A double-pass interferometer was developed for measuring dimensional changes of materials in a nanoscale absolute interferometric dilatometer. This interferometer realized the double-ended measurement of a sample using a single-detection double-pass interference system. The nearly balanced design, in which the measurement beam and the reference beam have equal optical path lengths except for the path difference caused by the sample itself, makes this interferometer have high stability, which is verified by the measurement of a quasi-zero-length sample. The preliminary experiments and uncertainty analysis show that this interferometer should be able to measure dimensional changes with characteristic uncertainty at the nanometer level.
Abstract:A method for measuring the nonlinearity of laser interferometer using optical frequency tuning technique is presented in this paper. The basic principle of this method is to make the fractional part of an interference fringe change by tuning the laser frequency and determining the nonlinearity of interferometer by comparing the fractional fringe change measured by the interferometer to that calculated from the laser frequency change. An experimental interferometric system with a wavelength tunable laser source is set up and the nonlinearity of the interferometer is measured. Since it does not require the precise displacement mechanism to produce the optical path difference change, this method is more convenient to use and may achieve a higher accuracy than the conventional measurement methods. The nonlinearity of the arbitrary interferometric phase can be measured by changing the laser frequency with this method. Experiments results have shown that the repeatability of nonlinearity measurement is less than 0.2 nm. This method can be applied to interferometry-based high precision dimensional measurements, such as coordinate measurement and displacement sensor calibration.
A traceable method for potential use in calibrating the micro-force of nanoindentation instrument using a laser interferometer is proposed. The calibration system consists of a laser interferometer and a cantilever. The cantilever is used as force-sensing element, and the interferometer is used to measure the deformation of the cantilever caused by the force. When a force is applied to the free end of the cantilever, the cantilever is elastically deformed. If the system is calibrated for the relationship between the force and the resulting displacement, it can be used to measure the loading force of a nanoindentation instrument by measuring the displacement of the measurement point on the cantilever. The system calibration can be performed using a set of calibrated masses. The design, calibration and application of the force calibration system are introduced. The experiment results of measuring the forces of a nanoindentation instrument ranging from 10μN to 1mN using this method are given. Preliminary experiments and analysis show that the proposed method can be used to measure the micro-force of nanoindentation instrument. By use of this method, the measurement of the micro-force in nanoindentation instrument can be traced to SI units.
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