Showing papers on "Coherence (physics) published in 1987"

Optical coherence-domain reflectometry: a new optical evaluation technique.

Abstract: An optical evaluation technique is described that is suitable for determining the positions and magnitudes of reflection sites within miniature optical assemblies. This method utilizes the coherence effects exhibited by a broadband optical source and is referred to as optical coherence-domain reflectometry. Background theory is given, and experimental results have demonstrated a resolution of 10 μm with an optical dynamic range of more than 100 dB.

Purely rotational coherence effect and time‐resolved sub‐Doppler spectroscopy of large molecules. II. Experimental

Abstract: In this and the accompanying paper we present a theoretical treatment and experimental study, respectively, of the phenomenon termed purely rotational coherence. This phenomenon has been demonstrated to be useful as a time domain means by which to obtain high resolution spectroscopic information on excited state rotational levels of large molecules [Felker et al., J. Phys. Chem. 90, 724 (1986); Baskin et al., J. Chem. Phys. 84, 4708 (1986)]. Here, the manifestations in temporally resolved, polarization-analyzed fluorescence of coherently prepared rotational levels in samples of isolated symmetric and asymmetric top molecules are considered. These manifestations, for reasonably large molecules at rotational temperatures characteristic of jet-cooled samples, take the form of polarization-dependent transients and recurrences with temporal widths of the order of tens of picoseconds or less. The transients, which arise from the thermal averaging of many single molecule coherences, are examined with respect to their dependences on molecular parameters (rotational constants, transition dipole directions) and experimental parameters (polarization directions and temperature). A physical picture of rotational coherence as a reflection of the time-dependent orientation of molecules in the sample is developed. And, the influence of rotational coherence in experiments designed to probe intramolecular energy flow is discussed. In the accompanying paper, we present experimental results for jet-cooled t-stilbene and anthracene. For t-stilbene we determine rotational constants for vibrational levels in the S1 electronic state (from the recurrences) and we monitor the trends in rotational coherence vs vibrational coherence as the total energy in the molecule increases.

High resolution imagery systems and methods

Abstract: The current limits of resolution of multi-element optical systems are exceeded by reducing the number of elements while introducing at the critical aperture a blazed transmission grating having grating rings of low bending power defined by multiple plateaus. By illuminating the optical train with monochromatic light that constitutes a multiplicity of distributed sources having a substantial temporal coherence but spatial incoherence and by varying the slopes and widths of the grating rings, local phase delays are introduced that adjust aberrations in the optical system, providing an aligned composite wavefront. The system and method may be used for presenting an image, as for a wafer stepper, or for viewing an image, as in a microscope.

Electrodynamics of the Semiconductor Band Edge

Abstract: The book is a presentation of an approach to electrodynamics in semiconductors It describes in detail the coherence phenomena appearing when the electromagnetic wavelength, the electron-hole coherence length and the single-particle wavelength are of the same order of magnitude

All-fiber 90° optical hybrid for coherent communications

Abstract: A 90° optical hybrid is a four-port optical device with two inputs and two outputs. The two output signals are proportional to E1 + E2 and E1 + E2 exp(j90°), respectively, where E1 and E2 are the complex amplitudes the two input signals. The 90° hybrids are needed in many applications, including homodyne optical receivers in both phase-locked and phase-diversity configurations. In this paper, the principle of operation of an all-fiber 90° hybrid is described, and an experimental unit using connectorized in-line single-mode fiber components is reported.

Disentanglement of quantum wave functions: Answer to ‘‘Comment on ‘Unified dynamics for microscopic and macroscopic systems’ ’’

Abstract: It is shown that the assumption of a stochastic localization process for the quantum wave function is essentially different from the suppression of coherence over macroscopic distances arising from the interaction with the environment and allows for a conceptually complete derivation of the classical behavior of macroscopic bodies.

Coherence properties of squeezed light and the degree of squeezing

Abstract: Certain two-time correlation functions of squeezed optical fields and their Fourier conjugates are investigated. These functions are related to the autocorrelation function and the spectral density of the photoelectric current that appears in measurements made of the squeezed light by a homodyne technique. Because the field is often assumed to contain a monochromatic carrier, it is only quasi-stationary, and modified quantum correlation functions, specially constructed to be time independent, are used to describe its properties. The symmetries of the corresponding conjugate spectral functions, which are not always spectral densities, are investigated. The concepts of homogeneous squeezing, inhomogeneous squeezing, and spectral component squeezing are introduced, and it is shown that the condition for cross-spectral purity, when satisfied, leads to homogeneous squeezing. A frequency-dependent parameter called the degree of squeezing, which lies between 0 and −1 for a squeezed state and is simply related to photoelectric measurements, is introduced. These ideas are then applied to the squeezing produced in resonance fluorescence, in parametric downconversion, and in four-wave mixing, and the degrees of squeezing under different conditions are compared.

Thermo-Optical Spectrophotometries in Analytical Chemistry

Abstract: I. INTRODUCTION A. Background The incorporation of lasers as light sources in analytical spectroscopic instrumentation has resulted in spectacular detection limits. These detection limits arise from several unique properties of laser radiation. As an example, the spectral purity and high power of the laser facilitates detection of individual gas phase atoms with isotopic resolution by both fluorescence and ionization techniques.1−3 The temporal coherence of the laser has been used to discriminate signals generated by very fast scatter processes from relatively slower luminescence relaxation.4, 5 In addition, the spatial coherence of the laser allows measurement by thermo-optical techniques of very small absorbance, the subject of this review. A recent review in this journal considered the related technique of photoacoustic spectroscopy, another high-sensitivity absorbance method.6

Anomalous magnetoconductance beyond the diffusion limit

Abstract: The weak localization contribution to the conductance depends sensitively on the applied magnetic field. This anomalous magnetoconductance provides a unique tool for the identification of weak localization and other phenomena associated with it. The standard theory of the anomalous magnetoconductance is based on the diffusion approximation, which applies to the case where the number of elastic scattering events is very large during a time of phase coherence in the electronic wave. For a strictly two-dimensional film, an arbitrary number of scattering events is considered and marked deviations are found from the standard theory if this number is not large.

Coherence multiplexing of optical sensors

Abstract: A multiplexed optical sensor system comprising a short coherence length source (SLD 60), a plurality of waveguide sensors (62, 64), a corresponding plurality of waveguide detectors (68, 70), and a common optical bus 84. Each sensor comprises a sensor interferometer having sensing and reference arms, each arm comprising an optical waveguide. Means are provided for varying the optical path length of the sensing arm based on a sensed input parameter. In one preferred embodiment, the detection subsystem comprises a plurality of detectors, each comprising a photodetector and a detector interferometer having first and second arms. The arms of each sensor interferometer (i) have an optical path length difference LS(i) that is greater than the coherence length of the SLD, and that differs from the path length difference LS(j) of each other sensor interferometer by an amount greater than the coherence length of the SLD. Each detector has a path length difference LD(i) that differs from the path length difference of an associated sensor LS(i) by not substantially more than the coherence length of the SLD. Thus variation of each sensed input parameter produces an amplitude variation in the output of a corresponding detector. An embodiment comprising a single swept detector interferometer is also disclosed.

Coherence of defect interactions with features in optical imaging

Abstract: For optical projection printing the variation of image intensity due to a defect in proximity to a feature is shown to be far greater than the image intensity produced by the same defect when it is isolated. This large impact is due to a nearly coherent interaction of electric fields of the defect with those of the feature. The effective mutual coherence μeff between a feature and a defect is defined and shown to be closely related to the degree of spatial coherence in the illumination across the mask. An algebraic model for feature variation as a function of defect size and location is derived from knowledge of defect intensity, feature line edge intensity slope, and μeff. It is predicted and confirmed by simulation that a 0.25λ/NA defect which has only a 3% isolated image intensity will create a 12% linewidth variation when adjacent to a 0.8λ/NA minimum feature size line. The linewidth variation perpendicular to the feature edge is directly proportional to the area of the defect. The length of the bulge produced parallel to the feature edge is given by the point spread function for the optical system and is thus independent of feature size. This makes defects appear larger than their actual size in both projection printing and inspection systems.

Evolution matrix in a coherence vector formulation for quantum Markovian master equations of N-level systems

Abstract: Quantum Markovian master equation in N dimensions are systematically transformed into vector form by using the Lie algebra of the special unitary group SU(N). Density operators are represented through coherence vectors and the infinitesimal Kossakowski generator of completely positive quantum dynamical semigroups appears as a real evolution matrix that is not completely diagonalisable, in general. A complete classification of the spectrum of the latter and its Jordan canonical form, together with all types of associated stationary states, is given in detail. The results of this analysis are particularly suited for computations in practical applications.

Second-harmonic generation by a partially coherent beam.

Abstract: The effect of degradation of the coherence of the pump beam by a random phase screen on the conversion efficiency in the second-harmonic generation process is considered. It is shown that, under suitable conditions, the conversion efficiency can be increased significantly.

Symmetry in coherence transfer

Abstract: The symmetry of coherence transfer between pairs of transitions in quantum mechanical systems is investigated. Conditions for symmetric transfer under composite processes consisting of pulses and precession periods are formulated. The symmetry of two-dimensional (2D) N.M.R. spectra with respect to reflection about the diagonal serves as a concrete example. The current experimental 2D N.M.R. techniques are analysed in view of symmetry and examples of experiments are discussed that lead to asymmetric coherence transfer and asymmetric 2D spectra.

III Interferometry with Lasers

Abstract: Publisher Summary This chapter focuses on interferometry with lasers. The development of the laser made available for the first time an intense source of light with a remarkably high degree of spatial and temporal coherence. The use of lasers has removed most of the limitations of interferometers imposed by thermal sources and has led to the development of several new and interesting techniques in interferometry. Two other factors that have contributed to this revolution have been the progressive replacement of the human eye by photodetectors and the increasing use of sophisticated techniques of signal processing made possible by digital computers. These developments and the availability of tunable lasers, have led to new methods of measurement, some based on heterodyne techniques and others involving direct evaluation of the interference phase. Finally, interesting possibilities have been opened up by the use of single mode optical fibers and nonlinear crystals to build new types of interferometers with entirely new applications.

Far-zone behavior of electromagnetic fields generated by fluctuating current distributions

Abstract: General expressions are derived for various quantities that characterize the far field generated by any fluctuating localized current distribution that is statistically stationary, at least in the wide sense. In particular, expressions are derived for the cross-spectral density tensors of the electromagnetic field, for the coherence matrix and the Stokes parameters, for the degree of polarization, and for the degree of coherence of the far field in terms of the cross-spectral density of the transverse part of the source current. The analysis is illustrated by considering radiation from a fluctuating linear current source.

Distinctive quantum features of electron intensity correlation interferometry

Abstract: Experiments employing intensity correlation of massive fermions, in particular electrons, are proposed that show novel quantum effects not observable by usual amplitude interferometry. The experiments permit new tests of quantum predictions concerning the wavelike properties, exchange symmetry, quantum statistics, and interaction with potentials of multiparticle fermion states. Experimental configurations considered includea) a direct fermion analogue of the optical Hanbury Brown-Twiss (HBT) experiment that manifests fermion antibunching irrespective of beam coherence properties;b) an experiment (with no quantum optical analogue) sharing features of the HBT experiment and Aharonov-Bohm effect that manifests a new quantum influence of confined magnetic flux on charged particles;c) an experiment sharing features of the HBT and Colella-Overhauser-Werner experiments that manifests a new gravity-induced quantum interference effect. In contrast to the intensity correlation of light, for which some fields (e.g. chaotic) can be analysed by either classical or quantum optics, the correlation of fermion intensities requires exclusive use of quantum theory.

Test of squeezing and coherence of a single-mode cavity field

Abstract: It is shown that off-diagonal elements of the photon density matrix of a single-mode cavity field can be determined by using test atoms that are initially prepared in a coherent superposition of the two states interacting with the cavity mode. In particular, this makes it possible to test the cavity field with respect to squeezing.

Temporal coherence properties of a dispersively propagating beam in a fiber-optic interferometer

Abstract: The temporal coherence properties of a dispersively propagating optical beam are clarified experimentally by means of a two-beam interferometer composed of optical fibers with 1.3- and 1.5-μm zero-chromatic-dispersion wavelengths. Experimental results fully explain and reflect theoretically predicted ones concerning both the magnitude of the degree of coherence and the shape of the coherence curve with respect to the optical path difference.