Abstract
We present a general method for calculating two-photon processes in real atoms by a variant of the usual multichannel quantum-defect theory (MQDT). Most notably, this method enables us to describe processes in which a single photon has enough energy to ionize the atom (above-threshold processes). All effects of intermediate Rydberg series, continua, or autoionizing series are treated on an equal footing and with the same ease; the final state is also treated properly by standard MQDT. This method should also work for many three- or four-photon processes.
- Received 13 June 1991
DOI:https://doi.org/10.1103/PhysRevLett.67.3066
©1991 American Physical Society