Showing papers on "Spatial filter published in 1975"
TL;DR: The design, construction, alignment, and calibration of a photometric ellipsometer of the rotating-analyzer type is described, which allows complex reflectance ratios to be determined as continuous functions of wavelength from the near infrared to the near ultraviolet spectral range.
Abstract: We describe the design, construction, alignment, and calibration of a photometric ellipsometer of the rotating-analyzer type Data are obtained by digital sampling of the transmitted flux with an analog-to-digital converter, followed by Fourier transforming of the accumulated data with a dedicated minicomputer With an operating mechanical rotation frequency of 74 Hz, a data acquisition cycle requires less than 7 msec The intrinsic precision attainable is high because precision is limited only by shot noise or intrinsic source instabilities, even when relatively weak continuum lamps are used as light sources Precision may be improved by accumulating the data for consecutive cycles at a fixed wavelength The system allows complex reflectance ratios to be determined as continuous functions of wavelength from the near infrared to the near ultraviolet spectral range Data reduction programs can be modified to calculate complex refractive index or dielectric function spectra, or film thicknesses and refractive indices, as well as the usual ellipsometric parameters tanpsi, cosDelta
564 citations
IBM1
TL;DR: In this article, a monolithic array of three homostructure GaAs laser arrays with their mirror faces antireflection coated are operated in an external optical cavity built of spherical lenses and plane mirrors.
Abstract: Spatially coherent radiation from a monolithic array of three homostructure GaAs lasers is reported. The three lasers, with their mirror faces antireflection coated, are operated in an external optical cavity built of spherical lenses and plane mirrors. The spatially coherent beam formation makes use of the Fourier transformation property of the internal lenses. The transverse mode control is performed by a spatial filter. The optical peak power at room temperature of the device was measured to be 5 W, three times the power of a single laser in the array. From the synthesized far-field distribution which was evaluated, we conclude that the laser radiation is of spatial coherence.
74 citations
TL;DR: In this paper, a method of combining specially designed halftone screens with a spatial filtering process to obtain a non-monotonic, non-linear image processing system is described.
34 citations
01 Dec 1975
29 citations
Patent•
27 Jun 1975
TL;DR: In this article, two kinds of light sources, one of which emits a coherent light and the other of which emit incoherent light, are provided, and a spatial filter, having a plurality of arms which extend in predetermined directions from the center thereof, is provided on the focal plane of the transform lens.
Abstract: Two kinds of light sources, one of which emits a coherent light and the other of which emits incoherent light, are provided. The coherent light and incoherent light respectively emitted from the two different kinds of light sources, proceed on the same optical axis. A photomask, such as for an integrated-circuit, or other objects, which have linear straight line features and nonlinear defects, are simultaneously illuminated by the coherent light and incoherent light. The two kinds of light which pass through the photomask or other objects are transformed into a Fourier-transform pattern by a transform lens. A spatial filter, having a plurality of arms which extend in predetermined directions from the center thereof, is provided on the focal plane of the transform lens. The spatial filter suppresses the passing of coherent light having information of the linear straight line features. The coherent light which has information of the defects of the photomask is not suppressed by the spatial filter. The coherent light and incoherent light passing through the spatial filter are directed to an image plane. As a result thereof, an image of the photomask or other object, obtained by the incoherent light and an image of the defects of the photomask or other objects obtained by the coherent light, are simultaneously projected on each other on the image plane.
29 citations
TL;DR: Both small-scale and large-scale partial self-focusing produce phase distortions which result in loss of optical quality of the beam, and both can result in significant power loss as discussed by the authors.
Abstract: Both small-scale and large-scale partial self-focusing produce phase distortions which result in loss of optical quality of the beam. Both effects are herein studied and both can result in significant power loss. Incipient fine-scale self-focusing losses can be mitigated by spatial filtering. Nonlinear lensing, i.e., partial large-scale self-focusing, is more or less serious depending on the size of the target onto which the beam is to be focused.
28 citations
TL;DR: A unique optical feedback system for coherent optical data processing with the introduction of feedback is described, and the well-known transfer function for feedback systems is obtained in two dimensions.
Abstract: A unique optical feedback system for coherent optical data processing is described. With the introduction of feedback, the well-known transfer function for feedback systems is obtained in two dimensions. Operational details of the optical feedback system are given. Experimental results of system applications in image restoration, contrast control and analog computation are presented.
27 citations
TL;DR: The experimental and quantitative study of the measurement of the lateral spherical aberration with the shearing interferometer using Fourier imaging and the moire method is given and the fringe pattern directly illustrating the lateralherical aberration can be obtained by the proposed optical arrangement using the plane reference wavefront.
Abstract: The experimental and quantitative study of the measurement of the lateral spherical aberration with the shearing interferometer using Fourier imaging and the moire method is given. When the aberration of a camera lens with small f/number(1.7) is measured with an optical arrangement employing the spherical wavefront as a reference at the observation plane, the distortion correction of the obtained fringes is necessary. However, the fringe pattern directly illustrating the lateral spherical aberration can be obtained by the proposed optical arrangement using the plane reference wavefront, without correcting the fringe distortion.
26 citations
TL;DR: A technique is described for recording representations of space-variant optical systems as volume holograms, where the transfer-function holographic representations obtained are then placed in the Fourier plane of a coherent optical processor for playback.
Abstract: A technique is described for recording representations of space-variant optical systems as volume holograms. The transfer-function holographic representations obtained are then placed in the Fourier plane of a coherent optical processor for playback. Due to the space-variant nature of the systems represented, the input plane of the system to be represented holographically is spatially sampled. As a result, the volume hologram medium actually contains a number of holograms that have been angle multiplexed to avoid interference problems. Limitations associated with the thickness of the recording medium are calculated for imaging systems, and experimental results are presented for one lens and two lens magnifiers.
26 citations
TL;DR: In this article, the optical configuration comprises an imaging lens with the reference point source on the optical axis in the centre of the exit pupil of the lens and the spatial frequency band is determined by the aperture and is independent of object size.
Abstract: The optical configuration comprises an imaging lens with the reference point source on the optical axis in the centre of the exit pupil of the lens. The spatial frequency band is determined by the aperture and is independent of object size. In spite of the similarity to inline image plane holograms, image and intermodulation wavefront terms are separated by means of slit apertures in the recording step and matched spatial filters in the reconstruction step. Reconstruction is performed with thermal light, the interferograms can be displayed or printed directly on photographic paper.
24 citations
TL;DR: High quality holograms of flat objects are produced by developing an achromatic-fringe system that consists of a monochromatic but spatially incoherent source, a holographic beam splitting device, and a pair of Fourier transform lenses.
Abstract: High quality holograms of flat objects are produced by developing an achromatic-fringe system that consists of a monochromatic but spatially incoherent source, a holographic beam splitting device, and a pair of Fourier transform lenses. The effects of using an incoherent extended source and the transfer characteristics of the holograms are discussed. Emphasis is also placed on the advantages of developing lens Fourier transform holography along with the practical lens systems. A further possible extension of the system to attain high storage density as well as high quality holograms is proposed by making use of a new type of pseudorandom phase sequence.
Patent•
11 Sep 1975
TL;DR: In this paper, a spatial filter geometry consisting of flat layers of high and low dielectric constant dielectrics separated by air or other low-dielectric-constant materials was proposed to suppress sidelobe suppression in directional beam forming antennas.
Abstract: Sidelobe suppression in directional beam forming antennas is accomplished by means of a spatial filter. The filter geometry consists of flat layers of high dielectric constant dielectric separated by air or other low dielectric constant dielectric substance. The filter is placed directly over the antenna radiating aperture and its dielectric materials have dielectric constant and thickness values that effect full transmission of beam power in a selected beam direction and substantial rejection of it in other directions.
TL;DR: In this paper, the radius of curvature of the phase front associated with the Laguerre-Gaussian modes is chosen to be equal to the radii of the beam that is to be propagated.
Abstract: The radius of curvature of the phase front associated with the Laguerre-Gaussian modes is chosen equal to the radius of curvature of the beam that is to be propagated. After the beam parameters and the set of complex coefficients { y t n ] are calculated in one transverse plane they are obtained in any other plane using (3)-(5). This algorithm has been used to calculate the diffracted light rays and the intensity distribution throughout the focal volume of the focused laser beam for various proposed beam intensity distributions. The effect of nonlinear phase distortions of 0 2 B < 471 on the focused beam characteristics will be shown.
Patent•
01 Aug 1975
TL;DR: A beam focused synthetic aperture has a lens or antenna for receiving radiation in a receiving beam from an object of interest, a detector for receiving the radiation from the lens or antennas, and an output and display circuit for using and viewing the detector output, with delay means internal or external to the lens and antenna and between the object and detector and for producing the matched spatial filtering of signals from objects crossing the receiving beam, and with the detector producing a pulse for each object crossing the received beam as discussed by the authors.
Abstract: A beam focused synthetic aperture having a lens or antenna for receiving radiation in a receiving beam from an object of interest, a detector for receiving radiation from the lens or antenna, and an output and display circuit for using and viewing the detector output, with delay means internal or external to the lens or antenna and between the object and detector and for producing the matched spatial filtering of signals from objects crossing the receiving beam, and with the detector producing a pulse for each object crossing the receiving beam.
TL;DR: It is found that the resolution capability of the recording and reconstruction of a multicolor image from a plane hologram by spatial filtering in the Fourier plane is adequate for many practical applications.
Abstract: The recording and reconstruction of a multicolor image from a plane hologram by spatial filtering in the Fourier plane are discussed. Conditions under which the reconstructed images are free from color crosstalk are described and analyzed. Experimental results for confirming the analysis by a two-color reconstruction is presented. The spatial filter size and the information recording capability are determined from hologram recording parameters. It is found that the resolution capability of this method is adequate for many practical applications. Methods for recording and reconstruction of multicolor images without an imaging lens are also discussed. Many possible applications are suggested.
TL;DR: The Doppler frequency shift of coherent light reflected from rotating objects is used to obtain one-dimensional resolution much greater than the classical limit for aperture limited imaging systems.
Abstract: The Doppler frequency shift of coherent light reflected from rotating objects is used to obtain one-dimensional resolution much greater than the classical limit for aperture limited imaging systems. The Doppler information is processed by using the temporal and spatial filtering properties of modulated-reference-wave holograms. The holographic reconstruction is a superresolved image. Resolution improvements greater than 200 times the classical limit were obtained at good signal-to-noise ratios.
30 Oct 1975
TL;DR: In this paper, successive frames of digital images are coded using two-dimensional spatial transforms combined with DPCM in the temporal domain in terms of coding efficiency, storage requirements, computational complexity, and sensitivity to channel noise.
Abstract: Interframe coding of television images encompasses techniques which make use of correlations between pixel amplitudes in successive frames. Intraframe coding techniques that exploit spatial correlations can, in principle, be extended to include correlations in the temporal domain. In this paper, successive frames of digital images are coded using two-dimensional spatial transforms combined with DPCM in the temporal domain. Specific transform techniques investigated are the two-dimensional cosine and Fourier transforms. Due to DPCM encoding in the temporal domain, the hybrid transform/DPCM encoders require storage of only the single previous frame of data. Hardware implementation of the Fourier transform involves manipulation of complex numbers where the cosine transform does not. However, the Fourier transform is attractive because frame-to-frame motion compensation can be introduced directly in the phase plane by application of appropriate phase correction factors. Results are presented in terms of coding efficiency, storage requirements, computational complexity, and sensitivity to channel noise.
TL;DR: In this article, a cross-sectional mapping of a beam of progressive ultrasonic waves can be obtained by conventional light-diffraction techniques, i.e., by passing a collimated beam of light through the sound field.
Abstract: A theory is proposed from which a cross-sectional mapping of a beam of progressive ultrasonic waves can be obtained by conventional light-diffraction techniques, i.e., by passing a collimated beam of light through the sound field. To obtain sufficient information, the sound field must be rotated around its major axis for a series of optical measurements. These measurements, along a line perpendicular to the sound-beam axis, are to yield the strength and phase of the effective phase grating. As an extensive amount of data is needed to compute one map by two-dimensional Fourier transformation, a data-acquisition system and digital computer are required. However, in the constraint of linear acoustics, one set of measurements will permit the calculation of the sound field in all space.
Patent•
30 Jun 1975
TL;DR: In this paper, a method for suppression of optical noise in an optical spatial filtering system using highly coherent light is described, where the optical processing system remains stationary while the image-producing light moves laterally through the pattern with the output film, thus averaging out the noise effect at the output.
Abstract: Disclosed is a device and method for suppression of optical noise in an optical spatial filtering system using highly coherent light. In the disclosed embodiment, input photographic film to be processed in the system, and output photographic film to be exposed, are each mounted on lateral translation devices. During application of the coherent light for exposure of the output film, the two translation devices are moved in synchronism by a motor-driven gear and linkage assembly. The ratio of the resulting output film translation to the input film translation is equal to the magnification of the optical data processing system. The noise pattern associated with the lenses and other elements in the optical processing system remains stationary while the image-producing light moves laterally through the pattern with the output film, thus averaging out the noise effect at the output film.
TL;DR: In this paper, a holographic spatial filter for direction independent differentiation can be produced with a multiple exposure technique by superimposing four holographic gratings with slightly different grating constants.
Abstract: A holographic spatial filter for direction independent differentiation can be produced with a multiple exposure technique by superimposing four holographic gratings with slightly different grating constants. A theoretical description of the filter is given and the experimental realisation is explained. Finally some experimental results are presented.
01 Jan 1975
TL;DR: In this paper, the authors measured the optical transfer function of water in vitro by spatial filtering of the projected image of a slit in the Fourier Transform plane, using Moire fringes with a smooth and continuous variation of spatial frequency obtained by counter-rotating Ronchi rulings.
Abstract: Particulate matter of the sizes, concentrations, and refractive indices found in situ renders the Optical Transfer Function of water a real quantity. Modulation Transfer Function (MTF) is measured in vitro by spatial filtering of the projected image of a slit in the Fourier Transform plane. Analysis is by Moire fringes with a smooth and continuous variation of spatial frequency (nominally 0-40,000 cycles/radian) obtained by counter-rotating Ronchi rulings. The analogue of convolution of impulse responses is tested as the cascadability in a scattering medium of true sinusoidal MTF's. Coulter Counter techniques are used to measure differential particulate count in 15 channels up to 100 \mu m. Experimental data for various ranges and particle distributions are compared to theoretical predictions based on volume scattering functions (VSF) obtained by Mie scattering calculations and the Fourier transform conversion relating MTF and VSF first obtained by Willard Wells. The equipment is being repackaged for in-situ measurements to accompany forthcoming flood-illuminated SEGAIP (SELF GATED IN-WATER PHOTOGRAPHY) trials.
TL;DR: In this paper, a monolithic array of three GaAs laser arrays in a free-running mode is reported, with their mirror faces antireflection coated, operating in an external optical cavity built of spherical lenses and plane mirrors.
Abstract: Spatially coherent radiation from a monolithic array of three GaAs lasers in a free-running mode is reported. The lasers, with their mirror faces antireflection coated, are operated in an external optical cavity built of spherical lenses and plane mirrors. The spatially coherent-beam formation makes use of the Fourier-transformation property of the internal lenses. Transverse mode control is accomplished by a spatial filter. The optical cavity is similar to that used for the phase-controlled mode of spatially coherent-beam formation; only the spatial filters are different. In the far field (when restored by an external lens), the intensities of the lasers in the array are concentrated in a single laser beam of spatial coherence, without any grating lobes. The far-field distribution of the laser array in the free-running mode differs significantly from the interference pattern of the phase-controlled mode. The modulation characteristics of the optical waveforms of the two modes are also quite different because modulation is related to the interaction of the spatial filter with the longitudinal modes of the laser array within the optical cavity. The modulation of the optical waveform of the free-running mode is nonperiodic, confirming that the fluctuations of the optical fields of the lasers are random.
Patent•
25 Jul 1975
TL;DR: In this paper, the primary or first order diffraction light is directed to and focused on a spectrum selecting spatial filter for selecting the spectra which contribute to form a multi-color image reconstructed by the hologram.
Abstract: A white light source is employed for illuminating a color image hologram have no effect of diffusion. The primary or first order diffraction light is directed to and focused on a spectrum selecting spatial filter for selecting the spectra which contribute to form a multi-color image reconstructed by the hologram. The spatial filter is provided with a central slit of the width substantially equally to the band width of the spatial frequency peculiar to the object recorded and reconstructed. The spatial filter is further provided with a red filter and a blue filter on the opposite sides of the slit adjacent thereto. By providing the red and blue filters adjacent to the slit of the spatial filter, the brightness of the image reconstructed by the color halogram reconstructing system is markedly enhanced.
TL;DR: In this article, the authors considered the problem of detecting a far-field signal source of known location and waveform which generates a known signal field at an array aperture, and the power of the ambient noise field was considered to be a random function of space and time and the Bayes approach was used to derive optimum receiver structures and their performance.
Abstract: In practical underwater signal detection problems using an array, the statistics of the ambient noise field vary spatially and temporally. This paper considers the problem of detecting a farfield signal source of known location and waveform which generates a known signal field at an array aperture. The power of the ambient noise field is considered to be a random function of space and time and the Bayes approach is used to derive optimum receiver structures and their performance. For all cases considered, the optimum array processor either requires spatial filtering which is not accomplished by a beam former or requires spatial processing in addition to that provided by a beam former. The loss of detection performance due to uncertainty in the parameters of the ambient noise field is determined for several specific cases.Subject Classification: 60.20; 25.35.
01 Nov 1975
TL;DR: In this article, volume holograms are used to store representations of space-variant optical systems based on a sampled-input-plane recording scheme, where the holograms were placed in the Fourier plane of a coherent optical processor.
Abstract: : Volume holograms may be used to store representations of space-variant optical systems. The thick media contain angle-multiplexed transfer functions of the space-variant optical systems based on a sampled-input plane recording scheme. The holograms are placed in the Fourier plane of a coherent optical processor for playback. A potentially significant space savings over conventional optics may be achieved, in addition to the other advantages normally attributed to hologram optical elements. Recent developments in the theoretical and experimental investigation are presented. (Author)
TL;DR: In this paper, a method based on spatial-frequency filtering with auxiliary sampling was proposed for obtaining more-intense multiple images, where auxiliary lattices of the same period, translated from each other by arbitrary vectors, were used to reinforce each other.
Abstract: A method is derived for obtaining more-intense multiple images. The method is based upon spatial-frequency filtering with auxiliary sampling. This method is derived and realized physically. The spatial filter, composed of periodically spaced holes in a black screen, is placed in the Fourier plane of the two-dimensional object. Filters were used that included auxiliary lattices of the same period, translated from each other by arbitrary vectors; consequently the multiple images that are formed in the image plane are superimposed and reinforce each other.
TL;DR: A Laplace transform computer is described in which it is found that spatial bandlimiting is a restriction on its usefulness and a convergence filter is described along with a method to produce this and other spatial filters physically for optical processors.
Abstract: Data processing in coherent optical systems has been limited to a large extent by operations involving spectrum manipulations through the Fourier transform. By appropriate modification of the Green function kernel of the Rayleigh-Sommerfeld diffraction integral, it should be possible to obtain transform relationships between the input and output of a coherent processor, other than the Fourier transform. Cutrona has suggested a possible implementation for a Laplace transformer but has apparently not attempted a physical realization [ IRE Trans. Inf. TheoryIT-6, 386 ( 1960)]. In this study, a Laplace transform computer is described in which it is found that spatial bandlimiting is a restriction on its usefulness. To compensate for this bandlimiting, a convergence filter is described along with a method to produce this and other spatial filters physically for optical processors.
Patent•
28 Feb 1975
TL;DR: An optical processing system for a synthetic aperture radar moving target indicator or otherwise in which a graduated light filter provides minimum to a maximum transmission over a laser beam width is described in this article. But this system is not suitable for the detection of moving objects.
Abstract: An optical processing system for a synthetic aperture radar moving target indicator or otherwise in which a graduated light filter provides minimum to a maximum transmission over a laser beam width. The laser beam then shines through the filter, an exposed film containing a phase history and through one or more field stop slits or a spatial filter to an unexposed film. The filter compensates for the lack of an infinitely long laser beam required for a Fourier transform of the phase history into what is not but is mostly indistinguishable from a photographic image of stationary and/or moving targets. The filter suppresses false images sometimes called side-lobes.