Escaping Electrons from Intense Laser-Solid Interactions as a Function of Laser Spot Size

Abstract

Abstract. The interaction of a high-intensity laser with a solid target produces an energetic distribution of electrons that pass into the target. These electrons reach the rear surface of the target creating strong electric potentials that act to restrict the further escape of additional electrons. The measurement of the angle, flux and spectra of the electrons that do escape gives insights to the initial interaction. Here, the escaping electrons have been measured using a differentially filtered image plate stack, from interactions with intensities from mid 10 20 -10 17 W/cm 2 , where the intensity has been reduced by defocussing to increase the size of the focal spot. An increase in electron flux is initially observed as the intensity is reduced from 4x10 20 to 6x10 18 W/cm 2 . The temperature of the electron distribution is also measured and found to be relatively constant. 2D particle-in-cell modelling is used to demonstrate the importance of pre-plasma conditions in understanding these observations.

Laser produced electromagnetic pulses: generation, detection and mitigation

“…Increase of the laser focal spot and of the pulse duration for a given absorbed pulse energy results in a decrease of laser intensity and, consequently, of the number of ejected electrons. Dependence of the number of ejected electrons could be more complicated in experiments where laser defocusing is accompanied by a variation of absorption due to nonlinear laser-plasma interaction [67] . However, laser focal spot and pulse duration have very different consequences if one increases them too much while keeping the laser energy unchanged.…”

Production of relativistic electrons at subrelativistic laser intensities

“…The ARC is unique as the high-est energy short pulse laser and is a source for highflux, moderate-energy x-ray radiography [31,32]; however peak intensities are only marginally relativistic due to the large spot size and long-focal length of the final optics. Previous experiments have hinted that electron temperatures exceeding ponderomotive scaling [33][34][35] may be possible at relatively low intensities. However, questions remain as to the exact mechanism responsible for these observations and whether one can take advantage of the high energies at ARC to generate spectra which have applications normally associated with relativistic intensity lasers.…”

Effect of rear surface fields on hot, refluxing and escaping electron populations via numerical simulations

“…The laser to electron conversion efficiency has been found to scale as a function of intensity [1,2] . The absorption efficiency depends on numerous laser pulse and plasma parameters, such as scale length of the preformed plasma [3,4] and focal spot size [5] , each of which changes how the laser energy is coupled to the electrons. The accelerated electrons typically have a thermal/Maxwellian or relativistic Maxwellian distribution of energies whose temperature directly scales to the on-shot laser intensity [6][7][8] , with temperatures from ≈100 keV to several MeV for the highest achievable intensities [9][10][11][12][13][14] .…”