EXCESS-PHOTON ABSORPTION IN A NEGATIVE-ION

A time-of-flight and angular selection of the electrons ejected by multiphoton detachment of F- at the wavelength 1064 nm yields the first experimental evidence for excess-photon absorption in a short-range potential. This makes the coherent character of excess-photon ionization or detachment conspicuous, for no photons could be absorbed by an electron which has untied its bonds to the atomic core. The experimental angular distributions are compared to theoretical angular distributions which were obtained within the free-electron approximation. The time-of-flight spectra of the ejected electrons show that slow detached electrons can receive a super-acceleration of more than 1 eV from ponderomotive effects.