Question

We have stimulated emission and spontaneous emission. Do we also have stimulated absorption and spontaneous absorption?

Answer 1

When a photon of energy (E₂ – E₁ = hυ) is incident on an atom in the ground state, the atom in the ground state E₁ may absorb the photon and jump to a higher energy state (E₂). This process is called stimulated absorption or induced absorption.

Spontaneous absorption is the process by which an atom in its ground state spontaneously jumps to a higher energy state, resulting in the absorption of a photon.
We do not have any process such as spontaneous absorption. This is because for absorption, we need to incident a photon of sufficient energy on the atom to stimulate the atom for absorption.