Coherent sources
Intermediate
Constant phase difference needed for interference.
Sources with a constant phase difference produce stable interference patterns. Light from two ordinary bulbs isn't coherent, but two slits lit by the same source are.
Lasers are highly coherent.
Same frequency is necessary but not sufficient.
In more detail
Coherent sources maintain a constant phase difference, which is needed for stable interference patterns. Lasers are highly coherent, while ordinary lamps are not.
Real-world uses
- Lasers are used in holography because they are coherent.
- Interference experiments require coherent light sources.
- Lasers are coherent sources, which produce stable interference patterns in holography and metrology.
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Frequently asked questions
Why do ordinary lamps not show interference?
Their light is emitted in random bursts, so phases change too quickly for stable patterns.
What is coherence length?
The distance over which the light stays coherent.
Why do two ordinary lamps not interfere?
Their light is emitted by many independent atoms, so their phase differences change randomly and no stable pattern forms.
Related topics in Optics
Camera and f-number · Wave theory of light · Huygens' principle · Young's double slit · Fringe width · Intensity in interference