Optical coefficients, dynamical nonlinear

By extension one may say that the power laws (5-7) which determine the magnitude of the linear and nonlinear optical coefficients are consequences of this strong electron-lattice coupling. We now make the conjecture that the time response of these coefficients is severely affected by the dynamics of the electron-lattice coupling in conjugated chains when two or more resonant chemical structures can coexist this is the case for many of the organic chains of Figure 2. 

Dynamical Nonlinear Optical Coefficients from the SDMRG Method... 

One of the main properties of interest in the field of conjugated polymers is the study of their dynamic nonlinear optical (NLO) response [112, 113]. It is a major challenge to obtain reliable dynamics of interacting electron systems. While for short oligomers there exist reasonable approximations for computing these properties [114], for longer chains even within model Hamiltonian approximations, the dynamic NLO coefficients had proved elusive. Yet most interest lies in the longer chains since the dynamic NLO properties exhibit dominant finite-size effects. 

Of central importance for understanding the fundamental properties of ferroelec-trics is dynamics of the crystal lattice, which is closely related to the phenomenon of ferroelectricity [1]. The soft-mode theory of displacive ferroelectrics [65] has established the relationship between the polar optical vibrational modes and the spontaneous polarization. The lowest-frequency transverse optical phonon, called the soft mode, involves the same atomic displacements as those responsible for the appearance of spontaneous polarization, and the soft mode instability at Curie temperature causes the ferroelectric phase transition. The soft-mode behavior is also related to such properties of ferroelectric materials as high dielectric constant, large piezoelectric coefficients, and dielectric nonlinearity, which are extremely important for technological applications. The Lyddane-Sachs-Teller (LST) relation connects the macroscopic dielectric constants of a material with its microscopic properties - optical phonon frequencies ... 

Theoretical calculations have been made on stilbene which are relevant to photoisomerization dynamics. MNDO calculations of stilbene potential energy properties shows no evidence of a doubly excited "phantom" state but a singly excited state with adiabatic rotation around the central ethylene bond has only a small barrier on this path23T Calculations of dipole moments, optical spectra, and second order hyperpolarizability coefficients of some mono- and disubstituted stilbene molecules allows the design of useful nonlinear optical molecules 38. 

The thermal optical nonlinearity of TM74A under short laser pulse excitation has also been studied by a dynamic grating technique. For visible laser pulses (the second harmonic of a Nd YAG laser at 0.53 pm) and an absorption constant a 2 cm (determined by the absorbing dye dopant concentrationX the measured nonUnear index coefficient 2 is on the order of about -2 X10 " cm AV. 

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