Photo induced dynamics in the low frequency regime

There is an increasing interest in the study of photo induced dynamics in the low frequency regime, mainly due to the rapid development of the attosecond physics. Expansion of Floquet quasi-energy solutions of the time dependent Schrodinger equation for time periodic fields, becomes hard to apply. This is due to the contribution of many coupled Floquet channels in the photo induced dynamics. In our study we derive methods to calculate numerically the resonance Floquet states, in the low frequency regime, in order to make the calculation of the photo induced low frequency dynamics more accessible.
We have developed a perturbation theory where the zero-order Hamiltonian is the adiabatic Hamiltonian, and by a simple transformation to dimensionless time units, the laser frequency is obtained as the perturbation strength parameter. We use the zero-order solutions as a basis set for variational Floquet approach in the low frequency regime.
The results show that few adiabatic solutions are sufficient for describing the dynamics of the system, thus greatly reducing the dimensions of the Floquet Hamiltonian. This approach also provides a physical intuition into low frequency dynamics.