A new understanding of the wurtzite-spalerite phase transition in CdTe and ZnTe compounds in connection with the vapor growth of single crystals.

Abstract. The application of optoelectronic techniques to the generation and detection of THz radiation is now well established. Wide gap semiconductor crystals of groups II-VI, III-V and III-VI are abundantly used. However, some limitations are occurred while using powerful laser systems. In this paper we introduce experimental results of two-photon absorption (2PA) in ZnSe, ZnTe and GaP studied with femtosecond pump-probe supercontinuum spectroscopy. Using of supercontinuum helps us to measure 2PA absorption dynamics and nonlinear index of refraction in wide frequency ranges. Besides influence of Fe concentration in ZnSe:Fe crystals on transmitted THz radiation is described.

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The work is devoted to experimental research of Gruneisen parameter of fullerite C60 (100) single crystal near structural phase transition at 260 K using photoacoustic technique. For measurements automated set-up with laser excitation and piezoelectric registration was used. For illumination of a sample the He-Ne laser was used, which radiation (with wavelength 0.63 microns and power 25 mW) was modulated on intensity on frequency of 32 Hz. The investigated sample of C60 single crystal had the sizes of 5*5*2 mm. Estimation was shown, that thermoelastic regime of photoacoustic signal generation was realized on this frequency, and electronichole system was not influenced on photoacoustic signal. The anomalous behavior of photoacoustic signal was revealed in the fields of temperatures near 260 K. Gruneisen parameter in high-temperature phase is less in two times, than in low-temperature phase, and increases in 5 times in the field of transition at decreasing of temperature.