Pulse power requirements for large aperture optical switches based on plasma electrode Pockels cells

摘要

We discuss very large-aperture optical switches (greater than 30 (times) 30 cm) as an enabling technology for inertial confinement fusion drivers based on multipass laser amplifiers. Large-scale laser fusion drivers such as the Nova laser have been based on single-pass amplifier designs in part because of the unavailability of a suitable large-aperture switch. We are developing an optical switch based on a Pockels cell employing plasma-electrodes. A plasma-electrode Pockels cell (PEPC) is a longitudinal-mode Pockels cell in which a plasma discharge is formed on each side of an electro-optic crystal (typically KDP or deuterated KDP, often designated KD*P). The plasmas formed on either side of the crystal act as transparent electrodes for a switching-pulse and are intended to allow uniform charging of the entire crystal. The switching-pulse is a nominally rectangular high-voltage pulse equal to the half-wave voltage V(sub x) ( 8 kV for KD*P or 17 kV for KDP) and is applied across the crystal via the plasma-electrodes. When the crystal is charged to V(sub x), the polarization of an incoming, linearly polarized, laser beam is rotated by 90(degree). When used in conjunction with an appropriate, passive polarizer, an optical switch is thus realized. A switch with a clear aperture of 37 (times) 37 cm is now in construction for the Beamlet laser which will serve as a test bed for this switch as well as other technologies required for an advanced NOVA laser design. In this paper, we discuss the unique power electronics requirements of PEPC optical switches.