The multiple-pulse driver line on the OMEGA laser

Abstract

The multiple-pulse driver line (MPD) provides on-shot co-propagation of two separate pulse shapes in all 60 OMEGA beams at the Laboratory for Laser Energetics (LLE). The two co-propagating pulse shapes would typically be (1) a series of 100-ps “picket” pulses followed by (2) a longer square or shaped “drive” pulse. Smoothing by spectral dispersion (SSD), which increases the laser bandwidth, can be applied to either one of the two pulse shapes. Therefore, MPD allows for dynamic bandwidth reduction, where the bandwidth is applied only to the picket portion of a pulse shape. Since the use of SSD decreases the efficiency of frequency conversion from the IR to the UV, dynamic bandwidth reduction provides an increase in the drive-pulse energy. The design of the MPD required careful consideration of beam combination as well as the minimum pulse separation for two pulses generated by two separate sources. A new combined-pulse-shape diagnostic needed to be designed and installed after the last grating used for SSD. This new driver-line flexibility is built into the OMEGA front end as one component of the initiative to mitigate cross-beam energy transfer on target and to demonstrate hydro-equivalent ignition on the OMEGA laser at LLE.