What are the coherent source of light ? What are the conditions for obtaining two coherent sources of light ?

Explanation

The sources of light which emit light waves of same wave length, same frequency and in same phase or having a constant phase difference are called coherent sources of light.
Conditions for obtaining two coherent sources
(i) Coherent sources of light should be obtained from a single source with the help of some device.
(ii) The two sources should give monochromatic light.
(iii) The path difference between two waves from two sources should be small.