  We study how the thermalization time of a single radiation cavity-field mode
changes drastically depending on the type of the atomic reservoir it interacts.
Temporal evolution of the field is analyzed within the micromaser scheme, where
each atomic reservoir is modeled as a beam of atoms crossing an electromagnetic
cavity in which they weakly interact with the field. The cavity-field
thermalizes when we consider either multi-atom or multi-level atom reservoirs.
We found that each atomic reservoir generates a different scaling law in the
thermalization time of the cavity-field. Such scaling laws can be used for a
faster or slower heating and cooling process. We have obtained analytical
expressions for the thermalization time that were verified by means of a
numerical simulation of the injection of each atomic reservoir into the cavity.
We also discussed how our results could boost the efficiency and power output
of some quantum heat engines during a finite time operation when the radiation
field mode acts as the working substance.
