Demonstration of high-energy 2 omega (526.5 nm) operation on the National Ignition Facility Laser System.

A single beamline of the National Ignition Facility (NIF) has been operated at a wavelength of 526.5 nm (2 omega) by frequency converting the fundamental 1053 nm (1 omega) wavelength with an 18.2 mm thick type-I potassium dihydrogen phosphate (KDP) second-harmonic generator (SHG) crystal. Second-harmonic energies of up to 17.9 kJ were measured at the final optics focal plane with a conversion efficiency of 82%. For a similarly configured 192-beam NIF, this scales to a total 2 omega energy of 3.4 MJ full NIF equivalent (FNE).

National Ignition Facility laser performance status.

The National Ignition Facility (NIF) is the world's largest laser system. It contains a 192 beam neodymium glass laser that is designed to deliver 1.8 MJ at 500 TW at 351 nm in order to achieve energy gain (ignition) in a deuterium-tritium nuclear fusion target. To meet this goal, laser design criteria include the ability to generate pulses of up to 1.8 MJ total energy, with peak power of 500 TW and temporal pulse shapes spanning 2 orders of magnitude at the third harmonic (351 nm or 3omega) of the laser wavelength. The focal-spot fluence distribution of these pulses is carefully controlled, through a combination of special optics in the 1omega (1053 nm) portion of the laser (continuous phase plates), smoothing by spectral dispersion, and the overlapping of multiple beams with orthogonal polarization (polarization smoothing). We report performance qualification tests of the first eight beams of the NIF laser. Measurements are reported at both 1omega and 3omega, both with and without focal-spot conditioning. When scaled to full 192 beam operation, these results demonstrate, to the best of our knowledge for the first time, that the NIF will meet its laser performance design criteria, and that the NIF can simultaneously meet the temporal pulse shaping, focal-spot conditioning, and peak power requirements for two candidate indirect drive ignition designs.

Random phase plates for beam smoothing on the Nova laser.

We discuss the design and fabrication of 80-cm-diameter random phase plates for target-plane beam smoothing on the Nova laser. Random phase plates have been used in a variety of inertial confinement fusion target experiments, such as studying direct-drive hydrodynamic stability and producing spatially smooth x-ray backlighting sources. These phase plates were produced by using a novel sol-gel dip-coating technique developed by us. The sol-gel phase plates have a high optical damage threshold at the second- and third-harmonic wavelengths of the Nd:glass laser and have excellent optical performance.

Temporal shaping of third-harmonic pulses on the Nova laser system.

We demonstrate temporal shaping of 0.35-microm-wavelength pulses produced by a third-harmonic conversion of the output from the Nova Nd:phosphate glass-laser amplifier system for use in inertial confinement fusion experiments. We describe the computer models used to calculate the pulse shape that is required as the input to the amplifier system, the experimental apparatus used to produce these pulses, and the high-power 0.35-microm shaped pulses produced in recent experiments.

Power, energy, and temporal performance of the Nova laser facility with recent improvements to the amplifier system.

High-powered glass-laser systems with multiple beams, frequency-conversion capabilities, and pulseshaping flexibility have made numerous contributions to the understanding of inertial confinement fusion and related laser-plasma interactions. The Nova laser at Lawrence Livermore National Laboratory is the largest such laser facility. We have made improvements to the Nova amplifier system that permit increased power and energy output. We summarize the nonlinear effects that now limit Nova's performance and discuss power and energy produced at 1.05-, 0.53-, and 0.35-microm wavelengths, including the results with pulses temporally shaped to improve inertial confinement fusion target performance.

Harmonic conversion of large-aperture 1.05-microm laser beams for inertial-confinement fusion research.

To provide high-energy, high-power beams at short wavelengths for inertial-confinement fusion experiments, we routinely convert the 1.05-microm output of the Nova, Nd:phosphate-glass, laser system to its second- or third-harmonic wavelength. We describe the design and performance of the 3 x 3 arrays of potassium dihydrogen phosphate crystal plates used for type-II-type-II phase-matched harmonic conversion of the Nova 0.74-m diameter beams. We also describe an alternate type-I-type-II phasematching configuration that improves third-harmonic conversion efficiency. These arrays provide conversion of a Nova beam of up to 75% to the second harmonic and of up to 70% to the third harmonic.

Stimulated rotational Raman scattering in nitrogen in long air paths.

We studied the growth from amplified spontaneous emission of stimulated Raman scattering in air using a 20-cm-diameter, linearly polarized, 1053-nm laser beam propagating over a 20-150-in air path. For 2.5-nsec square pulses we found about 1% conversion on the S(8) and S(10) rotational Raman lines of nitrogen at an intensity-length product of 12 TW/cm, which implies a small-signal gain coefficient of 2.5 cm/TW. For 1-nsec square pulses, 1% conversion requires an intensity-length product of about 16 TW/cm. The beam quality deteriorates severely above Raman threshold.

Electro-optical switches with plasma electrodes.

A transparent electrode concept using low-pressure ionized gas in the glow discharge regime is proposed for largeaperture electro-optic switch applications. A longitudinal Pockels cell and an electro-optically tuned second-harmonic-generation cell using KDP have successfully demonstrated the concept.

Electro-optic harmonic conversion switch for large-aperture multipass laser systems.

We have demonstrated electro-optically tuned second-harmonic generation using Type I KDP inside a plasma-electrode discharge cell. An axial voltage of +/-52 kV is required to switch a 1.064-microm beam by conversion to 0.53/microm, in agreement with theory. Electro-optically tuned harmonic generation may be combined with a recently developed transparent plasma electrode to produce a large-aperture switch for multipass laser systems.

Demonstration of electro-optical switching at the 26 cm x 26 cm aperture using plasma electrodes.

We have constructed and tested a longitudinal Pockels cell with a clear aperture of 26 cm x 26 cm. Transparent plasma electrodes formed in a low-pressure glow discharge were used to apply a uniform electric field to a 1-cm thick KDP crystal. Optical switching times of 50 nsec were achieved with a bare KDP crystal. Significant improvement in switching time resulted from using a glass-plate-KDP-crystal sandwich.

Absolute Raman frequency measurement of the Q(2) line in D(2) using cw CARS.

Coherent anti-Stokes Raman spectroscopy (CARS) is combined with high-resolution interferometry to measure the absolute Raman shift of the Q(2) vibrational line in D(2). The preliminary value found is 2987.237(1) +/- 0.001 cm(-1). Such precision is essential for the testing of ab initio energy-level calculations for the hydrogen isotopes.