page_title: Thin-film interference
section_title: Applications
hierarchical_section_title: Thin-film interference / Applications
caption_attribution_description: English: This photo shows an antirelection coated window. The window measures 2 inches (5.1 cm) square by 1/8 inch (3mm) thick. Made of borosilicate float-glass, the surface accuracy is 4λ per inch. The coating is a multilayer anti-reflection coat designed to give less than 0.5% reflection across the visual spectrum at a 0° angle of incidence. Transmittance is 96--99% between 400 and 700nm. The photo on the left shows the window when viewed at a 45° angle, reflecting the above fluorescent lighting in a rather purplish hue, which is common for antireflection coatings. This is due to the thickness of the coating upon the incident light, which causes it to shift toward the red and IR portion of the spectrum and allow reflections at the opposite end. The photo on the right shows the window when viewed at a 0° angle of incidence, for which the AR coating was designed, giving almost no reflection. (Some reflection of the camera and the photographer's face should normally be present.)
context_page_description: Thin-film interference is a natural phenomenon in which light waves reflected by the upper and lower boundaries of a thin film interfere with one another, either enhancing or reducing the reflected light. When the thickness of the film is an odd multiple of one quarter-wavelength of the light on it, the reflected waves from both surfaces interfere to cancel each other. Since the wave cannot be reflected, it is completely transmitted instead. When the thickness is a multiple of a half-wavelength of the light, the two reflected waves reinforce each other, increasing the reflection and reducing the transmission. Thus when white light, which consists of a range of wavelengths, is incident on the film, certain wavelengths are intensified while others are attenuated. Thin-film interference explains the multiple colors seen in light reflected from soap bubbles and oil films on water. It is also the mechanism behind the action of antireflection coatings used on glasses and camera lenses.
  The true thickness of the film depends on both its refractive index and on the angle of incidence of the light.
context_section_description: Thin films are used commercially in anti-reflection coatings, mirrors, and optical filters. They can be engineered to control the amount of light reflected or transmitted at a surface for a given wavelength. A Fabry–Pérot etalon takes advantage of thin film interference to selectively choose which wavelengths of light are allowed to transmit through the device. These films are created through deposition processes in which material is added to a substrate in a controlled manner. Methods include chemical vapor deposition and various physical vapor deposition techniques.
  Thin films are also found in nature. Many animals have a layer of tissue behind the retina, the Tapetum lucidum, that aids in light collecting. The effects of thin-film interference can also be seen in oil slicks and soap bubbles. The reflectance spectrum of a thin-film features distinct oscillations and the extrema of the spectrum can be used to calculate the thickness of the thin-film.
  Ellipsometry is a technique that is often used to measure properties of thin films. In a typical ellipsometry experiment polarized light is reflected off a film surface and is measured by a detector. The complex reflectance ratio, , of the system is measured. A model analysis in then conducted in which this information is used to determine film layer thicknesses and refractive indices.
  Dual polarisation interferometry is an emerging technique for measuring refractive index and thickness of molecular scale thin films and how these change when stimulated.
caption: An antireflection-coated optical window. At a 45° angle the coating is slightly thicker to the incident light, causing the center wavelength to shift toward the red and reflections appear at the purple end of the spectrum. At 0°, for which this coating was designed, almost no reflection is observed.
exif: {}