Hello Student,

To explain the process of light amplification in a laser requires an understanding of the energy transition phenomena in the atoms of its active medium. They include:  spontaneous emission, stimulated emission/absorption and non-radiative decay.

Spontaneous Emission

By quantum mechanics the lower energy level is more stable than higher energy levels, so electrons tend to occupy the lower level. Those electrons in higher energy levels decay into lower levels, with the emission of EM radiation. This process is called spontaneous emission. The radiation emitted is equal to the energy difference between the two levels.

E2 - E1 = hn0

Where E2 is the upper energy level

E1 is the lower energy level

h is Plank’s constant

n0 is frequency of the radiated EM wave.

Stimulated Emission

This is crucial if lasing is to occur. Suppose the atoms of the active medium are initially in E2. If external EM waves with frequency n0 that is near the transition frequency between E2 and E1 is incident on the medium, then there is a finite probability that the incident waves will force the atoms to undergo a transition E2 to E1. Every E2-E1 transition gives out an EM wave in the form of a photon. We call this stimulated emission since the process is caused by an external excitation. The emitted photon is in phase with the incident photon, has the same wavelength as it and travels in the same direction as the incident photon.

Stimulated Absorption

If the atom is initially in the ground level E1, the atom will remain in this level until it gets excited. When an EM wave of frequency n0 is incident on the material, there is a finite probability that the atom will absorb the incident energy and jump to energy level E2. This process is called Stimulated Absorption.

Hope this helps you. Feel free to ask more questions.

Have a good day!

Hello!

Stimulated emission process is a key factor for the laser action. This can be multiplies through chain reaction. This multiplication of photons through stimulated emission leads to coherent, powerful, monochromatic, collimated beam of light emission.

ALL THE BEST. Hope the answer was helpful.

Thank You