,the orthogonal-polarization quasi-three-level rate equations of Tm,Ho:LLF laser are established,and the output powers and net gain coefficients of the a-cut Tm,Ho:LLF laser as a function of the pump power are numerically calculated as well.According to the analysis on the net gain coefficients,the formation mechanism of optical bistability with polarization coexistence and switching is clarified.Then the influences of the nondiffraction loss and output coupler transmittance on the output characteristics of Tm,Ho:LLF laser are investigated as well.Moreover,the output performances of the single-longitudinal-mode Tm,Ho:LLF laser in the orthogonal-polarization,single ?-polarization,and single?-polarization states are also numericially calculated,respectively.Second,the single-and orthogonal-polarization Tm,Ho:LLF lasers are realized respectively by employing the a-cut and c-cut Tm,Ho:LLF crystals.Under the single-polarization operation,the Tm,Ho:LLF laser output performances in multimode,single-longitudinal-mode,and passively Q-switched operations are investigated,respectively.Then the orthogonally polarized a-cut Tm,Ho:LLF laser with optical bistability and polarization switching is researched in experiments.Through inserting two etalons into the cavity,the single-longitudinal-mode Tm,Ho:LLF lasers with the orthogonal-polarization,single ?-polarization,and single ?-polarization states are realized,respectively.Moreover,the orthogonally polarized Tm,Ho:LLF lasers are achieved in multimode and single-longitudinal-mode operations by using a c-cut Tm,Ho:LLF crystal,and the experimental results are analyzed and discussed as well.Third,the orthogonally polarized Tm,Ho:LLF lasers in multimode and single-longitudinal-mode operations are realized by using two a-cut Tm,Ho:LLF crystals as the gain media which the c-axes of the two crystals are kept orthogonally.Then the output performances of the orthogonally polarized dual-crystal Tm,Ho:LLF laser are investigated in multimode and single-longitudinal-mode operations for different output coupler transmissions,and the experimental results are analyzed and discussed as well.Compared with the orthogonally polarized single-crystal Tm,Ho:LLF laser,the optical bistability and polarization switching are not observed in the orthogonally polarized dual-crystal Tm,Ho:LLF laser.Furthermore,the output powers of the orthogonally polarized laser are more stable,and the gain competition and polarization rotation do not be observed.Last,the self-mode-locked Tm,Ho:LLF laser is realized without any additional devices in the cavity by using a a-cut Tm,Ho:LLF crystal as the laser gain medium.The average output power,laser spectrum,and pulse width of the self-mode-locked Tm,Ho:LLF laser are investigated.