基于Nd∶GdVO_(4)晶体的双波长被动调Q激光器

Passively Q-switched Dual-wavelength Laser Based on Nd∶GdVO_(4) Crystal

提出了一种基于Nd∶GdVO_(4)晶体的双波长正交偏振被动调Q激光器。建立了对应的速率方程模型,研究了激光器输出双波长脉冲和不同输出镜反射率条件下泵浦功率对激光输出时域特性的影响。理论研究结果表明,通过调节输出镜反射率改变双波长阈值反转粒子数密度,当π偏振阈值反转粒子数密度小于σ偏振阈值反转粒子数密度且差值较小时,激光器可以输出双波长被动调Q脉冲激光,通过增大泵浦功率可以依次产生π偏振单一波长脉冲、双波长多对一脉冲、双波长一对一脉冲、双波长一对多脉冲以及σ偏振单一波长脉冲。搭建实验装置,设置π偏振输出镜反射率为0.60,σ偏振输出镜反射率为0.95,对泵浦功率和激光输出时域特性之间的关系进行验证。随着泵浦功率的增大,激光器依次输出具有上述时域特性的脉冲激光,与数值仿真结果一致。当泵浦功率为5.51 W时,激光器输出正交偏振双波长一对一脉冲激光,其中π偏振和σ偏振的波长分别为1063.23 nm和1065.52 nm,平均功率分别为323 mW和462 mW,脉冲峰值功率分别为11.62 W和20.35 W,脉冲宽度分别为185 ns和168 ns,脉冲重复频率为141 KHz。

Dual-wavelength pulse lasers have a wide range of applications in terahertz wave generation,Doppler radar coherence detection,spectral studies and so on,so how to generate dual-wavelength pulse lasers is of great significance.Dual-wavelength pulse lasers can be realized by Q-switched technology,which can be divided into active Q-switching and passive Q-switching.Compared with the active Qswitched lasers,the passive Q-switched lasers have the advantages of simple technology and small size.In order to obtain a stable dual-wavelength pulsed laser,one approach is pumping two crystals or combinatorial crystals into a cavity,another approach is pumping a single crystal into a cavity.Compared with the dual-crystal laser,the single-crystal laser has the advantages of simple structure,convenient operation,and easier miniaturization.But there is gain competition between two wavelengths of single crystal laser,so it is difficult to output two-wavelength pulse laser.In this paper,a 1063 nm/1065 nm dual-wavelength pulsed laser using a single Nd∶GdVO_(4) crystal and a single Cr^(4+)∶YAG crystal is proposed.The Q-switched process of laser can be described by rate equation.By establishing a simulation model based on rate equation,the influence of pump power on the time-domain characteristics of laser output under different reflectivity of output mirror is studied.The theoretical results show that when the reflectivity of the output mirror is changed,the threshold inversion particle number density of the two wavelengths will change accordingly.Therefore,the dual-wavelength pulsed laser can be realized by changing the reflectivity of the output mirror.When theπ-polarized output mirror reflectivity is in the range of[0.52,0.71]andσ-polarized output mirror reflectivity is 0.95,the laser can output dual-wavelength passively Qswitched pulse.By increasing the pump power,π-polarized single-wavelength pulse,dual-wavelength multiple-on-one pulse,dual-wavelength one-on-one pulse,dual-wavelength one-on-multiple pulse andσ-polarized single-wavelength pulse can be generated in sequence.In order to verify the influence of pump power on time characteristics of dual-wavelength pulse,a Y-type-cavity dual-wavelength laser is designed.The reflectivity ofπ-polarized output mirror is set to 0.60,and that ofσ-polarized output mirror is set to 0.95.The stimulated emission cross section of Nd∶GdVO_(4) crystal is kept constant by setting the cooling temperature of the temperature controller at 20℃.The output of the Nd∶GdVO_(4) laser is coupled to two channels of the oscilloscope by two identical photodetectors.The pulse waveform of the Nd∶GdVO_(4) laser at different pump power is measured by changing the pump source.With the increase of the pump power,the pulse laser with the time mentioned above characteristics is output in turn,which is consistent with the numerical simulation results.When the pump power is 5.51 W,the output of the laser is a one-onone pulse of two orthogonal polarized wavelengths,of which theπandσpolarized wavelengths are 1063.23 nm and 1065.52 nm respectively,the average power is 323 mW and 462 mW respectively,and the peak pulse power is 11.62 W and 20.35 W respectively,the pulse repetition rate is 141 kHz.In this paper,by setting up the rate equation model of two-wavelength quadrature polarization passively Qswitched laser based on Nd∶GdVO_(4) crystal,the condition of laser output dual-wavelength pulse and the influence of pump power on the time characteristics of laser output under different reflectivity of output mirror are studied.The simulation results show that the dual-wavelength pulse can be realized by adjusting the reflectivity of the output mirror to change the double-wavelength threshold inversion of the particle number density.On the premise of realizing dual-wavelength pulse output,the output pulse waveform can be changed by changing the pump rate.The experimental results are in good agreement with the simulation results under the condition of 20℃.