Laser techniques in measurements and sensing

Laser techniques in measurements and sensing have received increased attention in the 1990s. The main reasons are the advantages of the optical techniques in general over the other measuring methods. They are non-invasive, quick to observe highly transient phenomena and have a high spatial and transient resolution. Therefore it is expected, taking into account the further development of components for optical probes, that optical techniques will continue to gain in importance in many fields of application. The purposes of this review are to discuss the principles of some laser measurement techniques and to provide an account of their recent developments. Translation and rotation can be measured in a variety of ways and they are valuable in the control of machine tool movements and calibration. A laser measuring system for resolving displacements consists of a laser, an interferometer, a reflector and a receiver. The laser, interferometer and receiver remain stationary while the retroreflector senses the variables to be measured, e.g. the straightness of a machine slideway. Also laser transducers can measure up to six independent axes of displacement using one transducer head. The transducer produces signals in the form of interference fringes and the system is able to resolve motion of the order of one quarter of a wavelength. Light scattered from a rough surface can be characterized by many different parameters, such as angular distribution, state of polarization, speckle contrast