The current research in optical metrology is focused on measurement principles with objective speckles. These
speckles appear by free field propagation of a randomly scattered coherent light wave field. The acquisition of objective speckle pattern allow for the measurement of strain and displacement on rough surfaces.
The main advantage of the new principle is the possibility of direct strain measurement, to be compared with the indirect methods using subjective speckles.This allows the determination of surface strain on a single illuminated spot on the specimen. The measurement spot can be made very small to obtain a high spatial resolution for the unique single-point strain measurement.