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CRC Press eBooks

“Coherence” Phenomenon

Chandrasekhar Roychoudhuri

Published May 7, 2014• 0 citations
Publisher

Abstract

Coherence is theorized as the normalized correlation between two superposed optical signals, usually replicated by a two-beam interferometer or by a double-slit system. Prevailing coherence theory is presented as field–field correlation, as it does not go into the technical details of how the measurable transformations are physically generated and registered. Teaching coherence theory using a semiclassical model has been very successful as is evidenced in literature from the extensive reference to the text by M. Born and E. Wolf. This has been further strengthened by the work of Sudarshan, who demonstrated the optical equivalence between Wolf’s classical theory and Glauber’s quantum coherence theories. The discussion about the classical concept of coherence remains incomplete without presenting the van Cittert–Zernike theorem on spatial coherence, because the concept of coherence evolved with historic attempts to understand spatial coherence.

DOI
10.1201/b16914-6

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The Quantum Theory of Optical Coherence

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The concept of coherence which has conventionally been used in optics is found to be inadequate to the needs of recently opened areas of experiment. To provide a fuller discussion of coherence, a succession of correlation functions for the complex field strengths is defined. The $n\mathrm{th}$ order function expresses the correlation of values of the fields at $2n$ different points of space and time. Certain values of these functions are measurable by means of $n$-fold delayed coincidence detection of photons. A fully coherent field is defined as one whose correlation functions satisfy an infinite succession of stated conditions. Various orders of incomplete coherence are distinguished, according to the number of coherence conditions actually satisfied. It is noted that the fields historically described as coherent in optics have only first-order coherence. On the other hand, the existence, in principle, of fields coherent to all orders is shown both in quantum theory and classical theory. The methods used in these discussions apply to fields of arbitrary time dependence. It is shown, as a result, that coherence does not require monochromaticity. Coherent fields can be generated with arbitrary spectra.

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The quantum theory of optical coherence

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An Introduction to Quantum Optics: Photon and Biphoton Physics

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Coherence is theorized as the normalized correlation between two superposed optical signals, usually replicated by a two-beam interferometer or by a double-slit system. Prevailing coherence theory is presented as field–field correlation, as it does not go into the technical details of how the measurable transformations are physically generated and registered. Teaching coherence theory using a semiclassical model has been very successful as is evidenced in literature from the extensive reference to the text by M. Born and E. Wolf. This has been further strengthened by the work of Sudarshan, who demonstrated the optical equivalence between Wolf’s classical theory and Glauber’s quantum coherence theories. The discussion about the classical concept of coherence remains incomplete without presenting the van Cittert–Zernike theorem on spatial coherence, because the concept of coherence evolved with historic attempts to understand spatial coherence.
The concept of coherence which has conventionally been used in optics is found to be inadequate to the needs of recently opened areas of experiment. To provide a fuller discussion of coherence, a succession of correlation functions for the complex field strengths is defined. The nthn\mathrm{th}nth order function expresses the correlation of values of the fields at 2n2n2n different points of space and time. Certain values of these functions are measurable by means of nnn-fold delayed coincidence detection of photons. A fully coherent field is defined as one whose correlation functions satisfy an infinite succession of stated conditions. Various orders of incomplete coherence are distinguished, according to the number of coherence conditions actually satisfied. It is noted that the fields historically described as coherent in optics have only first-order coherence. On the other hand, the existence, in principle, of fields coherent to all orders is shown both in quantum theory and classical theory. The methods used in these discussions apply to fields of arbitrary time dependence. It is shown, as a result, that coherence does not require monochromaticity. Coherent fields can be generated with arbitrary spectra.
The concept of coherence which has conventionally been used in optics is found to be inadequate to the needs of recently opened areas of experiment. To provide a fuller discussion of coherence, a succession of correlation functions for the complex field strengths is defined. The nthn\mathrm{th}nth order function expresses the correlation of values of the fields at 2n2n2n different points of space and time. Certain values of these functions are measurable by means of nnn-fold delayed coincidence detection of photons. A fully coherent field is defined as one whose correlation functions satisfy an infinite succession of stated conditions. Various orders of incomplete coherence are distinguished, according to the number of coherence conditions actually satisfied. It is noted that the fields historically described as coherent in optics have only first-order coherence. On the other hand, the existence, in principle, of fields coherent to all orders is shown both in quantum theory and classical theory. The methods used in these discussions apply to fields of arbitrary time dependence. It is shown, as a result, that coherence does not require monochromaticity. Coherent fields can be generated with arbitrary spectra.
Recent advances in quantum optics have highlighted the critical role of spatial propagation in controlling the quantum coherence of light beams. However, the evolution of quantum coherence for light beams undergoing fundamental optical processes at dielectric interfaces remains unexplored. Furthermore, manipulating multiphoton correlations typically requires complex interactions that challenge few-photon level implementation. Here, we introduce a quantum van Cittert-Zernike theorem for light beams, describing how their coherence-polarization properties are influenced by reflection and refraction, as well as how these properties evolve upon subsequent propagation. Our work demonstrates that the quantum statistics of photonic systems can be controllably modified through the inherent polarization coupling arising from reflection and refraction at an interface, without relying on conventional light-matter interactions. Our approach reveals regimes where thermal light can exhibit sub-Poissonian statistics with fluctuations below the shot-noise level through post-selected measurements, and this statistical property can be tuned by the incident angle. Remarkably, this quantum statistical modification is governed by a scaling law linking beam collimation to far-field thermalization. Our work establishes a robust, decoherence-avoiding mechanism for quantum state control, advancing the fundamental understanding of coherence in quantum optics and opening new avenues for applications in quantum information and metrology.
A reciprocal relationship between the autocovariance of the light intensity in the source plane and in the far-field detector plane is presented in a form analogous to the classical van Cittert-Zernike theorem, but involving intensity correlation functions. A "classical" version of the reciprocity relationship is considered first, based on the assumption of circular Gaussian statistics of the complex amplitudes in the source plane. The result is consistent with the theory of Hanbury Brown-Twiss interferometry, but it is shown to be also applicable to estimation of the source size or the spatial resolution of the detector from the noise power spectrum of flat-field images. An alternative version of the van Cittert-Zernike theorem for intensity correlations is then derived for a quantized electromagnetic beam in a coherent state, which leads to Poisson statistics for the intrinsic intensity of the beam.
Electromagnetic Wave Theory and Measurement of Light Electromagnetic Wave Theory of Light Classical Superposition Measurement of Light Intensity of Light: Expectation and Fluctuation Measurement of Intensity: Ensemble Average and Time Average Coherence Property of Light-The State of the Radiation Coherence Property of Light Temporal Coherence Spatial Coherence Diffraction and Propagation Diffraction Field Propagation Optical Imaging A Classic Imaging System Fourier Transform via a Lens First-Order Coherence of Light First-Order Temporal Coherence First-Order Spatial Coherence Second-Order Coherence of Light Second-Order Coherence of Coherent Light Second-Order Correlation of Chaotic-Thermal Radiation and the HBT Interferometer The Physical Cause of the HBT Phenomenon Near-Field Second-Order Spatial Coherence of Thermal Light Nth-Order Coherence of Light Nth-Order Near-Field Spatial Coherence of Thermal Light Homodyne Detection and Heterodyne Detection of Light Optical Homodyne and Heterodyne Detection Balanced Homodyne and Heterodyne Detection Balanced Homodyne Detection of Independent and Coupled Thermal Fields Quantum Theory of Light: Field Quantization and Measurement The Experimental Foundation-Part I: Blackbody Radiation The Experimental Foundation-Part II: Photoelectric Effect The Light Quantum and the Field Quantization Photon Number State of Radiation Field Coherent State of Radiation Field Density Operator and Density Matrix Composite System and Two-Photon State of Radiation Field A Simple Model of Incoherent and Coherent Radiation Source Pure State and Mixed State Product State, Entangled State, and Mixed State of Photon Pairs Time-Dependent Perturbation Theory Measurement of Light: Photon Counting Measurement of Light: Joint Detection of Photons Field Propagation in Space-Time Quantum Theory of Optical Coherence Quantum Degree of First-Order Coherence Photon and Effective Wavefunction Measurement of the First-Order Coherence or Correlation Quantum Degree of Second-Order Coherence Two-Photon Interference vs. Statistical Correlation of Intensity Fluctuations Second-Order Spatial Correlation of Thermal Light Photon Counting and Measurement of G(2) Quantum Entanglement EPR Experiment and EPR State Product State, Entangled State, and Classically Correlated State Entangled States in Spin Variables Entangled Biphoton State EPR Correlation of Entangled Biphoton System Subsystem in an Entangled Two-Photon State Biphoton in Dispersive Media Quantum Imaging Biphoton Imaging Ghost Imaging Ghost Imaging and Uncertainty Relation Thermal Light Ghost Imaging Classical Simulation of Ghost Imaging Turbulence-Free Ghost Imaging Two-Photon Interferometry I: Biphoton Interference Is Two-Photon Interference the Interference of Two Photons? Two-Photon Interference with Orthogonal Polarization Franson Interferometer Two-Photon Ghost Interference Delayed Choice Quantum Eraser Two-Photon Interferometry II: Quantum Interference of Chaotic Light Two-Photon Young's Interference Two-Photon Anticorrelation with Incoherent Chaotic Light Two-Photon Interference with Incoherent Orthogonal Polarized Chaotic Light Bell's Theorem and Bell's Inequality Measurement Hidden Variable Theory and Quantum Calculation for the Measurement of Spin 1/2 Bohm State Bell's Theorem and Bell's Inequality Bell States Bell State Preparation