ABSTRACT
We report the first demonstration of high-harmonic generation from plasma mirrors at a 1 kHz repetition rate. Harmonics up to nineteenth order are generated at peak intensities close to 10¹8 W/cm² by focusing 1 mJ, 25 fs laser pulses down to 1.7 µm FWHM spot size without any prior wavefront correction onto a moving target. We minimize target surface motion with respect to the laser focus using online interferometry to ensure reproducible interaction conditions for every shot and record data at 1 kHz with unprecedented statistics. This allows us to unambiguously identify coherent wake emission as the main generation mechanism.
ABSTRACT
High-energy petawatt lasers require large diffraction gratings for pulse compression. As an alternative to meter-sized gratings, we demonstrate the capability of a tiled-grating system to compress multiterawatt subpicosecond laser pulses. Using a 100 TW-class Nd:glass chirped-pulse amplification laser facility, we report on the performance of a two-grating mosaic to compress high-energy pulses to 2.5 J, 450 fs (5.5 TW) in air with a beam size of 50 mm and energy transmission of 63%. Stability of the grating mosaic alignment was realized by use of an accurate nanopositioning optomechanical system. The output Gaussian spectrum was preserved from grating-gap spectral clipping and was free of modulation.
ABSTRACT
We present and characterize a very efficient optical device that employs the plasma mirror technique to increase the contrast of high-power laser systems. Contrast improvements higher than 10(4) with 50% transmission are shown to be routinely achieved on a typical 10 TW laser system when the pulse is reflected on two consecutive plasma mirrors. Used at the end of the laser system, this double plasma mirror preserves the spatial profile of the initial beam, is unaffected by shot-to-shot fluctuations, and is suitable for most high peak power laser systems. We use the generation of high-order harmonics as an effective test for the contrast improvement produced by the double plasma mirrors.
ABSTRACT
We describe a compact, reliable, and high-average-power femtosecond x-ray source and its first application to diffraction on protein crystal. The setup relies on a homemade Ti: sapphire system delivering 12 mJ at a 1 kHz repetition rate, associated with a small vacuum chamber especially designed for laser-plasma interaction and x-ray applications. This device allows the generation of 5 x 10(9) photons/s/sr at 8 keV and optimized x-ray irradiation of the studied sample, which can be placed close to the source. We present the diffraction pattern of a protein crystal in a divergent beam geometry, which is a first step to a subpicosecond x-ray diffraction experiment.
Subject(s)
Muramidase/chemistry , Crystallography, X-Ray/instrumentation , Crystallography, X-Ray/methodsABSTRACT
We present a technique for simultaneous focusing and energy selection of high-current, mega-electron volt proton beams with the use of radial, transient electric fields (10(7) to 10(10) volts per meter) triggered on the inner walls of a hollow microcylinder by an intense subpicosecond laser pulse. Because of the transient nature of the focusing fields, the proposed method allows selection of a desired range out of the spectrum of the polyenergetic proton beam. This technique addresses current drawbacks of laser-accelerated proton beams, such as their broad spectrum and divergence at the source.
ABSTRACT
We report on direct observation of temporal contrast degradation of short pulses amplified by optical parametric chirped-pulse amplification. We show that, despite injection seeding, quantum-noise-induced fast modulations (< 50 ps) of the temporal profile of the pump pulse are imprinted on the spectrum of the amplified chirped pulse and give rise to a large picosecond pedestal in the time domain.
ABSTRACT
We demonstrate the use of a plasma mirror to obtain 60-fs 10-TW laser pulses with a temporal contrast of 10(8) on a nanosecond time scale and 10(6) on a picosecond time scale, and we use these high-contrast pulses to generate high harmonics by nonlinear reflection on a plasma with a steep electronic density gradient. Well-collimated harmonics up to 20th order are observed for a laser intensity of approximately equal to 3 x 10(17) W/cm2, whereas no harmonics are obtained without the plasma mirror.
