A high optical quality Cesium lithium borate (CLBO) crystal with dimensions of 146 x 132 x 118 mm was grown by the Kyropoulos method. The 4th harmonic generation of a frequency doubled Nd:YAG laser, from 532 to 266 nm, was carried out with a CLBO crystal doubler, and an average output power of 28.4 W was achieved at 266 nm. Polished surfaces were etched to reveal the cracking mechanism of CLBO crystals. Through observation and comparison of the surface etching patterns, it is proved that CLBO crystals crack under chemical attack by water molecules penetrating from the (100) and (010) crystallographic planes. (c) 2006 Elsevier B.V. All rights reserved.