Electronically exciting a medium with light, or specifically populating certain electronic levels.

Optically pumping some medium essentially means to inject Light in order to electronically excite the medium or some of its constituents into other (usually higher-lying) Energy levels. In the context of lasers or Laser amplifiers, the goal is to achieve a Population Inversion in the Gain medium and thus to obtain optical amplification via stimulated emission for some Range of optical frequencies. In other cases the goal can be to selectively populate a specific electronic level which does not necessarily have an energy well above the Ground state.