Holographic interferometry (HI) is a technique which enables static and dynamic displacements of objects with optically rough surfaces to be measured with optical interferometric precision (i.e to fractions of a wavelength of light). It can also be used to detect optical path length variations in transparent media, which enables, for example, fluid flow to be visualized and analyzed. It can also be used to generate contours representing the form of the surface. It has been widely used to measure stress, strain, and vibration in engineering structures.

Security holograms

Security holograms are very difficult to forge because they are replicated from a master hologram which requires expensive, specialized and technologically advanced equipment. They are used widely in many currencies such as the Brazilian real 20 note, British pound 5/10/20 notes, Canadian dollar 5/10/20/50/100 notes, Euro 5/10/20/50/100/200/500 notes, South Korean won 5000/10000 notes, Japanese yen 5000/10000 notes, etc. They are also used in credit and bank cards as well as quality products.