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

Photorefractive quantum wells operating by means of the Franz-Keldysh effec t were designed to diffract a bandwidth of approximately 8 nm, nearly match ing that of 100-fs pulses, with little dispersion in the diffracted pulses. Large diffraction bandwidths are engineered by adjustment of the well widt h of the quantum wells in a specific nonuniform distribution across the thi ckness of the device. The causal relationship between the real and the imag inary parts of the refractive index leads to an excitonic spectral phase wi th linear dependence on wavelength, resulting in almost distortion-free dif fraction. These features render photorefractive quantum-well devices suitab le candidates for femtosecond pulse-shaping and spectral holography applica tions, without the previous bandwidth limitations. (C) 2000 Optical Society of America [S0740-3224(00)00806-7].