Monitoring the ultrafast electric field change at a mid-infrared plasma Bragg mirror

The electric field change of a femtosecond mid-infrared (MIR) pulse reflect ed by a new type of Bragg mirror is directly measured by time-resolved cros s-correlation spectroscopy. The refractive-index contrast of the plasma Bra gg mirror is achieved by use of different doping levels of only one type of semiconductor material (n(+)-doped GaAs and undoped GaAs). The direct meas urement of the time dependence of the electric field of a reflected MIR pul se permits the observation of a noninstantaneous response of a Bragg mirror compared with a metallic surface, which is due to the penetration of the p ulse into the multilayer structure. (C) 2001 Optical Society of America.