Coherence Properties Of Light Research Articles

Polarization coherence frustration.

From the joint analysis of polarization and coherence properties of light, a remarkable concept referred to as polarization coherence frustration is introduced and analyzed. It is shown that two kinds of partially polarized and partially coherent light, with different levels of complexity, can be distinguished and that they mathematically correspond to different equivalence classes. On the one hand, light has polarization coherence properties that are not frustrated in a spatial domain D when there exists a configuration of local polarization devices at each location of the light field that allows the maximization of the modulus of the scalar degree of coherence between any couple of points in D. Two conditions are shown to hold for light to be polarization coherence unfrustrated and their physical interpretations are analyzed. On the other hand, if one of these conditions is not verified, polarization coherence frustration occurs. These notions are discussed in analogy with well-known concepts of frustration and gauge transformations developed in statistical physics for spin glasses. Their relevance in the field of statistical optics is demonstrated through different theoretical results and examples.

Randomness, determinism, and ignorance in coherence.

The effect of randomness and determinism on the coherence properties of light are studied in detail. As it is well known, a random field can have widely varying coherence properties. Here, it is shown that one can also produce a deterministic field with an arbitrarily low degree of coherence. The role of constant (non-random) fields are then considered, and some simulations with a toy model laser are presented. An interpretation of coherence as a measure of "ignorance" is presented.

Coherence properties of light in highly multimoded nonlinear parabolic fibers under optical equilibrium conditions.

We study the coherence characteristics of light propagating in nonlinear graded-index (GRIN) multimode fibers after attaining optical thermal equilibrium conditions. The role of optical temperature on the spatial mutual coherence function and the associated correlation area is systematically investigated. In this respect, we show that the coherence properties of the field at the output of a multimode nonlinear fiber can be controlled through its optical thermodynamic properties.

Speckle suppression and companion detection using coherent differential imaging

Residual speckles due to aberrations arising from optical errors after the split between the wavefront sensor and the science camera path are the most significant barriers to imaging extrasolar planets. While speckles can be suppressed using the science camera in conjunction with the deformable mirror, this requires knowledge of the phase of the electric field in the focal plane. We describe a method which combines a coronagraph with a simple phase-shifting interferometer to measure and correct speckles in the full focal plane. We demonstrate its initial use on the Stellar Double Coronagraph at the Palomar Observatory. We also describe how the same hardware can be used to distinguish speckles from true companions by measuring the coherence of the optical field in the focal plane. We present results observing the brown dwarf HD 49197b with this technique, demonstrating the ability to detect the presence of a companion even when it is buried in the speckle noise, without the use of any standard "calibration" techniques. We believe this is the first detection of a substellar companion using the coherence properties of light.

Quantum Correlations of Photons and Qudit States

We present briefly the historical aspects of studying the properties of light including both the classical theory of light based on the electromagnetic wave picture and the quantum corpuscular interpretation of light based on the notion of photons. We consider vibrations of electric and magnetic fields in light waves and quantum correlations described by the Heisenberg and Schrodinger–Robertson uncertainty relations valid for any vibrations in connection with specific statistical properties of coherent light and squeezed light. We review the qubit and qudit states and the new uncertainty relation for entropy and energy for qudit systems. We discuss the dynamical (nonstationary) Casimir effect providing a vacuum generator of squeezed photons based on the technique of superconducting circuits realized by Josephson junctions. We demonstrate new entropic inequalities for two qubits (polarization states of two photons) and hidden correlations of noncomposite quantum systems (quantum roulette).

Strain and Stress Analysis around the Notches Using ESPI Method

Modern speckle optical methods use the properties of coherent light for identification of displacement fields. One of these methods is method ESPI. Using of this method strain and stress fields on surface of flat test samples with symmetric notches by tensile and shear loading were identified. A special fixture for shear loading of test samples was designed. The shape and dimensions of the fixture were modified on the basic results of experimental measurements. A modification allowed us to obtain a better analyse of strain and stress fields of test samples with symmetric V notches.

Intensity and coherence properties of light in oceanic turbulence

Using the Rytov method and Belen'kii and Mironov's method of effective beam parameters for strong turbulence regimes, the intensity and coherence properties of a Gaussian beam propagating through the clear-water turbulent ocean are explored. The refractive index fluctuations are described by a recently developed power spectrum combining the effects from both temperature and salinity. Due to the complicated nature of the oceanic turbulence spectrum, the analysis is restricted to numerical computations.

Tailored leaky plasmon waves from a subwavelength aperture for optical particle trapping on a chip

Optical forces available on a chip that possess features of strong trapping at the subwavelength scale, in a coplanar geometry, and at specific and selective locations portend many useful applications. We demonstrate here a two-pronged approach to accomplish this. First, the plasmon fields emanating from a subwavelength aperture are manipulated so that they leak maximally to the sides on a surface through the use of tailored corrugations. Second, the location of secondary corrugation at some distance permits reflection of these leaky waves, which, with the coherence property of light used, generate optical standing wave fields capable of strong optical trapping. The linear optical forces generated with this scheme are presented here.

Analysis of non-ergodic behaviour in spatio-temporal coherence properties of speckle light

Spatio-temporal coherence properties of light scattered by rough surfaces that leads to speckle fluctuations are analysed. It is demonstrated that the scattered light is non-ergodic with the disorder due to the scattering process. Although the mutual coherence matrix vanishes with isotropic polarization fluctuations, it is shown that spatio-temporal coherence properties can be described with interference experiments that can be obtained between different speckles of the scattered light. For non-singular scattering processes, the maximal value of the modulus of the Wolf degree of coherence is analysed in the spatial time domain. This approach is also applied to totally unpolarized incident light with an isotropic and spatially independent scattering process. The mean value and the standard deviation of the Wolf degree of coherence are then determined from the coherence properties of the incident light.

Reconstruction of spatial, phase, and coherence properties of light.

Image reconstruction of partially coherent light is interpreted as quantum-state reconstruction. An efficient method based on the maximum-likelihood estimation is proposed for acquiring information from blurred intensity measurements affected by noise. Connections with incoherent-image restoration are pointed out. The feasibility of the method is demonstrated numerically. Spatial and correlation details significantly below the diffraction limit are revealed in the reconstructed pattern.

Coherent VUV- and X-ray generation with optical lasers

The laser concept, i.e. the active control over coherence properties of light, has partially transformed optical sciences into one of the most important key technologies of the next century. Consequently, various attempts have long been made to extend this concept towards VUV- and X-ray wavelengths, but have met considerable practical difficulties. Low-energy efficiency in inversion creation is one of the typical obstacles, extremely high-power requirements (e.g. for optical driver lasers) another. Only very recently several new, independent concepts have been successfully realized, and promise real breakthroughs in short-wavelength generation and application. Compact “table-top” X-ray lasers have been operated in a saturated gain conditions, either through electric discharge pumping in a capillary or through short-pulse optical laser pumping in a transient inversion scheme. In addition, direct conversion of optical laser light into the VUV- and soft X-ray region has been accomplished. These new sources are relatively compact, though not yet powerful, and will thus complement future highly brilliant free electron lasers in the short-wavelength regime. The paper illuminates the status, future directions and physical limits of some of these new concepts.

Atom optics: matter and waves in harmony

Our ability to manipulate the coherence properties of light has been at the heart of many of the most important scientific and technological innovations of this century. There can hardly be a home in this country that does not possess a laser in the form of a compact disc player or a CDROM. When we talk on the phone, or send messages on the Internet, there is a high probability that our message will be encoded by a laser into pulses of light to be passed through optical fibres. In the last few years physicists have been discovering that it is possible to control the coherence properties of atoms, and are now developing tools analogous to those which have been developed to take advantage of the coherence properties of light. In the next decade we can look forward to seeing the application of lasers, fibres, mirrors and waveguides for atoms. Already we have been able to construct interferometry experiments using beams of atoms and these have proved to be extremely sensitive measurement devices, allowing us to test physical theories and measure fundamental constants to a level of precision not previously possible. Will these developing technologies ever be as ubiquitous as their optical forebears? In this paper we discuss the anticipated uses of this technology for both fundamental science and industrial applications. Starting from an explanation of the meaning of coherence and a comparison of the properties of photons and atoms, we describe the development of the science of atom optics. The tortuous route towards the great achievement of producing a Bose–Einstein condensate is described, and we explain why this is the most important step towards a laser–like source of atoms. Numerous other optical elements for atoms have been built or are on the drawing board, and we describe how these may be used to manipulate atoms with a precision that has never before been achieved, and look ahead to what we can learn about physics using these tools and at how they can be put to practical use.

Coherence properties of light in Young's interference pattern formed with partially coherent light

It has been shown not long ago that the spectrum of light in Young's interference pattern formed by partially coherent light differs, in general, from the spectrum of light incident on the pinholes; and, moreover, that the spectrum depends on the position of the point of observation. In this paper we extend the analysis by deriving expressions for the spectral degree of coherence and for the cross-spectral density of intensity fluctuations of the light at any pair of points in the interference pattern. We illustrate the general results by examples.

An atomic dimmer switch

Work involving a new tool in optics, a pulse shaper, shows how atoms can be made to absorb light readily, or not at all, simply by controlling the phase of light shone at them. The method can be added to a growing list of techniques for manipulating the internal quantum dynamics of atoms and molecules using the coherence properties of light.

Decrease in spatial coherence of light propagating in free space

It is shown that a highly spatially incoherent light distribution may be generated from a highly coherent one on propagation in free space. This result essentially demonstrates that there exists an inverse of a classic result of optical coherence theory, namely, the van Cittert-Zernike theorem. The analysis also indicates that the technique of phase conjugation may be used to reverse changes in the coherence properties of light, at least those which are generated on propagation in free space.

Quantum phase and dynamical properties of light in the Jaynes-Cummings model via phase coupling

It is pointed out here that quantum phase properties, as well as dynamical properties, of light exhibit a sensitivity to the relative phase between the atomic dipole and light when the atom is prepared in a coherent superposition of its states in the two-level Jaynes-Cummings model interacting with a coherent state of light. The existence of the coherent-trapping of light is demonstrated by looking not only at the variance of the light phase about the coherent state value, and the number-phase uncertainty relation, but also at the factorization of the electric-field operator, and the photon-number distribution. We find also the factorization expression of the compound state of the atom-field system. We show once more that the phase properties of light based on the phase operator formalism of Pegg-Barnett and the coherence properties of light based on the coherence theory of Glauber are complementary in description of the optical quantum coherence.

Phase dynamics of coherent light in the M-photon Jaynes-Cummings model.

We have studied the phase properties of coherent light in the M-photon Jaynes-Cummings model using the Hermitian phase operator of Pegg and Barnett [Europhys. Lett. 6, 483 (1988)] and have found the collapse and revival phenomenon about the long-time behavior of the phase variance of the field. Also, we have given a reasonable interpretation of the phenomenon.

On a relationship between spectral properties and spatial coherence properties of light

It is shown that the cross-spectral density and the spectrum of a fluctuating, statistically stationary free optical field may be obtained from the knowledge of its spatial coherence properties. Explicit expressions for the cross-spectral density and for the spectrum are derived in terms of the mutual intensity function of the field.

Spatial coherence properties of light scattered by disclinations in a liquid crystal

The correlation length of optical inhomogeneities near disclinations, produced by ultrasound in a liquid crystal cell, is measured as a function of the applied ultrasonic power by determining the spatial coherence of scattered light. Some preliminary indications about the behavior of disclination properties as a function of the ultrasonic power are obtained.

Single-interval statistics of light scattered by identical independent scatterers

The authors consider the statistical properties of coherent light Rayleigh-scattered by a solution containing an arbitrary number N of independent, identical particles. Expressions are obtained for the single-interval intensity probability distribution and the moments of this distribution, which are equivalent to the measurable photocount factorial moments.