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Characterization and Application of Isolated Attosecond Pulses
 Date Issued:
 2012
 Abstract/Description:
 Tracking and controlling the dynamic evolution of matter under the influence of external fields is among the most fundamental goals of physics. In the microcosm, the motion of electrons follows the laws of quantum mechanics and evolves on the timescale set by the atomic unit of time, 24 attoseconds. While only a few timedependent quantum mechanical systems can be solved theoretically, recent advances in the generation, characterization, and application of isolated attosecond pulses and fewcycle femtosecond lasers have given experimentalists the necessary tools for dynamic measurements on these systems. However, pioneering studies in attosecond science have so far been limited to the measurement of free electron dynamics, which can in most cases be described approximately using classical mechanics. Novel tools and techniques for studying bound states of matter are therefore desired to test the available theoretical models and to enrich our understanding of the quantum world on asyet unprecedented timescales.In this work, attosecond transient absorption spectroscopy with ultrabroadband attosecond pulses is presented as a technique for direct measurement of electron dynamics in quantum systems, demonstrating for the first time that the attosecond transient absorption technique allows for stateresolved and simultaneous measurement of bound and continuum state dynamics. The helium atom is the primary target of the presented studies, owing to its accessibility to theoretical modeling with both ab initio simulations and to model systems with reduced dimensionality. In these studies, ultrafast dynamics () on timescales shorter than the laser cycle () are observed in prototypical quantum mechanical processes such as the AC Stark and ponderomotive energy level shifts, Rabi oscillations and electromagneticallyinduced absorption and transparency, and twocolor multiphoton absorption to (")dark(") states of the atom. These features are observed in both bound states and quasibound autoionizing states of the atom. Furthermore, dynamic interference oscillations, corresponding to quantum path interferences involving bound and free electronic states of the atom, are observed for the first time in an optical measurement. These first experiments demonstrate the applicability of attosecond transient absorption spectroscopy with ultrabroadband attosecond pulses to the study and control of electron dynamics in quantum mechanical systems with high fidelity and state selectivity. The technique is therefore ideally suited for the study of charge transfer and collective electron motion in more complex systems.The transient absorption studies on atomic bound states require ultrabroadband attosecond pulses ? attosecond pulses with large spectral bandwidth compared to their central frequency. This is due to the fact that the bound states in which we are interested lie only 1525 eV above the ground state, so the central frequency of the pulse should lie in this range. On the other hand, the bandwidth needed to generate an isolated 100 as pulse exceeds 18 eV () comparable to or even larger than the central frequency. However, current methods for characterizing attosecond pulses require that the attosecond pulse spectrum bandwidth is small compared to its central frequency, known as the central momentum approximation. We therefore explore the limits of attosecond pulse characterization using the current technology and propose a novel method for characterizing ultrabroadband attosecond pules, which we term PROOF (phase retrieval by omega oscillation filtering). We demonstrate the PROOF technique with both simulated and experimental data, culminating in the characterization of a worldrecordbreaking 67 as pulse.
Title:  Characterization and Application of Isolated Attosecond Pulses. 
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Name(s): 
Chini, Michael, Author Chang, Zenghu, Committee Chair Saha, Haripada, Committee Member Chow, Lee, Committee Member Schulzgen, Axel, Committee Member University of Central Florida, Degree Grantor 

Type of Resource:  text  
Date Issued:  2012  
Publisher:  University of Central Florida  
Language(s):  English  
Abstract/Description:  Tracking and controlling the dynamic evolution of matter under the influence of external fields is among the most fundamental goals of physics. In the microcosm, the motion of electrons follows the laws of quantum mechanics and evolves on the timescale set by the atomic unit of time, 24 attoseconds. While only a few timedependent quantum mechanical systems can be solved theoretically, recent advances in the generation, characterization, and application of isolated attosecond pulses and fewcycle femtosecond lasers have given experimentalists the necessary tools for dynamic measurements on these systems. However, pioneering studies in attosecond science have so far been limited to the measurement of free electron dynamics, which can in most cases be described approximately using classical mechanics. Novel tools and techniques for studying bound states of matter are therefore desired to test the available theoretical models and to enrich our understanding of the quantum world on asyet unprecedented timescales.In this work, attosecond transient absorption spectroscopy with ultrabroadband attosecond pulses is presented as a technique for direct measurement of electron dynamics in quantum systems, demonstrating for the first time that the attosecond transient absorption technique allows for stateresolved and simultaneous measurement of bound and continuum state dynamics. The helium atom is the primary target of the presented studies, owing to its accessibility to theoretical modeling with both ab initio simulations and to model systems with reduced dimensionality. In these studies, ultrafast dynamics () on timescales shorter than the laser cycle () are observed in prototypical quantum mechanical processes such as the AC Stark and ponderomotive energy level shifts, Rabi oscillations and electromagneticallyinduced absorption and transparency, and twocolor multiphoton absorption to (")dark(") states of the atom. These features are observed in both bound states and quasibound autoionizing states of the atom. Furthermore, dynamic interference oscillations, corresponding to quantum path interferences involving bound and free electronic states of the atom, are observed for the first time in an optical measurement. These first experiments demonstrate the applicability of attosecond transient absorption spectroscopy with ultrabroadband attosecond pulses to the study and control of electron dynamics in quantum mechanical systems with high fidelity and state selectivity. The technique is therefore ideally suited for the study of charge transfer and collective electron motion in more complex systems.The transient absorption studies on atomic bound states require ultrabroadband attosecond pulses ? attosecond pulses with large spectral bandwidth compared to their central frequency. This is due to the fact that the bound states in which we are interested lie only 1525 eV above the ground state, so the central frequency of the pulse should lie in this range. On the other hand, the bandwidth needed to generate an isolated 100 as pulse exceeds 18 eV () comparable to or even larger than the central frequency. However, current methods for characterizing attosecond pulses require that the attosecond pulse spectrum bandwidth is small compared to its central frequency, known as the central momentum approximation. We therefore explore the limits of attosecond pulse characterization using the current technology and propose a novel method for characterizing ultrabroadband attosecond pules, which we term PROOF (phase retrieval by omega oscillation filtering). We demonstrate the PROOF technique with both simulated and experimental data, culminating in the characterization of a worldrecordbreaking 67 as pulse.  
Identifier:  CFE0004781 (IID), ucf:49802 (fedora)  
Note(s): 
20121201 Ph.D. Sciences, Physics Doctoral This record was generated from author submitted information. 

Subject(s):  attosecond  femtosecond  laser  spectroscopy  ultrafast  atomic physics  optics  optical physics  
Persistent Link to This Record:  http://purl.flvc.org/ucf/fd/CFE0004781  
Restrictions on Access:  campus 20140615  
Host Institution:  UCF 