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Showing papers on "Spatial filter published in 2000"


Journal ArticleDOI
TL;DR: Off-axis holograms recorded with a CCD camera are numerically reconstructed with a calculation of scalar diffraction in the Fresnel approximation and the zero order of diffraction and the twin image are digitally eliminated by means of filtering their associated spatial frequencies in the computed Fourier transform of the hologram.
Abstract: Off-axis holograms recorded with a CCD camera are numerically reconstructed with a calculation of scalar diffraction in the Fresnel approximation. We show that the zero order of diffraction and the twin image can be digitally eliminated by means of filtering their associated spatial frequencies in the computed Fourier transform of the hologram. We show that this operation enhances the contrast of the reconstructed images and reduces the noise produced by parasitic reflections reaching the hologram plane with an incidence angle other than that of the object wave.

948 citations


Journal ArticleDOI
TL;DR: A new coherent anti-Stokes Raman scattering (CARS) microscopy system with a collinear configuration for use in the fingerprint region is developed and CARS imaging of a viable yeast cell is attempted.
Abstract: We have developed a new coherent anti-Stokes Raman scattering (CARS) microscopy system with a collinear configuration for use in the fingerprint region. The system consists of a picosecond laser system and a transmission-type laser scanning microscope without a pinhole in front of the detector. The observable Raman-shift region is 900–1750 cm-1, the spectral resolution is 30 cm-1, and the spatial resolution is smaller than 1 µm in the lateral direction and 3.2 µm in the depth direction, with objectives with a numerical aperture of 0.65. CARS spectra and images of polystyrene beads are demonstrated, and CARS imaging of a viable yeast cell is attempted.

208 citations


Patent
28 Dec 2000
TL;DR: In this article, volume holographic elements were made from Bragg diffractive gratings in photo-thermo-refractive (PTR) glass with absolute diffraction efficiency ranging from greater than approximately 50% up to greater than 93% and total losses below 5%.
Abstract: Novel volume holographic elements were made from Bragg diffractive gratings in photo-thermo-refractive (PTR) glass with absolute diffraction efficiency ranging from greater than approximately 50% up to greater than approximately 93% and total losses below 5%. Both transmitting and reflecting volume diffractive elements were done from PTR glasses because of high spatial resolution enabling recording spatial frequencies up to 10000 mm−1. The use of such diffractive elements as angular selector, spatial filter, attenuator, switcher, modulator, beam splitter, beam sampler, beam deflectors controlled by positioning of grating matrix, by a small-angle master deflector or by spectral scanning, selector of particular wavelengths (notch filter, add/drop element, spectral shape former (gain equalizer), spectral sensor (wavelength meter/wavelocker), angular sensor (pointing locker), Bragg spectrometer (spectral analyzer), transversal and longitudinal mode selector in laser resonator were described. Combinations of those elements in the same volume are available too.

121 citations


Journal ArticleDOI
TL;DR: Results are presented showing a rapid increase in Strehl ratio and focal spot quality as the system corrects for deliberately introduced aberrations.
Abstract: We describe the practical implementation of a closed-loop adaptive-optics system incorporating a novel modal wave-front sensor. The sensor consists of a static binary-phase computer-generated holographic element, which generates a pattern of spots in a detector plane. Intensity differences between symmetric pairs of these spots give a direct measure of the Zernike mode amplitudes that are present in the input wave front. We use a ferroelectric liquid-crystal spatial light modulator in conjunction with a 4–f system and a spatial filter as a wave-front correction element. We present results showing a rapid increase in Strehl ratio and focal spot quality as the system corrects for deliberately introduced aberrations.

103 citations


Journal ArticleDOI
TL;DR: A general expression for the isoplanatic angle thetaM of a system with M mirrors is derived in the limiting case of infinitely large apertures and Kolmogorov turbulence, which is a function only of the turbulence vertical profile, is scalable with wavelength, and is independent of the telescope diameter.
Abstract: Turbulence correction in a large field of view by use of an adaptive optics imaging system with several deformable mirrors (DM's) conjugated to various heights is considered. The residual phase variance is computed for an optimized linear algorithm in which a correction of each turbulent layer is achieved by applying a combination of suitably smoothed and scaled input phase screens to all DM's. Finite turbulence outer scale and finite spatial resolution of the DM's are taken into account. A general expression for the isoplanatic angle thetaM of a system with M mirrors is derived in the limiting case of infinitely large apertures and Kolmogorov turbulence. Like Fried's isoplanatic angle theta0,thetaM is a function only of the turbulence vertical profile, is scalable with wavelength, and is independent of the telescope diameter. Use of angle thetaM permits the gain in the field of view due to the increased number of DM's to be quantified and their optimal conjugate heights to be found. Calculations with real turbulence profiles show that with three DM's a gain of 7-10x is possible, giving the typical and best isoplanatic field-of-view radii of 16 and 30 arcseconds, respectively, at lambda = 0.5 microm. It is shown that in the actual systems the isoplanatic field will be somewhat larger than thetaM owing to the combined effects of finite aperture diameter, finite outer scale, and optimized wave-front spatial filtering. However, this additional gain is not dramatic; it is less than 1.5x for large-aperture telescopes.

100 citations


Patent
17 Oct 2000
TL;DR: In this article, a method and apparatus for performing optical coherence tomography using a wavelength multiplexed source is provided, where a collimating element and a diffraction grating are used to force each emitter within the array to lase at a distinct wavelength.
Abstract: A method and apparatus for performing optical coherence tomography using a wavelength multiplexed source is provided. The single output beam of the source is of a large bandwidth, thus providing a high resolution tomography system. In order to achieve high contrast as well, the wavelength multiplexed source has minimal wavelength separation between spectrally adjacent lasers and has an output beam with an approximately Gaussian spectral shape. The source is preferably comprised of one or more multi-gain element arrays multiplexed together within a single external resonator cavity. Interposed between the array and the resonator cavity output coupler are a collimating element and a diffraction grating. The collimating element can be a refractive optic, a reflective optic, or, for some applications, a ¼ pitch GRIN lens. The diffraction grating can either be transmissive or reflective. The combination of the diffraction grating and the collimating element forces each emitter within the array to lase at a distinct wavelength. In order to achieve an overall bandwidth greater than the gain bandwidth of a single emitter array, either multiple arrays of differing center wavelength are packaged together or a large array is used with a laterally varying quantum well thickness or epitaxy. An intracavity spatial filter can be used to improve the beam quality and reduce cross-talk. An optical coherence tomography imaging system is coupled to the resonator cavity.

100 citations


Patent
21 Mar 2000
TL;DR: In this article, a spatial filter is designed so as to be effective at separating up and down propagating acoustic energy over substantially the entire range of non-horizontal incidence angles in the fluid medium.
Abstract: An improved de-ghosting method and system that utilizes multi-component marine seismic data recorded in a fluid medium. The method makes use of two types of data: pressure data that represents the pressure in the fluid medium, such as sea water, at a number of locations; and vertical particle motion data that represents the vertical particle motion of the acoustic energy propagating in the fluid medium at a number of locations within the same spatial area as the pressure data. The vertical particle motion data can be in various forms, for example, velocity, pressure gradient, displacement, or acceleration. A spatial filter is designed so as to be effective at separating up and down propagating acoustic energy over substantially the entire range of non-horizontal incidence angles in the fluid medium. The spatial filter is applied to either the vertical particle motion data or to the pressure data, and then combined with the other data to generate pressure data that has its up and down propagating components separated.

97 citations


Patent
26 May 2000
TL;DR: An improved method and apparatus for microwave imaging of an inhomogeneous target, in particular of biological tissue, compensates for the interactions between active antennae and nonactive antennae as discussed by the authors.
Abstract: An improved method and apparatus for microwave imaging of an inhomogeneous target, in particular of biological tissue, compensates for the interactions between active antennae and nonactive antennae Measured electric field data are processed in magnitude and phase form so that unwrapped phase information may be used directly in the image reconstruction Initial finite element measurements and calculations are used to determine the perimeter dimensions of the target being examined, resulting in more accurate image reconstructions An improved regularization technique is a hybrid of a Marquardt regularization scheme with a spatial filtering technique and a Tikhonov regularization scheme An improved switching matrix enables simultaneous sampling of electric field data from a plurality of receiving antennae

97 citations


Journal ArticleDOI
TL;DR: This work reformulates the imaging process as a sequential estimation of the locations of astronomical sources and develops an extended CLEAN algorithm, which allows the insertion of other array signal processing techniques for direction finding and gives estimates of the expected image quality and the amount of interference suppression that can be achieved.
Abstract: Radio-astronomical observations are increasingly contaminated by interference, and suppression techniques become essential. A powerful candidate for interference mitigation is adaptive spatial filtering. We study the effect of spatial filtering techniques on radio-astronomical imaging. Current deconvolution procedures, such as CLEAN, are shown to be unsuitable for spatially filtered data, and the necessary corrections are derived. To that end, we reformulate the imaging (deconvolution/calibration) process as a sequential estimation of the locations of astronomical sources. This not only leads to an extended CLEAN algorithm, but also the formulation allows the insertion of other array signal processing techniques for direction finding and gives estimates of the expected image quality and the amount of interference suppression that can be achieved. Finally, a maximum-likelihood (ML) procedure for the imaging is derived, and an approximate ML image formation technique is proposed to overcome the computational burden involved. Some of the effects of the new algorithms are shown in simulated images.

94 citations


Patent
11 Dec 2000
TL;DR: In this article, a combination of temporal and spatial filters are used to substantially suppress the ghost artifacts in the resulting sequence of images, and the spatial filter receives spatial filter coefficients used in the filtering process.
Abstract: An apparatus and method for accelerating magnetic resonance imaging by decreasing the number of sequential phase encodes (undersampling). Image reconstruction of undersampled k-space data can cause ghost artifacts to be produced in the resulting sequence of images. A combination of temporal and spatial filters are used to substantially suppress the ghost artifacts. Additionally, the spatial filter receives spatial filter coefficients used in the filtering process. The spatial filter coefficients are adaptively or dynamically generated so that the coefficients are provided to the spatial filter while generating the sequence of images.

90 citations


Journal ArticleDOI
TL;DR: In this paper, a spatial filter is placed at the Fourier plane to remove the periodic grating structure of the fabric from the image and morphological operations with a critically selected structuring element are then applied to the image after suitable pre-processing.
Abstract: Morphological operations such as erosion and opening are applied to both direct and spatially filtered images of test fabrics to identify defects. Detecting defects morpholog ically on spatially filtered images of fabrics produces better results, particularly when the fabric is fine and contains defects of small size. The diffraction pattern of the test fabric is obtained optically by illuminating it with a collimated laser beam. A spatial filter is placed at the Fourier plane to remove the periodic grating structure of the fabric from the image. Morphological operations with a critically selected structuring element are then applied to the image after suitable pre-processing.

Journal ArticleDOI
TL;DR: It is demonstrated that the false alarm probability for a pixel containing object flux will never exceed the corresponding probability for an blank-sky pixel, provided the convolution kernel appropriately, which allows confident rejection of cosmic rays superposed on real objects.
Abstract: We present a convolution-based algorithm for finding cosmic rays in single well-sampled astronomical images. The spatial filter used is the point-spread function (approximated by a Gaussian) minus a scaled delta function, and cosmic rays are identified by thresholding the filtered image. This filter searches for features with significant power at spatial frequencies too high for legitimate objects. Noise properties of the filtered image are readily calculated, which allows us to compute the probability of rejecting a pixel not contaminated by a cosmic ray (the false alarm probability). We demonstrate that the false alarm probability for a pixel containing object flux will never exceed the corresponding probability for a blank-sky pixel, provided we choose the convolution kernel appropriately. This allows confident rejection of cosmic rays superposed on real objects. Identification of multiple-pixel cosmic-ray hits can be enhanced by running the algorithm iteratively, replacing flagged pixels with the background level at each iteration.

Patent
17 Mar 2000
TL;DR: In this paper, a laser printer utilizes a total internal reflection spatial light modulator that is optimized to work with a partially coherent laser source, where a spatial filter having a slit passes designated diffracted light which corresponds to an applied electric field and is ultimately imaged onto an image plane by way of an imaging lens.
Abstract: A laser printer utilizes a total internal reflection spatial light modulator that is optimized to work with a partially coherent laser source. The laser source is a laser diode array having a plurality of multi-mode emitters. The spatial light modulator diffracts light from said laser source according to an applied electric field. A spatial filter having a slit passes designated diffracted light which corresponds to an applied electric field and the light is ultimately imaged onto an image plane by way of an imaging lens.

Patent
30 Nov 2000
TL;DR: In this paper, an optical pickup apparatus having compatibility with a recodable compact disk (CD-R) and a digital video disk (DVD), which uses a wavelength of one of a first light beam and a second light beam according to the recording medium to be used.
Abstract: An optical pickup apparatus having compatibility with a recodable compact disk (CD-R) and a digital video disk (DVD), which uses a wavelength of one of a first light beam and a second light beam according to the recording medium to be used. In the optical pickup apparatus, laser light sources emit a first light beam having a relatively shorter wavelength for the DVD and a second light beam having a longer wavelength for the CD-R, respectively. An objective lens has a predetermined focal length in accordance with the position of an information recording surface in the DVD. An optical path control unit controls the path of light beams so that the light beam emitted from one of the laser light sources is directed to the objective lens and the light output from the objective lens is directed to the optical detection unit. A phase shift unit which is located between the optical path control unit and the objective lens, shifts the phase of the second light proceeding from the optical path control unit to the objective lens, to thereby reduce the size of a beam spot which is formed on a position of the information recording surface in the CD-R.

Journal ArticleDOI
TL;DR: In this paper, an approach to large-eddy simulation is developed whose subgrid-scale model incorporates Eulerian time-domain filtering, in contrast to conventional approaches that exploit spatial filtering.
Abstract: An approach to large-eddy simulation is developed whose subgrid-scale model incorporates Eulerian time-domain filtering, in contrast to conventional approaches that exploit spatial filtering. For applications to large-eddy simulation, time-domain filters enjoy certain advantages relative to spatial filters. Among these, they more naturally commute with differentiation operators than do spatial filters, and there is typically wide separation between numerical truncation error and the dissipation of the subgrid-scale model. Eulerian time-domain filtering is most appropriate for flows whose large coherent structures convect approximately at a common characteristic velocity. Such flows include jets, mixing layers, and wakes. The method is demonstrated in the large-eddy simulation of a heated, subsonic, axisymmetric jet, and results are compared with those obtained from well-resolved direct numerical simulation

Journal ArticleDOI
TL;DR: In this article, the authors study the effect of spatial filtering techniques on radio astronomical imaging and derive a maximum likelihood procedure for the imaging and an approximate ML image formation technique to overcome the computational burden involved.
Abstract: Radio-astronomical observations are increasingly contaminated by interference, and suppression techniques become essential. A powerful candidate for interference mitigation is adaptive spatial filtering. We study the effect of spatial filtering techniques on radio astronomical imaging. Current deconvolution procedures such as CLEAN are shown to be unsuitable to spatially filtered data, and the necessary corrections are derived. To that end, we reformulate the imaging (deconvolution/calibration) process as a sequential estimation of the locations of astronomical sources. This not only leads to an extended CLEAN algorithm, the formulation also allows to insert other array signal processing techniques for direction finding, and gives estimates of the expected image quality and the amount of interference suppression that can be achieved. Finally, a maximum likelihood procedure for the imaging is derived, and an approximate ML image formation technique is proposed to overcome the computational burden involved. Some of the effects of the new algorithms are shown in simulated images. Keywords: Radio astronomy, synthesis imaging, parametric imaging, interference mitigation, spatial filtering, maximum likelihood, minimum variance, CLEAN.

Journal ArticleDOI
TL;DR: In this article, the reflected image of a diffraction limited focused spot is investigated using confocal solid immersion microscopy and it is shown that the spot's image shows aberrations when reflected off objects with optical indexes lower than that of the solid immersion lens (SIL) material.
Abstract: The reflected image of a diffraction limited focused spot is investigated using confocal solid immersion microscopy. We find that the spot’s image shows aberrations when reflected off objects with optical indexes lower than that of the solid immersion lens (SIL) material. We demonstrate that such aberrations are only apparent and that the actual size of the spot at the SIL/object interface remains diffraction limited. The aberrations are due to lateral waves at the SIL surface. These von Schmidt waves originate from the total internal reflected components of a diverging spherical wave front. We make use of this image aberration in conjunction with the spatial filtering inherent to confocal microscopy in order to dramatically enhance the optical contrast of objects with low optical indexes.

Journal ArticleDOI
TL;DR: It is shown that a +/-150-microrad stainless-steel cone pinhole will pass a full-energy NIF ignition pulse with required margins for misalignment and for smoothing by spectral dispersion.
Abstract: We present results from a major experimental effort to understand the behavior of spatial filter pinholes and to identify and demonstrate a pinhole that will meet the requirements of the National Ignition Facility (NIF). We find that pinhole performance depends significantly on geometry and material. Cone pinholes are found to stay open longer and to cause less backreflection than pinholes of more conventional geometry. We show that a ±150-µrad stainless-steel cone pinhole will pass a full-energy NIF ignition pulse with required margins for misalignment and for smoothing by spectral dispersion. On the basis of a model fitted to experimental results, a ±125-µrad stainless-steel cone pinhole is also projected to meet these requirements.

Journal ArticleDOI
TL;DR: The optical characterization of a fiber-connected planar optics beam combiner dedicated to astronomical interferometry for two telescopes is presented and the intrinsic polarization-maintaining property of thePlanar optics component is characterized.
Abstract: The optical characterization of a fiber-connected planar optics beam combiner dedicated to astronomical interferometry for two telescopes is presented. The beam combiner, fully integrated on a single 5 mm × 40 mm glass chip, is tested as the central part of an astronomical instrument. The single-mode waveguides are made by silver-ion-exchange technology upon glass substrates and provide spatial filtering, which improves the visibility measurement accuracy by selecting only the fundamental mode of the beams at the telescope focal plane. A global optical throughput of 43% is measured, and the sources of losses are identified and examined in detail. Solutions for improving this throughput are proposed. High and stable contrasts are obtained with a 1.55-µm laser diode (≳96%) and with a white-light source (∼92%) in the astronomical H filter (1.43 µm; 1.77 µm). The need for accurate control of differential instrumental polarization is demonstrated. In this context the intrinsic polarization-maintaining property of the planar optics component is characterized. This validation of the important potential uses of integrated planar optics should be valuable for future design of optical telescope arrays.

Patent
17 Oct 2000
TL;DR: In this paper, a method and apparatus for achieving broad gain bandwidth in a Raman amplifier using a wavelength multiplexed pump source is provided, where the pump source offers high power, broad bandwidth, and the ability to tailor the pump spectrum, thus providing a means to achieve gain flattening within a specific band of the RAMan amplifier.
Abstract: A method and apparatus for achieving broad gain bandwidth in a Raman amplifier using a wavelength multiplexed pump source is provided. The pump source offers high power, broad bandwidth, and the ability to tailor the pump spectrum, thus providing a means to achieve gain flattening within a specific band of the Raman amplifier. The pump source is preferably comprised of one or more multi-gain element arrays multiplexed together within a single external resonator cavity. Interposed between the array and the resonator cavity output coupler are a collimating element and a diffraction grating. The collimating element can be a refractive optic, a ¼ pitch GRIN lens, or a reflective optic. The diffraction grating can either be transmissive or reflective. The combination of the diffraction grating and the collimating element forces each emitter within the array to lase at a distinct wavelength. In order to achieve an overall bandwidth greater than the gain bandwidth of a single emitter array, either multiple arrays of differing center wavelength are packaged together or a large array is used with a laterally varying quantum well thickness or epitaxy. An intracavity spatial filter can be used to improve the beam quality and reduce cross-talk between emitters.

Patent
Bruce W. Smith1
29 Jun 2000
TL;DR: In this paper, an angular specific transmission filter was introduced into this Fraunhofer diffraction field of the mask, allowing for a practical approach to frequency filtering, where zero-order mask diffraction information is reduced in an alternative pupil plane of the objective lens.
Abstract: An image enhancement apparatus and method are disclosed. The apparatus consists of a spatial frequency filter (12) where zero order mask diffraction information is reduced in an alternative pupil plane of the objective lens (9), specifically just beyond the mask plane. By introducing an angular specific transmission filter (12) into this Fraunhofer diffraction field of the mask (8), user accessibility is introduced, allowing for a practical approach to frequency filtering. This frequency filtering is accomplished using a specifically designed interference filter (14, 15) coated over a transparent substrate (16). Alternatively, filtering can also be accomplished in a complementary region near the wafer image plane or in both near-mask and near-wafer planes.

Journal ArticleDOI
TL;DR: Wavelet-based filters are useful for building binding parameter maps without loss of the original spatial resolution of the PET scanner, and can be extended far beyond the multi-injection protocol.

Patent
04 Mar 2000
TL;DR: In this paper, a method and apparatus for inspecting a surface of a semiconductor wafer having repetitive patterns for contaminant particles using scattered light by illuminating an area on the surface with two beams of light at different approach angles which are independent from each other and then imaging the area illuminated onto a camera positioned above the surface using an imaging lens.
Abstract: A method and apparatus for inspecting a surface of a semiconductor wafer having repetitive patterns for contaminant particles using scattered light by illuminating an area on the surface with two beams of light at different approach angles which are independent from each other and then imaging the area illuminated onto a camera positioned above the surface using an imaging lens. Each light beam striking the surface of the semiconductor wafer produces a Fourier diffraction pattern of light scattered from the surface in the back focal plane of the imaging lens. The two diffraction patterns are offset from each other if the two approach angles are not symmetrically disposed relative to an axis of the wafer. In setting up the apparatus, the angle of incidence of one of the beams is adjusted to shift one of the diffraction patterns, if necessary, so that it overlaps the other diffraction pattern. In this way, a spatial filter having masking bars sized and shaped to mask off the diffraction pattern from one beam will also mask off the diffraction pattern from the other beam. If the two approach angles are symmetrically disposed, then the two diffraction patterns overlap and adjustment of the angle of incidence of one of the beams is not necessary. The apparatus includes an arrangement for independently setting each one of the two approach angles and independently adjusting the angle of incidence of each light beam.

Patent
29 Aug 2000
TL;DR: In this paper, an image analyzer manipulates the filter kernel as a function of the image parameters so that the system produces a filtered image, adaptable in real time, as a result of the unfiltered image, external rules, predetermined constraints, or combinations thereof.
Abstract: A system for adaptively filtering an image so as to reduce a noise component associated with the image includes an image analyzer for determining image parameters related to the image. The system also includes a spatial filter, having an adjustable kernel responsive to the image parameters, for filtering the image sequence. The image analyzer manipulates the filter kernel as a function of the image parameters so that the system produces a filtered image, adaptable in real time, as a function of the unfiltered image, external rules, predetermined constraints, or combinations thereof. The spatial filter includes a time-invariant section and an adaptable section. The time-invariant section preferably applies a plurality of filters to the image, each of the filters having a distinct frequency response, so as to produce a plurality of distinct filtered outputs. The adaptable section scales each of the plurality of distinct filtered outputs with a corresponding distinct weighting value to produce a plurality of scaled filtered outputs, and combines the plurality of scaled filtered outputs to produce a composite filtered output.

Journal ArticleDOI
TL;DR: It is shown how the temporal gradient can be compromised by temporal aliasing arising from motion and how appropriate post-sampling spatial filtering improves the situation and a benefit of using higher-order gradient estimators is demonstrated.
Abstract: The accuracy of gradient-based optical flow algorithms depends on the ability to measure intensity gradients accurately. We show how the temporal gradient can be compromised by temporal aliasing arising from motion and how appropriate post-sampling spatial filtering improves the situation. We also demonstrate a benefit of using higher-order gradient estimators.

Journal ArticleDOI
TL;DR: In this article, a master-oscillator power amplification using a broad-area laser diode (BAL) emitting at a wave length of λ = 780 nm was reported.
Abstract: We report on master-oscillator power amplification using a broad-area laser diode (BAL) emitting at a wave- length of λ = 780 nm. The master oscillator is an injection- locked single-mode diode laser delivering a seeding beam of 35 mW, which is amplified in double pass through the BAL up to 410 mW. After beam shaping and spatial filtering by a single-mode fibre we obtain a clean Gaussian beam with a maximum power of 160 mW. There is no detectable contri- bution of the BAL eigenmodes in the spectrum of the output light. This laser system is employed for operation of a 87 Rb magneto-optical trap (MOT) and for near-resonant absorption imaging in a Bose−Einstein condensation experiment.

Journal ArticleDOI
TL;DR: In this paper, the influence of structured delayed optical feedback (SDOF) on a broad area laser is investigated experimentally with a miniature-sized convex external mirror, which takes into account the small time scales involved in semiconductor laser dynamics by employing short external resonator lengths.
Abstract: The influence of structured delayed optical feedback (SDOF) on a broad area laser is investigated experimentally. SDOF is realized with a miniature-sized convex external mirror. The setup takes into account the small time scales involved in semiconductor laser dynamics by employing short external resonator lengths. Careful choice of the feedback parameters leads to a narrow single-lobe farfield even at high pump currents. The experimental results confirm earlier microscopic dynamic simulations by O. Hess et al. predicting that SDOF might be capable of stabilizing the emission of broad area lasers.

Journal ArticleDOI
TL;DR: It is demonstrated how color-opponent detectors observed within the vertebrate visual system can be easily defined by linear filters within this representation of spatiochromatic Fourier transform, which explores a new form of the Cauchy-Schwartz inequality applied to complex-valued scalar products.
Abstract: We consider how to interpret, filter, and cross-correlate complex-value color (hue and saturation) images by using a single discrete Fourier transform: the spatiochromatic discrete Fourier transform. The model defines new types of spatiochromatic oriented sinusoidal gratings, termed rainbow gratings, which encode the variation of color over space. We demonstrate how color-opponent detectors observed within the vertebrate visual system can be easily defined by linear filters within this representation. This model also allows us to filter and detect both spatial and chromatic patterns in images by using a single cross-correlation procedure. In doing so, we explore a new form of the Cauchy-Schwartz inequality applied to complex-valued scalar products. Results demonstrate the power of this form of spatiochromatic matched filtering in detecting signals embedded in such a significant amount of noise that they are not visible to the unaided human eye.

Proceedings ArticleDOI
13 Jul 2000
TL;DR: In this paper, a novel adaptive spatial-temporal technique for clutter rejection is proposed, which is based on a multi-parametric approximation of clutter which, after estimation of parameters, leads to an adaptive spatialtemporal filter.
Abstract: In IRST applications, cluttered backgrounds are typically much more intensive than the equivalent sensor noise and intensity of the targets to be detected. This necessitates the development of efficient clutter rejection technology for track initialization and reliable target detection. Experimental study shows that the best existing spatial filtering techniques allow for clutter suppression up to 10 dB, while the desired level (for the reliable detection/tracking) is 25-30 dB or higher. This level of clutter suppression can be achieved only by implementing spatial-temporal rather than spatial filtering. In addition, the clutter rejection algorithm should be supplemented by a jitter compensation technique. Otherwise, due to the blurring effect, temporal filtering cannot be applied effectively. This paper discusses a novel adaptive spatial-temporal technique for clutter rejection. The algorithm is developed on the basis of the application of robust and adaptive methods that are invariant to the prior uncertainty with respect to statistical properties of clutter and adaptive with respect to its variability. The developed clutter rejection technique is based on a multi-parametric approximation of clutter which, after estimation of parameters, leads to an adaptive spatial-temporal filter. The coefficients of the filter are calculated adaptively to guarantee a minimum of empirical mean-square values of the filtering residual noise for every time moment. The adaptive spatial-temporal filtering allows one to suppress any background, regardless of its spatial variation. Simultaneously, the algorithm estimates LOS drift and allows for jitter compensation. Results of simulation show that the algorithm gives a tremendous gain compared to the best existing spatial techniques.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Patent
19 May 2000
TL;DR: In this article, a scanning optical system, including a laser for generating an excitation beam of coherent light and a lens to direct the beam of light on a columnar region of a sample container, was described.
Abstract: The apparatus and method of the present invention disclose a scanning optical system, including a laser (10) for generating an excitation beam of coherent light (80) and a lens (19) to direct the excitation beam of light (80) on a columnar region of a sample container (20), wherein a fluid sample is reacted with a fluorescently-labeled binding agent. The reacted sample undergoes minimal processing before it is placed into sample container (20). The sample is optically scanned, emitted fluorescence is collected by the lens (19) and directed as retrobeam (83) to a mirror (22) and through a collimating lens (23), and fluorescence excitation is recorded by a detector (31) from a plurality of columnar regions of the container (20), each columnar regino generally defined by the spot size (33) of the excitation beam (80) and the depth of field of detection. A spatial filter (24) of a sufficient pinhole diameter is selected to limit depth of field to allow simultaneous volumetric detection of fluorescent targets (45) in each columnar region.