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We characterize the temporal profile of the high-order harmonic emission from ablation plasma plumes using cross-correlations with the infrared (IR) laser beam provided by two-photon harmonic+IR ionization of rare gas atoms.We study both non-resonant plasmas (lead, gold and chrome) and resonant plasmas (indium and tin), i.e. plasmas presenting in the singly charged ions a strong radiative transition coinciding with a harmonic order. The cross-correlation traces are found to be very similar for all harmonic orders and all plasma targets. The recovered harmonic pulse durations are very similar to the driving laser, with a tendency towards being shorter, demonstrating that the emission is a directly laser-driven process even in the case of resonant harmonics. This provides a valuable input for theories describing resonant-harmonic emission and opens the perspective of a very high flux tabletop XUV source for applications. [ABSTRACT FROM AUTHOR] more...

The x-ray spectra of a plasma produced by heating CO[sub 2] clusters with intense femtosecond laser pulses with λ = 0.8 µm and λ = 0.4 µm are investigated. Spatially resolved x-ray spectra of the cluster plasma are obtained. The observed characteristic features of the x-ray emission spectra show unequivocally that such a plasma contains quite a large relative number of ions (...10[sup -]2 - 10[sup -3]) with energies of 0.1-1 MeV. The contour of the O VIII Ly[sub α] line is found to have characteristic features that are especially conspicuous when the clusters are heated with second-harmonic pulses. These features cannot be explained by any mechanisms known to the authors. [ABSTRACT FROM AUTHOR] more...

A photoconductive switch driving a Pockels cell ensures energy self-stabilization of ultra-fast laser pulses from single shot to hundreds of kHz. In this kind of stabilization, the pulse corrects itself. In a first experiment, the self-stabilization of a 20-Hz, 800-nm femtosecond Chirped Pulse Amplification laser shows a reduction of the energy fluctuations from 7% rms to 0.64% rms. [ABSTRACT FROM AUTHOR] more...

Abstract. Laser ablation efficiency and plasma plume expansion were studied using the interaction of Ti-Al[sub 2]O[sub 3] laser pulses (wavelength 800 nm; energy 20 micro J; mode TEM[sub 00]; waist diameter 11 micro m; pulse durations 70 fs, 150 fs, 0.4 ps, 0.8 ps, 2 ps, and 10 ps) with copper in air. A moderate laser pulse energy of 20 micro J was used to eliminate the sharply focused femtosecond laser beam disturbance caused by its nonlinear interaction with air. The craters formed at the surfaces were measured with 0.1 gm longitudinal and 0.5 micro m transverse resolution. Laser plasma expansion was measured by an ICCD camera with 3 micro m spatial and 1 ns temporal resolution. These measurements were performed in a time delay range of 0-50 ns. The laser pulse duration range used in our study was of particular interest as it corresponded to the characteristic time for electron-phonon interactions in solids (of the order of one picosecond). Thus we could study the different regimes of laser ablation without (fs pulses) and with (ps pulses) laser beam/plasma plume interaction. Laser ablation efficiencies, crater profiles, plasma plume shapes at different time delays, and rates of plasma expansion in both longitudinal and transverse directions to the laser beam were obtained for all the laser pulse durations mentioned above. The experimental results of our investigation on laser ablation with short laser pulses were analysed from the point of view of different the-... [ABSTRACT FROM AUTHOR] more...

We have measured quantitative L X-ray emission yields from (Xe)n clusters (with n between 104 and 106 atoms/cluster) irradiated by 60 fs 800 nm IR and 180 fs 400 nm UV laser pulses of 1015–1017 W cm−2 peak intensity. Measurements have been performed as a function of cluster size (backing pressure) and laser peak intensity. Identification of spectroscopic features as well as X-ray emission yield variation with laser wavelength, intensity and cluster size are in strong contradiction with results and interpretation from previous studies. [Copyright &y& Elsevier] more...