&lt;title&gt;Phase conversion of lasers with low-loss distributed phase plates&lt;/title&gt;

Kessler, T. J.; Lin, Yow−Jon; Armstrong, J. Joseph; Velazquez, Belimar

doi:10.1117/12.154474

Cited by 64 publications

(17 citation statements)

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“…169 However, with two-level phase plates, close to 20% of the laser energy is diffracted outside the first zero of the sinc 2 envelope and does not contribute to target drive. At LLE, two-level phase plates were replaced by continuous phase plates, developed by Kessler et al,170 in which the surface relief varied continuously, eliminating most of the diffraction losses and providing close to 100% of the beam energy on target. Initially, these phase plates were designed with phase distributions (translated into surface relief on fused-silica substrates) consisting of a random term combined with several spatial periodic terms.…”

Section: A Phase Platesmentioning

confidence: 99%

Direct-drive inertial confinement fusion: A review

et al. 2015

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The direct-drive, laser-based approach to inertial confinement fusion (ICF) is reviewed from its inception following the demonstration of the first laser to its implementation on the present generation of high-power lasers. The review focuses on the evolution of scientific understanding gained from target-physics experiments in many areas, identifying problems that were demonstrated and the solutions implemented. The review starts with the basic understanding of laser–plasma interactions that was obtained before the declassification of laser-induced compression in the early 1970s and continues with the compression experiments using infrared lasers in the late 1970s that produced thermonuclear neutrons. The problem of suprathermal electrons and the target preheat that they caused, associated with the infrared laser wavelength, led to lasers being built after 1980 to operate at shorter wavelengths, especially 0.35 μm—the third harmonic of the Nd:glass laser—and 0.248 μm (the KrF gas laser). The main physics areas relevant to direct drive are reviewed. The primary absorption mechanism at short wavelengths is classical inverse bremsstrahlung. Nonuniformities imprinted on the target by laser irradiation have been addressed by the development of a number of beam-smoothing techniques and imprint-mitigation strategies. The effects of hydrodynamic instabilities are mitigated by a combination of imprint reduction and target designs that minimize the instability growth rates. Several coronal plasma physics processes are reviewed. The two-plasmon–decay instability, stimulated Brillouin scattering (together with cross-beam energy transfer), and (possibly) stimulated Raman scattering are identified as potential concerns, placing constraints on the laser intensities used in target designs, while other processes (self-focusing and filamentation, the parametric decay instability, and magnetic fields), once considered important, are now of lesser concern for mainline direct-drive target concepts. Filamentation is largely suppressed by beam smoothing. Thermal transport modeling, important to the interpretation of experiments and to target design, has been found to be nonlocal in nature. Advances in shock timing and equation-of-state measurements relevant to direct-drive ICF are reported. Room-temperature implosions have provided an increased understanding of the importance of stability and uniformity. The evolution of cryogenic implosion capabilities, leading to an extensive series carried out on the 60-beam OMEGA laser [Boehly et al., Opt. Commun. 133, 495 (1997)], is reviewed together with major advances in cryogenic target formation. A polar-drive concept has been developed that will enable direct-drive–ignition experiments to be performed on the National Ignition Facility [Haynam et al., Appl. Opt. 46(16), 3276 (2007)]. The advantages offered by the alternative approaches of fast ignition and shock ignition and the issues associated with these concepts are described. The lessons learned from target-physics and implosion experiments are taken into account in ignition and high-gain target designs for laser wavelengths of 1/3 μm and 1/4 μm. Substantial advances in direct-drive inertial fusion reactor concepts are reviewed. Overall, the progress in scientific understanding over the past five decades has been enormous, to the point that inertial fusion energy using direct drive shows significant promise as a future environmentally attractive energy source.

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Section: A Phase Platesmentioning

confidence: 99%

Direct-drive inertial confinement fusion: A review

et al. 2015

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“…And a number of beam-smoothing technologies have been proposed [1][2][3][4][5][6][7][8][9][10] to reduce the modulation of beam intensity in high-power laser systems. The array optical system is one kind of the most important techniques, the typical examples of these system include lens array (LA) 3 , the orthogonal cylindrical lens arrays (OCLA) 5 , crossed segmented wedge arrays (CSWA) 6 .…”

Section: Introductionmentioning

confidence: 99%

Improved uniformity of target irradiation by combining an orthogonal cylindrical lens array and the polarization control

Jian-zhou

Zheng²,

et al. 2010

5th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Large Mirrors and Telescopes

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A scheme of combining technology of orthogonal cylindrical lens array (OCLA) and polarization control plate (PCP) is introduced to improve target irradiation uniformity in laser fusion. The feasibility of the scheme is also analyzed by detailed two-dimensional simulation. It shows that a focal pattern with flat-top and sharp-edge profile could be obtained with an OCLA, while interference stripes inside the pattern are smoothed out by the use of the polarization control plate (PCP) technique. Moving the target slightly from the exact focal plane of the principal focusing lens can eliminate middle-scale-length intensity fluctuation further. And a well-irradiated laser spot with small nonuniformity and great energy efficiency can be obtained in this scheme.

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“…The laser beams uniformly illuminated the target and were smoothed by polarization smoothing [17] , smoothing by spectral dispersion [18] and distributed phase plates [19] (fourth-order super-Gaussian with 95% of the energy contained within the initial target Figure 5. Comparison of the measured (red symbols, each of which corresponds to a different camera) mid-intensity point in (a) the inner gradient trajectory and (b) the velocity with the simulation (blue curve).…”

Section: Ablation-front Trajectory and Velocity On The Omega Laser Symentioning

confidence: 99%

Measurements of the ablation-front trajectory and low-mode nonuniformity in direct-drive implosions using x-ray self-emission shadowgraphy

Michel

Davis

Armstrong

et al. 2015

High Pow Laser Sci Eng

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Self-emission x-ray shadowgraphy provides a method to measure the ablation-front trajectory and low-mode nonuniformity of a target imploded by directly illuminating a fusion capsule with laser beams. The technique uses time-resolved images of soft x-rays (>1 keV) emitted from the coronal plasma of the target imaged onto an x-ray framing camera to determine the position of the ablation front. Methods used to accurately measure the ablation-front radius (δ R = ±1.15 µm), image-to-image timing (δ( t) = ±2.5 ps) and absolute timing (δt = ±10 ps) are presented. Angular averaging of the images provides an average radius measurement of δ(R av ) = ±0.15 µm and an error in velocity of δV /V = ±3%. This technique was applied on the Omega Laser Facility [Boehly et al., Opt. Commun. 133, 495 (1997)] and the National Ignition Facility [Campbell and Hogan, Plasma Phys. Control. Fusion 41, B39 (1999)].

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<title>Phase conversion of lasers with low-loss distributed phase plates</title>

Cited by 64 publications

References 0 publications

Direct-drive inertial confinement fusion: A review

Direct-drive inertial confinement fusion: A review

Improved uniformity of target irradiation by combining an orthogonal cylindrical lens array and the polarization control

Measurements of the ablation-front trajectory and low-mode nonuniformity in direct-drive implosions using x-ray self-emission shadowgraphy

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