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Peculiarities are described of the manufacturing process and the control of elements of slit collimators, the structural design of the required equipment and the process or assembling the collimators.
Zeolite crystals can be used to collimate electron and X-ray beams. Faujasite, naturally occuring crystal in this group, provides structure necessary for collimation.
An appartus is described for scanning relatively small near sources of penetrating radiation to obtain the energy distribution thereof, wherein a collimator assembly is interposed between a radiation source and a radiation detector. The collimator assembly has a plurality of plates aligned in parallel planes with respect to a common axis normal to their centers. All the plates have similar random distribution of apertures. All apertures on each plate are the same size. The size of respective plates, the size of the apertures of said respective plates, and the spacing between said respective plates vary precisely according to a predetermined ratio to produce radiation channels which converge to a focal point. The radiation incident to the radiation detector is maximized when the focal point and the radiation source are co-incident.
Results of the measurement of Bragg reflection properties of crystals suitable for use in X-ray astronomy are presented. Measurements with a double crystal spectrometer were performed on rubidium acid phthalate and thallium acid phthalate to yield values of the integrated reflectivity and diffraction width in the range 8-18 A, and measurements of integrated reflectivity were also performed on ammonium dihydrogen phosphate. The theory and design of an arc-minute range multigrid collimator to be flown on a rocket for solar X-ray studies are also described, along with a method for determining the collimator's X-ray axis.
The Scanning Modulation Collimator X-ray instrument for the HEAO-A satellite was designed to measure celestial radiation in the range between 1 and 15 KeV and to resolve, and correlate, the position of X-ray sources with visible light sources on the celestial sphere to within 5 arc seconds. The positional accuracy is made possible by mechanical collimation of the X-ray sources viewed by the instrument. High sensitivity is provided from two systems each containing four gas filled proportional counters followed by preamplification, signal summing, pulse height analysis, pulse shape discrimination, X-ray event accumulators and telemetry processing electronics.
The paper presents a general theory which predicts the angular response of a random array grid collimator (RAGC). Attention is given to two problems with pure random arrays: (1) there are strong wings in the response function and (2) the patterns are not self-supporting. The paper suggests restrictions on the randomness of the pattern which eliminate such problems with the disadvantage of putting an upper limit on the available throughput. It is reported that even in the worst case, the upper limit for a two-dimensional collimator is as high as 23%. Finally, suggestions are presented for easing the fabrication effort of the grids.
Observations made with the HEAO-1 scanning modulation collimator are used to determine the positions of 16 unidentified X-ray sources at low galactic latitudes. Positions were obtained to within 10-30 arcsec in one dimension from two four-grid collimator observations made at six-month intervals. Positions determined in addition for eight sources identified with optical objects verify the method employed. Of the unidentified sources, the positional uncertainties of ten are reduced by factors of two to eight, the precise X-ray positions (within 10 arcsec) obtained by lunar occultation experiments are confirmed for three and multiple precise positions (within 20 arcsec) which reduce the previous location uncertainties by factors of greater than 100 are obtained for the remaining three.
An optical manifold is described which transforms a collimated beam, such as a laser beam, into a plurality of parallel beams having uniform intensity or having a desired intensity ratio. The manifold comprises an optical substrate coated on its rear surface with a fully reflective layer and on its front surface with a partially reflecting layer having a reflectivity gradient. An input collimated beam entering the rear surface and impinging on the front surface is reflected, multiply between the front and rear surfaces producing a plurality of parallel beams that emerge from the front surface. The intensities of the emerging beams have a relationship that depends on the reflectivity of the front surface at the points where the beams emerge. By properly selecting the reflectivity gradient, the emerging beams have uniform intensity or a desired intensity ratio.
A need for an accurate but inexpensive method for measuring and evaluating time delays of large ground antennas for VLBI applications motivated the development of the collimation tower technique. Supporting analytical work which was performed primarily to verify time delay measurement results obtained for a large antenna when the transmitter was at a collimation distance of 1/25 of the usual far field criterion is discussed. Comparisons of theoretical and experimental results are also given.
The collimating mirror within the Fine Guidance Subsystem of the Space Telescope's Pointing Control System is aspherized in order to correct the pupil aberration. A null corrector is needed to test the collimating mirror in autocollimation. Triplet and doublet null corrector designs are subjected to tolerance sensitivity analyses, and the doublet design is chosen despite its more restricted tolerances because of its compactness and simplicity.
A simple double-slit system is described which allows a synchrotron beam to be collimated onto a small sample (approximately 150-micron diameter) in a diamond-anvil cell using remote control. The apparatus can be constructed easily and inexpensively, and allows the shutter positions to be monitored accurately using readily available electronic equipment. A desirable feature of the collimator is the relatively small time needed for adjustment.
A need for an accurate but inexpensive method for measuring and evaluating time delays of large ground antennas for VLBI applications motivated the development of the collimation tower technique. Supporting analytical work which was performed primarily to verify time delay measurement results obtained for a large antenna when the transmitter was at a collimation distance of 1/25 of the usual far field criterion is discussed. Comparisons of theoretical and experimental results are also given.
This paper extends the previous treatment (Lovelace et al., 1987) of the origin of self-collimated EM jets to the case of even field symmetry, where the magnetic flux function Psi(r, z) is an even function of z. A viscous resistive accretion disk is assumed to surround a black hole with a force-free plasma outside of the disk. Inside the disk, the induction equation is solved for Psi(r, z) and the toroidal magnetic field. Outside the disk, previous results are used to study the formation of self-collimated EM jets. In contrast with the odd-symmetry case, for even symmetry the toroidal magnetic field acts to vertically compress the disk; a comparatively large toroidal magnetic field can exist inside the disk; and an appreciable fraction (possibly all) of the available accretion power can go into the jets.
Researchers describe self-consistent 2-D magnetohydrodynamic (MHD) simulations of the collimation of an isotropic protostellar wind into bipolar outflows by magnetic stresses in the ambient medium. A variety of ambient field strengths, wind luminosities, and density profiles were studied. Collimation occurs when the energy of the magnetic field swept up by the expanding bubble approaches the bubble thermal energy. Measured axial and radial expansion rates are in good agreement with the analytical predictions of Konigl (1982).
This paper presents an improved technique for testing laser beam collimation using a phase conjugate Twyman-Green interferometer. The technique is useful for measuring laser beam divergence. It is possible using this technique to detect the defocusing of the order of one micrometer for a well corrected collimating lens. A relation is derived for the defocusing that can be detected by the phase conjugate interferometer.
Proposed unstable-resonator diode lasers produce solid, collimated output beams without external collimating optics. Simpler to construct, used as pumps for optical-fiber amplifiers in telecommunications, for other solid-state lasers, and sources of light for free-space communications.
Several approaches to imaging hard X-rays emitted from solar flares have been proposed or are planned for the nineties including the spatial modulation collimator (SMC) and the rotating modulation collimator (RMC). A survey of current solar flare theoretical literature indicates the desirability of spatial resolutions down to 1 arcsecond, field of views greater than the full solar disk (i.e., 32 arcminutes), and temporal resolutions down to 1 second. Although the sun typically provides relatively high flux levels, the requirement for 1 second temporal resolution raises the question as to the viability of Fourier telescopes subject to the aforementioned constraints. A basic photon counting, Monte Carlo 'end-to-end' model telescope was employed using the Astronomical Image Processing System (AIPS) for image reconstruction. The resulting solar flare hard X-ray images compared against typical observations indicated that both telescopes show promise for the future.
Typical stereo 3-D displays are produced using a single-image-source, which is time-multiplexed, to present disparate, directly-viewed views (stereo pairs) of the visual scene to each eye. However, current stereoscopic viewing techniques impose severe restrictions in the effective viewing-volume of the stereo 3-D display. Recent experiments at Langley Research Center determined that the effective region of stereopsis cuing, the depth-viewing volume, increased with increasing viewer-to-screen distances. This increase was also accompanied by a decrease in the field-of-view of the system. It was postulated that collimation of the display source would dramatically increase the depth-viewing volume, as the effective accommodation distance would be near infinity, while maintaining the field-of-view at required levels. The goal of this proof-of-concept effort was to investigate whether or not a dramatic increase in depth-viewing volume for stereo 3-D displays would be provided by the application of collimated optics to the stereo display source.