Third-order Optical Polarizabilities Research Articles

Chirality-dependent absorption and third-order polarizability spectra in open single-wall carbon nanotubes

The optimized configurations and electronic structures have been obtained based on the density-functional theory for finite open single-walled carbon nanotubes of (4,4) and (5,5). The calculated results show that the bond lengths, bond angles, and charge distributions at the tube ends are significantly different from those at the tube wall. Then, the electronic absorption spectra of the two tubes are calculated by the time-dependent density-functional theory. The evidences show agreement between the theoretical and available experimental results. A strong and wide absorption band occurs for the case of light polarized parallel to the tube axis; a weak absorption and large transparent range appear as the case of light polarized perpendicular to the tube axis. Finally, the dynamic third-order optical polarizabilities in the three optical processes are obtained in terms of the sum-over-states method combined with the above-mentioned method. It is found that the anisotropy of the polarizabilities is larger for the (4,4) than (5,5) tube, and the tube with a larger axial length and smaller diameter has a larger third-order optical polarizabilities at nonresonant frequencies. The largest third-order polarizability is in the direction of both the polarized light and basic light along with the tube axis, and two photon excitation states make main contributions to the polarizabilities of the (4,4) and (5,5) tubes.

Optimization of geometrical structure and simulation of the spectra of third-order nonlinear optical polarizabilities inC59SiandC58Si2heterofullerenes

We report the optimized geometrical structures using the ab initio method, and the calculated frequency dependence of the third-order nonlinear optical polarizabilities $\ensuremath{\gamma}$ in the different optical processes of the third-harmonic generation, electric-field induced second-harmonic generation, and degenerate four-wave mixing using the INDO/SDCI method coupled with the sum-over-states method for ${\mathrm{C}}_{59}\mathrm{Si}$ and two isomers of ${\mathrm{C}}_{58}{\mathrm{Si}}_{2}$ heterofullerenes. The optimized structures show that the stabilization of the para isomer of ${\mathrm{C}}_{58}{\mathrm{Si}}_{2}$ is larger than that of the dia isomer of ${\mathrm{C}}_{58}{\mathrm{Si}}_{2},$ and the geometrical modifications of ${\mathrm{C}}_{59}\mathrm{Si}$ and ${\mathrm{C}}_{58}{\mathrm{Si}}_{2}$ isomers occur in the vicinity of the Si-doped atom after the replacement of one or two C atoms by Si atoms in the ${\mathrm{C}}_{60}$ fullerene. The calculated hyperpolarizabilities at nonresonant frequency show the varied trends in the order of ${\mathrm{C}}_{59}\mathrm{Si}\ensuremath{\approx}$ dia isomer of ${\mathrm{C}}_{58}{\mathrm{Si}}_{2}<$ para isomer of ${\mathrm{C}}_{58}{\mathrm{Si}}_{2}$ at ground state and the charge transfers of two-photon states make significant contributions to third-order optical polarizabilities for the para isomer of ${\mathrm{C}}_{58}{\mathrm{Si}}_{2}.$ The enhancement of first excited singlet state is about one or two order of magnitude at nonresonant frequency. The susceptibilities of $\ensuremath{\chi}(\ensuremath{-}\ensuremath{\omega};\ensuremath{\omega},\ensuremath{\omega},\ensuremath{-}\ensuremath{\omega})$ of these Si-doped fullerene films are estimated to be about ${10}^{\ensuremath{-}10}$ esu at first excited state and ${10}^{\ensuremath{-}11}$ esu at ground state in nonresonant frequency.

Enhancement of Third-Order Nonlinear Response in Excited State of Metallophthalocyanines (PcM; M = H2, Mg, Ni)

In this paper we calculate the dynamic third-order nonlinear optical polarizabilities of three optical processes, third-harmonic generation, electric-field-induced second-harmonic generation, and degenerate four-wave mixing, for both ground and first excited singlet states in metal phthalocyanines in terms of the sum-over states formula. The transition moment elements and the transition energies in this formula are obtained using the INDO−SDCI method. The calculated second-order hypolarizabilities show a dispersion behavior with the difference from ground state and an enhancement of third-order nonlinear response in the first excited state. Among the PcM (M = H2, Mg, Ni), there is a large enhancement of the first excited singlet state when there is a small third-order optical polarizability of the ground state. The calculated value of PcNi is compared with the observed one of the substituted PcNi in the order of magnitude. We also gain an understanding of enhancement mechanism for nonlinear processes in t...

Linear and nonlinear optical response of dimethyl-amino-nitro-stilbene (DANS): coupled oscillator representation versus sum-over-states picture

The first-, second-, and third-order optical polarizabilities of dimethyl-amino-nitro-stilbene (DANS) have been calculated on the basis of a coupled oscillator picture and compared to the results obtained within the sum-over-states formalism. The two approaches lead to a very similar description for both static and dynamic responses. The correspondence between the nature of the dominant oscillators and the essential excited states contributing primarily to the linear and nonlinear optical response is emphasized.

Very large optical nonlinearity of semiconductor microcrystallites.

We analyze theoretically the oscillator strength and the third-order optical polarizability X 13, due to excitons in semiconductor microcrystallites. The nonlinear optical polarizability is shown to be greatly enhanced for an assembly of such microcrystallites as the exciton is quantized due to the confinement effect and the excitons in a single microcrystallite interact strongly enough to make the excitons deviate from ideal harmonic oscillators.

Optical Kerr effect induced by picosecond light pulses in tRNA solutions

The optical Kerr effect (OKE) of tRNA solutions induced by picosecond light pulses of a YAG-Nd 3+ laser, λ = 1060 nm, was investigated. A weak He-Ne laser light beam, λ = 632.8 nm, served as the measuring beam. The experimentally determined molecular Kerr constants B mol NL, and previously obtained values of the molecular total Kerr constants B mol TOT, allowed for the calculation of the molecular orientational-redistributional components B mol OR+RE of the OKE constants. The mean third-order optical polarizabilities c ai were also determined. The B mol NL, B mol OR + RE and c ai parameters estimated for tRNA macromolecules in water and in two different buffer solutions with and without magnesium ions are discussed in the light of data obtained by other methods. For different tRNA structures, different values of the optical Kerr constants and third-order optical polarizabilities were observed. It was found that the linear optical parameters, i.e., optical polarizability a and anisotropy δ a , obtained in the present studies, are much smaller in comparison with corresponding values obtained from the static light-scattering measurements. The relative nonlinear optical Kerr constants in pure water and salt buffers were measured, and are found to be opposite in sign. The relative values of the optical Kerr constants of both buffer solvents obtained in our picosecond measurements are smaller by a factor of two than those obtained in nanosecond studies.

Third-order optical polarizability of ZnS at low temperature

Third-order optical polarizability near deep centers in ZnS is experimentally investigated for the case of ultrashort light pulses at low temperature of the sample. Dispersion of the optical nonlinearity is characterized with resonant lines located at 16660, 17110, and 17540 cm−1. Higher resolution of the polarization four-photon spectroscopy is demonstrated, which delivers additional information about the energy structure. Use of the mode-locked laser pulses allows to extend the range of the pump intensity applied to the single crystal. Comparing of the experimental results with a conventional method is performed. [Russian Text Ignored].

Third-order optical polarizability of conjugated organic molecules

Third-order optical polarizability of conjugated organic molecules

Third-order optical polarizability of conjugated organic molecules

We present a theoretical investigation of the π-electron contribution to linear and non-linear polarizabilities of conjugated chains. Using simple models the respective influence of chain length and bond alternation on optical non-linearities are analyzed. The results are applied to symmetrical cyanines and polyenes.