referansestråle

A referansestråle, or reference beam, is a fundamental concept in interferometry, a technique used to measure displacements or changes in optical path length with extreme precision. In essence, the reference beam is a controlled beam of light that is kept stable and undisturbed. It serves as a benchmark against which another beam of light, known as the object beam, is compared.

The process begins with splitting a single light source, typically a laser, into two separate beams. One beam travels its designated path and is then reflected or transmitted by the object being measured. This is the object beam, and its optical path length can change due to various physical phenomena such as vibration, strain, or temperature fluctuations. The other beam, the reference beam, travels a different path, ideally one that is unaffected by the phenomenon being investigated.

After the object beam interacts with the sample, it is recombined with the reference beam. Because both beams originated from the same source, they are coherent, meaning they have a fixed phase relationship. When these two beams interfere, they create an interference pattern of bright and dark fringes. The position and spacing of these fringes are directly related to the difference in the optical path lengths of the object beam and the reference beam. By analyzing the changes in this interference pattern over time, extremely small displacements or deformations of the object can be accurately quantified. The stability and precise knowledge of the reference beam's path are therefore crucial for the accuracy of the interferometric measurement.