3. Pumping mechanisms

3.1 Optical pumping

Theoretically elaborated in 1950 by the team of Kastler, optical pumping was the first, in ruby, to produce the laser effect (T.H. Maiman, 1960); it is still employed today. A powerful pulsed discharge lamp delivers an intense flash of light over a wide spectrum (white light and ultraviolet). Because of conditions dictated by the operation of the lamp and by thermal phenomena the process is most often repetitive with a frequency from several hertz to several tens of hertz. The simplified mechanisms of three- or four-level systems presented above require very selective pumping to supply level E ₂ (figure