Wave Optics: Interference and Diffraction

Sep 14, 2024

Wave Optics Lecture Notes

Introduction

  • Instructor: Dr. Vanna Sharma (Ajay Kumar Garg Engineering College)
  • Subject: Engineering Physics (KS101T)
  • Topic: Wave Optics, focusing on Interference and Diffraction

Key Phenomena in Optics

  1. Interference
  2. Diffraction
  3. Polarization

Structure of the Lecture

  • Discussion on Interference as the first part of Wave Optics.
  • Topics covered include:
    • Meaning of interference of light
    • Types of interference
    • Conditions for interference
    • Coherent sources
    • Methods to obtain coherent sources
    • Interference in uniform and wedge-shaped thin films
    • Newton’s ring experiment
    • Applications of interference

Reference Materials

  • Books:
    • Engineering Physics by Namneet Gupta
    • Optics by Ajay Ghatak
    • Engineering Physics by SK Gupta and SL Gupta
    • Relevant internet links for additional resources.

Understanding Interference

  • Definition: Superposition of two coherent light waves of the same frequency and nearly the same amplitude redistributes light intensity in space.
  • Examples: Colors seen on soap bubbles and oil on water due to interference effects.

Dual Nature of Light

  • Geometrical Optics (Ray Optics): Evidence of particle nature of light.
  • Physical Optics (Wave Optics): Evidence of wave nature of light.

Types of Interference

  1. Constructive Interference: Occurs when the phase difference is an even multiple of π (maxima).
    • Conditions:
      • Phase difference (δ) = 0, 2π, 4π, ...
  2. Destructive Interference: Occurs when the phase difference is an odd multiple of π (minima).
    • Conditions:
      • Phase difference (δ) = π, 3π, 5π, ...

Conditions for Interference

  • Constructive Interference (Maxima):
    • Condition in terms of phase difference: δ = 2nπ (n = 0, 1, 2,...)
    • Intensity: I = I1 + I2 + 2√(I1 * I2)
  • Destructive Interference (Minima):
    • Condition in terms of phase difference: δ = (2n + 1)π (n = 0, 1, 2,...)
    • Intensity: I = I1 + I2 - 2√(I1 * I2)

Coherent Sources

  • Definition: Two sources are coherent if they emit light waves of the same frequency, nearly the same amplitude, and have a constant phase difference.
  • Incoherent Sources: Emit light waves whose phase varies with time.
  • Methods to Achieve Coherence:
    1. Division of Wavefront: Example - Young's Double Slit Experiment.
    2. Division of Amplitude: Example - Michelson Interferometer.

Newton's Ring Experiment

  • Setup involves a monochromatic light source and glass plate at 45 degrees, leading to the formation of concentric rings due to interference.

Conditions for Sustained Interference

  1. Light source must be monochromatic (single wavelength).
  2. Light source must be coherent.
  3. Nearly equal amplitude for good contrast in interference pattern.
  4. Waves must propagate in the same direction.

Conclusion

  • Next class will cover division of amplitude with interference and thin films of uniform thickness.

References

  • Review the provided reference books for further understanding.