Showing papers on "Optical filter published in 1976"

Optical notch filter utilizing electric dipole resonance absorption

Abstract: An optical notch filter having a suspension of small absorbing particles which blocks a narrow band of frequencies. The small absorbent particles are suspended as a colloidal system which can have either a solid, liquid or gas as host material. The absorbing particles can be incorporated in a solid matrix as a transmission filter or used on the surface of a mirror as a reflection filter. The filter can be tuned by an externally applied electric field or by applying hydrostatic pressure.

Optical analyzer for agricultural products

Abstract: An automatic test instrument for gaging the percentage of various constituents in organic substances by comparing the reflective optical density of the subject at various wavelengths. Narrow band optical filters are connected together in the form of a rotatable paddle wheel positioned so that the filters can be individually swept through the incident light path between the specimen and wideband light source. As the filter wheel turns, the band of light passed by each filter is progressively shifted with the changing angle of the filter relative to the light path. The filter wheel configuration includes opaque vanes extending from the ends of the filters to periodically interrupt the passage of light to the specimen. Photocells are positioned to sense the level of light reflected from the specimen. The output of the photocells is sampled at predetermined times relative to the rotation of the filter wheel to yield values indicative of reflected intensity at certain wavelengths. Using these values, an electronic circuit in one embodiment calculates three optical density difference values corresponding to moisture, protein and oil content of the specimen. The difference values are automatically inserted in three linear equations which are solved to obtain readings representing the true percentages of oil, water and protein contained in the specimen. Each time a new specimen is loaded for testing, the instrument is automatically calibrated against a standard sample, preferably Teflon (Trademark). The output of the photocells is amplified in a special circuit which subtracts the level of dark period current from the output when the photocells are illuminated.

Tunable Acousto-Optic Filters: An Overview

Abstract: The theory and practice of tunable acousto-optic filters are reviewed. Topics discussed include the basic principle of operation, filter characteristics and configurations. Experimental results of a noncollinear Te02 filter are also presented.

Water pollution monitoring using matched spatial filters

Abstract: Presented are some results obtained from the application of matched spatial filtering techniques to the identification of biological specimens called diatoms (i.e., water algae). A prototype semiautomatic optical processor has been developed that utilizes the Vander Lugt type complex spatial filters. We describe the optical filter averaging technique employed and discuss our semi in situ developing method for the filters. The advantage of this method with regards to the critical position requirements for time sharing optical filters is also presented. The filter holder is mounted on X, Y stages and precision positioned under the control of a PDP-11-40 computer.

Optical analysis system having rotating filters

Abstract: In an optical analysis system, six interference filters are mounted on a wheel on a cylindrical locus. The wheel rotates to move the filters in sequence through a beam of light and to vary the angle of incidence of the light to the filters as the filters move through the beam of light so that the wavelength passed by the filters is swept through a range of values. The intensity of light reflected from or transmitted through a test sample is detected to provide an indication of the reflective or transmissive optical density of the test sample at specific wavelengths. The angular position of each of the filters on the wheel is adjustable to make the range of light wavelengths transmitted by each filter adjustable.

Optical conversion method

Abstract: Disclosed is a method for converting an optical system, employing an electrooptic device in conjunction with a pair of crossed polarizing devices, between an activated mode and a deactivated mode. Embodiments in which the optical system is used as a neutral density filter, a selective color filter, or a light shutter, as applied to a television camera are described in which the electrooptic device and the polarizing analyzer are fixed with respect to the television camera, and the first polarizing device is selectively positioned in, or removed from, the optical path of the optical system to activate or deactivate the optical system, respectively. Where the optical system is used as a selective color filter to produce light beams of alternating colors in a field sequential color television system, deactivation of the optical system renders the television a black-and-white system.

Determination of the energy or pressure of a solar X-ray structure using X-ray filtergrams from a single filter

Abstract: While the X-ray fluxes measured through two different broadband filters can be used to derive the temperatures and emission measures of solar plasmas, it is generally assumed that no plasma parameters can be measured quantitatively with a single filtergram alone. We show that the thermal energy density (or pressure) of a solar plasma can be measured with an ideal single filtergram. Calculations have been done to compare the properties of the Skylab S-054 X-ray telescope filters to those of the ideal filter.

Optical filters using coupled light waves in mixed crystals

Abstract: Coupling of polarized optical waves in wurtzite II‐VI mixed crystals is studied. It is shown that these crystals provide narrow‐band optical filters over a wide spectral range.

Improvement in birefringent filters. 4: The alternate partial polarizer filter

Abstract: A design for a birefringent filter is proposed in which alternate polarizers are partial polarizers. Calculated performance characteristics of alternate partial polarizer filters (APP) are compared with those of Lyot and contrast element Lyot filters. These calculations show that the APP design has significant advantages in both transmission and profile shape. Using pulse techniques, partial polarizer systems are shown to be a natural evolution from the standard Lyot and contrast element Lyot systems. The APP filter using achromatic waveplates discussed in earlier papers of this series has been used to construct a universal alternate partial polarizer filter. This filter has a measured full width at half-maximum (FWHM) of 0.09 A at 5500 A and a transmission in polarized light of 38%. It is tunable from 4500 A to 8500 A. The measured characteristics of the filter agree well with theoretical predictions.

Laser radiation detection system

Abstract: A laser radiation detection system using a spatial/wavelength filter to "ulate" the response of a detector as a function of wavelength, allowing discrimination of laser sources against broad spectral sources, as well as wavelength determination

Airborne holography techniques for particle field analysis

Abstract: The three-dimensional recording and imaging of particle fields was perhaps the first practical application of holography and remains one of the most important. Holography continues as the only method by which high resolution viewing of dynamic particles dispersed through a volume can be achieved. Applications of holography in such studies are many, covering almost every field of The techniques and results of applications of holography are widely published and little new basic knowledge has been introduced in this area in nearly ten years. The field has been extremely dynamic, however, because of the many breakthroughs required t o make holographic application practical. Only a few brief introductory remarks will be made concerning basic holography, since these are amply covered in the references. In 1973, we began an extensive field program t o apply holography techniques t o problems of cloud physics. During these studies a variety of techniques have been investigated both in the laboratory as well as in the field. The program dealt not only with the problem of hologram recording, but also with data analysis and interpretation. One of the products of this program is the first airborne holography system for weather studies. This system has operated successfully in many flights and is currently considered an operational tool. Other ground-based cloud holocameras were used t o study ice, water, and snow clouds. These systems are capable of storing vast amounts of data in the form of holograms. To reduce and analyze these holograms is a tedius, time-consuming task that has spurred the search for automatic techniques for data reduction. Related studies have been conducted in other laboratories,6-8 and the first appears t o be that of Thompson and co-workers,6 who applied holography in the study of fog. During these studies, a number of unique techniques were applied and a number of unusual, previously unreported effects were observed. The purpose of this report is t o describe these applications and to report some of the more significant findings. Although the application is rather specific, the observations and methods apply t o a wide range of other applications. An optical hologram is a special type of recording of a light wave which stores all the information necessary to reconstruct an essentially identical light wave at a later time. The three-dimensional image of a field is viewed through a hologram as if the hologram were a window behind which the actual field was frozen in time. I t is a simple matter t o convert this virtual image (which lies behind the hologram) to a real spatial image (which lies on the viewer’s side of the hologram). A hologram is formed by mixing coherent light scattered from the field of interest (object beam) with a reproducible, mutually coherent (reference) beam and recording the intensity of the sum on a photographic emulsion or

Spot Shaping and Incoherent Optical Smoothing for Raster Scanned Imagery

Abstract: Raster in scanned imagery can be suppressed to improve visual observation of image detail. In the work reported here this is accomplished by optimal choice of the scanning spot and/or by optimal smoothing. Both techniques are based on selection of a Wiener filter. The optimal spot is shown to extend only over two scan lines, for scenes with 1 /f2 power spectra. The filter is designed to be used in an incoherent imaging system. It is constrained to a phase-only approximation of the optimum complex filter to avoid reducing light level in the optical system. Experimental results demonstrate the effectiveness of the filter design.

Narrowband wide field of view optical filter

Abstract: A wide angle narrowband optical filter is provided by an assembly in which a body member supports multiple absorption materials in a common optical path. Each of the multiple absorption materials contributes toward narrowing the spectral bandwidth region permitting transmittance of light energy. A bandpass glass color filter restricts light transmission to a relatively broad spectral range of approximately 250 nanometers and a selected coumarin dye material in solution used with a second solution of a selected rare earth material narrows the spectral range of transmittance. In a preferred embodiment an interference filter further narrows the transmitting bandwidth to approximately 12.5 nanometers at FWHM (measured at Full Width Half Maximum) in the spectral region which is desirably coincident with the wavelengths of light energy best transmitted in ocean waters.

Tunable Acoustooptic Filters And Their Applications To Spectroscopy

Abstract: Acoustically tunable narrow band optical filters are based on the phase-matched interaction of light and sound in certain crystals. With such filters, scanning in wavelength and adjustment of bandwidth can be done completely electronically, without mechanical devices. Such an approach can lead to reductions in instrument size and complexity, and facilitate incorporation of the spectrometer into computer-controlled systems. Some advantages over mechanical systems include rapid scanning, multiwavelength sampling, and fast, random access to spectral regions of interest. We review the basic interaction phenomena involved in the process. Parameters such as required acoustic power densities, bandwidths and angular apertures attainable, and the trade-offs among them are discussed. Acoustooptic filters based on presently available materials can now cover the visible and mid-infrared spectral regions. We describe the details of such systems, with emphasis on our own work in the mid-infrared. The potential of such filters for application in rapid scanning, random access and imaging spectroscopy is also discussed.© (1976) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Tunable metal film filters as narrowband ir laser reflectors

Abstract: An approximate mathematical description of tunable metal film reflector filters for the medium and far ir is derived. The absorptive film is characterized by two easily measured quantities, and a mirror reflectivity smaller than one is taken into account. The dependence of reflectivity, phase, and transmissivity on wavelength is studied. Expressions for the filter bandwidth and a lower limit of the bandwidth are obtained. Minimum losses depend primarily on the reflection coefficient of the mirror and not on the film properties. Two interesting configurations can be distinguished: one with high loss and small bandwidth (I) and one with low loss and large bandwidth (II). Measurements of bandwidth and minimum losses at 10 gm using Ge and ZnSe film substrates and gold and aluminum films show very good agreement with theory. Typical experimental results for configuration I yielded a 4.6% bandwidth (given as fraction of the free spectral range) and 2.9% additional reflection losses (caused by the insertion of the film). Smaller losses (≈0.5%) were obtained in configuration II in connection with broader bandwidths. Possible applications include low loss longitudinal mode suppression and rotational line selection in gas lasers.

Slotted Apertures for Multiplying Grating Frequencies and Sharpening Fringe Patterns in Moire Photography

Abstract: Slotted aperture filter masks can be used to "tune" a photographic system to an integral multiple of a fundamental grating frequency. Such a procedure can be used in moire photography for multiplying sensitivity and for obtaining improved rendering of fringe patterns. Depth of field is increased, and a camera lens of poorer quality than is normally required for high resolution photography of moire gratings is adequate. Also gained is flexibility in optical data processing of moire photographs and in the use of two-dimensional grid and dot specimen arrays.

The Design, Construction and Performance of a Large Hα and [N II] Interference Filter for the SRC 48-inch Schmidt

Abstract: The design, construction and performance of a 15-in. square mosaic interference filter is described. This is designed to improve the sensitivity of the SRC 48-in. Schmidt for the detection of gaseous nebulae in the light of Hα and [Nii] by approximately seven times. Its bandwidth with Kodak 098-04 emulsion is 105 A but when combined with 103aE emulsion the effective bandwidth is around 80 A.

An optical CCD convolver

Abstract: Some experimental and practical considerations of performing convolution or transversal filtering with charge-coupled devices (CCD's) using optical inputs are described. The basic principle involves shining light from a signal-modulated light-emitting diode (LED) onto an optical mask which controls the amount of light reaching the various CCD electrodes. The experimental results for a 91-tap Hamming window are presented. The relative advantages of using this approach as a means of obtaining fixed tap-weight transversal filters are discussed in comparison with the split electrode CCD filter. It is shown that a compact lens free optical signal processor is possible, using standard imaging structures. Although there is a disadvantage in terms of the need for an LED and current driver, this may be outweighed in certain contexts by improvements in linearity, intermodulation, dynamic range, and the scale of processing which is possible.

Filter radiometer: the selective interferometer.

Abstract: This paper describes a new type of filter radiometer—the Selective Interferometer Filter (SIF)—which has extremely high selectivity to the radiation from a given gas. The basic device is a double output Michelson interferometer, with mirrors fixed at zero geometrical path difference. It is shown that if a cell containing a gas is placed in each of the arms, the ensemble can be made to operate as a highly selective filter, passing radiation only very near the center frequencies corresponding to the absorption lines of this gas. This is a result of direct absorption effects and of the variation of refractive index with frequency and consequent modification of the optical path difference of the two arms of the interferometer. The device may, therefore, after calibration be operated as a highly selective ir radiometer; and a feature of importance in atmospheric and space applications is that it requires no internal moving parts to achieve this selectivity. Details of the device are presented, and a thorough examination of the practical realization of it is given.

Particle analysis system with photochromic filter

Abstract: A background light filter for use in an optical particle analysis system operates to attenuate light coupled thereto and pass an attenuated intensity light signal. If the light coupled to the filter takes the form of discrete beams or areas forming a pattern, the filter will selectively attenuate in only those portions of the filter struck by the light beams forming the pattern. The optical filter is substantially insensitive to short term variations in light coupled thereto so that changes in the received light pattern which may, for example, be produced by passage of a particle through the light beam producing the pattern, will be passed through the optical filter with substantially no attenuation.

Light control device

Abstract: PURPOSE:To improve responsibility and stability, while eleminating a moving part, by using a liquid crystal as an optical filter of light variable type.