Experiments on multiphoton free-free transitions

Abstract

Multiphoton free-free transitions are detected in the scattering of electrons on argon atoms and on hydrogen molecules in the presence of an intense pulsed CO, laser field. The authors present measurements for several values of the incoming electron energy, the electron scattering angle, and the angle between the laser polarization vector and the electron momentum transfer. All observations are in qualitative agreement with a recent theoretical model based on a low-frequency approximation.

Laser-assisted free-free transition in electron-atom collisions

“…= 0.117 eV, i.e., we are dealing with soft photons so that the KWA approach can be used safely [7], since the KWA [9] is mainly valid at low laser frequencies, where the photon energy is much less than the characteristic excitation energies of the atomic target and the incident electron energy [14]. This particular choice of the low-frequency laser field is in accordance with the experiments [3,4,7] performed for the LA FF transitions of the inert-gas atoms. The strength of the laser field ε 0 = 0.01 a.u.…”

“…Since in a FF transition the target does not change state, its own energy spectrum can be neglected for a less intense as well as a lowfrequency field. The measurements on the LA FF transitions [2][3][4][5][6][7][8] for single [2] or multiphoton exchanges [3][4][5][6][7][8] are so far limited to the experimentally preferred inert gas atomic targets only. For theoretical calculations, on the other hand, atomic hydrogen is the simplest and ideal target to have a better insight into the process.…”

“…Earlier measurements on the LA FF transition [3][4][5][6][7] for some inert gas atoms at low incident energies indicated that the Kroll-Watson [9] approximation (KWA) was inadequate for low scattering angles but works well for larger angles in the presence of a CO 2 laser. The origin of this discrepancy at lower scattering angles could be attributed to the fact that, at very low incident energies, the laser induces a dipole potential of the order 1/r 2 , the effect of which decreases with increasing incident energy as well as for backward angles [7].…”

Amplification of Millimeter-Wave Radiation by Stimulated Emission of Bremsstrahlung

“…3 They form a suprathermal tail, of temperature T h9 on the plasma electron energy distribution. In simulations, 1 kT h is found to coincide with the wave-breaking energy, given by the wellknown formula 4 It is interesting to note that there was considerable disagreement concerning amplification in a plasma about twenty years ago, especially between Browne 10 ' 11 and Twiss 12 * 13 over the possibility of maser action in space.…”

Multiphoton Absorption by Electrons

“…Interaction of electrons with the intense laser field may also be directly measured in a scattering experiment; a recent experiment in this direction has measured the absorption of up to three photons with the C0 2 laser, 4 and a more recent one measured up to five photons. 5 The experimental arrangement is shown in Fig. 1.…”