We have demonstrated single-shot measurement of electron diffraction patterns for a single-crystal gold foil using 340 keV electron pulses accelerated by intense femtosecond laser pulses with an intensity of 2×1018 W/cm2. The measured electron beam profile is faithfully reproduced by the numerical simulation of the electron trajectory, providing evidence that the electron pulse spontaneously expands in time owing to the velocity spread produced in the acceleration process, but is not distorted in an irreversible nonlinear manner. This study shows that the laser acceleration is promising for the development of pulse compression methods for single-shot femtosecond electron diffraction.
Highly stable operation of a two-stage multipass Ti:sapphire amplifier (a four-pass pre-amplifier and a four-pass power amplifier) for a 100-mJ-class chirped-pulse amplification system has been demonstrated by passive stabilization. By optimizing the ratio of pump energies to the two amplifiers and the optical losses artificially inserted into the second power amplifier, a root-mean-square fluctuation in pulse energy of 0.3% was achieved, which was 5 times lower than that of the pump laser. This is the lowest pulse-to-pulse fluctuation, to the best of our knowledge, obtained by the 100-mJ-class Ti:sapphire amplifiers.
The energy distributions of ions emitted from argon clusters Coulomb exploded at an intensity of Ͻ10 17 W/cm 2 with an intense femtosecond laser have been experimentally studied. The power m of energy E of the ion energy distribution ͑dN / dE ϳ E m ͒ is expected to be 1 / 2 for spherical ion clusters, but it is in fact reduced smaller than 1 / 2 as the laser intensity is decreased. This reduction can be well interpreted as resulting from the instantaneous ionization of the surface of the cluster. The validity of this interpretation was confirmed by experiments with double pulse irradiation. A cluster irradiated by the first pulse survives as a skinned cluster, and the remaining core part is Coulomb exploded by the second pulse. It is shown that a cluster can be skinned by an intense short laser pulse, and the laser-intensity dependence of the skinned layer thickness can be reasonably explained by the laser-induced space charge field created in the cluster.
A simple technique for single-shot microscopic electron imaging was demonstrated for the study of intense femtosecond laser-produced plasmas. Passed through a permanent magnet lens designed for 110-keV electrons, hot electrons emitted from the plasma produced by a single laser pulse of 0.8 mJ with intensity of 3 × 10(16) W/cm(2) were successfully imaged. Analyzing this image, we found that electrons were emitted from an area of 3 μm in diameter. At higher laser intensity of 10(18) W/cm(2), distinct structures were observed in and near the focal spot of the laser; that is, the electrons were emitted from several separate spots. These results show that laser-plasma electron imaging is promising for studying the interactions of femtosecond lasers with high-density plasmas.
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