What is the role of coherence in producing interference patterns?

Coherence plays a crucial role in producing clear and stable interference patterns.

Here’s why:

1. Definition of Coherence:
   • Coherence refers to the fixed phase relationship between two or more waves over time and space.
   • For interference to occur, the light waves must maintain a consistent phase difference.
2. Types of Coherence:
   • Temporal coherence ensures that the waves remain in phase over time. This depends on the monochromaticity (single wavelength) of the light.
   • Spatial coherence ensures that the waves remain in phase across different points in space. This is important when light comes from a single point source or narrow slit.
3. Stable Interference Patterns:
   • If the light is coherent (like from a laser), it produces sharp and stable interference fringes.
   • If the light is incoherent (like from a bulb), the phase changes randomly, and any interference patterns quickly blur or disappear.
4. Double-Slit Experiment Example:
   • To observe bright and dark fringes, the light from the two slits must be coherent.
   • That’s why a single slit or a laser is often used to ensure the waves reaching the two slits are coherent.