Showing papers on "Fresnel zone published in 1976"
TL;DR: The characteristics of and differences between additive, subtractive, and multiplicative pattern superposition are presented in this article, and the micro-and macro-Moire structures in these cases are different.
Abstract: The different ways of combining optical patterns with spatial periodicities are examined. The characteristics of and differences between additive, subtractive, and multiplicative pattern superposition are presented. The micro- and macro- (Moire) structures in these cases are different. Examples are shown for two-pattern and multiple-pattern superpositions.
72 citations
TL;DR: The basic conclusion is that rectangular aperture unstable resonators are quite insensitive to misalignment, in the sense that the lowest-loss mode continues to be essentially diffraction limited as long as the feedback mirror remains well within the output beam.
Abstract: A previously developed technique for the calculation of modes of perfectly aligned unstable resonators in the limit of large Fresnel number is here extended to include effects of misalignment. It is shown how asymptotic techniques may be employed to simplify the calculation of near- and far-field patterns produced by such modes. The basic conclusion is that rectangular aperture unstable resonators are quite insensitive to misalignment, in the sense that the lowest-loss mode continues to be essentially diffraction limited as long as the feedback mirror remains well within the output beam.
44 citations
TL;DR: In this paper, the effects of severe flattening of the Fresnel zone or source image by defocusing on occultations are presented, along with temporal power spectra, and some methods for a more accurate determination of atmospheric structure.
30 citations
TL;DR: In this paper, the authors provide an overview of the use of the occultation technique for radio sources with continuous spectra and the time scale of a point source's occultation curve.
Abstract: Publisher Summary This chapter provides an overview of lunar occultation measurements. The occultation technique is concerned only with sources that contain angular structure much smaller than the size of the Moon. The variation in received power when a source passes behind the Moon depends on the size of the source relative to the size of a Fresnel zone at the Moon's distance, which, over the range of frequencies of interest, ranges from a few seconds of arc to a maximum of about 20 arc sec. Provided the source size is much greater than the size of the Fresnel zone, diffraction effects can be neglected, and the shape of the occultation curve represents the strip integral of the brightness distribution in a direction perpendicular to the limb at the point of occultation. The true strip brightness distribution can then be recovered simply by differentiating the observed occultation curve. A discussion on the use of occultation technique in measurement of the positions and structures of small angular size radio sources with continuous spectra is presented and time scale of the occultation curve of a point source is also analyzed in the chapter.
11 citations
TL;DR: In this paper, light curves are calculated for stellar occultations by a planetary body with an isothermal atmosphere from diffraction theory, and the character of the resulting curves is determined by the scale height H, the Fresnel zone size l, the surface atmospheric refractivity and the planetary radius.
Abstract: From diffraction theory, light curves are calculated for stellar occultations by a planetary body with an isothermal atmosphere. The character of the resulting curves is determined by the scale height H, the Fresnel zone size l, the surface atmospheric refractivity, and the planetary radius. An exact general solution and two approximations are presented which are valid when H is much greater than l. The importance is assessed of accounting for diffraction effects of the limb when deducing atmospheric parameters from occultation light curves
10 citations
TL;DR: In this paper, it was shown that the zone plate is a circular diffraction grating, which in turn explains how a hologram works in a very direct manner, and that foci exist where there should be none.
Abstract: It is found that, when a zone plate is examined in practice, foci exist where there should be none. An approach is developed which reveals that the zone plate is a circular diffraction grating, which in turn explains how a hologram works in a very direct manner.
7 citations
TL;DR: In this article, the amplitude and phase of the reconstructed wave are modulated, except the case of exact reconstruction, and are determined by recording and reconstruction parameters and the hologram thickness, and the amplitude modulation by the volume hologram of a semitransparent object causes the space-variant or the space invariant bandpass filtering effect by the spherical-wave or the plane-wave illumination of the object, respectively.
Abstract: The “circular plane-wave” expansion of a spherical wave is newly proposed, and the reconstructed images from volume holograms are studied analytically by applying this method to the expansion of the object wave. The analysis is performed on the weakly coupled amplitude holograms in the Fraunhofer approximation. Both the amplitude and phase of the reconstructed waves are modulated, except the case of exact reconstruction, and are determined by recording and reconstruction parameters and the hologram thickness. The amplitude modulation by the volume hologram of a semitransparent object causes the space-variant or the space-invariant bandpass filtering effect by the spherical-wave or the plane-wave illumination of the object, respectively. The phase modulation causes aberrations and becomes small for a hologram having the large thickness.
7 citations
TL;DR: In this article, two techniques are described which remove this background by employing optical interference during the image reconstruction process, and the experimental results are presented for one of the techniques are compared to the other.
2 citations
TL;DR: The method of the contour integral of Maggi-Rubinowicz is used to calculate exactly the contribution of a Fresnel zone taken over a general plane for the case of an incident spherical wave.
Abstract: The method of the contour integral of Maggi-Rubinowicz is used to calculate exactly the contribution of a Fresnel zone taken over a general plane for the case of an incident spherical wave.
1 citations