optical pumping

optical pumping [′äp·tə·kəl ′pəmp·iŋ]

(optics)

The process of causing strong deviations from thermal equilibrium populations of selected quantized states of different energy in atomic or molecular systems by the use of electromagnetic radiation in or near the visible region.

---

Optical pumping

The process of causing strong deviations from thermal equilibrium populations of selected quantized states of different energy in atomic or molecular systems by the use of optical radiation (that is, light of wavelengths in or near the visible spectrum), called the pumping radiation.

Optical pumping is vital for light amplification by stimulated emission in an important class of lasers. For example, the action of the ruby laser involves the fluorescent emission of red light by a transition from an excited level E₂ to the ground level E₁. In this case E₂ is relatively high above E_l and the equilibrium population of E₂ is practically zero. Amplification of the red light by laser action requires that number of atoms N₂ exceed N₁ (population inversion). The inversion is accomplished by intense green and violet light from an external source which excites the chromium ion in the ruby to a band of levels, E₃ above E₂. From E₃ the ion rapidly drops without radiation to E₂, in which its lifetime is relatively long for an excited state. Sufficiently intense pumping forces more luminescent ions into E₂ by way of the E₃ levels than remain in the ground state E₁, and amplification of the red emission of the ruby by stimulated emission can then occur. See Laser