Abstract
The recent progress in experimental studies of laser-assisted electron scattering (LAES) induced by ultrashort intense laser fields is reviewed. After a brief survey of the theoretical backgrounds of the LAES process and earlier LAES experiments started in the 1970s, new concepts of optical gating and optical streaking for the LAES processes, which can be realized by LAES experiments using ultrashort intense laser pulses, are discussed. A new experimental setup designed for measurements of LAES induced by ultrashort intense laser fields is described. The experimental results of the energy spectra, angular distributions, and laser polarization dependence of the LAES signals are presented with the results of the numerical simulations. A light-dressing effect that appeared in the recorded LAES signals is also shown with the results of the numerical calculations. In addition, as applications of the LAES process, laser-assisted electron diffraction and THz-wave-assisted electron diffraction, both of which have been developed for the determination of instantaneous geometrical structure of molecules, are introduced.
Highlights
Laser-assisted electron scattering (LAES), which is known as free–free transition (FFT), consists of electron-atom scattering under the presence of laser fields, resulting in the appearance of laser-induced sidebands with the interval of the photon energy in the energy spectra of scattered electrons (i.e., Ef = Ei + nhω, where Ei and Ef are the kinetic energies of the incident electron and the scattered electron, respectively; his the Plank constant; ω is the angular frequency of the laser field; and n is an integer number)
In addition to the interest in collision physics, the LAES process is an important elementary process included in a wide variety of phenomena induced by laser fields such as electron heating in laser plasma [1], scattering of recolliding photoelectrons in intense laser fields [2,3], emission of high-energy photoelectrons from dense gas media in intense laser fields [4], and the conductance properties of doped semiconductors interacting with laser fields [5]
Experimental studies of LAES processes started in the 1970s [6,7,8], and for more than three decades, continuous CO2 lasers and pulsed CO2 lasers with a temporal duration of microseconds have been employed in experiments
Summary
Under the first Born approximation of the scattering process between a target atom and an electron expressed as an eigenfunction of a free electron in an electromagnetic field (i.e., a Gordon–Volkov wavefunction [13,14]), they derived the differential cross section for net n-photon absorption, dσ(n) BFA /dΩ, as (n) dσBFA dΩ. Where dσel (Ẽi ; s)/dΩ is the differential cross section of the elastic electron scattering; pf = pi − }s ← pi , occurring without laser fields with an incident electron whose initial momentum, pi , and the initial kinetic energy, Ẽi , are defined as pi = pi + nme ωα0 /(α0 · s) and Ẽi = pi /(2me ), respectively. Non-perturbative interactions between laser fields and atoms in high-energy electron-atom scattering processes can be treated in the Born–Floquet theory proposed by Faisal [25], or in the non-Hermitian. Other theoretical methods to investigate LAES processes have been proposed on the basis of a variety of models and approximations as reviewed in [8]
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