  Despite extensive work on high-temperature superconductors, the critical
behavior of an incipient condensate has so far been studied exclusively under
equilibrium conditions. Here, we excite Bi2Sr2CaCu2O8+d with a femtosecond
laser pulse and monitor the subsequent nonequilibrium dynamics of the
mid-infrared conductivity. Our data allow us to discriminate temperature
regimes where superconductivity is either coherent, fluctuating or vanishingly
small. Above the transition temperature Tc, we make the striking observation
that the relaxation to equilibrium exhibits power-law dynamics and scaling
behavior, both for optimally and underdoped superconductors. Our findings can
in part be modeled using time-dependent Ginzburg-Landau theory and provide
strong indication of universality in systems far from equilibrium.
