Three-dimensional relativistic model of a bound particle in an intense laser field. II

Using an exactly solvable model of a bound Klein-Gordon particle in an intense laser field we obtain the above-threshold energy spectra of the ejected electron for intensities in the range I=7×${10}^{14}$ W/${\mathrm{cm}}^2$ to ${10}^{20}$ W/${\mathrm{cm}}^2$, and compare them with the predictions of the Schrödinger theory. The present calculations also allow us to test an approximation for relativistic intensities, which should be useful for real systems.