Question

How do you make light coherent?

Answer 1

The features of the interrelationship between physical quantities of a single wave or between numerous waves are described by coherence. When two waves have the same frequency and have a constant relative phase difference, they are said to be coherent.

Therefore,

1. For high-frequency waves like visible light, stimulated emission is the most effective method of producing coherent beams.
2. Coherent beams are formed by feeding a sine-wave electrical current through an antenna for low-frequency radiation such as radio waves.

Hence, this is the way to make light coherent.