Erbium 3‐μm laser as an upconversion system

The possibilities to obtain efficient 3-mm lasing in erbium sys- tems on the self-saturated transition 4 I 11/2! 4 I 13/2 are analyzed. In the frame of the mathematical model based on analytical expressions for population inversion, photon flux density, and quantum efficiency, ob- tained in the stationary regime, and which explains the main character- istics of 3-mm generation, the influence of various interaction mecha- nisms such as cross-relaxations, transfer to impurities, excited-state absorption (ESA) and so on is analyzed. It is shown that, although ESA from the terminal laser level could improve the generation characteris- tics, the driving mechanism for 3-mm erbium lasers is the cooperative upconversion from the terminal laser level.