Electron kinetic energy measurements from laser irradiation of clusters

We have measured electron kinetic energy spectra from the interaction of a low-density beam of noble-gas clusters with a high-intensity femtosecond laser pulse. Electron energies were measured both through their time of flight and through measurements of electron signals as a function of retarding voltages up to 7 kV. We have observed electrons with energies up to 6 keV and a sharp peak at an arrival time consistent with the detection of photons. The electrons had a broad angular distribution peaked along the polarization axis, while the sharp peak had an isotropic angular distribution. We attribute this sharp peak to uv, xuv, or x-ray photons formed as a result of the laser-cluster interaction and were unable to observe the two-lobed electron kinetic energy distribution reported by Shao [Phys. Rev. Lett. 77, 3343 (1996)] with any combination of the laser and cluster parameters used.