Optical Switch
This is an optical switch called a plasma electrode Pockels cell, or PEPC. Technicians are testing the PEPC, which allows light to either pass through or reflect off of a polarizer. By rotating the polarization of the laser beam, the PEPC directs the laser light back and forth through the main amplifier system four times, picking up energy with each pass. Then it is switched out to continue on its way toward the power amplifier. Its four 40-by-40-centimeter apertures contain a crystal plate of potassium dihydrogen phosphate, or KDP, sandwiched between two fused silica windows. (See Optical Switch.)