A simple experiment to distinguish between replicated and duplicated compact discs using Fraunhofer diffraction

Compact discs are a useful tool for studying interference and diffraction. We propose an easy and inexpensive experiment to distinguish between replicated and duplicated compact discs based on Fraunhofer diffraction. The nonvisible differences of the surface of compact discs depend on the way that they have been manufactured and can be seen by using a laser beam in a simple diffraction experiment. The method has been tested on many different brands of CDs and is reliable.