The lifetime of atomic hydrogen exposed to an intense ‘‘high-frequency’’ linearly polarized laser field has been calculated, in a Sturmian-Floquet approach, for the case where the atom is initially in an excited state with m=3, 4, 5, or 6, l=m, m+1, or m+2, and n≤8, for several wavelengths between 455 and 1064 nm. In this range of parameters, the intensity at which the lifetime of the atom reaches a minimum value is given in good approximation by a simple ‘‘empirical’’ law. The lifetime is longer than that predicted by previous approximate Floquet calculations, and its minimum occurs at a smaller intensity. Results for higher-lying Rydberg states are also presented.

• Received 24 March 1993

DOI:https://doi.org/10.1103/PhysRevA.48.R46