Electromagnetic radiation (10) is provided in a gas mixture (12) including helium in the X(1) state and nitrogen in the Y(1) state. The helium is pumped to excite a high population density of its atoms from the X(1) state to the X(2) state; and photons (15) of suitable frequency are injected into the mixture (12) to excite, via a three-body radiative collision of an atom of X(2) with a molecule of Y(1) and a photon (15): a high population density of molecules of the nitrogen from the Y(1) state to the Y(3) state, followed by a substantially simultaneous return of a substantial portion of the excited helium atoms to the X(1) state and a substantial depopulation of the Y(3) state of the nitrogen, causing the molecules thereof to drop to the lower energy Y(2) state, thereby stimulating the emission from the nitrogen of two photons (10) at the same wavelength for each absorbed photon (15), and thus providing a total quantity of photon emission (10) with sufficient gain for amplification of electromagnetic radiation (10), and finally resulting in the depopulation of the molecules in the Y(2) state by autoionization.