Numerical Simulation Of Large-diameter Plasma Electrode Electro-optic Switch

High-power solid lasers for inertial confinement fusion (ICF) require large aperture optical switches as isolators to isolate the retroreflections from the target and the self-oscillations in multipass amplifier system. Gas discharge plasma can be used as transparent and high conductive electrodes of electro-optic crystal in pockels cell which makes the electric field distribute uniformly on the crystal and calibrates the electro-optical switch to large aperture by using thin crystal, it is found to be ideal component to control and isolate the laser beam in high-power laser.Being different with the regular two-pulse-process(TPP) driving plasma electrode pockels cell(PEPC) electro-optical switch, the one-pulse-process(OPP) driving PEPC electro-optical switch is driven only through the switching pulses with high voltage, without isolated large current plasma generator. Establishing a physical model of gas discharge in pockels cell to study the relationship of the microcosmic physical process of gas discharge plasma and the macrocosmic parameters of PEPC electro-optic switch is very significative for designing and optimizing electro-optic switch.In this paper, a physical model of the gas discharge in OPP driving PEPC electro-optic switch is present based on its working principle and particle's motions and reactions in He discharge. The discharge characteristics of two pockels cells with different structures in one switch pulse are computed separately by using MATLAB software, the time evolutions of voltage on electrodes, discharge current, charge density accumulated on crystal, voltage on crystal, switch efficiency of pockels cell as well as the space and time distribution of electric field are calculated; the space distributions of electron density, atomic ion density, molecular ion density, excited atom density, excited molecule density when the switch is on are given; the electron energy in the plasma is also given; the relationship between the microcosmic physical process of He discharge plasma and macrocosmic parameter of electro-optic switch is analyzed. The influences of switch pulse voltage and gas pressure on the PEPC working characteristic also have been computed in this paper, the results indicate that because of voltage divider of plasma sheath capacitance, the switch pulse voltage should higher than the half-wave voltage of clamped crystal, voltage on crystal increasing as the switch pulse voltage increases, the switch efficiency will be higher in the optimized range of the the switch pulse voltage. Electron density increases and electron energy decreases of the gas discharge plasma if gas pressure rises, they make plasma sheath capacitance increase and divider voltage on crystal becomes larger.