Nonlinear Propagation Of Intense Femtosecond Laser In Medium And Its Application

The rapid development of intense femtosecond laser technology has made it possible to generate strong light fields in the laboratory,which has brought the interaction be TWeen laser and matter into an unprecedented and highly nonlinear territory.It is of great scientific significance and application value to study these nonlinear effects.For example,with the development of nonlinear optics,nonlinear spectroscopy was born,which greatly improved spectral resolution;Through the research of nonlinear optical conjugation effect,the nonlinear optical phase conjugation technology appears,which promotes the progress of adaptive optics.In optical fiber optics,the research on the generation and transmission of optical soliton effect promotes the development of optical soliton communication.The nonlinear propagation of intense femtosecond laser in medium is an important research topic in the field of high power laser.The realization of these processes is a great breakthrough in science and technology,and will have a far-reaching impact on the development of science and technology in the future.In this paper,the transmission process of intense femtosecond laser in Ba F₂crystal and atmosphere is studied for TWo different applications,namely,contrast enhancement and cloud channel generation.The main research results and progress are as follows.In order to compensate for the neglect of higher order dispersion in the previous studies of cross-polarized waves(XPW),we have established a complete and robust coupled nonlinear Schrodinger equation,which is numerically solved by using a set of self-written code using the Fourier method and the fourth-order Runge Kutta method.The results show that:1.If the dispersion of each order is not sufficiently controlled,they can produce different distortions to the generation of XPW,which will greatly reduce the peak energy of the main pulse,resulting in reduced conversion efficiency and contrast.2.When the extinction ratio is not considered,the contrast improvement of the cross-polarized wave is about 3 orders of magnitude,and when the extinction ratio of 10^-6is considered,the contrast improvement is about 5 orders of magnitude.In order to verify the feasibility and controllability of cloud channels generated by femtosecond laser filamentation,and to analyze the main physical mechanism,we numerically simulated and experimentally investigated the effects of femtosecond laser parameters on the generation and control of filamentation in clean air.The effect of different laser parameters on cloud channels in cloud is experimentally studied.The results show that:1.The location and length of the filament can be controlled by changing the initial laser parameters.2.Under the condition of changing different initial laser parameters,filamentation is feasible,controllable and stable for the generation of cloud channels.3.The key physical mechanism affecting cloud channels is filamentation-induced acoustic effect.4.The lifetime of the cloud channel is greater than 1.0 ms,the channel diameter is greater than 2.0 mm,and the length is controllable.