Measuring Coulomb-Induced Ionization Time Lag with a Calibrated Attoclock

Abstract

Electrons in atoms and molecules can not react immediately to the action of intense laser field. A time lag (about 100 attoseconds) between instants of the field maximum and the ionizationrate maximum emerges. This lag characterizes the response time of the electronic wave function to the strong-field ionization event and has important effects on subsequent ultrafast dynamics of the ionized electron. The absolute time lag is not accessible in experiments. Here, a calibrated attoclock procedure, which is related to a simple Coulomb-induced temporal correction to electron trajectories, is proposed to measure the relative lag of two different ionization events. Using this procedure, the difference (i.e., the relative lag) between the ionization time lags of polar molecules in two consecutive half laser cycles can be probed with a high accuracy.

Strong-field response time and its implications on attosecond measurement

“…Further studies also show that due to the PD effect, there is a difference of the response time of polar molecules between the first half of the laser cycle and the second half. The difference can be characterized by the ratio of the PMD in different quadrants in the orthogonal two-color field [39], and also by the offset angle of the PMD in the elliptically-polarized laser field [40]. Considering the Coulomb-induced temporal correction to electron trajectory, the usual attoclock can be calibrated to establish a direct one-to-one correspondence between time and photoelectron momentum.…”

“…Considering the Coulomb-induced temporal correction to electron trajectory, the usual attoclock can be calibrated to establish a direct one-to-one correspondence between time and photoelectron momentum. Then the response time can be read directly from the Coulomb-corrected attoclock, especially the relative response time between different electronic states [40].…”

“…Due to the effect of permanent dipole, the dynamics of polar molecules in the intense laser field includes the basic quantum mechanical processes such as tunneling, excitation and Stark shift, and the motion of electrons relative to different nuclei forms a natural contrast. This provides an ideal platform for the study of response time, which is not only convenient to study the internal relationship between these basic processes and response time, but also convenient to study the relative response time, and to test the applicability of the strong-field theoretical model [39,40].…”

Response time of photoemission at quantum-classic boundary

“…Recent studies have also shown that the Coulomb effect can induce a large ionization time lag [21] relative to SM and SFA predictions. The inclusion of the time lag into the SM mapping relation is able to qualitatively explain complex strong-field phenomena [21][22][23]. However, a general theory description for this lag is not acquirable and the physical origin of this lag is unclear.…”

“…Here, γ L = w 2I p /E L is the Keldysh parameter [27]. A similar expression to the adiabatic one has been used in [23] to deduce the lag τ and has been termed as Coulombcalibrated attoclock (CCAC). Here, the theory description is given.…”