Speckle pattern is produced by the interference of a set of coherent light wavefronts. This phenomenon is commonly referred to as a source of imaging error, but it can contain useful information about the sample. Major advances in this field have been after the invention of the laser. This method can be used as a non-destructive, non-invasive, and non-contact method for remote study, measurement, and sensing of minor changes in different samples. For this reason, in recent years, it has found many applications in several science and technology disciplines, especially in biomedicine and industry. A key advantage of this method is its simple and relatively inexpensive setup. Speckle is a nanoscale pattern that shows the interaction between light and matter. Also, this method is a suitable sensor for measuring and detecting changes at the nanoscale.

The secondary speckle pattern analysis is an optical method in which a coherent light source illuminates the uneven sample surface and a defocused camera captures the pattern of scattered interfering spots from the surface. If the object is tilted at a slight angle, the speckle pattern will shift instead of changing in density distribution. Therefore, by tracking the movement of the speckle, it is possible to measure the movement of the surface without contact with the object.