The interaction of high-intensity contrast, picosecond, 1-μm laser pulses with solid metal targets is studied with Kα emission from multilayer targets, fast ion blowoff, and other diagnostics. It is found that the characteristics of the interaction are determined by the intensity of the p-polarized component of the incoming laser field, rather than the total intensity. Consistent with resonance absorption, 20%–30% of the laser energy is deposited into suprathermal electrons that have temperatures from 2–10 keV.

Strong Ka emission is observed in picosecond laser-plasma interactions with high-intensity-contrast, p-polarized, picosecond laser pulses. Ka emission from Si substrates overlaid with various thicknesses of Al is compared with a Monte Carlo simulation. The results show that the hot electrons which deposit their energy in the solid material have a 3-keV temperature and carry 10% of the incident laser energy. The shifted Ka emission indicates that the solid is heated to a temperature of 35 eV up to 5000 A from the target surface, which is consistent with the preheat of the hot electrons. PACS numbers: 52.40.Nk Short-pulse (~1 ps) laser-plasma interactions have aroused special interest because of the possibilities of producing ultrashortx-ray pulses [1-3] and near-soliddensity plasmas [4,5]. Recently, it has been shown that, for a high-intensity-contrast, picosecond, p-polarized laser pulse incident at a large oblique angle, the absorption can be as high as 60% [6]. Simulations predict that a large fraction of the absorbed laser energy can be carried by hot electrons in high-intensity, short-pulse laserplasma interactions [7,8]. Experimentally, the generation of hot electrons from the short-pulse laser plasma has been reported using an 80-fs pulse with a 3-ns pedestal (amplified spontaneous emission) at normal incidence [9].In this Letter, we report for the first time a quantitative measurement of the hot electrons generated in shortscale-length laser-plasma interactions by high-intensitycontrast (contrast of main pulse to the pedestal is greater than 10 ) picosecond laser pulses. This high contrast enables the main laser pulse to interact with a very shortscale-length (much less than the laser wavelength) plasma instead of interacting with a long-scale-length preformed plasma created by the prepulse. The results are significantly changed when a prepulse is present. The hot-electron energy was deduced from the Ka spectra of multilayered targets, a technique which has been successfully demonstrated for long-pulse laser plasmas [10,11]. The temperature of the hot electrons is measured to be 3 keV by fitting the experimental data by the Monte Carlo calculations and the total Ka yield shows that the hot electrons which deposit their energy in the solid target carry -10% of total laser energy assuming an isotropic Maxwellian distribution function. These hot electrons can preheat the target up to 100 eV producing a relatively cold solid-density plasma behind the hot surface plasma. This is consistent with the observed shifted Ka emission. A strong dependence of the Ka emission on the polarization of the laser pulse at 60 incidence angle is observed, consistent with resonance absorption in shortscale-length laser-plasma interactions [7,12].In the experiment, a 1.3-ps (FWHM), 1.05-pm pulse with an average energy of 10 m3 is provided by a Nd:glass laser system based on the chirped pulse amplification and compression (CPAC) technique [13,14]. With a saturable absorber (Kodak 9860 dye) after the compression gratings [13],a 5...

Kα emission is observed from the interaction of a picosecond, 1.05 μm laser pulse at 4×1015 W/cm2 with a silicon target coated with various thicknesses of aluminum. Strong Kα emission requires a p-polarized, high-intensity-contrast laser pulse. At 7.1 Å, the Kα yield is 1.5×108 photons/sr with a duration of emission of ≤8 ps and a source area of 1.6×10−6 cm2. The radiance is ≥3×109 W/cm2 sr. Monte Carlo simulations have suggested that under these conditions Kα emission is a promising candidate for an efficient, ultra-short-duration x-ray source at ∼1.5 Å.