The growth twinning in self-frequency-doubling laser crystal NdxGd1 xAl3 (BO3) 4 (NGAB) has been observed with white-beam synchrotron radiation topography (WBSRT). It is shown that the growth twinning in flux-grown NGAB crystal is the 180 rotation twin in which the twofold symmetric operation axis is parallel to the [0001] direction and this kind of twinning often shows the black-and-white contrast in X-ray topography. It is believed that the growth twinning in NGAB was induced by growth bands formed during crystal growth.

High purity KTiOPO4 (KTP) crystals have been grown using a flux method. The quality, SHG e ciency and damage threshold of KTP crystals grown from high purity reagents were compared with those grown from commercial reagents. Experimental results indicate that KTP crystals using a high purity charge contain less impurities and possess higher SHG efficiency and damage threshold than do crystals grown from commercial reagents. It is proposed that decreasing the concentrations of impurities is an effective way of raising the damage threshold for KTP crystals.

A Raman-scattering study of the vibrational modes in a BiB3O6 crystal was conducted at room temperature. The numbers of external and internal modes obtained in experiment are consistent with the results of a group theoretical analysis. The Raman lines below, 300cm-1 and from, 300 to 1600cm-1 are assigned to the external modes of the lattice and internal vibrations of the BO3 and BO4 subunits of the BiB3O6 structure, respectively.

The growth defects in Nd: YCa4O (BO3) 3 (Nd:YCOB) crystals were investigated by transmission synchrotron topography. It was found that growth striations were the primary defects in Nd: YCOB crystals. Grown-in dislocations, mosaic blocks and inclusions were also observed in the crystals. The effect of temperature field on the formation of growth defects in the crystals was discussed.

Using chemical etching. method, the growth twins in self-frequency doubling laser crystal YbxYl-xAl3 (B03)4 have been observed. The etching pits on both sides of growth twin boundaries in the (101l) slice are ofthe triangles with different orientations. The structure ofgrowth twins is investigated by trallsmission synchrotron topography. In the transmission synchrotron topograph, the growth twins are visible not bv domain contrast 'but by' boundary contrast', i.e. the twins appear in the topograph in form of X-rav kinematical diffraction contrast due to the lattice strain stemming from the impurity incorporaton in the boundaries. The growth twins in YbxY1-xAl3 (B03)4 crystal are of inversion types, since no domain cnntrast Was observed..