Showing papers on "Light field published in 2001"

A single ion as a nanoscopic probe of an optical field

Abstract: In near-field imaging, resolution beyond the diffraction limit of optical microscopy is obtained by scanning the sampling region with a probe of subwavelength size. In recent experiments, single molecules were used as nanoscopic probes to attain a resolution of a few tens of nanometres. Positional control of the molecular probe was typically achieved by embedding it in a crystal attached to a substrate on a translation stage. However, the presence of the host crystal inevitably led to a disturbance of the light field that was to be measured. Here we report a near-field probe with atomic-scale resolution a single calcium ion in a radio-frequency trap that causes minimal perturbation of the optical field. We measure the three-dimensional spatial structure of an optical field with a spatial resolution as high as 60 nm (determined by the residual thermal motion of the trapped ion), and scan the modes of a low-loss optical cavity over a range of up to 100 m. The precise positioning we achieve implies a deterministic control of the coupling between ion and field. At the same time, the field and the internal states of the ion are not affected by the trapping potential. Our set-up is therefore an ideal system for performing cavity quantum electrodynamics experiments with a single particle.

Slow and Fast Light

Abstract: Recent research has established that it is possible to exercise extraordinary control of the velocity of propagation of light pulses through a material system. Both extremely slow propagation (much slower than the velocity of light in vacuum) and fast propagation (exceeding the velocity of light in vacuum) have been observed. This article summarizes this recent research, placing special emphasis on the description of the underlying physical processes leading to the modification of the velocity of light. To understand these new results, it is crucial to recall the distinction between the phase velocity and the group velocity of a light field. These concepts will be defined more precisely below; for the present we note that the group velocity gives the velocity with which a pulse of light propagates through a material system. One thus speaks of “fast” or “slow” light depending on the value of the group velocity vg in comparison to the velocity of light c in vacuum.

Phase behavior of two-dimensional colloidal systems in the presence of periodic light fields.

Abstract: We investigate the phase behavior of a two-dimensional suspension of charge stabilized polystyrene spheres in the presence of a one-dimensional periodic light field. With increasing light intensity we observe a liquid-solid followed by a solid-liquid transition which are known as laser-induced freezing and melting, respectively. Here we report on measurements where, in addition to the light intensity, the single particle density was also systematically varied. As a result, we obtain for the first time the full thermodynamic information about the system which allows comparison with numerical predictions of other authors.

Optical amplification in coherent optical frequency modulated continuous wave reflectometry

Abstract: The present invention relates to an apparatus for optical coherence reflectometry, in particular for optical coherence tomography, wherein the apparatus for optical coherence reflectometry comprises a wavelength scanning laser source for providing a light signal, and splitting means for dividing said light signal into a sample light field and a reference light field, wherein the sample light field is directed to the sample being measured, and the light reflected from the sample is amplified without correspondingly amplifying the light reflected in the reference light field. Thereby, it is possible to direct substantially all light energy from the first reflected light field to the detectors, and to obtain fully the utilisation of the amplification of the first reflected light field. The optical amplifier inserted in the sample reflected light field is different from the source so that the effect of the light source may be regulated independent of the degree of amplification. In particular when using the apparatus in coherent optical FMCW reflectometry certain safety regulations for the power density towards the sample has to be observed to reduce the risk of damages to the sample under examination, such as biological tissue. The apparatus may be used for a variety of purposes, in particular for obtaining optical biopsies of transparent as well as non-transparent tissues.

Light field propagation by metal micro- and nanostructures.

Abstract: The ability to sustain plasmon oscillations gives rise to unique properties of metal nanostructures, which can be exploited for the controlled manipulation of light fields on the nanoscale. In this context we investigate electromagnetic coupling effects within lithographically produced ensembles of gold nanoparticles with a photon scanning tunnelling microscope. To provide an interface between these nano-optical devices and classical far-field optics, we investigate surface plasmon propagation on microstructured metal thin films.

Optical amplification in coherence reflectometry

Abstract: The present invention relates to an apparatus and a method for optical coherence reflectometry, in particular for optical coherence tomography. The invention particularly relates to the route of the light field in the sample arm. The reflected light field in the sample arm is amplified before being received by a combining means, said combining means being capable of receiving the reflected light field from the sample arm as well as the second reflected light field from the reference arm. Thereby, it is possible to direct substantially all light energy in the sample arm to the combining means, and to obtain fully the utilisation of the amplification of the reflected light field since preferably only the reflected light field is amplified by the optical amplifier. This leads to an improved signal-to-noise ratio (SNR) whereby an increase of the maximal penetration depth is obtained. Thereby, the apparatus is useful for obtaining optical biopsies of transparent as well as non-transparent tissues as well as new technical fields wherein the increased SNR allows the use of the present apparatus.

Process and system for the optical inspection of transparent containers

Abstract: In a process for the optical inspection of at least partially transparent containers in an inspection area with an illuminating device and a camera for producing images to be evaluated, the degree of transparency of each container is determined, and a light field is configured for this specific container. The light intensity of the light field and/or the imaging sensitivity is adapted to the determined degree of transparency, and the traveling light field is shifted through the inspection area in synchrony with the container. The system for implementing the process has an LED light screen with a plurality of LEDs, which can be activated individually or in groups, and a device upstream of the inspection area for measuring the individual degree of transparency of each container. These components are connected to a control unit, which produces the traveling light field for each container and shifts it in synchrony with the container. The control unit also adapts the light intensity of the traveling light field to the degree of transparency found for the container in question.

Structured doping with light forces

Abstract: Light forces are a powerful tool for neutral atom manipulation and have been used previously to focus an atomic beam onto a substrate to create periodic nanostructures. We utilize the material-selective characteristic of the atom–light interaction to structure the material composition of a film during growth. A host and a dopant material are evaporated simultaneously, but only the dopant is focused by the light field. The dopant concentration varies laterally on a sub-100-nm-length scale. This technique can be extended to three-dimensional patterning and opens up ways to engineer the photonic, electronic, or magnetic features of a solid.

Method and apparatus for minimizing optical proximity effects

Abstract: Optical proximity effects (OPEs) are a well-known phenomenon in photolithography OPEs result from the structural interaction between the main feature and neighboring features It has been determined by the present inventors that such structural interactions not only affect the critical dimension of the main feature at the image plane, but also the process latitude of the main feature Moreover, it has been determined that the variation of the critical dimension as well as the process latitude of the main feature is a direct consequence of light field interference between the main feature and the neighboring features Depending on the phase of the field produced by the neighboring features, the main feature critical dimension and process latitude can be improved by constructive light field interference, or degraded by destructive light field interference The phase of the field produced by the neighboring features is dependent on the pitch as well as the illumination angle For a given illumination, the forbidden pitch region is the location where the field produced by the neighboring features interferes with the field of the main feature destructively The present invention provides a method for determining and eliminating the forbidden pitch region for any feature size and illumination condition Moreover, it provides a method for performing illumination design in order to suppress the forbidden pitch phenomena, and for optimal placement of scattering bar assist features

Relighting with the reflected irradiance field: representation, sampling and reconstruction

Abstract: Image-based relighting (IBL) is a technique to change the illumination of an image-based object/scene. In this paper, we define a representation called the reflected irradiance field which records the reflection from an object surface irradiated by a point light source that moves on a plane. This representation is dual to that of the light field. It synthesizes a novel image under a different illumination by interpolating and superimposing appropriate recorded samples. Furthermore, we study the minimum sampling problem of the reflected irradiance field, i.e., how many point light sources are needed during sampling. We find that there exists a geometry-independent bound for the sampling interval whenever the second-order derivatives of the surface BRDF and the minimum depth of the scene are bounded. This bound ensures that the error in the reconstructed image is controlled by a given tolerance, regardless of the geometry. Experiments on both synthetic and real surfaces are conducted to verify our analysis.

The Wavelet Stream: Interactive Multi Resolution Light Field Rendering

Abstract: One of the most general image based object representations is the Light Field. Unfortunately, a large amount of data is required to reconstruct high quality views from a Light Field. In this paper, we present the wavelet stream which employs non-standard four-dimensional wavelet decomposition for Light Field compression. It allows for progressive transmission, storage, and rendering of compressed Light Field data. Our results show that 0.8% of the original coefficients or 0.3 bits per pixel, respectively are sufficient to obtain visually pleasing new views. Additionally, the wavelet stream allows for an adaptive multi-resolution representation of the Light Field data. Furthermore, a silhouetteencoding scheme helps to reduce the number of coefficients required. Our data structure allows to store arbitrary vector-valued data like RGB- or YUV-data. The Light Field data stored in the wavelet stream can be decompressed in real time for interactive rendering. For this, the reconstruction algorithm uses supplementary caching schemes.

Two-photon interferometry for high-resolution imaging

Abstract: We discuss advantages of using non-classical states of light for two aspects of optical imaging: creating of miniature images on photosensitive substrates, which constitutes the foundation for optical lithography, and conversely, imaging of micro objects. In both cases, the classical resolution limit given by the Rayleigh criterion is approximately a half of the optical wavelength. It has been shown, however, that by using multi-photon quantum states of the light field, and multi-photon sensitive material or detector, this limit can be surpassed. In the present work, we give a rigorous quantum mechanical treatment of this problem, address some particularly widespread misconceptions and discuss the requirements arising on the way of turning the research on quantum imaging into a practical technology.

Methodology for determining x-ray to light field decentering on digital radiographic image systems

Abstract: The present technique provides a method and system for centering a radiographic imaging system to provide minimal non-diagnostic radiation to a patient. The present technique incorporates a radio-opaque template that is substantially aligned to a light field produced from a light source. The present technique also incorporates a processing module that determines an offset distance from the features of the template to features detectable in data from an x-ray exposure. A processing module determines the offset distance utilizing an algorithm for recognizing the radio-opaque features and determining distances between the features and the detected edges or similar features of the exposure.

Unibiased light field models for rendering and holography

Abstract: An isotropic, direction and point parameterization (DPP) light-field model is used for rendering graphics images in a hologram production system. Using the DPP light-field models can reduce image artifacts, reduce oversampling, decrease rendering time, and decrease data storage requirements.

Optical element, light source apparatus, optical head apparatus, and optical information processing apparatus

Abstract: A first semiconductor laser emits a light beam L 1 with a first wavelength polarized in an x-axis direction. A second semiconductor laser emits a light beam L 2 with a second wavelength polarized in the x-axis direction. A wavelength plate functions as a (2m+1)λ/2 plate (m is an integer) with respect to the light beam L 1 , and functions as a nλ plate (n is an integer) with respect to the light beam L 2 . A polarization anisotropic hologram element diffracts the light polarized in the x-axis direction, and transmits the light polarized in the y-axis direction. Consequently, an apparent emission point of diffracted light L 2 ′ may be allowed to coincide with an emission point of the light beam L 1 . A light source apparatus thus constructed can emit two light beams with different wavelengths at a low cost and a high efficiency with optical axes aligned in a simple configuration.

Transparent container optical checking method, has illumination light field intensity and/or imaging sensitivity matched to individual container transparency

Abstract: The optical checking method has the transparent container (B) illuminated by a light source, e.g. a LED light screen (D) in an inspection zone, with evaluation of the container image provided via an electronic camera. An individual transparency level is calculated for each container, with corresponding matching of the light intensity of the illumination light field or the imaging sensitivity of the camera. The illumination light field is provided by a light fleck used for scanning the container synchronous with its movement through the inspection zone. An Independent claim is also included for a transparent container optical checking device.

Spatio-temporal dynamics of light amplification and amplified spontaneous emission in high-power tapered semiconductor laser amplifiers

Abstract: We investigate the spatio-temporal light field dynamics in high-power semiconductor lasers with continuous-wave optical injection. The amplification processes that characterize this system occur during the propagation of the injected signal within the active area and can be attributed to spatially dependent gain and refractive index variations. Those are shown to be determined by dynamic interactions between the light fields and the active charge-carrier plasma. This microscopic light-matter-coupling is described by a spatially resolved microscopic theory based on Maxwell-Bloch-Langevin equations taking into account many-body interactions, energy transfer between the carrier and phonon system and, in particular, the spatio-temporal interplay of stimulated and amplified spontaneous emission and noise. Results of our numerical modeling visualize the dynamic spatio-spectral beam shaping experienced by the propagating light in amplifiers of tapered geometry. This reveals the microscopic physical processes that are responsible for the particular amplitude and spatial shape of the light beam at the output facet.

Analysis of planar light fields from homogeneous convex curved surfaces under distant illumination

Abstract: We consider the flatland or 2D properties of the light field generated when a homogeneous convex curved surface reflects a distant illumination field. Besides being of considerable theoretical interest, this problem has applications in computer vision and graphics - for instance, in determining lighting and bidirectional reflectance distribution functions (BRDFs), in rendering environment maps, and in image-based rendering. We demonstrate that the integral for the reflected light transforms to a simple product of coefficients in Fourier space. Thus, the operation of rendering can be viewed in simple signal processing terms as a filtering operation that convolves the incident illumination with the BRDF. This analysis leads to a number of interesting observations for computer graphics, computer vision, and visual perception.

Microscopic calculation of noise current operators for electromagnetic field quantization in absorbing material systems

Abstract: We present a microscopic quantization scheme for the electromagnetic field in dispersive and lossy dielectrics of arbitrary geometry. This method also describes anisotropic media and media driven by light field via a spatially nonlocal permittivity. The method removes the need for complicated diagonalization of material, reservoir and field variables and allows us to include the effect of all the material excitations. Dissipation inside the medium is described by considering the coupling of the polarization quanta of the system with the reservoir oscillators in the usual Langevin approach.

Giant light shift of atoms near optical microstructures

Abstract: Atoms coupled to optical fields confined in one and two spatial dimensions in solid state microstructures can experience very large light shifts if the driving frequencies are close to a resonance of the microstructures and an atomic transition. Using the simple example of a quasi one-dimensional waveguide structure we can analytically calculate the atomic AC Stark shift and the modifications of the light field induced by the presence of the atom. A large enhancement of the effective interaction strength is found due to a non uniform mode density. Experimentally this should be visible by monitoring the scattered light field as well as by the modification of the atomic trajectories bouncing from the evanescent light.

Efficient Free Form Light Field Rendering

Abstract: We show a simple and efficient way for rendering arbitrary views from so-called free-form light fields , employing a convex free form camera surface and a set of arbitrarily oriented camera planes. This way directionally varying real-world imagery can be displayed without intermediate resampling steps, and yet rendering of free form light fields can be performed as efficiently as for two-planeparameterized light fields using texture mapping graphics hardware. Comparable to sphere-based parameterizations, a single free form light field can represent all possible views of the scene without the need for multiple slabs, and it allows for relatively uniform sampling. Furthermore, we extend the rendering algorithm to account for occlusion in certain input views. We apply our method to synthetic and real-world datasets with and without additional geometric information and compare the resulting rendering performance and quality to twoplane-parameterized light field rendering.

Manipulating a Bose-Einstein condensate with a single photon

Abstract: We propose a method to create macroscopic superpositions, so-called Schrodinger cat states, of different motional states of an ideal Bose-Einstein condensate. The scheme is based on the scattering of a freely expanding condensate by the light field of a high-finesse optical cavity in a quantum superposition state of different photon numbers. The atom-photon interaction creates an entangled state of the motional state of the condensate and the photon number, which can be converted into a pure atomic Schrodinger cat state by operations only acting on the cavity field. We discuss in detail the fully quantised theory and propose an experimental procedure to implement the scheme using short coherent light pulses.

Collective light forces on atoms in a high-finesse cavity

Abstract: Summary form only given. We investigate the motion of atoms in a cavity. For strong coupling, the back-action of an atom on the intra-cavity light field is large. In particular, the motion of an atom changes the amplitude of the fight field inside the cavity, which in turn changes the force on the atom, thereby influencing its motion.

Multi-hypothesis prediction for disparity compensated light field compression

Abstract: In this paper, we describe a multi-hypothesis prediction technique for disparity-compensated light field compression. Multi-hypothesis prediction has been used extensively in video compression. In this work, we apply multi-hypothesis prediction to the problem of light field compression. Most current techniques for light field compression utilize some form of disparity compensation with one hypothesis. We demonstrate that a multi-hypothesis approach, where two hypotheses are used, improves the overall efficiency of a light field coder. Our experimental results show an image quality gain of up to 1 dB in PSNR on our test data sets.

Method for illuminating an object with light from a laser light source

Abstract: The present invention relates to a method for illuminating an object with light (2) from a laser light source (3), preferably in a confocal scanning microscope (1). With the method according to the invention, it is possible to reduce the coherence length of the laser light, so that disruptive interference phenomena can be substantially eliminated. Should interference phenomena nevertheless be formed, these are to be influenced in such a way that they have no effect on the detection. The method according to the invention is characterized in that the phase angle of the light field is varied by a modulation means (4) in such a way that interference phenomena do not occur in the optical beam path, or occur only to an undetectable extent, within a predeterminable time interval.

Interactive view synthesis from compressed light fields

Abstract: A light field is a collection of multi-view images which represent a 3D scene. Rendering from a light field provides a simple and efficient way to generate arbitrary new views of the scene as the viewing position and angle change, thus offering the experience of immersive viewing. The enormous amount of data required in a light field poses a key challenge in rendering. Tree-structured vector quantization (TSVQ) provides 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. This paper describes a new compression scheme that supports interactive rendering directly from compressed light field data. The proposed algorithm provides a high compression ratio of as much as 10 times that of TSVQ, while only slowing down the rendering speed by a factor smaller than 2.

Computer Generated Holograms for Optical Neural Networks

Abstract: While numerous artificial neural network (ANN) models have been electronically implemented and simulated by conventional computers, optical technology provides a far superior mechanism for the implementation of large-scale ANNs. The properties of light make it an ideal carrier of data signals. With optics, very large and high speed neural network architectures are possible. Because light is a predictable phenomenon, it can be described mathematically and its behavior can be simulated by conventional computers. A hologram is in essence a capture of the light field at a particular moment in time and space. Later, the hologram can be used to reconstruct the three dimensional light field carrying optical data. This makes a hologram an ideal medium for capturing, storing, and transmitting data in optical computers, such as optical neural networks (ONNs). Holograms can be created using conventional methods, but they can also be computer generated. In this paper, we will present an overview of optical neural networks, with emphasis on the holographic neural networks. We will take a look at the mathematical basis of holography in terms of the Fresnel Zone Plate and how it can be utilized in making computer generated holograms (CGHs). Finally, we will present various methods of CGH implementation in a two layer holographic ONN.

Optically controlled rotation of multibeam light field

Abstract: We propose a method of rotation of higher-order Bessel light beams based on controlling phase difference between the interfering Bessel beam and a super-Gaussian or annular beam coaxial with it. TO realize the optically-controlled rotation of light field, a phase modulator based on quadratic or cubic nonlinearities can be used.

Influence of depolarization effects in interferometric measurement methods

Abstract: The quality of interferometric measurement methods, such as fault detection by shearography, is highly influenced by the intensity distribution of the illuminating light. Usually it is intended to obtain a homogeneous object illumination while common laser light sources provide a Gaussian intensity distribution. In this paper it is investigated how the intensity distribution of the detected light is influenced by the polarization states of the incident and the scattered light. In literature usually the Stratton-Chu equation is used to describe depolarization effects. However, this equation is valid only in the Fraunhofer region, which is unsuitable for most interferometric measurements. For this reason a still unpublished general expression for the amplitude of the electromagnetic field close to the scattering surface is derived. Based on this novel formula the correlation between the intensity distribution and the polarization state of the scattered light is investigated analytically, numerically and experimentally. In the numerical part the integral formula is used to generate the light field scattered by a metal plate. As input data for the simulation the measured surface structure of a real metal plate is used. Additionally, the theoretical results are compared to measured intensity distributions for several combinations of input and output polarization states.

Lorentz force effect in strong-field atomic stabilization

Abstract: The evolution of the electron wave packet at atomic ionization with a very intense laser pulse has been studied numerically beyond the dipole approximation in frame of a two-dimensional quantum model. The upper boundary of stabilization window has been found that is because of the Lorentz force effect due to the magnetic component of the light field. The similar window for efficient high-order harmonic generation has been also found.