Ultrafast nonlinear optical responses

The ability to achieve ultrafast nonlinear optical response in a nonabsorbing material is crucial in applications such as all-optical switches and other nonlinear devices for integrated optical circuits. In a conventional Fabry-Perot... 

For these classes of conjugated molecular and polymer structures, the principal property is that their nonreson-ant, nonlinear optical responses are dominated by ultrafast, virtual excitations of the ir-electron states. This was directly demonstrated by MNA (2-methyl-4-nitroaniline) single crystal measurements of macroscopic second order susceptibilities at do (j 3) and optical frequencies (13-1 ) and combined second harmonic measurements and theo-... 

A recent review on the nonlinear optical response and ultrafast dynamics in has emphasized on the difficulty of quantum chemistry methods to predict accurate second hyperpolarizabilities of Cgo over the whole frequency range, going from the static limit and small-frequency region to the resonant regions. 

Given this brief summary of the electron solvation data, the reader is urged to consult the references cited for the more extensive arguments that lie behind the points made above. In order to examine the microscopic response of the molecules in the liquid to the electron, we designed a series of ultrafast nonlinear optical experiments (in the absence of e ) in which we would specifically investigate the rotation, libration, vibration, and other (as then unknown) dynamical responses of a molecule suddenly polarized in a strong, transient laser field. This naturally led to the field of nonlinear optical phenomena and quantum electronics, which we will briefly discuss in the following section. 

An alternative quasiparticle description of the optical response is possible using the nonlinear exciton equations (NEE) (39). The response function is then represented in terms of one-exciton Green functions and exciton-exciton scattering matrix. Four coherent ultrafast 2D techniques have been proposed (16,17), and computer simulations of the 2D response were performed for model aggregates made out of a few two-level chromophores. 

For centuries, metal nanoparticles have never ceased to attract scientists and artists from many diverse cultures. In this section we briefly introduce a phenomenon of metal nanoparticles that still inspires scientists localized surface plasmon resonance (LSPR) (Hutter and Fendler, 2004). Metal nanoparticles show nonlinear electronic transport (single-electron transport of Coulomb blockade) and nonlinear/ultrafast optical response due to the SPR. Conduction electrons (—) and ionic cores (-F) in a metal form a plasma state. When external electric fields (i.e., electromagnetic waves, electron beams etc.) are applied to a metal, electrons move so as to screen perturbed charge distribution, move beyond the neutral states, return to the neutral states, and so on. This collective motion of electrons is called a plasma oscillation. SPR is a collective excitation mode of the plasma localized near the surface. Electrons confined in a nanoparticle conform the LSPR mode. The resonance frequency of the surface plasmon is different... 

Nonlinear optical properties of PTs which exhibit ultrafast responses and large nonlinearities attributed to one-dimensionality and delocalization of n-electrons along the polymer chains are also described [403,404]. Poly(4,4 -dipentoxy-2,2 -bithiophene) and poly(4,4 -dipentoxy-2,2 5, 2"-terthiophene) show a fast and high third-order nonlinearity [405]. Third-order nonlinearities depend on the nature of the polymer backbone and only slightly on the substituents [406], The optical transparency and the third-order optical nonlinearities can be tailored in random copolymers of 3-methylthiophene and methyl methacrylate [407]. A solution-processable thiophene copolymer with a side... 

NMR. nuclear magnetic resonance non-bridging oxygens (NBO), 25 nonlinear optical properties nonlinear electron polarization, 389 optical Kerr effect, 389 optical susceptibility, 389 second harmonic generation, 389 ultrafast response, 389 non-Newtonian flow, 240 non-oxides, 47... 

The remainder of this chapter is organized in four parts. ELECTRON SOLVATION TIMES IN POLAR LIQUIDS briefly summarizes the electron solvation data available from various laboratories by the NATO ASI 1987 conference date FEMTOSECOND LASER SPECTROSCOPY outlines the novel femtosecond laser spectroscopy techniques for studying ultrafast molecular motion EXPERIMENTAL RESULTS ON FEMTOSECOND KERR RESPONSES presents the femtosecond nonlinear optical data recently obtained by us for several simple organic liquids and, in concluding, examines how these ultrafast responses could be linked to future experiment and theory of electron localization and solvation. 

Ultrafast Responses in 7i-conjugated Polymers with Large Optical Nonlinearity... 

Incoherent light sources can effectively be used to determine ultrafast relaxation times, in particular T2, by means of transient four-wave mixing in relatively simple, inhomogeneously broadened two-level systems. The most important feature is that material nonlinear responses with incoherent light are dispersion-free, and are essentially suitable to achieve ultrahigh time-resolution in the extremely short time region. For optical transitions with very fast cross-relaxation or with complicated multi-level structure, incoherent sources are not so effective for the above purpose. 

The ultrafast optical nonlinearities of an aminonitrile 60 derivative and its complex were also studied. From ultrafast OKE experiments the second-order hyperpolarizability values (7,) of Cgo(H2NCN), and C6o[Cr(H20),+y(H2NCN)5 J are larger than that of 60 From the transient response, which was primarily pulse limited, the relaxation time of the samples has l en found to be shorter than the laser pulse width. 

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