Research On The Time Coherence Characteristics Of Parametric Fluorescence In The Process Of Optical Parameters

Optical parametric processes is one of the most important nonlinear optical process,which makes it widely used in generation of various laser,frequency and energy conversion.With the research and development of Petawatt(1015W)high peak power laser systems,Optical parametric processes have become the main technological approaches for energy amplification of ultra-short laser.In optical parametric processes,spontaneous parametric fluorescence that not only reduce the conversion efficiency of pulse energy amplification,but also influence pulse quality by reducing laser pulse contrast is an essential problem for high field physics research and application of high peak power laser.On the other hand,parametric fluorescence with broad spectrum show its application foreground of be a low coherence source.Partial coherence source research have special significance for high field physics experiment and suppressing laser-plasma instabilities.As a result,it's an important value in applications to study the coherence characteristic of parametric fluorescence and its internal relation with other physical quantity and development a coherence controllable source.Based on analysis of the basic physical processes of generation of parametric fluorescence,we have established a numerical simulation program which is suitable for parametric fluorescence.We design an experiment project to evaluate the time coherence of parametric fluorescence,and research the influence of pump pulse parametric to time coherence of parametric fluorescence.The main work of this thesis includes the followings:1.Based on traditional coupled wave equations and generation mechanism of quantum noise,the coupled wave equations for optical parametric amplification is partly modified to suit the generation and amplification of parametric fluorescence.Through the numerical simulation program,we analyze the relation between parametric down-converted fields group velocity and time coherence of parametric fluorescence.The results of the study show that group velocity different between parametric down-converted fields should keep big to improve time coherence of parametric fluorescence.2.Based on numerical simulation program,we analyze the influence of pump pulse width and intensity on the time coherence of parametric fluorescence.Using quasi-phase-matching crystal,we design corresponding experimental scheme pumped by picosecond pump pulse,and complete the optical path design.3.We carry out time coherence characteristic of parametric fluorescence research,compare the time coherence characteristic of parametric fluorescence under different pump pulse width conditions.Using the same structure quasi-phase-matching crystal,preliminarily study the influence of pump power and pump pulse width on coherence of parametric fluorescence.The results of our study show that the parametric of pump pulse could influence coherence of parametric fluorescence,especially under ultra-short pulse pump condition.The result would be the technological base for build a coherence controllable source,and also have important implications for contrast problem in femtosecond pulse parametric processes.