2.8 Lasers

Question 1

Stimulated emission

Answer 1

This is the emission of a photon from an excited atom, triggered by a passing photon of energy equal to the energy gap between the excited state and a state of lower energy in the atom. The emitted photon has the same frequency, phase, direction of travel and polarisation direction as the passing photon.

Question 2

Population inversion

Answer 2

A population inversion is a situation in which a higher energy state in an atomic system is more heavily populated than a lower energy state (i.e. a less excited state or the ground state) of the same system.

Question 3

Pumping

Answer 3

Pumping is feeding energy into the amplifying medium of a laser to produce a population inversion.