Intra- and intercycle interference of angle-resolved electron emission in laser-assisted XUV atomic ionization

Abstract

A theoretical study of ionization of the hydrogen atom due to an XUV pulse in the presence of an IR laser is presented. Well-established theories are usually used to describe the laser assisted photoelectron effect. However, the well-known softphoton approximation firstly posed by Maquet et al in Journal of Modern Optics 54 1847 (2007) and Kazansky's theory in Phys. Rev. A 82, 033420 (2010) completely fails to predict the electron emission prependicularly to the polarization direction. Making use of a semiclassical model, we study the angle-resolved energy distribution of photoelectrons for the case that both fields are linearly polarized in the same direction. We thoroughly analize and characterize two different emission regions in the angle-energy domain: (i) the parallel-like region with contribution of two classical trajectories per optical cycle and (ii) the perpendicular-like region with contribution of four classical trajectories per optical cycle. We show that our semiclassical model is able to asses the interference patterns of the angle-resolved photoelectron spectrum in the two different mentioned regions. Electron trajectories stemming from different optical laser cycles give rise to angle-independent intercycle interference known as sidebands. These sidebands are modulated by an angle-dependent coarse-grained structure coming from the intracycle interference of the electron trajectories born during the same optical cycle. We show the accuracy of our semiclassical model as a function of the time delay between the IR and the XUV pulses and also as a function of the laser intensity by comparing the semiclassical predictions of the angle-resolved photoelectron spectrum with the continuum-distorted wave strong field approximation and the ab initio solution of the time dependent Schrödinger equation

Retrieving intracycle interference in angular-resolved laser-assisted photoemission from argon

“…We can also observe in Fig. 2 (a) that the sidebands are modulated by angle-and energy-dependent stripes whose origin stem from the interference of electron emission within the same optical cycle, i.e., the intracycle interference pattern (see [16,17,18]). In Fig.…”

“…The respective TDSE and SFA energy-angle distributions in Fig. 2 (a) and (b) extend a bit beyond the classical boundaries drawn as dashed lines [18] due to the quantum nature of the final wave function. We observe that the electron emission is more probable along the polarization axis, i.e.…”

“…For example, the simple man's model [13] has been very useful for the case of above-threshold ionization (ATI) by one-color lasers where it is possible to describe the photoelectron spectra as the interplay of intra-and intercycle interferences of electrons' trajectories [14,15]. On equal footing, the photoelectron spectra of LAPE has recently been treated as an interference problem in the time domain [16,17,18]. Electron trajectories stemming from different optical laser cycles give rise to intercycle interference, which results in new peaks, known as sidebands, modulated by a coarse-grained structure coming from the intracycle interference of the electron trajectories born during the same optical cycle [16,17,18].…”

“…On equal footing, the photoelectron spectra of LAPE has recently been treated as an interference problem in the time domain [16,17,18]. Electron trajectories stemming from different optical laser cycles give rise to intercycle interference, which results in new peaks, known as sidebands, modulated by a coarse-grained structure coming from the intracycle interference of the electron trajectories born during the same optical cycle [16,17,18].…”

Interference in $ω-2ω$ atomic ionization within the strong-field approximation: Beyond the perturbative regime

“…3b). Such discontinuities are an artifact of the SPA and also appears for laser assisted photoionization emission (two colors with one frequency much higher than the other) [54,55]. Again, the minima of the interhalfcycle rings do not match with the sidebands of the intercycle factor in Figs.…”