On New NLO Crystals of the Borate series — LBO VS BBO

Abstract

β-BaB2O4(BBO) is an excellent UV NLO crystal(1). Its salient features may be summarized as follows: 1) it possesses a rather wide phase-matchable range from infrared region to ca. 190 nm; 2) it has a very high damage threshold up to 13 GW/CM2 at 1,064 nm and 1 ns pulsewidth as well as a very wide temperature acceptance width (55°C for SHG at 1,064 nm); 3) it exhibits a NLO coefficient ca. 4 times that of d-36(KDP). As a result, this crystal has been identified as a prime NLO crystal for frequency of dye lasers to generate deep UV radiation. However, BBO crystal has the following shortcomings: 1) since d31≈0, deff of this crystal will decrease with increasing phase-matching angle θpm, and thus BBO crystal cannot be used for 90° noncritical phase-matching; 2) the absorption edge of the crystal appears at 189 nm in the UV range, ca. 30 nm longer than that of the KB5 crystal, thus BBO cannot be used to generate deep UV radiation of wavelength shorter than 200 nm at room temperature; 3) its small angle acceptance width (≈0.80 mrad-cm) also limits its applications in harmonic generation of lasers with larger divergences.