Chapter 9 - Principles used in measurement

Abstract

This chapter describes the principles that are common to different measurement applications. Laser-based measurements are capable of being used for a variety of different measurements. The same physical principles recur in various applications. Some of the important applications of lasers involve their use for measurement of various quantities like: distance, product dimension, and angular rotation rate. The Michelson interferometer finds a useful application by producing an interference pattern between two beams of light that traverse different paths. One of the interference effects that is employed in measurement is the phenomenon of a beat note. If two light beams of slightly different frequency interfere, the interference fringes do not remain fixed in time, but are in motion. At a given position in space, the motion of the interference pattern produces a varying intensity. Many measurement applications involve a shift in the frequency of part of the beam from a laser. Subsequent recombination of the original beam and the frequency shifted beam yields the beat note, the frequency of which can be measured, providing a measurement of the parameter that caused the shift.