Characterizing subcycle electron dynamics of polar molecules by asymmetry in photoelectron momentum distributions

Strong-field ionization of polar molecules contains rich dynamical processes such as tunneling, excitation, and Stark shift. These processes occur on a subcycle timescale and are difficult to distinguish in ultrafast measurements. Here, with the developed strong-field model considering the effects of both Coulomb and permanent dipoles, we show that photoelectron momentum distributions (PMDs) in orthogonal two-color laser fields can be utilized to resolve these processes with attosecond-scale resolution. A feature quantity related to the asymmetry in PMDs is obtained, with which the complex electron dynamics of polar molecules in each half laser cycle is characterized and the subtle time difference when electrons escape from different sides of the polar molecule is identified.