| In this thesis, attosecond transient absorption spectroscopy is demonstrated. Firstly,the basic theory of high-order harmonic generation are introduced and the mechanism of quasi-phase-matching in a dual-gas multijet array is investigated. Secondly, various gating technologies for singling an isolate attosecond pulse out of an attosecond pulse train, as well as the methods used to characterize ultrabroadband attosecond pulses are introduced.In addition, we successfully compressed isolated attosecond pulses down to 67 attosecond by tailoring their spectrum and properly compensating their intrinsic chirp. Thirdly,an attoseond transient absorption spectroscopy experimental system was developed, and the basic theory of attosecond transient absorption spectroscopy is introduced. In addition, we designed an extreme ultraviolet spectrometer with high resolution, which was calibrated by an in-situ calibration method proposed by us. Fourthly, attosecond transient absorption experiments with helium atoms were performed. We observed sub-cycle AC Stark shift, Autler-Townes splitting, quantum path interference, light induced structure and sub-cycle change of ionization threshold in the experiments. Fifthly, attosecond transient absorption experiments were performed with complex atomic systems(neon atoms)and molecular system(hydrogen molecules). Although direct numerical simulation of the ten-electron neon atom is still impossible, we demonstrate that the dynamics can still be interpreted through time-dependent Schrodinger equation simulations relying on the single active electron approximation. Furthermore, we experimentally demonstrated the ability to ”turn off” the quantum interference by removing the indirect excitation pathway.In the transient absorption spectrum of hydrogen molecules, we observed both electronic and nuclear dynamics, and this is the first attosecond transient absorption experiment performed with molecular systems. |
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