Abstract

It is well known that the international system of units, as well as the institutions that regulate it, should mainly aim at making their base units reproducible across physical phenomena anywhere in the world. In the case of international standards of length, it is required to have very accurate measurements of time that will allow defining the unit based on the fact that light propagates at constant speed in vacuum. On the other hand, using optical interferometry, the distance between two flat surfaces can be determined by calculating the number of wavelengths that are contained in that distance. Due to the fact that in the most general case, the distance between surfaces is a real number instead of an integer multiple of wavelength, and that a real number is composed by an integer plus a fraction, it is necessary to find an unambiguous method that allows the calculation of those values. In this work, we propose measuring the distance between two flat-parallel reflective surfaces using a Twyman-Green interferometer at two different wavelengths. Image processing of digital phase shifting of the interference pattern generated by light travelling from two distant mirrors where fall upon the radiation field is proposed, along with a numerical method that solves a transcendental equation that results from repeating the experiment with the two wavelengths. Preliminary experimental and numerical results are shown.

© 2014 Optical Society of America