  We study the creation of photons in resonant cylindrical cavities with time
dependent length. The physical degrees of freedom of the electromagnetic field
are described using Hertz potentials. We describe the general formalism for
cavities with arbitrary section. Then we compute explicitly the number of TE
and TM motion-induced photons for cylindrical cavities with rectangular and
circular sections. We also discuss the creation of TEM photons in non-simply
connected cylindrical cavities.
