What device is used to create coherent light.?

Question

What device is used to create coherent light.?

Answer 1

A laser.

  Light amplification by stimulated emission of radiation.

Answer 2

Laser

"A laser is an optical device that emits coherent light"

Answer 3

To have interference of light you need the sources to be from a coherent light source - that is the light waves are always in the same phase. The only way you can do this is to pass the light from a single source through a double slit. The light that emerges from each slit will then be sources in phase and so coherent light sources.