Abstract

If multiphoton ionization of atoms is performed with short (~100 fs), intense (>10¹³ W/cm²) pulses the kinetic energy spectra of the emitted electrons show sharp peaks.¹ The explanation for these peaks is given in terms of resonance enhancement. Due to the strong ac electric field associated with the light, the ionization threshold and the atomic excited states shift in energy. An excited states shifts into resonance with the ground-state at a particular intensity during the pulse and population is transferred. Single photon ionization out of the excited state occurs during the rest of the pulse.² This gives sharp peaks in the kinetic energy spectrum of the emitted electrons at the photon energy minus the excited state binding energy.

© 1994 IEEE