PRECISION MICROMETER ADJUSTMENTS TO A PERKIN-ELMER INFRARED SPECTROMETER
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Date
1951
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Ohio State University
Abstract
Modifications to the standard optical supports of the Perkin-Elmer infrared spectrometer have been made to facilitate alignment, to obtain the best resolution, and to simplify change of prisms. Seventeen micrometer adjustments control the displacements of three figured mirrors, two plane mirrors, and the thermocouple, and allow (1) the setting of mirrors to the required tolerance, (2) the mapping of response over the full range of displacement, (3) the reproducibility of any configuration without loss of alternative settings, and (4) the compensations for the variations in homogeneity of different prisms. The precision of the micrometers is greater than the equivalent precision of the optical components. The tolerance of the settings, as found empirically, can be related to the limiting optical properties of the system, e.g., diffraction of the prism, circle of confusion, and flatness of the field of the collimator. The tolerance of adjustment of the collimator is approximately 0.001 inch in terms of displacements of the mirror for several independent adjustments. From this it is apparent how great is the number of configurations which approximate alignment but which do not adequately attain it, and how difficult it is to achieve adjustment which is not reproducible to this precision. An improved procedure for alignment of the optics has been achieved by utilizing a fine mesh screen, by mapping distortion over a range in units of the fundamental tolerances, and by judging a given image with-out recourse to comparison of image quality from memory. The alignment achieved by these means is demonstrated in terms of a new and exact theory of limiting resolution now in the course of development.
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Author Institution: Arthur D. Little. Inc.