MULTIPHOTON IONIZATION OF THE DELTA-FUNCTION ATOM

We study the one-dimensional and three-dimensional delta-function atom in an electric field with sinusoidal time dependence. Using the exact continuum states of the one-dimensional model we calculate the spectr a of the photoelectrons. The spectra show a series of very high and sh arp multiphoton peaks. The ponderomotive shift of these peaks is analy sed. The three-dimensional problem is reduced to an integro-differenti al equation in time which can be converted into a Volterra integral eq uation. The latter is well suited for functional analytic discussion a nd numerical solution.