Study on optical weak absorption of borate crystals

•The bulk weak absorption values of LBO-family crystals were studied at 1064nm.•We discussed the correlation between the bulk weak absorption and crystal structure.•The results show the bulk weak absorption value depends on the interstitial area. Borate crystal is an important type of nonlinear optical crystals used in frequency conversion in all-solid-state lasers. Especially, LiB3O5 (LBO), CsB3O5 (CBO) and CsLiB6O10 (CLBO) are the most advanced. Although these borate crystals are all constructed by the same anionic group-(B3O7)5−, they show different nonlinear optical properties. In this study, bulk weak absorption values of three borate crystals have been studied at 1064nm by a photothermal common-path interferometer. The bulk weak absorption values of them along [100], [010] and [001] directions were obtained, respectively, to be approximately 17.5ppmcm−1, 15ppmcm−1 and 20ppmcm−1 (LBO); 80ppmcm−1, 100ppmcm−1 and 40ppmcm−1 (CBO); 600ppmcm−1, 600ppmcm−1 and 150ppmcm−1 (CLBO) at 1064nm. The results showed an obvious discrepancy of the values of these crystals along three axis directions. A correlation between the bulk weak absorption property and crystal intrinsic structure was then discussed. It is found that the bulk weak absorption values strongly depend on the interstitial area surrounded by the B–O frames. The interstitial area is larger, the bulk weak absorption value is higher.