Showing papers on "Light field published in 1999"

Three-dimensional orientation measurements of symmetric single chromophores using polarization microscopy

Abstract: A complete understanding of any complex molecular system generally requires a knowledge of the three-dimensional (3D) orientation of its components relative both to each other, and to directional perturbations such as interfaces and electromagnetic fields. Far-field polarization microscopy is a convenient and widespread technique for detecting and measuring the orientation of single chromophores. But because the polarized electromagnetic field that is used to probe the system lacks a significant longitudinal component, it was thought that, in general, only 2D orientation information could be obtained1,2,3. Here we demonstrate that far-field polarization microscopy can yield the 3D orientation of certain highly symmetric single chromophores (CdSe nanocrystal quantum dots in the present case). The key requirement is that the chromophores must have a degenerate transition dipole oriented isotropically in two dimensions, which gives rise to a perpendicular ‘dark axis’ that does not couple to the light field. By measuring the fluorescence intensity from the dipole as a function of polarization angle, it is possible to calculate both the tilt angle between the dark axis and the sample plane, as well as the in-plane orientation, and hence obtain the 3D orientation of the chromophore

Techniques for spatial displacement estimation and multi-resolution operations on light fields

Abstract: Selective quality light field operations efficiently manipulate a multi-resolution representation of a light field. These operations include intra-image and inter-image decomposition and compression of a light field to a multi-resolution representation. These operations also include intra-image and inter-image decompression and reconstruction of a light field at selective quality. These selective quality operations also apply to storage, rendering, and transmission. Various techniques improve spatial displacement estimation of a prediction light field image from a reference light field image. These techniques includes constraining the placement and size of a search window based upon a geometrical relationship between prediction and reference light field images, hierarchical spatial displacement estimation, edge extension of a reference light field image, differential coding of displacement vectors, and multi-predictor spatial displacement estimation. Configuring reference and prediction light field images in view of geometrical relationships between light field images also improves spatial displacement estimation.

Near-field scanning optical microscope using a metallized cantilever tip for nanospectroscopy

Abstract: We have developed a NSOM which has a metallic probe tip and a highly focused evanescent light field spot Evanescent illumination effectively rejects the background light, eg the stray light from the shaft of the probe By suppressing the stray light and utilizing the field enhancement generated by the metallic probe, a sudden increment of the fluorescence was observed in the near-field region We have used this for near-field Raman scattering detection of molecules vibrations with the aid of surface enhanced Raman scattering One specific stokes-Raman-shifted lines was observed by near-field excitation together with several other lines that were excited by the far-field light

Cavity QED effects in semiconductor microcavities

Abstract: A theoretical investigation of cavity QED effects in semiconductor microcavities containing quantum wells is presented. A model Hamiltonian is used to derive equations of motion for the quantum photon and exciton fields in the cavity. Quantum effects such as squeezing and antibunching are predicted in the light field going out of the cavity under irradiation by a coherent laser field, if exciton-phonon scattering is weak enough. Exciton-phonon scattering is shown to destroy the nonclassical effects and to yield excess noise in the output field.

Cavity QED effects in semiconductor microcavities

Abstract: A theoretical investigation of cavity QED effects in semiconductor microcavities containing quantum wells is presented. A model Hamiltonian is used to derive equations of motion for the quantum photon and exciton fields in the cavity. Quantum effects such as squeezing and antibunching are predicted in the light field going out of the cavity under irradiation by a coherent laser field, if exciton-phonon scattering is weak enough. Exciton-phonon scattering is shown to destroy the nonclassical effects and to yield excess noise in the output field.

Hierarchical coding of light fields with disparity maps

Abstract: A coder for light fields is presented. Due to the large amount of data needed to represent a complete light field, a hierarchical decomposition is employed. The full light field is built up by recursively predicting intermediate images from a small subset of light-field images. Intermediate images are predicted by disparity-compensating multiple surrounding images. The predicted images are refined using DCT coding. Rate-distortion measurements for two standard light fields verify the efficiency of the proposed scheme. Compression ratios of 1000:1 are achieved at acceptable quality of the rendered views.

Image recording apparatus and method using light fields to track position and orientation

Abstract: The invention provides a simple method and apparatus for tracking image recording device (110) motion using a light field. The invention locates the image recording device's position and orientation in each frame very precisely by checking the radiance seen along lines captured in previous frames. The invention provides an interactive system that provides the operator with feedback, to capture a sequence of frames that sufficiently cover the light field, to provide sufficient data for reconstruction of three-dimensional structures.

Modeling of the performance of high-power diode amplifier systems with an optothermal microscopic spatio-temporal theory

Abstract: We present a detailed theoretical analysis of the dependence of spatio-temporal carrier and light field dynamics of high-power diode amplifier systems on their geometry and facet reflectivities as well as on the spatial and spectral characteristics of the optical input beam. The basis of the numerical modeling is the Maxwell-Bloch equations for spatially inhomogeneous semiconductor lasers which are self-consistently coupled to the nonequilibrium temperature dynamics of the electron-hole plasma. They microscopically describe the interaction between the optical fields, the charge carriers, and the interband polarization. Our numerical modeling allows an identification of the influence of dynamic internal laser effects such as diffraction, self-focusing, scattering, carrier diffusion, and heating on the performance of broad-area or tapered amplifiers (e.g., far field, near field). It thus provides a means of optimizing the epitaxial structure and geometry of high-power diode amplifier systems.

Interactive rendering of wavelet projected light fields

Abstract: Light field techniques allow the rendering of objects in time complexity unrelated to their geometric complexity. The technique discretely samples the space of light rays exiting the boundary around an object and then reconstructs a requested view from these data. In order to generate high quality images a dense sampling of the space is required which leads to large data sets. These data sets exhibit a high degree of coherence and should be compressed in order to make their size manageable. We present a wavelet-based method for storing light fields over planar domains. The parameterization is based on the Nusselt embedding, which leads to simplifications in shading computations when the light fields are used illumination sources. The wavelet transform exploits the coherence in the data to reduce the size of the data sets by factors of 20 times or more without objectionable deterioration in the rendered images. The wavelet representation also allows a hierarchical representation in which detail can be added incrementally, and in which each coarser view is an appropriately filtered version of the finer detail. The wavelet coefficients are compressed by thresholding the coefficients and storing them in a sparse hexadecary tree. The tree encoding allows random access over the compressed wavelet coefficients which is essential for extracting slices and point samples from the light field.

The Wavelet Stream – Progressive Transmission of Compressed Light Field Data

Abstract: In this paper we describe the compression of light field data using 4D nonstandard wavelet decomposition. For progressive transmission, storage, and rendering of the compressed light field data the new wavelet stream data structure is introduced. The wavelet coefficients are ordered in decreasing importance, encoding the position of the non discarded coefficients using significance maps. Compared to the vector quantization compression method, the wavelet stream achieves up to 3 times higher compression ratios while producing the same error during reconstruction of the light field data. Despite of the high compression of the data, reasonable frame rates during light field rendering are achieved. CR Categories: I.3.6 [Computer Graphics]: Methodology and Techniques—Graphics data structures and data types E.4 [Coding and Information Theory]: Data compaction and compression

Asymptotic light field in the presence of a bubble-layer.

Abstract: We report that the submerged microbubbles are an efficient source of diffuse radiance and may contribute to a rapid transition to the diffuse asymptotic regime. In this asymptotic regime an average cosine is easily predictable and measurable.

Device to determine plant states; has laser or light emitting diodes of two wavelengths fitted on measuring head to illuminate plants and has detector to register reflected light

Abstract: The device is arranged in a portable support and has laser diodes or light emitting diodes to direct light onto the plants and a detector to register reflected light. A signal-processing device has a microprocessor to evaluate the detector signal. The diodes are fitted on a measuring head, so that the plant is illuminated by a light spot (17) or strip from at least two types or groups (7,8)) of diodes of different wavelengths. The measuring head has a number of tightly arranged diodes forming a number of spotlight-like light fields (6). The diodes, or a group of diodes, are assigned to a common detector (9,10) arranged in the light field of the diodes. An Independent claim is included for a method for using the device.

Illumination optical system and projection-type image display apparatus

Abstract: An illumination optical system has a light source that emits white light having random polarization planes, a polarization separation device that separates the light from the light source into two types of light having polarization planes perpendicular to each other and traveling in directions at an angle to each other, a wavelength-specific polarization conversion device that receives the two types of light thus separated and that then subjects the light of a particular wavelength range included in them to polarization conversion, a convergence optical system that receives the two types of light after the light of the particular wavelength range included therein has undergone polarization conversion and that then makes them converge on different convergence positions, and a half-wave plate disposed near one of those convergence positions. This illumination optical system outputs white light that has different polarization planes in a particular wavelength range and in other wavelength ranges, and thus, when the light is subjected to color separation by being separated into light of the particular wavelength range and light of other wavelength ranges, the difference of the polarization planes serves to prevent loss of the amount of light.

Local-field approach to the interaction of an ultracold dense Bose gas with a light field

Abstract: The propagation of the electromagnetic field of a laser through a dense Bose gas is examined and nonlinear operator equations for the motion of the center of mass of the atoms are derived. The goal is to present a self-consistent set of coupled Maxwell-Bloch equations for atomic and electromagnetic fields generalized to include the atomic center-of-mass motion. Two effects are considered. The ultracold gas forms a medium for the Maxwell field which modifies its propagation properties. Combined herewith is the influence of the dipole-dipole interaction between atoms which leads to a density-dependent shift of the atomic transition frequency. It is expressed in a position-dependent detuning and is the reason for the nonlinearity. This results in a direct and physically transparent way from the quantum field-theoretical version of the local-field approach to electrodynamics in quantum media. The equations for the matter fields are general. Previously published nonlinear equations are obtained as limiting cases. As an atom-optical application the scattering of a dense beam of a Bose gas is studied in the Raman-Nath regime. The main conclusion is that for increasing density of the gas the dipole-dipole interaction suppresses or enhances the scattering depending on the sign of the detuning.

Optical phase-space distributions for low-coherence light.

Abstract: Using a novel heterodyne technique, we measure optical phase-space distributions in momentum and position for low-coherence light. Quantitative information is obtained simultaneously about the longitudinal and the transverse coherence properties as well as the wave-front curvature of the light field. This method can be used to monitor these optical parameters directly for signal fields scattered from samples of interest, for tomographic imaging.

Virtual light field projection for CT-simulation.

Abstract: We report a method to project a virtual light field over the patient during CT-simulations of external beam radiotherapy. It can be used to perform all the tasks associated with the physical light field of a conventional simulator. The system consists of a three-dimensional sonic digitizer interfacing with a window-based software on a personal computer. The digitizer can provide the three-dimensional coordinates of any point in space accessible by the digitizer probe. When these coordinates are transformed into the beam’s eye view, the position of the digitized point relative to the beam can readily be displayed. Thus, the system establishes a virtual light field in space, which can be “seen” only by the digitizer probe. For any digitized point, the system can immediately show, by the beam’s eye view display, whether the point is inside the field, outside of the field, or on the field border. Moreover, this virtual field projection allows one to evaluate external target coverage (or external normal tissue sparing) conveniently and interactively. By simply digitizing the concerned area and viewing its position in the beam’s eye view display, one can immediately assess the coverage and if necessary, modify the treatment field accordingly. The system also provides an efficient and essential procedure in CT-simulations for marking treatment portals on the patient. By cruising the digitizer probe on the patient’s skin surface under visual and audio guidances, one can promptly find the projection of the field center, field corners, etc., on the patient. Measurements have been performed to study the accuracy of the GP-12 sonic digitizer using rigid phantoms. Based on the measured data, the overall accuracy of the portal localization system is estimated to be ±2 mm. The system has been in clinical use for our CT simulator.

Localization and channeling of light in defect modes of two-dimensional photonic crystals

Abstract: The spatial distribution of the electromagnetic field in a two-dimensional photonic crystal with a lattice defect is investigated. It is shown that in such a structure the field can be localized in a region smaller than one wavelength in size. The dependence of the spectrum of defect modes on the parameters of a two-dimensional photonic crystal is investigated. The light field at the exit of the photonic crystal possesses properties of a nonradiative mode, making it possible to achieve spatial resolution in the near-field much higher than the radiation wavelength. The possibilities of using this phenomenon in optical near-field microscopy to produce optical memory devices and to increase the efficiency of nonlinear optical interactions are discussed.

Self-action of femtosecond pulses with continuum spectrum

Abstract: On the basis of the analysis of the wave equations for an electrical field of radiation and without use of slowly varying envelope approximation the self-action of femtosecond light pulses in transparent media is investigated. The results of numerical simulation of spectral supercontinuum evolution, accompanying temporary broadening of intensive pulses with a spectrum in the range of normal groupdispersion ofmedium both with only electronic nonlinearity, and with simultaneous electronic and electronic-vibrational nonlinearities are presented. The opportunity of compression of pulses with supercontinuum spectrum in light formations consisting of one cycle of anelectric field is predicted. It is shown that spectral superbroadening of the elliptically polarized radiation is accompanied by nonuniform rotation of a polarization ellipse.Keywords: extremely ultra-short pulses, electric field equations, self-action, supercontinuum spectrum, polarization ellipse. 1. INTRODUCTIONThe development of laser engineering of ultrashort pulses has resulted in creation of laser systems generating femtosecondpulses, which consist of several cycles of a light field'. The width of a spectrum of such extremely short pulses (ESP) becomes

Optical phase space distributions for low coherence light in turbid media

Abstract: Summary form only given. Optical phase space distributions are joint position and momentum distributions of light fields. They are related to the Wigner distributions for the optical field, which allows them to be placed on a firm theoretical footing. Since Wigner distributions are Fourier transforms of the mutual coherence function, optical phase space measurements are sensitive to the coherence properties of the light field. It has been suggested that coherence tomography based on measurement of the Wigner distributions may yield new avenues for medical imaging. The authors have demonstrated that smoothed Wigner phase space distributions of light fields can be measured directly as optical phase space contours using a simple heterodyne scheme.

Microscopic theory of spatiotemporal multiwave mixing in broad-area semiconductor laser amplifiers

Abstract: We investigate the interplay of multiwave-mixing processes with the microscopically coupled spatiotemporal light field and charge carrier dynamics in broad-area semiconductor laser amplifiers. Our theoretical description is based on extended spatially resolved Maxwell-Bloch equations including on the microscopic level spatiotemporal multiwave-mixing processes. Performing a third-order expansion in terms of the microscopic carrier distribution, we include in our description both the effects of population pulsations of the total carrier density at the beat frequency and the spatiospectral interactions of the light fields leading to gain nonlinearities as well as spatial and spectral hole burning. Our simulations show that in a broad-area semiconductor laser amplifier, spatiotemporal wave-mixing processes occur in both transverse and propagation directions of the multifrequency optical beams employed in a typical excite-probe configuration.

3-D Shape Reconstruction from Light Fields Using Voxel Projection

Abstract: We present a method for the 3-D reconstruction of objects from light fields. The estimated shape and texture information can be used for the compression of light fields or a better intermediate view interpolation. The representation of the objects is fully voxelbased and no explicit surface description is required. The approach is based on testing multiple voxel color hypotheses back-projected into the focal plane. Multiple views are incorporated in the reconstruction process simultaneously and no explicit data fusion is needed. The methodology of our approach combines the advantages of silhouette-based and image feature-based methods. Experimental results on light field data show the excellent visual quality of the voxel-based 3-D reconstruction. We also show the quality improvement for intermediate view generation that can be achieved using the estimated 3-D shape information.

Near field optical microspectroscope

Abstract: PROBLEM TO BE SOLVED: To provide an apparatus which can carry out mapping spectral measurement of a wider range in real time, eliminate mutual influences of noises of a near field optical microscope and a spectroscope, drive a stage loading a probe light projection apparatus and a probe light detector and automatically align positions of the probe light projection apparatus and the probe light detector to a probe SOLUTION: This apparatus includes an excitation light projection means 30 projecting an excitation light generating an evanescent light to a leading end of a probe 28, a condensing means 32 condensing a light to be measured which is generated at an evanescent light field when the probe 28 is brought close to an object 24 to be measured, a light-splitting means 34 splitting for every wavelength the light condensed by the condensing means 32, and a detecting means 36 detecting split lights obtained by the splitting means The detecting means 36 is a multichannel detection means that can detect lights of each wavelength at the same time

Lateral beam splitting in sodium vapour : magneto-optical origin and polarization competition effects

Abstract: An almost linearly polarized laser beam focused into a sodium vapour cell may split into spatially separated components of opposite circular polarization. The symmetry of the emerging structures is controlled by static magnetic fields of the order of the Earth's field. The mechanism of the decomposition of the light field into its two spin components is clarified by numerical simulations revealing the evolution of the spatial distribution of the light field during the propagation through the sodium vapour. In this context, the experimentally observed occurrence of a negative differential power transmission can be explained.

Efficient All-Optical Interband Light Modulation by Ultrafast Manipulation of Intersubband Transitions in an Asymmetric Quantum Well.

Abstract: An efficient modulation scheme at relatively lower control light intensities is proposed using ultrashort interband and intersubband-resonant coupling light pulses in a novel asymmetric InxGa1-xAs/AlAs semiconductor quantum well structure. The shape of the intersubband-control light pulses can manipulate the interband-signal light pulse absorption. The carrier relaxation rate of the quantum well system can be estimated from the interband nonlinear optical parameters induced by the intersubband control light field. The modulation efficiency in the proposed structure is twice than in a conventional symmetric quantum well structure. This reduces the threshold optical energy below 1 pJ in a 100-µm2 waveguide structure on using 500 fs control light pulses owing to the enhanced optical nonlinearities in the proposed structure.

Broadband detection of squeezed vacuum: A spectrum of quantum states

Abstract: We demonstrate the simultaneous quantum state reconstruction of the spectral modes of the light field emitted by a continuous wave degenerate optical parametric amplifier. The scheme is based on broadband measurement of the quantum fluctuations of the electric field quadratures and subsequent Fourier decomposition into spectral intervals. Applying the standard reconstruction algorithms to each bandwidth-limited quantum trajectory, a "spectrum" of density matrices and Wigner functions is obtained. The recorded states show a smooth transition from the squeezed vacuum to a vacuum state. In the time domain we evaluated the first order correlation function of the squeezed output field, showing good agreement with the theory.

General Properties Concerning Laser Cooling

Abstract: This chapter presents some of the general ideas regarding laser cooling. One of the characteristics of optical control of atomic motion is that the speed of atoms can be reduced by a considerable amount. Since the spread of velocities of a sample of atoms is directly related to its temperature, the field has been dubbed laser cooling, and this name has persisted throughout the years. Laser cooling has much in common with the field of optics. In laser cooling, light is used to manipulate atoms, whereas in optics matter is used to manipulate light. The more proper identification for the field would therefore be “atom optics” or “optical control of atomic motion”. The similarities between atom optics and electromagnetic optics will be pointed out.

Dynamics of a Peierls system in a light field

Abstract: Equations describing the temporal dynamics of the order parameter ξ(t) of a metal-semiconductor phase transition and the density n(t) of electron-hole pairs in a Peierls system in a light field are obtained on the basis of the Lagrange equation for the phonon mode and the Liouville equation for the density matrix of the electronic subsystem. The equations obtained are analyzed for a stationary state (with adiabatically slow variation of the light intensity I) and for a transient process near the initial and final states of dynamic equilibrium (with the light field switched on abruptly). It is shown that for adiabatically slow growth of the intensity I up to a certain critical value Ic the band gap of the electronic spectrum decreases but the semiconductor phase of the Peierls system remains stable. For I>Ic the stationary semiconductor state (ξ≠0) becomes unstable. When the light is switched on abruptly, the deviation of the system parameters from the initial values is described by an exponential law with a characteristic reciprocal of the rise time of the process linearly dependent on the irradiation intensity I. As a new position of equilibrium is approached, three qualitatively different regimes of behavior of the order parameter ξ and density n are possible. For low intensities I(I Ic the stationary semiconductor state with ξ≠0 is absent. The experimental data on the irradiation of a vanadium dioxide film with a powerful laser pulse is interpreted on the basis of the theory developed.