HIGH-PRECISION AUTOMATED MEASUREMENT OF SURFACE SEPARATION FOR THE SURFACE FORCES APPARATUS

Multiple beam interferometry is a simple, yet powerful, technique that can be used to determine changes in the distance between two surfaces; under optimal conditions, the resolution of the measurement is less than 1 Angstrom. Multiple beam interferometry is utilized effectively in conjunction with the surface forces apparatus to measure the forces acting between two opposed surfaces as a function of their separation, The conventional method of measurement is based on visual observations of interference fringes which shift continuously in wavelength as the distance between the surfaces is varied, Data collection is a slow and demanding process, and precision is limited by both the skill and the stamina of the experimenter, We report here on an automated system designed to measure the wavelengths of interference fringes produced in a typical surface forces experiment. The measurement precision obtained with the automated system exceeds that of the conventional manual method, while the measurement time required is comparable, The distinguishing feature of our system is the development and implementation of a versatile algorithm designed to quantify the shapes of the interference fringes. Capabilities of the automated system that are not afforded with the manual method include accurate curve fits to the observed fringes and simultaneous measurements of all fringes in the field of view. (C) 1995 Academic Press, Inc.