Effects of stimulated rotational Raman scattering on beam quality of fundamental frequency beams
Based on the model of transient stimulated rotational Raman scattering(SRRS) and the phase perturbation theory,the effects of pump intensity and pulse width on the threshold and the conversion efficiency of SRRS during the propagation in long air path were quantitatively analyzed.The effects of the phase perturbation on the beam quality of the pump field and the Stokes field were discussed.The results show that the threshold distance of SRRS decreases with increasing the intensity and the pulse width of the pump laser.The phase perturbation of the initial pump field has effect on the intensity distributions of the Stokes and the pump fields,and the influence of the phase perturbation of the initial pump field on the Stokes field is more obvious than that on the pump field.The SRRS effect can lead to the degradation of the beam quality of the Stokes field and the pump field,resulting in the reduction of the conversion efficiency of the harmonic generation process.