Harmonic generation in ionizing systems by the complex scaled adiabatic-switch method

An adiabatic-switch method for calculating harmonic generation under intense laser radiation is presented. The adiabatic switch is first applied to nonbound (i.e., ionizing or dissociative) time-periodic Hamiltonians when the energy spectrum is degenerate. Our derivation is based on the use of Floquet theory combined with complex scaling and of a generalized definition of the inner product for non-Hermitian operators. A model potential representing a Xe atom in the presence of a laser field is studied as an example to illustrate the numerical advantages of the present method and its stability.