Investigation of tunneling processes in laser-induced ionization of argon

Abstract

A method of determining the laser intensity necessary for ionization of atomic states is described. Results are presented for ionization of argon states I–V at 10−4 Torr using a short (25 psec)-pulse neodymium laser at intensities up to 4×1016 W cm−2. The results agree with computer calculations of the Keldysh tunneling model in the regime γ⩽1 and with results previously obtained in helium. The electron energy spectra technique employed further verifies the existence of the ponderomotive force.

Stopping of ions in a plasma irradiated by an intense laser field

“…The results have important applications in radiation and solid-state physics (Ritchie et al, 1975;Tung & Ritchie, 1977;Echenique, 1987), and more recently, in studies of energy deposition by ion beams in inertial confinement fusion (ICF) targets (Arista & Brandt, 1981;Mehlhorn, 1981;Maynard & Deutsch, 1982;Arista & Piriz, 1987;D'Avanzo et al, 1993;Couillaud et al, 1994). On the other hand, the achievement of high-intensity laser beams with frequencies ranging between the infrared and vacuum-ultraviolet region has given rise to the possibility of new studies of interaction processes, such as electronatom scattering in laser fields (Kroll & Watson, 1973;Weingartshofer et al, 1977Weingartshofer et al, , 1983, multiphoton ionization (Lompre et al, 1976;Baldwin & Boreham, 1981), inverse bremsstrahlung and plasma heating (Seely & Harris, 1973;Kim & Pac, 1979;Lima et al, 1979), screening breakdown (Miranda et al, 2005), and other processes of interest for applications in optics, solid-state, and fusion research. In addition, a promising ICF scheme has been recently proposed (Stöckl et al, 1996;Roth et al, 2001), in which the plasma target is irradiated simultaneously by intense laser and ion beams.…”

Measurement of intensity-dependent rates of above-threshold ionization (ATI) of atomic hydrogen at 248 nm

“…This factor, with an appropriate value of A, brings the Keldysh model in the tunneling limit (7 <C 1) into agreement with the accepted rate of tunneling ionization in a dc field (Keldysh 1965). In the case of atomic hydrogen and KrF radiation, A = 13 (Baldwin and Boreham 1981), and Fc « 35 for irradiances below 10 15 W/cm 2 .…”

Metastable noble gas atoms in strong-field ionization experiments

“…These works examined the ionization of helium and argon, comparing the expected electron energies of perturbative multiphoton ionization and a rough comparison of Keldysh tunnelling theory to their observed results for different ionization states. At this point in time, ADK theory had not been developed, but the results strongly disagreed with the expected perturbative electron energies and there was observation of the effect of the ponderomotive force on an ionized electron [44] .…”

“…Following the introduction of the Keldysh parameter as a metric for determining strong-field regime, there was almost two decades where examination of strong-field ionization of atoms could not be performed experimentally due to the lack of lasers capable of providing the electric field amplitude required to reach the strong-field regime. The earliest examples of work examining the strong-field ionization of atoms was performed in the early 1980s at the Australian National University with 1064-nm Nd:glass lasers capable of 1.8 J per 25 ps pulse [44, 45] . These works examined the ionization of helium and argon, comparing the expected electron energies of perturbative multiphoton ionization and a rough comparison of Keldysh tunnelling theory to their observed results for different ionization states.…”

“…The earliest examples of work examining the strong-field ionization of atoms was performed in the early 1980s at the Australian National University with 1064-nm Nd:glass lasers capable of 1.8 J per 25 ps pulse [44,45] . These works examined the ionization of helium and argon, comparing the expected electron energies of perturbative multiphoton ionization and a rough comparison of Keldysh tunnelling theory to their observed results for different ionization states.…”