Introduction to Optics

Introduction to Optics – Study Notes

1. What Is Optics?

• Definition: Branch of physics that deals with the behavior and properties of light (electromagnetic radiation in the visible, infrared, and ultraviolet ranges) and its interaction with matter.
• Main Goals:
  1. Explain how light propagates.
  2. Describe how light is reflected, refracted, diffracted, and absorbed.
  3. Design optical instruments (lenses, mirrors, microscopes, telescopes, fiber‑optic systems, etc.).

2. Historical Milestones

3. Fundamental Concepts

3.1 Light as a Wave

• Electromagnetic wave: oscillating electric (E) and magnetic (B) fields perpendicular to each other and to the direction of propagation.
• Key parameters
  • Wavelength (λ) – distance between successive crests.
  • Frequency (ν) – number of cycles per second; (c = λν) (c = speed of light ≈ 3.00 × 10⁸ m s⁻¹).
  • Amplitude – related to intensity (energy per unit area).

3.2 Light as a Particle (Photon)

• Photon energy: (E = hν = \frac{hc}{λ}) (h = Planck’s constant).
• Explains phenomena such as the photoelectric effect, Compton scattering, and quantum optics.

3.3 Geometrical Optics (Ray Approximation)

• Assumption: Light travels in straight lines (rays) when dimensions are much larger than λ.
• Core laws:
  1. Law of Reflection: Angle of incidence = angle of reflection (measured from the normal).
  2. Law of Refraction (Snell’s Law): (n_1 \sin θ_1 = n_2 \sin θ_2).
  3. Principle of Reversibility: Light paths are reversible in a static medium.

3.4 Wave Optics (Physical Optics)

• Interference: Superposition of two or more coherent waves → constructive or destructive patterns.
• Diffraction: Bending of light around obstacles or through apertures; described by Huygens–Fresnel principle.
• Polarization: Orientation of the electric field vector; can be linear, circular, or elliptical.

4. Optical Media & Indices