Question

As far as I have read in my textbooks, we can only use monochromatic light for making a laser. Why can't we use polychromatic one? What if we try to make a laser out of a polychromatic light?

Answer 1

Laser light must be coherent and monochromatic, characteristics that cannot be achieved with polychromatic light due to its multiple frequencies, undermining the laser's function.

Step-by-step explanation:

To understand why we cannot use polychromatic light for making a laser, it is important to consider the properties of laser light. A laser emits light that is both coherent and monochromatic. Coherent light means that the photons are in-phase with one another, and monochromatic refers to light consisting of a single frequency. In the process of creating laser light, electrons in a gas absorb radiation and are elevated to different energy levels. Some of these electrons do not immediately return to the ground state but instead enter a metastable state.

By ensuring that a majority of electrons are in this metastable state, a cascade of photons that are all in-phase and of the same frequency can be produced when these electrons return to a lower energy level. Attempting to create a laser with polychromatic light, which contains multiple frequencies, would not result in coherent, monochromatic light, which is necessary for a laser to function correctly.