Wave Optics Fundamentals

Wave Optics

• Wavefront: The locus of all points in a wave that are in the same phase.

• Types of wavefronts:

  • Spherical: Produced by a point light source. Examples include light bulbs.
  • Cylindrical: Produced by a linear or rectangular light source. Examples include tube lights.
  • Plane: Produced by a point source at a very large distance, or a linear source at significant distance from the wavefront being observed. Examples include distant stars or lights far away.

• Huygen's Principle: Each point on a wavefront acts as a source of secondary wavelets. The new wavefront is the envelope of these wavelets.

• Reflection (using wave theory):

  • Incident ray, reflected ray, and normal all lie in the same plane.
  • Angle of incidence equals angle of reflection.

• Refraction (using wave theory):

  • The emergent wavefront travels at a changed angle and speed.
  • Snell's Law describes the relationship between angles of incidence and refraction, along with the refractive indices of the two mediums.

• Interference: The redistribution of light energy when two or more light sources overlap.

  • Conditions for sustained interference:

    • Coherent sources of light
    • Sources need to be close to each other

  • Types of Interference:

    • Constructive: When the crests of two waves overlap, resulting in a larger amplitude and greater intensity.
    • Destructive: When the crest of one wave overlaps the trough of another, resulting in a smaller amplitude and decreased intensity.

• Coherent Sources: Two or more sources that emit light waves with a constant phase difference.

• Young's Double Slit Experiment: A demonstration of interference using coherent light sources.

• Diffraction: Bending of light around obstacles.

  • Types of Diffraction:
    • Fresnel
    • Fraunhofer

• Polarisation: Restriction of light waves to vibrate in a specific plane.

  • Unpolarized light: Vibrates in all planes perpendicular to the direction of propagation.
  • Polarized light: Vibrates in a single plane.
  • Polarization by Reflection: The phenomenon where reflected light becomes polarized when incident light strikes a surface at a specific angle (Brewster's angle).