NIF injection laser system

Abstract

The National Ignition Facility (NIF) is a high-power, 192-beam laser facility being built at the Lawrence Livermore National Laboratory. The 192 laser beams that will converge on the target at the output of the NIF laser system originate from a low power fiber laser in the Master Oscillator Room (MOR). The MOR is responsible for generating the single pulse that seeds the entire NIF laser system. This single pulse is phase-modulated to add bandwidth, and then amplified and split into 48 separate beam lines all in single-mode polarizing fiber. Before leaving the MOR, each of the 48 output pulses are temporally sculpted into high contrast shapes using Arbitrary Waveform Generators (AWG). Each output pulse is then carried by optical fiber to the Preamplifier Module (PAM) where it is amplified to the multi-joule level using a diode-pumped regenerative amplifier and a multi-pass, flashlamp-pumped rod amplifier. Inside the PAM, the beam is spatially shaped to pre-compensate for the spatial gain profile in the main laser amplifiers. The output from the PAM is sampled by a diagnostic package called the Input Sensor Package (ISP) and then split into four beams in the Preamplifier Beam Transport System (PABTS). Each of these four beams is injected into one of NIF's 192 beam lines. The combination of the MOR, PAM, ISP and PABTS constitute the Injection Laser System (ILS) for NIF. This system has proven its flexibility of providing a wide variety of pulse shapes and energies during the first experiments utilizing four beam lines of NIF.

Spectral and temporal properties of optical signals with multiple sinusoidal phase modulations

“…A comparison of Eqs. (6) and (9) indicates that the rms width and the Carson's rule bandwidth are loosely connected for arbitrary values of the modulation index. The rms width is computationally easy to use but it is not a precise indicator of the energy fraction present in a given frequency interval.…”

“…The statistical study is followed by general derivations of FM-to-AM conversion in optical signals with multiple phase modulations from spectral amplitude modulation, for example, resulting from spectral filters and optical amplifiers and from spectral phase modulation, for example, caused by chromatic dispersion in optical fibers in the front end. These impairments are inherently present in high-energy laser systems and their effects are reduced using compensation systems, for example, Lyot-type filters that compensate for the gain narrowing in a Nd:glass amplifier and a grating compressor that compensates for chromatic dispersion [6,16]. The design and performance of these subsystems are intrinsically linked to understanding the modulation magnitude in critical parts of the system where optical damage might occur.…”

“…The growth of SBS waves is inhibited by increasing the bandwidth of the optical wave, typically by phase modulation in the low-energy front end to generate multiple sidebands. Phase modulation at a few GHz with index modulation sufficient to create approximately ten sidebands is used on systems like the National Ignition Facility (NIF) and the Laser Mégajoule Facility (LMJ) [5][6][7]. Uniform compression of the target is required to reach the conditions for fusion in the target core, but such compression is hindered by instabilities [8].…”

A compact UV timing fiducial system for use with x-ray streak cameras at NIF

“…8 This seed is delivered to the VISAR room at NIF which is located just outside the target chamber. A rack-mounted fiber amplifier boosts the signal, which is then sent to a pulse stacker which splits the pulse into multiple different fibers of different lengths and then recombines them into a single fiber so that there is a 300-ps delay between each of the pulses.…”

Improved method for laser damage testing coated optics

“…The National Ignition Facility (NIF) project is in the production phase of procuring approximately 25,000 small optics (<20 cm) that will be used in the main beamlines and diagnostic systems 1 . Of these, roughly 8,000 will be exposed to beam fluences high enough to warrant a laser damage specification for the optical coatings.…”