Itek Corporation was founded in 1957. A major business quickly developed in the manufacture of large precision optical systems principally for aerospace photography. While the company is now highly diversified, this work continues as a major activity. This article discusses the work of the group especially in the field of image formation as it has been described in the scientific literature. An outline is given of the historical roots in earlier laboratory programs beginning at Boston University in 1946 and at Harvard University in 1941.
The use of a lateral shear interferometer in measuring the power variation of ophthalmic lenses is described and demonstrated. It is shown that an appropriate lateral shear interferometer directly measures the power variation of an ophthalmic lens. If the ophthalmic lens has a toric surface, the power for each axis can be measured separately. Individual surfaces can be tested, as well as the whole lens or the different segments of a multifocal lens. The sensitivity of the test can be selected by varying the amount of lateral shear. Because of the demonstrated simple relationship between fringe spacing and dioptric power, qualitative examination of the fringes has proved a useful adjunct to conventional quality control methods.
The Admiralty cathode ray oscillograph indicator was developed for use on compression-ignition engines of medium- and high-speed types. The size of the engine has not necessitated the development of the smallest possible unit. It consists of a pressure-sensitive device based on the magnetophone principle. The pressure to be recorded deflects a steel diaphragm and changes an air gap in a magnetic circuit. The magnet is energized by a high-frequency (20,000 cycles per sec.) alternating current flowing in an encircling coil. The pressure on the diaphragm modulates the high-frequency current, and the modulations are observed on the screen of a cathode ray oscillograph. The advantages of a high-frequency current in this connexion are: (1) all frequencies below about 2,000 cycles per sec. are faithfully reproduced; (2) steady pressures are recorded and calibration is effected with an ordinary pressure gauge; (3) amplifier and circuits have to transmit only a comparatively narrow band of frequencies. A disadvantage is that the upper limit of frequency (2,000 cycles per sec.) is not sufficiently high for the study of very rapid variations. The precautions necessary to ensure accuracy are discussed, and some examples of typical records obtained with the instrument are reproduced.
In intermediate-mass systems, collective excitations of the target and projectile can greatly enhance the subbarrier capture cross section sigma(cap) by giving rise to a distribution of Coulomb barriers. For such systems, capture essentially leads directly to fusion [formation of a compound nucleus (CN)], which then decays through the emission of light particles (neutrons, protons, and alpha particles). Thus, the evaporation-residue (ER) cross section is essentially equal to sigma(cap). For heavier systems, the experimental situation is significantly more complicated owing to the presence of quasifission (QF) (rapid separation into two fragments before the CN is formed) and by fusion-fission (FF) of the CN itself. Thus, three cross sections need to be measured in order to evaluate sigma(cap). Although the ER essentially recoil along the beam direction, QF and FF fragments are scattered to all angles and require the measurement of angular distributions in order to obtain the excitation function and barrier distribution for capture. Two other approaches to this problem exist. If QF is not important, one can still measure just the ER cross section and try to reconstruct the corresponding sigma(cap) through use of an evaporation -model code that takes account of the FF degree of freedom. Some earlier results on sigma(cap) obtained in this way will be reanalyzed with detailed coupled-channels calculations, and the "extra-push" phenomenon discussed. One may also try to obtain sigma(cap) by exploiting unitarity, that is, by measuring instead the flux of particles corresponding to quasielastic (QE) scattering from the Coulomb barrier. Some new QE results obtained for the Kr-86 + Pb-208 system at iThemba LABS in South Africa will be presente
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