LLE Builds New High Voltage, Large Aperture Pockels Cell Drivers

December, 2006

To meet the demands of its OMEGA EP laser, the Laboratory for Laser Energetics (LLE) added four solid-state high voltage, large-aperture Pockels-cell drivers in 2006.

LLE’s OMEGA EP laser system utilizes a large-aperture square beam and multi-pass amplifier design to generate high-energy laser pulses that extend the capabilities of inertial confinement fusion experiments. A large-aperture beam is required to keep the beam fluence below the damage threshold of various optics within the laser system. The beam requires a corresponding large-aperture optical switch to control the number of times the laser pulse traverses the multi-pass amplifier cavity.

The PEPC (Plasma Electrode Pockels Cell) is an electro-optic switch, originally developed at Lawrence Livermore National Laboratory (LLNL), can support the stringent requirements of high contrast (>1000:1) switching over a clear aperture of nearly 1600 square centimeters. When used in conjunction with a cavity polarizer, the PEPC switches the polarization of the laser pulse briefly to hold the pulse in the laser amplifier cavity for a total of four passes, thereby allowing the pulse to be amplified more efficiently.

To perform this switching function, a drive potential of approximately 17kV must be applied across the electro-optic KDP (KH2PO4) crystal within the PEPC at the appropriate laser operation timing intervals. The drive is produced by a high-voltage, solid-state-switch pulse generator called the SPG (Switch Pulse Generator), also referred to as the PEPC driver. The SPG is required to produce pulses up to 20kV with a duration of 300ns and rise/fall times of 100ns.