Polarization Smoothing Implemented

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2000:

Polarization smoothing using distributed polarization rotators (DPR’s) was implemented on OMEGA along with high-bandwidth (1-THz) 2-D SSD in 2000. The improved level of beam smoothing led to increased performance by direct-drive capsules.

“Experimental Investigation of Smoothing by Spectral Dispersion” by S. P. Regan et al. was published in the September Journal of the Optical Society of America B, reporting on measurements of smoothing rates for smoothing by spectral dispersion (SSD) of high-power, solid-state laser beams used for inertial confinement fusion (ICF) research.

Image shown is Higher irradiation uniformity produces less imprint, particularly with DPR’s and 2-D SSD

S. P. Regan, J. A. Marozas, J. H. Kelly, T. R. Boehly, W. R. Donaldson, P. A. Jaanimagi, R. L. Keck, T. L. Kessler, D. D. Meyerhofer, W. Seka, S. Skupsky, and V. A. Smalyuk, “Experimental Investigation of Smoothing by Spectral Dispersion,” J. Opt. Soc. Am. B 17 (9) 1483-1489 (2000).

First Cryogenic Implosions of D2-filled Targets

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2000:

The first cryogenic implosions of D2-filled targets using the new Cryogenic Target Handling System (CTHS) was carried out on 14 July 2000. This was a major milestone in the program that would eventually lead to direct-drive, high-gain implosions on the National Ignition Facility. The primary capabilities for the CTHS included filling thin-walled plastic shells with a room-temperature-equivalent pressure of 1500 atm of DT; producing four targets per fill cycle, up to 12 targets per week; cryogenically manipulating and transporting targets to the center of the target chamber; using infrared heating to smooth the D2 or DT-ice surface into an ice shell; characterizing the ice smoothness; and safely operating with tritium. This system was the first of its kind to become operational.

Shown here are First cryogenic implosions on the 60-beam OMEGA laser showing remnants of the spider webs on either side of the imploding target

NIF Deformable Mirror

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1999:

The NIF deformable mirror will allow wavefront correction of the NIF beam when the 39 posts on the back of the mirror are bonded to actuators on a reaction block. LLE will be coating the substrates with a low-stress, dielectric high reflector and assembling the deformable mirrors for Lawrence Livermore National Laboratory (LLNL).

Hope D’Alessandro, electronics technician, prepares a NIF deformable mirror substrate for surface figure testing on LLE’s 18-in.-aperture interferometer

Moving Cryostat

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1999:

The moving cryostat maintains a target at a constant temperature to layer the DT ice and transports the target to the center of the target chamber. The cryostat base is shown. At the bottom is the cryo cooler. Above the cooler are the four-axis positioner and two thermal shrouds that are maintained at 45 K and 16 K. The target assembly is at the top. The target is mounted on spider-silk in a C-shaped beryllium support.

2-D Smoothing by SSD

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1999:

A two-dimensional smoothing by spectral dispersion (2-D SSD) system was installed on OMEGA and was capable of producing phase-modulated spectra that can be frequency tripled to 1-THz bandwidth in the ultraviolet. This 2-D SSD system incorporated a high-frequency bulk-phase modulator operating at 0.4 GHz to produce an 11 Å of bandwidth in the infrared.

Efficient frequency tripling of this broadband signal requires dual-tripler frequency-conversion crystals that are currently installed on only 13 beams. The high-frequency bulk-phase modulator can also be operated at 3 Å with a higher dispersion grating to produce three SSD color cycles, which significantly improves beam smoothing at lower bandwidths on all 60 OMEGA beams.

Target Designs for NIF

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1999:

LLE developed moderate-gain, direct-drive designs for the NIF.

Cryogenic Target Handling System

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1999:

LLE integrated the OMEGA Cryogenic Target Handling System into the OMEGA facility.

(Permeation and target-transfer equipment inside the cryostat)

LLE CEA Collaboration

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1999:

LLE began a long-standing collaboration with Commissariat à l’Énergie Atomique Division of Military Applications (the Military Applications Division of the French Atomic Energy Commission, CEA). Their collaboration has produced scientific results ranging from improved understanding of laser–plasma interaction, to high-resolution neutron imaging diagnostic development.

Saturation Growth in Planar Targets

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1998:

A paper authored by V. A. Smalyuk et al. was published in Physical Review Letters. It showed for the first time that 3-D broadband imprinted features exhibit saturated growth at amplitudes consistent with theoretical models.

[1] V. A. Smalyuk, T. R. Boehly, D. K. Bradley, V. N. Goncharov, J. A. Delettrez, J. P. Knauer, D. D. Meyerhofer, D. Oron, and D. Shvarts, “Saturation of the Raleigh–Taylor Growth of Broad-Bandwidth Laser-Imposed Nonuniformities in Planar Targets,” Phys. Rev. Lett. 81 (24) 5342–5345 (1998).

(Fully processed subimages of the target optical depth captured at 1.9 ns)

High-Density Charged-Particle Diagnostics

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1998:

In collaboration with MIT’s Plasma Science and Fusion Center (PSFC), LLE began the development of a charged-particle spectrometer to measure charged particles from high-density implosions on OMEGA.

(A figure showing a novel technique for measuring ρR simultaneously in three different regions of the compressed target)