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[en] The efficient THz generation by optical rectification from an indigenously grown organic DAST crystal using the 140 fs oscillator laser pulses tunable in between 780 and 850 nm, has been reported in this article. The generated THz pulse profile and powers have been measured using the photoconductive (PC) antennas and pyroelectric detector, respectively. The highest THz peak amplitude and power is obtained at 825 nm central wavelength. The theoretically explanation of the enhancement of THz radiation based on the matching of average optical group refractive index and average THz refractive index of the DAST crystal at 825 nm. In addition, the dependence of THz peak amplitude and THz power on laser power have been carried out. The measured quantum conversion efficiency (QCE) of 0.5 and 1.5 THz bands are of the order 3.7 × 10⁻³, 1.4 × 10⁻³, respectively. Finally, an attempt has been made to study the effect of polarizations on generated THz signal. (author)

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[en] The dependence of current on polarization is studied in the photoemission from the heterostructure of GaAs-(Al Ga)As in an electrostatic uniform external field in case of a slight doping of a p-type GaAs film. The photocurrent emission intensity is estimated as a function of the emitted electron beam polarization. For an electron beam with ρ=0,8 polarization, the emission current density can reach I_e∼10^-3 A/cm². It is shown that there are imposed upper restrictions on the light intensity, and lower restrictions on the acceptor density. 11 refs

[en] Different methods of trap parameter measurement are analysed. Transient photoconductivity and thermally stimulated effects were used to investigate the influence of traps in LEC SI-GaAs and high-resistivity epitaxial GaAs. The peculiarities of the TSC were analysed and shown to be related to the influence of crystal micro-inhomogeneities. (author)

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[en] The study's main objective was the production and characterization of rather closely defined solid-state fullerenes as well as the examination of their photoconductivity and luminescence in the presence of low and high excitation densities. The study was so designed as to throw further light on the changes to be observed for photophysical properties, when the excitation densities are high. (orig.)

[en] In this work, we present photoconductivity measurements performed on metallic p-type Pb_1−xEu_xTe epitaxial films for x ∼ 0.02 and x ∼ 0.03 in the temperature range of 77K–300 K. The results show that sample with x ∼ 0.02 presented negative photoconductivity effect in the whole range of temperatures measured, while sample with x ∼ 0.03 presented a transition from positive to negative photoconductivity. Hall measurements were also performed to investigate the effects observed in both samples, but could not give any conclusive explanation. On the other hand, we showed that disorder changes considerably the generation/recombination ratios as temperature is varied giving rise to the anomalous effects observed. (paper)

[en] Electronic conduction in various polymeric insulating material was investigated. Specially photocurrent was observed in low density and 30*m thick polyethylene when the sample was exposed by low-intensity white light from a tungsten lamp. A large photo-current was observed for the pre-irradiated sample by high dosage gamma-ray. Photo-current was measured for many factors, wave length, voltage, temperature. Photo-current is fairly sensitive to photons with a certin range of energy (about 0.83eV), which might support that charge carriers are optically released from trap centers, it has approximately the same activation energy as the dark current. A tentative energy diagram for irradiated polyethylene is proposed on the assumption of band model. It includes two kinds of shallow trap and deep trap which are considered to play an important role in electrical conduction of polymeric insulator. (Author)