<title>Fusion laser oscillator and pulse-forming system using integrated optics</title>

Abstract

In order to demonstrate new technology for the proposed National Ignition Facility (NIF), we are currently building a 5-kilojoule laser called Beamlet. The oscillator and pulse shaping system for Beamlet represents a major technological improvement over previous designs. Using integrated optics, fiber optics, and diode-pumped lasers instead of bulk optics and flashlamp-pumped lasers, this new master oscillator takes advantage of current technology to make a system with numerous advantages. The requirements for a NIF for greater flexibility and reliability necessitate this new approach; the pulse-forming system for the Beamlet demonstrates a subset of the capabilities required for a NIF. For the Beamlet, we must produce a single 1 - 10 ns, shaped- and frequency-modulated pulse. The Beamlet needs only to generate square output pulses for technology demonstration purposes, but the input pulses must be shaped to compensate for gain saturation in the power amplifier. To prevent stimulated Brillouin scattering (SBS) from damaging the output optics, the output pulse must have some bandwidth, and thus the pulse-forming system phase modulates the input pulse. These requirements are very similar to those for the Nova master oscillator system, but Nova technology is not the best choice for the Beamlet. In developing an oscillator design for a fusion laser system, the system requirements are defined by the oscillator's place in the overall laser architecture. Both Nova and Beamlet use a master oscillator-power amplifier (MOPA) architecture. In a MOPA-laser architecture, a low-power oscillator is followed by a high-gain, high-power amplifier. If the output signal is to have a high signal-to-noise ratio (SNR), the oscillator-signal power must be high above the amplifier noise power.