Effect of vacuum degree on high power ultraviolet laser beams in long air path

Using the model of transient stimulated rotational Raman scattering (SRRS) and considering many factors, such as the molecular density of nonlinear medium, the gain coefficient, the depletion of pump laser, the nonlinear amplification of the Stokes field, and the initial random Stokes scattered field, etc, the effect of vacuum degree on the SRRS of high-power ultraviolet laser beams in long air path has been studied. The Stokes conversion efficiency decreases and the propagation distance of the threshold increases with the increase of vacuum degree. In practice, in order to decrease the effect of SRRS on the energy and beam quality of high power ultraviolet laser beam, the atmospheric envionment of laser propogation with high vacuum degree can be used to suppress the SRRS effect.