Sensing of ultrasonic fields based on polarization parametric indirect microscopic imaging

This Letter tackles the issue of non-contact detection of ultrasonic fields by utilizing a novel optical method based on the parametric indirect microscopic imaging(PIMI) technique. A general theoretical model describing the three-dimensional anisotropic photoelastic effect in solid was developed. The mechanism of polarization status variations of light passing through the stress and strain fields was analyzed. Non-contact measurements of the ultrasonic field propagating in an isotropic quartz glass have been fulfilled by the PIMI technique under different ultrasonic excitation conditions. PIMI parameters such as sin δ, Φ, and the Stokes parameters have been found to be sensitive to ultrasonic fields.     

Modeling the pulse shape of Q-switched lasers to account for terminal-level relaxation

To account for the effect of lower-level relaxation,we have derived a characteristic equation for describing the laser pulse from the modified rate equations for Q-switched lasers.The pulse temporal profile is related to the ratio of the lower-level lifetime to the cavity lifetime and the number of times the population inversion density is above the threshold.By solving the coupled rate equations numerically,the effect of terminal-level lifetime on pulse temporal behaviour is analysed.The mode is applied to the case of a diode-pumped Nd:YAG laser that is passively Q-switched by a Cr 4+:YAG absorber.Theoretical results show good agreement with the experiments.     

Cr4:YAG被动调Q激光器脉冲波形数值模拟及优化

从Nd:YAG晶体Cr4+:YAG被动调Q激光耦合速率方程组出发,数值求解该方程组,获得了激光脉冲的波形。从能量分布和时间分布的角度分析了被动调Q激光脉冲波形的不对称性。定义了描述脉冲波形的对称因子并分析了其与饱和吸收体初始透过率和输出镜反射率的关系。提出了计算脉冲宽度的新方法,重新计算了在脉冲波形非对称条件下的脉冲宽度及其与饱和吸收体初始透过率和输出镜反射率的关系。提出了优化脉冲波形和脉宽的简便方法。     

Cr4+:YAG被动调Q激光器脉冲波形数值模拟及优化

为了研究被动调Q激光器脉冲的波形对称特性,采用数值求解Nd:YAG晶体Cr4+:YAG被动调Q激光耦合速率方程组的方法,获得了激光脉冲的波形,绘制出了"脉冲对称因子"与饱和吸收体初始透过率和输出镜反射率的关系曲线图;并根据脉冲波形的不对称性,更精确地计算了脉冲宽度,及其与饱和吸收体初始透过率和输出镜反射率的关系.得到参数b=0.6时,脉冲波形对称;b=0.78时,脉宽最小的结论.结果表明,可以通过调整b参数来优化被动调Q脉冲波形对称性和脉宽.