| Summary: | 碩士 === 國立交通大學 === 物理研究所 === 102 === The atomic and molecular processes induced by intense (~1014 W/cm2) femto-second (10-15 s) lasers have attracted significant attention, both theoretical and experimental. When an intense femto-second laser is irradiated to a molecule, fluorescence signals are emitted from neutral fragments of the molecule. This phenomenon, called the neutral fragmentation, is expected to open new possibilities in laser technologies such as remote sensing and remote lasing. The mechanism may be understood as: (1) highly nonlinear excitation of the molecule, (2) the dissociation of the excited state molecule into electronically excited neutral fragments, (3) fluorescence from the neutral fragments. In spite of its importance, the mechanism of the highly nonlinear excitation has not been well understood.
In this thesis, we take hydrogen atom as an example to examine the mechanism of the highly nonlinear excitation using the Fourier-Floquet spectra. We succeeded in proposing the detailed mechanism, which we find different depending on the parity of the angular momentum of the final state. Furthermore we have shown that the Ramsey fringe, which is believed only applicable in the perturbatively weak field, works nicely in highly nonlinear processes.
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