How Does a Laser Work? (IMAGE) Forschungszentrum Juelich Caption In a laser (short for "light amplification by stimulated emission of radiation"), energy is fed into the "active medium" through a pumping process. This pumping process can occur optically through irradiation with light or electrically. The necessary pumping power can vary considerably, depending on the type of laser. The excited electrons are thus excited to a higher, metastable energy level. These states should last as long as possible so that a "population inversion" can be established, in which a large number of atoms or molecules are in a state of excitation. Stimulierte Emission All that is needed now is stimulation by a photon with the energy to be emitted, so that the excited atom falls back into its ground state and in the process sends out a photon with identical energy. This multiplication by 2 of the stimulating photon makes the laser medium act as an amplifier. The newly produced photon, in turn, excites other excited atoms or molecules so that they also emit photons. This leads to the chain reaction that produces laser radiation. Credit Copyright: Forschungszentrum Jülich Usage Restrictions Please give credit. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.