Paul Kirkpatrick

Formation of Optical Images by X-Rays

Several conceivable methods for the formation of optical images by x-rays are considered, and a method employing concave mirrors is adopted as the most promising. A concave spherical mirror receiving radiation at grazing incidence (a necessary arrangement with x-rays) images a point into a line in accordance with a focal length f=Ri/2 where R is the radius of curvature and i the grazing angle. The image is subject to an aberration such that a ray reflected at the periphery of the mirror misses the focal point of central rays by a distance given approximately by S=1.5Mr2/R, where M is the magnification of the image and r is the radius of the mirror face. The theoretically possible resolving power is such as to resolve point objects separated by about 70A, a limit which is independent of the wave-length used. Point images of points and therefore extended images of extended objects may be produced by causing the radiation to reflect from two concave mirrors in series. Sample results are presented.

On the Theory and Use of Ross Filters

Resolving power, preferred thickness and balance errors of Ross filters for x‐ray monochromatization are discussed. It is theoretically impossible to balance two filters of elementary composition because of scattering, L limits and K jump, even if the absorption coefficients of the two filters vary similarly with wave‐length between the limits, which is not known to be the case. It suffices, however, to obtain good balance for wave‐lengths near the pass band since others longer and shorter may be relatively reduced by pre‐filtration through a filter whose composition is the same as that of the high atomic number member of the balanced pair. The K jump balance error may be completely removed by adding a slightly absorbing filter of low atomic number to one member of the pair. By employing a specially designed ionization chamber Ross filters may be used simultaneously instead of alternately and a considerable gain in speed and accuracy achieved.

Image Formation by Reconstructed Wave Fronts. I. Physical Principles and Methods of Refinement

The process of image formation by reconstructed wave fronts, brought to notice and placed upon a broad theoretical foundation through the writings of D. Gabor, is here discussed from a less abstract standpoint in an attempt to establish a satisfying conceptual explanation of the phenomena. The imperfections which the photographically recorded images ordinarily exhibit are accounted for and classified, and means for their removal are described. Sample reconstructions are presented.

Theory and Use of Ross Filters. II

It is often advantageous to use Ross filters of a thickness much greater than that which has been judged to be optimum by the criterion of maximum pass‐band transmission. The thicker filters show a larger ratio of measurable pass‐band radiation to total spectrum power received and to received power resulting from balance errors. Prefiltration, though useful in connection with thin filters, confers no advantage when thick filters are used. Balance errors caused by the variation with atomic number of the function representing the variation of absorption coefficient with wave‐length may, in principle, be eliminated at an indefinite number of chosen wave‐lengths by giving one filter a particular type of thickness non‐uniformity. Techniques for the construction and adjustment of Ross filters are described.

Ion Optics of Equal Coaxial Cylinders

The potential distribution along the axis of two long equal coaxial conducting cylinders has been found to be empirically expressible in terms of the radius and separation of the cylinders. The empirical expression checks well with the single special case (zero separation) which is known to have been solved analytically. The general empirical expression, combined with the theoretical lens equation of Hansen and Webster yields an algebraic formula for lenses of this type directly relating object and image distances to readily measurable quantities.

A rotary voltmeter

A new electrostatic voltmeter for measuring either a-c or d-c potentials has been developed; it has a range limited only by its insulation, possesses high accuracy, and draws no current. This article describes the new meter and some of its uses.

History Of Holography

Holograms existed in the nineteenth century, though they were not so called and were not very exciting or newsworthy. Going back even farther into the seventeenth and eighteenth centuries we find the diffraction of light being studied with keen interest by Grimaldi, Newton, Hooke, Delisle, Young, Fresnel and numerous others. All could have had holograms if they had had photography. All looked at the diffraction patterns but had no method of recording them except by drawings.

Determination of Voltage Wave Forms with the Rotary Voltmeter

The electrical theory of the rotary voltmeter is developed and the conclusion drawn that the instrument may be employed for analysis of the wave forms of a large class of periodically varying voltages. Two experimental methods for performing these analyses are described and experimental results are presented, pertaining to both high and low potentials.

A Ring‐Target X‐Ray Generator Adapted to Scattering, Fluorescence and Irradiation Experiments

An x‐ray generator is described which is especially adapted to the production of strong scattered and fluorescent x‐rays. Geometrical conditions are well suited to the study of spectra of scattered radiation. The essential novelty of the apparatus is a ring‐shaped target 3 inches in diameter. Sample spectra are presented.

High Intensity X‐Ray Monochromator

A monochromator for concentrating radiation of wave‐length 0.71A has been made by disposing about a common symmetry axis a group of eight rocksalt crystals each plastically deformed and ground to the spindle surface curvature required for focusing radiation from a point source to a point image. The maximum monochromatic intensity at the focus exceeds the intensity of the total radiation from the molybdenum‐target source when received directly at the same location.