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.

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.

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..

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.

YbxY1 xAl3 (BO3) 4 (x 0:1, 0.07 and 0) crystals have been grown by the flux method. The growth defects of YbxY1 xAl3 (BO3) 4 crystals were detected by X-ray topography. It is found that the perfection of YbYAB crystal with low Yb dopant is better than that with high Yb dopant. In Yb0. 1Y0. 9Al3 (BO3) 4 crystal, growth bands, growth boundaries, grown-in dislocations and inclusions were observed. However, the densities of growth defects for Yb0. 07Y0. 93Al3 (BO3) 4 and YAl3 (BO3) 4 are low and no obvious inclusions are observed in these crystals. In addition, growth twins were detected in YbxY1 xAl3 (BO3) 4 crystal by using the chemical etching method. It is found that the rowth twins occur frequently in Yb0. 1Y0. 9Al3 (BO3) 4 crystal whereas no growth twin appears in YAl3 (BO3) 4 crystal. Based on the experimental observations, the formation mechanism of growth twins is discussed. In the meantime, the e ective measures for reducing the growth twins and defects are proposed.

The growth defects in #ux grown RbTiOAsO 4 crystal have been investigated by white-beam synchrotron radiation topography. It is found that growth sector boundaries are the primary growth defects and they show strong X-ray kinematical contrast in the topograph. All the dislocations are growth induced and appear only in the near capping region. The area away from the capping region is nearly dislocation free. Growth bands show weak contrast in the X-ray topograph, which implies that the impurity contents are relatively low in various growth sectors and each growth sector is uniform in composition. (1999 Elsevier Science B.V. All rights reserved.

The growth defects in flux-grown NdxYl-xAl3 (B03)4 (NYAB) single crystals have been investigated by means of chemical etching and synchrotron radiation techniques. The band-shaped and polysynthetic twins were detected by optical microscopy due to the difference in etching rates between the host crystal and the twin. In the meantime, the orientation and symmetry of the twins were analyzed from their etching patterns. A large number of etch pits with regular shapes were also found on the surface, and these etch pits correspond to outcrops of the dislocations originating from the seed crystal or inclusions. The growth defects in flux-grown NdxYl-xAl3 (B03)4 (NYAB) single crystals have been investigated by means of chemical etching and synchrotron radiation techniques．The band-shaped and polysynthetic twins were detected by optical microscopy due to the difference in etching rates between the host crystal and the twin. In the meantime, the orientation and symmetry of the twins were analyzed from their etching patterns. A large number of etch pits with regular shapes were also found on the surface, and these etch pits correspond to outcrops of the dislocations originating from the seed crystal or inclusions.

The inhomogeneity in a congruent LiTaO3 crystal has been observed by transmission synchrotron topography. Many extraordinary regions exist in congruent LiTaO3 crystal and they often show diffraction intensity different from that of ordinary regions in synchrotron topographs. Differential thermal analysis indicates that the Curie temperature of the extraordinary region is lower than that of ordinary region, and the extraordinary region is really a high defect density region. The diffraction contrast of the extraordinary region in synchrotron topographs is explained qualitatively by a calculation at the selected wavelength.

Studies of photochromic damage induced in KTiOPO4 single crystals by 514.5nm laser irradiation is reported. A dependence of photochromic damage on polarization was observed. Along the same propagation direction (y901j23:31), the gray-track susceptibility for 8z polarization irradiation is one order magnitude lower than that for >z polarization irradiation for KTP crystal. The results clearly show that in KTiOPO4, a correlation exists between the gray-track susceptibility and the ionic electrical conductivity. Due to a high ionic electrical conductivity along the polar z-axis, the optical absorption centers will be annihilated with 8z polarization irradiation as soon as they are produced. This results in a lower gray-track susceptibility for 8z polarization irradiation.

Large GdCa4O (BO3) 3 crystal has been grown by the Czochralski method. The quality of GdCa4O (BO3) 3 crystal was assessed by white-beam synchrotron radiation topography. It has been found that there is a sub-grain boundary in the GdCa4O (BO3) 3 crystal. The boundary divides the large GdCa4O (BO3) 3 crystal into two individuals. Due to the misorientation between the two individuals, the image shifts can be observed in the synchrotron topographs. Based on the misorientation determined by high resolution X-ray diffractometer, the image shifts were calculated for several reflections. The calculations are in agreement with the measurements from the topographs very well. In addition, the formation mechanism of sub-grain boundary is discussed.