What is a 3 level laser system?

A three-level laser system is a type of laser configuration that involves three energy levels: the ground state, an excited state, and a higher energy state. When an atom or molecule in the ground state is pumped to the higher energy state, it quickly relaxes to the excited state, where it can remain for a brief period before transitioning back to the ground state, emitting a photon in the process. This photon emission can stimulate further emissions, leading to laser action. The three-level system is commonly used in many laser types, including solid-state and gas lasers.