Hyperpolarizabilities of Chiral Molecules Based on Three-Coupled-Oscillator Model

A chiral molecular model of three coupled oscillators is established. A set of coupling equations and hyperpolarizabilities for the chiral molecules with the tripod structure are presented. The expression of second-order nonlinear susceptibility is derived for an isotropic molecular system. The calculated hyperpolarizabilities o[ NPAN and NPP chiral molecules are consistent with the experimental results and the applicability of this model is validated.     

Linear and nonlinear properties for a dilute suspension of coated ellipsoids

The effects of geometric structures of coated particles on the dielectric properties of composites are derived. For a dilute suspension of coated ellipsoids with dielectric core and metallic shell embedded in a linear dielectric host, we find that the optical absorption peak of maximum wavelength shifts due to the core-shell structure, and has a significant red shift from that of pure metallic particles, especially for thin metallic coating. Meanwhile, the shape of coated ellipsoid can tune the absorption peak in a wide frequency range by properly choosing the depolarization factor. When the composite is made of linear materials, we obtain the condition of partial resonance for coated ellipsoids, which is relative to the particle shape. Under such a condition, the property of the inner core can be extended to the outer shell. When the inner core is a weakly nonlinear material, the nonlinearity of the composite can be greatly enhanced at the linear partial resonance. To achieve the condition of partial resonance, a metallic shell may be suitable to reach the case if the frequency is far away from the plasmon frequency. It indicates that the nonlinearity can also be enhanced in terms of the geometric structure of materials as well as the properties of themselves.     

Chemical-bond analysis of the nonlinear optical properties of the borate crystals LiB3O5, CsLiB6O10, and CsB3O5

The second-order nonlinear optical properties of practical borate crystals, LiB₃O₅, CsLiB₆O₁₀, and CsB₃O₅, which all contain the identical basic structural unit [the (B₃O₇)^5- group], have been quantitatively studied from the chemical-bond viewpoint. Differences in the nonlinear optical properties among these three borate crystals arise from the contributions of the different cations, i.e., the different interaction between the cation and the (B₃O₇)^5- anionic group. The chemical-bond method quantitatively expresses this important difference. At the same time, the current calculation also shows that the B₃O₇ group is a very important crystallographic frame in the crystalline borate solids; it offers different cations an excellent coordination environment. Received: 20 February 2001 / Accepted: 14 June 2001 / Published online: 30 August 2001     

Optical limiting in cobalt-doped polyvinylpyrrolidone

The results of optical limiting investigations of cobalt-doped polyvinylpyrrolidone solutions are presented. The optical limiting studies have shown that this process is due to self-defocusing at the wavelength of 1064 nm and also due to reverse saturable absorption and self-defocusing at the wavelength of 532 nm. The results of measurements on the non-linear optical characteristics of organometallic complexes are presented. Received: 10 July 2001 / Revised version: 15 October 2001 / Published online: 29 November 2001     

Optical multistability in nonlinear negative index Fibonacci multilayers

We have demonstrated numerically that the nonlinear negative index Fibonacci multilayer can exhibit optical multistability and offer a wide variety of switching between states of various contrasts. The stepwise up-switch and one-step or stepwise down-switch operations can take place in such structures. It is also shown that multistable operations and contrasts can be controlled by regulating the width of the negative index slabs.     

A precise data processing method for extracting χ from Z-scan technique

We present a precise data processing method, in the Z-scan experiments using a Gaussian beam and trimmed Airy beam, for directly extracting nonlinear refraction from the closed aperture Z-scan trace with the aid of the open aperture Z-scan trace when the materials exhibit nonlinear refraction and nonlinear absorption simultaneously. This method is still applicable when the nonlinear absorption is dominant and the closed aperture Z-scan curve degenerates into a single valley configuration, which is a salient advantage over other methods. In addition, we give gracefully empirical formulas with very high precision, which have good practicability for characterizing the optical nonlinearities of materials by use of the Gaussian beam and trimmed Airy beam Z-scan technique, respectively.     

Ultraviolet and soft X-ray photon-photon elastic scattering in an electron gas

We have considered the processes which lead to elastic scattering between two far ultraviolet or X-ray photons while they propagate inside a solid, modeled as a simple electron gas. The new ingredient, with respect to the standard theory of photon-photon scattering in vacuum, is the presence of low-energy, nonrelativistic electron-hole excitations. Owing to the existence of two-photon vertices, the scattering processes in the metal are predominantly of second order, as opposed to fourth order for the vacuum case. The main processes in second order are dominated by exchange of virtual plasmons between the two photons. For two photons of similar energy , this gives rise to a cross section rising like ² up to maximum of around 10^–32 cm², and then decreasing like ^–6. The maximal cross section is found for the photon wavevectorkk _F , the Fermi surface size, which typically means a photon energy in the keV range. Possible experiments aimed at checking the existence of these rare but seemingly measurable elastic photon-photon scattering processes are discussed, using in particular intense synchrotron sources.     

Third-Order Nonlinear Optical Properties of a Series of Polythiophenes

The third-order nonlinear optical properties of a series of polythiophenes are investigated with the Z-scan method under picosecond pulse laser irradiation at 532nm. The copolymers exhibit a good nonlinear response： large nonlinear refraction coefficients without nonlinear absorption. The signs of nonlinear refraction coefficients are positive, which are opposite to the negative signs of the polythiophene reported before. The mechanism accounting for the process of nonlinear refraction under pulse laser excitation is analyzed from the viewpoint of the electrondonor/acceptor units of polythiophenes. Moreover, changes of nonlinearity according to the lengths of main chains in polythiophene molecules are discussed.     

Optical transition pathways in type-II Ga(As)Sb quantum dots

We present results of room temperature photoreflectance (PR) and photoluminescence (PL) measurements of molecular-beam epitaxy (MBE)-grown GaAsSb/GaAs quantum dot structures: one with an In_0.14Ga_0.86As capping quantum well and one without it. PL was used to determine the structures’ ground-state transition energies. This result was employed in an 8-band k·p Hamiltonian to achieve a band structure of the structures, which have different electron confinement. The dot emission energies suggest a large amount of As incorporation into the dots, which is due to enhanced adatom mixing at a higher than normal growth temperature of 510 °C. Our calculations indicate a dot composition of 25-50% Sb gives the best fit to experiment. This uncertainty in composition arises due to the fact that different bowing parameters of the ternary alloy could be applied in the calculations. The theoretical analysis accounts well for the main feature in the PR spectra of both samples.     

Large Third-Order Optical Nonlinearity of a Novel Copper Phthalocyanine--Ferrocene Dyad

Third-order optical nonlinearity of a novel copper phthalocyanine-ferrocene dyad is measured by femtosecond forward degenerate four-wave mixing （DFWM） technique at 800 nm. The second-order hyperpolarizability of the novel copper phthalocyanine-ferrocene dyad is measured to be 1.74 ×10^-30 esu. This large and ultrafast thirdorder optical nonlinear response is mainly enhanced by the formation of intramolecular charge-transfer which can enhance the delocalized movements of the large π-electrons in the molecules.     

Influence of cubic nonlinearity on laser radiation transmission in a photonic crystal with spatially modified media properties

The transfer matrix method was modified to explore the Kerr nonlinearity influence on laser radiation propagation in a one‐dimensional photonic crystal. The suggested spatial distribution of the refractive index allows to remove minibands and to make the transmission curve much steeper. Plain and steep photonic band gap edges are effective in creation of transmission anisotropy of powerful laser radiation. The investigated photonic crystal has a strong anisotropic optical transmission and acts as an optical analog of the electronic diode. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Nonlinear optics of chiral surface systems

Differential SHG signals from chiral surfaces are recorded using right and left circularly polarized incident light. We show that chiral information from the surface is conveyed through this SHG process. This study focuses on the model protein system, cytochrome c, adsorbed on various self-assembled mono- and bi-layers at the solid/liquid interface. SHG-CD signals are shown to be related to the oxidation state of the protein and are utilized to observe changes in this feature of the protein in situ at surfaces of varying chemical properties. Received: 20 September 1998 / Revised version: 9 December 1998     

Large Positive and Negative Lateral Displacements from Total Internal Reflection Configuration with a Weakly Absorbing Dielectric Film

It is theoretically shown that the simultaneously large positive and negative lateral displacements will appear when the resonant condition is satisfied for a TE-polarized light beam reflected from the total internal reflection configuration with a weakly absorbing dielectric film. Appearance of the enhanced negative lateral displacement is relative to the incidence angle, absorption of the thin film and its thickness. If we select an appropriate weakly absorbing dielectric film and its thickness, the simultaneously enhanced positive and negative lateral displacements will appear at different resonant angles. These phenomena may lead to convenient measurements and interesting applications in optical devices.     

Nonlinear optical response of Ge nanocrystals in silica matrix with excitation of femtosecond pulses

We report an investigation of third-order optical nonlinearities in Ge nanocrystals (∼6 nm radius) embedded in silica matrix using the Z-scan and pump-probe techniques with femtosecond laser pulses at 780-nm wavelength. The nanocrystallite Ge samples were prepared using magnetron co-sputtering and post-thermal annealing at 800 °C. The nonlinear absorption coefficient and refractive index of the Ge nanocrystals were determined to be in the range from 1.8×10^-7 to 6.8×10^-7 cm/W and 1.5×10^-12 to 8.0×10^-12 cm²/W, respectively, which are proportional to the Ge atomic fraction in the matrix. Relaxation of the nonlinear response was found to have two characteristic time constants, 1.8 ps and 65 ps. The mechanisms responsible for the observed nonlinear response are discussed. Received: 21 August 2000 / Revised version: 17 January 2001 / Published online: 30 March 2001     

Optical response of aggregates of clusters with different dielectric functions

Received: 19 December 1997/Revised version: 24 March 1998     

Features of the simplest model of second-harmonic magneto-optical Kerr effects

A generalised formalism of characteristic matrices is presented to analyse second-harmonic magneto-optical Kerr effects in an optically anisotropic centrosymmetric ferromagnetically ordered multilayer if its response can be described in terms of electric polarisation. Features of the model associated with ideal (infinitely thin) interfaces are highlighted. These are due to both the existence of two versions of unconventional boundary conditions and an inevitable conventional approach to defining the surface polarisations through the fundamental electric field and surface-susceptibility tensors. New analytical results for linear and second-harmonic Kerr effects are shown to be advantageous for developing an effective algorithm for their numerical simulation. The linear approximation with respect to magnetisation is pursued, thereby also making our results suitable for investigating a great variety of magneto-optical effects and (in the second-harmonic case) effects related to anisotropy. Received: 16 October 2001 / Published online: 24 April 2002     

Optical hyperlens composed of multilayered metallodielectric nanofilms

We present a study of the properties of metamaterial consisting of multilayered nanofilms and numerically demonstrate the subwavelength imaging effect. We find that a point source placed in the vicinity of the structure can form an image in the opposite side of the slab, even when the permittivity of metal and dielectric materials is not matched. When light is incident obliquely on the interface, the intensity of transmitted field is smaller than the one when light is incident upon the structure, and the image becomes blurred. This structure verifies that the multilayered metallodielectric structure can act as optical hyperlens.     

Intrinsic Bistability and Critical Slowing in Tm^3＋/Yb^3＋ Codoped Laser Crystal with the Photon Avalanche Mechanism

We present theoretically a novel intrinsic optical bistability （IOB） in the Tm^3＋ /Yb^3＋ codoped system with a photon avalanche mechanism. Numerical simulations based on the rate equation model demonstrate distinct 10B hysteresis and critical slowing dynamics around the avalanche thresholds. Such an 10B characteristic in Tm^3＋ /Yb^3＋ eodoped crystal has potential applications in solid-state bistable optical displays and luminescence switchers in visible-infrared spectra.     

Optical manipulation of third-harmonic generation via either one- or two-photon excitation in diarylethene-polymethylmethacrylate polymer thin films

Optical manipulation of third harmonic (TH) generation in diarylethene-polymethylmethacrylate (DE-PMMA) polymer thin films is obtained by either one- or two-photon excitation. TH intensity generated from a DE-PMMA polymer thin film decreases, when it is pumped by either 325 nm or 442 nm laser irradiation, which changes the molecular structure of DE molecules from an open-form (A form) to a closed-form (B form). TH intensity recovers to its original intensity level when all B form DE molecules return to an A form after being induced by either 532 nm or 1064 nm laser irradiation. The experimental results reveal that the second-order hyperpolarizability () of the A form molecules may be larger than that of the B form molecules. Moreover, TH output efficiency is independent of the angle between the pump and probe polarization directions. This result is attributed to the two-dimensional structure of DE molecules.This revised version was published online in March 2005. In the previous version, the published online date was missing     

Dielectric Properties of GaN in THz Frequencies

The complex refractive indices and the dielectric function of GaN for frequencies ranging from 0.25 to 1.22THz are obtained using THz time-domain spectroscopy. The real part of the dielectric function first decreases from 0.25 to 0.42THz and then oscillates from 0.42 to 1.22THz, whereas the imaginary part of the dielectric function is oscillating within the whole range of frequency. The simple Drude model is extended to take into account the effect of defects on the dielectric function. The extended model is in agreement with the experimental data.