Intensity-dependent nonlinear coupling

Figure 5. Experimental setup for the intensity-dependent nonlinear coupling measurement. The sample, as shown in the inset, is mounted on an x-ray spectrogoniometer and the polarized light is incident on the PDA film surface at an angle, 0.

The experimental technique used to measure the third order nonlinear susceptibilities of polydiacetylenes was developed recently at our laboratory. (15) This technique utilizes the intensity-dependent dispersion relation of confined modes of PDA films and determines by measuring the change of coupling angles with... 

The existence of the nonlinear polarization field does not ensure the generation of significant signal fields. With the exception of phenomena based on an intensity-dependent refractive index, the generation of the nonlinearly produced signal waves at frequency cos can be treated in the slowly varying amplitude approximation with well-known guided wave coupled mode theory (1). As already explicitly assumed in Equation 1, the amplitudes of the waves are allowed to vary slowly with... 

Induced-charge and second-kind electrokinetic phenomena arise due to electrohydrodynamic effects in the electric double layer, but the term nonlinear electrokinetic phenomena is also sometimes used more broadly to include any fluid or particle motion, which depends nonlinearly on an applied electric field, fit the classical effect of dielectrophoresis mentioned above, electrostatic stresses on a polarized dielectric particle in a dielectric liquid cause dielectro-phoretic motion of particles and cells along the gradient of the field intensity (oc VE ). In electrothermal effects, an electric field induces bulk temperature gradients by Joule heating, which in turn cause gradients in the permittivity and conductivity that couple to the field to drive nonlinear flows, e.g., via Maxwell stresses oc E Ve. In cases of flexible solids and emulsions, there can also be nonlinear electromechanical effects coupling the... 

This is the case for CdS in acidic or basic aqueous solution where photocurrents are nonlinear at low-light intensities and the dependence of on pH is non-Nernstian. (20) Recent observations by Bard and Wrighton(14,15) indicate that Fermi level pinning and therefore supra-band edge charge transfer can occur in Si and GaAs in those systems (i.e., CH CN/t n-Bu NjClO ) with various redox couples where little electrolyte interaction is anticipated. 

The SHG intensity from interfaces is determined by the second-order nonlinear susceptibility and the Fresnel coefficients. The SHG spectra of the probe pulses change depending on the transient electronic population and the orientation of the chromophores through these physical quantities. Hohlfeld and coworkers have studied hot electron dynamics in thin metal films by this technique [21]. From the transient response of the SHG intensity, electronic temperature decay due to the electron-phonon coupling in the metal substrate is extracted. Eisenthal and coworkers have studied ultrafast excited state dynamics of dye molecules at liquid interfaces [22]. Particularly, the isomerization dynamics of an organic dye at the interfaces was found to become significantly slower than in the bulk. 

A wide variety of molecular properties can be accurately obtained with ADF. The time-dependent DFT implementation " yields UV/Vis spectra (singlet and triplet excitation energies, as well as oscillator strengths), frequency-dependent (hyper)polarizabilities (nonlinear optics), Raman intensities, and van der Waals dispersion coefficients. Rotatory strengths and optical rotatory dispersion (optical properties of chiral molecules ), as well as frequency-dependent dielectric functions for periodic structures, have been implemented as well. NMR chemical shifts and spin-spin couplingsESR (EPR) f-tensors, magnetic and electric hyperfme tensors are available, as well as more standard properties like IR frequencies and intensities, and multipole moments. Relativistic effects (ZORA and spin-orbit coupling) can be included for most properties. 

Phase-dependent coherence and interference can be induced in a multi-level atomic system coupled by multiple laser fields. Two simple examples are presented here, a three-level A-type system coupled by four laser fields and a four-level double A-type system coupled also by four laser fields. The four laser fields induce the coherent nonlinear optical processes and open multiple transitions channels. The quantum interference among the multiple channels depends on the relative phase difference of the laser fields. Simple experiments show that constructive or destructive interference associated with multiple two-photon Raman channels in the two coherently coupled systems can be controlled by the relative phase of the laser fields. Rich spectral features exhibiting multiple transparency windows and absorption peaks are observed. The multicolor EIT-type system may be useful for a variety of application in coherent nonlinear optics and quantum optics such as manipulation of group velocities of multicolor, multiple light pulses, for optical switching at ultra-low light intensities, for precision spectroscopic measurements, and for phase control of the quantum state manipulation and quantum memory. 

---