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Horvath, Balint (2009): Generation, characterization and sub-cycle shaping of intense, few-cycle light waveforms for attosecond spectroscopy. Dissertation, LMU München: Faculty of Physics
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Abstract

Our desire to observe electron dynamics in atoms and molecules on their natural timescale with the tools of attosecond physics demands ever shorter laser pulse durations. The reliance of this young eld on laser pulses is understandable: both the generation and the characterization of attosecond pulses, as well as time-resolved measurements directly use the electrical field that lasts only for a few oscillations of the wave. This also means that exerting control over the evolution of the waveform on a sub-cycle scale can modify the characteristics of attosecond pulses and possibly in a favorable way. In this thesis we introduce a laser system that provides near single-cycle laser pulses and generate through their interaction with gases coherent XUV radiation. Our measurements indicate that the thus produced XUV spectrum supports the potential compressibility to an isolated attosecond pulse of a sub-100 as duration. Considering our already broadband fundamental laser spectrum, we demonstrate moreover a technique to further enhance our spectral intensity in the blue. By frequency-doubling a part of the original spectrum, and controlling the time-delay between the two harmonic laser pulses we show that we can induce a change in the waveform on an attosecond time-scale, suppress or increase some half-cycles or change the effective wavelength of the laser light. Our method's influence on the generation of XUV light is tested via spectral characterization, and we found that broad tunability of the central XUV-energy is possible by a change of the time-delay between the fundamental and the second-harmonic laser pulses. Our results furthermore give strong evidence that waveform-dependent interference of two quantum-paths was observed, which effect comes from two electron-trajectories that are inside one half-cycle of the laser field. It is also of utmost importance to know the level of control over the waveform. To characterize the waveform, we demonstrate here the first single-shot measurement of the carrier-envelope phase (CEP) of a lightpulse. We measured with no phase-ambiguity the CEP of high repetition-rate (3 kHz) non-phase-stabilized and phase-stabilized laser pulses consecutively with an unprecedented measurement precision. Our method uniquely requires no prior phase-stabilization. It opens the door to CEP-tagging with non-phase-stabilized pulses using emerging few-cycle laser systems with relativistic peak intensities.