Showing papers on "Coherence (physics) published in 1985"
TL;DR: It is shown that the predictions of quantum mechanics are incompatible with the conjunction of two general assumptions which are designated ``macroscopic realism'' and ``noninvasive measurability at the macroscopic level.
Abstract: It is shown that, in the context of an idealized ``macroscopic quantum coherence'' experiment, the predictions of quantum mechanics are incompatible with the conjunction of two general assumptions which are designated ``macroscopic realism'' and ``noninvasive measurability at the macroscopic level.'' The conditions under which quantum mechanics can be tested against these assumptions in a realistic experiment are discussed.
1,067 citations
TL;DR: In this paper, the distribution of coherence in a multiple-quantum spectrum was modeled as a Gaussian distribution and the variance of the distribution was associated with the number of coupled spins effectively interacting, and its steady growth with time reflected the continual expansion of the system under the action of dipolar interactions.
Abstract: Recently developed solid state multiple‐quantum NMR methods are applied to extended coupling networks, where direct dipole–dipole interactions can be used to create coherences of very high order (∼100). The progressive development of multiple‐quantum coherence over time depends upon the formation of multiple‐spin correlations, a phenomenon which also accompanies the normal decay to equilibrium of the free induction signal in a solid. Both the time development and the observed distributions of coherence can be approached statistically, with the spin system described by a time‐dependent density operator whose elements are completely uncorrelated at sufficiently long times. With this point of view, we treat the distribution of coherence in a multiple‐quantum spectrum as Gaussian, and characterize a spectrum obtained for a given preparation time by its variance. The variance of the distribution is associated roughly with the number of coupled spins effectively interacting, and its steady growth with time reflects the continual expansion of the system under the action of the dipolar interactions. The increase in effective system ‘‘size’’ is accounted for by a random walk model for the time development of the density operator. Experimental results are presented for hexamethylbenzene, adamantane, and squaric acid. The formation of coherence in systems containing physically isolated clusters is also investigated, and a simple method for estimating the number of spins involved is demonstrated.
360 citations
TL;DR: In this paper, a method of multiplexing several optical signals onto a single spatial channel using a short coherence length continuous wave light source is described, and some design considerations are discussed Experimental results for a single sensor and receiver are presented and compared with theoretical predictions.
Abstract: This paper describes a method of multiplexing several optical signals onto a single spatial channel (eg, a single-mode fiber) using a short coherence length continuous wave light source Several system configurations which utilize this technique are proposed, and some design considerations are discussed Experimental results for a single sensor and receiver are presented and compared with theoretical predictions
274 citations
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01 Jan 1985
TL;DR: In this article, the basic equations of the semiclassical laser theory are presented, and a theoretical treatment of the two-photon laser is given, based on quantum mechanics.
Abstract: Preface. List of symbols. 1. Introduction. 2. Basic properties and types of lasers. 3. Laser resonators. 4. The intensity of laser light. Rate equations. 5. The basic equations of the semiclassical laser theory. 6. Applications of semiclassical theory. 7. Ultrashort pulses. 8. Instability hierachies of laser light. Chaos, and routes to chaos. 9. Optical bistability. 10. Quantum theory of the laser I. A first approach via quantum mechanical Langevin equations. Coherence, noise and photon-statistics. 11. Quantum theory of the laser II. A second approach via the density matrix equation and quantum classical correspondence. 12 A theoretical treatment of the two-photon laser. 13. The laser - trailblazer of synergetics. References. Subject index.
187 citations
TL;DR: A quantum theory of stimulated Raman scattering is presented that takes into account three-dimensional propagation and collisional dephasing, allowing the study of the spatial and temporal coherence properties of the generated Stokes light.
Abstract: A quantum theory of stimulated Raman scattering is presented that takes into account three-dimensional propagation and collisional dephasing, allowing the study of the spatial and temporal coherence properties of the generated Stokes light. Maxwell-Bloch equations for the Stokes field operator and the collective atomic operators are solved analytically under low-signal-gain conditions, where the laser field and the atomic ground states remain undepleted. The intensity and the space-time autocorrelation function of the Stokes field are calculated. The Stokes field is expanded into a set of statistically independent ``coherence modes,'' which are determined explicitly for the case of a cylindrically shaped pumped volume. The Stokes pulse energy W is found to fluctuate from pulse to pulse. The probability distribution function for pulse energies P(W) is calculated for a range of Fresnel numbers of the excited volume and collisional dephasing rates. For small values of Fresnel number and dephasing rate, P(W) is a negative exponential distribution. For large values of either, P(W) narrows and approaches a Gaussian-shaped distribution. This occurs because many independent modes contribute to the Stokes emission, making it spatially and/or temporally incoherent.
123 citations
TL;DR: In this article, the interference of atoms caused by the wave nature of their motion is considered, and the amplitude and phase perturbation are taken into account both for instantaneous excitation and for scattering under Bragg conditions.
Abstract: We consider the interference of atoms caused by the wave nature of their motion. Coherently interfering beams of particles may be obtained by using the diffraction of atoms from separated standing waves resonant with the transition between the ground and excited states of the atoms. Interference arises with and without spatial separation of the diffracted atomic beams. A problem concerning two-quantum perturbation of the wave function of an atom in the ground state by a standing-wave field has been solved. Both amplitude and phase perturbation are taken into account. We show that in spite of the absence of coherence in the incident beam and a rapid decay of the coherence induced by the standing wave for scattered spatially overlapping beams, the interference can be observed for the conditions of an echo. We first consider the phenomenon of an echo under the quantum-mechanical action of light on the translational degrees of freedom. We show that owing to this phenomenon phase memory can be transferred through the ground state over unlimitedly large distances. Owing to the interference of the density harmonics, a periodic structure in the spatial distribution of the atomic density with a period of less than one wavelength of the light is localized at distances of the order of the distance between the fields. The harmonic amplitude is calculated for instantaneous excitation in the case in which the duration of the excitation is comparable with the backward Doppler linewidth in the beam and for scattering under Bragg conditions. In the latter case we show that the effective temperature of the atoms participating in the interference is less than one recoil energy.
68 citations
IBM1
TL;DR: A generalized perturbation theory for an inhomogeneously broadened two-level quantum system interacting with an optical field of arbitrary temporal shape concludes that at low fields any coherence effect can be interpreted as a generalized stimulated echo phenomenon.
Abstract: A generalized perturbation theory is developed for an inhomogeneously broadened two-level quantum system interacting with an optical field of arbitrary temporal shape. Solutions of the Liouville equation carried out to nth order in the optical field strength exhibit a rephasing behavior and therefore are interpreted as an n-pulse echo where each pulse corresponds to one power of the field strength. We conclude that at low fields any coherence effect can be interpreted as a generalized stimulated echo phenomenon. Several well-understood coherence effects are explained and a few new ones are predicted, including one example where the light source is incoherent.
54 citations
TL;DR: In this article, a new method for selection of coherence-transfer pathways involving formation of rotary echoes in an inhomogeneous rigid field held is presented, which shares many of the advantages of the existing techniques of phase cycling and field gradient pulses while avoiding some of their disadvantages.
43 citations
TL;DR: In this article, the authors considered the imaging of an object located an arbitrary distance behind a random phase screen and illuminated with light of arbitrary spatial coherence, and evaluated the limiting cases of smooth and diffuse objects illuminated with either spatially incoherent or spatially coherent light.
Abstract: We have considered the imaging of an object located an arbitrary distance behind a random phase screen and illuminated with light of arbitrary spatial coherence. The limiting cases of smooth and diffuse objects illuminated with either spatially incoherent or spatially coherent light are evaluated in detail.
41 citations
TL;DR: In this paper, pulse sequences which generate multiple and zero-quantum coherence and suppress the detection of singlequantum Coherence have been used to reduce greatly the intensity of the water peak in 1H NMR spectra of biological interest.
41 citations
TL;DR: In this paper, the authors present a numerical solution for the fourth-order coherence function of a plane wave propagating in a random medium, where the random medium is taken to be two dimensional, homogeneous, and isotropic with a universal Kolmogorov (pure) power-law form.
Abstract: We present a numerical solution for the fourth-order coherence function of a plane wave propagating in a random medium. The random medium is taken to be two dimensional, homogeneous, and isotropic with a universal Kolmogorov (pure) power-law form. Our results differ from previous numerical calculations principally in the way in which the scintillation index approaches saturation. We display the full spatial dependence of the fourth moment and the spatial evolution of the covariance function of the intensity fluctuations. Our results are compared with previously obtained numerical results, with several asymptotic expressions, and with recent analytical methods.
TL;DR: In this paper, a theory of photodissociation in a strong laser field is developed in a systematic way and the connection between the physically realizable situation, in which a multimode coherent pulse dissociates a molecule and the computationally convenient occupation number representation is made in a very explicit way.
Abstract: Theory of photodissociation in a strong laser field is developed in a systematic way. Photon absorption and molecular dissociation are treated uniformally using time‐dependent quantum scattering theory. The connection between the physically realizable situation, in which a multimode coherent pulse dissociates a molecule and the computationally convenient occupation number representation, is made in a very explicit way. The coherence (or incoherence) of the radiation field and that of the wave packet of scattering states generated by it are shown to be linked together in a very straightforward fashion. The analytic properties of the scattering wave functions and the existence and duration of off‐the‐energy‐shell transients are shown to be connected. The theory is applied to studying the laser assisted dissociation, in a two color experiment, of IBr. The role of two‐photon absorption vs photon catalyzed dissociation is investigated.
TL;DR: The role of symmetry in two-dimensional NMR is examined in this article, where it is shown that symmetry considerations may lead to selection rules restricting the number of allowed coherence transfer pathways.
TL;DR: Etude d'un systeme de spin AX 2 (bromure de propargyle) mettant en jeu des modes collectifs pour comprendre les phenomenes de transfert de coherence en presence of un couplage scalaire.
Patent•
06 Mar 1985TL;DR: In this article, a glass delay plate is placed in the path of one of the beams such that only received radiation having a temporal coherence greater than a minimum determined by the plate thickness produces an output signal from detector 46.
Abstract: A remote sensor for detecting gas, vapour or aerosol comprising means to measure the change in temporal coherence of light of a selected narrow waveband when it interacts with the gas etc. The light can be provided by a laser source or spectrally filtered sunlight etc. Received radiation 41 is split in to two, beams by a Fresnel biprism 44 and then detected by a detector 46 sensitised by a modulating reticle 47 to interference fringes. A glass delay plate 45 of suitable thickness is placed in the path of one of the beams such that only received radiation having a temporal coherence greater than a minimum determined by the plate thickness produces an output signal from detector 46. The minimum temporal coherence is set higher than the temporal coherence of the illuminating radiation. In alternative arrangements a band-pass temporal coherence filter may be used and the sensor can be made to spectrally scan the field of view by using a tunable laser or a variable centre frequency band-pass optical filter.
TL;DR: In this article, the spatial partial coherence of a beam wave source was introduced to the Rytov method and evaluated the intensity covariance and the scintillation index due to a spatially partially coherent beam-wave source.
Abstract: All the existing Rytov method solutions in atmospheric turbulence deal with coherent sources. In this paper we introduce the spatial partial coherence of a beam wave source to Rytov’s method and evaluate the intensity covariance and the scintillation index due to a spatially partially coherent beam wave source. The advantage of this solution is that in the calculation of the scintillations, the need for the use of the quadratic approximation for the medium structure functions is eliminated. The disadvantage is that, since it is a weak-fluctuation solution, we cannot extend the results to the incoherent source limit when (weak) turbulence is present.
TL;DR: It is argued that the limit of the ear reaches a limit imposed by the uncertainty principle only if the receptor cell holds the detector elements in a special nonequilibrium state which has the same noise characteristics as a ground state.
Abstract: It is argued that the sensitivity of the ear reaches a limit imposed by the uncertainty principle. This is possible only if the receptor cell holds the detector elements in a special nonequilibrium state which has the same noise characteristics as a ground (T = 0 K) state. To accomplish this 'active cooling' the molecular dynamics of the system must maintain quantum mechanical coherence over the time scale of the measurement.
TL;DR: In this paper, the authors examined the effect of the use of narrow packets, causing a partial coherence of the incident beam, on the differential intensity of the beam and found that the demands of representing beam coherence correctly conflict with the requirements for the validity of the propagation scheme and suggested some improvements that should increase the reliability of the method without affecting greatly its remarkable computational and conceptual advantages.
Abstract: We use analytic models, valid for neutron scattering, and numerical calculations to examine a method proposed by Drolshagen and Heller for computing atom diffraction from surfaces. Our main concern is the manner in which the use of narrow packets, causing a partial coherence of the incident beam, might affect the differential intensity. We find that the demands of representing beam coherence correctly conflict with the requirements for the validity of the propagation scheme. We suggest some improvements that should increase the reliability of the method without affecting greatly its remarkable computational and conceptual advantages.
Journal Article•
Journal Article•
TL;DR: In this article, a simplified operator formalism is introduced for liquid-state NMR and various transformation rules are tabulated for the POMMIE family of pulse sequences and a detailed analysis is made of the extensive phase cycling possible with this pulse train.
01 Mar 1985
TL;DR: In this paper, the authors discuss the dynamics of intramolecular vibrational energy redistribution in two limits: the coherent and incoherent limits, which describe coherence (quantum beats), congestion and nonexponentional decays.
Abstract: In this paper, we discuss the dynamics of intramolecular vibrational-energy redistribution (IVR) in two limits: the coherent and incoherent limits. These descriptions are introduced to account for experiments done in time and frequency domains. We present a more general model for IVR, namely the model of overlapping resonances, which describes coherence (quantum beats), congestion and nonexponentional decays.
Journal Article•
TL;DR: Low-intensity laser light coherence is considered in relation to biological objects under normal physiological conditions and it is shown that the role of coherent interaction processes is negligible.
Abstract: Low-intensity laser light coherence is considered in relation to biological objects under normal physiological conditions. Estimations show that the excitation rate (the rate of coherent states generation) of typical biomolecules in visible range (sigma abs = 10(-17) cm2, I = 10(-3) W/cm2) is 10(12)-10(13) times lower than that of their phase relaxation. It means that the role of coherent interaction processes is negligible. This conclusion is confirmed by the experimental results obtained with living cells of different types.
01 Jan 1985
TL;DR: In this paper, a method of multiplexing several optical signals onto a single spatial channel (e.g., a singlemode fiber) using a short coherence length continuous wave light source is described.
Abstract: This paper describes a method of multiplexing several optical signals onto a single spatial channel (e.g., a single-mode fiber) using a short coherence length continuous wave light source. Several system configurations which utilize this technique are proposed, and some design considerations are discussed. Experimental results for a single sensor and receiver are presented and compared with theoretical predictions.
TL;DR: In this paper, the 13C-nmr spectrum of the helical molecule phenanthro[4,3-a]dibenzothiophene at 125.762 MHz is reported.
TL;DR: In this article, an algebraic characterisation of the dynamical systems which preserve the coherence of a generalised coherent state defined for a Lie group is given, where the breaking of coherence is related to singularities appearing in the S matrix.
Abstract: The authors give an algebraic characterisation of the dynamical systems which preserve the coherence of a generalised coherent state defined for a Lie group. The breaking of coherence is related to singularities appearing in the S matrix. They show a regularisation procedure to eliminate such singularities based on the jet realisation of the diffeomorphism group induced by contact transformations on the state manifold.
TL;DR: In this article, the emission characteristics of unstable resonator semiconductor lasers were measured and a high degree of spatial coherence of the laser output was measured, indicating single lateral mode operation for currents I < 3 Ith.
Abstract: The emission characteristics of unstable resonator semiconductor lasers were measured. The output of an 80-µm-wide laser consists of a diverging beam with a virtual source 5 µm wide located 50 µm behind the laser facet. A high degree of spatial coherence of the laser output was measured, indicating single lateral mode operation for currents I ~< 3 Ith.
TL;DR: In this paper, the authors investigated the creation of spectrally ordered nuclear and electronic Zeeman coherences in a gas-phase sample and found that the solid-state analog of this process will exist only if the inhomogeneous broadening of the two optical transitions is highly correlated.
Abstract: We have experimentally investigated the creation of spectrally ordered nuclear and electronic Zeeman coherences in a gas-phase sample. A Zeeman coherence is generated through the sequential excitation of two coupled optical transitions. In our experiment, one transition was excited by a data pulse and the other by a short reference pulse. Subsequent excitation of one of these transitions by a short reading pulse transforms the Zeeman coherence into an optical coherence and leads to the emission of a time-forward or time-reversed duplicate of the data pulse. Output signals up to 5% as intense as the original data pulse were observed. We present a general analysis that is applicable to both gases and solids and find that the solid-state analog of this process will exist only if the inhomogeneous broadening of the two optical transitions is highly correlated.
TL;DR: In this paper, the quantum tunnelling and coherence of a particle moving in a biased or unbiased double well potential and subject to ohmic dissipation is considered, and the complete time dependence of the reduced density matrix is determined for the case where the dimensionless friction constant alpha <<1.
Abstract: The quantum tunnelling and coherence of a particle moving in a biased or unbiased double well potential and subject to ohmic dissipation is considered. The complete time dependence of the reduced density matrix is determined for the case where the dimensionless friction constant alpha <<1.