Nb∶KTiOPO_4 晶体的生长和倍频性能

Crystal Growth and Second Harmonic Generation Properties of Nb∶KTP Crystal

通过研究晶体生长工艺参数对 Ｎｂ∶ Ｋ Ｔｉ Ｏ Ｐ Ｏ４（ Ｎｂ∶ Ｋ Ｔ Ｐ） 晶体生长的影响，用熔盐顶部籽晶法获得尺寸为５５ｍｍ ×２５ｍ ｍ ×５ｍ ｍ 的 Ｎｂ∶ Ｋ Ｔ Ｐ 透明单晶。研究中发现熔体的温度梯度、籽晶和降温速率将严重影响 Ｎｂ∶ Ｋ Ｔ Ｐ 晶体的生长。 Ｎｂ 离子的引入不利于 Ｎｂ∶ Ｋ Ｔ Ｐ 晶体的生长，尤其是造成晶体易开裂，且沿ａ 轴方向生长速度非常缓慢。同时， Ｎｂ 的引入大大改变 Ｎｂ∶ Ｋ Ｔ Ｐ 晶体的倍频性能。掺杂 Ｎｂ 浓度的摩尔分数为１３ ％ 时， Ｎｂ∶ Ｋ Ｔ Ｐ 晶体的倍频的Ⅱ型相位匹配的截止波长缩短至９３７ｎｍ ，且有效产生４６９ｎｍ 倍频蓝光；掺杂 Ｎｂ 浓度的摩尔分数为３ ％ 时， Ｎｂ∶ Ｋ Ｔ Ｐ 晶体对 Ｎｄ∶ Ｙ Ａ Ｇ 的１ ．０６４２μｍ激光倍频的最佳相位匹配角为θ＝ ８８ ．３２°，＝ ０°，非常接近９０°非临界相位匹配方向。

Base on the study of the effect of crystal growth technological parameters on the crystal growth of Nb∶KTiOPO 4(Nb∶KTP)crystal,the large transparent single crystals of Nb∶KTP crystal with the size of 55mm×25mm×5mm are obtained by top seed flux method.It shows that the temperature gradient in solution,seed crystal and temperature lowering rate have greatly effected on crystal growth.The presence of Nb ion increases the difficulties during crystal growth,especially in making crystals crack easily and greatly decreasing the growth rate along an axis.At the meantime,Nb ion also greatly modifies the nonlinear optical properties of Nb∶KTP crystal. The cut off wavelength for type Ⅱ phase matched (PM) second harmonic generation (SHG) is blueshifted to 937nm and the 469nm blue SHG light is effectively produced in 13mol% Nb∶KTP crystal;the optimum type Ⅱ PM angle for SHG of Nd∶YAG 1.0642μm laser are θ = 88.32° ,  =0° in 3mol% Nb∶KTP crystal,very close to 90° non critical PM direction.