Retrieval of target structure information from laser-induced photoelectrons by few-cycle bicircular laser fields

Abstract

By analyzing theoretical results from a numerical solution of the time-dependent Schrödinger equation for atoms in few-cycle bicircular laser pulses, we show that high-energy photoelectron momentum spectra can be used to extract accurate elastic scattering differential cross sections of the target ion with free electrons. We find that the retrieval range for a scattering angle with bicircular pulses is wider than with linearly polarized pulses, although the retrieval method has to be modified to account for different returning directions of the electron in the continuum. This result can be used to extend the range of applicability of ultrafast imaging techniques such as laser-induced electron diffraction and for the accurate characterization of laser pulses. DOI: 10.1103/PhysRevA.95.031402 With the advent of few-cycle intense laser technology, ultrafast imaging techniques such as laser-induced electron diffraction (LIED) [1][2][3][4][5][6][7][8][9][10][11][12] and high-order harmonic spectroscopy (HHS) [13][14][15][16][17][18][19] have recently been proposed. These techniques have been demonstrated to be capable of imaging molecular structural changes with unprecedented subangstrom spatial and few-femtosecond temporal resolutions [10,11,14,19]. Both these techniques are based on the rescattering physics [20,21] with linearly polarized laser pulses.Quite recently, efficient high-order harmonic generation with bicircular pulses has been achieved [22,23], which provides a new tabletop circularly polarized coherent extreme ultraviolet to soft x-ray source with photon energies up to 160 eV [24]. Subsequently, these harmonics have been demonstrated to be very sensitive to electronic structure [25][26][27][28][29][30][31]. Clearly, in a bicircular pulse, after tunneling ionization from the target, the electron in the continuum is driven in a two-dimensional (2D) plane of the laser polarizations, instead of being confined to the laser polarization direction, as in the linearly polarized case. This fact has been utilized by Mancuso et al. [32] as a way to decouple the electron tunneling angle from the rescattering angle. Mancuso et al. found that this decoupling in turn leads to the separation of rescattered electrons in the low-energy region, in contrast to the linearly polarized case, where they are normally contaminated by the direct electrons.Previous experimental studies of electron spectra in bicircular laser fields have been mostly limited to the low-energy region so far [32,33]. On the theory side, both low-and high-energy regions have been studied by the strong-field approximation (SFA) [34,35] as well as the classical trajectory Monte Carlo method [33]. However, these works mainly focused on a comparison with experiments at low energies [33] or analyzing the SFA results in terms of the quantum orbit theory [34,35].In this Rapid Communication, based on the numerical solution of the time-dependent Schrödinger equation (TDSE) for different atoms in few-cycle bicircular laser pulses, we show that high-energy ph...

Attoclock with counter-rotating bicircular laser fields

“…There is thus a true need to devise an approach for cleaner investigation of the time structure of ionization in linear polarization. In this work we demonstrate that the ionization step in (almost) linear polarization can be probed using an attoclocklike setup involving bicircular fields [42], which have already been used successfully to investigate various aspects of strong-field ionization [43][44][45][46][47][48][49]. The term bicircular field refers to the superposition of two circularly polarized fields with different wavelength.…”

Symmetries and Selection Rules of the Spectra of Photoelectrons and High-Order Harmonics Generated by Field-Driven Atoms and Molecules

“…The situation would be similar for an elliptically polarized field, but radically different for two-color fields. Few-cycle bicircular laser fields were considered in [128].…”

Pulse-length effects in strong-field ionization of atoms by co-rotating and counter-rotating bicircular laser pulses

“…In recent years, the use of BC laser pulses to explore ionization dynamics and high-order-harmonic generation (HHG) from atoms and molecules in strong laser fields [1][2][3][4][5][6][7][8][9][10][11][12][13] has led to breakthroughs in controlling the ionization process [5,6], probing the phase and amplitude of the emitted wave packets [12], and producing circularly polarized extreme ultraviolet high harmonics [13]. Here our focus is strong-field ionization of atoms and molecules by BC pulses, and investigation of the information contents of above-threshold ionization (ATI) spectra and photoelectron momentum distributions (PMDs) produced by such lasers.…”