Abstract: This paper discusses the development of infrared filters of both lowpass and bandpass types for the wavelength region λ>40 μm. The design techniques of multilayer filters have been extended to mesh filters. Bandpass filters at wavelengths near 50 and 100 μm with bandwidths between 5% and 10% and up to 90% transmission have been made using either double-halfwave or Fabry-Perot systems. Lowpass filters of high performance, passband transmission 70% and rejection greater than 103 are shown with edges near 100 μm. Narrowband filters for the HCN laser line at 30 cm−1 are also shown.

Abstract: The fabrication of Fabry-Perot Etalon Filters with spacer elements of solid fused silica is described. Typically spacer thicknesses of 120pm are used to provide filters with .05nm to .07nm FWHM at 656.3nm centre wavelength. More complex devices having two coherently coupled cavities are described. The effect of optical system parameters on the spectral performance of the solid etalon filters is discussed and suitable operating parameters are suggested. The performance of solid etalon filters is compared with the birefringent filters of the Lyot type.

Abstract: An intensity spatial filter has been devised and used for the semiautomatic photoelectric detection of 2.5-µ defects in 5-cm2photolithography masks for silicon integrated circuits. The filter is based on a simple geometric approximation to the form factor or envelope function for the intensity in the Fourier-transform plane, and permits small-area diffraction-limited illumination. This approach complements the Watkins' method.

Abstract: The output center wavelength of a rhodamine 6G dye laser was tuned by using variable birefringence filters in the cavity. The electrooptic properties of two different lead lanthanum zirconate titanate (PLZT) ceramics were used in these filters to achieve up to 120 A of wavelength tuning. Spectral bandwidths varied from 20 to 120 A with these particular filters.

Abstract: A photometer system of the type having a photoelectric sensor receiving light through selectable different-sized apertures and selectable different density optical filters is provided with electronic circuitry including a numerical read-out means for automatically compensating the photo-sensor output in accordance with selected aperture and filter settings and for providing a direct numerical reading of the measured light. The circuitry automatically calculates the proper scale or multiplier of the direct reading, again in accordance with the selected apertures and filters, and provides a numerical display of such scale multiplier. Additionally, a gain control for changing the sensitivity of the photoelectric sensor is provided with an output indicative of the gain setting. This gain setting information is electronically fed to the computer along with the aperture and filter information for automatically computing and displaying the correct scale or multiplier factor from all of these independent variables.

Abstract: This paper describes some liquids that have been found to be useful as sharp cutoff optical filters in the uv, visible, and near ir. The range of useful transmission extends to approximately 6 μ in the ir.

Abstract: AN IMPROVED HIGH OPTICAL QUALITY, PLASTIC OPTICAL FILTER FOR RED AND NEAR INFRARED WAVELENGTHS HAS VERY LOW TRANSMITTANCE IN THE RED PORTION OF THE VISIBLE SPECTRUM, A REDUCED NEAR INFRARED TRANSMITTANCE, AND A HIGH ABRASION RESISTANCE. THE OPTICAL FILTER IS FORMED BY DISSOLVING A SUFFICIENT QUANTITY OF CUPRIC OR CUPROUS CHLORIDE IN A MIXTURE OF MONOPROPYLENE GLYCOL MONOMALEATE, AND ALLYL DIGLYCOL CARBONATE, MIXING THE SOLUTION WITH DIISOPROPYL PEROXYDICARBONATE INITIATOR, FILTERING THE RESULTANT MIXTURE, AND CASTING THE FILTERED MIXTURE.

Abstract: A system for measuring velocities of radiating particles based on doppler shift is disclosed. Light from the particles is directed through a narrow band optical filter to a Fabry-Perot interferometer initially tuned to a selected center line corresponding to zero particle doppler shift. The movable mirror of the interferometer is made to sweep about the center line by the output of a modulation oscillator. The fringe pattern output is imaged onto a pin hole through which light is directed to a photomultiplier. The output of the photomultiplier is supplied to a phase sensitive detector which is supplied with the oscillator output as a reference signal and which operates in the quadrature mode. The detector's output is gain controlled and is combined with the oscillator's output to adjust the interferometer's movable mirror to acquire the line center.

Abstract: An Anger-type scintillation camera system fitted with a gamma ray filter between the object under study and the detector and an output signal filter in the form of a funnel-type optical filter between the cathode ray tube of the detector and an image recording film. The gamma ray filter and funnel-type optical filter scan in synchronism so that the total radioactivity distribution in the object is documented on the film.

Abstract: This paper provides a tutorial exposition of the possible use of sequency filters for the processing of signals that are functions of two space variables. Historically, optical and, more recently, digital techniques have been used for two variable processing of images with the computer providing a domain for other than sinecosine filtering. Sequency filters based on Walsh or similar functions can be implemented with about equal effort for time and space variable signals. They could actually be built with electronic components up to the ultimate case of signals with one time and three space variables. Two kinds of filters have emerged so far: instantaneous filters and sampling filters. In the following sections we briefly discuss other possible transforms for space filters before investigating sequency-oriented filtering techniques. The sequency techniques include instantaneous filters, efficient practical implementation, and some potential circuits for imagery applications.

Abstract: An approach for designing a recursive digital MTI radar filter in the z plane is described. The resultant filter exhibits a sharp spectrum rolloff and an almost flat passband in the amplitude response.

Abstract: A laser-light mixing device in which the nonlinear medium for mixing two collinear laser beams comprises the chemical compound hexafluoroisopropanol, (CF3)2CHOH, which has an index of refraction which varies by only one part per thousand over a spectral range of 6,300 to 7,700 A, thus enabling mixing to occur over a long pathlength. The light resulting from the mixing action is then passed through an optical filter which allows only the sum or difference frequency to pass.

Abstract: The operation of a six channel interference filter spectrum analyser is described which was used in laser scattering measurements on a pulsed plasma. The spectral resolution of the system was 6 AA and the width of the spectrum measured was about 50 AA. The image dissector which directed the dispersed light to the six photomultipliers was a transmitting type multiprism made of clear plastic.

Abstract: A quantitative basis is established for determining the optimum spectral shape of the transmission of optical filters used with information displaying light sources for contrast enhancement. Examples are given for several ideal and practical cases, and performance is evaluated for these.

Abstract: For the past several years a group at Perkin-Elmer Corporation has been developing techniques for the manufac-ture of Solid Fabry-Perot Etalons. The etalons are suitable for use as very nar-row band-width isolating filters when combined with a conventional all-dielectric interference filter and some form of temperature stable environment.© (1972) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Abstract: We report on a new method for increasing the linear dynamic range of coherent-optical spatial filters, with special reference to holographic image-deblurring filters. In the filter-generating step, a transmission grating is placed in contact with the transparency representing the spread function of the blur. The spectrum of the spread function then appears in a series of equally spaced islands of different intensities, each occupying a different region of the nonlinear characteristic of the recording medium. Each spatial frequency can then be properly exposed somewhere on the filter, even with a film of limited dynamic range. In the image -processing step, the grating is superposed on the blurred image, the spectrum of which then falls on all the islands of the filter. In this way, the filtering operation is done in parallel channels, each with a different nonlinear characteristic. The channels are combined in the output plane by superposing a grating on the filtered aerial image and viewing this plane through an optical system that does not resolve the grating. Theory, computer simulations, and experimental results are presented. The results show in particular that a good transfer function can be achieved with a hologram-only filter.

Abstract: A detailed account is given of efforts to develop a three layer, polychromic filter that can be tuned electronically. The operation of the filter is based on the cooperative alignment of pleochroic dye molecules by nematic liquid crystals activated by electric fields. This orientation produces changes in the optical density of the material and thus changes in the color of light transmitted through the medium. In addition, attempts to improve materials and devices which employ field induced changes of a cholesteric to a nematic liquid crystal are presented.

Abstract: With the advent of practical non-minimum phase microwave networks, greater flexibility is now achievable in the design of frequency selective microwave filters. Design techniques are presented for the construction of generalized TEM mode interdigital filters and waveguide generalized direct coupled cavity filters which exhibit selective amplitude characteristics simultaneously approximating arbitrary prescribed phase characteristics.

Abstract: The basic principles of incoherent image processing are presented and the advantages and disadvantages of this approach are discussed.

Abstract: : Contents: Radar signals and the method of their processing; Output signals of filter devices; Detection of signals against a background of interference and other signals; Signal parameter measurements; Signal processor design principles; Methods for the technical realization of signal-processing devices; Analog electronic filters; Digital electronic filters; Optical filters

Abstract: Basic techniques for microwave holography are considered, giving attention to ways of approaching the problem, swept frequency depth resolution, optical processing of swept frequency data, B-scans with optical processing, and the side-looking radar principle. Aspects of image formation with Vander Lugt filters are discussed together with holograms for Vander Lugt filter imaging. It is shown that a single basic scanning operation with microwaves can produce records for optical processing to provide any of the common readouts used in flaw detection.

Abstract: The effect of simulated Nimbus spacecraft orbital (1100 km, circular, and polar) radiation on wide-band-pass glass filters, narrow-bandpass thin-film interference filters, and several fused silicas was determined by transmittance measurements over the 200-3400-nm wavelength region. No changes were observed in the filters, which were shielded with fused silica during irradiation, after exposure to a 1-yr equivalent orbital dose of electrons, nor were changes observed in the fused silicas after the same electron exposure plus a 1-yr equivalent dose of protons. Exposure to a 1/2-yr equivalent dose of solar uv radiation, however, caused a significant degradation in the transmittance of two uv-transmitting interference filters but had no effect on two colored glass filters that transmitted in the visible and near-ir regions. As a result of the uv exposure, the fused silicas exhibited losses of several percent over the 200-300-nm wavelength region.