  The ultrafast response of a high-reflectivity GaAs/AlAs Bragg mirror to
optical pumping is investigated for all-optical switching applications. Both
Kerr and free carrier nonlinearities are induced with 100 fs, 780 nm pulses
with a fluence of 0.64 kJ/m^2 and 0.8 kJ/m^2. The absolute transmission of the
mirror at 931 nm increases by a factor of 27 from 0.0024% to 0.065% on a
picosecond timescale. These results demonstrate the potential for a
high-reflectivity ultrafast switchable mirror for quantum optics and optical
communication applications. A design is proposed for a structure to be pumped
below the bandgaps of the semiconductor mirror materials. Theoretical
calculations on this structure show switching ratios up to 2200 corresponding
to switching from 0.017% to 37.4% transmission.
