Smoothing Techniques Based On The Spectral Dispersion Of The Fm Pulse

In high power laser drivers used for Inertial Confinement Fusion (ICF) research, the propagation, amplification and control are always the research emphases of high power laser physics and technology. To promote the load ability of laser facility and uniformity of target intensity distribution, it is necessary to study and develop new concepts and technologies to improve beam quality and promote beam control precision.According to the main requirements of future ICF physical experiments and developing trend of high power laser drivers, the new concept of "moving" beam based upon angular spectral dispersion, was proposed for the first time. The optimized combination of stacked chirped pulse and special gratings was adopted in this new technical route. Multi-dimensional spectral scan was used to realize spatial smoothing (including far field and near field). The chief aim of this new technology was to realize smoothing of the far field to meet the basic requirements of physical experiments on target intensity distribution. The thesis also explored the possibility to diminish high frequency modulations by the movement of near field, in order to promote the load ability of high power laser facilities.Nowadays, the mainstream of far field beam smoothing technology adopted by foreign high power laser drivers is smoothing by spectral dispersion (SSD) based upon sinusoidal frequency modulation. Through systematic analysis of this smoothing technology, results indicated uniformity attained by SSD was mostly determined by two factors: bandwidth and angular spectral dispersion (ASD). Among them, bandwidth determined the smoothing speed, and ASD determined the uniformity attained and the largest target modulation that could be smoothed. Analysis also indicated the deficiency of traditional SSD was caused by adopting sinusoidal frequency modulation, which lead to zero velocity points when the beam swept in the far field. These points were corresponding to peaks and valleies of the sinusoidally frequency modulated wave, and would affect the uniformity of far field distribution.To solve the problems above and explore the possibility of near field spectral sweep, a new technical route, with periodical frequency modulation using chirped pulse stacking, and angular spectral dispersion using novel special gratings, were proposed for the first time to obtain temporal smoothing of the focal spot. The smooth spectrum of chirped pulse was made full use of to eliminate high frequency modulations in the near field and far field of high power laser facilities. To compensate for the single dispersing direction of linear grating, circular grating, "star" grating and grating array were designed to smooth high frequency modulations in various directions. The main simulation results indicated this new technical...