Showing papers on "Light field published in 2003"

Attosecond control of electronic processes by intense light fields

Abstract: The amplitude and frequency of laser light can be routinely measured and controlled on a femtosecond (10(-15) s) timescale. However, in pulses comprising just a few wave cycles, the amplitude envelope and carrier frequency are not sufficient to characterize and control laser radiation, because evolution of the light field is also influenced by a shift of the carrier wave with respect to the pulse peak. This so-called carrier-envelope phase has been predicted and observed to affect strong-field phenomena, but random shot-to-shot shifts have prevented the reproducible guiding of atomic processes using the electric field of light. Here we report the generation of intense, few-cycle laser pulses with a stable carrier envelope phase that permit the triggering and steering of microscopic motion with an ultimate precision limited only by quantum mechanical uncertainty. Using these reproducible light waveforms, we create light-induced atomic currents in ionized matter; the motion of the electronic wave packets can be controlled on timescales shorter than 250 attoseconds (250 x 10(-18) s). This enables us to control the attosecond temporal structure of coherent soft X-ray emission produced by the atomic currents--these X-ray photons provide a sensitive and intuitive tool for determining the carrier-envelope phase.

Mechanical effects of light in optical resonators

Abstract: We review the modifications and implications of the effect of light forces on atoms when the field is enclosed in an optical resonator of high finesse. The systems considered range from a single atom strongly coupled to a single mode of a high-Q microcavity to a large ensemble of atoms in a highly degenerate quasi-confocal resonator. We set up general models that allow us to obtain analytic expressions for the optical potential, friction, and diffusion. In the bad-cavity limit the modified cooling properties can be attributed to the spectral modifications of light absorption and spontaneous emission in a form of generalized and enhanced Doppler cooling. For the strong coupling regime in a good cavity, we identify the dynamical coupling between the light field intensity and the atomic motion as the central mechanism underlying the cavity-induced cooling. The dynamical cavity cooling, which does not rely on spontaneous emission, can be enhanced by multimode cavity geometries because of the effect of coherent photon redistribution between different modes. The model is then generalized to include several distinct frequencies to account for more general trap geometries. Finally we show that the field-induced buildup of correlations between the motion of different particles plays a central role in the scaling behavior of the system. Depending on the geometry and parameters, its effect ranges from strong destructive interference, slowing down the cooling process, to self-organized crystallization, implying atomic self-trapping and faster cooling to lower temperatures by cooperative coherent scattering.

Relighting with 4D incident light fields

Abstract: We present an image-based technique to relight real objects illuminated by a 4D incident light field, representing the illumination of an environment. By exploiting the richness in angular and spatial variation of the light field, objects can be relit with a high degree of realism.We record photographs of an object, illuminated from various positions and directions, using a projector mounted on a gantry as a moving light source. The resulting basis images are used to create a subset of the full reflectance field of the object. Using this reflectance field, we can create an image of the object, relit with any incident light field and observed from a flxed camera position.To maintain acceptable recording times and reduce the amount of data, we propose an efficient data acquisition method.Since the object can be relit with a 4D incident light field, illumination effects encoded in the light field, such as shafts of shadow or spot light effects, can be realized.

A new reconstruction filter for undersampled light fields

Abstract: This paper builds on previous research in the light field area of image-based rendering. We present a new reconstruction filter that significantly reduces the "ghosting" artifacts seen in undersampled light fields, while preserving important high-fidelity features such as sharp object boundaries and view-dependent reflectance. By improving the rendering quality achievable from undersampled light fields, our method allows acceptable images to be generated from smaller image sets. We present both frequency and spatial domain justifications for our techniques. We also present a practical framework for implementing the reconstruction filter in multiple rendering passes.

Spatial weak-light solitons in an electromagnetically induced nonlinear waveguide.

Abstract: We show that a weak probe light beam can form spatial solitons in an electromagnetically induced transparency (EIT) medium composed of four-level atoms and a coupling light field. We find that the coupling light beam can induce a highly controllable nonlinear waveguide and exert very strong effects on the dynamical behavior of the solitons. Hence, in the EIT medium, it is not only possible to produce spatial solitons at very low light intensities but also simultaneously control these solitons by using the coupling-light-induced nonlinear waveguide.

Chapter 9 – Stimulated Brillouin and Stimulated Rayleigh Scattering

Abstract: Publisher Summary A light scattering process is said to be stimulated if the fluctuations are induced by the presence of the light field. Stimulated light scattering is typically very much more efficient than spontaneous light scattering. Stimulated Brillouin scattering (SBS) process leads to amplification of a Stokes wave propagating in any direction except for the propagation direction of the laser wave. However, SBS is usually observed only in the backwards direction, because the spatial overlap of the laser and Stokes beams is largest under these conditions. Electrostriction is also important both as a mechanism leading to a third-order nonlinear optical response and as a coupling mechanism that leads to stimulated Brillouin scattering. The scattering of light from isobaric density fluctuations that are driven by the process of electrostriction leads to electrostrictive stimulated Rayleigh scattering, whereas the scattering of light from isobaric density fluctuations that are driven by the process of optical absorption leads to thermal stimulated Rayleigh scattering.

Image multiplying and high-frequency oscillations effects in the Fresnel region light propagation simulation

Abstract: A new effect during light propagation simulation in the Fresnel region is discovered. Image multiplying and high-frequency noise effects are caused by the sampling of the complex light field. Image multiplying is observed in the case of the standard integral calculation. High-frequency noise is observed in the convolution approach. These effects are observed in a computer simulation only and do not exist in nature. The analysis of these effects enable us to define the range of the numerical algorithms application.

Organic Microcavity Photodiodes

Abstract: The interaction of light and matter lies at the heart of the principle of optoelectronic devices. By tuning the strength of the electric field component of the light wave, one can gain control over this interaction. A simple way of achieving this is by employing microcavities, which are one-dimensional photonic structures. These give rise to an effective quantization of the light field in one direction. The largest enhancements in the strength of light–matter coupling are achieved for cavities with dimensions on the order of the effective wavelength of light. As organic materials have the very large oscillator strengths required for light–matter coupling, as well as excellent thin film forming properties, they are ideal materials with which to exploit tunable electron–photon coupling. We demonstrate the influence of the optical field strength in organic microcavity photodiodes. Besides allowing tunability of the response spectrum by varying the effective resonator thickness, a large increase in the photocurrent sensitivity is observed below the absorption threshold of the optically active material. The microcavity induced field enhancement plays a particularly important role under two-photon excitation. In this case we observe a 500-fold increase in the photocurrent response with respect to a non-cavity device. This opens up a range of applications for organic microcavity photodiodes as nonlinear detector elements.

When is the shape of a scene unique given its light-field: a fundamental theorem of 3D vision?

Abstract: The complete set of measurements that could ever be used by a passive 3D vision algorithm is the plenoptic function or light-field. We give a concise characterization of when the light-field of a Lambertian scene uniquely determines its shape and, conversely, when the shape is inherently ambiguous. In particular, we show that stereo computed from the light-field is ambiguous if and only if the scene is radiating light of a constant intensity (and color, etc.) over an extended region.

Opacity light fields: interactive rendering of surface light fields with view-dependent opacity

Abstract: We present new hardware-accelerated techniques for rendering surface light fields with opacity hulls that allow for interactive visualization of objects that have complex reflectance properties and elaborate geometrical details. The opacity hull is a shape enclosing the object with view-dependent opacity parameterized onto that shape. We call the combination of opacity hulls and surface light fields the opacity light field. Opacity light fields are ideally suited for rendering of the visually complex objects and scenes obtained with 3D photography. We show how to implement opacity light fields in the framework of three surface light field rendering methods: view-dependent texture mapping, unstructured lumigraph rendering, and light field mapping. The modified algorithms can be effectively supported on modern graphics hardware. Our results show that all three implementations are able to achieve interactive or real-time frame rates.

Interactive rendering from compressed light fields

Abstract: A light field is a collection of multiview images which represent a three-dimensional scene. Rendering from a light field provides a simple and efficient way to generate arbitrary new views of the scene, bypassing the difficult problem of acquiring accurate geometric and photometric models. The enormous amount of data required in a light field poses a key challenge in rendering. Tree-structured vector quantization (TSVQ) provides a moderate compression ratio of around 24:1, which alleviates, but does not solve, the problem. Compression schemes based on video coding techniques exploit the data redundancy very effectively, but do not provide adequate random access for rendering. The paper presents an analysis of the data-access pattern during the rendering process and describes a compression scheme that supports interactive rendering directly from compressed light field data. The proposed algorithm provides a high compression ratio of as much as ten times that of TSVQ, while slowing down the rendering speed by only a factor smaller than 2.

Inter-view wavelet compression of light fields with disparity-compensated lifting

Abstract: We propose a novel approach that uses disparity-compensated lifting for wavelet compression of light fields. Disparity compensation is incorporated into the lifting structure for the transform across the views to solve the irreversibility limitation in previous wavelet coding schemes. With this approach, we obtain the benefits of wavelet coding, such as scalability in all dimensions, as well as superior compression performance. For light fields of an object, shape adaptation is adopted to improve the compression efficiency and visual quality of reconstructed images. In this work we extend the scheme to handle light fields with arbitrary camera arrangements. A view-sequencing algorithm is developed to encode the images. Experimental results show that the proposed scheme outperforms existing light field compression techniques in terms of compression efficiency and visual quality of the reconstructed views.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Utilizing an electronic portal imaging device to monitor light and radiation field congruence

Abstract: A method to investigate light and radiation field congruence utilizing a commercially available amorphous silicon electronic portal imaging device (EPID) was developed. This method employed an EPID, the associated EPI software, and a diamond-shaped template. The template was constructed from a block tray in which Sn/Pb wires, 1 mm in diameter, were embedded into a diamond shaped groove milled into the tray. The collimator jaws of the linac were aligned such that the light field fell directly on the corners of the diamond. A radiation detection algorithm within the EPI software determined the extent of the radiation field. The light and radiation field congruence was evaluated by comparing the vertexes of the diamond reference structure to the detected radiation field. In addition, the digital jaw settings were recorded and later compared to the light field detected on the films and EPIs. Three linear accelerators were tracked for a period ranging from 28 months. Light radiation field congruence tests with films and EPIs were comparable, yielding a difference of less than 0.6 mm, well within the allowed 2-mm tolerance. A disparity was observed in the magnitude of the detected light field. The X and Y dimensions of the light field measured with film differed by less than or equal to 1.4 mm from the digital collimator settings, whereas the values extracted from the EPIs differed by up to 2.5 mm. Based on these findings, EPIs were found to be a quick and reliable alternative to film for qualitative and relative analyses. 2003 American College of Medical Physics.

Atomic nanofabrication with complex light fields

Abstract: The method of neutral atom lithography allows one to transfer to a substrate a 2D intensity modulation of an atomic beam imposed by an inhomogeneous light field. The complexity of the pattern depends on the properties of the light field constructed from the superposition of multiple laser beams. For the design of suitable light fields we present a mathematical model with a corresponding numerical simulation of the so-called inverse problem. Furthermore, details of an experiment carried out with a holographically reconstructed light field are discussed.

Shape adaptation for light field compression

Abstract: We propose a method of using shape adaptation for compression of light fields of 3D objects. Shape adaptation is incorporated into two light field coders, both applying disparity compensation with an explicit geometry model, to improve the compression efficiency. The shape information can be derived at the decoder from an accurate geometry model. If the available geometry is inaccurate, we propose to code the exact 2D shapes with the aid of the approximate geometry. Experiments show that shape adaptation greatly improves the compression performance of both coders.

LED based light source with uniform light field & well defined edges

Abstract: An LED light device comprising an LED for generating a light beam, and a reflector that concentrates the light beam to have bright illumination, uniform light field, and sharp edge contrast. The LED light device may be used in an x-ray collimator to facilitate positioning a patient and an x-ray machine relative to each other so that an x-ray beam is directed along a defined axis and onto a specified target zone on the patient. The collimator comprises at least one high energy LED array for generating a light beam and directing the light beam along the defined axis, wherein the light beam expands outward from the LED array at a beam cone angle, and an optical concentrator having a reflective surface, wherein the light beam is emitted from the LED array at a beam cone angle defined by the reflective surface of the optical concentrator.

Illumination optical system of image reader

Abstract: PROBLEM TO BE SOLVED: To obtain a light guide which is uniform for a region to be read and has less loss in an image reader. SOLUTION: A light emitted from an LED is reflected under a total reflection condition if possible inside a light guide body and guided to a light emitting surface of the light guide body to improve the optical intensity in a short axis direction (sub-scanning direction) on an original surface, the shape of light incident surface of the light guide body is optimized, and the angle of a light in a long axis direction (main scanning direction) is controlled. In this way, the shape of the light guide body for irradiating an illumination light of uniform intensity distribution on the original surface is obtained. COPYRIGHT: (C)2005,JPO&NCIPI

Numerical simulations on the motion of atoms travelling through a standing-wave light field

Abstract: The motion of metastable helium atoms travelling through a standing light wave is investigated with a semi-classical numerical model. The results of a calculation including the velocity dependence of the dipole force are compared with those of the commonly used approach, which assumes a conservative dipole force. The comparison is made for two atom guiding regimes that can be used for the production of nanostructure arrays; a low power regime, where the atoms are focused in a standing wave by the dipole force, and a higher power regime, in which the atoms channel along the potential minima of the light field. In the low power regime the differences between the two models are negligible and both models show that, for lithography purposes, pattern widths of 150 nm can be achieved. In the high power channelling regime the conservative force model, predicting 100 nm features, is shown to break down. The model that incorporates velocity dependence, resulting in a structure size of 40 nm, remains valid, as demonstrated by a comparison with quantum Monte-Carlo wavefunction calculations.

Feature-based surface light field morphing

Abstract: A surface light field is a function that gives the colors of each object point viewed from different directions. Object representation with a surface light field provides a nice structure for 3D photography. This paper presents a feature-based morphing technique for two objects equipped with surface light fields. The technique consists of geometry morphing and in-between light field mapping. Geometry morphing is accomplished by 3D mesh morphing, where we introduce a vertex merging technique to generate a simpler metamesh. In in-between light field mapping, an in-between object is rendered by extracting necessary fragments from input surface light fields. We also propose an acceleration technique for rendering an in-between object. Experimental results with real and synthetic data show natural and plausible morphing between objects with surface light fields. The proposed morphing technique can be used as an editing tool for 3D photography.

Numerical simulations on the motion of atoms travelling through a standing-wave light field

Abstract: The motion of metastable helium atoms travelling through a standing light wave is investigated with a semi-classical numerical model. The results of a calculation including the velocity dependence of the dipole force are compared with those of the commonly used approach, which assumes a conservative dipole force. The comparison is made for two atom guiding regimes that can be used for the production of nanostructure arrays; a low power regime, where the atoms are focused in a standing wave by the dipole force, and a higher power regime, in which the atoms channel along the potential minima of the light field. In the low power regime the differences between the two models are negligible and both models show that, for lithography purposes, pattern widths of 150 nm can be achieved. In the high power channelling regime the conservative force model, predicting 100 nm features, is shown to break down. The model that incorporates velocity dependence, resulting in a structure size of 40 nm, remains valid, as demonstrated by a comparison with quantum Monte-Carlo wavefunction calculations.

Apparatus for illuminating a probe plate to be examined

Abstract: Apparatus for illuminating a sample plate (12) which is to be examined for example by fluorescent light excitation of the samples. This apparatus has a plurality of light-emitting diodes (15), which are arranged in an array and whose radiated light is guided in a homogeneous light field through an optical arrangement (19) onto a sample field (22). The intensity of the light field suffices in particular for generating a fluorescent light excitation of the samples (23), which can be determined by a CCD camera (29). This provides a cost-effective light source for generating a light field with sufficient intensity.

Transversal light forces in semiconductors

Abstract: The transversal light force is a well established effect in atomic and molecular systems that are exposed to spatially inhomogeneous light fields. In this paper it is shown theoretically that in an excited semiconductor, containing an electron–hole plasma or excitons, a similar light force exists, if the semiconductor is exposed to an ultrashort spatially inhomogeneous light field. The analysis is based on the equations of motion for the Wigner distribution functions of charge carrier populations and interband polarizations. The results show that, while the light force on the electron–hole plasma or the excitons does exist, its effects on the kinetic behaviour of the electron–hole plasma or the excitons are different compared to the situation in an atomic or molecular system. A detailed analysis presented here traces this difference back to the principal differences between atoms and molecules on the one hand and electron–hole plasmas or excitons on the other hand.

Spectral and spatial characteristics of third-harmonic generation in conical light beams

Abstract: Generation of resonance-enhanced third harmonic in Bessel and other conical beams is analyzed from a simple picture, where the fundamental light field is decomposed into elementary configurations of crossed plain-wave sub-beams. We show that the overall harmonic output can be derived as a superposition of all partial harmonic components driven by elementary configurations of the fundamental field. Good agreement with experimental observations has been obtained in simulation of spectral and spatial characteristics of the generated third harmonic. Some peculiarities of harmonic generation in conical light fields are discussed.

Inverse computation of phase masks for two layer diffractive optic element system

Abstract: A two layer system can transform an arbitrary specified light field at an input plane to a desired light field at an output plane. The light field includes both intensity and phase. Such a system can be cascaded for higher level functionality. There are two computations involved. The first computes a sensitivity matrix symbolically. The elements of the matrix hold the variation in each element at the output plane with variation in each element of both phase screens. An element of this matrix is provided for reference. The second algorithm iteratively updates the phase screen values to bring the output field to that desired. On each iteration, the algorithm performs a forward computation from input to output. The phase values are updated using the sensitivity matrix and the error at the output relative to that desired.