The scanning of light is considered in terms of a generalized deflector exhibiting controlled inhomogeneity. An expression is developed for the differential scan angle in terms of the gradient of wavelengths in the medium, and thus to the gradient of the index of refraction in optical media. A gradient deflector is shown to impose aberrations upon convergent light flux which are directly related to the magnitude of the scan angle and the f-number of the focusing bundle. A linear-gradient case is analyzed and magnitudes of distortions are evaluated. Distortion is shown to increase drastically as f-number is reduced. Since diffraction limitations dominate at high f-numbers, an optimum f-number exists at which the maximum number of spots may be subtended per scan increment. This optimum for the case analyzed is f/28, and exhibits a maximum of 2300 spots over a scan angle of ±3.6°. At f/8, only 300 spots may be subtended over the same scan angle. Thus, a need is indicated for investigating the magnitude of aberration and means for its control prior to the development of any high-resolution deflector which falls into the gradient class. This consideration may be further generalized for all ray-like flux tubes, such as electron beams.
© 1967 Optical Society of AmericaFull Article | PDF Article
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