Femtosecond pulses can be shaped in the time domain by diffraction from dynamic holograms in a photorefractive multiple quantum well placed inside a Fourier pulse shaper. We present several examples of shaped pulses obtained by controlling the amplitude or the phase of the hologram writing beams, which modifies the complex spectrum of the femtosecond output.

No abstract

Coded ultrafast optical pulses can be treated as onedimensional (1-D) images in the time domain. We have converted space-domain images into time-domain images using diffraction from dynamic holograms inside a Fourier pulse shaper, with photorefractive quantum wells (QW's) used as the dynamic holographic medium. We present several examples, in which amplitude or phase modulation of the hologram writing beams modifies the complex spectrum of the femtosecond output, resulting in a time-domain image. Both storage and processing of time-domain images can be achieved, depending on the hologram writing geometry and power densities. Time-domain processing operations such as edge enhancement, Fourier transform, and correlation are demonstrated.

The Bragg selectivity of volume holograms makes them not well suited for many Fourier imaging processing applications in the space domain because they perform the function of a spatial filter and limit the field of view. Similarly, for femtosecond pulse holography they reduce the spectral bandwidth of the diffracted signal. However, we show both theoretically and experimentally that it is much easier in the frequency domain than in the space domain to achieve a large enough diffraction bandwidth of volume holograms for the bandwidth of 100-fs pulses to be used for frequency-domain femtosecond pulse shaping. The experiments were performed by nondegenerate four-wave mixing in photorefractive InP:Fe with femtosecond readout at 1.5 m.

The diffraction of 100-fs pulses from the static gratings of photorefractive quantum wells (QW's) produces diffracted pulses that are nearly transform-limited, despite the strong dispersion near the quantum-confined excitonic transitions. This quality makes the QW's candidates for use in femtosecond pulse shaping, although the currently limited bandwidth of the quantum-confined excitonic transitions broadens the diffracted pulses. Femtosecond electric-field cross correlation and spectral interferometry techniques completely characterize the low-intensity pulses diffracted from stand-alone photorefractive QW's, and from QW's placed inside a Fourier-domain femtosecond pulse shaper.