Nonresonant Excess Photon Detachment of Negative Hydrogen Ions

We report the first observation of nonresonant excess photon absorption (for ionization as well as detachment) in competition with the single photon process. A 35keV negative hydrogen ion beam is irradiated with focused Nd:YAG laser pulses; the 1.165eV photon energy exceeds the electron binding energy by 0.41eV. The time of flight spectrum of detached electrons exhibits the absorption of one and two photons. The detached electrons exit with a P wave angular distribution for the one-photon detachment and primarily a D wave for the two photon excess photon detachment. {copyright} {ital 1997} {ital The American Physical Society}