Floquet analysis of real-time wavefunctions without solving the Floquet equation

摘要

We propose a method to obtain Floquet states---also known as light-inducedstates---and their quasi-energies from real-time wavefunctions without solvingthe Floquet equation. This is useful for the analysis of various phenomena intime-dependent quantum dynamics if the Hamiltonian is not strictly periodic, asin short laser pulses, for instance. There, the population of the Floquetstates depends on the pulse form and is automatically contained in thereal-time wavefunction but not in the standard Floquet approach. Severalexamples in the area of intense laser-atom interaction are exemplarilydiscussed: (i) the observation of even harmonics for an inversion-symmetricpotential with a single bound state; (ii) the dependence of the population ofFloquet states on (gauge) transformations and the emergence of an invariant,observable photoelectron spectrum; (iii) the driving of resonant transitionsbetween dressed states, i.e., the dressing of dressed states, and (iv) spectralenhancements at channel closings due to the ponderomotive shift ofabove-threshold ionization peaks.