Study Of Optical Enhancement Cavity For Thomson Scattering Light Sources

High-average-power optical enhancement cavities(OEC),have a wide range of applications including Thomson scattering producing high average flux quasi-monochromatic X/?-rays,cavity-enhanced high-order harmonic generation(HHG),grav-itational wave interferometers,steady-state microbunching(SSMB)light sources and fu-sion energy experiments etc.The works of this thesis focus on the theoretical and experimental studies of high-average-power OEC dedicated to Thomson scattering light sources.With the purpose of increasing the average flux of Thomson scattering generated photons,it is demanded for the laser beam inside OEC to have small waist with radius size of few tens of microns,pulse length at the order of picosecond and stable intra-cavity average power of few hun-dreds of kilowatts.To precisely and effectively describe the highly focused laser field inside OEC to be used in simulations of Thomson scattering,a field expression of nonparaxial corrected highly focused linearly polarized laser field is derived with a generalized Lax series ex-pansion method.To suppress the modal instabilities start to appear apparently on OEC with an intra-cavity average power reaching?100 kW which affect cavity stability and could lead to lose of lock,the modal instabilities are well described with mode degeneracies induced by mirror surface thermoelastic deformation characterized by Winkler model.We brought up the D-shape mirror method for suppressing modal instabilities and proved its effec-tiveness with simulation.An hour-time-scale stable intra-cavity average power of 200 kW was realized on the prototype OEC of Thomson scattering light source ThomX with implementation of D-shape mirrors inside.Analysis is carried out for understanding the fast power drop phenomenon appearing on OEC which affects the cavity stability and hinders the intra-cavity power reaching the designed goal.Intra-cavity power drops appeared with magnitude and time scale depend-ing on the power level.Increasing further the incident power led to irreversible damage of the cavity coupling mirror surface.The origin of this phenomenon is investigated with postmortem mirror surface imaging and analysis of the signals transmitted and reflected by the OEC.Scattering loss induced by mirror surface deformation due to a hot-spot con-taminant is found to be most likely the dominant physics behind this phenomenon and the cavity behavior could be well reproduced by simulation.This analysis could help to understand the physical process behind this kind of power drop phenomenon appearing on OEC being applied in wide range of applications and to prevent permanent mirror damage.Full design of the prototype OEC of Tsinghua Thomson scattering X-ray light source(TTX)is presented and preliminary experiment is carried out on it,realizing the goal of locking a continuous wave injection laser with the cavity with the cavity gain measured to be 133.Design of the high power experimental setup for TTX prototype OEC and the design for TTX OEC to be coupled with the electron storage ring are provided.