Showing papers on "Lens (optics) published in 1997"

Velocity map imaging of ions and electrons using electrostatic lenses: Application in photoelectron and photofragment ion imaging of molecular oxygen

Abstract: The application of electrostatic lenses is demonstrated to give a substantial improvement of the two-dimensional (2D) ion/electron imaging technique. This combination of ion lens optics and 2D detection makes “velocity map imaging” possible, i.e., all particles with the same initial velocity vector are mapped onto the same point on the detector. Whereas the more common application of grid electrodes leads to transmission reduction, severe trajectory deflections and blurring due to the non-point source geometry, these problems are avoided with open lens electrodes. A three-plate assembly with aperture electrodes has been tested and its properties are compared with those of grid electrodes. The photodissociation processes occurring in molecular oxygen following the two-photon 3dπ(3Σ1g −)(v=2, N=2)←X(3Σg −) Rydberg excitation around 225 nm are presented here to show the improvement in spatial resolution in the ion and electron images. Simulated trajectory calculations show good agreement with experiment and ...

Power vectors: An application of Fourier analysis to the description and statistical analysis of refractive error

Abstract: The description of sphero-cylinder lenses is approached from the viewpoint of Fourier analysis of the power profile. It is shown that the familiar sine-squared law leads naturally to a Fourier series representation with exactly three Fourier coefficients, representing the natural parameters of a thin lens. The constant term corresponds to the mean spherical equivalent (MSE) power, whereas the amplitude and phase of the harmonic correspond to the power and axis of a Jackson cross-cylinder (JCC) lens, respectively. Expressing the Fourier series in rectangular form leads to the representation of an arbitrary sphero-cylinder lens as the sum of a spherical lens and two cross-cylinders, one at axis 0 degree and the other at axis 45 degrees. The power of these three component lenses may be interpreted as (x,y,z) coordinates of a vector representation of the power profile. Advantages of this power vector representation of a sphero-cylinder lens for numerical and graphical analysis of optometric data are described for problems involving lens combinations, comparison of different lenses, and the statistical distribution of refractive errors.

Distortion compensation for generalized stereoscopic particle image velocimetry

Abstract: Optical distortion due to inaccurate optical alignment, lens nonlinearity, and/or refraction by optical windows, fluid interfaces, and other optical elements of an experiment causes inaccuracy by introducing variable magnification. Since fractional changes in the magnification have a one-to-one effect on the accuracy of measuring the velocity, it is important to compensate for such distortions. A general experimental calibration procedure is described which determines the magnification matrix of a distorted imaging system, and an algorithm is presented to compute accurate velocity field displacements from measurements of distorted PIV images. These procedures form a basis for generalized stereoscopic PIV procedures which permit easy electronic registration of multiple cameras and accurate recombination of stereoscopic displacement fields to obtain the three-dimensional velocity vector field.

Distortion Compensation for Generalized Stereoscopic Particle Image Velocimetry

Abstract: Optical distortion due to inaccurate optical alignment, lens nonlinearity, and/or refraction by optical windows, fluid interfaces, and other optical elements of an experiment causes inaccuracy by introducing variable magnification. Since fractional changes in the magnification have a one-to-one effect on the accuracy of measuring the velocity, it is important to compensate for such distortions. A general experimental calibration procedure is described which determines the magnification matrix of a distorted imaging system, and an algorithm is presented to compute accurate velocity field displacements from measurements of distorted PIV images. These procedures form a basis for generalized stereoscopic PIV procedures which permit easy electronic registration of multiple cameras and accurate recombination of stereoscopic displacement fields to obtain the three-dimensional velocity vector field.

Anatomically accurate, finite model eye for optical modeling

Abstract: There is a need for a schematic eye that models vision accurately under various conditions such as refractive surgical procedures, contact lens and spectacle wear, and near vision. Here we propose a new model eye close to anatomical, biometric, and optical realities. This is a finite model with four aspheric refracting surfaces and a gradient-index lens. It has an equivalent power of 60.35 D and an axial length of 23.95 mm. The new model eye provides spherical aberration values within the limits of empirical results and predicts chromatic aberration for wavelengths between 380 and 750 nm. It provides a model for calculating optical transfer functions and predicting optical performance of the eye.

Image combining system for eyeglasses and face masks

Abstract: An optical system combines a first image formed by a main lens (300) with a second image provided by an electronic display, slide, or other image source (320) The image combining system includes one or more inserts such as a set of reflecting image combiners to redirect light on an optical pathway within the main lens to the user's eye The image combining system is highly compact, allowing the integration of a display system with eyeglasses or a face mask, such as a diver's mask A number of implementations of the optical system make possible other types of image integration including uses in image acquisition systems such as cameras

Laser printer with array of laser diodes

Abstract: The laser printer uses an array of laser diodes (11), a cross array of illuminating optical elements (21), a laser lens array (24), a light modulating array (40) and an integrator (23) that ensures that the modulator receives a uniform lighting effect. The cross array reduces the divergence of the laser diode emitters. The output is focussed by a printing lens onto the light sensitive medium.

Stereoscopic Digital Particle Image Velocimetry for Application in Wind Tunnel Flows

Abstract: A particle image velocimetry system capable of accurately recovering the out-of-plane velocity component has been realized based on a stereoscopic viewing arrangement. To allow a large viewing angle with long focal length objective lenses, the angular displacement or Scheimpflug imaging configuration is employed in which the image, object and lens planes intersect in a common line. The varying magnification factor associated with this imaging configuration is accounted for using an accurate and simple-to-use calibration procedure based on solving the projection equations for each of the two cameras. A pair of high-resolution cameras, both capable of recording image pairs in the microsecond range, are synchronized to a pulsed Nd-YAG laser. By placing the cameras on either side of the light sheet the favourable light scattering characteristics of micron-sized seeding particles in forward scatter provide images at significantly higher illumination than at normal or backscatter viewing angles. Ultimately designed for use in industrial wind tunnels, the camera system is capable of working with non-symmetric arrangements. It has been successfully tested in a laboratory environment by imaging the unsteady flow field of a vortex ring passing through a laser light sheet. Adaptive processing software capable of dynamically adjusting the sample location of the interrogation windows to the local displacement vector significantly improves data yield. The algorithm requires only the selection of the final window/overlap size. The hierarchical interrogation approach permits the processing of images whose displacement dynamic range exceeds the interrogation window size.

Microlens scanner for microlithography and wide-field confocal microscopy

Abstract: A microscopy and/or lithography system uses a comparatively low-resolution image projection system, which has a very small numerical aperture but large image field, in conjunction with a microlens array comprising miniature lens elements, each of which has a large numerical aperture but very small field. The projection system contains a small aperture stop which is imaged by the microlenses onto an array of diffraction-limited microspots on the microscope sample or printing surface at the microlens focal point positions, and the surface is scanned to build up a complete raster image from the focal point array. The system design thus circumvents the tradeoff between image resolution and field size which is the source of much of the complexity and expense of conventional wide-field, high-NA microscopy and microlithography systems. The system makes possible flat field, distortion-free imaging, with accurate overlay, focus, and warp compensation, over very large image fields (larger than the practical limits of conventional imaging means). In one embodiment it would use a Digital Micromirror Device as the image source, potentially eliminating the need for photomasks in semiconductor manufacture.

Evidence for substructure in lens galaxies

Abstract: We discuss whether one should expect that multiply imaged QSOs can be understood with `simple' lens models which contain a handful of parameters. Whereas for many lens systems such simple mass models yield a remarkably good description of the observed properties, there are some systems which are notoriously difficult to understand quantitatively. We argue that at least in one case (B 1422+231) these difficulties are not due to a `wrong' parametrization of the lens model, but that the discrepancy between observed and model-predicted flux ratios are due to substructure in the lens. Similar to microlensing for optical fluxes, such substructure can distort also the radio flux ratios predicted by `simple' mass models, in particular for highly magnified images, without appreciably changing image positions. Substructure also does not change the time delay significantly and therefore has little effect on the determination of the Hubble constant using time delays. We quantify these statements with several simple scenarios for substructure, and propose a strategy to model lens systems in which substructure is suspected.

Method of and apparatus for viewing an image

Abstract: Light from an image displayed on a display screen (10) is transmitted to an observer's eye (11) by way of a dynamic optical element (12) (such as a spatial light modulator or an electrically switchable holographic composite) which acts as a lens. Emitters (17) on the display screen (10) emit infrared radiation which is projected by the dynamic lens (12) as a broad wash onto the eye (11). Infrared radiation reflected back from the eye (11) is focused by the dynamic lens (12) onto detectors (18) also provided on the display screen (10). The detectors (18) are thus able to sense the direction of eye gaze, and the dynamic lens (12) is controlled in dependence on this to create an area of high resolution in an area of interest centred on the direction of gaze, which is moved to follow the eye gaze as its direction alters. Other than in the area of interest, the dynamic lens (12) has a relatively low resolution.

Display device incorporating one-dimensional grating light-valve array

Abstract: A display system for providing a two dimensional image includes an essentially one dimensional light valve array. The diffractive light valve array includes modulator elements which diffract or reflect light incident thereon to an extent determined by an image element to be represented. The display system is arranged such diffracted light from the light-valve array passes through a magnifying lens and is separated from the reflected light from the array. A magnified virtual image of the array formed by the diffracted light is viewed through the magnifying lens. A scanning arrangement between the viewer and the magnifying lens scans the image of the light-valve array across the field of view of the viewer sufficiently quickly that the viewer perceives the scanned image as a two-dimensional image. In another arrangement a printer is formed by scanning a real image of the diffractive light valve array over a printing or recording medium.

Shear and ellipticity in gravitational lenses

Abstract: Galaxies modeled as singular isothermal ellipsoids with an axis ratio distribution similar to the observed axis ratio distribution of E and S0 galaxies are statistically consistent with both the observed numbers of two-image and four-image lenses and the inferred ellipticities of individual lenses. However, no four-image lens is well fitted by the model (typical χ2/Ndof ~ 20), the axis ratio of the model can be significantly different from that of the observed lens galaxy, and the major axes of the model and the galaxy may be slightly misaligned. We found that models with a second, independent, external shear axis could fit the data well (typical χ2/Ndof ~ 1), while adding the same number of extra parameters to the radial mass distribution does not produce such a dramatic improvement in the fit. An independent shear axis can be produced by misalignments between the luminous galaxy and its dark matter halo, or by external shear perturbations due to galaxies and clusters correlated with the primary lens or along the line of sight. We estimate that the external shear perturbations have no significant effect on the expected numbers of two-image and four-image lenses but that they can be important perturbations in individual lens models. However, the amplitudes of the external shears required to produce good fits are larger than our estimates for typical external shear perturbations (10%-15% shear instead of 1%-3%), suggesting that the origin of the extra angular structure must be intrinsic to the primary lens galaxy in most cases.

Miniature scanning confocal microscope

Abstract: A scanning optical microscope which includes an optical fiber which serves as a point source of light and for collecting reflected light is disclosed. A lens for focusing the light from the optical fiber onto an image plane and for gathering light reflected from the image plane and focusing it into the optical fiber is also disclosed, together with a scanning mechanism for scanning the light to scan a field of view.

Standardizing constants for ultrasonic biometry, keratometry, and intraocular lens power calculations

Abstract: Purpose: To provide a method and values that facilitate standardization of constants for ultrasonic biometry, keratometry, and intraocular lens (IOL) power calculations. Setting: University of Texas Medical School, Houston, Texas, USA. Methods: Keratometry and ultrasonic biometry provide the two measured input variables for the six variable vergence equations used to calculate the appropriate IOL power for a specific patient with a cataract. A review of the literature reflecting the past 156 years of research and development reveals the appropriate index of refraction to be used with the keratometer for net optical corneal power, the location of the principal planes of the cornea, the nominal value for retinal thickness, and the appropriate velocities for ultrasonic measurement of the axial length. The relationship of the thick IOL to the thin IOL is derived along with the physical location of the thick lens. Two methods are described that provide the best IOL constant to be used by a manufacturer to minimize the prediction error for a surgeon using the lens for the first time. The formulas for phakic IOLs and secondary piggyback IOLs are also derived and applied to methods described above for standard IOLs. Results: Using a standardized net index of refraction of 4/3 for the cornea eliminates a variability of 0.56 diopter (D) in the predicted refraction. Using a standardized 1532 m/s velocity for axial length measurements and adding a value of 0.28 mm reduces the tolerance of axial length measurements to ±0.03 mm for any length eye. The physical location of the thick IOL's secondary principal plane must be anterior to the thin lens equivalent by approximately the separation of the principal planes of the thick lens. For biconvex poly(methyl methacrylate) IOLs, the separation in the principal planes is approximately 0.10 mm. Using these relationships, the physical position of the thick lens within the eye can be used to confirm the lens constant for any IOL style. Conclusions: Standardizing the constants for keratometry, ultrasonic biometry, and IOL power calculations can significantly improve the predictability of refractive outcomes. Back-calculating and physically measuring the position of the lens within the eye can provide surgeons with an initial lens constant known to have a standard error of the mean of ±0.05 mm (±0.10 D). Other parameters such as the cardinal points of a lens, the shape factor, the lens-haptic plane, and the center lens thickness would allow further refinement of IOL power calculations.

Method and apparatus for the production of a structure by focused laser radiation on a photosensitively coated substrate

Abstract: A system for writing geometric structures on a photosensitive substrate including a modulated laser beam source, a focusing lens, a deflector for producing a scanning action between the light source and the lens, and a device for mechanically moving the surface relative to the laser beam. Compressed data for use in writing the geometric structures is read out of a memory into a data delivery circuit such that the data is formatted to have both beam power and position information. A modulator logic circuit operates to call up the data from the data delivery circuit, form a modulation drive signal based on the power information, and delay the modulation drive signal based the position data. The modulator logic circuit thus operates to vary the modulation drive signal to begin or end exposure along the scan lines with greater resolution or pixel density by at least a factor of four more than the resolution or spacing density between adjacent scan lines. The scan lines are arranged within stripes, and adjacent stripes preferably are made to overlap such that the stripes are blended in the overlap according to a predetermined stepwise changing function.

Array detection for speckle reduction in optical coherence microscopy

Abstract: This paper introduces a spatial-diversity method for speckle suppression in optical coherence microscopy. The method is based on combining interference signals from an array of detectors placed in the back focal plane of the objective lens, such that elements receive light backscattered from the sample volume at different angles. Incoherently adding ('compounding') the signals increases the signal-to-noise ratio of the processed image compared to that attainable with a single detector. The speckle-reduction method was demonstrated with a benchtop microscope equipped with a quadrant photodiode. To evaluate its potential application in dermatology, images of living skin acquired with and without compounding were compared. The quality of the compounded images was found to be substantially better. A signal-to-noise gain close to a factor of two (the theoretical maximum attainable using four detectors) was achieved without a significant loss in resolution. The method can be applied to arrays with a larger number of elements, potentially enabling more advanced forms of spatial-diversity and adaptive-optics methods.

Optical system and method for angle-dependent reflection or transmission measurement

Abstract: An angle-dependent reflectometer or transmissometer includes an optical imaging array in the incident and reflected or transmitted light path that breaks up an incident light beam into mutually spatially incoherent light bundles. The individual light bundles are then focused to a common spot by a high numerical aperture objective lens so as to provide a range of incidence angles on a sample surface. In a reflectometer, reflected light returns through the objective lens and imaging array and is imaged onto a detector array where different incidence and reflection angles are received by different groups of detection elements. In the angle-dependent transmissometer, the imaging array and high numerical aperture focusing objective lens are used for illuminating a spot on the sample, with a second high numerical aperture collection objective lens and detector array used for receiving transmitted light over a wide range of collection angles. The angle-dependent reflectance or transmittance measurement provided by the detector array can be analyzed to determine a desired characteristic parameter of the illuminated area of the sample surface. For example, a periodic text pattern on a wafer or mask surface can be illuminated to obtain a linewidth measurement. The break up of the light by the imaging array into light bundles allows the spot size to be controlled independently of the range of illumination angles so that areas much larger than the diffraction limit can be illuminated.

Imager package substrate

Abstract: An image head assembly comprising: a substrate with at least a pair of apertures formed in the substrate; an optical assembly having at least a pair of pins that mate with the apertures within the substrate, the pins to the optical assembly being fixedly secured to the apertures within the substrate; an image sensor located between the apertures covered by a cover glass above the image sensor on the optical assembly; interface means for providing an electrical connection between the substrate and the image sensor; a lens system mounted on top the cover glass; and a single element blur filter contained within the lens system. The assembly contains a single element blur filter such as a cross-pleated blur filter. The lens system is prevented from being a reverse telephoto lens system with use of a blur filter that does not require a large back focus and is instead a telephoto lens system.

The Art and Science of Optical Design

Abstract: The Art and Science of Optical Design is a comprehensive introduction to lens design, covering the fundamental physical principles and key engineering issues. Several practical examples of modern computer-aided lens design are worked out in detail from start to finish. The basic theory and results of optics are presented early on in the book, along with a discussion of optical materials. Aberrations, and their correction, and image analysis are then covered in great detail. Subsequent chapters deal with design optimisation and tolerance analysis. Several design examples are then given, beginning with basic lens design forms, and progressing to advanced systems, such as gradient index and diffractive optical components. In covering all aspects of optical design, including the use of modern lens design software, this book will be invaluable to students of optical engineering as well as to anyone engaged in optical design at any stage.

Ultrasound transducer with focused ultrasound refraction plate

Abstract: A system for performing surgery by vibrational heating employs an ultrasonic transducer 80 for focusing a spherical ultrasound wave on a focal region. In one embodiment a refraction plate 410 having a spherical surface facing the transducer and a refracting surface with refracting pyramid elements 450 facing the subject causes the ultrasound beam to impinge on a plurality of overlapping focal regions and thereby expand the focal area of the transducer. In a second embodiment the refraction plate comprises a phased lens 600 having a constant thickness at any angular location but with its thickness varying linearly over 2π radians or multiples thereof.

Impact of lens aberrations on optical lithography

Abstract: All optical projection systems for microlithography depart from perfection because of various lens aberrations, especially when large image field size is combined with high numerical aperture (NA). Such aberrations have a variety of effects on lithographic imaging: shifts in the image position, image asymmetry, reduction of the process window, and the appearance of undesirable imaging artifacts. These undesirable effects are sometimes exacerbated through use of resolution enhancement techniques such as phase-shift masks or nonstandard illumination. This paper examines the impact of different types of aberrations on lithographic imagery through simulation. New techniques for measuring aberrations by examining lithographically printed resist patterns are considered.

Credit card with magnifying lens

Abstract: A financial transaction card (10) adapted for use in reading externally stored information includes a transparent, substantially non-foldable rigid base and a strip for carrying machine readable information (14). The rigid base comprises a magnifying lens (24). The lens is formed by machining a shallow cavity (204) in the rigid base; partially filling the cavity with a radiation curable liquid resin; impressing a lens pattern (36) on the surface of the resin with a die; and exposing the resin to radiation of sufficient intensity to cure the resin.

Dual PDLC-projection head-up display

Abstract: An optical system is provided that produces bright, high contrast head-up display images which are not adversely affected by the direct exposure to sunlight of the system's virtual image source. The optical system comprises a light source system which projects a focused light beam to a segmented, electronically-addressed polymer-dispersed liquid crystal ("PDLC")-type film, which serves as a primary image source. Selected segments of the image source are made transmissive while other selected segments scatter light. Accordingly, the portions of the focused light beam incident to transmissive segments are transmitted to form a real image, while the balance of the focused light beam is scattered. A stray light-blocking means, such as a lens/aperture combination, is employed to block the scattered light. The real image is projected onto an unsegmented, electronically-addressed PDLC-type film serving as an image screen. The image screen is the head-up display image source and replaces other emissive light sources in conventional head-up displays. The PDLC-type image screen is unsegmented so that there are no display elements to provide false information upon exposure to sunlight. Moreover, the image screen is highly forward scattering, so that stray sunlight incident to the image screen is forward scattered in the direction opposite to the image source, thereby preventing the reflection of sunlight into viewers' eyes. The light transmitted through the PDLC-type image screen comprises the head-up display image, which is then projected by a projection means, such as a concave mirror or lens, to the desired location for viewing as a virtual image.

Creating image-based VR using a self-calibrating fisheye lens

Abstract: Image-based virtual reality is emerging as a major alternative to the more traditional 3D-based VR. The main advantages of the image-based VR are its photoquality realism and 3D illusion without any 3D information. Unfortunately, creating content for image-based VR is usually a very tedious process. This paper proposes to use a non-perspective fisheye lens to capture the spherical panorama with very few images. Unlike most of camera calibration in computer vision, self-calibration of the fisheye lens poses new questions regarding the parameterization of the distortion and wrap-around effects. Because of its unique projection model and large field of view (near 180 degrees), most of the ambiguity problems in self-calibrating a traditional lens can be solved trivially. We demonstrate that with four fisheye lens images, we can seamlessly register them to create the spherical panorama, while self-calibrating its distortion and field of view.

Optical metrology tool and method of using same

Abstract: A metrology apparatus for determining bias or overlay error in a substrate formed by a lithographic process includes an aperture between the objective lens and the image plane adapted to set the effective numerical aperture of the apparatus. The aperture is adjustable to vary the effective numerical aperture of the apparatus and the aperture may be non-circular, for example, rectangular, to individually vary the effective numerical aperture of the apparatus in horizontal and vertical directions. To determine bias or overlay error there is provided a target having an array of elements on a substrate, the array comprising a plurality of spaced, substantially parallel elements having a length and a width, the sum of the width of an element and the spacing of adjacent elements defining a pitch of the elements, edges of the elements being aligned along a line forming opposite array edges, the distance between array edges comprising the array width. The numerical aperture is adjusted such that the pitch of the elements is less than or approximately equal to the ratio of the wavelength of the light source to the numerical aperture value of the optical metrology tool in the direction of the array edges, and the edges of the array are resolved with the optical metrology tool and the width of the array are measured to determine bias or overlay error in the substrate. A camera may be adapted to create a digital image of a target and the components of the digital image in the direction of the pitch of the elements, normal to the length of the elements, may be suppressed to resolve the edges of the array and measure the width of the array. Preferably, the means for suppressing components of the digital image comprises a microprocessor adapted to perform a fast Fourier transform on the digital image to convert image intensity to a spatial frequency domain and a filter to suppress high spatial frequency components of the image in the direction of the pitch of the elements.

Boundary integral methods applied to the analysis of diffractive optical elements

Abstract: We apply boundary integrals to the analysis of diffraction from both conductive and dielectric diffractive optical elements. Boundary integral analysis uses the integral form of the wave equation to describe the induced surface distributions over the boundary of a diffractive element. The surface distributions are used to determine the diffracted fields anywhere in space. In contrast to other vector analysis techniques, boundary integral methods are not restricted to the analysis of infinitely periodic structures but extend to finite aperiodic structures as well. We apply the boundary element method to solve the boundary integral equations and validate its implementation by comparing with analytical solutions our results for the diffractive analysis of a circular conducting cylinder and a dielectric cylinder. We also present the diffractive analysis of a conducting plate, a conducting linear grating, an eight-level off-axis conducting lens, an eight-level on-axis dielectric lens, and a binary dielectric lens that has subwavelength features.

Method and apparatus for simultaneous capture of a spherical image

Abstract: A method and apparatus for capture of a spherical image is disclosed. The present invention includes at least one camera having a lens with at least a 180° field-of-view for capturing a hemispherical image. In a first embodiment, a second hemispherical image is created corresponding to a mirror image of the hemispherical image captured by the camera. In a second embodiment, two back-to-back cameras capture first and second hemispherical images, respectively. In both embodiments, a converter combines the two images along their outside edges to form a single, spherical image. Finally, the converter stores the complete spherical image for later retrieval and perspective corrected viewing.

Electronic imaging apparatus

Abstract: PROBLEM TO BE SOLVED: To provide an electronic image pickup device in which a lens system can easily be exchanged to a different image pickup element and can easily deal with model change is good without the fear of wasting an expensive beam splitter and an image pickup element when the image pickup lens system breaks down. SOLUTION: The beam splitter 27 and the image pickup element 33 are incorporated in an optical finder unit with optical parts for optical finder. The optical finder unit is constituted of a finder case storing the optical parts for finder and a holding member holding the beam splitter 27 and the image pickup element 33. The image pickup face of the image pickup element 33 is slantingly arranged against the incident luminous flux of the beam splitter 27. Incident luminous flux to the image pickup element 33 is reflected twice in the beam splitter and the incident luminous flux of a finder optical system 35 to the finder passes through the beam splitter 27 without reflection.