Subject：The departure time of electrons in strong-field ionization
Speaker：Prof. Manfred Lein
Emcee：Prof. Hongcheng Ni
Time：17:00 pm. 29th Oct, 2020
Place：Tencent Meeting（ID：918 247 205）
Abstract：
When atoms or molecules are ionized by a short intense laser pulse, the variation of the electric field strength on a subcycle time scale implies that the outgoing electrons depart preferentially around the maximum of the electric field. We will discuss several methods to observe the electron departure time with attosecond precision. From previous work it is well known that the ionization time in a near-circularly polarized pulse can be measured using the attoclock technique, where the electron emission angle is mapped to the departure time by an appropriate model. On the other hand, two-color high-harmonic generation, i.e. measurement of the emitted extreme violet radiation upon irradiation of a strong fundamental field and a weak additional probe field, is a tool to measure the ionization time in a linearly polarized field. We will see that a bicircular ionizing field, i.e. a waveform composed of two different circularly polarized colors, offers the possibility to compare the attoclock and two-color method for one and the same ionizing field. For the two-color high-harmonic generation scheme, we find that a high-frequency probe field rather than the commonly used second-harmonic field is suitable for measuring the shift of the electron departure time due to the Coulomb binding potential.
