Guest Editorial

Optical measurement techniques – A push for digitization

Over the years, optical measurement techniques have been the problem-solving backbone of many engineering applications such as nondestructive testing of materials, measurement of various material properties, structural analysis and experimental mechanics [1], [2], [3]. Probably the most important advantage associated with any optical measurement system over other systems is its non-contact type of measurement capability. Apart from their non-contact nature, the optical measurement systems are capable of providing full-field measurements at scales ranging from milli-meters to nano-meters.

The revolutionary change witnessed by the optical community had at its source the invention of laser light source which propelled the developments of optical measurement systems on the fast lane. As a highly coherent light source, laser is a perfect tool for highly precise and accurate measurements. However, after an initial euphory, a time came when these techniques were at the risk of being considered under-performers as they groped to meet the high expectations engendered by them. Especially unfavorable to them was their time consuming manual evaluation of the interference phase over the object surface. A push to see how technological innovations, and computer based digital image and signal processing approaches can be combined together to automate the quantitative determination of the interference phase has lead these methods on a resurgent path which has resulted in their development in their digital avatars [4].

The second revolution that has thus come about in the field of optics has had at its source the invention of charged coupled device (CCD) cameras which by virtue of recording images digitally have handed over tremendous power to optical imaging systems. The developments in digital electronics have continuously contributed to improving the quality and affordability of the CCD cameras. At the same time, increasingly faster processing of the recorded images is being invariably made possible by a parallel progress in computer technology. The post-processing of digital images by signal and image processing algorithms has not only improved their image quality and information extraction capability but they have also made the imaging systems less dependent on the physical experimental conditions.

With high quality laser light source and digital technology at our disposal, optical measurement techniques have found wide range of applications. Both interferometric and non-interferometric optical measurement techniques have been developed and improved over the years. In this article, we will briefly review the key features of some of such representative optical measurement techniques along with their advantages and limitations.