Saturation effects Pump Ip np sp Signal I n0 s 2 level system

Ip= 0 ph/s/cm2

Ip= 1.1022 ph/s/cm2

Ip= 5.1022 ph/s/cm2

Ip= 1.1023 ph/s/cm2

Ip= 1,5.1023 ph/s/cm2

Ip= 2.1023 ph/s/cm2

Ip= 3.1023 ph/s/cm2

Ip= 5.1023 ph/s/cm2

Ip= 1.1024 ph/s/cm2

Comments Differences between 2, 3 and 4 level systems The 3 level system shows clearly its properties : absorbant medium at the beginning and then a gain medium when the pumping intensity is high enough The 4 level is always a gain medium whereas the 2 level system is always an absorbing medium Saturation on the laser transition When the laser intensity increases, all the curves are closer to the x axis : it is the saturation of the laser transition : absorption and stimulated emission rates become more important than the other rates. Saturation intensity versus pumping intensity The curves show that it is more difficult to saturate a medium if the pump intensity is important