Electronic dephasing time

Passino S A, Nagasawa Y, Joo T and Fleming G R 1996 Photon echo measurements in liquids using pulses longer than the electronic dephasing time Ultrafast Phenomena X ed P Barbara, W Knox, WZinth and J Fujimoto (Berlin Springer) pp 199-200... 

Lawless, M.K., Mathies, R.A. Excited state structure and electronic dephasing time of nile blue from absolute resonance Raman intensities, J. Chem. Phys. 96, 8037-8045 (1992)... 

In the last chapter, we used a steady-state treatment to relate the shape of an absorption band to the dynamics of relaxations in the excited state. Because a period on the order of the electronic dephasing time will be required to establish a steady state, Eqs. (10.43) and (10.44) apply only on time scales longer than this. We need to escape this limitation if we hope to explore the relaxation dynamics themselves. Our first goal in this chapter is to develop a more general approach for analyzing spectroscopic experiments on femtosecond and picosecond time scales. This provides a platform for discussing how pump-probe and photon-echo experiments can be used to probe the dynamics of structural flucmations and the transfer of energy or electrons on these short time scales. 

To is the pure electronic dephasing time, Ti is the excited-state lifetime, and... 

In order to obtain kinetic parameters for the electron transfer of [11] /K +, the dephasing time tm of the electron-spin echo near the phase-transition temperature Tt was measured. These experiments gave a correlation time tc of 100 ns for the electron transfer at Tg = 170 K. From the assumption of an exponential decrease of c in solution, a value of 100 ps was estimated for tc at room temperature (Rautter, 1989 Rautter et al., 1992). 

In the first reported measurements made with picosecond pulses, an optical beam splitter was used to pick off a portion of the pulse train and a variable optical delay path was introduced between the two beams [7]. The main beam was used to excite (pump) a dye sample, and the weak (probe) beam was used to monitor the recovery of dye transmission as a function of delay. Over the past two decades, this pump-probe method has been extended to a variety of measurement geometries and used to measure electronic polarization dephasing times as well as population lifetimes. 

Interactions of pump and probe pulses with a material absorption are usually described by density matrix equations for a distribution of two-level or three-level systems. The formulation of these equations can be found in textbooks and other reviews [8,9]. We try here simply to describe in physical terms the ways in which the different parameters of the equations manifest themselves experimentally. The simplest theoretical case is the two-level system, in which is the dephasing time of the coherently induced electronic polarization and Tj is the energy relaxation time. We begin our discussion by simplifying even further and assuming that Tj is very short compared to the optical pulse durations. Then, the coherent polarization follows the optical... 

Quite often, spin dephasing times are orders of magnitude shorter than the decay times measured in the (incoherent) population relaxation experiments. For a few transition metal chelates in the excited triplet state we will argue later that the homogeneous spin dephasing is determined by hyperfine interactions of the triplet electron spin with randomly flipping ligand nuclear spins. 

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