| Orthogonally polarized lasers operating in the 2μm eye-safe spectrum waveband have important applications in differential absorption lidar,coherent Doppler wind lidar,remote sensing,and nonlinear frequency conversion in the mid-infrared range.In this work,we present an experimental research of the output characteristics and polarization properties of a Tm:YAl O3（Tm:YAP）self-pulsing intracavity-pumped Ho:Lu Li F4（Ho:LLF）gain-switched orthogonally polarized dual-wavelength laser.We provide a detailed analysis and discussion of the experimental results and optimize the output performance and parameters of the dual-wavelength orthogonally polarized laser.This expands its value as a new type of laser source for various optical researches and applications.Firstly,a Tm:YAP solid-state laser was established and operated in continuous wave mode,active Q-switched mode,passive Q-switched mode,and self-pulsing mode.The self-pulsing Tm:YAP laser with a maximum output power of 2.10 W was selected as the intracavity-pumped source for the Ho:LLF laser.In addition,the stability issue of the self-pulsing Tm:YAP laser was theoretically studied.The temporal characteristics of the self-pulsing output under longitudinal-mode random drift and mode competition mechanisms were numerically simulated.The research results showed that longitudinal mode random drift could lead to unstable self-pulsing laser amplitude,and the severity of the amplitude instability was directly related to the longitudinal mode random drift.The laser exhibited intrinsic unstable output pulse shapes.To address the instability of the self-pulsing laser,a Fabry-Perot（F-P）etalon was added in the experiment to achieve frequency locking and obtain stable self-pulsing laser output.To achieve efficient and stable Ho:LLF laser output,Tm:YAP and Ho:LLF laser crystals are placed in the same resonant cavity.This reduces the intra-cavity losses and accelerates the energy conversion process,allowing for the generation of Ho:LLF pulse laser output through intra-cavity pumped gain-switched.Through utilizing the self-pulsing mechanism of Tm:YAP and the gain-switched mechanism of Ho:LLF,paired-pulse with different wavelengths of Tm3+laser and Ho3+laser are generated.The pulse output characteristics of the paired-pulse are analyzed and discussed,and their temporal dynamics are studied.The repetition frequency of the paired-pulse can be adjusted within the range of 8-22 k Hz,and the time delay between the paired-pulse can be adjusted from 9.5 to 2.9μs.The polarization of Tm:YAP laser and the polarization of Ho:LLF laser keep orthogonal.Due to the absorption stabilization effect of the Ho:LLF crystal,the operating wavelengthes of the dual-wavelength paired-pulse laser remains stable without inserting the additional F-P etalon to stabilize the self-pulsing laser.With a intracavity-pumped structure,a slight angle between the Ho:LLF crystal axis and the cavity axis was made,utilizing the strong natural birefringence of the Ho:LLF crystal to achieve orthogonal polarized dual-wavelength laser output.The output characteristics of the Ho:LLF crystal orthogonal polarized dual-wavelength laser were experimentally studied,and its polarization characteristics were thoroughly discussed.The maximum output power of theπ-polarized laser at 2052 nm and theσ-polarized laser at 2066 nm were measured to be 299m W and 126 m W,respectively.As the pump power increased,the two polarizations laser remained orthogonal to each other,and orthogonal polarized dual-wavelength laser achieved balanced energy output.By controlling the pump power and adjusting the crystal axis direction to change the gain-loss balance condition in the cavity,the switching of the orthogonal polarized laser was realized.Due to the gain switched mechanism,the Ho:LLF laser output exhibited pulsed laser characteristics,with a minimum pulse width of 326 ns,a maximum repetition frequency of 24 k Hz,and a maximum average energy of 28μJ.In addition,a comparative experiment was conducted by using a Ho:YLF crystal under the same experimental conditions,which confirmed the excellent output characteristics and polarization characteristics of the Ho:LLF orthogonal polarized dual-wavelength laser. |
