Study On Propagation Property Of Broadband Laser In The Nonlinear Medium

"Broadband" and "Nonlinearity" are the two key issues in the high-power laser research. The investigation of the propagation and self-focusing properties of broadband laser pulse is of very great theoretical and practical significance for the development of high-power laser system. Wide specrtum laser due to the different spectral components in the instantaneous case is different from the ultrashort pulse. In this paper, we extended the monochromatic laser propagation theory to the broadband laser. We simulated the linear and nonlinear propagation properties of the monochromatic and broadband laser with or without small-scale modulation.Based on the Fourier transform method, we simulated the propagation properties for monochrome laser and broadband laser propagated in the free space. Through the curve of laser beam contrast with the increase of bandwith, we concluded that the broader bandwidth of the broadband laser beam, the more uniformity of the output light field. We simulated the output light field properties for monochrome laser and broadband laser in the case of small-scale modulation propagated in the free space. Through the curve of the laser beam contrast with the increase of bandwith, we concluded that the broader bandwidth of the broadband beam, the stronger inhibitory effect of the small-scale modulation.Based on the Split-Step Fourier Method, we simulated the propagation properties for monochrome laser and broadband laser propagated in the neodymium glass rob and neodymium glass sheet medium. Through the propagation evolution and the B-integral curve with the growth of propagation distance, we concluded that the nonlinear self-focusing effect of broadband laser is stronger because of the existence of cross-phase modulation effect. We simulated the propagation properties for monochrome laser and broadband laser propagated in the two mediumin in the case of the small-scale modulation. Through the curve of the beam contrast with the increase spatial frequency, we concluded that the small-scale modulation growth rate is of parabolic distribution. Through the comparison of rob and sheet structure, we concluded that the growth of rate of small-scale modulation mainly concentrated in certain spatial frequency range in the sheet structure.