We separate the field generated by a spherically symmetric bounded scalar monochromatic source into a radiative and non-radiative part. The non-radiative part is obtained by projecting the total field on the space spanned by the non-radiating inhomogeneous modes, i.e. the modes which satisfy the inhomogeneous wave equation. Using residue techniques, introduced by Cauchy, we obtain an explicit analytical expression for the non-radiating component. We also identify the part of the source distribution which corresponds to this non-radiating part. The analysis is based on the scalar wave equation.
The concept of second-order anticoherence of two optical fields is defined via a cross-correlation function of the form . It is shown that the corresponding signal and idler fields produced in the process of parametric downconversion are mutually anticoherent, and it is pointed out that this anticoherence has already been observed experimentally, if somewhat indirectly.
When small amounts of suitable dyes are added to a pure nematic liquid crystal, its nonlinear optical response may be enhanced by over two orders of magnitude and even be reversed in sign. This feature may be interesting for applications. We measured the enhancement of the nonlinear optical Kerr coefficient of several dye-nematic mixtures, in order to gain some insight on the molecular mechanism that is supposed to be the basis of the phenomenon.
A discussion on the effective wavelength in two-wavelength interferometry is given. A definition, different from the commonly adopted one, is presented and its validity is discussed. By adopting this new effective wavelength the range over which lengths can be measured using interferometric techniques can be vastly increased, without introducing phase unwrapping ambiguities within this increased range. A graph is presented from which a method is derived, enabling an efficient use of this new effective wavelength.
We present an experimental method to obtain the point spread function (PSF) of human eyes, based on two techniques: the conventional symmetric double-pass method and the recently introduced asymmetric one-and-a-half-pass method. The symmetric double-pass method provides the autocorrelation of the retinal PSF and thus, the modulation transfer function (MTF). Here, we show that the double-pass MTF can be combined with partial phase information provided by the one-and-a-half-pass method to estimate the PSF. Two reconstruction methods were used, depending on the relative contribution of diffraction and aberrations. When aberrations are dominant (large pupils), the PSF can be obtained directly by combining the modulus and phase. When aberrations are small (small to medium pupils), however, a partial phase-retrieval algorithm has to be applied. In agreement with previous findings, the PSFs show substantial intersubject variability and for large pupils, they display the characteristic ray-pattern of star images.
We consider a simple model, based on currently accepted models for active galactic nuclei, for a quasi-stellar object (QSO or "quasar") and examine the influence that correlation-induced spectral changes ("The Wolf Effect") may have upon the redshifts of the optical emission lines.
The theory and results concerning the class of spherically symmetric non-radiating sources and fields established in an earlier paper by Gamliel et al are generalized to the non-spherically symmetric case. A procedure is described for constructing bases for the spaces of all non-radiating sources and associated fields confined to a spherical volume. An example is presented illustrating the developed theory.
We consider the problem of the characterization of beams by moments of the field intensity in the aperture and its moments in the far field. The well known beam propagation factor, , is considered. We give convergence criteria for these factors and also discuss a new approach to optimization of the even moments of the far-field intensity.
Nonlinear optical waveguide elements have to be operated at wavelengths where the waveguide material exhibits minimum linear alpha and higher-order alpha(2) absorption parameters and where the nonlinear refractive index parameter n(2) is as large as possible. The dispersion of these two quantities has been measured in the wavelength range between 780 and 990 nm. A stable semi-integrated Mach-Zehnder interferometer as well as a spectral broadening set-up were used. The light source was an Ar-pumped tunable Ti:sapphire laser, generating picosecond light pulses.The measurements have been performed on one class of conjugated polymers, substituted poly(phenylene-vinylene) (PPV), which are promising candidates for the demonstration of nonlinear switching in waveguide elements. Low-loss waveguides (<1 dB cm(-1)) with extreme stability against pulsed optical intensity (up to 16 GW cm(-2)), allowing for a nonlinear induced phase shift of more than 3 pi, have been demonstrated. The nonresonant n(2) values are several times 10(-14) cm(2) W-1 for the two PPV derivatives measured. Spatial solitons have been observed for the first time in a polymer waveguide.
This paper describes low-molecular-mass liquid crystals doped with suitable dyes which can be used for real-time holographic purposes. We describe the origins of the diffraction gratings or holograms induced by a light intensity pattern in a dye-doped nematic liquid crystal sandwiched between two conducting glass plates. The mechanism is linked to electric-field-driven reorientation of the nematic director. The modulation of the electric field is induced mainly by the bulk photoconductivity of the system. Design and characterization (response time, diffraction efficiency) of the optically addressed spatial light modulator (OA-SLM) is presented. Interesting applications of these materials enabling phase conjugation and optical correlation are discussed.
This paper describes the use of an integrated optical Bragg-reflector as a chemo-optical sensor. It is shown that these types of Bragg-reflectors for a wavelength of 630 nm can be realized with a bandwidth smaller than 0.2 nm in a optical channel waveguide. Measurements show that a refractive index change of the waveguide cladding of can be detected.
The confinement of electrons and holes in quantum wells allows the fabrication of structures exhibiting enhanced nonlinear optical effects associated with excitonic transitions. By applying femtosecond spectroscopy, it has become possible to study the coherent and incoherent properties of these systems with high temporal resolution, thus gaining a detailed insight into the processes involved in the interactions of photons, electrons and the crystal lattice on a subpicosecond time scale. We present investigations of the nonlinear optical behaviour governed by the relaxation and thermalization dynamics in GaAs-AI(x)Ga(1-x)As multiple quantum wells and in low-temperature grown GaAs. Experiments with high temporal and energetic resolution provide a detailed insight into the inter-valence-band thermalization in quantum wells and the influence of shallow bound defect levels in low-temperature grown GaAs.
Frequency doubling and difference-frequency generation in a doubly resonant GaAs cavity are discussed. It is shown that a one-coherence-length cavity is an interesting geometry for second harmonic generation: cavity phase matching can be obtained using well suited multilayer mirrors and a good approximation of double resonance is possible with only one tuning parameter. Experimentally, first results on high-quality (111) GaAs microcavities are presented.
We study the behaviour of a plane-wave delta-function pulse that is diffracted at an edge in a dispersive medium. In particular, we show that the edge-diffraction process by itself is dispersive and adds to the dispersion induced by the medium in such a way as to completely change the behaviour of the Brillouin precursor. The dispersion associated with edge diffraction manifests itself through the appearance of a new algebraic singularity near the origin. Since the Sommerfeld precursor field is due to asymptotic contributions from saddle points that always stay far from the origin, the character of this field is not changed by the new singularity induced by edge diffraction. The Brillouin precursor field, however, is due to asymptotic contributions from saddle points that are close to the origin, and therefore the new singularity changes its behaviour dramatically. Numerical illustrations of the evolution of the edge-diffracted pulse are given and the behaviour of the Brillouin precursor field is explained both mathematically and physically.
We summarize and review our theoretical and experimental work on spontaneous emission and nonlinear effects in one-dimensional, photonic bandgap (PBG) structures. We present a new result: a method for calculating the normal-mode solutions - and hence the spontaneous emission of embedded emitters - in an arbitrary, linear, lossless, one-dimensional, PBG structure.
The possibility of correctly detecting immersed targets with a lidar through the air-water interface is discussed in this paper. The water surface roughness, in relation with wind direction, greatly disturbs light dispersion. Nevertheless, a detection of immersed targets is always possible. This paper reports on an attempt to improve the quality of detection. It was carried out by a polarimetric coding of optical signals based upon the Stokes-Mueller polarimetric formalism, and by choosing a special orientation for the transceiver.
Emissions from operational natural gas flares are examined by a remote sensing technique using a commercial moderate-resolution Fourier-transform infrared spectrometer. The thermal radiation emitted by the post-combustion gas is analysed to determine plume temperatures and concentrations of CH4,CO2,CO,NO and H2O. The multicomponent air pollution software (MAPS) is applied which is based on radiative transfer line-by-line calculations and least-squares fit procedures. Emission rates and combustion efficiencies are calculated which indicate that the local environmental impact of methane emissions from natural gas flares is small, while significant amounts of carbon dioxide are released.
Shell Research Ltd has been using an infrared DIAL (differential absorption lidar) facility for two and a half years to measure hydrocarbon emissions to the atmosphere from petroleum industry process units. This paper describes the procedures used for measurement, emission rate calculation and data display, and then discusses the factors that affect the accuracy and detection limits of column content and emission rate measurements under practical operating conditions.
New legislation requiring the monitoring and reduction of polluting gases in both Europe and the US has increased the demand for reliable and affordable Open Path Monitoring Systems, suitable for hazardous area operation. We report on the research and development of a UV Fourier-transform spectrometer based system for open path monitoring of both hazardous and environmental gases. The device has no moving parts and is designed for unattended operation. Laboratory tests have successfully detected the present of and differentiated between SO2 and H2S present in a 1 meter test cell down to 1.0 ppm.m levels. the real time response of the system allows for the use of maximum entropy modeling to predict the size and location of a gas leak. Initial field tests with open air gas releases of SO2 and H2S have verified this. The multiple gas feature of the instrument allows for additional possible applications with regards to environmental monitoring.
