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RESEARCH PRODUCT

Ultrafast ionization and rotational dynamics of molecules in strong laser fields

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The investigation of ultrafast molecular dynamics is of great importance towards the understanding of a variety of natural phenomena in physical and chemical sciences. With the rapid development of femtosecond laser systems and precision detection technologies, it is possible now to visualize and steer the motion of molecules in matter as well as the ultrafast dynamics of electrons and nuclei in molecules on a microscopic timescale. When a molecule is exposed to a strong laser field, its electrons can be freed or excited, which often triggers a rapid dissociation of the system, in which the released electrons and nuclei exhibit a strong correlation, while the electronic motion on attosecond timescale is much faster than that of the nuclear ranging from femtosecond to picosecond timescale. One example is the absorbed photon energy shared between electrons and nuclei in a molecular dissociation process. In addition, a lot of physical processes such as electron tunneling ionization show a strong dependence on the spatial direction of the molecular axes with respect to the polarization of the laser field. Confining molecular axes to a specific direction is significant in unambiguously understanding and controlling the ultrafast response of the molecules to the laser fields. Impulsive alignment induced by ultrafast laser pulses with field-free revivals is considered as a powerful method to control the spatiotemporal distribution of the molecules. Field-free alignment is also recognized as an important tool for studying basic physical processes such as rotational dynamics of complex molecules and ultrafast collisional dissipation.By using advanced technologies based on intense femtosecond laser systems, multi-particle coincidence measurements of Cold target recoil ion momentum spectroscopy (COLTRIM), and high-sensitive time-resolved birefringence detections, this thesis reports a variety of studies revealing ultrafast dynamics observed in molecules exposed to strong laser fields, including dissociative Rydberg excitation, tunneling-site-sensitive ionization and dissociation, molecular alignment, rotational echo, and ultrafast collisional dissipation probed by rotational alignment echo.