Introduction to imaging

Introduction to Imaging

Basic Properties of Light

  • Light exhibits properties of both waves and particles.
  • Light travels in straight lines in homogeneous mediums.
  • Speed of light in a vacuum is the maximum speed at which information or matter can travel.
  • When light encounters a different medium, it can be reflected, refracted or diffracted.

Reflection

  • Laws of reflection state that angle of incidence is equal to the angle of reflection.
  • Specular reflection occurs when light hits a smooth surface; diffuse reflection occurs when the surface is rough.
  • The normal is a line perpendicular to the reflecting surface at the point of incidence.

Refraction

  • Refraction is the bending of light as it travels from one medium to another.
  • The amount of bending, or refraction, is determined by the difference in refractive indices of the two substances.
  • Snell’s law relates the ratio of the refractive indices to the ratio of the sines of the incidence and refraction angles.
  • Total Internal Reflection occurs when the transmitted angle is 90°.

Diffraction

  • Diffraction is the slight bending of light as it passes around the edge of an object.
  • The object does not need to be opaque. Any object which restricts the passage of light will cause light diffraction.

Interference and Superposition

  • When two waves meet, they interfere. This could result in constructive or destructive interference.
  • Interference patterns are formed by the superposition, or overlap, of light waves.
  • Interference patterns can be observed in many situations, including thin films and double slits.
  • Two-source interference is a pattern where alternating light and dark bands, or fringes, are formed.

Polarisation

  • Polarisation is the process of restricting the vibrations of a light wave to only one direction.
  • It helps reduce glare and other reflections, making images clearer or objects easier to see.
  • Polarised light can only pass through a filter if the vibrations occur in the direction of the filter’s transmission axis.

Lasers

  • A laser (Light Amplification by Stimulated Emission of Radiation) is a device that emits a beam of light through optical amplification.
  • The beam of light is spatially and temporally coherent, allowing it to stay focused over a great distance.
  • Lasers have a vast range of applications, from cutting and welding materials, to optical disk drives, and laser surgery and skin treatments.