Showing papers on "Coherence (physics) published in 1977"
TL;DR: In this paper, the concept of quasihomogeneous sources is introduced and an important reciprocity relation is shown to exist between light in the far zone and in the source plane, which implies that the degree of coherence in far zone is given by the classic form of the van Cittert-Zernike theorem, even though the source may have a high degree of spatial coherence over arbitrarily large areas.
Abstract: The concept of a quasihomogeneous source is introduced. Unlike a source that is strictly homogeneous in its statistical properties, a quasihomogeneous source may be finite. Many physical sources, both primary and secondary ones, are adequately approximated by this model. Coherence and radiometric properties of light generated by such sources (assumed, for simplicity, to be planar) are discussed and an important reciprocity relation is shown to exist between light in the far zone and in the source plane. This relation implies that the degree of coherence in the far zone is given by the classic form of the van Cittert-Zernike theorem, even though the source may have a high degree of spatial coherence over arbitrarily large areas. The reciprocity relation also provides a generalization of a recently derived result that expresses the angular dependence of the radiant intensity in terms of the degree of spatial coherence of light in the source plane. The dependence of all the basic radiometric quantities on the distribution of the optical intensity across the source and on the degree of spatial coherence of the light emerging from the source is discussed and is illustrated, for some typical sources, by computed curves.
287 citations
TL;DR: In this article, subjective preference tests with a simulated single reflection in an anechoic chamber were conducted in order to get a knowledge of the preferred properties of sound fields, and the degree of preference in relation to a long-time autocorrelation function of source signal and the interaural cross correlation of the sound field was discussed.
Abstract: Subjective preference tests with a simulated single reflection in an anechoic chamber were conducted in order to get a knowledge of the preferred properties of sound fields. The degree of preference in relation to a long‐time autocorrelation function of source signal and the interaural cross correlation of the sound field is discussed here. The preferred time delay gap between the direct sound and the first echo can be determined by the coherence of autocorrelation function and the amplitude of the echo. The preferred echo direction to a listener may be obtained by minimizing the interaural cross correlation which relates to the ’’subjective diffuseness.’’ Results of the autocorrelation function, which was measured with an A‐weighting filter, and the interaural cross correlation are presented for several music motifs. convection velocity and wavelength. The vortex strength, convection
57 citations
TL;DR: In this article, the effect of spatial source coherence on jet noise has been investigated theoretically for a normalized cross-spectral density of the source quantity based on a convected Gaussian form and for different special source intensity distributions, Lighthill's approach being used.
55 citations
TL;DR: The Hanbury-Brown and Twiss effect in particle physics is used to infer information about the amount of coherence of mesonic fields by using recent theoretical results of quantum optics as discussed by the authors.
52 citations
TL;DR: In this article, a description of photon-interference experiments of the Young's type using the techniques of quantum field theory is presented, and an explicit illustration of Dirac's statement that a photon interferes only with itself is given.
Abstract: A description of photon‐interference experiments of the Young’s type using the techniques of quantum‐field theory is presented. In particular, an explicit illustration of Dirac’s statement that a photon interferes only with itself is given. The interference patterns produced by a one photon, an n photon and a coherent photon field are calculated. A discussion of the degree of optical coherence possessed by the above fields is also incorporated. by the above fields is also incorporated.
49 citations
TL;DR: In this article, it was shown that the spatial coherence radius of the field of a singlemode laser beam traveling in a turbulent atmosphere exceeds that of plane and spherical waves, and that this excess is greatest in the case of strong fluctuations of the beam intensity.
Abstract: It is shown theoretically that the spatial coherence radius of the field of a single-mode laser beam traveling in a turbulent atmosphere exceeds the coherence radius of plane and spherical waves. It is established that this excess is greatest in the case of strong fluctuations of the beam intensity. A study is made of the influence of a partial coherence of a light source on the coherence radius of the beam field. It is demonstrated that the radius of the spatial coherence of a beam becomes independent of the diffraction size and coherence of the source when the random phase shifts increase sufficiently over a distance equal to the radius of the first Fresnel zone. A solution is obtained of the problem of turbulence-induced spreading of the image of a partly coherent laser source formed in the focal plane of the receiver lens.
40 citations
TL;DR: Using sampling theory, it is shown that in order to reconstruct images of partially coherent objects it is necessary to sample the mutual intensity on a discrete array of translations as well as on an array of spacings, and the required spacing and translation increments are shown to be inversely proportional to the object size and coherence extent.
Abstract: It is known that if the mutual intensity is sampled on an array of spacings, such samples can be Fourier transformed to yield images of incoherently radiating objects. In this paper, this result is extended to the imaging of partially coherent and coherent objects. An analysis of partially coherent imaging is first developed using a rather new approach, and the role of the complex ambiguity function in such imaging is emphasized. Next, using sampling theory, it is shown that in order to reconstruct images of partially coherent objects it is necessary to sample the mutual intensity on a discrete array of translations as well as on a discrete array of spacings. The required spacing and translation increments are shown to be inversely proportional to the object size and coherence extent, respectively. These requirements are stated in the form of a sampling theorem. Based on these results, an image synthesis procedure is outlined, and the capability of such a procedure for removing misfocus and other imaging aberrations is discussed. Lastly, experimental results are presented that demonstrate the aberration removal capability of this technique, using a coherent imaging system with defocus error.
37 citations
TL;DR: In this article, a formula is derived to express the PR coherence between the progressive and retrogressive components in terms of the CS coherence of the cosine and sine space Fourier coefficients.
Abstract: A formula is derived to express the PR coherence between the progressive and retrogressive components in terms of the CS coherence between the cosine and sine space-Fourier coefficients. By the use of the PR coherence the space-time power spectra are partitioned into standing and traveling wave parts. If the PR coherence is zero, the progressive and retrogressive components do not interfere with each other to form standing wave oscillations with nodes. In this case the CS coherence also becomes zero, if and only if these components have equal amplitudes.
33 citations
TL;DR: In this paper, the relationship between the degree of spatial coherence of a statistically homogeneous planar source and the angular distribution of the radiant intensity is investigated allowing for the finiteness of the source area.
Abstract: The relationship between the degree of spatial coherence of a statistically homogeneous planar source and the angular distribution of the radiant intensity is reinvestigated allowing for the finiteness of the source area. The approximate relations due to Wolf and Carter are reproduced in the limits of very large source area or very small coherence area. The generalized relation is illustrated by plotting the spatial frequency spectra and the spectral coherence areas of Bessel-correlated statistically isotropic free-field model sources that are bound by circular apertures. The effects of the variations of both the degree of spatial coherence and the source diameter are studied. In the case of the blackbody, the introduction of the finite aperture leads to deviations from the Lambert cosine law and removes the divergence of the coherence area obtained previously. Implications for the inverse scattering problem and the concept of generalized radiance are discussed.
30 citations
IBM1
TL;DR: In the early days, the early practitioners of nuclear magnetic resonance (NMR) probably never dreamed that their sophisticated coherence techniques would one day be adapted to the optical region.
Abstract: The early practitioners of nuclear magnetic resonance [1,2] probably never dreamed that their sophisticated coherence techniques would one day be adapted to the optical region. Coherent radiation sources were needed and in those days, the early 1950’s, lasers were not being discussed. We now know that the subject of coherent optical transients has developed steadily, beginning in 1964 with the initial photon echo measurement of Kurnit, Abella, and Hartmann [3]. Indeed, at the present time, the optical analogs of pulsed NMR transients have to some degree been realized.
26 citations
01 Oct 1977
TL;DR: In this article, it was shown that the sound field radiated from subsonic jets as well as the source field are statistically axially symmetric at lower frequencies and that the sources are coherent with respect to phase and compact with respect of acoustic wavelength.
Abstract: It is shown, by measurements and analysis, that the sound field radiated from subsonic jets as well as the source field are statistically axially symmetric at lower frequencies. In this range, the source field behaves like a line-quadrupole. The sources are coherent with respect to phase and compact with respect to acoustic wavelength. The results are developed in terms of correlation, coherence, and phase. A new and simpler form of the source integral is obtained in the range where the phases are linear functions of frequency through symmetry, translation, and rotation of the axis.
Patent•
25 Mar 1977
TL;DR: In this article, a continuous wave, phase measurement system was proposed for the determination of the thicknesses of layered targets consisting of a known number of dielectric layers, each having a known maximum thickness.
Abstract: A continuous wave, phase measurement system which provides at least an order of magnitude improvement in accuracy over modulated carrier systems is disclosed for the determination of the thicknesses of layered targets consisting of a known number of dielectric layers, each of a known maximum thickness. This system uses related frequencies such as the fundamental and its harmonics to establish a multi-harmonic coherence relationship whereby a homodyne phase reference between harmonics can be conserved and information extracted from just the received and not the transmitted signals. Consequently doppler effects due to motion between the target and the apparatus, as well as severe local oscillator stability and drift limitations are avoided, and thus this system can measure remote target parameters by interferometric techniques without the distance being a constraint.
TL;DR: In this paper, a review is presented of various recent investigations on the classical optical radiation laws in the light of the modern concepts of coherence and statistical optics, including temporal coherence, spatial coherence of Lambertian and non-Lambertian sources, and the interaction of matter with radiation.
Abstract: A review is presented of various recent investigations on the classical optical radiation laws in the light of the modern concepts of coherence and statistical optics. Temporal coherence of black-body radiation, spatial coherence of Lambertian and non-Lambertian sources, and the interaction of matter with radiation of any state of coherence are emphasized.
TL;DR: In this paper, the authors present analytical results in the case of Gaussian-correlated sources with Gaussian intensity profile and establish simultaneous scaling properties of the choerence angle and the intensity spread in the far zone.
Abstract: Using Schell's method we calculate the far-zone angular coherence and angular intensity from primary or secondary sources of arbitrary effective size and correlation length. We present analytical results in the case of Gaussian-correlated sources with Gaussian intensity profile, and establish simultaneous scaling properties of the choerence angle and the intensity spread in the far zone. We discuss the implications for the inverse-scattering problem and the pertinent radiometric concepts. Our theory comprises previous results in the limit of small correlation length and large beam width. We calculate the radiant emittance of Bessel-correlated sources with slowly varying intensity profile.
TL;DR: In this paper, the response of a polyatomic gas to microwave radiation, including steady state (pressure broadening) and time dependent (coherence transients) effects, is described theoretically.
Abstract: The response of a polyatomic gas to microwave radiation—including both steady state (pressure broadening) and time dependent (coherence transients) effects—is described theoretically. The treatment is based on solutions of a quantum Boltzmann equation and employs kinetic theory methods which have previously been used in the explanation of the field dependence of transport phenomena (Senftleben–Beenakker effects). Such methods allow for a proper description of the rotational aspects of a real molecular system, in contrast to standard approaches which effectively model the molecular system as having only two nondegenerate energy states. In the present work the magnetic quantum number degeneracies of two rotational levels connected by microwave radiation are specifically considered, and the resulting vector (and tensor) nature of the motions is emphasized throughout. The relaxation processes involved are related to matrix elements of the (rotationally invariant) collision superoperator occuring in the quantu...
TL;DR: An expression for a generalized nth order spherical wave mutual coherence function in terms of the two-source wave structure function and log-amplitude covariance function was developed in this article.
Abstract: An expression is developed for a generalized nth order spherical wave mutual coherence function in terms of the two-source wave structure function and log-amplitude covariance function.
TL;DR: In this article, the Boltzmann distribution at 3.5 x 1015/ cm -3 was obtained for a low pressure oxyacetylene flame when their measured number density is scaled to atmospheric pressure, and a good agreement with the two level model for a partially saturated system was obtained.
Abstract: Boltzmann distribution at 3000\"K at time t= 0, A good agreement with the two level model for a partially saturated system is obtained, It should also be noted that our value of 4. 5 x 1015/ cm -3 agrees well with the value found by Bleekrode and Nieuwpoort5 in a low pressure oxyacetylene flame when their measured number density is scaled to atmospheric pressure, Experimental details and a discussion of the kinetics and the assumptions made in the treatment of the data will be given elsewhere,3 An experimental uncertainty of plus or minus a factor of 3 due to uncertainties in the detector and collection effiCiencies, the power, and the laser beam waist measurements will be reduced to ± 50% by a more careful calibration of the experimental parameters on an atomic two level system. The applicability of the model can be stringently evaluated best for this type system. Extension of the two level model for systems with intermediate states is underway.6,7 The appl~cation of these techniques for absolute measurement of transient number densities in the reactive zone of a hot atmospheric pressure combust or reported herein represents a significant advance in the application of optical techniques for combustion diagnostics.
TL;DR: In this paper, it is shown that the Stokes parameters are insufficient for a complete physical and mathematical description of the light ray, and it is necessary to introduce the threedimensional distribution function of the wavelet trains over the polarization states; the problem of spin spectroscopy, i.e., of spatial selection of incoherent trains in accordance with the state of their polarization, is discussed.
Abstract: The electrodynamic aspects of the concept of the light ray, of the principal concepts and laws of photometry, polarimetry, and ray optics as a unified approximation of actual optics are explained. The apparatus-related origin of these concepts is demonstrated and the structure of the general theory of the light field is explained, including algebraic optics and the theory of radiative transfer. The principal premise of the photometric or ray approximation is the concept of the wavelet or the wave packet, the energy and the dynamic parameters of which are defined essentially in frequency-momentum rather than coordinate-time representation. The ray (photometric) approximation operates exclusively with observable quantities that are connected with the finite character of the dimensions and characteristic times of the square-law receivers used in optics. The generalization of photometric, polarimetric, and ray concepts to include a radiation field of arbitrary structure follows from the fact that the action of such a field on an optical receiver is equivalent to the action on this receiver of a beam of incoherent wavelets, the region of coherence of which is determined by the parameters of the receiver. This makes it possible to regard the field as an aggregate of light rays, each of which is described in a photometric approximation generalized with allowance for the polarization effects (Stokes parameters), which leads to formulation of the principal laws of photometry and polarimetry, and also to the photometric formulation of the conservation laws, and makes it possible to establish a direct relation between photopolarimetry and general theory of coherence. The limited nature of the region of coherence of the wavelet train leads to the problem of its transformation in time and in space, the description of which is effected by methods of algebraic optics by introducing the operators of differential and local transformations of the ray, and this leads directly to formulation of the radiative-transfer equation and to a delineation of the limits of its applicability. It is shown that the Stokes parameters are insufficient for a complete physical and mathematical description of the light ray, and it is necessary to introduce the three-dimensional distribution function of the wavelet trains over the polarization states; the problem of spin spectroscopy, i.e., of spatial selection of incoherent trains in accordance with the state of their polarization, is discussed.
TL;DR: In this paper, the degree of coherence of the field along an optical fiber excited by a spatially coherent source is discussed, and it is shown that the coherence undergoes a transitions as the source becomes less coherent; initially it is determined by the source coherence properties but for highly incoherent source it is controlled by fibre acceptance parameters.
TL;DR: In this article, the theory of coherent excitation of hydrogenic states with opposite parity was developed and a set of multipole parameters was defined which characterised the excited states and which enable the formulation of Fano and Macek to be generalised.
Abstract: The angular distribution and polarisation of hydrogenic line radiation excited by electron impact is considered for the case of coincidence experiments. The theory of coherent excitation of hydrogenic states with opposite parity is developed. A set of multipole parameters is defined which characterise the excited states and which enable the formulation of Fano and Macek to be generalised.
TL;DR: In this paper, the authors used four closely-spaced vector-averaging current meters near 2000m depth in the Sargasso Sea to provide estimates of the intensity and vertical coherence scale of non-internal wave motions in the inertial-to-buoyancy frequency range.
TL;DR: In this article, a direct measurement of the density of quasiparticle states corresponding to a single vortex has been obtained for both Sn and Pb and the measured vortex density of states is in disagreement with predictions of the normal cores model and previously published data.
TL;DR: In this paper, a simple analysis of reversing front interferometers is presented by means of the Fourier transform formalism, and it is shown that the output interference pattern furnishes the complex degree of coherence o12 of the input field.
Abstract: A simple analysis of reversing front interferometers is presented. By means of the Fourier transform formalism, it is shown that the output interference pattern furnishes the complex degree of coherence o12 of the input field. An experimental demonstration of the method has been obtained by using a modified Mach-Zehnder interferometer and processing the output signal by optical and electronic means. The coherence areas of different sources have been photographed.
TL;DR: In this article, the free decay of a four-level system is solved analytically and two regimes are found: one with oscillations displaying a beat and another with two decay rates.
Abstract: Considers the transfer of optical coherence from one level pair to another. The effect is isolated from the general collision expression derived by Berman (1976) and it is argued that it is best observed in transient measurements. The free decay of a four-level system is solved analytically and two regimes are found: one with oscillations displaying a beat and another with two decay rates. At the border the exponential dependence is modified. The implications for free induction decay and echo experiments are presented. Both phenomena can be used to detect the collisional transfer of coherence, and some experimental aspects of their observation are discussed.
01 Jan 1977
TL;DR: The characteristics of laser light i.e. good coherence, monochromaticity, high intensity and parallel nature, provide the basic conditions for different types of applications within dentistry as mentioned in this paper.
Abstract: The characteristics of laser light i. e. good coherence, monochromaticity, high intensity and parallel nature, provide the basic conditions for different types of applications within dentistry.
TL;DR: In this article, the coherence of the electromagnetic field in a plane dielectric waveguide excited by an external field with specific coherence properties is investigated, and the form of the radiation modulation spectrum is deduced.
Abstract: An investigation is made of the coherence of the electromagnetic field in a plane dielectric waveguide excited by an external field with specific coherence properties. The quantum theory of an electromagnetic field in one-dimensionally inhomogeneous media is employed to derive an expression which relates the correlation functions of the field inside the waveguide to the external field. This expression is used to study the variation of the coherence of the radiation at various distances z from the area where the radiation is coupled into the waveguide. If the external field has a finite line width, the spatial coherence is a periodic function of z when zzcr and tends to a constant value when zzcr. When zzcr, the temporal coherence is the same as for the external source, whilst when zzcr, the temporal coherence as a function of τ has maxima which move away from the point τ = 0 with increasing z. It is found that the coherence tunes τ1 and τ2 determined following Wolf and Mandel behave differently when zzcr: τ12 increases quadratically with increasing z, whereas τ2 tends to a constant value. The form of the radiation modulation spectrum is deduced. Curves are plotted for the spatial and temporal coherence by way of a specific example.
TL;DR: In this paper, the excitation characteristics and spatial coherence of partially coherent optical waves in gradient fibres are demonstrated for incident light waves radiated from semiconductor lasers and light emitting diodes.
Abstract: The excitation characteristics and spatial coherence of partially coherent optical waves in gradient fibres are demonstrated for incident light waves radiated from semiconductor lasers and light emitting diodes. Lower modes are efficiently excited in the case of coherent laser beams, while incident waves of low coherence such as lightwaves of LEDs excite higher modes. Pulse propagation of partially coherent optical waves in dispersive gradient fibres is also discussed for random index fluctuations. Mode coupled equations for temporal correlation functions of the electric field that are generalizations of coupled power equations are found. Mode filtering and pulse improvement with a lossy inhomogeneous cladding are described.
TL;DR: In this paper, a method for obtaining source coherence functions corresponding to specified far-field radiation patterns is presented, where the sources are assumed to be planar, large and quasi-monochromatic.
Abstract: A method is presented for obtaining source coherence functions corresponding to specified far-field radiation patterns. The sources are assumed to be planar, large and quasi-monochromatic. Examples given include incoherent and lambertian sources.
TL;DR: In this article, the response of a microwave radiometer to thermal radiation passing normally through a lossless dielectric slab, either separated from the thermal source or adjoining it, is described in terms of its ability to recognize coherence effects introduced by the filter.
Abstract: The response of a radiometer to thermal radiation passing through a spatial filter is described in terms of its ability to recognize coherence effects introduced by the filter. This is illustrated by considering the response of a microwave radiometer to thermal radiation passing normally through a lossless dielectric slab, either separated from the thermal source or adjoining it. The observed degree of coherence is defined and is shown to depend in a simple manner on the slab thickness (related to spatial bandwidth) as well as the temporal bandwidth of the radiometer. Rules of thumb are given for estimating whether a given situation requires a coherent model, an incoherent model, or a partially coherent model.