Femtosecond dynamics of photogenerated quasiparticles in ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ superconducting thin films shows, at T\ensuremath{\le}${\mathit{T}}_{\mathit{c}}$, two main electronic processes: (i) quasiparticle avalanche production during hot-carrier thermalization, which takes about 300 fsec; (ii) recombination of quasiparticles to form Cooper pairs, which is completed within 5 psec. In contrastr, nonsuperconducting epitaxial films such as ${\mathrm{PrBa}}_{2}$${\mathrm{Cu}}_{2}$${\mathrm{O}}_{7}$ and ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6}$ show regular picosecond electronic response.