Enhanced inverse bremsstrahlung heating rates in a strong laser field

Abstract

Test particle studies of electron scattering on ions, in an oscillatory electromagnetic field have shown that standard theoretical assumptions of small angle collisions and phase independent orbits are incorrect for electron trajectories with drift velocities smaller than quiver velocity amplitude. This leads to significant enhancement of the electron energy gain and the inverse bremsstrahlung heating rate in strong laser fields. Nonlinear processes such as Coulomb focusing and correlated collisions of electrons being brought back to the same ion by the oscillatory field are responsible for large angle, head-on scattering processes. The statistical importance of these trajectories has been examined for mono-energetic beam-like, Maxwellian and highly anisotropic electron distribution functions. A new scaling of the inverse bremsstrahlung heating rate with drift velocity and laser intensity is discussed.

Cluster-assisted multiple-ionization of methyl iodide by a nanosecond laser: Wavelength dependence of multiple-charge ions

“…Initially, the electron energy is less than that of single photon, so only photon absorption occurs. During this process, the rate of photon absorption varies with k 4 [25][26][27][28], where k is the laser wavelength. Once the electron energy is larger than that of single photon, induced photon emission will also occur.…”

“…Once the electron energy is larger than that of single photon, induced photon emission will also occur. Then, the rate of energy increase by inverse bremsstrahlung absorption (i.e., the averaged rate of photon absorption minus the rate of induced photon emission) is defined as the product of the ponderomotive potential (given by U p (eV) = 9.3 Â 10 À14 [I(W/cm 2 )] [k 2 (lm 2 )]) and the total effective collision frequency [29], which depends on the electron-neutral species collision frequency and electron-ion collision frequency [28,30]. At the beginning of stage 2, the cluster is only singly ionized, and the energy gain for the caged electrons is mainly ascribed to electron-neutral species collisions.…”

Electron–ion collision rates in atomic clusters irradiated by femtosecond laser pulses

“…The influence of the laser field on the scattering processes could be neglected for typical laser intensities of approximately 10 15 W/cm 2 . For higher intensities, staying in the non-relativistic regime, one has to generalize the approach of Fraiman et al [28], see also [29], who considered the scattering on Coulomb centers in external fields, for the case of realistic model potentials.…”

Cluster assistant generation of C2+ and C3+ ions in nanosecond laser ionization of seeded benzene beam

“…The laser deposits its energy into the electrons in the plasma and this energy deposition is through collisional inverse bremsstrahlung (IBS) due to the collisions between the ions and electrons [25][26][27]. The electrons are heated to very high temperature (higher than the ionized potential of clusters), and the primary ionized process in the plasma is collisional ionization.…”