研究了同成分掺镁铌酸锂晶体中的紫外光致吸收效应。通过对不同掺Mg浓度铌酸锂晶体的紫外光致吸收系数和双色存储灵敏度的测量,发现同成分掺镁铌酸锂晶体的紫外光致吸收效应具有Mg离子浓度阈值效应。只有当掺Mg摩尔分数大于3.0%时,从近紫外一直延伸到近红外波段的紫外光致吸收效应才显示出来。这一Mg离子浓度阈值效应进一步为双色存储灵敏度的测量结果所证实。该浓度阈值小于掺镁铌酸锂晶体抗光损伤效应的摩尔分数阈值4.6%。这种紫外光致吸收现象可能和掺镁铌酸锂晶体中反位铌NbLi浓度的急剧减少基本消失有关。

The ultraviolet-light-induced absorption (UV-LIA) coefficient change is investigated in congruent LiNbO3 crystals doped with Mg2+ of different concentrations. By measuring the UV-LIA coefficient change and the two-color recording sensitivity in congruent LiNbO3∶Mg, it is found that the UV-LIA coefficient change in congruent LiNbO3∶Mg has a threshold effect with respect to the Mg2+-doping concentration. It is only when the molar fraction of Mg2+ is more than 3.0% that the UV-LIA change from the near-UV to the near-infrared spectral regions appears. The threshold behaviour is further confirmed by the measurement of the two-color recording sensitivity. This threshold molar fraction is lower than the so-called optical damage-resistant threshold concentration of 4.6% in LiNbO3∶Mg. The UV-LIA absorption effect is assumed to be related to the decrease and even elimination of the antisite defect NbLi in LiNbO3∶Mg.