dorsal/arxiv
View SchemaInvestigations of Amplitude and Phase Excitation Profiles in Femtosecond Coherence Spectroscopy
| Authors | Anand T. N. Kumar, Florin Rosca, Allan Widom, Paul M. Champion |
|---|---|
| Categories | |
| ArXiv ID | physics/0008221 |
| URL | https://arxiv.org/abs/physics/0008221 |
| DOI | 10.1063/1.1329640 |
Abstract
We present an effective linear response approach to pump-probe femtosecond coherence spectroscopy in the well separated pulse limit. The treatment presented here is based on a displaced and squeezed state representation for the non-stationary states induced by an ultrashort pump laser pulse or a chemical reaction. The subsequent response of the system to a delayed probe pulse is modeled using closed form non-stationary linear response functions, valid for a multimode vibronically coupled system at arbitrary temperature. When pump-probe signals are simulated using the linear response functions, with the mean nuclear positions and momenta obtained from a rigorous moment analysis of the pump induced (doorway) state, the signals are found to be in excellent agreement with the conventional third order response approach. The key advantages offered by the moment analysis based linear response approach include a clear physical interpretation of the amplitude and phase of oscillatory pump-probe signals, a dramatic improvement in computation times, a direct connection between pump-probe signals and equilibrium absorption and dispersion lineshapes, and the ability to incorporate coherence such as those created by rapid non-radiative surface crossing. We demonstrate these aspects using numerical simulations, and also apply the present approach to the interpretation of experimental amplitude and phase measurements on reactive and non-reactive samples of the heme protein Myoglobin. The role played by inhomogeneous broadening in the observed amplitude and phase profiles is discussed in detail. We also investigate overtone signals in the context of reaction driven coherent motion.
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"abstract": "We present an effective linear response approach to pump-probe femtosecond\ncoherence spectroscopy in the well separated pulse limit. The treatment\npresented here is based on a displaced and squeezed state representation for\nthe non-stationary states induced by an ultrashort pump laser pulse or a\nchemical reaction. The subsequent response of the system to a delayed probe\npulse is modeled using closed form non-stationary linear response functions,\nvalid for a multimode vibronically coupled system at arbitrary temperature.\nWhen pump-probe signals are simulated using the linear response functions, with\nthe mean nuclear positions and momenta obtained from a rigorous moment analysis\nof the pump induced (doorway) state, the signals are found to be in excellent\nagreement with the conventional third order response approach. The key\nadvantages offered by the moment analysis based linear response approach\ninclude a clear physical interpretation of the amplitude and phase of\noscillatory pump-probe signals, a dramatic improvement in computation times, a\ndirect connection between pump-probe signals and equilibrium absorption and\ndispersion lineshapes, and the ability to incorporate coherence such as those\ncreated by rapid non-radiative surface crossing. We demonstrate these aspects\nusing numerical simulations, and also apply the present approach to the\ninterpretation of experimental amplitude and phase measurements on reactive and\nnon-reactive samples of the heme protein Myoglobin. The role played by\ninhomogeneous broadening in the observed amplitude and phase profiles is\ndiscussed in detail. We also investigate overtone signals in the context of\nreaction driven coherent motion.",
"arxiv_id": "physics/0008221",
"authors": [
"Anand T. N. Kumar",
"Florin Rosca",
"Allan Widom",
"Paul M. Champion"
],
"categories": [
"physics.chem-ph",
"physics.bio-ph",
"physics.optics"
],
"doi": "10.1063/1.1329640",
"title": "Investigations of Amplitude and Phase Excitation Profiles in Femtosecond Coherence Spectroscopy",
"url": "https://arxiv.org/abs/physics/0008221"
},
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