Nazim Mamedov

Lasing Possibility in Rare-earth Element Doped Thiogallate Compounds

In this paper discussions based on the result of a pump-probe experiment are given on a possibility of application of the emission from Ce doped CaGa2S4 to production of a new laser. Existence of enough gain for laser action was clearly demonstrated from the analysis of the experimental result. Using the phonon-terminated character of this emission, construction of an unique laser having wide wavelength tunability covering violet to green region is thought to be possible. As far as optically pumped lasers are concerned, the only problem to be solved is to grow good single crystals having a suitable size (1×1×1 mm3 or more). In order to realize injection type semiconductor lasers with this material, we have to study conduction type and conductivity control technique together with a suitable epitaxial growth method for obtaining thin films of this material. It is pointed out that Ce doped SrGa2S4 and BaGa2S4 are also strong candidates for construction of similar lasers.

Dielectric Function Spectra and Intraband Density-of-States in TlSe

Room temperature spectroellipsometric study of TISe was performed in the photon energy region 1.5-4.6eV. The tensor components of the dielectric function spectrum of TlSe were obtained. Interband density-of-states (DOS) derived from XX (YY) and ZZ components of the obtained dielectric function spectrum was then compared with the calculated intraband DOS, taking into account for selection rules and transition probabilities. It is found that contribution of the interband optical transitions in Γ, T and N points quite plausibly explains main structures in the obtained dielectric function spectra. However, some structures cannot be explained due to optical transitions in these symmetry points. A corresponding assignment is given and discussed.

One-Phonon Spectra and Effective Phonon Density-of-States in CaGa2S4

Room temperature Raman study of the crystalline and amorphous CaGa2S4 was done. Stokes and Anti-Stokes spectra were obtained in back-scattering geometry using a high rejection double monochromator and the 5 14.5nm line of an argon ion laser. Except for polarization characteristics, the Raman spectra of the polycrystalline CaGa2S4 represent one-phonon spectra at the center of the Brillouin zone. The spectra consist of 18 lines rather than 84 Raman-active lines given by the factor-group analysis. The distribution of the one-phonon density-of-states from ωmin=74.7cm-1 to ωmax=4 12.7cm-1 exhibits a frequency gap between 199.8 cm-1 and 284.7cm-1. The effective phonon density-of-states across the Brillouin zone, which was derived from the Raman spectrum of the amorphous CaGa2S4, exhibits somewhat different distribution of the peak densities compared to one-phonon spectra. The upper limit for Debye approximation in CaGa2S4 is found at 21.7 cm-1. The applicability of the molecular approach to the Raman spectra of CaGa2S4 is discussed. It is proposed that two different structural units generate the most intense 284.7cm-1- and 360.7cm-1 -vibrations above the frequency gap.

Molecular Modes in Vibration Spectra of CaGa2S4

Polarization dependence of the effective phonon density-of-states (DOS), and the depolarization ratio were investigated on amorphous CaGa2S4 by means of Raman spectroscopy at room temperature in ∥- and ⊥-configurations of the scattered light vector with respect to the scattering plane. It was found that the structures are more intense in the DOS derived from the Raman spectra in ∥-configuration. Position of the DOS maximum is moved away from its location at 360.7cm-1 in one phonon spectra by -20cm-1 and +20 cm-1 for ∥- and ⊥-configurations, respectively. The depolarization ratio exhibits a plateau and a clear-cut minimum at around 220cm-1 and 290cm-1, respectively The minimum comes to the intense 284.7cm-1 mode in the one-phonon spectra of CaGa2S4. The intense 360.7 cm-1 mode in the one-phonon spectra falls in the region of a drastic increase in depolarization ratio. Vibration modes in the orthorhombic CaGa2S4 can be classified as \varGammaν(Raman-active)=19Ag+22B3g+222g+21Blg and \varGammaν(IR-active)=21B3u+21B2u+20B1u, respectively. However, the obtained experimental results point to the molecular character of some modes in the vibration spectra of CaGa2S4.