Large area electron beam pumped krypton fluoride laser amplifier

Sethian, J. D.; Obenschain, S. P.; Gerber, K. A.; Pawley, C. J.; Serlin, V.; Sullivan, C. A.; Webster, W.; Deniz, A. V.; Lehecka, T.; McGeoch, Malcolm W.; Altes, R.; Corcoran, Patrick; Smith, I.; Barr, O.

doi:10.1063/1.1148118

Cited by 46 publications

(16 citation statements)

References 18 publications

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“…3; i.e., a "top- Using a setup similar to that described in ref. [12], we recorded time-integrated near-field images of several Nike beams on photochromic UV-sensitive PERM film (manufactured by GAF Chemicals). [21] For each beam, we measured the image at both the collimator and the target chamber window during the same laser shot by placing film over one half of the recollimator and allowing the unblocked half of the beam to propagate on to the window.…”

Section: Resultsmentioning

confidence: 99%

“…This structure, which builds up the beams propagate away from the pupil-plane images at the amplifiers, arises primarily from upstream random phase aberration; it is distinct from the generally long scalelength variations due to residual gain nonuniformities across the amplifier apertures. [12] In angularly-multiplexed KrF systems, it develops primarily in the long delay path optics (e.g., demultiplexing mirrors and focusing lenses) after the final amplifier. The speckle nonuniformities of ISI beams are much smaller than those created by coherent light, and so far they have not caused any serious damage in the Nike output optics because the average fluences (typically less than 0.5 J/cm 2 ) are well below damage threshold.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Resultsmentioning

confidence: 99%

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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“…Nike routinely (up to 20 shots in eight hours) demonstrates efficient laser amplifier extraction (angularly multiplexing), uniform focal spatial profile utilizing induced spatial incoherence (ISI) [4], and pulse shape control. The largest amplifier of the Nike laser system has been discussed in detail elsewhere [5]. Nike is pumped with two counter streaming electron beams.…”

Section: Introductionmentioning

confidence: 99%

KrF Laser Development for Fusion Energy

Wolford

Sethian

Myers

et al. 2013

Plasma and Fusion Research

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The United States Naval Research Laboratory is developing an electron beam pumped krypton fluoride laser technology for a direct drive inertial fusion energy power plant. The repetitively pulsed krypton fluoride laser technology being developed meets the fusion energy requirements for laser beam quality, wavelength, and repetition rate. The krypton fluoride laser technology is projected, based on experiments, to meet the requirements for wall plug efficiency and durability. The projected wall plug efficiency based on experiments is greater than 7 percent. The Electra laser using laser triggered gas switches has conducted continuous operation for 90,000 shots at 2.5 Hertz operation (ten hours). The Electra laser has achieved greater than 700 Joules per pulse at 1 and 2.5 Hertz repetition rate. The comparison of krypton fluoride laser performance with krypton fluoride kinetics code shows good agreement for pulse shape and laser yield. Development and operation of a durable pulse power system with solid state switches has achieved a continuous run of 11 million pulses into a resistive load at 10 Hz.

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“…Such a KrF laser module would be pumped by repetitively pulsed, counterstreaming, large-area electron beams (e-beams). Theory, simulation, [2,3] and experiments [4] performed on the NIKE [5] KrF laser at the Naval Research Laboratory have shown that large-area, e-beam diodes are susceptible to the transittime instability. The instability modulates the electron beam spatially and temporally, producing a wide spread in electron energy and momentum distributions.…”

Section: Introductionmentioning

confidence: 99%

Suppression of the Transit -Time Instability in Large-Area Electron Beam Diodes

Myers

Friedman

Swanekamp

et al. 2002

AIP Conference Proceedings

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Abstract. Experiment, theory, and simulation have shown that large-area electron-beam diodes are susceptible to the transit-time instability. The instability modulates the electron beam spatially and temporally, producing a wide spread in electron energy and momentum distributions. The result is gross inefficiency in beam generation and propagation. Simulations indicate that a periodic, slotted cathode structure that is loaded with resistive elements may be used to eliminate the instability. Such a cathode has been fielded on one of the two opposing 60 cm x 200 cm diodes on the NIKE KrF laser at the Naval Research Laboratory. These diodes typically deliver 600 kV, 500 kA, 250 ns electron beams to the laser cell in an external magnetic field of 0.2 T. We conclude that the slotted cathode suppressed the transit-time instability such that the RF power was reduced by a factor of 9 and that electron transmission efficiency into the laser gas was improved by more than 50%.

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Large area electron beam pumped krypton fluoride laser amplifier

Cited by 46 publications

References 18 publications

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

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

KrF Laser Development for Fusion Energy

Suppression of the Transit -Time Instability in Large-Area Electron Beam Diodes

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