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** Dynamics of Slowly Phase-Modulated Periodic Waves **

** Effects of Modulation during the Evolution Period **

** Modulated Structures with Large Periods in Homeotropic Nematics **

Under MAS the quadrupole splitting becomes time dependent, Qg = Qg (f) (see Sect. 2.3.4). This influences both the spin-locking behavior [223] and the polarization transfer [224], with the latter being further affected by the periodic modulation of the IS dipolar interaction. The effect of MAS on spin-locking of the S magnetization depends on the magnitude of the so-called adiabaticity parameter ... [Pg.167]

The CP dynamics is affected both by the periodic modulation of Qg and by the periodic modulation of the I-S dipolar interaction [216, 224]. Assuming that the... [Pg.167]

Summary. Coherent optical phonons are the lattice atoms vibrating in phase with each other over a macroscopic spatial region. With sub-10 fs laser pulses, one can impulsively excite the coherent phonons of a frequency up to 50THz, and detect them optically as a periodic modulation of electric susceptibility. The generation and relaxation processes depend critically on the coupling of the phonon mode to photoexcited electrons. Real-time observation of coherent phonons can thus offer crucial insight into the dynamic nature of the coupling, especially in extremely nonequilibrium conditions under intense photoexcitation. [Pg.23]

With development of ultrashort pulsed lasers, coherently generated lattice dynamics was found, first as the periodic modulation in the transient grating signal from perylene in 1985 by De Silvestri and coworkers [1], Shortly later, similar modulation was observed in the reflectivity of Bi and Sb [2] and of GaAs [3], as well as in the transmissivity of YBCO [4] by different groups. Since then, the coherent optical phonon spectroscopy has been a simple and powerful tool to probe femtosecond lattice dynamics in a wide range of solid... [Pg.23]

The most striking feature of the coherent G mode was the periodic modulation in its frequency (Fig. 2.16) [55]. As the modulation period coincided... [Pg.37]

Coherent optical phonons can couple with localized excitations such as excitons and defect centers. For example, strong exciton-phonon coupling was demonstrated for lead phtalocyanine (PbPc) [79] and Cul [80] as an intense enhancement of the coherent phonon amplitude at the excitonic resonances. In alkali halides [81-83], nuclear wave-packets localized near F centers were observed as periodic modulations of the luminescence spectra. [Pg.42]

In combination with DFT calculations, the time- and depth-dependent phonon frequency allows to estimate the effective diffusion rate of 2.3 cm2 s 1 and the electron-hole thermalization time of 260 fs for highly excited carriers. A recent experiment by the same group looked at the (101) and (112) diffractions in search of the coherent Eg phonons. They observed a periodic modulation at 1.3 THz, which was much slower than that expected for the Eg mode, and attributed the oscillation to the squeezed phonon states [9]. [Pg.49]

Coherent lattice motions can create periodic modulation of the electronic band structure. Time-resolved photo-emission (TRPE) studies [20-22] demonstrated the capability to detect coherent phonons as an oscillatory shift of... [Pg.52]

film/substrate (or at both) interface (Fig. 15.4b). The incident beam illuminates this grating and one of the diffraction orders will excite the modes. The mode s effective refractive index can be calculated from the so-called grating equation10,30. [Pg.403]

The first observations on the development of periodic modulations were made on Pt surfaces annealed in vacuum in the temperature range 920 to 1300C[9J. The 1-dimensional grating structures were made by mechanically ruling portions of gratings on polycrystalline Pt specimens. Annealing caused extensive... [Pg.25]

The periodic modulation decay method can in principle be applied to any type of material, metals, semiconductors, ceramics, polymers and to bofli... [Pg.36]

The signal for the 41 amu transient, a measure of the time-dependent rise and fall of BrCH2CH2CH2, rises (xi = 2.5 ps) and then decays (X2 = 7.5 ps), and it shows the same periodic coherent modulation, with a characteristic oscillation time Xc = 680 fs, phased shifted by n radians The local peaks of signal intensity proportionate to the BrCH2CH2CH2 radical concentration match the local troughs of signal decay for the 202 amu periodic modulation they are 180° out of phase. [Pg.909]

The optimal parameters for maximal IC/EET converge reproducibly in successive optimisation runs. Most importantly, we find that the optimal value of the periodic modulation is 2re/viightb=160 25cm 1 (Fig. 2b). The control of IC/EET is best if the modulation is as deep as possible, with a=n, generating 8 subpulses. Previously we have shown that also parameter c, and thus the relative carrier phase, has a decisive influence on the control effect [2],... [Pg.92]

[Pg.93]

system driven by a combination of the stochastic reference beam and the periodically modulated input beam (Im(t) = /m I A cosilt), the equation for the phase takes on the form... [Pg.482]

With directional quenching we present an effective mechanism to induce periodic stripe patterns in phase separating systems, where the wavelength of the patterns is uniquely selected by the velocity of a quench interface. If an additional spatially periodic modulation of the quench interface is introduced, cellular patterns can also be generated. [Pg.189]

Finally, we have studied the influence of a periodic modulation... [Pg.192]

For systems where thermodiffusive effects can be neglected, we have presented results on the effects of directional quenching where the control parameter jumps the critical temperature from above to below and where the location of the jump is moved with a finite velocity v. We have shown how, by this method, regular structures are created during the process of phase separation behind the moving quench interface. Moreover, it was shown that the wavelength of periodic stripe patterns is uniquely selected by the velocity of the quench interface. If an additional spatially periodic modulation of the quench interface is introduced, cellular patterns can also be generated. [Pg.195]

** Dynamics of Slowly Phase-Modulated Periodic Waves **

** Effects of Modulation during the Evolution Period **

** Modulated Structures with Large Periods in Homeotropic Nematics **

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