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Applied Optics

Applied Optics

APPLICATIONS-CENTERED RESEARCH IN OPTICS

  • Editor: Joseph N. Mait
  • Vol. 49, Iss. 19 — Jul. 1, 2010
  • pp: 3723–3731

High-energy flat-top beams for laser launching using a Gaussian mirror

Hiroki Fujiwara, Kathryn E. Brown, and Dana D. Dlott  »View Author Affiliations


Applied Optics, Vol. 49, Issue 19, pp. 3723-3731 (2010)
http://dx.doi.org/10.1364/AO.49.003723


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Abstract

Converting a Gaussian to a flat-top beam is useful for many applications including laser-launched thin-foil flyer plates. A flat-top beam is needed to maintain a constant launch velocity across the flyer; otherwise, the flyer can disintegrate in flight. Here we discuss and demonstrate the use of a variable reflectivity mirror (VRM) with a Gaussian reflectivity profile with an additional hard aperture and compare it to a refractive beam shaper. An ideal VRM would generate a flat-top beam with 37% efficiency. Readily available high-power Gaussian or super-Gaussian mirrors create an approximate flat-top profile, but there is a trade-off between flatness and efficiency. We show that a super-Gaussian mirror can, in principle, convert an input Gaussian beam with 30% efficiency to a flat-top beam with 3% (maximum-to- minimum) variation. With a Gaussian mirror and a high-energy pulsed Nd:YAG laser having relatively poor beam quality, we generate flat-top beams with 25% conversion efficiency having 6% variation (standard deviation σ = 4.2 % ). The beams are used to launch 400 μm diameter, 25 μm thick Al flyer plates, whose flight was monitored by a high-speed displacement interferometer. The plates flew across a 300 μm gap at 1.3 km / s . The distribution of arrival times at the witness plate was 5 ns , as determined by the rise time of the impact emission. Compared to a total flight time of 260 ns , the velocity spread of different parts of the flyer plate was 2%.

© 2010 Optical Society of America

OCIS Codes
(300.6500) Spectroscopy : Spectroscopy, time-resolved
(140.3295) Lasers and laser optics : Laser beam characterization

ToC Category:
Lasers and Laser Optics

History
Original Manuscript: April 22, 2010
Manuscript Accepted: May 24, 2010
Published: June 23, 2010

Citation
Hiroki Fujiwara, Kathryn E. Brown, and Dana D. Dlott, "High-energy flat-top beams for laser launching using a Gaussian mirror," Appl. Opt. 49, 3723-3731 (2010)
http://www.opticsinfobase.org/ao/abstract.cfm?URI=ao-49-19-3723

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