Repetition Frequency Plasma Optical Switch With Thermal Control

High power solid-state laser is widely used for micro-machining, material-machining, laser radar, beacon laser, main laser in the intense-laser directional energy system, and future inertial fusion energy system. Electro-optic switch, delivered to reforming beam quality in high power laser, is studied on broadly. Temperature in electro-optic crystal is rising by absorbing incident laser. Although, the absorption coefficient is small, the switch, held to be endowed with birefringence property, is sensitive to thermo-depolarization. So electro-optic switch is one of limiting devices in high power laser. Plasma electrode pockels' cell (PEPC), which can be used longitudinally, adopting thin crystal, scaling to large aperture, eases the thermo-effects. It is ideal choice for medium-scale and large aperture average power optical switch. But, delivering it to repetition frequency application, thermo-effects and thermo-control needs to be studied on farther.The finite volume modular of fluid-solid coupling, the finite element modular of heat transfer, depolarized loss modular, and wave-front distortion modular are created for studying on thermo-effects of repetition frequency PEPC. Based on these modulars, thermo-effects on repetition frequency plasma electrodes switch are studied and managed.In respects of thermo-effects, three aspects are included: firstly, influencing factors of temperature distribution as well as strain distribution in electro-optic crystal are studied. The simulated results indicate: to reduce temperature rise, temperature gradient, and strain in electro-optic crystal, absorption coefficient of crystal should be smallest possible; thickness of crystal should be thinnest possible; the edge of facula should be submarginal to the edge of electro-optic crystal. Secondly, depolarized loss, which is induced by temperature dependence of the refractive index, electro-optic coefficient, and by thermal stress, is calculated. The results indicate: The main factor of depolarized loss is stress birefringence in static state, but in dynamic state, temperature dependence of electro-optic coefficient also contributes to depolarized loss. The main factor of wave-front distortion is thermo-strain in electro-optic crystal. When the average power of the incident laser is 1kW, and the wavelength is 1.064μm, the biggest and average depolarized loss is respectively 12.82%, 3.70%. When the switch is operating in dynamic state, the biggest depolarized loss, induced by temperature dependence of electro-optic coefficient, is 2.74%, and the average depolarized loss is 1.69%. Thirdly, wave-front distortion is analysed which is induced by end-face strain, and by thermo-optic effects. The results indicate: The main factor of wave-front distortion is thermo-strain in electro-optic crystal. When the average power of the incident laser is 1kW, and the wavelength is 1.064μm, the total PV value is 0.9558 wavelengths.In respects of thermo-management, two aspects are included: firstly, by enhancing convective heat transfer, thermo-effects are reduced greatly. The coefficient of convective heat transfer finally reached up to 8.02 W/m~2·K, about eight times increased comparing to traditional situation. Secondly, two schemes are come up with, which are used to compensate for stress-birefringence in average power plasma electro-optic switch. The simulation indicates, the two stress compensation schemes can totally eliminate the depolarized loss induced by stress-birefringence, but invalid to wave-front distortion.Finally, depolarized loss and temperature distribution is measured in static state. The results correspond with simulated outcomes commendably. It is illuminated that the modular, created for studying on thermo-effect in repetition frequency plasma electro-optic switch, is proper and valid.