Showing papers on "Fresnel zone published in 1969"

Zone plates produced optically.

Abstract: The nature of optically produced zone plates is briefly discussed in contrast to the conventional type of Fresnel zone plate. A rather simple method for generating zone plates is described, and some of the experimental results are given.

Fresnel Zone-Plate Diffraction Patterns

Abstract: The diffraction patterns of the central aperture and the first 10 rings of the classical Fresnel zone plate are calculated in the principal focal plane for off-axis distances as large as the radius of the 10th ring. The zone-plate pattern is found by summation; near the axis it is compared with closed-form approximations. The integrated flux within circles as large as the 10th ring is also calculated.

Fourier-Transform Holograms by Fresnel Zone-Plate Achromatic-Fringe Interferometer*

Abstract: Fourier-transform holograms are produced by using achromatic-fringe interferometer arrangements in which the beam splitting is achieved by offset Fresnel zone plates. The effects of the size and the spectral bandwidth of the spatially incoherent source are discussed. Coherence requirements of the source are the same as those for in-line holograms. Experimental examples with object transparencies and a high-pressure mercury-arc lamp are given.

Solution to the Fresnel Zone Plate Problem

Abstract: The diffraction problem for the Fresnel half-period zone plate is solved. The zone plate behaves as a lens with marked chromatism which can be taken advantage of for use in a spectrometer. The multiplicity of foci associated with the zone plate are examined in detail, and it is shown that the spectral range that can be focused without overlap is 3λmin≥λmax. The wavelength resolution is λ/Δλ ≈ (m+1)/0.445, where m is the number of transparent half-period zones. For m = 300, this corresponds to a 34-wave number resolution at 20 microns. The intensity at the focus is given approximately by 4I (m+1)2, where I is the intensity at the zone plate. The transmitted power that falls within the airy disk is proportional to the area of the zone plate.

Spherically corrected fresnel lenses

Abstract: The optically effective face of a Fresnel lens is so shaped that two separate points in its optical axis are imaged without spherical aberration. Said face carries the Fresnel echelons. If there are echelons on both sides of the Fresnel lens, both echelon carrying faces have a form which is defined by an equation.

Exact Calculation of the Field Due to a Single Fresnel Zone by the Use of the Maggi–Rubinowicz Contour Integral

Abstract: The exact calculation of the field at a point due to a single Fresnel zone is carried out by using the Maggi–Rubinowicz contour integral. The result agrees with the Fresnel theorem in the limit for k very large, k being the propagation constant of the incident wave. The results obtained suggest a new interpretation of the physical meaning of the Maggi–Rubinowicz contour integral in diffraction theory as representing a contribution of elementary or Fresnel zones, in exactly the same manner that the Kirchhoff integral does when considered as an expression of Huygens’ principle.

Statistical Gain Characteristics of Radar Antennas at Very Short Fresnel Zone Distances

Abstract: This paper extends the existing knowledge of statistical gain characteristics of radar antennas to include very short Fresnel zone ranges. The data indicate that the median gain and the standard deviation remain essentially the same as those observed in the Fraunhofer zone until the range begins to approach the physical dimensions of the antenna; however, as the range is decreased closer toward physical contact, the median gain decreases and the standard deviation increases. The site-effects tests which were conducted in the Fresnel zone indicate that the geometrical configuration of an object, the position of an object, and the clear-site median gain of an antenna help to determine the magnitude of the effects of objects on the clear-site statistical gain characteristics.

Geophysical surveying using fresnel pilot signals

Abstract: In seismic geophysical surveying, a servo-controlled vibrator is driven by a pilot signal that corresponds generally to the variations in density that are encountered in scanning at a constant rate along a radial segment of a Fresnel zone plate, and the resulting seismic waves that arrive at a spaced receiver are recorded as a conventional variable density trace. The pilot signal is thus one that becomes self-compressing by the diffraction of monochromatic light to a focal point on the axis of the zone plate. Accordingly, illumination of the recorded variable density trace by monochromatic light effectively time-compresses each repetition of the pilot signal in the recorded trace by producing in the plane of the Fresnel zone plate focus a concentration of illumination that represents by its intensity and position the amplitude and travel time of seismic wave energy from the vibrator to the receiver by a particular path. In practice, any pilot signal for which the frequency varies linearly with time is so closely similar to a true Fresnel signal that it focuses monochromatic light in the same way.