Showing papers on "Coherence (physics) published in 1986"

Experimental Evidence for a Photon Anticorrelation Effect on a Beam Splitter: A New Light on Single-Photon Interferences

Abstract: We report on two experiments using an atomic cascade as a light source, and a triggered detection scheme for the second photon of the cascade. The first experiment shows a strong anticorrelation between the triggered detections on both sides of a beam splitter. This result is in contradiction with any classical wave model of light, but in agreement with a quantum description involving single-photon states. The same source and detection scheme were used in a second experiment, where we have observed interferences with a visibility over 98%. During the past fifteen years, nonclassical effects in the statistical properties of light have been extensively studied from a theoretical point of view (l), and some have been experimentally demonstrated (2-71. All are related to second-order coherence properties, via measurements of intensity correlation functions or of statistical moments. However, there has still been no test of the conceptually very simple situation dealing with single- photon states of the light impinging on a beam splitter. In this case, quantum mechanics predicts a perfect anticorrelation for photodetections on both sides of the beam splitter (a single-photon can only be detected once!), while any description involving classical fields would predict some amount of coincidences. In the first part of this letter, we report on an experiment close to this ideal situation, since we have found a coincidence rate, on both sides of a beam splitter, five times smaller than the classical lower limit. When it comes to single-photon states of light, it is tempting to revisit the famous historical .single-photon interference experiments. (8). One then finds that, in spite of their

Aharonov-Bohm effect in normal metal quantum coherence and transport

Abstract: We review some of the recent surprising theoretical and experimental results obtained on the transport properties of small disordered metal samples. Even in the presence of disorder, the quantum mechanical interference of electron wavefunctions can still be observed. The Aharonov-Bohm effect is a particularly clear demonstration of this. In doubly connected structures (such as loops of wire) threaded by a magnetic flux, the electrical conductance oscillates because of the Aharonov-Bohm effect. In fact, because the electron trajectories are diffusive (i.e. random walks), even a lone wire (a singly connected structure) will exhibit a random pattern of conductance fluctuations as a function of the magnetic field because of the same interference effects. All that is required for the observation of these interferences is that the electrons retain ‘phase memory’ duing the period of transit through the sample. The length over which memory is maintained (the phase coherence length) can be much larger tha...

Phase noise in semiconductor lasers

Abstract: The subject of phase noise in semiconductor lasers is reviewed. The description of noise in lasers and those aspects of phase noise that are relevant to optical communications are emphasized. The topics covered include: Langevin forces; laser linewidth above threshold and below threshold; line structure due to relaxation oscillations; phase fluctuations; line narrowing by a passive cavity section and by external feedback; coherence collapse due to optical feedback; the shot noise limits of several schemes of coherent optical communication, and the linewidth required to approach these ideal limits.

Application of the Wigner distribution function to partially coherent light

Abstract: The paper presents a review of the Wigner distribution function (WDF) and of some of its applications to optical problems, especially in the field of partial coherence. The WDF describes a signal in space and in spatial frequency simultaneously and can be considered the local spatial-frequency spectrum of the signal. Although derived in terms of Fourier optics, the description of an optical signal by means of its WDF closely resembles the ray concept in geometrical optics; the WDF thus presents a link between partial coherence and radiometry. Properties of the WDF and its propagation through linear optical systems are considered; again, the description of systems by WDF’s can be interpreted directly in geometric-optical terms. Some examples are included to show how the WDF can be applied to practical problems that arise in the field of partial coherence.

Correlation of connected transitions by two‐dimensional NMR spectroscopy

Abstract: A novel and general concept of restricting coherence transfer in nuclear spin systems is described. It opens new possibilities for editing one‐ and two‐dimensional NMR spectra. For example, the widely applied two‐dimensional correlation experiment COSY can be modified such as to restrict coherence transfer to take place exclusively between connected transitions in the energy level diagram. Such two‐dimensional spectra possess ideal features for assignment of complex scalar coupling networks and for computer assisted analysis. Experimental 1H spectra of a cyclic decapeptide are presented. Other applications of the general filtering concept are briefly discussed.

Nonlinear Optics and Quantum Electronics

Abstract: Partial table of contents: PART I: GENERAL CONCEPTS AND METHODS OF NONLINEAR OPTICS. Electromagnetic Fields. Classical Description. The Quantized Free Radiation Field. Interaction Between Radiation and Matter. Semiclassical Description of Nonlinear Optics. Statistical and Coherence Properties of the Radiation Field and Their Measurement. Nonstationary Processes. PART II: EFFECTS AND PROCESSES OF NONLINEAR OPTICS. Nonlinear One--photon Processes in Lasers. Nonlinearities in Transient One--photon Processes. Nonlinearities and Qunatum Phenomena in Transient One--photon Processes. Multiphoton Absorption and Emission. Generation of Harmonics and Sum and Difference Frequencies. Parametric Amplification and Oscillation. Stimulated Raman Scattering. Optical Bistability. APPENDIX A: Compilation of Quantum--Theoretical Definitions and Relations. General References. Index.

New theory of partial coherence in the space-frequency domain. Part II: Steady-state fields and higher-order correlations

Abstract: In Part I of this investigation [ WolfE., J. Opt. Soc. Am.72. 343 ( 1982)] new representations were introduced for the cross-spectral density of a steady-state source of any state of coherence. The central concept in that formulation was the notion of a coherent source mode (a natural mode of oscillation). In the present paper the theory is developed further and new representations are obtained for the cross-spectral densities of all orders, both of the source and of the field that the source generates. These representations involve only the previously introduced coherent source modes and the moments of certain random coefficients that characterize the statistical properties of the source. The results provide a new mathematical framework for analyzing coherence properties of all orders of stationary sources and of stationary fields. Some potential applications of the theory are mentioned.

Rephasing of collisionless molecular rotational coherence in large molecules

Abstract: We present experimental results on the rephasing of collisionless rotational coherence in jet-cooled trans-stitbene. The results represent the first observation of quantum coherence effects arising from the rotational level structure of molecules. We discuss the nature of the effect, its possible influence in time-resolved polarization experiments designed to probe intramolecular energy flow, and its possible uses as a new spectroscopic tool.

Coherence and Coulomb effects on pion interferometry.

Abstract: The effects of coherence and final-state Coulomb interactions on the Bose-Einstein correlations of identical particles are studied. It is shown that these corrections can be important, reducing the apparent source size by 20%. Coherence effects are shown to significantly reduce the coherence parameters for small sources. Other causes of correlation are also discussed.

Detailed measurements of inelastic scattering in Anderson localization.

Abstract: Considerable progress has been made in the experimental observation of Anderson localization and quantum eigenstate coherence for electrons in disordered solids. The coherence effects deduced from conductivity measurements require some corrections for inelastic scattering, and often the necessary information is imprecisely known. In this letter we report detailed observations of inelastic effects in an acoustic localization experiment where parameters may be precisely controlled and measured; some phase correlation effects are evident.

Direct observation of the second-order coherence of parametrically generated light.

Abstract: The second-harmonic spectrum of the output of an optical parametric emitter at degeneracy exhibits a narrow peak, much sharper than the spectrum of the parametric light. This peak is a manifestation of the second-order correlations in parametric light. Alternatively, it can be considered as resulting from the recombination of simultaneously generated (twin) wave packets. The twin-wave-packet correlation time is shown to be limited by the first-order coherence time of parametric light.

Fourth-order partial-coherence effects in the formation of integrated-intensity gratings with pulsed light sources

Abstract: We performed theoretical calculations of the relative diffraction efficiency of partially coherent light-induced integrated-intensity gratings using pulsed sources, paying particular attention to thermal gratings. We provided a simple intuitive picture of the phenomenon and then calculated exact expressions that, unlike instantaneous-intensity-grating results, necessarily require the use of fourth-order coherence functions. Assuming several radiation models, we evaluated these expressions and found that the results proved to be insensitive to the specific radiation model assumed. The application of these results to a previously performed pulsed-laser experiment yielded a better fit to the data than an expression involving only second-order coherence, which is valid only in the cw limit. We included the effects of grating decay and, in addition, compared the use of integrated-intensity gratings for ultrashort-pulse-length measurement with standard techniques. Finally, we calculated expressions for the relative diffraction efficiency of integrated-intensity gratings created with excitation beams from two separate and independent sources of different frequency, and we report an experiment whose results were found to agree with this theory.

Direct detection of two-quantum coherence

Abstract: A theoretical analysis of the oscillating voltage at twice the Larmor frequency (2ω0), due to quadrupolar polarization of 14N nuclei, predicts a signal at least ten orders of magnitude smaller than...

Weak Localization in Thin Films

Abstract: The resistance of two-dimensional electron systems such as thin disordered films shows deviations from Boltzmann theory, which are caused by quantum corrections and are called "weak localization" Theoretically, weak localization is originated by the Langer-Neal graph in the Kubo formalism In this review the physics of weak localization is discussed It represents an interference experiment with conduction electrons split into pairs of waves interfering in the back-scattering direction The intensity of the interference (integrated over the time) can be easily measured by the resistance of the film A magnetic field introduces a magnetic phase shift in the electronic wave function and suppresses the interference after a "flight" time proportional to 1/H Therefore the application of a magnetic field allows a time-of-flight experiment with conduction electrons Spin-orbit scattering rotates the spin of the electrons and yields an observable destructive interference Magnetic impurities destoy the coherence of the phase The experimental results as well as the theory is reviewed The role of the spin-orbit scattering and the magnetic scattering are discussed The measurements give selected information about the inelastic lifetime of the conduction electrons in disordered metals and raise new questions in solid state physics Future applications of the method of weak localization are considered and expected

A common optical path interferometric gauge

Abstract: A common optical path interferometric gauge comprises an optical beam (14) that is split into two beams. Both beams are modulated and recombined after introducing an optical path length difference greater than the coherence length of the optical source (12). The combined beam is guided along a common optical path (46) and is subsequently split into reference and measurement beams. The measurement beam is guided along a measurement optical path that includes a moving workpiece surface (60). Both beams are recombined after interposing an optical path length difference therebetween so as to reestablish coherence between portions thereof producing optical interference indicative of the surface (60) movement.

Coherent transient optical pulse-shape storage/recall using frequency-swept excitation pulses.

Abstract: We demonstrate that frequency-chirped laser excitation pulses may be employed to generate coherent transient signals possessing the same temporal profile as a particular excitation pulse. In comparison with the short, fixed-frequency pulses used in previous studies of this effect, chirped pulses can be temporally longer, of lower intensity, and hence easier to generate. The experiment was performed on the 555.6-nm transition of vapor-phase atomic ytterbium, and pulse-shape information was stored in a coherence between excited-state Zeeman levels. A simple theoretical analysis of our results is presented.

Coherence, cooperation and fluctuations

Abstract: This book presents the papers given at a conference on quantum optics. Topics considered at the conference included the growth of precipitates in a super saturated system, a space-time picture of relativistic propagation of medium energy hadrons through nuclei, lattice gauge theories, electron-nucleus scattering, short optical pulses, gaussons of the electromagnetic field, collision-induced coherence, spontaneous oscillations in a laser with injected signals, amplitude and phase in quantum optics, and Rydberg atoms in resonant cavities.

Interpretation of the Coherence Function When Using Pseudorandom Inputs to Identify Nonlinear Systems

Abstract: Use of certain types of pseudorandom input stimuli to identify linear transfer function models of biological or physiological systems can lead to bias errors if the system is nonlinear. Moreover, use of the coherence function to assess the linearity of the system may yield misleading results. Results from a computer simulation are presented, along with example experimental data.

Propagation of Partially Coherent Light Pulses

Abstract: The propagation of light pulses with partial spatial and temporal coherence is analysed. It is shown that the introduction of the second-order coherence function enables the description of both spatial and temporal radiation characteristics to be described in the angular spectrum approach. A strong correlation between the spatial and temporal parameters is obtained.

Water suppression in 1H magnetic resonance images by the generation of multiple-quantum coherence.

Abstract: Pulse sequences which generate multiple-and zero-quantum coherence and suppress the detection of single-quantum coherence have ben used to greatly reduce the intensity of the water signal in NMR images. In the experiment, image signals having multiple-quantum behavior add constructively while single-quantum signals, such as the signal arising from water, are canceled. Since the generation of multiple-quantum coherence is only a function of spin-spin coupling, water suppression by this technique is independent of chemical shift. Consequently, suppression of the water resonance in a 1H NMR image can be accomplished in an inhomogeneous magnetic field provided that the excitation profile of the rf pulses is equal for all spins. Furthermore, variations in the T1 and T2 of coupled and uncoupled spins do not affect the efficiency of the multiple-quantum filter. © 1986 Academic Press, Inc.

Lateral coherence properties of broad‐area semiconductor quantum well lasers

Abstract: The lateral coherence of broad-area lasers fabricated from a GaAs/GaAlAs graded index waveguide separate confinement and single quantum well heterostructure grown by molecular-beam epitaxy was investigated These lasers exhibit a high degree of coherence along the junction plane, thus producing a stable and very narrow far field intensity distribution

Graphic printing device including a fiber optic bundle with electronic means for providing coherence

Abstract: Coherence of an optical fiber bundle with randomly different geometries at its two ends is achieved electronically. A photosensitive random access memory is used as a sensor array to determine the addresses of fiber at which light exits when light is sequentially directed into consecutive fibers at the other end. The addresses are stored in a ROM and used to provide coherence of an otherwise unordered fiber optic bundle having one end formed in a linear array, for example, and used to scan documents. A printer also is described using electronically achieved coherence.

Uncertainty principle and informational entropy for partially coherent light

Abstract: It is shown that, among all partially coherent wave fields having the same informational entropy, the product of the effective widths of the intensity functions in the space and the spatial-frequency domains takes its minimum value for a wave field with a Gaussian-shaped cross-spectral density function. Furthermore, it is shown how this minimum value is related to the informational entropy and how this informational entropy is related to other quantities that can measure the overall degree of coherence of the partially coherent wave field.

Disorder and coherence in heavy-fermion systems.

Abstract: The effects of disorder on the formation of the coherent state in heavy-fermion systems are studied. The renormalized heavy band, characterized by an effective hybridization parameter, is destabilized by a critical strength of impurity scattering leading to self-energy corrections of order ${T}_{K}$. For a higher degree of disorder the heavy-fermion system will behave much like a collection of independent Kondo impurities, lacking the characteristic signatures of coherence in resistivity, specific heat, etc. The substitution of impurities on the conduction-electron side has a little influence on coherence; most of the effect comes from the strength of impurity scattering on the f-electron sites. The results are discussed in connection with experimental data.

Coherent-mode propagation in spatially band-limited wave fields

Abstract: Some new results are established regarding a recently developed coherent-mode representation of steady-state sources and fields of any state of coherence. It is shown that when a planar source is spatially band limited in the sense that its cross-spectral density function contains only spatial frequencies smaller than the corresponding wave number, the mode representation has some very simple and useful properties. Some potential applications of the results are mentioned.