Abstract
Zero-displacement electro-optic sampling has a demonstrated rise-time resolution of 150 fs.1 We use this technique to investigate photoconductivity in semiconductors for these very short times. As shown in Fig. 1, for optical excitation adjacent to one electrode it is possible to locally excite carriers while minimizing the current flow through the adjacent high-resistivity region. As a result, very high field changes can be generated. These fields contribute to the energy of the excited carriers and can cause scattering into the satellite valleys for excitation energies well below the satellite-valley energy. Unlike transient reflectivity measurements, photoconductive measurements are made in the presence of an applied electric field. The available energy is divided into radiative and kinetic contributions2 and can be large enough to scatter carriers into an otherwise inaccessible satellite valley (as well as to cause a radiated pulse).
© 1993 Optical Society of America
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