Coherence and interference

Coherence
When waves interfere they tend to be coherent.

A light field is called coherent, when there is a fixed phase between EM fields in different location and time.


 * spatial coherence - correlation between the electric fields at different locations
 * temporal coherence - correlation between the electric fields at different times

Interference
Newton's rings experiment shows interference patterns, produced by two lenses and the air between. Wave reflected from the first lense interfere with reflected light from the second lense.

Interference can be:


 * constructive - when waves overlap together, their crests combines
 * destructive - when the waves cancel each other, not combines

Double slit experiment shows a product of interference between two diffracted beams of laser light which sent through two slits.