ABSTRACT
This chapter describes the principles of highest-level length measurements by optical interferometry. It focuses on measurements in which the length of a body is represented by a step height, which allows measurement by probing in one direction. The chapter shows that length measurements by interferometry, which provide the link between the lengths of macroscopic bodies to the International System of Units-definition of the meter, can be performed highly accurately when the light waves and their alignment are provided on a very high level. Under certain conditions where additional phase corrections can be regarded as constant. The provision of length standards and the ability to measure length to a required accuracy are of fundamental importance to any technologically developed society. The practical realization of length measurements depends upon the application. The wavelength of visible light is typically 400 – 700 nm, and hence, the basic unit of measurement is 200 – 350 nm in size.
