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Articles you may be interested inExtreme optical nonlinearities in chalcogenide glass fibers embedded with metallic and semiconductor nanowires Appl.Third-order optical nonlinearities and recombination processes of photoexcited electron-hole plasma in PbSe and PbTe are directly monitored by picosecond pump-probe experiments in the wavelength range from 3 to 10 ,WI. After excitation, a strong blue shift of the absorption edge and large changes of the refractive index are found. Time-resolved studies of the absorption changes at lattice temperatures between 70 and 160 K reveal a fast partial decrease of the carrier density within 100 ps at excitation densities exceeding 7X 1017 cme3. Comparative emission spectra demonstrate that this behavior is due to recombination by stimulated emission. At room temperature the nonradiative Auger recombination dominates on a 0.5-2 ns time scale below the threshold of stimulated emission. The overall Auger coefficients for carrier densities of about 101* cmm3 are derived from the data and have values of ~f;~~~=1.1+0.3XlO-~~ cm6/s and ~~~~=2.5+-1.3XlO-~~ cm"/s. 0 I995 American Institute of Physics.

We measure the transmission of THz pulses through thin films of YBa 2 Cu 3 O 7−δ at temperatures between 10 K and 300 K. The pulses possess a usable bandwidth extending from ∼0.1 -1.5 THz (3.3 cm −1 -50 cm −1 ). Below T c we observe pulse reshaping caused by the kinetic inductance of the superconducting charge carriers. From transmission data, we extract values of the London penetration depth, as a function of temperature, and find that it agrees well with a functional form (λ(0)/λ(T )) 2 = 1 − (T /T c ) α , where λ(0) = 148 nm, and α = 2.

Degenerate-four-wave-mixing experiments have been performed on crystalline silicon at 620 nm using 100-fs pulses. Symmetry analysis has been applied to monitor the fourfold (bulk) symmetry of the [100] direction. Deviations from orthogonal polarization of the pump-and-probe beam with respect to the diffracted-signal beam have been studied in detail. The rotation patterns exhibit the transformation behavior of the relevant y"' tensor. Preliminary time-resolved measurements reveal distinct variations of the signal occurring on a time scale of 10 fs upon excitation with 100-fs pulses, which cannot be detected by standard correlation techniques.

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