No abstract

No abstract

No abstract

Acousto-optic programmable dispersive filters (AOPDF) can compensate in real time for large amounts of group-delay dispersion. This feature can be used in chirped-pulse amplification femtosecond laser chains to compensate adaptively for dispersion. An analytical expression relating the group delay at the output of the AOPDF to the input acoustic signal is obtained with coupled-wave theory in the case of collinear and quasicollinear bulk acousto-optic interactions and also in the case of planar waveguides and optical fibers. With this relation, the acoustic signal that will induce an arbitrary group-delay variation with frequency can be easily obtained. Numerical simulations are shown to support the principle of arbitrary group-delay control with an AOPDF.

With 31 FiguresThe light-induced changes of refractive indices in electro-optic crystals are based on the spatial modulation of photocurrents by nonuniform illumination. The generation of photocurrents at low light intensity depends on the presence of suitable donors, because most of the crystals of interest are intrinsically transparent in the visible. The electrons or holes, which are excited from the impurity centers by light of a suitable wavelength, are upon migration, retrapped at other locations, leaving behind positive or negative charges of ionized trap centers. The photoexcited charges will be reexcited and retrapped until they finally drift out of the illuminated region and are trapped. The resulting spacecharge field between the ionized donor centers and the trapped charges modulates the refractive indices via the electro-optic effect. Uniform illumination erases the space-charge fields and brings the crystal back to its original state (which process is known as optical erasure).