Observation of full ponderomotive shift for the photodetachment threshold in a strong laser field

Electron-energy-resolved measurements of the threshold shift of negative chlorine ions have been performed under the influence of a strong (4.5 x l0¹³ W/m²) infrared laser field. The threshold shift is found to be in accordance with a full ponderomotive shift. Explanations are proposed for previously measured smaller-than-expected threshold shifts.