Showing papers on "Coherence (physics) published in 1998"
TL;DR: An optical coherence tomography system is described which can image up to video rate and features a high speed scanning delay line in the reference arm based on Fourier-transform pulse shaping technology.
Abstract: An optical coherence tomography system is described which can image up to video rate. The system utilizes a high power broadband source and real time image acquisition hardware and features a high speed scanning delay line in the reference arm based on Fourier-transform pulse shaping technology. The theory of low coherence interferometry with a dispersive delay line, and the operation of the delay line are detailed and the design equations of the system are presented. Real time imaging is demonstrated in vivo in tissues relevant to early human disease diagnosis (skin, eye) and in an important model in developmental biology (Xenopus laevis).
624 citations
TL;DR: In this article, the authors demonstrate that nuclear magnetic resonance spectroscopy is capable of emulating many of the capabilities of quantum computers, including unitary evolution and coherent superpositions, but without attendant wave-function collapse.
377 citations
347 citations
TL;DR: In this article, the temporal coherence of high-order harmonics (up to the 15th order) produced by focusing 100 fs laser pulses into an argon gas jet was studied.
Abstract: We have studied the temporal coherence of high-order harmonics (up to the 15th order) produced by focusing 100 fs laser pulses into an argon gas jet. We measure the visibility of the interference fringes, produced when two spatially separated harmonic sources interfere in the far field, as a function of the time delay between the two sources. In general, we find long coherence times, comparable to the expected pulse durations of the harmonics. For some of the harmonics, the interference pattern exhibits two regions, with significantly different coherence times. These results are interpreted in terms of different electronic trajectories contributing to harmonic generation. [S0031-9007(98)05569-7].
270 citations
TL;DR: A new method for eliminating speckles in the far field by using a diffractive optical element is proposed, which can be reduced to a few percent while good beam quality is preserved.
Abstract: In laser projection systems the observer in the far field of the image points on the screen will recognize serious speckle noise There are many methods to reduce or eliminate speckles in the near field by reducing or eliminating temporal or spatial coherence of the laser But for the far field it is hardly possible to change the coherence properties of laser sources so that speckles will disappear We propose a new method for eliminating speckles in the far field by using a diffractive optical element The intensity modulation depth in the far-field speckle pattern can be reduced to a few percent while good beam quality is preserved
262 citations
TL;DR: A matrix method is outlined for dealing with quasi-monochromatic, partially polarized light when spatial coherence is not necessarily complete and propagation occurs along beams that can account for differences that would be revealed by a scalar treatment or by a locally defined polarization matrix.
Abstract: A matrix method is outlined for dealing with quasi-monochromatic, partially polarized light when spatial coherence is not necessarily complete and propagation occurs along beams. Both spatial coherence and polarization properties are described by a single 2x2 matrix whose elements have the structure of mutual intensity functions. Through a simple example it is shown that this matrix can account for differences that would not be revealed by a scalar treatment or by a locally defined polarization matrix.
231 citations
TL;DR: It is observed that cross-polarized backscatter measured by optical coherence tomography of human skin in vivo is surprisingly strong and its main origins are single scattering from nonspherical particles and multiple scattering by particles with sizes much larger than a wavelength.
Abstract: We have observed that cross-polarized backscatter measured by optical coherence tomography of human skin in vivo is surprisingly strong. We identify and give evidence of its main origins:?single scattering from nonspherical particles and multiple scattering by particles with sizes much larger than a wavelength. Our findings show that depolarized light scattered by dense large-diameter particles maintains a high degree of temporal coherence and that differential-polarization imaging improves contrast between particles of different sizes.
210 citations
Patent•
11 Jun 1998
TL;DR: In this paper, two dimensional images of optical birefringence in turbid samples as a function of depth are measured using a low coherence Michelson interferometer.
Abstract: Employing a low coherence Michelson interferometer, two dimensional images of optical birefringence in turbid samples as a function of depth are measured Polarization sensitive detection of the signal formed by interference of backscattered light from the sample and a mirror or reference plane in the reference arm which defines a reference optical path length, give the optical phase delay between light propagating along the fast and slow axes of the birefringence sample Images showing the change in birefringence in response to irradiation of the sample are produced as an example of the detection apparatus and methodology The technique allow rapid, noncontact investigation of tissue or sample diagnostic imaging for various medical or materials procedures
197 citations
TL;DR: In this article, a generalized bidirectional distribution function (BRDF) was proposed to describe the specific intensity of the scattered light from a semi-infinite medium to the incident light in the framework of coherence theory.
Abstract: A generalized bidirectional distribution function (BRDF) that relates the specific intensity of the scattered light from a semi-infinite medium to the specific intensity of the incident light is introduced in the framework of coherence theory. This derivation allows us to obtain from first principles several fundamental properties: First, it is established that the generalized BRDF takes the form of a nonlocal relation between the incident and the scattered specific intensities. This nonlocal structure allows us to account naturally for the lateral shift of a beam. Second, the generalized BRDF is the Fourier transform of the correlation function that describes the memory effect. Third, the Helmholtz principle for specific intensities is derived as a theorem from the reciprocity property of the scattering operator for wave fields. This result allows us to prove Kirchhoff’s law.
185 citations
TL;DR: In this paper, the effects of spontaneously generated coherence on the formation of a trapped state in the presence of two coherent fields of arbitrary intensity were investigated and showed that such coherence preserves both electromagnetically induced transparency and coherent population trapping (CPT) phenomena.
Abstract: Near-degenerate lower levels in a $\ensuremath{\Lambda}$ system have an additional coherence term due to interaction with the vacuum of the radiation field. We report the effects of this spontaneously generated coherence on the formation of a trapped state in the presence of two coherent fields of arbitrary intensity. We show that such coherence preserves both electromagnetically induced transparency and coherent population trapping (CPT) phenomena. However, it changes the time scales associated with the formation of the CPT state, and brings about quantitative changes in the line profiles. We present a clear analytical explanation for our numerical results. We also report the dependence of line shapes on the relative phase between the two applied fields.
182 citations
TL;DR: In this paper, the authors demonstrate the effect of the beat effect on partial coherence interferometry (PCI) signal peaks and discuss the implications of this effect for optical coherence tomography of human retina.
TL;DR: In this paper, the authors generalized the input-output relations for an optical beam splitter to allow linear absorption by the medium forming the mirror, and showed that the degree of second-order coherence of antibunched light can be maintained on transmission through the beam-splitter but any amplitude squeezing in the incident light is degraded.
Abstract: The familiar input-output relations for an optical beam splitter are generalized to allow for linear absorption by the medium forming the mirror. Beam-splitter losses generally affect the noise levels detectable in experiments involving nonclassical Light. When employed to investigate two-photon interference effects, a lossy beam splitter can lead to apparent nonlinear absorption, which, in the most extreme case, leads to either both or neither of the photons being absorbed. The degree of second-order coherence of antibunched light can be maintained on transmission through the beam splitter but any amplitude squeezing in the incident light is degraded.
TL;DR: In this article, the authors studied nonlinear optical parametric processes in a resonantly driven multilevel system displaying quantum interference effects and showed that a pair of correlated Stokes and anti-Stokes fields can be generated from infinitesimally small initial values.
Abstract: Nonlinear optical parametric processes are studied in a resonantly driven multilevel system displaying quantum interference effects. It is shown that in such systems a new regime of nonlinear amplification is possible, in which a pair of correlated Stokes and anti-Stokes fields can be generated from infinitesimally small initial values. An atomic coherence grating emerges during this process of efficient nonlinear amplification. The present analysis explains the results of recent optical phase conjugation experiments involving atomic phase coherence.
Patent•
26 Oct 1998
TL;DR: In this article, a method and apparatus for elimination of speckle pattern in optical system by reducing coherence is presented, which is based on the use of a rotating microlens array having a rotational speed chosen with reference to laser parameter.
Abstract: A method and apparatus for elimination of speckle pattern in optical system by reducing coherence. The invention is based on the use of a rotating microlens array having a rotational speed chosen with reference to laser parameter. For a continuous laser this relationship consists in that the exposure time is sufficient for overlapping at least 104 spot sizes of the speckle. For a pulse laser, the laser pulse time should be sufficient for shifting the speckle spot at least by the magnitude of its diameter. Several embodiments with modified coherence reduction units are available. One modified embodiment describes a rotating inclined plate which enhances coherence reduction by scanning the over the surface of the diffuser. Another embodiment describes the use of an optical conical rod with total internal reflection for creation of a plurality of non-coherent light sources.
TL;DR: In this article, a beam coherence-polarization matrix is proposed for describing the properties of a quasi-monochromatic, beam-like field that is both partially polarized and partially coherent from the spatial viewpoint.
Abstract: We present an approach for describing the properties of a quasi-monochromatic, beam-like field that is both partially polarized and partially coherent from the spatial standpoint It is based on the use of a single matrix, called the beam coherence-polarization matrix, whose elements have the form of mutual intensities This approach, which can be viewed as an approximate form of Wolf's general tensorial theory of coherence, appears to be very simple, yet it is able to cover significant aspects of the beam behaviour that would not be accounted for by a scalar theory or by a local polarization matrix approach A peculiar interference law applying to mutual intensities is derived We show through simple examples how this approach leads to distinguish fields that would appear identical in a scalar treatment or in a local polarization matrix description Hints for extensions are given
TL;DR: In this article, the temporal and spatial coherence widths of the microscopic process by which a neutrino is detected are incorporated in the quantum mechanical wave packet treatment of Neutrino oscillations, confirming the observation of Kiers, Nussinov, and Weiss that an accurate measurement of the neutrer energy in the detection process can increase the coherence length.
Abstract: The temporal and spatial coherence widths of the microscopic process by which a neutrino is detected are incorporated in the quantum mechanical wave packet treatment of neutrino oscillations, confirming the observation of Kiers, Nussinov, and Weiss that an accurate measurement of the neutrino energy in the detection process can increase the coherence length. However, the wave packet treatment presented here shows that the coherence length has an upper bound, determined by the neutrino energy and the mass-squared difference, beyond which the coherence of the oscillation process is lost.
TL;DR: In this article, a dual beam version of partial coherence interferometry has been developed for measuring intraocular distances in vivo with a precision on the order of 0.3 to 3 mm.
Abstract: In the past 10 years, a dual beam version of partial coherence interferometry has been developed for measuring intraocular distances in vivo with a precision on the order of 0.3 to 3 mm. Two improvements of this technology are described. A special diffractive optical element allows matching of the wavefronts of the divergent beam reflected at the cornea and the parallel beam reflected at the retina and collimated by the optic system of the eye. In this way, the power of the light oscillations of the interfering beams incident on the photodetector is increased and the signal-to-noise ratio of in vivo measurements to the human retina is improved by 20 to 25 dB. By using a synthesized light source consisting of two spectrally displaced superluminescent diodes with an effective bandwidth of 50 nm, and by compensating for the dispersive effects of the ocular media, it was possible to record the first optical coherence tomogram of the retina of a human eye in vivo with an axial resolution of ; 6t o 7 m m. This is a twofold improvement over the current technology. © 1998 Society of Photo-Optical Instrumentation Engineers. [S1083-3668(98)01601-3]
TL;DR: In this article, a technique for producing subfemtosecond pulses of radiation was proposed based on using electromagnetically induced transparency to produce a strongly driven molecular coherence, which results in a Raman spectrum with Bessel function amplitudes and phases corresponding to a frequency modulated signal.
Abstract: We suggest a technique for producing subfemtosecond pulses of radiation. The technique is based on using electromagnetically induced transparency to produce a strongly driven molecular coherence. This coherence results in a Raman spectrum with Bessel function amplitudes and phases corresponding to a frequency modulated signal, thereby allowing compression by the group velocity dispersion of the same medium.
TL;DR: In this paper, the authors studied phase synchronization in periodically driven stochastic bistable systems in terms of phase synchronization effects and the degree of phase coherence was estimated by employing the effective diffusion constant for the phase difference.
Abstract: We study stochastic resonance in periodically driven stochastic bistable systems in terms of phase synchronization. By introduction of an instantaneous phase for the output we show explicitly the effect of phase locking between the input and output. The stochastic dynamics of the phase difference between input and output appears to be similar to that of synchronized classical self-sustained oscillators. The degree of phase coherence is estimated by employing the effective diffusion constant for the phase difference. This coherence becomes maximal for optimal noise intensities. However, phase synchronization effects can only be observed for sufficiently large magnitude of the periodic inputting signal.
TL;DR: The analysis of two-layer solid phantoms shows that the backscattered light gets stronger with decreasing anisotropic factor and increasing scattering coefficient, as predicted by Monte Carlo simulations.
Abstract: A new noninvasive technique that reveals cross sectional images of scattering media is presented. It is based on a continuous wave frequency modulated radar, but uses a tunable laser in the near infrared. As the full width at half maximum resolution of 16 mm is demonstrated with an external cavity laser, the chirp optical coherence tomography becomes an alternative to conventional short coherence tomography with the advantage of a simplified optical setup. The analysis of two-layer solid phantoms shows that the backscattered light gets stronger with decreasing anisotropic factor and increasing scattering coefficient, as predicted by Monte Carlo simulations. By introducing a two-phase chirp sequence, the combination of lateral resolved perfusion and depth resolved structure is shown. © 1998 Society of Photo-Optical Instrumentation Engineers. [S1083-3668(98)00503-6]
TL;DR: In this article, the subthreshold oscillatory properties of inferior olivary neurons in vitro were analyzed and it was shown that the oscillation is nonlinear and supports low dimensional chaotic dynamics.
Abstract: Mathematical analysis of the subthreshold oscillatory properties of inferior olivary neurons in vitro indicates that the oscillation is nonlinear and supports low dimensional chaotic dynamics. This property leads to the generation of complex functional states that can be attained rapidly via phase coherence that conform to the category of “generalized synchronization.” Functionally, this translates into neuronal ensemble properties that can support maximum functional permissiveness and that rapidly can transform into robustly determined multicellular coherence.
TL;DR: In this article, an effective model for the spacetime foam is constructed in terms of nonlocal interactions in a classical background, and the evolution of the low-energy density matrix is determined by a master equation that predicts loss of quantum coherence.
Abstract: An effective model for the spacetime foam is constructed in terms of nonlocal interactions in a classical background. In the weak coupling approximation, the evolution of the low-energy density matrix is determined by a master equation that predicts loss of quantum coherence. Moreover, spacetime foam can be described by a quantum thermal field that, apart from inducing loss of coherence, gives rise to effects such as gravitational Lamb and Stark shifts as well as quantum damping in the evolution of the low-energy observables.
TL;DR: In this article, the authors analyzed the linearized approximation (LA) and showed that it is not capable of describing quantum interference/coherence effects in the longer time recrossing behavior of the isomerization dynamics.
Abstract: An earlier paper of ours [J. Chem. Phys. 108, 9726 (1998)] used an approximate (linearized) version of the semiclassical initial value representation (SC-IVR) to calculate reactive flux correlation functions for a model of unimolecular isomerization, namely a 1-d double well potential coupled to an infinite set of harmonic oscillators, obtaining excellent agreement with accurate quantum results for this system. Here we analyze this linearized approximation (LA) further, however, and show that it is not capable of describing quantum interference/coherence effects in the longer time recrossing behavior of the isomerization dynamics. (The recrossing effects seen in our earlier work were due to classical mechanics.) To accentuate quantum effects in the recrossing dynamics, the present article considers the double well potential without the harmonic bath, using both the LA and the full SC-IVR. The results of the calculations show that the flux correlation functions given by the LA agrees well with the exact qu...
TL;DR: In this article, a monomode semiconductor laser is subjected to external injection from another laser and the system stability is investigated as a function of detuning and of the relative injected power.
Abstract: In this paper, we analyze the phenomena arising when a monomode semiconductor laser is subjected to external injection from another laser. The system stability is investigated as a function of detuning and of the relative injected power. Different regimes, spanning from phase locking to chaos and coherence collapse, are described by analytical and numerical methods for weak and moderate injection. Previous theoretical studies are extended by describing the inverse transition from chaos to stability and by deriving the final locking condition. Also, further investigation on the coherence collapse regime has been performed. Besides contributing to the exploration of an interesting fundamental phenomenon, the results of this analysis are useful for different applications, including coherent detection and chaotic cryptography.
Proceedings Article•
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TL;DR: In this article, a system for time-resolved refleclance measurements' was used to estimate In vivo and non-invasively the absorption and transport scattering spectra of different human tissues.
Abstract: The knowledge of the optical properties of biological tissues in VIVO is of great importance for optical techniques presently being developed for medical diagnosis. Exfensive studies were performed in vitro, but in vivo only results obtained at single wavelengths or in a limited wavelength ranye are reported in the literature A system for time-resolved refleclance measurements' was used to estimate In vivo and non-invasively the absorption and transport scattering spectra of different human tissues. in the wavelength ranye from 610 nm to 1010 nm, every 5 nm. lilumlnation was performed with a synchronously pumped dye laser (610-700 nm) and an actively mode-iocked Ti:Sapphire laser (700 nm-1010 nm) A couple of I-mm diameter optical fibers was used for both light injection and coilection, setting the intediber distance to 2 cm Time-resolved data were collected with an electronic chain for time-correlated single photon counting with a response function of e150 ps FWHM. and interpreted with the diffusion theory for the evaluation of the absorption and transport scattering coefflcienls. Spectra were obtained from breast, arm muscle. head. and abdomen on healthy voiunteers. The scattering coefficient reduces upon increasing the wavelength, with minor changes amoig different tissue types. The absorption spectrum of 0 35 the various tissues reveals -0 30 the spectral features of oxy6 0 2 5 and deoxy-hemoglobin. iipid and water. A typical example for breast is shown In Fig 1. 0 20
TL;DR: In this paper, the modal theory of coherence is applied to partially coherent sources whose modes belong to the class of Laguerre-Gauss functions for which the Laguero polynomial has zero order.
Abstract: On the basis of the modal theory of coherence, we study partially coherent sources whose modes belong to the class of Laguerre-Gauss functions for which the Laguerre polynomial has zero order. Thes...
TL;DR: A system for simultaneous display or superimposing of an en-face image produced by optical coherence tomography and of a confocal image similar to that produced by a scanning laser ophthalmoscope is demonstrated for the first time, to the authors' knowledge, for the retina in the living eye.
Abstract: A system for simultaneous display or superimposing of an en-face image produced by optical coherence tomography and of a confocal image similar to that produced by a scanning laser ophthalmoscope is demonstrated for the first time, to our knowledge, for the retina in the living eye.
TL;DR: In this article, the authors point out that many wavepacket discussions for the coherence properties of particle beams are unnecessary since they deal with stationary sources; and when the problem is stationary, essentially all information is in the energy spectrum.
Abstract: We point out that many wavepacket discussions for the coherence properties of particle beams are unnecessary since they deal with stationary sources; and when the problem is stationary, essentially all information is in the energy spectrum. This recognition allows a simple answer to a number of long-debated points, usually framed in terms of the``length of the wavepacket.'' In particular we discuss neutrino oscillations, and some issues in neutron physics. The question as to whether two simple beams with the same energy spectrum are distinguishable is answered negatively for stationary situations. The question as to whether neutrino oscillations should be thought of as taking place between states of the same energy or the same momentum is answered in favor of energy for stationary situations. The consequences for proposals involving the ${}^{7}\mathrm{Be}$ neutrino line of the Sun, the observation of oscillations in supernova neutrinos, and wavepacket studies with neutrons are briefly discussed, as well as the connection with the coherence notions of quantum optics.
TL;DR: In this paper, the authors study the dynamics of a Bose-Einstein condensate in a double-well potential in the two-mode approximation and show that the self-locked population imbalance in the macroscopic quantum self-trapping decays away.
Abstract: We study the dynamics of a Bose-Einstein condensate in a double-well potential in the two-mode approximation. The dissipation of energy from the condensate is described by the coupling to a thermal reservoir of noncondensate modes. As a consequence of the coupling, the self-locked population imbalance in the macroscopic quantum self-trapping decays away. We show that a coherent state predicted by spontaneous symmetry breaking is not robust and decoheres rapidly into a statistical mixture due to the interactions between condensate and noncondensate atoms. However, via stochastic simulations we find that with a sufficiently fast measurement rate of the relative phase between the two wells the matter wave coherence is established even in the presence of the decoherence.
TL;DR: In this paper, the authors present a systematic investigation of the dynamical behavior of semiconductor lasers subject to external optical feedback dependent on the injection current and the optical feedback strength, identifying the regimes of low-frequency fluctuations (LFFs), fully developed coherence collapse, and a large regime of the coexistence of LFFs and stable emission on single high-gain external-cavity mode extending over more than one order of magnitude of optical feedback strengths.
Abstract: We present a systematic investigation of the dynamical behavior of semiconductor lasers subject to external optical feedback dependent on the injection current and the optical feedback strength. We identify the regimes of low-frequency fluctuations (LFFs), fully developed coherence collapse, and a large regime of the coexistence of LFFs and stable emission on single high-gain external-cavity mode extending over more than one order of magnitude of optical feedback strengths. Thus, we provide experimental evidence for one major prediction of the theoretical model based on the Lang-Kobayashi equations, which proposes a deterministic mechanism underlying the LFFs.