Investigation Of Hot-image Formation In ICF Laser Drivers

To satisfy the need of ICF ignition experiment, ICF laser driver must provide both high-power and high-quality laser beam. It is well known that nonlinear self-focusing effect is one of the important factors to limit ICF laser energy and worsen beam quality. Therefore in ICF laser driver design and construction, it is very important to study the physical principle of the self-focusing effect. Based on this, a case of typical external self-focusing effect, hot-image, has been analytically and experimentally investigated in this dissertation. The principal work is as follows.(1) Intense laser beam propagation equation, the paraxial wave equation, has been derived. Based on this equation, the principle of the small-scale self-focusing is further analyzed. This work is called the B-T theory, which is the groundwork of the dissertation.(2) Combining the B-T theory and the scalar quantity diffraction theory, a diffraction theory method for the analysis of the hot-image formation is developed. It is shown by the analysis that the hot-image formation is akin to real-time, in-line, and volume-phase Fraunhofer holographic imaging.(3) Analytical results and computer simulations on the hot-image formation in an intense laser beam have been presented. Both media with gain and loss as well as amplitude-phase scatterer are considered. A new functional expression is derived for predicting the hot-image intensity. It is seen that the hot-image appears in a plane located downstream from the nonlinear medium at a distance equal to that from the scatterer to the medium. A quantitative comparison between the analytical and numerical approaches is carried out and good agreement is observed.(4) An analytical theory is developed for predicting the second-order hot-image formation, which is focused by the negative second order diffraction of the Fraunhofer hologram. Further, the image location and its intensity are derived.(5) In order to expand the application of the analytical theory, the hot-image formation in several-arrange media is further analyzed.(6) The spatial filter is introduced to avoid the damage from the hot-image. It is indicated by the numerical results that this work is valuable.(7) The experiment of the hot-image from phase scatterer in N31 Nd-glass is carried out. The experimental results are found to be in good agreement with previous analytical and numerical results.