Direct pumping is also called "in-band pumping" or resonnant pumping. These are the same idea realizing high slope efficiency in laser oscillator. The efficiency of a laser oscillation is defined by mainly 3 conditions: the first is the setup of its resonnator, the second is the effeciecy of gain media, and the third is the stokes shift between pump and output. This stokes shift reduce the photon energy and this is expressed by "Atomic quantum efficiency". The direct pumping technplogy can improve this atomic quantum efficiency by the appropriate selection of the frequency domain of pumping source.