High harmonic generation by an atom confined in nanoscale cavity

We consider optical high harmonic generation in a hydrogen-like atom confined in a spherical cavity caused by interaction with a monochromatic field. The whole system is considered as to be centrally symmetric, i.e., atomic nucleus as fixed at the center of sphere. In such a spherically symmetric atom, the high harmonic generation spectrum is calculated at different values of the oscillation amplitude, frequency of the external field and size of the confining domain.