Dephasing times

Balk M W and Fleming G R 1985 Dependence of the coherence spike on the material dephasIng time In pump-probe experiments J. Chem. Phys. 83 4300-7... 

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... 

Figure 16. Channel phase versus photon energy i/h Ij) centered at intermediate state peak for r=40fs (a) f — — 1.6eV (above resonance) and r 1 = 1010fs. The dephasing time I 1...

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). 

Fig. 5 Radio frequency pulse sequences for measurements of Sj and Si in DSQ-REDOR experiments. The MAS period rR is 100 ps. XY represents a train of 15N n pulses with XY-16 phase patterns [98]. TPPM represents two-pulse phase modulation [99]. In these experiments, M = Nt 4, N2+ N3 = 48, and N2 is incremented from 0 to 48 to produce effective dephasing times from 0 to 9.6 ms. Signals arising from intraresidue 15N-13C DSQ coherence (Si) are selected by standard phase cycling. Signal decay due to the pulse imperfection of 15N pulses is estimated by S2. Decay due to the intermolecular 15N-I3C dipole-dipole couplings is calculated as Si(N2)/S2(N2). The phase cycling scheme can be found in the original figure and caption. (Figure and caption adapted from [45])...

If the dephasing time of the coherent phonons depend critically on the carrier density, photo-injection of carriers with the second pump pulse can annihilate them partially or completely, depending on its fluence but not on its relative timing. Such incoherent control was demonstrated for the LO phonons of GaAs [37],... 

Figure 41 shows the absorption spectrum for the 24-mode model of pyrazine. As was done by Raab et al. [277], we have included a phenomenological dephasing time of T2 = 150 fs to model the experimental broadening due to hnite resolution and rotational motion. It can be seen that the inclusion of all 24 normal modes of the pyrazine molecule leads to a shape of the spectrum which is in good agreement with the experimental result (Fig. 38b). The semiclassical result is seen to be in fairly good agreement with the quantum result. The spurious structure in the semiclassical spectrum is presumably due to the statistical error.

In our context, especially C-Li distances are of interest. A first successful Li- C REDOR study was undertaken in order to establish the structure of the previously discussed TMEDA complex of fluorenyllithium °, prepared from Li-enriched w-butyllithium and fluorene with at natural abundance. The REDOR pulse sequence used is depicted in Figure 20. The number of rotor cycles is increased in a symmetric fashion about the central jr-pulse in order to increase the dephasing time. 

One can see that n2 is close to 1 for strong interaction when Q4/3 [—Ar(0)]1/3. Using results of Ref. [11], one can show that in order of magnitude, [-i(O)]1 4 is equal to 1 /V - reciprocal irreversible dephasing time. By this means relaxation does not destroy ARP for strong interaction when the Rabi frequency exceeds the reciprocal irreversible dephasing time ... 

Determination of femtosecond dephasing times of organic dyes confined in a single spherical microparticle... 

Morphology dependent resonances (MDR) are observed in the fluorescence of 9-amino acridine hydrochloride hydrate (9AAHH) impregnated single microparticles. These MDRs influence the radiative rate of the molecule. From the time-resolved measurement with a resolution of ns we have determined the femtosecond dephasing time of the molecule in a polymer matrix at room temperature. 

However, a study of a few dyes of higher fluorescence quantum yield in polymer microparticles did not show any change in the fluorescence lifetime even though the modification of the fluorescence spectra was observed [4]. In this work, a new molecule (9-amino acridine hydrochloride hydrate, 9AAHH) is reported in which we have observed the effect of MDR in both, the steady state spectra and the fluorescence lifetimes. The dephasing time of 9AAHH in polymer matrix at room temperature have been determined from this study. 

The effect of MDR is experimentally observed in the steady state fluorescence spectra and lifetimes of 9AAHH in single microspheres. From this study, we have determined the femtosecond dephasing time of 9AAHH in PMMA matrix at room temperature. The dephasing time of 9AAHH in PMMA is determined to be 22 fs. 

Bond breaking Bond making time scales Spreading in space dephasing time scales Analogy with Ti and T2... 

S. A. Rice Prof. Woste, your data indicate that rotational dephasing of the coherent wavepacket is unimportant for the time regime you have studied. Unless your beam has an unusually low rotational temperature, it is to be expected that a heavy molecule such as K2 will have many rotational states excited. Because the different isotopic species you have studied, one homonuclear and the other heteronu-clear, would then have different numbers of rotational states in the initial wavepacket, one should expect to observe different rotational dephasing times for the two species. What is the effective rotational temperature of your beam Is it likely that only a very few rotational states are present in the initial wavepacket ... 

---