Showing papers on "Coherence (physics) published in 1975"
TL;DR: In this article, the statistical, spatial and temporal coherence properties of electromagnetic radiation scattered into the far field by a deep random phase screen are investigated, and it is shown that significant departures from Gaussian behaviour can occur even when the phase correlation length is much smaller than the dimensions of the scattering region.
Abstract: The statistical, spatial and temporal coherence properties of electromagnetic radiation scattered into the far field by a deep random phase screen are investigated. It is shown that significant departures from Gaussian behaviour can occur even when the phase correlation length is much smaller than the dimensions of the scattering region-a situation in which the central limit theorem might be expected to apply. Formulae are derived relating these departures to elementary properties of the scattering structure, which may therefore be determined by measurement of the fluctuations in the scattered radiation. Application of the results to scattering from very rough surfaces is discussed.
123 citations
TL;DR: In this article, general theorems about spatial coherence properties of a two-dimensional statistically homogeneous source that gives rise to any prescribed angular distribution of radiant intensity are derived about sources that radiate in accordance with Lambert's law.
Abstract: Some general theorems are derived about spatial coherence properties of a two-dimensional statistically homogeneous source that gives rise to any prescribed angular distribution of radiant intensity. The results are applied to sources that radiate in accordance with Lambert’s law. It is found that lambertian sources cannot be spatially strictly incoherent and that they have, in fact, certain unique coherence properties. This result is illustrated by calculations for a blackbody source. The idealized case of a spatially completely incoherent source is discussed for comparison.
120 citations
TL;DR: Re receptive-field coherence may account for various spatial frequency effects previously thought to require a cortical mechanism, particularly in the spatial frequency domain.
115 citations
TL;DR: In this paper, the coherent superposition of the states between which magnetic dipole transition is forbidden has been excited and detected by means of a multi-step application of resonant rf pulses in a three-level NMR system.
Abstract: The coherent superposition of the states between which magnetic dipole transition is forbidden has been excited and detected by means of a multi-step application of resonant rf pulses in a three-level NMR system. The experiment was carried out on 27 Al nuclei in Al 2 O 3 where the quantization axes of the quadrupole and the magnetic coupling were parallel. Free decay and echo signals associated with the coherence were observed, and transfer of coherence between nonresonant pairs of levels was studied in detail.
100 citations
TL;DR: The lesser known phenomenon of the imaging of a grating by a second grating is described from which the fringe forming capacity of multiple-grating interferometers stems; this can occur regardless of the coherence of the source.
Abstract: A general analysis of an n-grating interferometer under various conditions of illumination is presented, where n = 1,...,4. Conditions for fringe localization and effects of misalignment are given. The lesser known phenomenon of the imaging of a grating by a second grating is described from which the fringe forming capacity of multiple-grating interferometers stems; this can occur regardless of the coherence of the source.
97 citations
TL;DR: In this article, the first observation of transient nutations, spin echoes and stimulated echoes associated with two-quantum transition between levels for which single-quadratic transition is forbidden was made on a multi-level NMR system.
Abstract: We report the first observation of transient nutations, spin echoes and stimulated echoes associated with two-quantum transition between levels for which single-quantum transition is forbidden. The experiment was made on a multi-level NMR system, 27 Al in Al 2 O 3 with its c -axis parallel to the static magnetic field H 0 , where level spacings were unequal and no state mixing existed. To detect the coherence between levels with Δ m =2 the technique of transfer of coherence was used. The equation of motion of the spins was simpler than that usually used in a three-level system.
86 citations
TL;DR: In this paper, an exact solvable model describing the interaction between a two-level system and the electromagnetic field is presented, and the model is shown to be exactly solvable for long interaction times.
Abstract: We present an exactly solvable model describing the interaction between a two-level system and the electromagnetic field. For long interaction times we evidence some purely quantum-mechanical effects, such as the destruction of coherence of radiation and the Gaussian envelope of the transition probability.
67 citations
TL;DR: The relationship between the spatial coherence of a source and the angular distribution of the radiant intensity is investigated in this article, where the Fourier transform of a Gaussian correlated source is used to measure the degree of coherence.
66 citations
TL;DR: In this article, a method for monitoring the time development of coherent components in a multilevel system using an observable which can measure only the relative populations in the levels is presented.
Abstract: A method for monitoring the time development of the coherent components in a multilevel system using an observable which can measure only the relative populations in the levels is presented. Using standard density matrix formulation, expressions are obtained for the conventional and this new ’’probe’’ pulse method. For several of the more common coherence experiments, optically detected magnetic resonance of molecular excited triplet states is used to illustrate the principles. The effect of coherent averaging of relaxation terms in the spin Hamiltonian is discussed and specifically applied to excited triplet states in zero field. Finally, experimental results of coherence measurements are presented along with a detailed description of the apparatus and methods used.
61 citations
TL;DR: In this paper, a review of theoretical and experimental work performed in the USSR on strong fluctuations of the intensity of light is presented, where the authors focus on the effects of strong fluctuations.
Abstract: This paper deals with a review of theoretical and experimental work performed in the USSR on strong fluctuations of the intensity of light.
54 citations
TL;DR: In this article, the authors studied the statistical, spatial coherence and temporal coherence properties of non-Gaussian fluctuations in light scattered by a thin layer of liquid crystal (MBBA) in its dynamic scattering state.
Abstract: For pt.I see ibid., vol.8, 369 (1975). The authors have studied experimentally the statistical, spatial coherence and temporal coherence properties of non-Gaussian fluctuations in light scattered by a thin layer of liquid crystal (MBBA) in its dynamic scattering state. The results are consistent with the deep phase-screen theory developed in the previous paper. With 20 V applied to the sample, experimental values of the parameters of the model are: mean square phase deviation phi 2=45.6+or-8.0 rad2, phase correlation length xi =2.63+or-0.24 mu m and phase coherence time 2.2+or-0.2s. Indications are found that, while phase fluctuations in the emergent wave-front are probably dominant, amplitude fluctuations are not entirely negligible. It is argued, however, that the effects of amplitude fluctuations on the values of the above parameters are probably quite small. Taking a broader view, the results confirm that, in many scattering experiments, detailed information concerning the scattering process can be obtained from measurements in the non-Gaussian regime.
01 Jan 1975
TL;DR: In this paper, the effects of light of arbitrary coherence may be considered, and the results derived in that section are the only new results presented here; the rest of the material is taken from published work, much of which has been reported during the last five years.
Abstract: In this section we shall study speckle patterns produced by partially coherent light. Most published work considers the effects of spatial coherence separately from the effects of temporal coherence. I have followed this convention for most of this chapter, but have indicated in the final section how the effects of light of arbitrary coherence may be considered. The results derived in that section are the only new results presented here. The rest of the material is taken from published work, much of which has been reported during the last five years. The field is interesting from an academic point of view, but the many applications which have developed have been mainly responsible for the current interest.
01 Jan 1975
TL;DR: In this article, the authors describe wave motion, reflection and transmission, interference and coherence, and Fourier Optics for wave motion and reflectance and transmission in a geometrical system.
Abstract: Wave Motion. Electromagnetic Waves and Photons. Reflection and Transmission. Geometrical Optics. Polarization. Interference and Coherence. Diffraction. Fourier Optics
TL;DR: In this article, the effects of coherence brightening are also important, and in the super-radiant regime, the laser output approaches that predicted by the usual calculation, and the linear gain expected in certain x-ray laser amplifiers is reduced.
Abstract: The lethargic response of the lasting medium produced by the combined effects of finite bandwidth and rapid decay of the population inversion leads to a reduction of the linear gain expected in certain x-ray laser amplifiers. However, the effects of coherence brightening are also important, and in the superradiant regime, the laser output approaches that predicted by the usual calculation.
TL;DR: In this article, a theoretical basis for studying the nature of ionospherically reflected radio waves is described, and the expected statistical properties of the amplitude and phase variations of the radio wave ground pattern sampled at a pair of pacing receiving antennas are derived for general correlation conditions, assuming different models of the angular spectrum of reflected radio wave.
Abstract: A theoretical basis for studying the nature of ionospherically reflected radio waves is described. The expected statistical properties of the amplitude and phase variations of the radio wave ground pattern sampled at a pair of paced receiving antennas are derived for general correlation conditions, assuming different models of the angular spectrum of reflected radio waves. The esults provide a basis for experimental measurements of the angular spread and coherence ratio of the angular spectrum of reflected waves.
TL;DR: In this paper, the coherence time and the anisotropy of the resonance interactions in the excited state were established for a molecular crystal of 1,2,4,5-tetrachlorobenzene at low temperatures (below 4.2 K).
Abstract: The observation of coherent dimers in their excited triplet state is reported for a molecular crystal of 1,2,4,5-tetrachlorobenzene at low temperatures (below 4.2 K). Utilizing the theory developed in our previous paper, the coherence time (10^-6 sec) and the anisotropy of the resonance interactions in the excited state were established. The identification of the dimer as translationally equivalent, from the zero-field optically detected magnetic-resonance spectra, establishes the effective dispersion for the triplet exciton band of the neat crystal. Morover, the magnitude of the resonance transfer time was shown to be much less than the coherence time: the dimer is coherent for a period of 10^5 times that associated with the stochastic limit.
TL;DR: The coherence between vertical temperature profiles separated in time is studied in this article, where time lags from 12 min to 19 hours and vertical wavelengths from 2 to 300 m are considered.
Abstract: The coherence between vertical temperature profiles separated in time is studied. Time lags from 12 min to 19 hours and vertical wavelengths from 2 to 300 m are considered. The wavelengths shorter than 10 m show no significant coherence even for 12-min separations. The longer wavelength bands exhibit coherence time series with significant structure out to the largest lag measured. For the wavelength band between about 21 and 42 m the results are directly interpretable as vertical modes. In the other wavelength bands considered, there is evidence that the perturbations are propagating. The coherence and phase time series are compared with the Garrett and Munk internal wave model.
TL;DR: The investigation covers the strong turbulence regime (scintillation saturation regime) where wave coherence is essentially determined by phase effects and in this regime a breakup of the phase front is found to occur.
Abstract: The phase-front distortion of laser radiation propagating through the turbulent atmosphere has been measured simultaneously at several wavelengths in the visible using a long-range Mach-Zehnder interferometer with high spatial and temporal resolution (476 nm ≤ λ ≤ 647 nm, 0.5 mm ≤ Δr < 60 mm, Δt = 0.5 msec, z ≤ 2 km, Cn = 1.3 × 10−7 m−1/3). Phase-structure function, transverse coherence length, and arrival-angle fluctuations are interpreted in terms of the meteorological quantities turbulence strength and turbulence structure and inner and outer scale. The investigation covers the strong turbulence regime (scintillation saturation regime) where wave coherence is essentially determined by phase effects. In this regime a breakup of the phase front is found to occur.
TL;DR: In this paper, the authors reported the first reported observation of the coherence of an atomic system induced by two-photon absorption, a coherence which persists after the passage of the excitation pulse and decays inhomogeneously as a result of thermal motion.
Abstract: Calcium vapor has been excited by two-photon absorption of a mode-locked dye-laser pulse, and emission from a coherent superposition state of the $4{s}^{2}^{1}S_{0}$ and $4s3d^{1}D_{2}$ levels has been observed using a delayed off-resonant interrogation pulse in the picosecond regime. The emission signal intensity was measured as a function of the delay time of the interrogation pulse, and showed a peak well delayed from that of the dye-laser pulse. This reflects the fact that the induced coherence is expressed by a time integral of the excitation. The emission signal was then found to decay as a result of the Doppler effect. The above process is analyzed by Bloch and Maxwell equations. This is the first reported observation of the coherence of an atomic system induced by two-photon absorption, a coherence which persists after the passage of the excitation pulse and decays inhomogeneously as a result of thermal motion. In carrying out the experiment, deformation of the input dye-laser pulse during propagation through the two-photon resonant medium was carefully avoided.
TL;DR: In this paper, cross bispectra among a set of 17 traces of internal waves separated in increments of about 3 m show apparent nonlinear interactions over a wide range of frequency triplets.
Abstract: Cross bispectra among a set of 17 traces of internal waves separated in increments of about 3 m show apparent nonlinear interactions over a wide range of frequency triplets. Evidence suggests that a strong peak found in the ordinary spectra of the deeper waves results at least in part through acquisition of energy by nonlinear interaction with numerous other lower-energy components. There is also evidence of non-linear interaction between two components of like frequency in the presence of a third, zero frequency component.
TL;DR: The characteristic fringe function of hologram interferometry has been evaluated for the case of periodic, nonsinusoidal vibrations represented by a Jacobian elliptic function and it is shown that the intensity of the fringes increases considerably as compared with that for a pure sinusoidal case.
Abstract: In this paper the characteristic fringe function of hologram interferometry has been evaluated for the case of periodic, nonsinusoidal vibrations represented by a Jacobian elliptic function. To consider the reconstructed holographic image of an object, use has been made of an equation derived from considerations of the effect of motion on coherence. Graphical representation of the fringe irradiance distribution in the reconstructed image is given. It is shown that, as the motion departs from pure sinusoidal form, the intensity of the fringes increases considerably as compared with that for a pure sinusoidal case.
TL;DR: In this article, an analytical solution for the time dependence of the joint photon probability distribution of the two light beams is obtained and then employed to calculate some numerical results for various special cases of interest, and the significance of these results is discussed in physical terms.
Abstract: The nonlinear process of the stimulated Raman effect is treated theoretically. Simple expressions are derived for the initial rates of change and limiting steady state values of the first two moments, the degrees of second-order coherence and the correlation function of the pump and Stokes beams. An analytical solution for the time dependence of the joint photon probability distribution of the two light beams is obtained and then employed to calculate some numerical results for various special cases of interest, and the significance of these results is discussed in physical terms. Simpler approximate expressions are also derived for the case where the pump beam is much more intense than the Stokes beam.
TL;DR: In this paper, coherence in multidimensional excited systems was established using optical and zero-field magnetic resonance spectroscopy using high resolution phosphorescence microwave double resonance at the Larmor frequency of the excited phenazine dimer.
TL;DR: In this article, the coherent superposition state of an atomic gas system excited by Doppler-free, two-photon absorption is analyzed and shown that this zero-momentum coherent state does not dephase by thermal motion of the atoms, but decays only by homogeneous relaxation mechanisms.
TL;DR: In this paper, a theoretical discussion of a coherence effect in the excitation of hydrogen atoms to the n = 3 state by electron bombardment is presented. But it is not restricted to hydrogen.
Abstract: This paper is a theoretical discussion of a ''coherence effect'' in the excitation of hydrogen atoms to the n = 3 state by electron bombardment. By coherence is meant that the density matrix describing the atom after the collision has off-diagonal matrix elements in the field-free basis. The differential cross section for producing Balmer-$alpha$ photons at 90$sup 0$ to the electron beam is calculated as a function of an applied longitudinal electric field. The off-diagonal elements show up as a dependence of the observed light on the direction of the electric field. Theoretical results based on the Born approximation are compared with an experiment at 200 and 500 eV. It is pointed out that this method for measuring relative phases of scattering amplitudes can be generally applied and is not restricted to n = 3 excitation of hydrogen. (AIP)
TL;DR: In this article, the results of a statistical study of the temperature field of several examples of regular wave, vacillating flow and irregular flow in a rotating annulus with a gap width of 10 cm using a limited number of thermocouples were reported.
Abstract: This paper reports the results of a statistical study of the temperature field of several examples of regular wave, vacillating flow and irregular flow in a rotating annulus with a gap width of 10 cm using a limited number of thermocouples. The primary results indicate that the regular waves produce several wavenumber harmonies through nonlinear interactions. The wavenumber harmonies decrease in the vacillating flow and are not detectable in the irregular flow. Further, the azimuthal coherence of the flow in the irregular regime decreases very rapidly in azimuth, and yet the vertical coherence is extremely high at all frequencies indicating a strong two-dimensional character of the irregular regime.
TL;DR: In this paper, the authors present a theoretical analysis of fringes formation with partially coherent light, based on the propagation laws of the mutual coherence function, and they show the existence of critical coherence field srtuctures which reduce the fringe visibility even in he Fourier planes.
Abstract: We present a theoretical analysis of miore fringes formation with partially coherent light. This analysis is based on the propagation laws of the mutual coherence function. Γ. With perfectly coherent light (i.e. laser light) the fringe visibility is maximum only in the Fourier planes. We show the existence of « critical coherence » field srtuctures which reduce the fringe visibility even in he Fourier planes. This analysis shows that periodic object image formation is strongly influenced by the coherence strucure of the light field.
TL;DR: In this article, a study of the harmonic wave properties (intensity and coherence) in connection with the statistics of the fundamental: coherent, chaotic and non-ideal laser cases are considered for the fundamental.
Abstract: The author presents a study of the harmonic wave properties (intensity and coherence) in connection with the statistics of the fundamental: coherent (ideal laser), chaotic and non-ideal laser cases are considered for the fundamental. Two approximations of different order are considered and their validity range is studied. The author shows that a coherent wave generates a coherent harmonic only it its photon number is great, while a chaotic one always creates a harmonic with different statistics. He shows also that a fundamental with Lorentzian spectral width generates a harmonic with a coherence time four times smaller.
Patent•
12 Dec 1975
TL;DR: In this article, a system for measuring the complex degree of coherence of beams of optical radiation is disclosed, which consists of a polarizer for preparing initially the state of the radiation field entering the device, a retarder oriented so as to divide the polarized beam into two orthogonally polarized components with a specific relative temporal retardation, and an electro-optic modulator which modulates the relative temporal phase shift as a function of time.
Abstract: A system for measuring the complex degree of coherence of beams of optical radiation is disclosed. The system generally consists of a polarizer for preparing initially the state of the radiation field entering the device, a retarder oriented so as to divide the polarized beam into two orthogonally polarized components with a specific relative temporal retardation, and an electro-optic modulator which modulates the relative temporal phase shift as a function of time. The resultant beam is divided into three beams having independent states of polarization so that each is caused to fall upon a separate detector. The teachings of this disclosure show how these three measurements of intensity together with the known degree of modulation can be used to compute the complex degree of coherence and also the mean wavelength of quasi-monochromatic light analyzed by the system.