Ultrafast Control and Probing on Electron Dynamics in Solids and Gases by Waveform-controlled Sub-2-Cycle Optical Pulses

Abstract

Measurement and manipulation of electron dynamics is a flourishing area of research which catches attention nowadays. Fundamental phenomena, in which electrons are involved, such as electron transition between bands in condensed matter and energy states in atoms, mostly occur at femtosecond or sub-femtosecond time scale. The observation and control of electrons’ behavior has been facilitated owing to the utmost development of laser technology. In this thesis, one of the state-of-the-art light sources, waveform-controlled sub-2-cycle optical laser, was employed to explore the interaction with media in solid and gas phases. In a study with solid media, semimetallization was observed in dielectric crystals subjected to strong laser field. A current was generated and directed by the instantaneous light field. A series of theoretical calculation, based on quadruple sub-band model, showing good agreement with experiment, implies that the semimetallization was brought about by electron transition between and within valence and conduction sub-bands. Semimetallization was observed to be a general response of dielectrics to intense light field. It is accounted for by Wannier-Stark localization, a confinement of electrons in a unit cell of crystal lattice under strong field; the effect of long range crystal structure becomes less important. On the other hand, for a study with gaseous medium, an instrument for single-isolated attosecond pulse, which permits one to trace sub-femtosecond electron dynamics, was constructed. By means of high harmonics generation, a train of XUV attosecond pulses were produced and then underwent spectral filtering to select single XUV burst. The temporal profile of the XUV pulse was attained by analyzing the photoelectron kinetic energy spectrogram, ensuring the generation of a single-isolated attosecond pulse. The attosecond pulse was utilized to examine the AC Stark splitting of noble gas atom exposed to intense light field. The attosecond transient absorption spectroscopy was applied to xenon atoms exposed to an NIR intensity of ~1013W/cm2. The asymmetric AC Stark splitting (or, in other words, Autler-Townes splitting) and sub-cycle oscillation in absorption lines were revealed. Theoretical estimation relying on TDCIS, which was in accordance with experimental findings, asserted that the counter rotating wave effect is responsible for the observation.