The harmonic spectra generated by atoms in the presence of an ionized neighborhood are investigated. Numerical calculations in a one-dimensional model show an increase of the maximum harmonic energy radiated that leads to photon frequencies well beyond the single-atom cutoff Ip + 3.17Up. We identify these harmonics with those generated when the atom's detached electron is captured by a neighboring ion. By means of classical considerations, we give simple laws for the new harmonic cutoff in the tunneling and the multiphoton ionization regimes.
© 1996 Optical Society of America
Pablo Moreno, Luis Plaja, and Luis Roso, "High-order harmonic generation in a partially ionized medium," J. Opt. Soc. Am. B 13, 430-435 (1996)