Attoclock with counter-rotating bicircular laser fields

Abstract

The attoclock technique which maps the emission time of a photoelectron to its detection angle is an important tool in strong-field physics. Previously, it was implemented only with circularly or elliptically polarized laser fields. Here, we show how counter-rotating bicircular laser fields can be used as an attoclock to investigate the ionization dynamics in quasilinear polarization. This is achieved by choosing the ratio of the two field strengths in a way such that the vector potential has aspects of the attoclock and time is mapped directly to the photoelectron momentum, but the shape of the electric field corresponds to approximately linear polarization during three intervals per optical cycle. We report momentum distributions calculated by solving the time-dependent Schrödinger equation for a model helium atom and obtain the mapping from photoelectron momentum to ionization time using a trajectory-free method. Unlike circular polarization where the time of maximal ionization rate typically deviates less than 5 attoseconds from the maximium of the electric field, we find positive ionization times of more than 10 attoseconds in the quasilinear case.

Quantum battles in attoscience: tunnelling

“…The numerical saddle-point method [62] uses a trajectory-free language and establishes a connection between the final momentum of the photoelectron and the numerical saddle-point time for the full Hamiltonian including the Coulomb potential. It supports the conclusion of instantaneous tunnelling.…”

“…-Figure 3 exemplifies the pulse duration and wave form dependence, as well as an energy dependence between the different ATI rings in the long pulse case, which show different angular maxima [55][56][57]. This raises concerns about the validity of one single time (rather than a distribution of times) extracted typically from data, thus averaging over the energy dependence.…”

“…The resulting shifts in the extracted values were smaller than or of the order of the reported error bars for experimental data. Nevertheless, it is important to keep in mind that different coordinate system transforms and peak angle extraction methods lead to significant shifts in the extracted angle and thus the interpreted delay time [62]. Regarding the third component, the laser propagation direction, so far no significant difference has been found between a projection to or a cut along the polarisation plane.…”

Photoionization of chiral molecules by counter-rotating bicircular laser fields: a chiral attoclock

“…In our studies we replace the elliptically polarized field of the standard attoclock by a tailored field synthesized by combining a fundamental and its second harmonic counter-rotating circularly polarized fields [24][25][26][27] . This combination produces an electric field of C 3 rotational symmetry (inset in Fig.…”

“…The relevance of Counter-rotating BiCircular BiChromatic (CBCBC) fields for attoclock measurements was recently theoretically established 27 . In order to obtain an intuitive picture of the electron dynamics in such fields, we start by studying atomic photoionization, using classical trajectory Monte Carlo (CTMC) simulations.…”