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参考文献 1
Yang X, Zhao X, Yang K, et al. Biomedical applications of terahertz spectroscopy and imaging[J]. Trends in Biotechnology, 2016, 34(10): 810-824.
参考文献 2
Tonouchi M. Cutting-edge terahertz technology[J]. Nature Photonics, 2007, 1(2): 97-105.
参考文献 3
Siegel P H. Terahertz technology in biology and medicine[J]. Microwave Theory & Techniques IEEE Transactions on, 2004, 52(10):2438-2447.
参考文献 4
Sirtori C. Applied physics: bridge for the terahertz gap[J]. Nature, 2002, 417(6885):132-133
参考文献 5
Davies A G, Burnett A D, Fan W, et al. Terahertz spectroscopy of explosives and drugs[J]. Materials Today, 2008, 11(3): 18-26D.
参考文献 6
Takida Y, Namata K J, Suzuki S, et al. Nonlinear optical detection of terahertz-wave radiation from resonant tunneling diodes[J]. Optics Express, 2017, 5(25):5389-5396.
参考文献 7
Yamashita M, Takahashi H, Ouchi T, et al. Ultra-broadband terahertz time-domain ellipsometric spectroscopy utilizing GaP and GaSe emitters and an epitaxial layer transferred photoconductive detector[J]. Applied Physics Letters, 2014, 104(05):1694-1696.
参考文献 8
Jooshesh A, Fesharaki F, Bahrami-Yekta V, et al. Plasmon-enhanced LT-GaAs/AlAs heterostructure photoconductive antennas for sub-bandgap terahertz generation[J]. Optics Express, 2017, 18(25):22140-22148.
参考文献 9
Carnio B N, Greig S R, Firby C J, et al. Terahertz electro-optic detection using a <012>-cut chalcopyrite ZnGeP2 crystal[J]. Applied Physics Letters, 2016, 108(261109):1-4.
参考文献 10
Ding Y J. Progress in terahertz sources based on difference-frequency generation [Invited][J]. Journal of the Optical Society of America B, 2014, 31(11):2696-2711.
参考文献 11
Liu H, Bai W, Feng J, et al. The synthesis of large-diameter ZnTe crystal for THz emitting and detection [J]. Journal of Crystal Growth, 2017, 475:115–120.
参考文献 12
Naftaly M, Molloy J F, Magnusson B, et al. Silicon carbide-a high-transparency nonlinear material for THz applications.[J]. Optics Express, 2016, 24(3):2590-2595.
参考文献 13
Fischer M P, Bühler J, Fitzky G, et al. Coherent field transients below 15  THz from phase-matched difference frequency generation in 4H-SiC[J]. Optics Letters, 2017, 42(14):2687.
参考文献 14
Marder S R, Perry J W, Schaefer W P. Synthesis of organic salts with large second-order optical Nonlinearities[J]. Science, 1989, 245:626-628.
参考文献 15
Ruiz B, Jazbinsek M, and Günter P. Crystal growth of DAST[J]. Crystal Growth & Design, 2008, 8(11):4173-4184.
参考文献 16
Pan F, Knopfle G, Bosshard C, et al. Electro-optic properties of the organic salt 4-N,N-dimethylamino-4'-N'-methyl-stilbazoliumtosylate[J]. Applied Physics Letters, 1996, 1(69):13-15.
参考文献 17
Jazbinsek M, Mutter L, Gunter P. Photonic applications with the organic nonlinear optical crystal DAST[J]. IEEE Journal of Selected Topics in Quantum Electronics, 2008, 14(5):1298-1311.
参考文献 18
Takahashi Y, Adachi H, Taniuchi T. Organic nonlinear optical DAST crystals for electro-optic measurement and terahertz wave generation[J]. Journal of Photochemistry and Photobiology A: Chemistry. 2006, 183: 247-252.
参考文献 19
Cao L F, Teng B, Xu D G, et al. Growth, transmission, Raman spectrum and THz generation of DAST crystal, RSC Advances, 2016, 6(103), 101389–101394.
参考文献 20
Yabuzaki J, Takahashi Y, Adachi H, et al. High-quality crystal growth and characterization of organic nonlinear optical crystal: 4-dimethylamino-N-methyl-4-stilbazoliumtosylate (DAST)[J]. Bulletin Materials Sciences, 1999, 1(22): 11-13
参考文献 21
Hameed S, Yu C, Chen B. An investigation on the growth and characterization of DAST crystals grown by two zone growth technique[J]. Journal of Crystal Growth, 2005, 282:117-124.
参考文献 22
Adachi H, Takahashi Y, Yabuzaki J, et al. Growth of high quality nonlinear optical crystal 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST)[J]. Crystal Growth & Design, 1999, 198(99): 568-571.
参考文献 23
Hameed A, Rohani S, Yu W, et al. Surface defects and mechanical hardness of rapidly grown DAST crystals[J]. Journal of Crystal Growth, 2006, 97:146-151.
参考文献 24
Kawase K, Mizuno M, Sohma S, et al. Difference-frequency terahertz-wave generation from 4-dimethylamino-N-methyl-4-stilbazolium-tosylate by use of an electronically tuned Ti:sapphire laser[J]. Optics Letters, 1999, 15(24):1065-1067.
参考文献 25
Kawase K, Hatanaka T, Takahashi H, et al. Tunable terahertz-wave generation from DAST crystal by dual signal-wave parametric oscillation of periodically poled lithium niobate[J]. Optics Letters, 2000, 23(25):1714-1716.
参考文献 26
Taniuchi T, Okada S, Nakanishi H. Widely tunable terahertz-wave generation in an organic crystal and its spectroscopic application[J]. Journal of Applied Physics, 2004, 11(95):5984-5988.
参考文献 27
Liu P X, Feng Q, Pang Z B, et al. Competition between two parametric processes in a pump source of terahertz-wave difference frequency generation[J]. Journal of Physics D: Applied Physics, 2018,51(39):1-5.
参考文献 28
Suizu K , Miyamoto K , Yamashita T , et al. High-power terahertz-wave generation using DAST crystal and detection using mid-infrared powermeter[J]. Optics Letters, 2007, 32(19):2885-2887.
参考文献 29
Tang M, Minamide H, Wang Y, et al. Tunable terahertz-wave generation from DAST crystal pumped by a monolithic dual-wavelength fiber laser[J]. Optics Express, 2011, 2(19): 779-786.
参考文献 30
Nawata K, Abe T, Miyake Y, et al. Efficient terahertz wave generation using a 4-Dimethylamino-N-methyl-4-stilbazolium tosylate pumped by a dual-wavelength neodymium-doped yttrium aluminum garnet laser[J]. Applied Physics Express, 2012, 5(112401):1-3.
参考文献 31
Dolasinski B, Powers P E, Haus J W, et al. Tunable narrow band difference frequency THz wave generation in DAST via dual seed PPLN[J]. Optics Express, 2015, 3(23): 3669-3680.
参考文献 32
Tokizane Y, Nawata K, Han Z, et al. Tunable terahertz waves from 4-dimethylamino-N-methyl-4-stibazolium tosylate pumped with dual-wavelength injection-seeded optical parametric generation[J]. Applied Physics Express, 2017, 10(022101):1-4.
参考文献 33
He Y X, Wang Y Y, Xu D G, et al. High-energy and ultra-wideband tunable terahertz source with DAST crystal via difference frequency generation[J]. Applied Physics B, 2018, 124(1):16-23.
参考文献 34
Cunningham P D, Hayden L M. Optical properties of DAST in the THz range[J]. Optics Express, 2010, 18(23): 23620-23625.
目录 contents

    摘要

    基于双温区法生长的高质量DAST晶体,成功搭建了高能量、超宽带可调谐差频THz辐射源,系统尺寸40 cm×25 cm,调谐范围达到0.3~19.6 THz,最大输出能量达到4.02 μJ/pulse@18.6 THz,信噪比最高达到32.24 dB,结合振镜扫描技术,以0.1 THz为步长,超宽带光谱扫描时间小于1 min。实验中观测到差频产生THz波的输出饱和现象并研究了基于DAST晶体差频产生THz波的偏振特性与传输特性,证明基于DAST晶体差频产生的THz波消光比达到0.05,且差频过程满足0类相位匹配条件。基于该太赫兹辐射源,对多种固体样品在2~14 THz范围内的超宽带THz光谱信息进行了有效获取。

    Abstract

    We have demonstrated a compact, high-energy and broadly tunable monochromatic terahertz (THz) source with the dimensional size of 40 cm×25 cm, based on difference frequency generation (DFG) in DAST crystal, grown in two-zone growth method. The THz frequency was tuned randomly and rapidly in the range of 0.3~19.6 THz due to the widely tunable KTP-OPO and galvano-optical beam scanner. The highest pulse energy of 4.02 μJ was obtained at 18.6THz in our system. And the highest signal to noise ratio of 32.24 dB was realized at 4.3 THz using 4K-Bolometer detector. Furthermore, the characteristics of THz polarization and divergence angle were measured experimentally. Saturation phenomenon for THz output was observed and studied. Moreover, the transmission THz spectroscopies of materials in solid state were measured with the ultra-wideband tunable THz source based on DAST crystal.

  • 引言

    太赫兹(Terahertz THz)波段是介于毫米波与红外光之间的电磁波谱区域,该频段处于宏观经典理论向微观量子理论以及电子学向光子学的过渡区。由于THz波所处频率范围覆盖了多种物质振转能级,其在物理、化学、生命科学等基础学科以及毒品鉴定、爆炸物检测等光谱应用领域具有重要研究价值与重大应用前[1,2,3,4,5]。宽带THz辐射源是THz光谱测量应用中的核心器件之一。目前,基于飞秒激光泵浦的光整流技术以及基于纳/皮秒激光泵浦的非线性光学差频技术是宽带THz辐射源的技术基础,基于非线性光学差频技术的THz辐射源具有结构紧凑、无阈值、窄线宽、宽调谐且易于集成等优点。基于非线性光学差频技术的THz辐射源性能与非线性光学晶体密切相关,传统无机晶体如:LiNbO3、GaSe、GaAs、ZnGeP2、GaP、ZnTe[6,7,8,9,10,11],其具有非线性系数小、光学波段色散与THz波段色散差异大、高频THz波段吸收系数大等特点,导致传统无机晶体难以实现宽带范围内的THz波高效差频输出。基于传统无机晶体的THz辐射源单脉冲能量难以达到μJ量级,且其调谐范围一般限制在5THz以下。最近,SiC等半导体材料也被证明可以用于差频产生可调谐THz波,调谐范围达到15 THz,但其输出能量较[12,13]。利用无机晶体尚无法同时实现高能量且超宽调谐范围的THz辐射源。与传统无机晶体相比,有机晶体具有非线性系数大、色散曲线平坦、THz波段吸收系数小等诸多优势,使其在基于非线性光学频率变化方法产生THz波的研究中具有转换效率高、带宽大、相位匹配条件简单、易于实现等优势。

    目前报到的多种新型中,吡啶盐体系的有机盐:DAST(4-(4-二甲基氨基苯乙烯基甲基吡啶对甲苯磺酸盐)晶体凭借其成熟的生长工艺、良好的晶体质量、较大的非线性光学系数以及较低的介电常数成为了最佳的THz非线性光学晶体之[14,15,16]。其分子结构如图1所示。

    图 1
                            DAST的分子结构[12]

    图 1 DAST的分子结[12]

    Fig. 1 Molecular structure of the DAST[12]

    在DAST晶体生长方面,瑞士、日本等国家的科研工作者开展了大量工[17,18]。由于DAST晶体的熔点只有256oC,只能利用水浴法控温并在有机溶液环境中进行晶体生[19]。DAST晶体的生长方法主要有自发成核[20]、斜板[21]、籽晶[22]以及双温区[23]。自发成核法是目前最为成熟的DAST晶体生长方法,其结构简单,易于操作;斜板法可以对晶体成核位置以及晶体生长取向进行有效控制;籽晶法可以有效控制晶体成核位置和晶体生长取向,适合大尺寸DAST晶体的生长,成品率高;双温区法可以使溶液实现扩散与对流,晶体生长过程中不断获得溶质分子,加快DAST晶体的结晶生长,易于使晶体以恒定生长速率稳定生长。

    在基于DAST晶体的差频THz辐射源方面,1999年,日本理化学研究所K. Kawase等人利用800nm双波长钛宝石激光器泵浦有机晶体DAST,通过差频手段获得了频率为1.4 THz的THz波输出。2000年,该课题组利用双周期PPLN-OPO替代原有双波长泵浦源获得了1.9~2.5 THz范围内的可调谐THz波输[24,25]。2004年后,日本东北大学T. Taniuchi利用KTP-OPO产生双波长泵浦光,进而在DAST晶体中差频,这大幅拓宽了THz波的调谐范[26]。目前报道的基于DAST晶体的差频THz辐射源中,调谐范围最宽可达30 THz,已远超THz频率范围到达中红外波段,单脉冲能量最大可达μJ量级,转换效率接近10-4 [27,28]。自2011年,针对DAST晶体差频产生超宽带THz波的研究主要集中在如何产生高性能双波长差频泵浦光,一系列新型双波长泵浦系统得以开发,其中包括双波长可调谐连续光纤激光器、Nd:YAG双波长激光器、超宽调谐范围BBO-OPO、窄线宽PPLN-OPG、非共线相位匹配BBO-OPO[29,30,31,32,33]。在众多双波长泵浦源中,双波长KTP-OPO具有调谐范围宽、输出能量高、损伤阈值高、模式匹配好以及结构简易紧凑等优点,是目前针对DAST晶体较为理想的差频泵浦源。

    本文利用双温区法制备出高质量DAST晶体,利用高能量双波长KTP-OPO作为泵浦源,搭建了高能量、超宽带连续可调谐准单色THz辐射源,系统尺寸达到40 cm×25 cm,调谐范围达到0.3~19.6 THz,THz单脉冲输出最大能量达到4.02 μJ/pulse,转换效率达到2.09×10-4,系统信噪比最高达到32.24 dB,结合振镜快速扫描技术,实现了超宽带光谱快速调谐。在实验上观测到差频产生THz波的输出饱和现象并研究了差频产生THz波的偏振特性与传输特性,差频产生THz波消光比达到0.05,并实验证明该差频过程满足0类相位匹配条件。基于该高性能THz辐射源,对多种固体样品的2~14 THz范围内的THz光谱信息进行了有效获取。

  • 1 晶体制备方法与THz辐射源的实验装置

  • 1.1 DAST晶体制备方法

    本研究中DAST晶体生长基于双温区法实现。晶体生长池的下部高温区盛有过量的DAST源粉,加注溶剂甲醇后可形成饱和溶液,上部低温区与下部高温区通过毛细管连接,既可以实现下部饱和溶液在温度场驱动力下向上部低温区传质,也可以避免下部高温区过多的向上部低温区传热影响晶体生长速率,处于低温区中的DAST籽晶可以恒定速率稳定生长,从而获得透过率高、内部应力低的DAST晶体,设定下部高温区温度为50℃、上部低温区温度为41℃,通过10天的生长,2 mm×2 mm×0.2 mm的DAST籽晶稳定生长至4.5 mm×4 mm×0.6 mm。晶体形貌以及晶轴方向如图2所示。

    图 2
                            基于双温区法培养出的DAST晶体照片

    图 2 基于双温区法培养出的DAST晶体照片

    Fig. 2 Photograph of the DAST crystal grown in two-zone method

  • 1.2 基于DAST晶体的超宽带差频THz辐射源实验装置

    基于DAST晶体的超宽带差频THz辐射源实验系统如图3(a)所示。采用高能量Nd:YAG激光器(1064 nm, 12 ns, 10 Hz)作为泵浦源,经1064 nm半波片调整1064 nm激光的偏振态以满足倍频相位匹配条件并入射到KTP倍频晶体中(7 mm×7 mm×10 mm, θ=90°, φ=23.5°),产生高能量532 nm绿光。绿光经特殊镀膜镜片M1(1064 nm和1300~1600 nm HT,532 nm HR)反射进而泵浦双波长KTP-OPO。KTP-OPO采用双通结构以实现走离补偿,由M2(800~900 nm HR,532 nm & 1300~1500 nm HT)、M3(532 nm 和800~900 nm & 1300~1500 nm HR)以及两块相同参数的KTP晶体(7 mm×10 mm×15 mm, θ=65°, φ=0°)构成,其中KTP1晶体固定,KTP2晶体置于电控振镜上(Cambridge Technology, 6230H),通过控制外加电压实现对旋转角度的精确控制和波长的精确调谐。双波长KTP-OPO产生的可调谐双波长近红外闲频光作为DAST晶体的差频泵浦光,其中KTP1晶体产生固定波长的闲频光λ1,KTP2晶体相位匹配角可调,产生波长可在1300~1500 nm范围内连续可调谐的闲频光λ2。差频泵浦光经谐波镜DM(532 nm HR,1300~1500 nm HT)以及双凸透镜(f=200 mm)聚焦后入射到DAST晶体(4 mm×4.5 mm×0.6 mm)上,DAST晶体厚度选择为0.6 mm以尽可能优化超宽带差频输出性能,调整DAST晶体角度使得晶体a轴与双波长偏振方向重合以满足差频0类相位匹配条件。通过调整差频泵浦光的双波长分布,DAST晶体可实现超宽带THz波输出,产生的THz波进入室温工作的THz波探测器Golay Cell中进行探测,探测器窗口覆盖0.55 mm厚的黑色聚乙烯片作为低通滤波器以避免双波长近红外光对于探测器的影响。整个实验装置实物图如图3(b)所示,该系统结构紧凑,尺寸达到40 cm×25 cm,适于作为便携式超宽带THz辐射源与THz光谱检测系统。

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    (a)

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    (b)

    图 3 (a)基于DAST晶体的超宽带差频THz辐射源实验系统示意图,(b)实验装置实物图

    Fig. 3 (a) Diagram of the experimental setup of THz DFG source based on DAST crystal,(b) Photograph of the experimental setup

  • 2 实验结果与分析

  • 2.1 双波长KTP-OPO的输出特性

    KTP-OPO的输出特性是后续DAST晶体差频的决定性因素之一,其输出能量决定了差频产生THz波的泵浦强度,双波长调谐范围决定了差频产生THz波的频率范围。自行搭建的KTP-OPO腔长为30 cm,以避免短腔条件下腔内振荡的高功率密度信号光的复杂非线性过程产生的蓝光现[33]。首先,我们利用光谱仪(Yokogawa,AQ6375)和光电二极管(Thorlabs,DET08C)分别测量了KTP-OPO系统的调谐特性以及双波长差频泵浦光的时域脉冲特性,结果如图4(a)所示。结果表明,双波长各自线宽半高全宽约为70GHz,双波长脉冲半高全宽宽度为11.36ns,且双波长时域波形图无分裂现象,证明产生的双波长闲频光在时域上高度重合。实验中,KTP-OPO中的KTP1晶体保持不动,其输出波长为1311.44 nm,通过控制外加电压改变电控振镜上的KTP2晶体角度以实现波长精确调谐,可实现1300~1500 nm连续可调谐的闲频光输出,理论上可覆盖0-28.75THz的调谐范围。KTP-OPO系统的输出特性如图4(b)所示,当532 nm绿光泵浦能量为134.5 mJ/pulse时,该OPO系统实现最大的输出能量21.3 mJ/pulse,对应的光光转换效率为15.83%,且未见输出饱和现象。为评估DAST晶体中差频过程的泵浦强度,我们采用刀口法测量了DAST晶体处双波长闲频光的聚焦光斑尺寸,其光斑直径达到0.75 mm,根据以上测量结果,我们计算了双波长KTP-OPO系统提供的最大差频泵浦强度为424.6 MW/cm2,以该泵浦强度照射DAST晶体15 min,借助肉眼以及光学显微镜均未观察到DAST晶体表面存在烧灼等损伤情况。

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    (b)

    图 4 (a)KTP-OPO系统的调谐特性以及时域脉冲特性,(b)KTP-OPO系统的输出特性

    Fig. 4 (a) The tunability and pulse characteristics of the KTP-OPO,(b) The output characteristics of the KTP-OPO

  • 2.2 基于DAST晶体的超宽带差频THz辐射源的输出特性

    以高能量、宽调谐双波长KTP-OPO作为差频泵浦源,借助Labview程序,我们利用Golay Cell(TYDEX,GC-1P)采集了DAST晶体差频的THz输出谱,结果如图5所示。由图可知,基于DAST晶体的超宽带THz辐射源调谐范围可达到0.3~19.6 THz。借助振镜扫描技术,以0.1 THz为步长在0.1~20 THz范围内实现单次THz波宽带扫频输出的时间小于1 min。当双波长差频泵浦能量为19.26 mJ/pulse,对应的泵浦峰值功率密度达到384 WM/cm2。根据Golay Cell的校准值85.6 kV/W以及0.55 mm厚的黑色聚乙烯片的衰减系数,计算了该晶体在超宽带范围内各个频点的差频THz输出强度。其中,在18.6 THz处获得最大差频输出能量为4.02 μJ/pulse,对应的转换效率为2.09×10-4。此外,以Golay Cell作为探测器,系统在4.3 THz处的信噪比最高,可达到222.5:1(23.47 dB),若采用液氦制冷的Bolometer作为探测器,可进一步提高信噪比至1675:1(32.24 dB)。由DAST晶体的差频输出结果可知, DAST晶体在超宽带范围内的输出特性并不平坦,这主要是由DAST晶体自身的吸收特性以及相位失配造成的。根据差频理论、DAST晶体在红外波段以及THz波段的色散参数以及吸收系数,考虑目前DAST晶体在THz波段的拟合色散方程的有效应用频率范[34]、差频过程中的相位失配、晶体吸收以及晶体表面菲涅尔反射损耗,理论计算了0.6 mm厚度的DAST晶体在1~9 THz范围内的特征差频输出光谱,如图5中蓝色曲线所示。除2 THz附近处外,基于DAST晶体差频产生THz波的输出特性的理论与实验结果符合较好。造成低频THz频率处理论与实验差异的主要原因为,理论计算中对非线性过程中的三波采用平面波近似,忽略了晶体对于THz波高斯光束的衍射效应。

    图 5
                            THz输出谱的理论计算结果(蓝线)与实验测量结果(红线)

    图 5 THz输出谱的理论计算结果(蓝线)与实验测量结果(红线)

    Fig. 5 The theoretical estimation (blue line) and experimental result (red line) of the THz output in DAST crystal

    为研究基于DAST晶体差频产生THz波的最佳泵浦条件,测量了THz辐射源在4.3THz以及6THz的输入输出特性。图6(a)为不同泵浦能量下的THz波输出能量。由图可知,在4.3 THz以及6 THz频点处的THz波强度均先随双波长泵浦强度的增加而增加,但随着泵浦强度的进一步增加,各频点的THz波输出强度均出现饱和现象。为探究差频过程中饱和现象的原因,利用红外Raman滤波片(Semrock,LP02-1319RU-25)对KTP-OPO产生的双波长进行分光,并分别测量了在不同532 nm绿光泵浦条件下的双波长闲频光各自的输出特性,结果如图6(b)所示。实验结果表明,KTP-OPO腔内两块晶体KTP1与KTP2在OPO振荡过程中由于腔内模式竞争,造成其产生的λ1与λ2的能量增益特性不一致,KTP1晶体的增益明显大于KTP2晶体。在泵浦能量高于51.7 mJ/pulse时,λ1能量开始高于λ2且差距逐渐增大,推断劣化的两波长分量能量比,最终造成了差频过程中出现饱和现象。

    /html/hwyhmbcn/180418/alternativeImage/d630fd2a-ff60-4371-a49e-f7b227954a1a-F011.png

    (a)

    /html/hwyhmbcn/180418/alternativeImage/d630fd2a-ff60-4371-a49e-f7b227954a1a-F012.png

    (b)

    图6 (a)THz波的输入输出特性, (b)不同532nm绿光泵浦条件下的λ1与λ2的输出特性

    Fig. 6 (a) The input-output characteristics of the generated THz wave, (b) The output energies of λ1 and λ2 pumped under different energies of 532nm laser

    实验中采用金属线栅作为检偏器研究了差频产生THz波的偏振特性。考虑金属线栅的条纹间隔,选取4.3 THz作为检测频率,通过旋转金属线栅角度,测量透过线栅的THz波能量以评估THz波偏振态,结果如图7(a)所示。实验结果表明,基于DAST晶体差频产生的THz波具有良好的线偏振特性,消光比达到0.05,且偏振方向与双波长差频泵浦光平行。

    /html/hwyhmbcn/180418/alternativeImage/d630fd2a-ff60-4371-a49e-f7b227954a1a-F014.png

    (a)

    /html/hwyhmbcn/180418/alternativeImage/d630fd2a-ff60-4371-a49e-f7b227954a1a-F015.png

    (b)

    图 7 (a)差频产生THz波偏振态, (b) DAST晶体不同旋转角度下差频产生的THz波强度

    Fig. 7 (a) The polarization measurement of the generated THz wave via DFG, (b) The generated THz intensities with different rotation angles of DAST crystal

    为进一步实验证明DAST晶体中的差频相位匹配条件为0类相位匹配,将DAST晶体在其ab平面内旋转,改变其a轴与双波长差频泵浦光之间的夹角,观测在不同夹角条件下差频产生THz波的强度,实验结果如图7(b)所示。根据DAST晶体的晶格对称性以及0类相位匹配条件,差频THz波强度应满足以下公式,

    ITHzd11I1I2×cos4(θ) ,
    (1)

    其中,d11为DAST晶体差频中的有效非线性系数,I1、I2分别表示差频双波长泵浦光的强度,θ为晶体a轴与双波长差频泵浦光偏振方向的夹角,理论计算结果如图7(b)中蓝线所示。实验结果与理论计算结果相符,证明基于DAST晶体的差频过程中满足0类相位匹配且无其他非线性相位匹配过程。

    THz波的空间传输特性对于其后续光谱与成像应用具有重要的影响,我们对距离晶体后表面不同位置处(7 mm、20 mm、30 mm、45 mm以及55 mm)的THz光斑进行了测量,以明确THz源的光束发散情况。实验中以18.6 THz频率处的输出为例,利用二维扫描平台控制直径为1 mm的小孔对THz光斑进行扫描成像,扫描步长为300 μm,不同距离处的THz光斑分布如图8所示,插图表示距离晶体7 mm处的THz光斑在XY轴向上的光斑分布,由结果可知THz光斑符合高斯光斑分布。基于DAST晶体差频产生的THz波光斑形状近似为椭圆,其横向(X)光斑较小,纵向(Y)光斑较大,光斑尺寸在空间中沿传输方向逐渐扩大,光斑分布沿传输方向逐渐劣化。根据光斑尺寸测量结果,其在XY方向上的发散角为0.09 rad以及0.15 rad。

    图 8
                            不同距离处的THz光斑发散情况;插图为距离晶体7 mm处THz光斑高斯分布情况

    图 8 不同距离处的THz光斑发散情况;插图为距离晶体7 mm处THz光斑高斯分布情况

    Fig. 8 The distribution of THz beam at different distances from DAST crystal; The inset shows the Gaussian beam of the THz wave in X and Y direction at the distance of 7 mm from the DAST crystal

    与现有THz差频辐射源相比,基于DAST晶体的超宽带THz辐射源在调谐范围、输出能量以及转换效率方面具有巨大优势,同时其优良的偏振特性、输出稳定性以及调谐速度使其在物质超宽带光谱研究方面具有研究潜力。该系统的光谱分辨率较低,仍有较大提升空[31],主要是受限于本实验系统中的1064 nm激光器性能,若采用单频激光器泵浦同时结合种子注入OPO等技术可大幅提高该系统的光谱分辨率。

  • 2.3 基于DAST晶体的超宽带THz辐射源的物质光谱测量

    物质在THz波段的光谱特性在物质鉴定分析以及基础物理研究当中具有重要的研究价值。目前一般采用THz-TDS系统以及FT-IR系统评估物质在THz波段的光谱特性,但是常用THz-TDS的光谱范围有限(~1-3THz),FT-IR在低频范围内的信噪比较低。本文自主搭建的基于DAST晶体的超宽带THz辐射源具有光谱范围宽的优势,同时其准单色、可调谐、线偏振的输出特性,使其在物质超宽带THz光谱信息获取方面具有巨大应用潜力。

    基于上述超宽带THz源,我们对多种固体样品进行了透射式光谱测量,样品包括:透明胶带、白色聚乙烯片、SiC晶片、高阻Si片、石英片以及普通玻璃,光谱扫描步长设置为0.1THz,扫描光谱范围为2~14 THz,测量结果如图9所示。现有研究基础证明了该系统的测量稳定性与准确[33],进一步将部分样品测量结果与THz-Database中利用FT-IR系统的测量结果进行了对比,两者符合较好,再次证明该系统的测量准确性。结果表明,透明胶带、白色聚乙烯片,SiC晶片以及高阻Si片在超宽带THz频率范围内具有较为稳定且优良的透过率,因此可作为理想的超宽带THz波段的基底材料或窗口材料;石英片的透过率随THz频率升高而下降,且在5 THz频率以上基本无法透过THz波,因此其适合作为低频THz波段的基底材料;普通玻璃在整个THz波段的透过率均极低,较为适合作为THz波滤光片等功能器件材料。基于DAST晶体的超宽带THz辐射源有效补充了物质在超宽带THz频率范围内的光谱信息,为物质在THz波段的特性鉴别与分析提供了更为丰富的光谱选择区间,且具有小型化、室温运转等优势。

    图 9
                            不同固体样品的超宽带THz光谱

    图 9 不同固体样品的超宽带THz光谱

    Fig. 9 The ultrawide THz spectroscopies of materials in solid state

  • 3 结论

    本文基于双温区法生长的高质量DAST晶体(4 mm×4 mm×0.6 mm),以高能量双波长KTP-OPO系统作为差频泵浦源,实现了高能量、超宽带可调谐小型化差频THz辐射源的设计与搭建,系统尺寸达到40 cm×25 cm。该辐射源的调谐范围达到0.3~19.6 THz,系统最大THz单脉冲能量在18.6 THz处达到4.02 μJ,以Bolometer作为探测器时,系统信噪比最高可达32.24dB,同时结合振镜扫描技术,以0.1 THz为步长实现了超宽带光谱扫描时间小于1 min的调谐速度。实验观察到差频产生THz波存在输出饱和现象并研究了差频产生THz波的偏振特性以及传输特性,实验表征了基于DAST晶体差频产生的THz波具有线偏振特性,消光比达到0.05,并证明差频过程满足0类相位匹配。基于该系统对透明胶、白色聚乙烯、SiC、高阻Si、石英片以及普通玻璃等常见材料的在2~14 THz范围内的超宽带THz光谱信息进行了有效获取。结果表明,基于DAST晶体的超宽带差频THz辐射源极大地拓展了THz波的输出频率范围,对THz光谱测量以及多光谱成像领域的研究具有重要的推动作用。

    -----------------------------------------------------------

  • References

    • 1

      Yang X, Zhao X, Yang K, et al. Biomedical applications of terahertz spectroscopy and imaging[J]. Trends in Biotechnology, 2016, 34(10): 810-824.

    • 2

      Tonouchi M. Cutting-edge terahertz technology[J]. Nature Photonics, 2007, 1(2): 97-105.

    • 3

      Siegel P H. Terahertz technology in biology and medicine[J]. Microwave Theory & Techniques IEEE Transactions on, 2004, 52(10):2438-2447.

    • 4

      Sirtori C. Applied physics: bridge for the terahertz gap[J]. Nature, 2002, 417(6885):132-133

    • 5

      Davies A G, Burnett A D, Fan W, et al. Terahertz spectroscopy of explosives and drugs[J]. Materials Today, 2008, 11(3): 18-26D.

    • 6

      Takida Y, Namata K J, Suzuki S, et al. Nonlinear optical detection of terahertz-wave radiation from resonant tunneling diodes[J]. Optics Express, 2017, 5(25):5389-5396.

    • 7

      Yamashita M, Takahashi H, Ouchi T, et al. Ultra-broadband terahertz time-domain ellipsometric spectroscopy utilizing GaP and GaSe emitters and an epitaxial layer transferred photoconductive detector[J]. Applied Physics Letters, 2014, 104(05):1694-1696.

    • 8

      Jooshesh A, Fesharaki F, Bahrami-Yekta V, et al. Plasmon-enhanced LT-GaAs/AlAs heterostructure photoconductive antennas for sub-bandgap terahertz generation[J]. Optics Express, 2017, 18(25):22140-22148.

    • 9

      Carnio B N, Greig S R, Firby C J, et al. Terahertz electro-optic detection using a <012>-cut chalcopyrite ZnGeP2 crystal[J]. Applied Physics Letters, 2016, 108(261109):1-4.

    • 10

      Ding Y J. Progress in terahertz sources based on difference-frequency generation [Invited][J]. Journal of the Optical Society of America B, 2014, 31(11):2696-2711.

    • 11

      Liu H, Bai W, Feng J, et al. The synthesis of large-diameter ZnTe crystal for THz emitting and detection [J]. Journal of Crystal Growth, 2017, 475:115–120.

    • 12

      Naftaly M, Molloy J F, Magnusson B, et al. Silicon carbide-a high-transparency nonlinear material for THz applications.[J]. Optics Express, 2016, 24(3):2590-2595.

    • 13

      Fischer M P, Bühler J, Fitzky G, et al. Coherent field transients below 15  THz from phase-matched difference frequency generation in 4H-SiC[J]. Optics Letters, 2017, 42(14):2687.

    • 14

      Marder S R, Perry J W, Schaefer W P. Synthesis of organic salts with large second-order optical Nonlinearities[J]. Science, 1989, 245:626-628.

    • 15

      Ruiz B, Jazbinsek M, and Günter P. Crystal growth of DAST[J]. Crystal Growth & Design, 2008, 8(11):4173-4184.

    • 16

      Pan F, Knopfle G, Bosshard C, et al. Electro-optic properties of the organic salt 4-N,N-dimethylamino-4'-N'-methyl-stilbazoliumtosylate[J]. Applied Physics Letters, 1996, 1(69):13-15.

    • 17

      Jazbinsek M, Mutter L, Gunter P. Photonic applications with the organic nonlinear optical crystal DAST[J]. IEEE Journal of Selected Topics in Quantum Electronics, 2008, 14(5):1298-1311.

    • 18

      Takahashi Y, Adachi H, Taniuchi T. Organic nonlinear optical DAST crystals for electro-optic measurement and terahertz wave generation[J]. Journal of Photochemistry and Photobiology A: Chemistry. 2006, 183: 247-252.

    • 19

      Cao L F, Teng B, Xu D G, et al. Growth, transmission, Raman spectrum and THz generation of DAST crystal, RSC Advances, 2016, 6(103), 101389–101394.

    • 20

      Yabuzaki J, Takahashi Y, Adachi H, et al. High-quality crystal growth and characterization of organic nonlinear optical crystal: 4-dimethylamino-N-methyl-4-stilbazoliumtosylate (DAST)[J]. Bulletin Materials Sciences, 1999, 1(22): 11-13

    • 21

      Hameed S, Yu C, Chen B. An investigation on the growth and characterization of DAST crystals grown by two zone growth technique[J]. Journal of Crystal Growth, 2005, 282:117-124.

    • 22

      Adachi H, Takahashi Y, Yabuzaki J, et al. Growth of high quality nonlinear optical crystal 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST)[J]. Crystal Growth & Design, 1999, 198(99): 568-571.

    • 23

      Hameed A, Rohani S, Yu W, et al. Surface defects and mechanical hardness of rapidly grown DAST crystals[J]. Journal of Crystal Growth, 2006, 97:146-151.

    • 24

      Kawase K, Mizuno M, Sohma S, et al. Difference-frequency terahertz-wave generation from 4-dimethylamino-N-methyl-4-stilbazolium-tosylate by use of an electronically tuned Ti:sapphire laser[J]. Optics Letters, 1999, 15(24):1065-1067.

    • 25

      Kawase K, Hatanaka T, Takahashi H, et al. Tunable terahertz-wave generation from DAST crystal by dual signal-wave parametric oscillation of periodically poled lithium niobate[J]. Optics Letters, 2000, 23(25):1714-1716.

    • 26

      Taniuchi T, Okada S, Nakanishi H. Widely tunable terahertz-wave generation in an organic crystal and its spectroscopic application[J]. Journal of Applied Physics, 2004, 11(95):5984-5988.

    • 27

      Liu P X, Feng Q, Pang Z B, et al. Competition between two parametric processes in a pump source of terahertz-wave difference frequency generation[J]. Journal of Physics D: Applied Physics, 2018,51(39):1-5.

    • 28

      Suizu K , Miyamoto K , Yamashita T , et al. High-power terahertz-wave generation using DAST crystal and detection using mid-infrared powermeter[J]. Optics Letters, 2007, 32(19):2885-2887.

    • 29

      Tang M, Minamide H, Wang Y, et al. Tunable terahertz-wave generation from DAST crystal pumped by a monolithic dual-wavelength fiber laser[J]. Optics Express, 2011, 2(19): 779-786.

    • 30

      Nawata K, Abe T, Miyake Y, et al. Efficient terahertz wave generation using a 4-Dimethylamino-N-methyl-4-stilbazolium tosylate pumped by a dual-wavelength neodymium-doped yttrium aluminum garnet laser[J]. Applied Physics Express, 2012, 5(112401):1-3.

    • 31

      Dolasinski B, Powers P E, Haus J W, et al. Tunable narrow band difference frequency THz wave generation in DAST via dual seed PPLN[J]. Optics Express, 2015, 3(23): 3669-3680.

    • 32

      Tokizane Y, Nawata K, Han Z, et al. Tunable terahertz waves from 4-dimethylamino-N-methyl-4-stibazolium tosylate pumped with dual-wavelength injection-seeded optical parametric generation[J]. Applied Physics Express, 2017, 10(022101):1-4.

    • 33

      He Y X, Wang Y Y, Xu D G, et al. High-energy and ultra-wideband tunable terahertz source with DAST crystal via difference frequency generation[J]. Applied Physics B, 2018, 124(1):16-23.

    • 34

      Cunningham P D, Hayden L M. Optical properties of DAST in the THz range[J]. Optics Express, 2010, 18(23): 23620-23625.

贺奕焮

机 构:

1. 天津大学 精密仪器与光电子工程学院 激光与光电子研究所,天津 300072

2. 天津大学 光电信息技术教育部重点实验室,天津 300072

Affiliation:

1. Institute of Laser and Optoelectronics, School of Precision Instrument and Opto-electronics Engineering, Tianjin University, Tianjin 300072, China

2. Key Laboratory of Opto-electronics Information Technology (Ministry of Education), Tianjin University, Tianjin 300072, China

邮 箱:tju_heyixin@tju.edu.cn

作者简介:(Biography):(Biography):贺奕焮(1993-), 男, 辽宁沈阳人,博士研究生, 主要研究领域为太赫兹辐射源. E-mail:tju_heyixin@tju.edu.cn

庞子博

机 构:中国电子科技集团公司第四十六研究所,天津 300220

Affiliation:The 46th research institute of China Electronics Technology Group Corporation, Tianjin 300220, China

朱先立

机 构:

1. 天津大学 精密仪器与光电子工程学院 激光与光电子研究所,天津 300072

2. 天津大学 光电信息技术教育部重点实验室,天津 300072

Affiliation:

1. Institute of Laser and Optoelectronics, School of Precision Instrument and Opto-electronics Engineering, Tianjin University, Tianjin 300072, China

2. Key Laboratory of Opto-electronics Information Technology (Ministry of Education), Tianjin University, Tianjin 300072, China

徐德刚

机 构:

1. 天津大学 精密仪器与光电子工程学院 激光与光电子研究所,天津 300072

2. 天津大学 光电信息技术教育部重点实验室,天津 300072

Affiliation:

1. Institute of Laser and Optoelectronics, School of Precision Instrument and Opto-electronics Engineering, Tianjin University, Tianjin 300072, China

2. Key Laboratory of Opto-electronics Information Technology (Ministry of Education), Tianjin University, Tianjin 300072, China

角 色:通讯作者

Role:Corresponding author

邮 箱:xudegang@tju.edu.cnyuyewang@tju.edu.cn

作者简介:E-mail: xudegang@tju.edu.cn; yuyewang@tju.edu.cn

王与烨

机 构:

1. 天津大学 精密仪器与光电子工程学院 激光与光电子研究所,天津 300072

2. 天津大学 光电信息技术教育部重点实验室,天津 300072

4. 第三军医大学西南医院神经外科,重庆,400038

Affiliation:

1. Institute of Laser and Optoelectronics, School of Precision Instrument and Opto-electronics Engineering, Tianjin University, Tianjin 300072, China

2. Key Laboratory of Opto-electronics Information Technology (Ministry of Education), Tianjin University, Tianjin 300072, China

4. Institute of Neurosurgery, Southwest Hospital, Third Military Medical University, Chongqing 400038, China

角 色:通讯作者

Role:Corresponding author

邮 箱:xudegang@tju.edu.cnyuyewang@tju.edu.cn

作者简介:E-mail: xudegang@tju.edu.cn; yuyewang@tju.edu.cn

孟大磊

机 构:中国电子科技集团公司第四十六研究所,天津 300220

Affiliation:The 46th research institute of China Electronics Technology Group Corporation, Tianjin 300220, China

武聪

机 构:中国电子科技集团公司第四十六研究所,天津 300220

Affiliation:The 46th research institute of China Electronics Technology Group Corporation, Tianjin 300220, China

程虹娟

机 构:中国电子科技集团公司第四十六研究所,天津 300220

Affiliation:The 46th research institute of China Electronics Technology Group Corporation, Tianjin 300220, China

徐永宽

机 构:中国电子科技集团公司第四十六研究所,天津 300220

Affiliation:The 46th research institute of China Electronics Technology Group Corporation, Tianjin 300220, China

姚建铨

机 构:

1. 天津大学 精密仪器与光电子工程学院 激光与光电子研究所,天津 300072

2. 天津大学 光电信息技术教育部重点实验室,天津 300072

Affiliation:

1. Institute of Laser and Optoelectronics, School of Precision Instrument and Opto-electronics Engineering, Tianjin University, Tianjin 300072, China

2. Key Laboratory of Opto-electronics Information Technology (Ministry of Education), Tianjin University, Tianjin 300072, China

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图 1 DAST的分子结[12]

Fig. 1 Molecular structure of the DAST[12]

图 2 基于双温区法培养出的DAST晶体照片

Fig. 2 Photograph of the DAST crystal grown in two-zone method

图 3 (a)基于DAST晶体的超宽带差频THz辐射源实验系统示意图,(b)实验装置实物图 -- (a)

Fig. 3 (a) Diagram of the experimental setup of THz DFG source based on DAST crystal,(b) Photograph of the experimental setup -- (a)

图 3 (a)基于DAST晶体的超宽带差频THz辐射源实验系统示意图,(b)实验装置实物图 -- (b)

Fig. 3 (a) Diagram of the experimental setup of THz DFG source based on DAST crystal,(b) Photograph of the experimental setup -- (b)

图 4 (a)KTP-OPO系统的调谐特性以及时域脉冲特性,(b)KTP-OPO系统的输出特性 -- (a)

Fig. 4 (a) The tunability and pulse characteristics of the KTP-OPO,(b) The output characteristics of the KTP-OPO -- (a)

图 4 (a)KTP-OPO系统的调谐特性以及时域脉冲特性,(b)KTP-OPO系统的输出特性 -- (b)

Fig. 4 (a) The tunability and pulse characteristics of the KTP-OPO,(b) The output characteristics of the KTP-OPO -- (b)

图 5 THz输出谱的理论计算结果(蓝线)与实验测量结果(红线)

Fig. 5 The theoretical estimation (blue line) and experimental result (red line) of the THz output in DAST crystal

图6 (a)THz波的输入输出特性, (b)不同532nm绿光泵浦条件下的λ1与λ2的输出特性 -- (a)

Fig. 6 (a) The input-output characteristics of the generated THz wave, (b) The output energies of λ1 and λ2 pumped under different energies of 532nm laser -- (a)

图6 (a)THz波的输入输出特性, (b)不同532nm绿光泵浦条件下的λ1与λ2的输出特性 -- (b)

Fig. 6 (a) The input-output characteristics of the generated THz wave, (b) The output energies of λ1 and λ2 pumped under different energies of 532nm laser -- (b)

图 7 (a)差频产生THz波偏振态, (b) DAST晶体不同旋转角度下差频产生的THz波强度 -- (a)

Fig. 7 (a) The polarization measurement of the generated THz wave via DFG, (b) The generated THz intensities with different rotation angles of DAST crystal -- (a)

图 7 (a)差频产生THz波偏振态, (b) DAST晶体不同旋转角度下差频产生的THz波强度 -- (b)

Fig. 7 (a) The polarization measurement of the generated THz wave via DFG, (b) The generated THz intensities with different rotation angles of DAST crystal -- (b)

图 8 不同距离处的THz光斑发散情况;插图为距离晶体7 mm处THz光斑高斯分布情况

Fig. 8 The distribution of THz beam at different distances from DAST crystal; The inset shows the Gaussian beam of the THz wave in X and Y direction at the distance of 7 mm from the DAST crystal

图 9 不同固体样品的超宽带THz光谱

Fig. 9 The ultrawide THz spectroscopies of materials in solid state

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  • References

    • 1

      Yang X, Zhao X, Yang K, et al. Biomedical applications of terahertz spectroscopy and imaging[J]. Trends in Biotechnology, 2016, 34(10): 810-824.

    • 2

      Tonouchi M. Cutting-edge terahertz technology[J]. Nature Photonics, 2007, 1(2): 97-105.

    • 3

      Siegel P H. Terahertz technology in biology and medicine[J]. Microwave Theory & Techniques IEEE Transactions on, 2004, 52(10):2438-2447.

    • 4

      Sirtori C. Applied physics: bridge for the terahertz gap[J]. Nature, 2002, 417(6885):132-133

    • 5

      Davies A G, Burnett A D, Fan W, et al. Terahertz spectroscopy of explosives and drugs[J]. Materials Today, 2008, 11(3): 18-26D.

    • 6

      Takida Y, Namata K J, Suzuki S, et al. Nonlinear optical detection of terahertz-wave radiation from resonant tunneling diodes[J]. Optics Express, 2017, 5(25):5389-5396.

    • 7

      Yamashita M, Takahashi H, Ouchi T, et al. Ultra-broadband terahertz time-domain ellipsometric spectroscopy utilizing GaP and GaSe emitters and an epitaxial layer transferred photoconductive detector[J]. Applied Physics Letters, 2014, 104(05):1694-1696.

    • 8

      Jooshesh A, Fesharaki F, Bahrami-Yekta V, et al. Plasmon-enhanced LT-GaAs/AlAs heterostructure photoconductive antennas for sub-bandgap terahertz generation[J]. Optics Express, 2017, 18(25):22140-22148.

    • 9

      Carnio B N, Greig S R, Firby C J, et al. Terahertz electro-optic detection using a <012>-cut chalcopyrite ZnGeP2 crystal[J]. Applied Physics Letters, 2016, 108(261109):1-4.

    • 10

      Ding Y J. Progress in terahertz sources based on difference-frequency generation [Invited][J]. Journal of the Optical Society of America B, 2014, 31(11):2696-2711.

    • 11

      Liu H, Bai W, Feng J, et al. The synthesis of large-diameter ZnTe crystal for THz emitting and detection [J]. Journal of Crystal Growth, 2017, 475:115–120.

    • 12

      Naftaly M, Molloy J F, Magnusson B, et al. Silicon carbide-a high-transparency nonlinear material for THz applications.[J]. Optics Express, 2016, 24(3):2590-2595.

    • 13

      Fischer M P, Bühler J, Fitzky G, et al. Coherent field transients below 15  THz from phase-matched difference frequency generation in 4H-SiC[J]. Optics Letters, 2017, 42(14):2687.

    • 14

      Marder S R, Perry J W, Schaefer W P. Synthesis of organic salts with large second-order optical Nonlinearities[J]. Science, 1989, 245:626-628.

    • 15

      Ruiz B, Jazbinsek M, and Günter P. Crystal growth of DAST[J]. Crystal Growth & Design, 2008, 8(11):4173-4184.

    • 16

      Pan F, Knopfle G, Bosshard C, et al. Electro-optic properties of the organic salt 4-N,N-dimethylamino-4'-N'-methyl-stilbazoliumtosylate[J]. Applied Physics Letters, 1996, 1(69):13-15.

    • 17

      Jazbinsek M, Mutter L, Gunter P. Photonic applications with the organic nonlinear optical crystal DAST[J]. IEEE Journal of Selected Topics in Quantum Electronics, 2008, 14(5):1298-1311.

    • 18

      Takahashi Y, Adachi H, Taniuchi T. Organic nonlinear optical DAST crystals for electro-optic measurement and terahertz wave generation[J]. Journal of Photochemistry and Photobiology A: Chemistry. 2006, 183: 247-252.

    • 19

      Cao L F, Teng B, Xu D G, et al. Growth, transmission, Raman spectrum and THz generation of DAST crystal, RSC Advances, 2016, 6(103), 101389–101394.

    • 20

      Yabuzaki J, Takahashi Y, Adachi H, et al. High-quality crystal growth and characterization of organic nonlinear optical crystal: 4-dimethylamino-N-methyl-4-stilbazoliumtosylate (DAST)[J]. Bulletin Materials Sciences, 1999, 1(22): 11-13

    • 21

      Hameed S, Yu C, Chen B. An investigation on the growth and characterization of DAST crystals grown by two zone growth technique[J]. Journal of Crystal Growth, 2005, 282:117-124.

    • 22

      Adachi H, Takahashi Y, Yabuzaki J, et al. Growth of high quality nonlinear optical crystal 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST)[J]. Crystal Growth & Design, 1999, 198(99): 568-571.

    • 23

      Hameed A, Rohani S, Yu W, et al. Surface defects and mechanical hardness of rapidly grown DAST crystals[J]. Journal of Crystal Growth, 2006, 97:146-151.

    • 24

      Kawase K, Mizuno M, Sohma S, et al. Difference-frequency terahertz-wave generation from 4-dimethylamino-N-methyl-4-stilbazolium-tosylate by use of an electronically tuned Ti:sapphire laser[J]. Optics Letters, 1999, 15(24):1065-1067.

    • 25

      Kawase K, Hatanaka T, Takahashi H, et al. Tunable terahertz-wave generation from DAST crystal by dual signal-wave parametric oscillation of periodically poled lithium niobate[J]. Optics Letters, 2000, 23(25):1714-1716.

    • 26

      Taniuchi T, Okada S, Nakanishi H. Widely tunable terahertz-wave generation in an organic crystal and its spectroscopic application[J]. Journal of Applied Physics, 2004, 11(95):5984-5988.

    • 27

      Liu P X, Feng Q, Pang Z B, et al. Competition between two parametric processes in a pump source of terahertz-wave difference frequency generation[J]. Journal of Physics D: Applied Physics, 2018,51(39):1-5.

    • 28

      Suizu K , Miyamoto K , Yamashita T , et al. High-power terahertz-wave generation using DAST crystal and detection using mid-infrared powermeter[J]. Optics Letters, 2007, 32(19):2885-2887.

    • 29

      Tang M, Minamide H, Wang Y, et al. Tunable terahertz-wave generation from DAST crystal pumped by a monolithic dual-wavelength fiber laser[J]. Optics Express, 2011, 2(19): 779-786.

    • 30

      Nawata K, Abe T, Miyake Y, et al. Efficient terahertz wave generation using a 4-Dimethylamino-N-methyl-4-stilbazolium tosylate pumped by a dual-wavelength neodymium-doped yttrium aluminum garnet laser[J]. Applied Physics Express, 2012, 5(112401):1-3.

    • 31

      Dolasinski B, Powers P E, Haus J W, et al. Tunable narrow band difference frequency THz wave generation in DAST via dual seed PPLN[J]. Optics Express, 2015, 3(23): 3669-3680.

    • 32

      Tokizane Y, Nawata K, Han Z, et al. Tunable terahertz waves from 4-dimethylamino-N-methyl-4-stibazolium tosylate pumped with dual-wavelength injection-seeded optical parametric generation[J]. Applied Physics Express, 2017, 10(022101):1-4.

    • 33

      He Y X, Wang Y Y, Xu D G, et al. High-energy and ultra-wideband tunable terahertz source with DAST crystal via difference frequency generation[J]. Applied Physics B, 2018, 124(1):16-23.

    • 34

      Cunningham P D, Hayden L M. Optical properties of DAST in the THz range[J]. Optics Express, 2010, 18(23): 23620-23625.


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