Rami Arieli: "The Laser Adventure"

Rami Arieli: "The Laser Adventure" Chapter 2.10 page 6

Conclusion:
As the length of the active medium increases, the amplification increases.

Attention !
There is a limit to this conclusion. In the above discussion absorption in the active medium was not taken into account.

Later we shall see how to calculate both absorption and amplification.
An example for such mathematical calculations are:

Radioactive decay chain.
Chain of water tanks in which the water is flowing from the higher to the lowest through all the tanks.

Result:
If the absorption rate is proportional to N₁, and the emission rate is proportional to N₂, with the same proportionality factor, than the number of photons in the output laser beam depends on N₁-N₂.