  A time-resolved analysis of the amplitude and phase of THz pulses propagating
through three-dimensional photonic crystals is presented. Single-cycle pulses
of THz radiation allow measurements over a wide frequency range, spanning more
than an octave below, at and above the bandgap of strongly dispersive photonic
crystals. Transmission data provide evidence for slow group velocities at the
photonic band edges and for superluminal transmission at frequencies in the
gap. Our experimental results are in good agreement with
finite-difference-time-domain simulations.
