40 research outputs found
Stimulated Raman Scattering in MeliliteâType Crystals Ca2MgSi2O7 and Ca2Ga2SiO7
Ď(3)ânonlinear optical interactions in two meliliteâtype stimulated Raman scattering (SRS)âactive nonâcentrosymmetric crystals, Ca2MgSi2O7 and Ca2Ga2SiO7, formerly known as Nd3+âlaser media, are presented. Under picosecond pumping at 1.064 and 0.532Â Âľm cascaded and crossâcascaded effects occur in these tetragonal silicates. Besides the SRSâpromoting phonon modes with energy of ĎSRS1 â 908 cmâ1 and ĎSRS2 â 668 cmâ1 for Ca2MgSi2O7, and ĎSRS1 â 720 cmâ1 and ĎSRS2 â 550 cmâ1 for Ca2Ga2SiO7, respectively, combined phonon modes are observed. For Ca2MgSi2O7 new data in a broad wavelength range of refractive indices and their dispersion are given as well. The observed Ď(3)ânonlinear properties expand the functionality of the studied silicates and foreshadow their use in selfâfrequency Raman laser converters (selfâSRS lasers)
Structural investigations of the tetraborates MB4O7 M Pb, Sr, Ba
The crystal structures of the tetraborates MB4O7 were investigated at room temperature for M Sr, Pb, Ba and at 100 K for M Pb, Ba. The influence of the lone electron pair of Pb2 in PbB4O7 can be studied by comparing the isostructural compounds PbB4O7 and SrB4O7. The lone pair shows a clear displacement of the lead atom which increases upon cooling. In contrast with the Sr and Pb compounds, BaB4O7 crystallizes in a centrosymmetric structure. However, this structure seems to be on the border of stability, as we find strong internal stres
Dielectric constants of BaO and melilites and the oxide additivity rule
The constant-stress "free" dielectric constants and dissipation factors of BaO and a series of X_2YZ_2O_7
melilites were measured at 1 MHz using a two-terminal method and empirically determined edge corrections. The
results are:
BaO K = 31.1
Ca_2MgSi_2O_7 K^T_a = 11.83 K^T_c = 7.97
Ca_2CoSi_2O_7 K^T_a = 12.44 K^T_c = 9.00
Ca_2ZnSi_2O_7 K^T_a = 12.03 K^T_c = 8.21
Sr_2CoSi_2O_7 K^T_a = 8.93 K^T_c = 6.87
Ba_2MgGe_2O_7:Nd,Ce = K^T_a = K^T_c= 7.51.
The discrepancies between measured dielectric polarizabilities as determined from the Clausius-Mosotti equation and those calculated from the sum of oxide polarizabilities according to É_D(X_2YZ_2O_7) = 2 É_D(XO) + É_D(YO) + 2 Îą_D(Z0_2) are + 13.6 to + 16.0% for Ca-containing melilites, + 6.1% for Sr_2CoSi_2O_7 and + 1.0% for Ba_(1.92)Nd_(0.04)Ce_(0.04)MgGe_2O_7. The deviations from additivity in the Ca- and Sr-melilites are believed to result from structural misfit between the alkaline earth X ion and the YZ_2O_7 layers which leads to rattling X ions