Optical spatial smoothing of Nd-Glass laser beam

Véron, D.; Ayral, H.; Gouédard, C.; Husson, D.; Lauriou, J.; Martin, Olivier J. F.; Meyer, Bernard De; Rostaing, M.; Sauteret, C.

doi:10.1016/0030-4018(88)90438-5

Cited by 79 publications

(24 citation statements)

References 6 publications

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“…The Rayleigh-Taylor gain each t-mode amplitude experiences during the acceleration is then approximated by the modified Takabe7 formula 'm(')=expm='ha]} (4) the wave vector k= 1/1 mm,~=3, v.=3.4 x I@ cm/s, At= 4.16 ns, g = 9 X1015 cm /s2, L= 0.5 pm. The amplitude at peak velocity is then given by aA-wq(O = a+,h(O" Gm(O (5) The aggregate variance of the surface perturbation at peak velocity is then given by # =~1(21+ l)a~e~.,elmi~(l) /4n.…”

Section: Analytic Modelmentioning

confidence: 99%

<title>Impact of beam smoothing method on direct-drive target performance for the NIF</title>

Rothenberg

Weber

1997

SPIE Proceedings

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Section: Analytic Modelmentioning

confidence: 99%

<title>Impact of beam smoothing method on direct-drive target performance for the NIF</title>

Rothenberg

Weber

1997

SPIE Proceedings

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“…Other beam-smoothing techniques, such as smoothing by spectral dispersion (SSD), [16], [17] optical fiber smoothing (OFS), [18] and partially coherent light (PCL), [19] are also subject to timeintegrated near-field structure due to laser phase aberration. These techniques are normally applied to glass lasers, where optical relaying is easier to implement because there are fewer beams; however glass lasers are also more susceptible to small-scale self-focusing, which tends to amplify the near-field nonuniformities.…”

Section: Introductionmentioning

confidence: 99%

“…Their evaluation therefore follows the same steps as those for the amplitudes; i.e., S F (X) is found by applying the FFT directly to expression (18), but S L (X) requires that we express T A (X A ) in terms of its …”

Section: Introductionmentioning

confidence: 99%

Near-field nonuniformities in angularly multiplexed KrF fusion lasers with induced spatial incoherence

Lehmberg

Chan

2005

Appl. Opt.

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Induced Spatial Incoherence (ISI) has been proposed for KrF laser drivers to achieve the high degree of spatial beam uniformity required for direct-drive inertial confinement fusion.Although ISI provides ultrasmooth illumination at the far-field of the laser, where the target is located, it can still allow the beams in the quasi near-field to develop time-averaged spatial structure. This speckle, which arises primarily from random phase aberration, builds up as the laser beams propagate away from the pupil plane located at the final amplifier stage; it is distinct from any structure imposed by gain nonuniformities in the amplifiers. Because of the spatial incoherence, the speckle is significantly smaller than that experienced by coherent beams; nevertheless, it remains a damage issue, especially for the long beam delay paths required in angularly-multiplexed KrF lasers. This paper develops a novel algorithm for calculating the time-integrated intensities, compares simulations and measurements of the near-field speckle in the Nike KrF laser, and explores options, such as aberration reduction and optical relaying, for controlling the problem in future angularly-multiplexed KrF drivers.OCIS numbers: 030.6140, 030.6600, 070.2590, 140.2180, 350.2660, 350. ABSTRACTInduced Spatial Incoherence (ISI) has been proposed for KrF laser drivers to achieve the high degree of spatial beam uniformity required for direct-drive inertial confinement fusion. Although ISI provides ultrasmooth illumination at the far-field of the laser, where the target is located, it can still allow the beams in the quasi near-field to develop time-averaged spatial structure. This speckle, which arises primarily from random phase aberration, builds up as the laser beams propagate away from the pupil plane located at the final amplifier stage; it is distinct from any structure imposed by gain nonuniformities in the amplifiers. Because of the spatial incoherence, the speckle is significantly smaller than that experienced by coherent beams; nevertheless, it remains a damage issue, especially for the long beam delay paths required in angularly-multiplexed KrF lasers. This paper develops a novel algorithm for calculating the time-integrated intensities, compares simulations and measurements of the near-field speckle in the Nike KrF laser, and explores options, such as aberration reduction and optical relaying, for controlling the problem in future angularly-multiplexed KrF drivers.

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“…However, variants of ISI have been implemented on glass lasers at low power by Nakano et al at Osaka, [181][182][183] where it is referred to as partially coherent light (PCL), and by V eron et al at Limeil. 184,185 Nakano et al 181 implemented PCL in a 1-lm laser, producing 800 J per beam with 13 Å of bandwidth using an amplified spontaneous emission (ASE) source at the front end that introduced temporal bandwidth and transverse spatial modes. They observed some temporal spikes in the beam.…”

Section: B Induced Spatial Incoherence (Isi)mentioning

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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Optical spatial smoothing of Nd-Glass laser beam

Cited by 79 publications

References 6 publications

<title>Impact of beam smoothing method on direct-drive target performance for the NIF</title>

<title>Impact of beam smoothing method on direct-drive target performance for the NIF</title>

Near-field nonuniformities in angularly multiplexed KrF fusion lasers with induced spatial incoherence

Direct-drive inertial confinement fusion: A review

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