Example of A Model of Gain Medium
A universal model valid for all laser types does not exist. The simplest model includes two systems of sub-levels: upper and lower. Within each level, the fast transitions lead to the Boltzmann distribution of excitations among sub-levels (fig.1). The upper level is assumed to be metastable. Also, gain and refractive index are assumed independent of a particular way of excitation.
For good performance of the gain medium, the separation between sub-levels should be larger than working temperature; then, at pump frequency, the absorption dominates.
In the case of amplification of optical signals, the lasing frequency is called signal frequency. However, the same term is used even in the laser oscillators, when amplified radiation is used to transfer energy rather than information. The model below seems to work well for most optically-pumped solid-state lasers.
Read more about this topic: Active Laser Medium
Famous quotes containing the words model, gain and/or medium:
“The playing adult steps sideward into another reality; the playing child advances forward to new stages of mastery....Child’s play is the infantile form of the human ability to deal with experience by creating model situations and to master reality by experiment and planning.”
—Erik H. Erikson (20th century)
“I find myself ... hoping a total end of all the unhappy divisions of mankind by party-spirit, which at best is but the madness of many for the gain of a few.”
—Alexander Pope (1688–1744)
“All propaganda or popularization involves a putting of the complex into the simple, but such a move is instantly deconstructive. For if the complex can be put into the simple, then it cannot be as complex as it seemed in the first place; and if the simple can be an adequate medium of such complexity, then it cannot after all be as simple as all that.”
—Terry Eagleton (b. 1943)