Guangxia Liu

Effect of Fe3+ on third-order optical nonlinearity of KDP single crystals

A series of trace Fe3+-doped KH2PO4 single crystals were grown using the conventional temperature cooling method. The Fe3+ ion content in the as-grown crystals and the corresponding transmission spectrum were measured, respectively. With an increase of Fe3+ ion concentration, the transmittance of the crystal gradually decreases within the wavelength range of 200 nm to 370 nm. Under picosecond pulse laser irradiation, third-order nonlinear optical characteristics were systematically measured at λ = 532 nm. The existence of nonlinear absorption and nonlinear refraction was demonstrated. The results show that the nonlinear refractive index n2 is positive, indicating the presence of a self-focusing effect for the as-grown crystals. Specially, nonlinear absorption and refraction have a heavy dependence on the Fe3+ ion content and crystal directions (II and z). With increasing Fe3+ ion concentration, a significant variation has been observed with respect to the nonlinear absorption coefficient β, nonlinear refractive index n2 and third-order nonlinear susceptibility χ(3). A similar pattern for II < z has been presented for nonlinear absorption and refraction. The investigations suggest that nonlinear absorption and refraction caused by distortion of the electron cloud might be associated with the H2PO4− and (FeO4)2− groups.

Investigation on (100) face of KDP crystal poisoned by MoO42− impurity

Potassium dihydrogen phosphate (KDP) single crystals doped with molybdate (MoO42−) were grown via the conventional temperature cooling and rapid growth methods, respectively. MoO42− made KDP crystals tapering for conventional temperature cooling method. When KDP crystals were grown by rapid growth method, MoO42− could induce liquid inclusions and simultaneous crystals. The measurement on growth rates indicated that MoO42− broadened the dead zone and decreased the growth rate of (100) face of KDP crystals. The growth kinetic analysis in terms of two-dimensional nucleus and screw dislocation models implied that the energetic parameter γ/kT decreased with an increase of MoO42− concentration. The influence of MoO42− growth steps on (100) face of KDP crystal was observed through ex situ AFM technique. It gave evidence that MoO42− could postpone the step bunching and make the step edge curving and knaggy to reduce the edge free energy, which was in agreement with the growth kinetics calculations. Additionally, the poisoned mechanism of MoO42− and Fe3+ on step morphologies was detailed contrasted. The interaction process was discussed according to electro negativity analysis, which indicated MoO42− (actually were HMoO4− and H2MoO4) could be absorbed onto (100) face through charge-assisted hydrogen bonds and caused more Mo element distributed in prismatic sector.

Effect of Cr 3+ Dopant on Growth Habit and Optical Properties of Rapid Grown KDP Crystal: Effect of Cr 3+ Dopant on Growth Habit and Optical Properties of Rapid Grown KDP Crystal

采用快速法生长了掺杂不同Cr 3+ 浓度的KDP晶体, 测试了KDP晶体(100)面在不同Cr 3+ 掺杂浓度下的生长速度及死区,表征了Cr 3+ 掺杂的KDP晶体的Cr 3+ 元素分布、透过光谱、散射颗粒分布和光损伤阈值. 实验表明Cr 3+ 易吸附在晶体(100)面, 从而增大了(100)生长死区, 并降低了(100)面生长速度. Cr 3+ 使快速生长的晶体产生柱、锥面生长区分界线. 元素分析表明Cr 3+ 更容易通过柱面生长进入晶体, 从而导致晶体在可见光波段及紫外波段透过率的降低,最明显的是在220、450和650nm三处吸收峰的出现. Cr 3+ 进入晶体后使晶体中散射颗粒增多, 基频和三倍频脉冲激光照射下晶体的损伤阈值随Cr 3+ 掺杂浓度的增加而降低,且柱面区的损伤阈值要低于锥面区的损伤阈值.采用快速法生长了掺杂不同Cr 3+ 浓度的KDP晶体, 测试了KDP晶体(100)面在不同Cr 3+ 掺杂浓度下的生长速度及死区,表征了Cr 3+ 掺杂的KDP晶体的Cr 3+ 元素分布、透过光谱、散射颗粒分布和光损伤阈值. 实验表明Cr 3+ 易吸附在晶体(100)面, 从而增大了(100)生长死区, 并降低了(100)面生长速度. Cr 3+ 使快速生长的晶体产生柱、锥面生长区分界线. 元素分析表明Cr 3+ 更容易通过柱面生长进入晶体, 从而导致晶体在可见光波段及紫外波段透过率的降低,最明显的是在220、450和650nm三处吸收峰的出现. Cr 3+ 进入晶体后使晶体中散射颗粒增多, 基频和三倍频脉冲激光照射下晶体的损伤阈值随Cr 3+ 掺杂浓度的增加而降低,且柱面区的损伤阈值要低于锥面区的损伤阈值.

Study on the cracking of a KDP seed crystal caused by temperature nonuniformity

The phenomenon of the cracking of KDP z-cut seed crystals with a series of sizes due to the temperature difference of the growth solution was explored in detail. Thermal stress generated in the KDP seed crystal at the moment of cracking was calculated using the finite-element method. Temperature differences leading to cracking for heated samples were nearly twice those of cooled specimens. For the cooled samples, the cracks occurred mainly along the (100), (110) and (001) crystal planes and expanded from the sample periphery to the interior spaces, and the opposite crack propagation direction was displayed in the heated samples, with cracks observed mainly along the (110) plane. More importantly, the temperature differences were observed to decrease with an increase in the sample size. In addition, the calculated results indicated that the field distribution of tensile stress is coincident with the points of crack initiation. The maximum stresses calculated were found to be greater than the fracture strength of 6.67 MPa for the KDP crystal along the [100] direction, and the direction of large stresses was found to be normal to the fracture surface. It is interesting that the maximum stress in fracture crystals decreases with an increase in the crystal size as cracks are generated.