Measuring ionization time lag of polar molecules with a calibrated attoclock

Electrons in atoms and molecules can not respond immediately to the action of intense laser field. There is a time lag (about 100 attoseconds) between instants of the field maximum and the ionization-rate maximum. This lag characterizes the response time of the electronic wave function to a strong-field ionization event and has important effects on dynamics of the ionized electron. For polar molecules with a large permanent dipole, the direct measurement or calculation of the absolute time lag is difficult. Here, a calibrated attoclock procedure, which is related to a simple Coulomb-induced temporal correction to electron trajectories, is proposed to measure the relative time lag of two different ionization events. Using this procedure, the relative lag of polar molecules in two consecutive half laser cycles can be probed with high time resolution.