Subcycle laser control and quantum interferences in attosecond photoabsorption of neon

The dynamics of an atom in a strong infrared laser field (1013 W/cm2) result in substantial changes to the field-free electronic energy levels, which can be probed on time scales shorter than the laser cycle using isolated attosecond pulses. Here, we measure the transient absorption of an isolated attosecond pulse by laser-dressed bound states of neon near the first ionization threshold. The observed subcycle changes in the absorption spectrum result from both laser-induced ac Stark shifts and from quantum interferences between different multiphoton excitation pathways. We further demonstrate the ability to experimentally turn off the quantum interference mechanism by eliminating one of the interfering pathways