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

摘要： We study strong-?eld ionization of H and selected rare-gas atoms by solving the three-dimensional time-dependent Schr?dinger equation in the single-active-electron approximation with particular attention to the effect of pulse length on the total ionization yields (TIYs) produced by counter-rotating bicircular (CRBC) lasers compared to co-rotating bicircular (COBC) lasers. To this end, TIYs, photoelectron momentum distributions, and above-threshold ionization spectra are presented for various pulse durations and peak intensities. For pulses containing ?ve or more cycles of the fundamental near-infrared laser ?eld, the CRBC/COBC ratio of TIYs is affected due to ionization via excited states and multiphoton ionization channels. For pulses containing less than ?ve cycles, the CRBC/COBC ratio of TIYs depends on both the frequency combination and number of optical cycles: With the 1ω-2ω frequency combination, the ratio of TIYs is enhanced (reduced) for pulses with an odd (even) number of optical cycles. The 1ω-3ω frequency combination was considered for pulses containing two or three optical cycles, and for both pulse lengths the CRBC/COBC ratio of TIYs is less than unity.