T. J. Kessler

Initial performance results of the OMEGA laser system

Abstract OMEGA is a 60-terawatt, 60-beam, frequency-tripled Nd:glass laser system designed to perform precision direct-drive inertial-confinement-fusion (ICF) experiments. The upgrade to the system, completed in April 1995, met or surpassed all technical requirements. The acceptance tests demonstrated exceptional performance throughout the system: high driver stability (

Reduction of laser imprinting using polarization smoothing on a solid-state fusion laser

We demonstrate a laser beam-smoothing technique known as polarization smoothing. A birefringent optical wedge splits the individual laser beams into two orthogonally polarized beams that, when coupled with a distributed phase plate, produce two speckle patterns shifted with respect to one another. This instantaneously reduces the on-target nonuniformity by a factor of √. We measured this reduction optically and its effect is demonstrated in laser-driven targets.

OMEGA EP high-energy petawatt laser: progress and prospects

OMEGA EP (extended performance) is a petawatt-class addition to the existing 30-kJ, 60-beam OMEGA Laser Facility at the University of Rochester. It will enable high-energy picosecond backlighting of high-energy-density experiments and inertial confinement fusion implosions, the investigation of advanced-ignition experiments such as fast ignition, and the exploration of high-energy-density phenomena. The OMEGA EP short-pulse beams have the flexibility to be directed to either the existing OMEGA target chamber, or the new, auxiliary OMEGA EP target chamber for independent experiments. This paper will detail progress made towards activation, which is on schedule for completion in April 2008.

Fourier-space image processing for spherical experiments on OMEGA (invited)

Studies of compressed shell integrity of spherical targets on the 60-beam 30 kJ UV OMEGA laser system involve spatially and temporally resolved measurements of core emission at different x-ray energies. Hot-core emission backlights a titanium-doped shell that is imaged at x-ray energies above and below the titanium K edge. The difference between the two images is related to perturbations in the cold, or absorbing, part of the shell. The core emission has been imaged by a pinhole array on a framing camera and recorded on film. The resolution and noise of all parts of the imaging system have been characterized. Using this information, a Wiener filter that reduces noise, compensates for detector resolution, and facilitates measurement of shell nonuniformities has been formulated.

Inertial confinement fusion experiments with OMEGA-A 30-kJ, 60-beam UV laser

Abstract The Laboratory for Laser Energetics (LLE) experimental program supports the US inertial confinement fusion (ICF) effort by investigating the requirements for attaining ignition using direct drive targets. The primary tool for this research is OMEGA, a 60-beam, 351-nm, Nd:glass laser with an on-target energy capability in excess of 30 kJ. The laser is designed to ultimately achieve an irradiation uniformity of ∼1% on direct-drive capsules with shaped laser pulses (dynamic range>400:1). In addition, OMEGA provides unique capabilities for irradiating indirect-drive targets. This paper reports on a number of recent laser enhancements, including a new design for distributed phase plates (DPPs), two-dimensional smoothing by spectral dispersion (2-D SSD), distributed polarization rotators (DPRs) and laser pulse shaping. A variety of spherical-implosion, planar-target, and indirect-drive experiments attest to the versatility of the OMEGA laser. A key result is the highest thermonuclear yield (10 14 neutrons) and yield efficiency (1% of scientific breakeven) ever attained in laser fusion experiments.

Electron-beam–deposited distributed polarization rotator for high-power laser applications

Electron-beam deposition of silica and alumina is used to fabricate distributed polarization rotators suitable for smoothing the intensity of large-aperture, high-peak-power lasers. Low-modulation, low-loss transmittance with a high 351-nm laser-damage threshold is achieved.

High-density, direct-drive implosion experiments

A critical test of direct-drive laser-fusion has been conducted with the demonstration of DT compression to densities in the range of 100–200 times liquid density in experiments on the University of Rochesters OMEGA laser facility. The high-density cyrogenic experiments used 351-nm laser pulses with energies of 1500–1800 J and pulse widths in the range of 600–700 ps.

The OMEGA EP High-Energy, Short-Pulse Laser System

OMEGA EP (Extended Performance) is a petawatt-class addition to the existing 30-kJ, 60-beam OMEGA Laser Facility at the University of Rochester. Activation of the OMEGA EP Laser is complete and results will be described.

Liquid crystal chiroptical polarization rotators for the near-UV region: theory, materials, and device applications

The helical structure of a chiral-nematic liquid crystal (CLC) material produces a number of interesting optical properties, including selective reflection and optical rotatory power. To take advantage of the high optical rotation near the selective reflection peak for applications in the UV, either large concentrations of chiral components or those possessing very large helical twisting powers (HTP’s) are necessary. It is difficult to find chiral twisting agents with high HTP that do not degrade the UV transmission. We report what we believe to be the first experimental observation of extraordinarily high optical rotation (<30°/μm) in the near UV for a long-pitch (13.8-μm) CLC mixture composed of the low-birefringence nematic host ZLI-1646 doped with a low concentration (e.g., 1 wt%) of the chiral dopant CB 15. This experimental finding is verified theoretically using a mathematical model developed by Belyakov, which improves on de Vries’ original model for optical rotation far from the selective reflection peak by taking into account the nonlinearity of optical rotatory power as a function of liquid crystal (LC) layer thickness. Using this model, the optical rotation at λ = 355 nm for the 1% CB 15/ZLI-1646 mixture is determined computationally, with the results in agreement with experimental data obtained by evaluating a series of wedged cells using an areal mapping, Hinds Exicor 450XT Mueller Matrix Polarimeter. This finding now opens a path to novel LC optics for numerous near-UV applications. One such envisioned application for this class of materials would be UV distributed polarization rotators (UV-DPR’s) for largeaperture, high-peak-power lasers.

Laser uniformity and hydrodynamic stability experiments at the OMEGA laser facility

Experiments to demonstrate the effects of various beam-smoothing techniques have been performed on the 60-beam, 30-kJ UV OMEGA laser system. These include direct measurements of the effect beam-smoothing techniques have on laser beam nonuniformity and on both planar and spherical targets. Demonstrated techniques include polarization smoothing and dual-tripler third-harmonic generation required for future broad bandwidth (∼ 1 THz) smoothing by spectral dispersion (SSD). The effects of improvements in single-beam uniformity are clearly seen in the target-physics experiments, which also show the effect of the laser pulse shape on the efficacy of SSD smoothing. Saturation of the Rayleigh-Taylor (RT) growth of the broad-bandwidth features, in agreement with the Haan model (Haan, 1989), produced by laser imprinting has also been observed.