Recent Measurements on the Prototype Preamplifier Module for the National Ignition Facility

Summary form only given. The preamplifier module or PAM is a high gain, Nd:glass laser system that amplifies the temporally and frequency formatted pulse produced in the master oscillator room (MOR), up to a level that is sufficient for seeding the main amplifier chains of the NIF laser system. The PAM consists of two separate laser amplifiers, a diode-pumped, regenerative amplifier, and a 5 cm., flashlamp-pumped-rod, four-pass amplifier. The amplifiers boost the 1 nJ input pulse from the MOR up to 10-20 Joules in a pulse that ranges from 0.2 to 20 ns. In addition to amplification, the PAM spatially shapes the beam to precompensate for the spatial gain profiles of the main amplifiers, and angularly disperses the beam as part of the smoothing by spectral dispersion (SSD) feature of the laser system. In the past we have demonstrated the performance specifications of the preamplifier on a tabletop, development system. We assembled the first engineering prototype PAM and are conducting final measurements on a system that will become the first of 48 PAMs in the NIF laser system. We made improvements to various subsystems in the PAM that are now included in the engineering prototype. We now operate the regenerative amplifier in energy saturation to reduce the pulse-to-pulse variation in the PAM. We improved the efficiency of the spatial beam shaping masks by including the effects of diffraction from the chrome pixels in designing the masks. We eliminated temporal pulse overlap in the four-pass amplifier by lengthening the relay telescopes in the four-pass optical layout. In the presentation we discuss the latest results from performance measurements of PAM engineering prototype.