Critical angle

Description

When a beam of light strikes the interface between an optically dense material, such as glass, and a less dense material, such as air, the light will normally pass through unless the angle of incidence of the ray is at or above the critical angle. The critical angle is the smallest angle of incidence at which total internal reflection occurs and the beam is reflected back into the incident medium. Critical angle is important for some analysis techniques, such as attenuated total reflectance (ATR) in infrared spectroscopy.

Authority

• Walter C. McCrone, John Gustave Delly, The Particle Atlas, W. McCrone Associates, Chicago, IV, 1972

• The American Heritage Dictionary or Encarta, via Microsoft Bookshelf 98, Microsoft Corp., 1998

• Wikipedia, the free encyclopedia, at http://www.wikipedia.com Comment: http://en.wikipedia.org/wiki/Critical_angle (Accessed Jan. 6, 2006)