Prof. Shih-I Chu

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Coherent and Optimal Control of Atomic and Molecular Processes

The study of the coherent control of quantum dynamics in atomic and molecular systems, both the internal and external degrees of freedom, is currently a very active research field in science and technology. In particular, temporally shaped ultrashort laser pulses have been successfully used to design well-defined Rydberg atom wavepackets, to control multiphoton absorption, selective chemical bond dissociation, and optimization of high-order harmonic generation processes, etc. An important operating principle for quantum control of any type is the manipulation of constructive and destructive quantum mechanical interferences. Professor Chu's recent activity in this direction is focused on the investigation of the coherent control of very-high-order (~ 100th-300th order) harmonic generation (HHG) processes for the optimal production of (table-top) x-ray laser light, comb laser, and attosecond (10^-18 second) ultra short laser pulses, etc. We have recently found several new mechanisms for the enhancement and optimization of HHG processes: (a) The coherent control of electron wavepacket motion by means of appropriate application of additional external fields such as crossed laser beams or crossed laser and d.c. magnetic fields, etc., (b) the optimal control of intra-atomic phase matching, namely, optimization of the "dynamical phases" of dipole emission within each half-optical cycle, in attosecond time resolution, by means of genetic algorithm optimization and wavelet time-frequency analysis techniques. This leads to marked improvement in both emission intensity and purity of a given harmonic. These methods are quite general and can be extended to the study of coherent control of other field-induced chemical and physical processes as well. Our most recent activity in this direction is to investigate the optimal generation of single attosecond pulse by coherent control of the carrier-envelope phase (CEP) and dynamical phase of few-cycle laser pulses.

Representative Publications:

D. A. Telnov, J. Y. Wang, and S. I. Chu, Two-color phase-control of high-order harmonic-generation in intense laser fields, Phys. Rev. A 52, 3988–3996 (1995) [BibTeX] [link] [pdf]
X. M. Tong and S. I. Chu, Generation of circularly polarized multiple high-order harmonic emission from two-color crossed laser beams, Phys. Rev. A 58, R2656–R2659 (1998) [BibTeX] [link] [pdf]
X. M. Tong and S. I. Chu, Multiple high-order harmonic generation in the presence of intense laser and static magnetic fields, J. Phys. B: At. Mol. Opt. Phys. 32, 5593–5603 (1999) [BibTeX] [link] [pdf]
X. M. Tong and S. I. Chu, Probing the spectral and temporal structures of high-order harmonic generation in intense laser pulses, Phys. Rev. A 61, 021802(R) (2000) [BibTeX] [link] [pdf]
X. Chu, S. I. Chu, and C. Laughlin, Spectral and temporal structures of high-order harmonic generation of Na in intense mid-ir laser fields, Phys. Rev. A 64, 013406 (2001) [BibTeX] [link] [pdf]
X. Chu and S. I. Chu, Optimization of high-order harmonic generation by genetic algorithm and wavelet time-frequency analysis of quantum dipole emission, Phys. Rev. A 64, 021403(R) (2001) [BibTeX] [link] [pdf]
Z. Y. Zhou and S. I. Chu, Exploration of Coulomb explosion dynamics through excited vibrational states of molecule, Phys. Rev. A 71, 011402(R) (2005) [BibTeX] [link] [pdf]

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Dept. of Chemistry
The University of Kansas