Multiple thin films and dielectric mirrors

Multiple thin films of transparent materials can be laid down one on top of the other in such a way as to form perfect mirrors. These are often called dielectric mirrors. The simplest formulae for the reflectance of such a mirror refers to the specific case in which all layers are A/4 thick and of alternating high 

The general approach used to make a dielectric mirror is to lay down a stack of thin films that have alternately higher and lower refractive indices. Manipulation of the thickness and the refractive index of each layer in the stack allows the optical properties to be modified at will to produce virtually perfect mirrors and virtually perfect antireflection coatings - both of which can be mned to respond to very specific wavelengths - as well as a variety of optical filters. The fabrication of such devices falls 

The reflectivity of a stack of transparent thin films that are not carefully engineered in terms of thickness or refractive index will give a reflection that appears to be metallic silver. This can be seen in a less-than-perfect fashion with a stack of microscope slides or a roll of thin transparent plastic film, such as cling film . 

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