Complex spatial structure of ion yield arising from high-intensity multiphoton ionization

Recent measurements of the electron-energy distribution for high-intensity short-pulse multiphoton ionization in xenon have yielded a spectrum unexpectedly rich in well-resolved peaks, apparently arising from optical Stark shifts of atomic levels into resonance with harmonics of the ionizing laser. Here we show that such a resonance structure is, quite generally, accompanied by a surprisingly complex spatial structure of the total ionization yield. We predict this spatial structure to arise in a wide variety of multiphoton experiments.