Abstract
A description is given of a photoelectric microscope which is suitable for the accurate measurement of linear scales of high precision. A real image of a graduation line, formed by means of an ordinary microscope objective, is caused to oscillate across a fixed slit in front of a photoelectric cell. A phase-sensitive rectifier determines when the mean position of the line image coincides with the centre line of the slit. When this is so, the d c. output of the rectifier is zero and for small displacements of the mean position of the line image, the d.c. output - which is measured on a microammeter - is proportional to the displacement. The standard deviation of a single setting of the microscope is about 0.03 μ and by associating the microscope with an interferometer, short linear scales have been measured directly in wavelengths with a standard deviation of about 0.1 μ. It is thought that, with a properly designed interferometer to measure the displacement of a scale with respect to a fixed photoelectric microscope, a standard deviation of 0.05 μ would be achieved.
Published Version
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