ABSTRACT
Length is one of the basic quantities whose measurement plays a vital role in science, engineering, trade, and so on. Optical systems such as microscopes, telescopes, and interferometers are used for the length measurement; choice depends on the requirement. In this chapter, authors discuss techniques and methods that use light wavelength as the measurement unit rather than calibrated mechanical scales. Earlier the interferometric measurement of length was generally confined to Standards laboratory. However, the advent of laser revolutionized the field and brought the technique to shop floor and to everyday use. Prior to laser, quasi-monochromatic sources were used in the interferometers. The authors discuss the techniques using these sources and then introduce laser as a coherent source. They consider measurement of displacement and its derivatives. The authors show an optical comb in frequency domain and intensity pulses in time domain.
