Optical coatings are often used to enhance the performance of optical components.  They are also used to reflect, absorb, and selectively reflect/transmit light based on wavelength or the state of polarization.  Some commonly used optical coatings are:

• Anti-reflection coating (AR) is used to reduce the surface reflection of optical components over a narrow or broad range of wavelength. Commonly used AR coating types are: a single layer of MgF2 or a broad band anti-reflection coating (BBAR) consisting of several layers of optical materials.  AR coating is used on most multi-element lens designs to increase light transmission and reducing ghost images.

Typical theoretical single layer MgF2 AR coating spectrum:

Typical theoretical broad band anti-reflection coating (BBAR) spectrum:

• High reflective coatings:  These coatings are applied to optical components to form highly reflective mirror surfaces:

• Intensity beam splitting coating which transmits a portion of the incident light and reflects the balance.

• Polarization beam splitting coating which separate light by its state of polarization:

• Long-pass and short-pass filters:  A long-pass coating transmits light above certain wavelength.  A short-pass coating transmits light below a certain wavelength:   The reflective IR cut-off filter is a short-pass filter which passes visible while blocking near infrared light.

• Band-pass and notch filters: band-pass filters transmit light within a narrow band of wavelength while notch filter reflects light over a narrow band of wavelength.

For a detailed discussion of optical coatings, please refer to the book "Optical Thin Film Filters" by H. A. Macleod.