-
PbIn6Te10晶体生长难度较大,影响因素也较多。下面主要从以下两点探讨。
(1)特殊的晶体生长组分控制。PbIn6Te10相图显示[11],它的固溶体范围很大,从70%的In2Te3、30%的PbTe至83%的In2Te3、17%的PbTe。不同的PbTe与In2Te3组分比例对晶体的生长影响很大,甚至难以生长出晶体。合适的组分比例对生长高品质单晶尤为重要,实验室进行了PbTe与In2Te3多种组分比例配比生长,发现大部分情况下长出的晶体质量较差,光学透过率低。通过深入研究PbTe与In2Te3相图,发现适量偏向In2Te3方向可能有助于PbIn6Te10晶体的生长,通过多次的实验摸索,并对不同的实验配比结果进行检测,最终寻找到一个较适合的适合PbIn6Te10单晶生长的组分配比(In2Te3过量10%左右)。
(2)合适的籽晶熔接温度及梯度控制。优质的籽晶是生长高品质晶体的一个重要影响因素,籽晶熔接温度控制是这一过程的关键,需要长期的实验积累和经验总结。另外,合适的温度梯度选择和稳定的温度梯度维持也非常重要,从维持结晶界面的角度考虑,通常希望温度梯度较大,但过大的温度梯度可能会导致晶体内结晶质量较差。此外,在晶体生长之前,对熔体进行降温过冷,再升温使原料熔融,多次反复操作降低了多晶核结晶的可能,并在此基础上进行籽晶熔接,效果较好。
-
为确认生长的晶体成分及结构,从图2单晶棒中部、顶部取少量单晶研磨成粉末,采用丹东DX-2700X射线衍射仪(扫描速率0.05°·s−1,λ=0.154 06 nm,扫描范围10°~70°),进行XRD测试。图4(a)为中部单晶的粉末衍射图,与标准图谱(PDF#97-007-8951)对比发现,所有衍射峰都可指标为三方结构的PbIn6Te10,峰位与标准图谱完全吻合,没有其他杂峰出现,峰较强,结晶度较高。依据所得的测试数据,计算出的晶格参数为:a=1.496 1 nm,c=1.825 7 nm,与参考文献[6]报道的也非常相近。图4(b)为顶部单晶的衍射图谱,可以看出,出现了In2Te3杂质衍射峰,这可能是生长结束后过量的In2Te3有自动排杂至熔体顶部导致。
-
为检测生长的单晶结晶质量,从生长的晶体棒上中部切割、加工出(131)单晶样品。采用荷兰PANalytical公司的X'PertX射线衍射仪(ω扫描模式)对图3(b)中3号样品进行摇摆曲线测试,测试结果如图5所示,晶面摇摆曲线峰形尖锐,对称性较好,半高宽(FHWM)约0.253°,结晶质量较好,后续将计划降低生长速度,看能否对结晶质量进一步提升、改善。
-
为了检验生长出的单晶在红外波段的透过率,采用两种仪器进行了不同波段的测试,包括美国Midwest公司Lam950型紫外可见近红外分光光度计(范围1~2.5 μm)和德国Bruker公司Vertex 70型傅里叶红外光谱仪(范围2.5~25 μm)。图3(b)中2号样品测试的透过率曲线如图6(a)所示(其中黑线为理论透过极限,蓝线与红线分别代表两台不同范围仪器测得的数据),晶体的截止透光波段约1300 nm(见图6(a)插图),在1.7~25 μm波段具有较高的透过率,在2.5~25 μm波段透过率在50%以上,波动较小。另外,值得注意的是,由于受到仪器测试范围的限制,长波段截止到25 μm,但PbIn6Te10透过率没有显示出下降趋势,也验证了晶体的长波的透光波段非常宽广。
利用下式,进行了晶体吸收系数α[12]的计算:
$$\alpha = - \frac{1}{L}\ln \left( {{{\left\{ {{{\left[ {\frac{{{{\left( {1 - R} \right)}^2}}}{{2T{R^2}}}} \right]}^2} + \frac{1}{{{R^2}}}} \right\}}^{\frac{1}{2}}} - \frac{{{{\left( {1 - R} \right)}^2}}}{{2T{R^2}}}} \right)$$ 式中:T为所测晶体透过率;L为晶体厚度;R为入射光垂直通过界面的反射率(
$R = \dfrac{{{{\left( {n - 1} \right)}^2}}}{{{{\left( {n + 1} \right)}^2}}}$ ,n为晶体折射率[13])。计算的吸收系数α如图6(b)所示,2.5~25 μm波段吸收系数处于0.3~0.6 cm−1之间,后续将进行退火实验,探索能否实现晶体吸收系数的降低。
Growth of the new long-wave infrared nonlinear crystal PbIn6Te10
-
摘要: 新型长波红外非线性晶体PbIn6Te10具有透光波段宽(1.3~31 μm)、非线性系数大(d11=51 pm/V),双折射适宜(~0.05)等优点,在14~25 μm乃至25 μm以上波段具有较大应用潜力。文中通过相图分析结合具体实验,筛选出较合适的组分配比,并采用高温单温区法合成多晶,布里奇曼法生长出尺寸φ11 mm×55 mm的单晶棒。对生长的PbIn6Te10晶体进行X射线衍射、摇摆曲线、透过率等测试,结果表明,晶体为三方结构,晶格常格为a=b=1.496 1 nm,c=1.825 7 nm,生长出的单晶结晶性较好,半高宽(FHWM)约0.253°,2.5~25 μm波段晶体的平均透过率在50%以上,对应收系数处于0.3~0.6 cm−1之间。
-
关键词:
- 非线性光学晶体 /
- PbIn6Te10晶体 /
- 晶体生长 /
- 布里奇曼法 /
- 长波红外
Abstract: The new far-IR nonlinear crystal material PbIn6Te10 has great application potential among 14-25 μm even more than 25 μm because of its special optical properties, including clear transparency(1.3-31 μm), large nonlinear coefficient(d11=51 pm/V) and suitable birefringence(~0.05). The phase diagram analysis combined with the experiment was used to select the appropriate group distribution ratio, the PbIn6Te10 polycrystal was synthesized by high temperature single-temperature zone method(STZM), and single crystal with size ofφ11 mm×55 mm was grown by Bridgman Method. The as-grown crystals were characterized by X-ray diffraction, X-ray rocking curve, infrared transmittance et al. XRD analysis indicates that the crystal has a trigonal structure, the lattice constants of a, b and c are 1.496 1 nm and 1.825 7 nm, respectively. The as-grown crystal is crystallized well (FHWM=0.253°), the infrared transmission is above 50% in the spectral region of 2.5-25 μm, the coefficient is 0.3-0.6 cm−1. -
-
[1] Zhang Guodong, Wang Shanpeng, Tao Xutang. Research progress of infrared nonlinear optical crystals [J]. Journal of Synthetic Crystals, 2012, 41(S1): 17−23. (in Chinese) [2] Zhang Yongchang, Zhu Haiyong, Zhang Jing, et al. Compact widely tunable continuous-wave MgO: PPLN optical parametric oscillator [J]. Infrared and Laser Engineering, 2018, 47(11): 1105008. (in Chinese) [3] Feng Xi, Li Fuquan, Lin Aoxiang, et al. Polarization and intensity dependence of all-optical poling in germanosilicate glass [J]. Infrared and Laser Engineering, 2019, 48(8): 0817002. (in Chinese) [4] Jia Ning, Wang Shanpeng, Tao Xutang. Research progress of mid-and far-infrared nonlinear optical crystals [J]. Acta Physica Sinica, 2018, 67(24): 7−18. (in Chinese) [5] Xu Degang, Zhu Xianli, He Yixin, et al. Advances in organic nonlinear crystals and ultra-wideband terahertz radiation sources [J]. Chinese Optics, 2019, 12(3): 535−558. (in Chinese) doi: 10.3788/co.20191203.0535 [6] Zhao Hangbin, Zhang Zongcun, Chai Mengyang, et al. Wide-swath and long-wave infrared zoom imaging method with variable frame rate [J]. Optics and Precision Engineering, 2018, 26(7): 1758−1765. (in Chinese) doi: 10.3788/OPE.20182607.1758 [7] Andreev Y M, Badikov V V, Ionin A A, et al. Optical properties of PbIn6Te10 in the long-wave IR [J]. Laser Physics Letters, 2016, 13(12): 125405. doi: 10.1088/1612-2011/13/12/125405 [8] Avanesov S, Badikov V, Tyazhev A, et al. PbIn6Te10: new nonlinear crystal for three-wave interactions with transmission extending from 1.7 to 25 μm [J]. Optical Materials Express, 2011, 1(7): 1286−1291. doi: 10.1364/OME.1.001286 [9] Reshak A H, Parasyuk O V, Kamarudin H, et al. Experimental and theoretical study of the electronic structure and optical spectral features of PbIn6Te10 [J]. RSC Advances, 2016, 6(77): 73107−73117. doi: 10.1039/C6RA12734G [10] Ionin A A, Kinyaevskiy I O, Klimachev Y M, et al. Frequency conversion of molecular gas lasers in PbIn6Te10 crystal within mid-IR range [J]. Optics Letters, 2016, 41(10): 2390−2393. doi: 10.1364/OL.41.002390 [11] Avanesov S A, Badikov D V, Badikov V V, et al. Phase equilibrium studies in the PbTe-Ga2Te3 and PbTe-In2Te3 systems for growing new nonlinear optical crystals of PbGa6Te10 and PbIn6Te10 with transparency extending into the far-IR [J]. Journal of Alloys and Compounds, 2014, 612: 386−391. doi: 10.1016/j.jallcom.2014.05.168 [12] Huang Chenghui, Huang Jianhong, Zhang Ge, et al. A method for accurate calculation of the absorption coefficients of optical materials [J]. Laser Journal, 2001(6): 45−46. (in Chinese) [13] Cheng Wendan, Lin Chensheng, Zhang Hao, et al. Theoretical evaluation on terahertz source generators from ternary metal chalcogenides of PbM6Te10(M=Ga, In) [J]. The Journal of Physical Chemistry C, 2018, 122(8): 4557−4564. doi: 10.1021/acs.jpcc.7b10972