The Dicke Effect in Nonlinear Spectroscopy

Abstract

It is shown that deceleration of atoms by the dynamic force of friction leads to a narrowing of Voigt's contour in linear spectroscopy and to the Bennett hole being shifted, narrowed and asymmetric in nonlinear spectroscopy. Estimates are presented for the argon-ion laser plasma, where the friction force is to be taken into account in precise calculation.     

Mechanical stability of metal foam cylindrical shells with various porosity distributions

Abstract

The paper deals with the nonlinear buckling analysis of imperfect cylindrical shells made of porous metal foam subjected to axial compression. For the metal foam shells, porosities are dispersed by uniform, symmetric, and asymmetric distributions in the thickness direction. Using Donnell shell theory and von-Karman nonlinear kinematics, nonlinear equilibrium equations are derived. The critical buckling load and buckling equilibrium curves for both perfect and imperfect shells are solved by using the Galerkin's procedure. A comprehensive investigation into the influence of porosity coefficient, imperfections, porosity distribution, and geometry on the buckling behaviors of the cylindrical shell is performed.     

Spectroscopy of Nonlinear Gyrotropic Medium and Surface Diagnostics Based on Polarization Effects Due to Self-action of Light

Abstract

Amplitude and polarization characteristics of the light reflected and passed through crystals are found. Four mechanisms of polarization-ellipse nonlinear optical rotation and deformation are studied. A new scheme of nonlinear polarization spectroscopy of uniaxial and cubic crystals is put forward.     

Are Free-free Transitions a Good Basis for Nonlinear Optics?

Abstract

It is known that a low-frequency light induces very efficient transitions between the continuous spectrum states of an atom. We show, however that these transitions are not effective sources of nonlinear optical processes, such as generation of higher harmonics of the low frequency light.     

Self-phase Modulation in Quadratically Nonlinear Media

Abstract

We discuss self-phase modulations and related transverse effects accompanying interaction of a light beam with a second harmonic radiation generated by it. Some experimental observations are explained by a simple perturbative approach. Numerical simulations provide a further insight into the nature of transverse self-effects in quadratically nonlinear media. An effective x ⁽³⁾-like behaviour of dispersive quadratically nonlinear media is discussed. Such feature may lead to important consequences for measurements of the x ⁽³⁾ tensor in complex nonlinear media.     

Self-deflection of Three-dimensional Optical Beams by a Thin Nonlinear Layer with Saturable Dispersive and Absorptive Nonlinearity

Abstract

This paper describes self-deflection effects arising from the propagation of symmetric and asymmetric three-dimensional scalar optical beams through thin nonlinear layers. The model of nonlinearity used includes both saturation and absorption. In several cases, significant differences are observed between the present three-dimensional results and previous two-dimensional results based on the Kerr model of nonlinearity. Also, the existence of a large axial component of the self-deflected beam for a three-dimensional geometry against the absence of this component for a two-dimensional geometry is discussed.     

Squeezed Light

Abstract

In this paper we review the current state of progress in research on squeezed light. We discuss the basic theory of squeezing and the nature of quantum noise in optical fields. We examine various atomic sources of squeezed light and discuss phase-sensitive detectors of quantum noise including homodyne and heterodyne detectors. Various successful nonlinear optical methods for generating squeezed light are reviewed. We conclude with a discussion of the possible applications of squeezed light.     

Interaction of Counter-propagating Elliptically Polarized Light Waves in Isotropic Nonlinear Media

Abstract

The nonlinear interaction of elliptically polarized counter-propagating waves in an isotropic transparent medium is analysed. Self-induced changes in the polarization of the counter-propagating light waves, are described. Using these results, a new type of modulator giving self-induced rotation of the polarization ellipse (SIRPE) is studied. The transmission of counter-propagating waves in the SIRPE modulator is shown to exhibit saturation with increase in light intensity and to be a multiple-valued function of the light intensity.     

Analytic theory of coherent cross-gain modulation in semiconductor travelling-wave amplifiers

Abstract

We report a simple analytic solution to the problem of cross amplitude-phase modulation in nonlinear two-wave mixing, under the approximation of constant saturating power. The results are applied to travelling-wave semiconductor laser amplifiers where the linewidth enhancement factor inevitably leads to amplitude-phase coupling and asymmetric energy transfer. Our solution is used to obtain the transmission gain of each beam, the spectral profile and the amplifier input-output characteristics. Limits are established as to the applicability of the analytic solution, by comparison with numerical solutions to the related full four-wave mixing problem.     

Trends in optical biomedical imaging

Abstract

Recent progress in the development of optical techniques for non-invasive imaging in biology and medicine is reviewed. We start with some fundamental considerations of light propagation in random media. We then discuss imaging using coherent unscattered light and diffuse light. Microscopic techniques based on one- and two-photon fluorescence are described and several types of nonlinear and time-resolved microscopy are explained. We conclude with some application examples and an outlook.     

Nonlinear optical properties of mercury dithizonate in a polymer film

Abstract

The absorption spectra of trans and cis isomers of mercury dithizonate in a doped poly(methyl methacrylate) film are measured, and the optical properties of the two isomers are analysed. The properties indicate that different isomers of mercury dithizonate can convert into each other when irradiated by light of appropriate wavelength. With the Z-scan method, the nonlinear optical properties of mercury dithizonate are investigated, and experimental data on the nonlinear refractive index and the change in refractive index are obtained. The changes in refractive index as a function of wavelength are obtained by the Kramers-Kronig transformation.     

Interference and the lossless lossy beam splitter

Abstract

By directing the input into a particular mode it is possible to obtain as output all of the input light for a beam splitter which is 50% absorbing. This effect is also responsible for nonlinear quantum interference when two photons are incident on the beam splitter.     

Momentum in nonlinear optics

Abstract

Although it is well known that light carries momentum and exerts a pressure on objects, a conservation of momentum principle is apparently rarely used in optics. In nonlinear optics light waves interact and may exchange both energy and momentum. We demonstrate that a conservation of momentum principle holds in these cases and in fact its use is widespread but generally unrecognized in the standard mathematical methods. In both the cases of linear basis waves interacting nonlinearly, e.g. coupled-wave theory and frequency mixing, and fully nonlinear waves, we demonstrate that a governing Hamiltonian is related to momentum. Action principles are used to discuss the generality of these results.     

Self-action of Counterpropagating Axially Symmetric Light Beams in a Transparent Cubic-nonlinearity Medium

Abstract

The stationary effect of self-action of counterpropagating axially symmetric light beams in a medium with cubic nonlinearity is discussed. Self-similar solutions for initial radiation parameters and nonlinear medium characteristics in the case of slowly varying amplitudes of beams are found. The analysis of approximate solutions obtained on the basis of motion constants is carried out and results are compared with numerical experimental data.     

Use of AL307 light-emitting diodes as photodetectors for diagnostics of femtosecond light pulses

A nonlinear electrical response has been observed for the first time from AL307 light-emitting diodes exposed to femtosecond light pulses. When used in an unconventional fashion as unbiased photodiodes, these AL307 light-emitting diodes give an electrical response proportional to the square of the recorded radiation intensity of ultrashort light pulses. Autocorrelation functions are given for femtosecond pulses obtained using AL307 light-emitting diodes in the autocorrelator instead of the conventional photodetector and nonlinear crystal system. Pis’ma Zh. Tekh. Fiz. 24, 62–65 (January 12, 1998)     

Reflection and refraction of light at saturating active boundaries

Abstract

This study deals with the topic of reflection and refraction of light from the boundary of a high-gain saturating laser amplifier. Expressions for the electric field and intensity reflection and transmission coefficients are obtained for the case of a wave in a uniform dielectric that is incident normally on a nonlinear saturating active medium. Bistability effects are predicted even for the simplest case of zero frequency detuning from the line centre of the saturating transition.     

Quantum Statistics of Stimulated Raman and Hyper-Raman Scattering of Squeezed Light with Pump Depletion

Abstract

Using the approximation of small fluctuations around a stationary solution, photon statistics and quadrature variances are derived in stimulated Raman and hyper-Raman scattering including the coupling of pumping, Stokes, anti-Stokes and phonon modes. The depletion of pump light is included. Compared to Raman scattering, additional regimes to generate anti-bunched, sub-Poisson and squeezed light were found caused by self-interaction of the pump mode. It was possible to include effects of nonlinear dynamics, initial squeezing of radiation and phonon system, external noise and losses.     

Beam Splitter Model of Two-beam Coupling in Photorefractive Materials

Abstract

The phenomenon of two-beam coupling in photorefractive crystals results from the interaction of two beams with the index grating written by those two beams. In this paper we show that the process can be understood by considering the photorefractive crystal to be a nonlinear beam splitter, with reflectivity and transmission coefficients dependent upon the relative intensities of the two beams. The relative phase relationships upon reflection, determined by the Fresnel equations, as well as the phase shift between the intensity and index grating, are the sources of the asymmetric coupling. A simple derivation of coupled mode equations describing two-beam coupling based upon the beam splitter model is proffered.     

Quantum statistics and dynamics of nonlinear couplers

Abstract

We investigate both codirectional and contradirectional nonlinear couplers composed of two nonlinear waveguides operating by second-harmonic generation. We take into account possible mismatches inside the waveguides and between them. We calculate the photon number distribution, its factorial moments, quadrature and integrated intensity variances and quadrature uncertainty product taking into account the effects of transmission of light between waveguides. Incident beams are assumed to be coherent, squeezed and mixed with external noise. Second-harmonic modes are assumed to be pumped with strong coherent beams. We show that non-classical behaviour of beams generated by the nonlinear waveguides can be transferred between them and controlled by linear and nonlinear mismatches. In the contradirectional regime of propagation, asymptotic non-classical states can be generated.     

The non-degenerate optical parametric oscillator in the strong-coupling regime

Abstract

A fully quantum treatment of the non-degenerate optical parametric oscillator in the extreme quantum limit of small photon numbers and very high nonlinear coupling strength is presented. When the nonlinear coupling constant becomes comparable with the cavity decay rate, the sharp threshold that is usually encountered disappears, a situation reminiscent of microlasers. Furthermore the output light exhibits unusual statistical properties such as strong super-Poissonian behaviour of the pump mode for (very) large coupling constants.