Photodetachment-threshold shifts in two-frequency radiation fields

The one-dimensional Schrödinger equation was solved numerically to observe the effects of a strong radiation field on the photodetachment-threshold behavior of a model negative ion. The negative ion is exposed to a near-threshold single-photon detaching radiation pulse while in the presence of a second, constant-intensity, low-frequency field. As the second field frequency is increased from zero to the photodetachment threshold, we observe a gradual transition from the interference effects found for detachment into a static field (dc limit) to the increased energy required to detach an electron into a strong oscillatory field (ac limit). The detachment-threshold shift occurs because the second field drags temporarily detached low-energy electrons back across the potential, where they are reattached. This detachment, excursion, and reattachment process is quite fragile, particularly in three dimensions, and will lead to leakage detachment below the shifted threshold.