The Study Of Spatiotemporal Perturbation In The Nonlinear Propagation Of Broadband Chirped Pulse Laser

With the development of laser technology and ultrafast optics, the frequency spectrum width of laser pulse advances to the wide band from the narrow band. As the broadband pulsed-laser has some new features, such as the pulse width is very narrow, high peak power and broadband frequency width, so the nonlinear propagation process demonstrated the new features. Self-focusing is one of the fundamental problems in nonlinear propagation process of laser pulses, and is also one of the main factors which troubled the performance of high power laser system. Broadband pulsed-laser is an important technology way which would breakthrough these restrictions, and the mode locking technology and chirped pulse amplification technology are two core technologies in laser optics, so the propagation and amplification of laser pulses are associated with the chirp of pulse. Therefore, study the spatiotemporal perturbation characteristic in nonlinear propagation of the broadband chirped-pulse laser both from theoretically and actual remand has important significance. In this paper, on the basis of existing self-focusing research, we studied the propagation characteristic of the broadband pulsed-laser from two aspects:Firstly, we extended the propagation equation of the large chirped pulse based on the nonlinear Schrodinger equation, and then analyzed the spatiotemporal instability of chirped pulsed-beam by using the perturbation theory. The influence of the spatiotemporal noise and the effects of chirp on the perturbation modulation of noise of the broadband pulsed-laser with large chirp were investigated theoretically, the results showed that the chirp of pulse had no direct influence on the modulation growth of noise under the same value ofγI0 (the product of the nonlinear coefficient and the peak intensity). Then the spatial small-scale self-focusing of chirped pulse was measured in experiment using nonlinear medium, and the modulation growth of the temporal noise of the broadband chirped pulse were also simulated numerically, and the result was basically consistent with the analysis of perturbation theory.Secondly, by combining the homogeneous balance principle and the F-expansion technique, we studied the exact periodic wave solutions and spatiotemporal soliton solutions to the generalized (3+1)-dimensional nonlinear Schrodinger equation with distributed coefficients. And then based upon the solution we analyzed several distinct cases separately under the cases of without the time dimension, without the spatial dimension and both were existent, of which we emphasized on the case of soliton wave. We also analyzed the stability of spatiotemporal soliton in spatiotemporal dimensional case. The result showed that the forms of solitons were related to the utilized Jacobi elliptic function and the elliptic modulus and the diffraction and dispersion coefficients, and its amplitude was related to the diffraction and dispersion coefficients and chirp. In the spatiotemporal dimensional case, when the diffraction coefficient and dispersion coefficient were distributed coefficients which produce a periodic variation along the propagation direction and their absolute values are identical, the solution is stable, however, it is unstable in other cases.