Coherence plays a crucial role in Young’s double-slit experiment, as it ensures that a stable and observable interference pattern forms. Coherence refers to the constant phase relationship between two waves. Here’s how it matters:
- Steady Interference:
For clear and stable interference fringes to appear, the two waves from the slits must have a fixed phase difference over time. This is only possible if the light sources are coherent. - Maintains Fringe Visibility:
If the waves are not coherent, the phase relationship fluctuates randomly, causing the interference pattern to wash out or disappear. Coherence maintains the contrast between bright and dark fringes. - Common Origin:
In the experiment, a single source of light is usually split into two slits to ensure that the light waves reaching both slits are coherent and in phase with each other. - Temporal and Spatial Coherence:
- Temporal coherence ensures consistent phase over time.
- Spatial coherence ensures that the waves maintain a uniform phase across the slit width.