Observation of resonant excess-photon detachment via a window resonance in the cesium negative ion

Efficient excess-photon detachment to lowest nonvanishing order is observed with long (∼0.7 ns) optical pulses and intensities of ≤6×109 W/cm2. A Feshbach (‘‘window’’) resonance in Cs- suppresses single-photon detachment, while simultaneously enhancing the probability of absorption of one or more excess photons. The perspectives for future spectroscopic excess-photon detachment and studies of direct two-electron multiphoton detachment are briefly discussed.