Optical dephasing

Nagasawa Y, Passino S A, Joo T and Fleming G R 1997 Temperature dependence of optical dephasing in an organic polymer glass J. Chem. Phys. 106 4840-52... 

Kummer S, Mais S and Basche T 1995 Measurement of optical dephasing of a single terrylene molecule with nanosecond time resolution J. Chem. Phys. 99 17 078-81... 

Wlrile tire Bms fonnula can be used to locate tire spectral position of tire excitonic state, tliere is no equivalent a priori description of the spectral widtli of tliis state. These bandwidtlis have been attributed to a combination of effects, including inlromogeneous broadening arising from size dispersion, optical dephasing from exciton-surface and exciton-phonon scattering, and fast lifetimes resulting from surface localization 1167, 168, 170, 1711. Due to tire complex nature of tliese line shapes, tliere have been few quantitative calculations of absorjDtion spectra. This situation is in contrast witli tliat of metal nanoparticles, where a more quantitative level of prediction is possible. 

If the system under consideration possesses non-adiabatic electronic couplings within the excited-state vibronic manifold, the latter approach no longer is applicable. Recently, we have developed a simple model which allows for the explicit calculation of RF s for electronically nonadiabatic systems coupled to a heat bath [2]. The model is based on a phenomenological dissipation ansatz which describes the major bath-induced relaxation processes excited-state population decay, optical dephasing, and vibrational relaxation. The model has been applied for the calculation of the time and frequency gated spontaneous emission spectra for model nonadiabatic electron-transfer systems. The predictions of the model have been tested against more accurate calculations performed within the Redfield formalism [2]. It is natural, therefore, to extend this... 

Radiationless Relaxation and Optical Dephasing of Molecules Excited by Wide- and Narrow-Band Lasers. II. Pentacene in Low-Temperature Mixed Crystals, T. E. Orlowski and A. H. Zewail, J. Chem. Phys. 70, 1390 (1979). 

Vohringer P, Arnett D, Westervelt R, Feldstein M, Scherer NF. Optical dephasing on femtosecond timescales direct measurement and calculation from solvent spectral densities. J Chem Phys 1995 102 4027-4036. 

Yang T-S, Vohringer P, Arnett DC, Scherer NF. The solvent spectral density and vibrational multimode approach to optical dephasing two-pulse photon echo response. J Chem Phys 1995 103 8346-8359. 

Bai YS, Fayer MD. Time scales and optical dephasing measurements Investigation of dynamics in complex systems. Phys Rev B 1989 39 11066-11084. 

The accumulated 3-pulse stimulated photon-echo method " was used in order to monitor vibrational relaxation times of the first excited electronic state of pentacene. Two amplified dye lasers were used to perform ps photon-echo measurements on pentacene and naphthalene samples, which established that pseudo-local photon scattering was responsible for optical dephasing in vibronic transitions. A mode-locked cavity-dumped synchronously pumped dye laser system was used to demonstrate long coherence times for the delocalized optical excitation of dimer states, by ps photon-echo spectroscopy. ... 

Hesselink W H and Wiersma D A 1980 Optical dephasing and vibronic relaxation in molecular mixed crystals a picosecond photon echo and optical study of pentacene in naphthalene and p-terphenyl J. Chem. Phys. 73 648-63... 

In recent years high-resolution photochemical hole-burning has shown to be an important technique to study homogeneous lineshapes of molecules in the condensed phase. Especially the unique possibility of measuring simultaneously the low-temperature linewidth and shift" has added much to our understanding of optical dephasing processes. So far however, the relationship between the observed hole-width and optical dephasing constants was not firmly established. 

We will defer discussion of the proposed mechanism for optical dephasing to Section IX. In a recent paper by Voelker and Macfarlane photochemical hole-burning is used to monitor (supposedly) the vibrational relaxation times of over a dozen excited state modes in porphin. A large variation in vibrational lifetimes ( l-50 ps) was measured whereby no systematic variation as a function of vibrational frequency was found. This result is graphically depicted in Fig. 12. It is not yet clear whether the... 

In Fig. 18 we exhibit the results of both a two-pulse and a three-pulse echo measurement at low temperature on pentacene in p-terphenyl. The important point to note is that the echo decay times are identical but shorter than the fluorescence lifetime for this more concentrated crystal. The implication is that at higher concentration, optical dephasing is also caused by energy-transfer processes in this system and that the process is irreversible (7 ,-type). 

In molecules, as noted by de Vries and Wiersma, the application of free induction decay to study optical dephasing may be frustrated by the presence of an intermediate triplet state. The level scheme, which is representative for most molecules with an even number of electrons, is shown in Fig. 26. For an applied laser field E =EQCOs t-k ), that is resonant with the (2 <- 1) transition, we may write, in the RWA approximation, the following steady-state density matrix equations, which describe the coherent decay after laser frequency switching ... 

Recently quite a number of theories have been advanced to explain optical dephasing in electronic transitions of molecules in solids. 

There are several ways of proceeding from here to arrive at the master equation for the reduced density matrix. The Zwanzig projection operator technique in Liouville space or the Kubo cumulant expansion may be used and both methods have recently been applied to study optical dephasing in solids. 

Prior to presenting some results of these approaches it seems useful to discuss the hamiltonian and partitioning thereof to describe optical dephasing. 

Presently there is no consensus whether or not resonant phonons play a dominant role in optical dephasing phenomena. Indeed the only clear example of resonant phonon-induced dephasing is the case of tetracene in p-terphenyl. ... 

This motivated de Bree and Wiersma, following the theories presented for dephasing by van t Hof and Schmidt and Harris, to try and define the microscopic mixed-crystal Hamiltonian that would be suitable to emphasize the special role that resonant phonons may play in optical dephasing phenomena. For the simple case of an electronic transition... 

Recently Jones and Zewail have, using a Green function approach, also studied optical dephasing in solids. The Hamiltonian is partitioned as follows ... 

We conclude this section by noting that, in contrast to a statement of Jones and Zewail in Ref. 90, the contribution of the optical phonon branch to optical dephasing may well be distinguished from that of exchange by studying the optical dephasing characteristics of several different guests in the same host crystal. 

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