Broadband low-dispersion diffraction of femtosecond pulses from photorefractive quantum wells

Photorefractive quantum wells operating by means of the Franz-Keldysh effect were designed to diffract a bandwidth of approximately 8 nm, nearly matching that of 100-fs pulses, with little dispersion in the diffracted pulses. Large diffraction bandwidths are engineered by adjustment of the well width of the quantum wells in a specific nonuniform distribution across the thickness of the device. The causal relationship between the real and the imaginary parts of the refractive index leads to an excitonic spectral phase with linear dependence on wavelength, resulting in almost distortion-free diffraction. These features render photorefractive quantum-well devices suitable candidates for femtosecond pulse-shaping and spectral holography applications, without the previous bandwidth limitations. (C) 2000 Optical Society of America [S0740-3224(00)00806-7].