Showing papers on "Light field published in 1996"

Light field rendering

Abstract: A number of techniques have been proposed for flying through scenes by redisplaying previously rendered or digitized views. Techniques have also been proposed for interpolating between views by warping input images, using depth information or correspondences between multiple images. In this paper, we describe a simple and robust method for generating new views from arbitrary camera positions without depth information or feature matching, simply by combining and resampling the available images. The key to this technique lies in interpreting the input images as 2D slices of a 4D function the light field. This function completely characterizes the flow of light through unobstructed space in a static scene with fixed illumination. We describe a sampled representation for light fields that allows for both efficient creation and display of inward and outward looking views. We hav e created light fields from large arrays of both rendered and digitized images. The latter are acquired using a video camera mounted on a computer-controlled gantry. Once a light field has been created, new views may be constructed in real time by extracting slices in appropriate directions. Since the success of the method depends on having a high sample rate, we describe a compression system that is able to compress the light fields we have generated by more than a factor of 100:1 with very little loss of fidelity. We also address the issues of antialiasing during creation, and resampling during slice extraction. CR Categories: I.3.2 [Computer Graphics]: Picture/Image Generation — Digitizing and scanning, Viewing algorithms; I.4.2 [Computer Graphics]: Compression — Approximate methods Additional keywords: image-based rendering, light field, holographic stereogram, vector quantization, epipolar analysis

Evanescent-wave guiding of atoms in hollow optical fibers.

Abstract: An atom placed in a near-resonant laser field is either attracted to or repelled from regions of high intensity depending on the sign of the laser’s detuning from atomic resonance. We have demonstrated that the optical forces induced by laser light guided in a fiber may be used to reflect atoms from the inner wall of a hollow-core optical fiber in a recent work [1,2]. In that demonstration, light was coupled to the lowest-order grazing incidence mode [3] and the laser frequency was tuned to the red side, so that atoms were attracted to the high-intensity region at the center of the fiber. Atoms guided in this way undergo a series of lossless oscillations in the transverse plane and unconstrained motion along the axis. Atoms can also be guided by the evanescent light field of the glass surface surrounding a hollow fiber. With a detuning on the blue side of resonance, atoms are expelled from the high-intensity-field region near the fiber wall. The intensity in the evanescent field is significant at a distance of .=X/2.rr into the hollow region. Consequently, the atoms are nearly specularly reflected from the potential walls. Atom propagation through the fiber in this case is similar to the propagation of light in a multimode, step-index fiber. Evanescent guiding has several advantages over guiding by grazing incidence modes: heating of the atoms due to spontaneous scattering of photons is small in the evanescent case because the atoms spend most of the time in a dark region away from the high laser intensity at the wall. In the grazing incidence configuration, atoms are guided in the high-intensity region, and consequently the spontaneous scattering rate is relatively high. Furthermore, in evanescentwave guiding, the optical potential is generated by light traveling in lossless guided modes. Small-diameter atomic guides of very long length may be practical. By contrast, grazing incidence optical modes decay exponentially with distance [3], effectively limiting the guiding distance to a

Photon Chopping: New Way to Measure the Quantum State of Light

Abstract: We propose the use of a balanced $2N$-port as a technique to measure the pure quantum state of a single-mode light field. In our scheme the coincidence signals of simple, realistic photodetectors are recorded at the output of the $2N$-port. We show that applying different arrangements both the modulus and the phase of the coefficients in a finite superposition state can be measured. In particular, the photon statistics can be so measured with currently available devices.

Illumination system for ocr of indicia on a substrate

Abstract: An illumination system (10, 40, 74, 100) is provided having one or more light sources (24, 26), opaque baffles (30, 32), and mirrors (50, 64, 66) for illuminating indicia on a substrate, such as a semiconductor wafer (18), for viewing by a camera (12, 42) aligned parallel to or at an angle (14) to the substrate. The light sources (24, 26) include light emitting diodes for illuminating soft marks and broad spectrum incandescent lamps for illuminating hard marks. Dark field and light field illuminators are provided for enhanced reading of light indicia on a dark background and dark indicia on a light background, respectively. A light control unit (158) allows for manual or automated control of light source selection and light intensity. Opposing mirrors extending along the optical paths of the light sources reflect light emitted from the light sources into the camera's field of view, thereby increasing the illumination efficiency and permitting the use of fewer light sources.

Maxwell-Bloch equations for spatially inhomogeneous semiconductor lasers. II. Spatiotemporal dynamics

Abstract: The spatiotemporal dynamics of broad-area lasers is analyzed on the basis of a space- and momentum-dependent density-matrix approach. To this means the space-dependent Maxwell-Bloch equations for the semiconductor laser (derived in our preceding paper I) are solved by direct numerical integration. The space and momentum resolved dynamics of the active semiconductor medium, described by microscopic charge-carrier distributions and nonlinear polarization functions, are treated self-consistently with the spatiotemporal dynamics of the light field. Carrier transport dynamics are approximated on the basis of an ambipolar diffusion approximation consistent with the microscopic processes. Boundary-influenced macroscopic waveguiding properties of typical conventional as well as tapered broad-area laser cavities are taken into account. The dynamics of the formation and longitudinal propagation of unstable transverse optical filamentary structures are analyzed. Simultaneous spectral and spatial hole burning with dynamical spatiospectral variations on ultrashort (ps and sub-ps) time scales are observed in the charge-carrier distributions, reflecting the interplay between stimulated emission and the relaxation dynamics of the carrier distributions as well as the polarization. The transverse hole burning leads to complex spatiotemporal patterns in the macroscopic intensity picture with different optical frequencies associated with various locations of the modelike near-field patterns. \textcopyright{} 1996 The American Physical Society.

Bragg scattering of slow atoms from a standing light wave

Abstract: Slow atoms from a magneto-optical trap are used to study diffraction from a near-resonant standing-wave light field. Long interaction times make it possible to observe unidirectional Bragg scattering. In particular, the Pendellosung interference effect between two resonant momentum states is demonstrated for first- and second-order diffraction. The oscillation frequency of second-order scattering shows a transition from a four-photon–type process at low light intensity to a two-photon–type process at higher intensity. The data are in quantitative agreement with a theoretical description which takes into account lowest-energy momentum states.

Light-driven global illumination with a wavelet representation of light transport

Abstract: This thesis considers the problem of global illumination: the modelling of light as it travels through a scene interacting with the objects contained within the scene. Starting with a description of the problem and a discussion of previous work, we explore a new approach called light-driven global illumination that offers several advantages over its predecessors: a lower asymptotic complexity, a wider range of representable surface interaction phenomena, and an absence of the need for “meshing”—object surface subdivision needed primarily to represent shadows. Light-driven global illumination is intermediate between local and global illumination. Representing light with wavelet basis functions, we are able to treat both the interaction between two surfaces and the interaction of a surface with a radiation field in a source-to-destination model that applies to whole surfaces, not just small elements. We have found this “wavelet radiative transfer” to be a valid way to generate and store complex global light field data as four-dimensional textures for incorporation in local illumination solutions. Wavelets can considerably reduce the otherwise substantial storage and reconstruction problems associated with doing this. We include several examples of this. We also discuss plausible illumination models, which are required to make light-driven global illumination work theoretically. Like wavelet radiative transfer, these models have application in other areas of rendering besides global illumination. Finally, we develop the theory behind light-driven global illumination and apply it successfully to some simple examples. While we find the algorithm to be quite slow compared to other well-known rendering algorithms, we analyze what is needed to make it competitive. In conclusion, we find that representing light with wavelets has a set of advantages that are independent of the comparative inefficiency of the light-driven algorithm.

Application of a pseudogeometrical optical approach for calculation of the field formed by a focusator

Abstract: The present work deals with the application of pseudogeometric optics techniques to calculating a light field generated by a focusator of laser radiation into the rectangular domain We have derived an analytical expression for the principal term of the asymptotic expansion in the focal plane including the geometric-optics shadow domain

Quantum kinetics of semiconductor light emission and lasing.

Abstract: Semiconductor light emission is analyzed as a paradigm of a nonequilibrium quantum mechanical many-body problem. The medium excitations and the quantized light field inside and outside a semiconductor slab are treated consistently. Splitting the photon density of states into a medium and a vacuum induced contribution the arbitrarily strong semiconductor emission is described as spontaneous emission into the vacuum induced part. With increasing gain narrowing peaks of growing intensity evolve for each propagation direction, whereas under laser conditions one propagation direction is favored by the cavity.

Enhanced backscattering of partially coherent light.

Abstract: The backscattering enhancement of light from random media is analyzed for situations in which the scatterers are illuminated with spatially partially coherent light. The effect of coherence is incorporated into the existing theories by use of the angular correlation description for the illuminating light field. When the area of illumination is infinite, an analogy to the van Cittert–Zernike theorem leads to the expression for the intensity distribution that is given by the sum of backscattered intensities, each of which would arise from each incident plane-wave component of the angular spectrum. It is shown that the backscattering cone is partially suppressed and deformed owing to breaking of the time-reversal symmetry of mutiple-scattering paths.

Method and system for dynamically establishing field size coincidence

Abstract: A method of establishing coincidence between a field size of a light field used in a setup mode of a radiation system and a field size of a radiation field used in an operation mode of the system includes providing automatic adjustment of field-defining structure to compensate for differences in optical properties of the light and the radiation. A light beam passing through the field-defining structure typically exhibits greater scattering than an X-ray beam passing through the structure. For each of a number of different settings of the field-defining structure, the difference between the field sizes of the light and the radiation are determined and recorded. Then, for a particular desired field size, the field-defining structure can be automatically adjusted to provide compensation. In the preferred embodiment, the field-defining structure includes jaws of a collimator of a radiation system and the determination of field size differences of the light and the radiation occurs for each of various energy level settings of the radiation system.

Quantum-state homodyne measurement with vacuum ports.

Abstract: We show that the quantum state of an N-mode light field can be reconstructed from the difference statistics recorded in multiport homodyning with N unused input ports. The theory is applied to balanced homodyne six-port detection, which is shown to be suited for measuring the Q function of a single-mode radiation field. \textcopyright{} 1996 The American Physical Society.

Low-loss light redirection apparatus

Abstract: The apparatus of this invention redirects light input to the apparatus without significant light loss, and preferably without increasing the light's etendue. The apparatus includes a light guide and a redirection member. The member has input, output and reflective surfaces. The member's input surface is joined to the light guide to define an interface, and the member's output surface is situated adjacent to a medium that can be another light guide or redirection member, a gas such as ambient air, or a vacuum, for example. The member is configured to redirect light traveling in the light guide from its reflective surface by a predetermined redirection angle. To prevent light at the largest spread angle present in the light traveling in the light guide, from traveling into the member, reflecting from the reflective surface and traveling back through the input surface to be lost, the relative refractive indices for the light guide or interface material, and member cause the light from the reflective surface to again reflect internally at the member's input surface. Also, to prevent light from traveling from the light guide through the input surface, the output surface and through the medium at an angle that would result in light loss, the relative refractive indices of the member and medium or interface material cause internal reflection of light in the member at the output surface-medium interface. Accordingly, the apparatus of this invention can redirect light with little or no light loss or increase in etendue. For use in relatively large-scale photolithography, the apparatus can include a plurality of light guides and respective redirection members that are combined to create a large, uniform light field. Also, the redirection members can be implemented as beam splitters optically coupled in succession, whose combined output surfaces generate a relatively large light field of uniform intensity. Groups of beam splitters can also be joined by light guides to produce a plurality of separated light fields.

Non-contact edge detector

Abstract: A non-contact substrate alignment system for a lithography system is disclosed that comprises three substrate edge detectors. Each edge detector comprises a projector, preferably located above the substrate, that projects a light field down onto a substrate and a stage. The light field has a predetermined shadow line that is straight and runs perpendicularly to the direction of the substrate's edge. A camera is also located above the substrate and detects the light from the light field. The height differential between the substrate and stage causes a shift in the shadow line from the perspective of the camera. A controller connected to the camera utilizes this shift to locate the edge of the substrate. The problems associated with the mechanical banking techniques are thus avoided. Moreover, the technique uses detectors and projectors that can be located entirely above the substrate; specially designed stages with incorporated detectors or projectors are not required. The technique is also very tolerant of different types of substrates with different edge characteristics.

Bichromatic atomic lens.

Abstract: We investigate the focusing of three-level atoms with a bichromatic standing wave laser field, using both classical and quantum treatments of the problem. We find that, for the appropriate ratio of detunings to Rabi frequencies, the atoms will experience a periodic potential which is close to harmonic across half an optical wavelength. The field thus becomes equivalent to a periodic array of microlenses, which could be utilized to deposit lines of atoms upon a substrate. We consider and compare two regimes, differentiated by the interaction time of the atoms in the optical field. The first case considered, the Raman-Nath regime, is analogous to the thin lens regime in classical optics. The second case treats the transverse atomic motion within the light field, and investigates the distribution of atoms upon a substrate placed within the field. We investigate the extent to which this case can be modeled classically.

Statistical Properties of Laser Light

Abstract: The Fokker-Planck equation has become a very useful tool for treating noise in quantum optics. In this chapter we investigate noise in a laser, which is the most important device in quantum optics. This subject together with other applications of the Fokker-Planck equation in quantum optics are already treated in a number of handbooks, books and review articles [12.1 – 13, 1.28, 4.8]. The main purpose of this chapter is to demonstrate how some of the methods of Chaps. 2 – 9 can be applied to a simple laser model (one mode, adiabatic elimination of all variables with the exception of the laser field, threshold region). The following two points make it difficult but also interesting to investigate the statistical properties of laser light.

Marine asymptotic daylight field: effects of inelastic processes.

Abstract: The governing equations are developed for the marine asymptotic daylight field in the scalar approximation, including the effects of inelastic processes-Raman scattering and chromophoric dissolved organic matter fluorescence. The governing equations are solved numerically and compared with Monte Carlo simulations. It is found that these solutions are the actual radiance distributions approached by the asymptotic field in the Monte Carlo simulations. Sample solutions are provided to show the sensitivity of the light field to the various parameters of the medium. For certain values of the parameters, inclusion of inelastic processes can drastically alter the radiance distribution, e.g., from a near-Dirac delta function in the absence of inelastic processes to a near-isotropic distribution in their presence. The results suggest that in a real ocean, the asymptotic (and near-asymptotic) radiance distribution will tend to become more uniform as the wavelength increases beyond ~500 nm. Finally, it is shown that even for depths far from the asymptotic regime, the radiance distribution of the inelastic component of the light field can be well approximated by the asymptotic theory developed here for inelastic processes. Two exact analytical solutions to the governing equations are also provided.

Quantum measurements in atom optics

Abstract: We consider atoms traversing a cavity filled with an optical field. When the atoms are well detuned from the optical resonance the output momentum distribution of the atoms is found to be a sensitive probe of the photon statistics of the light field. Near resonance spontaneous emission smears the diffractive peaks. We obtain a good fit to the experimental data of Gould et at. (1991). As the atoms pass through the optical field they impart a position-dependent phase shift to the field. By making a quadrature phase measurement on the optical field a position measurement of the atom is achieved. We show that it is possible to prepare the atom in a 'contractive state' which beats the standard quantum limit for position measurements.

High-velocity dark states in velocity-selective coherent population trapping

Abstract: Some of the most interesting and important topics in the field of optical control of atomic motion occur in the quantum domain. In this domain the motion is described in terms of de Broglie wave fields of massive particles, and the interactions between these fields and the optical fields result in manipulation of the atoms by optical pumping and Raman transitions. Perhaps the most spectacular example results from the accumulation of atoms in ‘‘dark states,’’ atomic states that cannot be excited by the light field. Some atomic states are trivially dark, that is, they cannot be excited because the light has the wrong frequency or polarization. The more interesting cases are superposition states created by coherent Raman coupling by the optical field. A very special case occurs when those states whose evolution to excitable states vanishes exactly because their external ~de Broglie wave! states are characterized by a particular momentum. Such velocity-selective coherent population trapping ~VSCPT! has been a subject of considerable interest @1,2# since its first demonstration by Aspect et al. in 1988 @3#. VSCPT is of special interest because it enables atoms to accumulate steadily in dark states, creating arbitrarily narrow peaks in the momentum distribution. This paper presents our experimental and theoretical studies of high-velocity superposition dark states that to our knowledge have not been previously observed. Any description of the quantum nature of the atomic motion, including VSCPT, requires that the energy of such motion be included in the Hamiltonian:

Light box, e.g. for through illumination of transparent film or foil, e.g. for medical evaluation of X=ray images

Abstract: The light box (10) contains at least one surface of an optically diffuse plate (15) which is subjected to light from within in the region of the desired light field. The surface of a diffusely reflecting plate (17) is arranged in the light box at a distance from and parallel to the diffuse plate essentially corresponding to a surface of the desired light field.The facing surfaces of the diffuse plate and diffusely reflecting plate are associated with sections (16a,16b) of transparent foil with one smooth side and a prismatic structure on the other. The foil sections are oriented so that their prismatic structures lie parallel and facing one or other plate. At least one rod-shaped light source emits light laterally into the space between the foil sections in the prism direction.

Interaction of ultrashort relativistically intense laser pulses with matter: conservative models and instabilities of the light field

Abstract: Recently, in connection with the development of superintense lasers, a number of researchers have considered the interaction of ultrashort laser pulses with matter at relativistic intensities of the light field. The optics of ultrashort pulses of nonrelativistic intensities have been completely worked out. The basic results in this field are summarized, for example, in the monographs of Akhmanov, Visloukh, and ~hirkin' and ~ukhorukhov.~ A number of questions on the physics of the interaction of strong laser radiation with matter have been discussed in the book of Koroteev and ~ h u m a i . ~ When laser radiation of relativistic intensity interacts with matter, the leading edge the pulse produces rapid ionization, and therefore the radiation propagates in an induced plasma. The pioneering papers on the corresponding plasma nonlinearities (relativistic and striction) are those of Akhiezer and ~olovin? ~ s k a r ' ~ a n ? ~ i tvak? and others. Recent work on the interaction of laser radiation of relativistic intensities with matter can be summarized as follows. A mathematical model of the interaction of long laser pulses with a plasma was formulated in Ref. 7. A detailed mathematical study of this modelg showed that the equations given in Ref. 7 have a denumerable set of eigenmodes. In addition, it was established in Ref. 8 by numerical simulation that at large depths, laser pulses of supercritical intensity experience stabilization and their asymptotic transverse profiles are described by the lowest eigenmodes of the problem. This phenomenon is called relativistic-striction selfchanneling of laser radiation. The model of Refs. 7 and 8 was extended in Refs. 9 and 10 to take into account the effect of higher-order dispersion on the nature of the propagation, and it was shown that under conditions of sharp self-focusing of light in the plasma there is strong self-modulation of an ultrashort laser pulse. Physical effects associated with the finite duration of the laser pulse have also been considered in a number of other For example, a model of the propagation of infinitely wide laser pulses of finite length was worked out in Ref. 11, and the equations of this model were extended in Ref. 12 to three spatial dimensions. However, these equations do not transform into the equations obtained in Ref. 7 in the limit of an infinitely long pulse. We recall that the nonrelativistic three-dimensional interaction of laser pulses with a plasma was considered in Ref. 13, where a number of dispersion terms in the equations describing the propagation of the radiation were neglected. Equations closest to those derived in the present paper were given in Ref. 14. However, a number of terms associated with the dependence of the Langmuir waves generated by the laser radiation on the transverse coordinates were omitted in Ref. 14, with the result that the problem became nonconservative. Most theoretical studies of the problem are based on Maxwell's equations and the equations of cold, collisionless, relativistic hydrodynamics of charged particles in an electromagnetic field in the absence of collisions and thermal effects. These equations can be written in relativistically invariant notation or in the usual three-dimensional form and have an energy-momentum tensor of matter and field whose components are conserved quantities (see Ref. 9, for example). Because of the complexity of these equations, in most papers they are averaged over the period of the laser radiation, and other approximations are introduced, leading to a system of simplified equations, which are also required to be conservative. The present paper is devoted to the derivation of a conservative, time-dependent, three-dimensional model taking the following physical effects into account: diffraction and refraction of the radiation, relativistic and striction nonlinearities in its interaction with the plasma, and the generation of plasma waves by the propagating laser pulses. The Lagrangian formulation of the problem is given below and the general instability of a uniform light field is analyzed. As a starting point we use Maxwell's equations in the Coulomb gauge and the equations of cold, relativistic hydrodynamics for the electronic component of the plasma:

Image formation in an optical-electronic system with spatial coherent transformation of light field

Abstract: A possibility of creation of optical-electronic system with no lines for image formation based on light field spatial coherence transform and of detecting nonstationary wave fronts with the help of wide-aperture photodetectors is considered. Methods of useful signal independent time modulation implementation are considered. Experimental results on image formation of 1D objects are shown.

Squeezing the Light with Laser Cooled Atoms

Abstract: Cold atomic clouds were used as a nonlinear medium to reduce the quantum noise of a light field. The cold atoms were placed in a resonant optical cavity. Quadrature squeezing as high as 40% was measured on the beam going out of the cavity containing the cold atoms.