Measurements of direct drive laser imprint in thin foils by XUV radiography using an X-ray laser backlighter

In direct drive inertial confinement fusion, the residual speckle pattern remaining after beam smoothing plays an important role in the seeding of instabilities at the ablation front. We have used an x-ray laser as an XUV backlighter to characterize the imprinted modulation in thin foils for smoothing by random phase plate and spectral dispersion at both 0.35 pm and 0.53 pm irradiation, and induced spatial incoherence at 0.53 pm irradiation. We also demonstrate measurements of the modulation due to a single mode optical imprint generated by a narrow slit interference pattern, and modification of the imprint with a superposed smooth irradiation to study time dependence of the imprinting process. 8 refs., 10 figs

XUV probing of laser imprint in a thin foil using an x-ray laser backlighter

For direct drive ICF, a capsule is imploded by directly illuminating the surface with laser light. Beam smoothing and uniformity of illumination affect the seeding of instabilities at the ablation front. We have developed a technique for studying the imprint of a laser beam on a thin foil using an x-ray laser as an XUV backlighter. We use multilayer XUV optics to relay the x-ray laser onto the directly driven foil, and then to image the foil modulation onto a CCD camera. This technique allows us to measure small fractional variations in the foil thickness. We have measured the modulation due to imprint from a low intensity 0.35 pm drive beam incident on a 3 {mu}m Si foil using an yttrium x-ray laser on Nova. We present results from a similar technique to measure the imprinted modulation due to a low intensity 0.53 {mu}m drive beam incident on a 2 {mu}m Al foil using a germanium x-ray laser at the Vulcan facility

Measurements of laser-hole boring into overdense plasmas using x-ray laser refractometry(invited)

Copyright 1999 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Review of Scientific Instruments, 70(1), 543-548, 1986 and may be found at http://dx.doi.org/10.1063/1.114938

Recollisions, bremsstrahlung, and attosecond pulses from intense laser fields

Published versio

Optimization of x-ray sources for proximity lithography produced by a high average power Nd:glass laser

We measured the conversion efficiency of laser pulse energy into x-rays from a variety of solid planar targets and a Xe gas puff target irradiated using a high average power Nd:glass slab laser capable of delivering 13 ns FWHM pulses at up to 20 J at 1.053 {mu}m and 12 J at 0.53 {mu}m. Targets where chosen to optimize emission in the 9-19 {Angstrom} wavelength band, including L-shell emission from materials with atomic numbers in the Z=24-30 and M-shell emission from Xe (Z=54). With 1.053 {mu}m a maximum conversion of 10% into 2{pi} sr was measured from solid Xe and type 302 stainless steel targets. At 0.527 {mu}m efficiencies of 12-18%/(2{pi} sr) were measured for all of the solid targets in the same wavelength band. The x-ray conversion efficiency from the Xe gas puff target was considerably lower, at about 3%/(2{pi} sr) when irradiated with 1.053 {mu}m

Optimization of x-ray sources for proximity lithography produced by a high average power Nd:glass laser. Revision 1

We measured the conversion efficiency of laser pulse energy into keV x-rays from a variety of solid planar targets and a Xe gas puff target irradiated using a high average power Nd:glass slab laser capable of delivering 13 ns FWHM pulses at up to 20 J at 1.053 {mu}m and 12 J at 0.53 {mu}m. Targets where chosen to optimize emission in the l0--15 {angstrom} wavelength band, including L-shell emission from materials with atomic numbers in the range Z=24-30 and M-shell emission from Xe (Z=54). With 1.053 {mu}m a maximum conversion of 11% into 2{pi} sr was measured from solid Xe targets. At 0.527 {mu}m efficiencies of 12--18%/(2{pi}sr) were measured for all of the solid targets in the same wavelength band. The x-ray conversion efficiency from the Xe gas puff target was considerably lower, at about 3%/(2{pi}sr) when irradiated with 1.053 {mu}m

Plasma mediated ablation of biological tissues with ultrashort laser pulses

Plasma mediated ablation of collagen gels and porcine cornea was studied at various laser pulse durations in the range from 350 fs to 1 ns at 1,053 nm wavelength. A time resolved stress detection technique was employed to measure transient stress profiles and amplitudes. Optical microscopy was used to characterize ablation craters qualitatively, while a wide band acoustic transducer helped to quantify tissue mechanical response and the ablation threshold. The ablation threshold was measured as a function of laser pulse duration and linear absorption coefficient. For nanosecond pulses the ablation threshold was found to have a strong dependence on the linear absorption coefficient of the material. As the pulse length decreased into the subpicosecond regime the ablation threshold became insensitive to the linear absorption coefficient. The ablation efficiency was found to be insensitive to both the laser pulse duration and the linear absorption coefficient. High quality ablation craters with no thermal or mechanical damage to surrounding material were obtained with 350 fs laser pulses. The mechanism of optical breakdown at the tissue surface was theoretically investigated. In the nanosecond regime, optical breakdown proceeds as an electron collisional avalanche ionization initiated by thermal seed electrons. These seed electrons are created by heating of the tissue by linear absorption. In the ultrashort pulse range, optical breakdown is initiated by the multiphoton ionization of the irradiated medium (6 photons in case of tissue irradiated at 1,053 nm wavelength), and becomes less sensitive to the linear absorption coefficient. The energy deposition profile is insensitive to both the laser pulse duration and the linear absorption coefficient

Measurements of laser imprint by XUV radiography using an x-ray laser

We have developed a technique for studying the imprint of a laser beam on a thin foil using an x-ray laser as an XUV backlighter and XUV multilayer optics. This technique allows us to measure small fractional variations in the foil thickness due to hydrodynamics imprinted by direct laser irradiation. We present results of imprinted modulation and growth due to a low intensity 0.53 {mu}m drive beam incident on a 2 {mu}m Al foil using a germanium x-ray laser at the Vulcan facility. We present measurements of the modulation due to static RPP, SSD smoothed, and ISI smoothed speckle patterns at 0.53 {mu}m irradiation