Duration-controlled amplified spontaneous emission with an intensity of 10(13) W/cm(2) is used to convert a 7.5-microm -thick polyimide foil into a near-critical plasma, in which the p -polarized, 45-fs , 10(19) -Wcm (2) laser pulse generates 3.8-MeV protons, emitted at some angle between the target normal and the laser propagation direction of 45 degrees . Particle-in-cell simulations reveal that the efficient proton acceleration is due to the generation of a quasistatic magnetic field on the target rear side with magnetic pressure inducing and sustaining a charge separation electrostatic field.
Absolute energy distribution of hard x rays produced in the interaction of a kilohertz femtosecond laser with tantalum targets Rev. Sci. Instrum. 77, 093302 (2006); Fast protons are observed by a newly developed online time-of-flight spectrometer, which provides shot-to-shot proton-energy distributions immediately after the irradiation of a laser pulse having an intensity of ϳ10 18 W/cm 2 onto a 5-m-thick copper foil. The maximum proton energy is found to increase when the intensity of a fs prepulse arriving 9 ns before the main pulse increases from 10 14 to 10 15 W/cm 2 . Interferometric measurement indicates that the preformed-plasma expansion at the front surface is smaller than 15 m, which corresponds to the spatial resolution of the diagnostics. This sharp gradient of the plasma has the beneficial effect of increasing the absorption efficiency of the main-pulse energy, resulting in the increase in the proton energy. This is supported by the result that the x-ray intensity from the laser plasma clearly increases with the prepulse intensity.
Microstructure surface texture is studied with the Scanning Tunneling Microscope operated at atmospheric air pressure. A standardization procedure for surface microstructure is proposed. We introduce two parameters in order to characterize surface areas in the micrometre and submicrometre range, which we term "granular roughness" and "microroughness". Measurements of a class "0" standard block gauge give a granular roughness R, value of 0.02 pm.
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