自混频激光理论模型及应用

Modeling of the Self-Sum-Frequency-Mixing Laser and Its Application

建立了在同一块非线性激光晶体上实现自混频激光的理论模型。该模型计入了具有任意腰斑大小的泵浦光和腔内基频光的空间分布 ,并将该模型应用到NYAB和Nd∶GdCOB的自混频蓝光实验。理论分析预测和证实了一些实验结果 ,同时 ,讨论和总结了提高自混频激光输出效率的途径。

The self sum frequency mixing (self SFM) process is recently recognized as a new way of obtaining blue lasers,that is,summing the fundamental laser generated by a LD and remaining LD light by means of a single nonlinear laser crystal.This kind of scheme can achieve both laser action and nonlinear conversion in one crystal,which results in more compact,robust and manageable devices. A theoretical model for describing the self SFM laser generation is developed,in which spatial distributions of the pump and fundamental lasers with arbitrary beam waists are fully taken into account.The analysis can be simplified by using the average approximation.The output power of the self SFM laser is related to many physical parameters such as crystal length,doped ion concentration,pump waist,cavity mode size,walk off angle,pump power,absorption coefficient at the pump wavelength,phase mismatch and effective nonlinear coefficient.Hence it is necessary to reach a compromise among the above parameters in order to optimize the self SFM laser output.The model is applied to the self SFM laser generated by two kinds of crystals of current interest,NYAB and Nd∶GdCOB.Their self SFM laser output properties are theoretically discussed,predicted or verified.The calculated results are compared with the experiments,which shows the validity of our model. Based on the analysis of applying the model to NYAB and Nd∶GdCOB,some useful information can be summarized on improving the output power of the self SFM laser,that is,large effective nonlinear coefficient,small walk off angle,small internal loss,small phase mismatch,suitable beam waists(pump and fundamental),appropriate crystal length and ion concentration. The model is not limited to self SFM lasers and may be applied to general analysis of the laser generation with Gaussian beams,for instance,fundamental oscillation,SFD lasers,intracavity frequency doubling lasers and microchip lasers.Particularly,for microchip lasers,the model can be further simplified by assuming that the pump waist and cavity mode size are constant in the gain medium.