Role of the plasma scale length in the harmonic generation from solid targets

Coherent Wake Emission of High-Order Harmonics from Overdense Plasmas

“…Second, this intensity dependence is almost the same for all harmonics, which means that the harmonic spectrum hardly changes with intensity. Both observations are in contradiction with the OM mechanism [2,3,5], which predicts a highly nonlinear behavior in this intensity range. This definitely excludes this process in interpreting our observations.…”

“…This last effect is confirmed experimentally. High-order harmonic generation (HHG) by reflection of an intense laser beam from an overdense plasma has been observed with very different types of lasers, from nanosecond CO 2 lasers to picosecond (ps) Nd-glass and femtosecond (fs) Ti-Sa lasers ( [1][2][3][4][5][6], and references therein). Two strong motivations drive these studies.…”

Multi-μJ harmonic emission energy from laser-driven plasma

“…This is attributed to the laser pulse characteristics that determine to a great extent the steepness of the density ramp at the plasma-vacuum interface. As has been already reported [19,27,29], the initial density gradient scalelength L has a profound influence on the spectral and spatial properties of the harmonic emission. In our experiment, we were able to observe "beaming" of the harmonic emission and a reproducible spectrum, only when we attenuated the laser beam energy to the level that the pre-pulse effects were switchedoff.…”

Generation of MeV electrons and positrons with femtosecond pulses from a table-top laser system

“…13,14 In this report we give a comprehensive account of the work we have performed on the generation of a relativistic electron beam employing a table-top laser system delivering femtosecond pulses at the rate of 10 Hz. Also, of an application in which, using the laser accelerated electrons, we produced 10 6 positrons (e ϩ ) per laser pulse with a mean energy of ϳ2 MeV. The measured electron energy spectra, resolved in angle and absolutely calibrated, pertain to electron acceleration during self-channeling in a previously unexplored regime, characterized by fs-laser pulses of relatively low energy (Ͻ1 J) interacting with a high-density gas jet producing electron densities n e ϳ0.3n c where n c ϭm L 2 /(4e 2 ) is the plasma critical density corresponding to the laser frequency L .…”