Showing papers on "Coherence (physics) published in 1994"
TL;DR: The uncertainty limit in distance sensing by laser triangulation is discussed, and the same distance uncertainty that was obtained from a single-photon experiment and from Heisenberg's uncertainty principle is obtained.
Abstract: We discuss the uncertainty limit in distance sensing by laser triangulation. The uncertainty in distance measurement of laser triangulation sensors and other coherent sensors is limited by speckle noise. Speckle arises because of the coherent illumination in combination with rough surfaces. A minimum limit on the distance uncertainty is derived through speckle statistics. This uncertainty is a function of wavelength, observation aperture, and speckle contrast in the spot image. Surprisingly, it is the same distance uncertainty that we obtained from a single-photon experiment and from Heisenberg's uncertainty principle. Experiments confirm the theory. An uncertainty principle connecting lateral resolution and distance uncertainty is introduced. Design criteria for a sensor with minimum distanc uncertainty are determined: small temporal coherence, small spatial coherence, a large observation aperture.
455 citations
TL;DR: In this article, a framework for understanding impulsively photoinduced vibrational coherent motion on the ground electronic surface was presented, in particular strong resonant excitation to a directly dissociative electronic surface is considered.
Abstract: A framework for understanding impulsively photoinduced vibrational coherent motion on the ground electronic surface is presented. In particular strong resonant excitation to a directly dissociative electronic surface is considered. Three distinct approaches are employed. A two surface Fourier wavepacket method explicitly including the field explores this process in isolated molecules. A coordinate dependent two‐level system is employed to develop a novel analytical approximation to the photoinduced quantum dynamics. The negligible computational requirements make it a powerful interactive tool for reconstructing the impulsive photoexcitation stage. Its analytical nature provides closed form expressions for the photoinduced changes in the material. Finally the full simulation of the process including the solvent effects is carried out by a numerical propagation of the density operator. In all three techniques the excitation field is treated to all orders, allowing an analysis of current experiments using strong fields, resulting in substantial photoconversion. The emerging picture is that the impulsive excitation carves a coherent dynamical ‘‘hole’’ out of the ground surface density. A rigorous definition of the dynamical ‘‘hole’’ is constructed and used to define a measure of its coherence. In particular all photoinduced time dependence in the system can be directly related to the dynamical ‘‘hole.’’ All three techniques are used to simulate the pump probe experiment on the symmetric stretch mode of I3−, including electronic and vibrational dephasing.
213 citations
TL;DR: The dynamical and information aspects of the behavior of complex physical systems are considered in this article, where the Einstein-Podolsky-Rosen paradox is discussed in detail together with its possible role in the processes of information transfer over a distance.
Abstract: The dynamical and information aspects of the behaviour of complex physical systems are considered. In classical physics the information coupling appears in the interaction of nonlinear systems with stohastic behaviour when a small external perturbation may greatly alter the paths of a classical system in phase space. In quantum systems the information coupling to the environment appears in measurement processes when the coherence of the wave function of a quantum object is destroyed and corresponding information appears in the external environment. These processes can be described in terms of the collapse of wave functions. Numerous examples of the collapse are considered, including those leading to the classical behaviour of macroscopic bodies with the information coupling to a nonequilibrium environment. The Einstein–Podolsky–Rosen paradox is discussed in detail together with its possible role in the processes of information transfer over a distance.
156 citations
Patent•
29 Mar 1994
TL;DR: In this article, a simple and economical reflectometer apparatus is achieved with which a rapid sequence of image recordings is possible, in which light signals can be recorded in a position sensitive and simultaneous fashion and both partial beams in the object arm and in the reference arm are so guided that a spatial interference pattern occurs along the lateral extent of the detector configuration.
Abstract: In an optical imaging apparatus for the investigation of strongly scattering media, in particular biological tissue samples, with at least one-dimensional position resolution in a depth direction of a measuring object, with a radiation source for radiating low coherence light, with a device for splitting the low coherence light into two partial beams, of which one is guided in an object arm to the measured object and the other in a reference arm to a reflecting element, and with a detector configuration to which the partial beams reflected from the reflecting element in the reference arm and from the measured object in the object arm can be guided, brought into interference with another, and detected, the detector configuration exhibits a spatial extent transverse to the incident direction of both partial beams on the detector configuration along which light signals can be recorded in a position sensitive and simultaneous fashion and both partial beams in the object arm and in the reference arm are so guided that a spatial interference pattern occurs along the lateral extent of the detector configuration, whereby the reflecting element in the reference arm exhibits only static parts which, in any event, are non-mechanically moving. In this fashion a simple and economical as well as especially mechanically stable reflectometer apparatus is achieved with which a rapid sequence of image recordings is possible.
139 citations
TL;DR: In this article, the role of correlated isotropy in the study of microroughness in high-quality optical coatings is emphasized and compared, and the sensitivity of the investigation method to the stack parameters is studied.
Abstract: We emphasize the role of correlated isotropy in the study of microroughness in high-quality optical coatings. First, cross correlation between surfaces and cross coherence between scattering sources are discussed and compared. An isotropy degree of roughness is then introduced as a quantitative value to describe the angular disorder of a surface connected with the polar dependence of scattering. We show how the frequency variations of this isotropy degree allow one to solve the inverse problem and obtain a unique solution for the scattering parameters that describe structural irregularities of the stacks. Light scattering can also be used to detect an oblique growth of the materials in thin-film form. Finally, we study the sensitivity of the investigation method to the stack parameters.
139 citations
TL;DR: The loss of transverse spatial coherence of an atomic wave function after a single spontaneous emission is demonstrated and the period of the standing light wave is changed to mapped the loss of spatial coherent as a function of the transverse coordinate.
Abstract: We have demonstrated the loss of transverse spatial coherence of an atomic wave function after a single spontaneous emission. ${\mathrm{He}}^{*}$ atoms were both diffracted and excited by a standing light wave with a variable period. After the interaction, the excited atoms decay by a single spontaneously emitted photon. By changing the period of the standing light wave, we have mapped the loss of spatial coherence as a function of the transverse coordinate. By detecting the emitted photon one could "erase" the position information available and recover the transverse coherence in a correlation experiment, or realize a Heisenberg microscope.
128 citations
TL;DR: It is shown that the down-converted light is spatially incoherent in the second order, and that the signal-idler fourth-order coherence extends over finite entanglement angles.
Abstract: We investigate the amplitude and intensity spatiotemporal coherence and the photon coincidence rates of far-field down-converted light resulting from the interaction of a pump wave of finite spectral width with a nonlinear crystal of finite spatial width. We examine the interplay between energy and phase mismatches and their effects on the intrabeam and interbeam spatial and temporal coherence of the down-converted beams. We show that the down-converted light is spatially incoherent in the second order, and that the signal-idler fourth-order coherence extends over finite entanglement angles. We also study the effect of the apertures through which the down-converted light is collected, when they are centered at phase-matched or misaligned directions.
125 citations
TL;DR: An optical magnetometer based on atomic coherence effects is analyzed using a quantum Langevin approach and effects of Doppler broadening and fluctuations of the driving field are discussed and a comparison to standard optical-pumping magnetometers is made.
Abstract: An optical magnetometer based on atomic coherence effects is analyzed using a quantum Langevin approach. The large dispersion of a phase-coherent atomic medium (``phaseonium'') at a point of vanishing absorption is used to detect magnetic level shifts via optical phase measurements in a Mach-Zehnder interferometer with sensitivities potentially superior to state-of-the-art devices. Effects of Doppler broadening and fluctuations of the driving field are discussed and a comparison to standard optical-pumping magnetometers is made.
119 citations
TL;DR: In this paper, a Pancharatnam phase shift was introduced into the idler path between two down-converters in an experiment on induced coherence without induced emission.
Abstract: A Pancharatnam phase shift, which is similar to Berry's topological phase, is introduced into the idler path between two down-converters in an experiment on induced coherence without induced emission. Although the idler beams in such an experiment do not take part in interference, the Pancharatnam phase shift is observable in the interference of the signal beams. This is clearly a nonlocal manifestation of Pancharatnam's phase.
95 citations
TL;DR: A linear stability analysis is given which demonstrates the existence of a Hopf bifurcation for low values of the pump parameter and the value of the newly introduced coherence lifetime parameter is discussed.
Abstract: The temporal dynamics of an erbium-doped fiber laser shows various interesting modes of behavior. In the stationary regime, a behavior going from a cw working mode to deterministic chaos through different self-pulsed working modes has been observed. In the transient regime, effects such as antiphase phenomena, between two orthogonal states of polarization, can be observed. To describe the dynamics of the fiber laser we have studied a theoretical model based on two coupled lasers coherently pumped. A linear stability analysis is given which demonstrates the existence of a Hopf bifurcation for low values of the pump parameter. Numerical calculation results allow a good description of the experimental results. The value of the newly introduced coherence lifetime parameter is discussed.
86 citations
Patent•
14 Sep 1994
TL;DR: In this article, a particle analyzer includes a flow device having a light-transmissive flow cell for allowing subject particles in a sample liquid to flow in a separated state, a laser beam illuminator for illuminating a subject particle flowing in the flow cell with a laserbeam and a coherence lowering device for lowering coherence of the laser beam.
Abstract: A particle analyzing apparatus includes a flow device having a light-transmissive flow cell for allowing subject particles in a sample liquid to flow in a separated state, a laser beam illuminator for illuminating a subject particle flowing in the flow cell with a laser beam and a coherence lowering device for lowering coherence of the laser beam. The particle analyzing apparatus further includes an image capturing device receiving light from the subject particle, for capturing an image of the subject particle and an image processor for processing and analyzing the captured image of the subject particle. By use of the coherence lowering device, both temporal and spatial coherence of the laser beam is lowered. Thus, image quality is improved and a high quality particle image can be obtained which is bright and high in S/N ratio.
TL;DR: In this paper, light-induced spin-correlated radical pairs in plant photosystem I are studied by high-time resolution transient EPR following pulsed laser excitation, which implies a two-dimensional variation of the signal intensity with respect to both the magnetic field and time axis.
Abstract: Light-induced spin-correlated radical pairs in plant photosystem I are studied by high time resolution transient EPR following pulsed laser excitation. The time evolution of the transverse magnetization is monitored at various static magnetic fields. This implies a two-dimensional variation of the signal intensity with respect to both the magnetic field and time axis. Zero quantum coherence between two of the four eigenstates of the radical pair is observed at early times after the laser pulse. Model calculations, based on the stochastic Liouville equation, provide detailed information about the spin dynamics of correlated radical pairs. 48 refs., 6 figs., 1 tab.
TL;DR: A dynamic theory that connects electronic motions and the nonlinear optical response of conjugated polyenes is developed by introducing the concept of electronic normal modes and establishes a close analogy with small semiconductor particles (quantum dots).
Abstract: A dynamic theory that connects electronic motions and the nonlinear optical response of conjugated polyenes is developed by introducing the concept of electronic normal modes. A useful picture for the mechanism of optical nonlinearities is obtained by identifying the few dominant modes. This quasi-particle electron-hole representation establishes a close analogy with small semiconductor particles (quantum dots) and is very different from the traditional approach based on electronic eigenstates. The effective conjugation length (coherence size), which controls the scaling and saturation of the static third-order susceptibility X (3) with the number of double bonds, is related to the coherence of the relative motion of electron-hole pairs created upon optical excitation.
TL;DR: In this paper, the color opacity effects in nuclear quasielastic reactions were investigated. But the results were limited to the average value of color fluctuations near the average values, and they did not consider the effect of nuclear inelastic diffraction.
Abstract: CONTENTS. 1.Introduction, 1.1 QCD ideas to be tested; 2. Coherence phenomena in QED, 2.1 Charge transparency, 2.2 Charge filtering, 2.3 Charge opacity; 3. Color transparency in perturbative QCD, 3.1 Coherence length in QCD, 3.2 Bjorken scaling for deep inelastic processes, 3.3 Hard Coherent Diffraction {}From Nucleons and Nuclei; 4. Soft Diffractive Physics and Color Fluctuations, 4.1 Scattering eigenstates formalism; 4.2 Current information on color fluctuations in Hadrons, 4.3 Small Size Configurations in Pions, 4.4 Nuclear inelastic diffraction as evidence for color fluctuations near the average value, 4.5 Inelastic screening corrections to the total cross sections; 5. Color transparency in nuclear quasielastic reactions. 5.1 Is a small system made?, 5.2 Time development, 5.3 Relevant data; 6. Color fluctuations in nucleons and nucleus-nucleus collisions, 6.1 Color opacity effects, 6.2 Color fluctuations and central collisions, 6.3 Leading hadron transparency effects in central collisions.
Patent•
13 Jan 1994TL;DR: In this article, a method of profiling a rough surface of an object includes the steps of producing an interference pattern of the object surface (14) using an interferometer (1) to produce an illumination intensity on the pixels of an imaging device (18), varying the optical path difference between the object surfaces and a reference surface (22) of the interferer (1), through a range including a position of zero opticalpath difference for each pixel, calculating values of an interference discriminator function to identify the regions of coherence, gathering at the imaging device and storing for each
Abstract: A method of profiling a rough surface of an object includes the steps of producing an interference pattern of the object surface (14) using an interferometer (1) to produce an illumination intensity on the pixels of an imaging device (18), varying the optical path difference between the object surface (14) and a reference surface (22) of the interferometer (1) through a range including a position of zero optical path difference for each pixel, calculating values of an interference discriminator function to identify the regions of coherence, gathering at the imaging device (18) and storing for each pixel a plurality of intensity values about the region of coherence - as identified by the state or value of the interference discriminator function calculations - at consecutive data points spaced along the range by a predetermined phase difference, storing for each pixel the relative position of the plurality of intensity values along the range, and calculating from the stored intensity values the difference in height between two selected pixels using methods known in the art. An apparatus for practising the invention is also disclosed.
TL;DR: In this article, the dominant effects of the biexciton-induced two-photon coherence on polarization-dependent four-wave mixing in GaAs quantum wells were demonstrated.
TL;DR: In this article, a generalized Huygens-Fresnel integral is used to derive a general expression for the mutual coherence function (MCF) associated with a Gaussian-beam wave in the weak-fluctuation regime.
Abstract: A generalized Huygens–Fresnel integral, valid for optical wave propagation through random inhomogeneities in the presence of any complex optical system characterized by an ABCD ray matrix, is used to derive a general expression for the mutual coherence function (MCF) associated with a Gaussian-beam wave in the weak-fluctuation regime. The mean irradiance obtained from this expression shows excellent agreement with all known asymptotic relations. By introducing a pair of effective beam parameters Θt and Λt that account for additional diffraction on the receiving aperture, resulting from turbulence, the normalized MCF and the related degree of coherence are formally extended into the regime of strong fluctuations. Results for the normalized MCF from this heuristic approach compare well with numerical calculations obtained directly from the formal solution of the parabolic equation. Also, the implied spatial coherence length from this analysis in moderate-to-strong-fluctuation regimes generally agrees more closely with numerical solutions of the parabolic equation than do previous approximate solutions. All calculations are based on the modified von Karman spectrum for direct comparison with established results.
TL;DR: The quantum-noise properties near the threshold of microcavity lasers are studied theoretically and experimentally in the weak-coupling regime and it is shown that there always exists a finite threshold for these lasers defined by the peak of the photon-number correlation function corresponding to the spontaneous-to-stimulated transition.
Abstract: The quantum-noise properties near the threshold of microcavity lasers are studied theoretically and experimentally in the weak-coupling regime. Computations based on two-level quantum theory show that the microlasers exhibit a high degree of second-order coherence compared with conventional lasers as a result of the suppression of spontaneous emission into nonlasing modes, and that there always exists a finite threshold for these lasers defined by the peak of the photon-number correlation function corresponding to the spontaneous-to-stimulated transition.
TL;DR: The theoretical results implied that there was a reduction in the degree of induced coherence due strictly to the spatial distribution of the down-conversion beams, and an unexpected quantitative discrepancy between second- and fourth-order visibilities in previous induced-coherence experiments was explained.
Abstract: The quantum state for spontaneous parametric down-conversion was evaluated to include information about the transverse spatial characteristic of the down-conversion fields. This state was used to calculate the angular spectrum of down-conversion in the case of both single-channel and coincidence measurements, while retaining the characteristic nonclassical correlations. Actual transverse profiles for typical experimental parameters were evaluated numerically and measurements were performed with results that compared well with the numerical calculation. This theoretical spatial model was then applied nonrigorously to the case of induced coherence without induced emission. The theoretical results implied that there was a reduction in the degree of induced coherence due strictly to the spatial distribution of the down-conversion beams. This was interpreted as a result of increased distinguishability of the overlapping idler photons. Measurements were conducted which support these results qualitatively. In addition, the present theory explained an unexpected quantitative discrepancy between second- and fourth-order visibilities in previous induced-coherence experiments. This discrepancy was interpreted phenomenologically as a difference between intrinsic and nonintrinsic indistinguishability, and some implications towards quantum measurement theory and the role of the observer were suggested.
TL;DR: Two-dimensional versions of HNCA and HNCO experiments are described, which provide essentially the same information as the 3D sequence, but with different information content.
Abstract: Two-dimensional versions of HNCA and HNCO experiments are described, which provide essentially the same information as the 3D sequence. A multiple-quantum coherence involving either 15N and 13C alpha or 15N and 13CO is created. One of the two frequencies is given by the middle point between the two cross peaks (zero- and double-quantum) and the other by their separation. Quadrature detection can be performed on either nucleus, modifying only the appearance of the 2D spectrum, but not the information content. These experiments, named MQ-HNCA and MQ-HNCO, are illustrated on a (15N, 13C) doubly labelled cytochrome c2 from Rhodobacter capsulatus (116 amino acids).
TL;DR: In this paper, the authors present results from quantum dynamical simulations of electron transfer, obtained using a multilevel version of Redfield relaxation theory, which illustrate the complex dynamics that result when electron tunneling and vibrational relaxation processes occur on similar time scales.
Abstract: We present results from quantum dynamical simulations of electron transfer, obtained using a multilevel version Redfield relaxation theory, which illustrate the complex dynamics that result when electron tunneling and vibrational relaxation processes occur on similar time scales. By treating the system‐field interaction quantum mechanically, we examine the extent to which the time‐ and frequency‐resolved emission signal reflects the electron transfer dynamics. The results from these simulations provide new insight into the role of quantum coherences in ultrafast rate processes and time‐resolved spectral measurements.
TL;DR: In this paper, the authors discuss the effects of shaping of the optical fields in both amplitude and phase on terahertz radiation emission from a short laser pulse exciting semiconductor heterostructures.
Abstract: A short laser pulse exciting semiconductor heterostructures will induce a time-varying polarization that in turn leads to the generation of terahertz radiation. Although there are several possible mechanisms for this time-dependent polarization, some depend critically on the dephasing time of the photoexcited carriers. For long dephasing times it is possible to control both the populations and the coherence of these particles by proper shaping of the optical pulse. We discuss our recent experimental and theoretical work on coherent terahertz radiation emitted from semiconductor heterostructures when the exciting optical fields are shaped in both amplitude and phase. Our shaping techniques include phase-locked pulse generation in a Michelson interferometer and pulse-train generation by phase-only filtering.
TL;DR: In this article, an asymptotic analysis of on-axis intensity fluctuation variance of a finite-sized light beam is performed starting from the functional integral representation for the field in a random medium.
Abstract: Asymptotic analysis of on-axis intensity fluctuation variance of a finite-sized light beam is performed starting from the functional integral representation for the field in a random medium. Collimated, diverging and converging beams with different diffraction properties are considered. A complete set of asymptotes is obtained using the main and additional coherence channels approach to the fourth moment of field analyses. We study the conditions of weak and strong fluctuation regimes for all these types of beams and obtain relatively simple formulae for on-axis intensity variance, which are valid for the case of stratified turbulence. It is shown that scintillations in the vicinity of the beam focus are governed by double-scattering processes for weak scintillations and double scattering from coherence channels for strong fluctuations.
TL;DR: This work presents a temporal, multiframe extension of the dense optical flow estimation formulation proposed by Horn and Schunck (1981) in which a temporal coherence constraint is used to yield the optimal fusing of data from multiple frames of measurements.
Abstract: In the computation of dense optical flow fields, spatial coherence constraints are commonly used to regularize otherwise ill-posed problem formulations, providing spatial integration of data. We present a temporal, multiframe extension of the dense optical flow estimation formulation proposed by Horn and Schunck (1981) in which we use a temporal coherence constraint to yield the optimal fusing of data from multiple frames of measurements. Conceptually, standard Kalman filtering algorithms are applicable to the resulting multiframe optical flow estimation problem, providing a solution that is sequential and recursive in time. Experiments are presented to demonstrate that the resulting multiframe estimates are more robust to noise than those provided by the original, single-frame formulation. In addition, we demonstrate cases where the aperture problem of motion vision cannot be resolved satisfactorily without the temporal integration of data enabled by the proposed formulation. Practically, the large matrix dimensions involved in the problem prohibit exact implementation of the optimal Kalman filter. To overcome this limitation, we present a computationally efficient, yet near-optimal approximation of the exact filtering algorithm. This approximation has a precise interpretation as the sequential estimation of a reduced-order spatial model for the optical flow estimation error process at each time step and arises from an estimation-theoretic treatment of the filtering problem. Experiments also demonstrate the efficacy of this near-optimal filter. >
TL;DR: Attention has been given to identifying the transition from stable strong-feedback operation to the coherence collapse regime obtained with moderate optical feedback.
Abstract: Dynamical and noise properties of laser diodes subject to strong optical feedback have been investigated. Under strong optical feedback a conventional rate-equation approach is not valid, and thus an iterative traveling-wave model has been developed to describe this operating regime. Attention has been given to identifying the transition from stable strong-feedback operation to the coherence collapse regime obtained with moderate optical feedback.
TL;DR: In this article, the authors examined the use of wave-packet interferometry to study the dynamic properties of packets created by two-photon absorption, and found several interference populations.
Abstract: The excitation of a molecule by a short pulse creates a wave packet whose motion depends on the nuclear forces of the excited electronic state. The properties of such a packet can be studied interferometrically. This is done by exposing the molecule to two identical pulses delayed from each other. Two packets are thus created and the excited state population has a term which depends on the interference between them. This interference population is a quantum effect and its dependence on the delay time reflects the coherence properties of the packet and is very sensitive to the potential energy surface. In this paper, we examine the use of wave‐packet interferometry to study the dynamic properties of packets created by two‐photon absorption. We find several interference populations since the packets created by two‐photon absorption interfere with each other and with packets created by absorption of one photon from each pulse. The single interference terms contain different physical information and we discuss how each can be measured separately. This method provides a sensitive way for studying the dynamic properties of high energy electronic states that can be reached by two‐photon absorption.
TL;DR: In this article, color coherence effects in pp\ifmmode\bar\else\textasciimacron\fi{} collisions are observed and studied with CDF, the Collider Detector at the Fermilab Tevatron collider.
Abstract: Color coherence effects in pp\ifmmode\bar\else\textasciimacron\fi{} collisions are observed and studied with CDF, the Collider Detector at the Fermilab Tevatron collider. We demonstrate these effects by measuring spatial correlations between soft and leading jets in multijet events. Variables sensitive to interference are identified by comparing the data to the predictions of various shower Monte Carlo programs that are substantially different with respect to the implementation of coherence.
Patent•
18 Mar 1994TL;DR: In this article, a low-coherence reflectometer for measuring optical backscattering was proposed, which utilizes an optical attenuation in the reference arm of a Michelson interferometer to reduce the relative intensity noise.
Abstract: A low-coherence reflectometer for use in measuring optical backscattering. The invention utilizes an optical attenuation in the reference arm of a Michelson interferometer to reduce the relative intensity noise. The invention obtains essentially the same performance as obtained with balanced detector schemes while maintaining the simplicity of the Michelson interferometer design and increased scan distance.
TL;DR: Two formulations of quantum mechanics, inequivalent in the presence of closed timelike curves, are studied in the context of a soluable system, demonstrating how quantum field nonlinearities lead to a breakdown of unitarity, causality, and superposition using a path integral.
Abstract: Two formulations of quantum mechanics, inequivalent in the presence of closed timelike curves, are studied in the context of a soluable system. It illustrates how quantum field nonlinearities lead to a breakdown of unitarity, causality, and superposition using a path integral. Deutsch's density matrix approach is causal but typically destroys coherence. For each of these formulations I demonstrate that there are yet further alternatives in prescribing the handling of information flow (inequivalent to previous analyses) that have implications for any system in which unitarity or coherence is not preserved.