Combined reciprocal and non-reciprocal birefringence in optical monomode fibres

We analyse the overall birefringence which arises from the combined effects of Faraday rotation (non-reciprocal) and bending stress (reciprocal) applied to a monomode optical fibre loop. The theory is substantiated by numerical evaluations and appropriate experimental data are reported. These indicate how it is possible to build non-reciprocal birefringent components, i.e. rotators and isolators, by means of monomode coils.     

Time-dependent propagation of high energy laser beams through the atmosphere

The computation of time-dependent three-space-dimensional laser beam propagation is described. The methods are applicable to the propagation of high energy laser beams through the atmosphere in the presence of a horizontal wind and turbulence for most situations of interest. Possible cases are propagation of cw beams through stagnation zones, multi-pulse propagation, including the self-consistent treatment of pulse self-blooming, and propagation involving transonic slewing. The solution of the Maxwell wave equation in Fresnel approximation is obtained by means of a discrete Fourier transform method, which, surprisingly, gives excellent results for diffraction problems. The latter provide a stringent test for the accuracy of any solution method. Considerable use is also made of discrete Fourier transform methods in solving the hydrodynamic equations. The treatment of turbulence is based on the generation of random phase screens at each calculation step along the propagation path. In a time-dependent calculation the random phase screens can be either made to move with the wind at a given propagation position or generated anew for each successive time. This work was done under contract to the Advanced Research Projects Agency of the Department of Defense, the Army Missile Command, Huntsville, Alabama, and the U.S. Energy Research and Development Administration.     

Coherent and incoherent reflection and transmission of multilayer structures

The complex-amplitude reflection and transmission coefficientsr andt of a pile of films are represented as a product of matrices. The matrices describe the transformation of two plane waves travelling in opposite directions between the films, and their development within the films.If one of the films is significantly thicker than the other layers (e.g., several films on a substrate), the calculated reflectanceR=rr ^* and transmittanceTt ^* show narrow Fabry-Perot oscillations which, in a lot of cases, are not observed in the experiment. Since the matrix method is equivalent to the representation of the amplitudesr andt as a coherent superposition of multiple reflected waves within the thick slab, we are able to suppress, in the calculation, the interference within this thick film by adding the absolute squares of the partial waves corresponding to an incoherent treatment. This procedure is shorter and more simple than averaging over an appropriate interval of frequency or thickness, which, in most cases, leads to the same results.     

Transient propagation of optical beams in active media

The coherent interaction of short optical pulses with a nonlinear active resonant medium is calculated. The rigorous and self-consistent solution of the coupled nonlinear Maxwell-Bloch equations including transverse and time-dependent phase variations predicts the onset on an on-resonance self-focusing that agrees very well with a previous perturbation treatment and with recent experiments in sodium and neon. The formation of this dynamic self-action effect is elucidated as being due to the combined effects of diffraction and the inertial response of the active media. Accuracy and computational economy are achieved simultaneously by redistributing the computational grid points according to the physical requirements of the problem. Evenly spaced computational grids are related to variable grids in physical space by a range of stretching and rezoning techniques including adaptive rezoning where the coordinate transformation is determined by the actual physical solution. Work supported in part by the Mobil Oil Corporation and the Office of Naval Research.     

Time-dependent propagation of high-energy laser beams through the atmosphere: II

Various factors that can effect thermal blooming in stagnation zone situations are examined, including stagnation-zone motion, longitudinal air motion in the neighborhood of the stagnation zone, and the effects of scenario noncoplanarity. Of these effects, only the last offers reasonable hope of reducing the strong thermal blooming that normally accompanies stagnation zones; in particular, noncoplanarity should benefit multipulse more than cw beams. The methods of treating nonhorizontal winds hydrodynamically for cw and multipulse steady-state sources are discussed. Aspects of pulse “self-blooming” are also considered. Work was performed under the auspices of the U. S. Energy Research and Development Administration under contract W-7405-Eng-48, U. S. Navy Contract N00014-76-F-0017 and U. S. Army Contract W31U31-73-8543.     

Modulation of radiation in nonstationary resonant media

We study the propagation of radiation in a gas, the resonant frequency of which changes with time when affected by external electric and magnetic fields. It is shown that for an harmonic change of the resonant frequency under appreciable energy exchange between electromagnetic field and medium, deep amplitude modulation of radiation may be achieved. The analytical expressions obtained for a field in a gas allow rather accurate calculation of the space-time structure of the radiation penetrated through the medium layer. The numerical calculations are compared with the known experiment [4], good agreement is obtained. The transformation of radiation between dispersive branches with adiabatic stepwise variation of the resonant frequency has been also studied. Branch-tobranch transformation is investigated and the adiabatic invariant is found to be the total number of the high and low frequency radiation quanta corresponding to two dispersive branches.     

Dynamic laser speckles and their application to velocity measurements of the diffuse object

In connection with the parameters of the optical configuration used to produce speckles and under illumination of a Gaussian beam over a moving diffuse object, this paper discusses the statistical properties of dynamic speckles produced in the diffraction and image fields by the diffuse object moving in a plane with constant velocity. Especially, the space-time correlation function of the dynamic speckle intensity is examined in detail. Two typical speckle motions of translation and boiling are interpreted for various optical configurations in the diffraction and image fields. As one of the interesting applications of dynamic speckles to metrology, various methods for velocity measurements of the diffuse object are introduced.     

Reciprocity in the wave reflection and transmission problem: Part 1. Symmetry of the matrices of reflection coefficients

The reciprocity theorem in Lyamshev’s formulation is used to derive a general symmetry relationship for the matrices of reflection coefficients in homogeneous media and one-dimensional waveguides. This relationship is shown to be equivalent to the normalization of the amplitudes by the cross power flux of the forward and backward waves. The relationship is valid for both propagating and evanescent waves, and all the symmetry relationships known from the literature represent its particular cases.     

Transverse and soliton instabilities due to counterpropagation through a reflection grating in Kerr media

Transverse instabilities are shown to accompany counterpropagation of optical beams through reflection gratings in Kerr media. The instability threshold of continuous waves is analytically derived, and it is shown that the presence of the grating broadens and narrows the stability region of plane waves in focusing and defocusing media, respectively. Furthermore, counterpropagating soliton stability is numerically investigated and compared with the transverse modulation instability analysis, revealing an underlying physical link.     

An effect of curvature of rotating diffuse objects on the dynamics of speckles produced in the diffraction field

The time correlation function is analyzed of the speckel intensity fluctuation produced in the Fresnel diffraction field from a rotating diffuse object under illumination of a Gaussian laser beam. The dependence of the curvature radius of the rotating diffuse object on the time correlation length of the speckle intensity fluctuation is especially explored by taking into account the size of the detecting aperture. The theoretical results are confirmed experimentally for detecting apertures with various sizes. It is shown that a detecting aperture with an appropriate size is required. It becomes useful for determining the radius of curvature of the rotating diffuse object from measurements of the time correlation length of the speckle intensity fluctuation.     

Rotation of the polarization plane in a gas near resonance

Spectroscopic investigation of the Xe line at λ=5823.89 Å in a gas discharge by measuring the angle of rotation of the polarization plane of the laser radiation passing through a gas-discharge cell in a longitudinal magnetic field is discussed in the paper. An optical scheme of the experiment is described. It is predicted that the sensitivity of this method which implies the measurement of an absorption coefficient is characterized by a value ～10^?9 cm^?1     

Shape and delay of CO2-laser pulses in fog

The problem of propagation of 10.6 m-CO₂ laser pulses in fog has been formulated and solved numerically, making use of Duhammel's principle. Fog droplets are considered Mie scatterers in the Rayleigh limit. Evaporation, power loss and time delay of pulse peak have been studied. Possible extensions of the technique have been discussed.     

Andreev reflection current through a molecule quantum dot in the presence of the electron-phonon interaction and the spin-flip scattering

With the aid of the nonequilibrium Green's function and the Lang-Firsov canonical transformation, we investigate the joint effects of a phononic environment and the spin-flip scattering on the Andreev reflection (AR) in a ferromagnet/single-molecular quantum dot/superconductor (FM/MQD/SC) system. In the presence of the strong electron-phonon interaction (EPI), it is found that the EPI strongly suppresses the AR current (called the Franck-Condon blockade). When the coherent spin-flip (similar to a transverse magnetic field) is taken into account within the MQD, the AR current is significantly enhanced, furthermore, the spin-polarized AR current or even the pure spin-polarized AR current can be generated. By tuning the system parameters, the amplitude and direction of the AR current can be changed, this provides an efficient mechanism for controlling the AR process.     

Determination of gas concentrations and temperature in the exhaust of a power plant with a cw chemical HF laser

A cw chemical hydrogen fluoride laser system was used to investigate the exhaust of a gas and garbage burning power plant for the period of three months. The concentration of water vapor and carbon dioxide as well as the temperature in the exhaust was measured online with a time resolution as small as 5 ms. The temperature could be determined with a relative accuracy of better than 0.1 K over an averaging time of 9 s. This high accuracy together with the fast response make the system well suited not only for industrial combustion control but also for remote and precise measurement of temperature profiles.     

A cumulant analysis for non-Gaussian displacement distributions in Newtonian and non-Newtonian flows through porous media

We use displacement encoding pulsed field gradient (PFG) nuclear magnetic resonance to measure Fourier components S(q) of flow displacement distributions P(zeta) with mean displacement (zeta) for Newtonian and non-Newtonian flows through rocks and bead packs. Displacement distributions are non-Gaussian; hence, there are finite terms above second order in the cumulant expansion of ln(S(q)). We describe an algorithm for an optimal self-consistent cumulant analysis of data, which can be used to obtain the first three (central) moments of a non-Gaussian P(zeta), with error bars. The analysis is applied to Newtonian and non-Newtonian flows in rocks and beads. Flow with shear-thinning xanthan solution produces a 15.6+/-2.3% enhancement of the variance sigma(2) of displacement distributions when compared to flow experiments with water.     

Photochemical transformations of the azidonitroxyl radical in glassy media

The kinetic characteristics of the photochemical decomposition of the azido group of 3-azido-4-hydroxyimino-2,2,6,6-tetramethylpiperidine-1-oxyl in solid matrices at 293 and 77 K were studied. It was revealed that the presence of the nitroxyl radical center in the molecule is responsible for the realization of the radical mechanism of the decomposition of the azido group. The values of the quantum yield φ of the decomposition of the azido group were found to be 0.056 in toluene at 77 K, 0.14 in polystyrene at 77 K, and 0.16 in polystyrene at 293 K. It was demonstrated that the number of radicals remaining after photolysis correlates with the molecular mobility of the medium.     

Spectral and temporal study of picosecond-pulse propagation in a single-mode optical fibre

The power-dependent pulsewidth variations for input 85 ps pulses from a cw mode-locked Nd: YAG laser propagating through 125 m of single-mode optical fibre have been examined using a Synchroscan streak camera. Simultaneous spectral and temporal measurements provide information as to the optimum parameters for pulse compression in fibres.