The third-order optical nonlinearities of poly (ether) urethane open cell (PEUOC)/MgO nanocomposites, dissolved in dimethylformamide are characterized by Z-scan technique with CW Nd:YAG laser at its second harmonic frequency of 532 nm with TEM00 Gaussian profile. The synthesized samples are also characterized by optical microscopy and scanning electron microscopy imaging. The nonlinear refractive indices and nonlinear absorption coefficients of the synthesized samples are obtained in the order of 10^{-8} cm^{2}/W with negative sign and 10^{-5} cm/W, respectively. The origin of optical nonlinearity in this case may be attributed due to the presence of strong saturable absorption effect. All the results suggest that the nonlinear coefficients of the synthesized samples can be controlled by nanoparticles content into PEUOC. Furthermore, the results show that PEUOC/MgO may be promising candidate for the application to optical limiting in the visible region.
We study theoretically TM-polarized electromagnetic waves at a plane interface between two nonabsorbing, optically defocusing, nonlinear Kerr-type media. Numerical results are obtained for the dispersion equation and propagation constants of the field modes. The power guided by TM waves on interface was calculated and illustrated as a function of electric field value on interface.
The origin of the Kerr type nonlinearity of the medium as a result of the interaction between photons via the Dirac delta-potential is presented in the formalism adopted from the photon wave function approach. In the view of the result the optical soliton may be treated as a bound state (cluster) of many photons.
In this work a new type of solution for TE field on a plane interface of two nonabsorbing, optically self-focusing, nonlinear Kerr-type media has been presented. Numerical results are obtained for the dispersion equation and propagation constants of the field modes. The power guided by TE waves in the nonlinear interface was found and graphically illustrated.
This paper discusses Er-doped optical waveguides implemented in glass materials. The emphasis is put on physical limitations posed by concentration dependent nonlinear effects and on methods for their characterization. Examples of recently demonstrated, best performance integrated active devices are also given.
A new phenomenological model of self-organized second-harmonic generation is proposed describing the photoinduced χ^{(2)} grating formation as a cumulative third-order nonlinearity via a complex χ^{(2)} encoding function being dependent upon the light intensities of fundamental and second-harmonic writing radiations. The theoretical results attained are confronted with recent experimental measurements by Lambelet and Feinberg and the χ^{(2)} encoding function is constructed for this special case.
In the paper numerical calculations of the results of propagation in a nonlinear planar waveguide are performed. A type of nonlinearity is the Kerr nonlinearity. The wave equation, the solution of wave equation are shown, the dispersion equation, and the numerical solution of dispersion equation are analysed.
In this paper the detailed study of the self-diffraction phenomena due to reorientational optical nonlinearity in nematic liquid crystalline cell is presented. The optical nonlinear effect is additionally modified by external low-frequency electric field. The dependence of nonlinear response on light polarization is also analyzed. The theoretical investigations are compared with experimental results and the theoretical predictions are in excellent agreement with experimental data.
We analyse an asymmetric directional coupler with a thin photorefractive grating as a switching and demultiplexing element with memory. The grating is induced by two external beams interfering in the structure of AlGaAs/GaAs multiple quantum wells with an electric field applied along the quantum well planes.
Quantum mechanical arguments show that any optical amplifier must add noise to the amplified beam of light. For the case of a high gain amplifier with a coherent (Poissonian) input, the signal-to-noise ratio of the amplified beam must be at least two times smaller than that of the incident beam. We review the theoretical basis of this prediction. We also describe the results of our experimental investigations of the noise properties of optical amplifiers that utilize the nonlinear optical response of strongly driven atomic transitions.
An interaction between the signal wave propagating in a planar waveguide and a photorefractive grating is analysed. The waveguide contains an AlGaAs/GaAs multiple quantum well guiding layer biased with an external electric field applied along the wells plane. The grating is formed by two external beams interfering in the multiple quantum well layer. The dependence of the steady-state grating properties on the external waves parameters and applied electric field intensity is presented. Possible application of the grating as an optically controlled Bragg reflector with memory is analysed.
The purpose of this paper is a description of the dispersive dielectric medium, both linear and nonlinear, from first principles using the field theoretic methods based on the Feynman path integrals over classical trajectories. The main idea is to use notion of effective fields, in the present case the electromagnetic field modified by presence of a polarizable medium. Interaction of the field with the medium on the microscopic level is described by a modified Hopfield Lagrangian containing terms corresponding to the electromagnetic field, the matter polarization field modelled by harmonic oscillators with some resonance frequency and other matter fields describing the degrees of freedom responsible for absorption in the medium (reservoir fields). The polarization field is coupled both to the electric field and the reservoir fields. Effective theory is obtained by elimination of the matter degrees of freedom which is achieved by functional integration over all matter fields. For a linear medium all calculations can be done exactly leading to the effective Lagrangian from which, among others, an expression for frequency dependent dielectric constant can be extracted. Explicit form of the dielectric constant depends on the way by which the polarization field couples to the reservoir fields. In particular, uniform coupling to all reservoir modes gives the standard Lorentz oscillator model, and for any type of coupling the Lorentz form of dielectric constant is retrieved for frequencies close to the resonance. For weak damping the dispersion ω(k) is little sensitive to the form of coupling leading to polariton modes not different from those of the Lorentz model. It is also outlined briefly how the functional integration method could be used to description of nonlinear effects in the medium.
Nonlinear reorientation phenomena in nematic liquid crystals cause extremely large refractive index changes. However, this effect is relatively slow and the determination of the time necessary to appearing or disappearing of the nonlinear effect is an important issue. In this work we present measurements of the time of increasing the nematics reorientation induced by the light beam passing through the liquid crystalline layer. The influence of external low-frequency electric field suppressing reorientation is also reported. The obtained results describing relations between time and optical power of light as well as between time and external electric field intensity are in good agreement with theory.
A photorefractive grating in a slab waveguide based on a semi-insulating AlGaAs/GaAs multiple quantum well structure with an electric field applied along the quantum well planes as an optically controlled, frequency selective mode coupling element with memory is analysed.
Population inversion in the 3391 nm transition in a He-Ne discharge was experimentally measured with transparency and rate equations methods. Experiment shows large differences between the results obtained with the two methods.
We demonstrate generation of isolated XUV attosecond pulses in the sub-200 as regime (1 as = 10^{-18} s). They are generated utilizing waveform-controlled few-cycle laser pulses and advanced broad-band XUV multilayer optics.
Nematic liquid crystals are characterized by a giant optical nonlinearity which has its origin in the molecular reorientational phenomenon. Uniqueness of this nonlinear mechanism causes that response of the medium is dependent on many conditions. Among various circumstances, both an initial alignment of liquid crystal cell and geometry of the system are very important, but in this paper a significant role of light polarization in nonlinear effects observed in nematics is emphasized. Additionally, it is underlined that dependence on light polarization does not have only trivial aspect of initial conditions. More complex seems to be the fact that due to the high optical anisotropy of the medium the state of light polarization is changing on the way of beam propagation. As a consequence, the modifications of molecular orientation in the liquid crystal cell are strongly dependent upon light polarization.
The dynamics of solitary waves in second-order nonlinear materials are discussed using a multiple scales model. After making some comments on the applicability of other perturbation techniques the multiple scales approach is developed with a view to setting up a line of approach that, in principle, permits radiative effects to be modelled. After a closure condition is applied, equations for the evolution of dynamical variables are developed. Applications of these equations to loss and interactions are presented together with confirmation from numerical simulations. It is emphasised that the method is capable of extension to higher-order perturbations and, hence, into the solitary wave fusion region. The established interpretation of quasi-phase-matching fluctuations as loss is discussed and the simple problems of soliton (solitary wave) pair interactions in both loss-free and lossy media are analysed.
We report on the investigation of the spectral dependence of nonlinear optical susceptibilities, that describe second harmonic generation - circular dichroism, the nonlinear optical analogue of circular dichroism. The design and implementation of a state of the art experimental setup, used for the characterization of a series of organic molecules in the near-infrared range, will be discussed. We emphasize on the main characteristics like wavelength control, polarization and data-acquisition to present the setup. Some preliminary results show its strength to detect chirality at the molecular and supramolecular level.
A new method of measurements of elastic constants of nematic liquid crystals by applying the nonlinear optical effect is presented. This method bases on measurements of a value of the reorientation threshold in a liquid crystal layer while the reorientation is induced by the light beam passing through the layer. The obtained results are in a qualitative compatibility with the results obtained by classical methods.
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