利用LiNbO3晶体的拉曼散射获得太赫兹辐射的研究

对利用LiNbO3晶体拉曼活性的E对称模(ωTO=236 cm-1≈7.08 THz)产生太赫兹辐射进行了研究, 采用输出波长为1.064 μm 的Nd:YAG脉冲激光器作为泵浦源, 根据光学参量振荡的基本原理, 推导计算了非共线第二类相位匹配条件下的晶体长度、有效非线性系数、相位匹配角等技术参量, 最后根据所计算的各技术参量设计了太赫兹光学参量振荡器(TPO)。     

基于MgO:SLN晶体的环形腔太赫兹参量振荡器

基于摩尔分数为1%的氧化镁掺杂的近化学计量比铌酸锂晶体,采用环形腔结构的浅表垂直出射方式组成太赫兹波参量振荡器。该振荡器的太赫兹波输出调谐范围为0.99～3.84 THz,频率调谐响应时间为600μs。当抽运能量为150.30 mJ、太赫兹频率为1.59 THz时,太赫兹脉冲的输出能量达到最大值,为16.28μJ,对应的能量转换效率为1.08×10~(-4)。在相同的实验条件下,该环形腔结构太赫兹波参量振荡器输出的最大太赫兹波能量是传统线形腔结构的2.35倍,实现了高能量、快速可调谐的太赫兹波输出。     

高性能85mm短腔光学参变振荡器的THz电磁波输出特性分析

报道了以MgO∶LiNbO3为非线性光学介质,采用85 mm长的法布里珀罗单谐振腔结构形式的光学参变振荡器,产生THz电磁波的实验结果。使用波长为1064 nm的Nd∶YAGQ开关脉冲激光器作为抽运光源,通过改变入射角度使参变振荡器的相位匹配条件发生变化。采用Si真空量热器,并利用THz波干涉测量仪;或通过测量闲频光的频率对产生的THz波频率进行了测量。实验表明该参变振荡器输出频率调谐范围为0.9~3.0 THz。在抽运光能量为20 mJ/pulse,脉冲宽度16 ns,重复频率50 Hz条件下得到输出峰值位于1.2 THz,能量为102.5 PJ/pulse的THz波输出。通过引入Si棱镜阵列减小了THz波在晶体中的全反射,从而提高THz波的能量输出。使用金属缝隙探测器,对辐射的THz波的波束水平方向空间分布进行了测量,分析了Si棱镜阵列的衍射效应对THz波束空间分布的影响。     

外腔式宽调谐被动调QNd:YVO_4/PPMgLN光学参量振荡器

报道了一个低阈值宽调谐、被动调Q、单谐振掺MgO的周期性极化铌酸锂晶体(PPMgLN)光学参量振荡器。利用被动调Q的Nd:YVO4激光器作为泵浦源,采用外腔结构,在室温下,实现了PPMgLN晶体的准相位匹配光学参量振荡。光参量振荡的阈值仅为0.27W(单脉冲能量4.5μJ、脉宽35ns);在泵浦光为1.35W(脉冲能量8.2μJ、脉宽35ns),PPMgLN周期为31μm时,获得了161.9mW,3.202μm脉冲激光输出;同时获得了98.5mW的1.594μm信号光输出,总的光光转化效率达到19.3%。通过改变晶体的周期,实现了闲频光3.13～4.19μm,信号光1.43～1.65μm的宽带可调谐激光输出。     

LD侧泵的声光调Q Nd∶YAG/KTP人眼安全激光器

为获得人眼安全的激光,在一个由激光二极管（LD）阵列侧泵、声光调Q的Nd∶YAG激光器谐振腔中放置一非临界相位匹配的KTP晶体,形成了一个内腔式光学参量振荡器,实现了准连续的1.57 μm激光振荡.通过对单谐振光学参量振荡器阈值公式进行讨论,采用了平凹腔的结构和尽可能短的光学参量振荡器腔长,有效地降低了光学参量振荡器的泵浦阈值.测量了不同声光重复率和不同透射率输出镜下光学参量振荡器输出的各项特性参量.分析了声光重复率和输出镜的透过率对光学参量振荡器的泵浦阈值和输出脉冲波形的影响,并对实验中出现的饱和现象作了解释.当泵浦电流14.5A,声光重复率10 kHz,光学参量振荡器输出镜透过率15%时,在保持单脉冲输出的情况下,获得了1.57 μm激光的最高平均功率输出值1.748 W.     

基于DAST晶体差频的可调谐THz辐射源

基于自发成核法自行生长的4-(4-二甲基氨基苯乙烯基)甲基吡啶对甲苯酸盐(DAST)晶体,可实现宽带可调谐THz辐射输出。实验探究饱和生长溶液质量浓度对晶体生长形态和光学质量的影响,并结合晶体的拉曼光谱,对其生色团振动和转动特性进行分析。采用波长为1.3～1.5μm的高能量、可调谐双波长的激光为泵浦光,基于0类相位匹配外腔差频和电控振镜快速扫描技术,实现了0.1～20.0THz的宽带THz辐射输出。在18.9THz处,每个脉冲最大输出能量为3.59μJ,转换效率为2.39×10-4。基于宽带THz输出谱可知,DAST晶体对THz波的吸收主要是因为晶格振动引起的。     

二极管侧面抽运Nd：YAG4波长同时输出激光

为了获得1064nm,1319nm,589nm及660nm4波长激光同时输出,设计了双激光晶体同步声光调Q“T”型复合谐振腔。通过软件模拟与计算,筛选出理想的谐振腔参数,使2波长基频光在大泵浦电流范围内能稳定运转。以KTP晶体和LBO晶体为和频晶体和倍频晶体,在泵浦电流为17A,重复频率为10kHz时,获得了1064nm,1319nm,589nm和660nm4波长激光输出,最高平均功率分别为150mW,80mW,2．3W和1．7W,同时测得589nm激光和660nm激光的脉冲宽度分别为110ns和130ns。结果表明：使用热稳“T”型复合腔,可以获得4波长激光同时稳定输出。     

利用自制的单频激光器获得近通讯波段正交振幅压缩态光场

利用自制的1.34 μm和0.67 μm双波长输出单频激光器作为泵浦源,泵浦基于PPKTP晶体的光学参量放大器,通过边带锁频技术将光学参量放大腔腔长锁定在激光频率上,将泵浦光和信号光相对相位锁定在π相位,经参量缩小过程获得低于散粒噪声极限约3 dB的正交振幅压缩光.压缩光位于光纤通信窗口——1.3 μm波段.     

宽波段连续调谐全固态CW PPMgLN光学参量振荡器

利用半导体激光泵浦输出1064 nm波长的全固态连续Nd:YVO4激光器作为泵浦源,采用周期调谐和温度调谐组合调谐技术,对基于掺氧化镁周期性极化铌酸锂晶体（MgO:LiNbO3, PPMgLN）准相位匹配（QPM）的全固态连续波（CW）光学参量振荡器（OPO）宽波段无分立连续调谐输出特性进行研究。实验采用连续工作模式和外腔结构,基于多周期PPMgLN晶体的30.2,30.4和30.6 m周期,在改变晶体的极化周期的基础上,同时在30～100 ℃范围内调节晶体工作温度。实验结果表明:CW PPMgLN OPO的泵浦阈值仅为0.22 W;不同极化周期需要的温度调谐范围不同;信号光在1 559.8～1 597.2 nm近红外波段和闲频光在3 187.3~3 347.3 nm中红外波段连续调谐输出。实现了外腔式全固态CW OPO在信号光和闲频光波段的无分立连续调谐输出。     

1J高光束质量免水冷脉冲Nd:YAG激光器

研制了一种TEC制冷LD侧泵高能量、高光束质量、电光调Q全固态Nd∶YAG激光器。在主振荡器中晶体棒的尺寸为φ7 mm×100 mm,Nd原子数比例为1.1%,LD泵浦的最大峰值功率为15 kW,在重复频率为10 Hz时,获得了350 mJ输出能量,脉冲宽度为9.7 ns,光束质量因子M~2在水平和垂直方向分别为3.3和3.8。使用主振荡功率放大结构,提高了最终的输出功率。第一级放大器Nd∶YAG晶体棒尺寸为φ7.5 mm×134 mm,在输出重复频率10 Hz、泵浦电流80 A、泵浦脉冲宽度200μs时,得到最大单脉冲能量700 mJ,脉冲宽度10 ns。第二级放大器Nd∶YAG晶体棒尺寸为φ8 mm×100 mm,泵浦电流为80 A。最终我们获得了最大的单脉冲能量1 085 mJ,脉冲宽度10 ns,能量不稳定度小于3%,测量的光束质量因子M~2在水平和垂直方向分别为3.9和4.8,实现了焦耳级高光束质量Nd∶YAG激光器的小型化、无水冷化。     

High-power tunable terahertz generation from a surface-emitted THz-wave parametric oscillator based on two MgO:LiNbO3 crystals

A high-powered tunable terahertz wave (THz-wave) has been parametrically generated via a surface-emitted THz-wave parametric oscillator (TPO) pumped by a multi-longitudinal-mode Q-switched Nd:YAG laser. The effective parametric gain length was enlarged by employing two MgO:LiNbO₃ crystals. The tunable THz-wave radiation from 0.8 to 2.8 THz was realized via varying phase-matching angle between the pump wave and the Stokes wave. The maximum THz-wave radiation was 173.9 nJ/pulse at 1.7 THz as the pump energy was 82 mJ, corresponding to an energy conversion efficiency of about 2.12 × 10⁻⁶ and a photon conversion efficiency of about 0.035%. The first-order, the second-order and the third-order Stokes waves were observed during the experiments.     

High-power terahertz radiation from surface-emitted THz-wave parametric oscillator

We report a pulsed surface-emitted THz-wave parametric oscillator based on two MgO:LiNbO3 crystals pumped by a multi-longitudinal mode Q-switched Nd:YAG laser.Through varying the phase matching angle,the tunable THzwave output from 0.79 THz to 2.84 THz is realized.The maximum THz-wave output was 193.2 nJ/pulse at 1.84 THz as the pump power density was 212.5 MW/cm 2,corresponding to the energy conversion efficiency of 2.42×10-6 and the photon conversion efficiency of about 0.037%.When the pump power density changed from 123 MW/cm 2 to 148 MW/cm 2 and 164 MW/cm 2,the maximum output of the THz-wave moved to the high frequency band.We give a reasonable explanation for this phenomenon.     

Noncascading THz-wave parametric oscillator synchronously pumped by mode-locked picosecond Ti:sapphire laser in doubly-resonant external cavity

A noncascading terahertz (THz) wave parametric oscillator synchronously pumped by a mode-locked picosecond Ti:sapphire laser whose average power was less than 1 W was demonstrated with a noncollinear phase-matching MgO:LiNbO₃ crystal in an external enhancement cavity doubly resonant for both pump (780 nm) and signal (781-784 nm) waves. In the external cavity, in which the pump wave enhanced so as to reduce the pumping threshold of parametric processes, the signal wave could also resonate and thus be enhanced simultaneously, resulting in a THz wave output at approximately 0.9 THz as the idler wave. The novel dual enhancement of pump and signal waves reduced the threshold pumping intensity to approximately 50 MW/cm², which was much lower than that of a conventional externally pumped THz wave parametric oscillator with a crystal.     

Investigation of pump-wavelength dependence of terahertz-wave parametric oscillator based on LiNbO3

This paper investigates the performances of terahertz-wave parametric oscillators(TPOs) based on the LiNbO 3 crystal at different pump wavelengths.The calculated results show that TPO characteristics,including the frequency tuning range,the THz-wave gain and the stability of THz-wave output direction based on the Si-prism coupler,can be significantly improved by using a short-wavelength pump.It also demonstrates that a long-wavelength-pump allows the employment of a short TPO cavity due to an enlarged phase-matching angle,that is,an increased angular separation between the pump and oscillated Stokes beams under the THz-wave generation at a specific frequency.The study provides an useful guide and a theoretical basis for the further improvement of TPO systems.     

Compact and widely tunable terahertz source based on a dual-wavelength intracavity optical parametric oscillation

In this paper, a continuously tunable terahertz (THz) source is obtained using a compact intracavity pumped dual-wavelength optical parametric oscillation operating around 2.1 μm as difference-frequency generation pump source. The tuning range of the THz-wave frequency covers from 0.147 THz to 3.651 THz. Based on the collinear difference-frequency generation in the GaSe crystal, the experiment result shows that our schematic is a good option to construct a compact and portable terahertz source with widely tunable range.     

Threshold analysis for a THz-wave parametric oscillator with a quasi-phase-matching scheme in lithium niobate

The analytical expressions of the parametric gain for the terahertz wave (THz-wave) and the Stokes wave of THz-wave parametric oscillator (TPO) with a quasi-phase-matching scheme in periodically poled LiNbO₃ (PPLN) are deduced. The pump threshold expression of the TPO with a quasi-phase-matching scheme in PPLN is derived based on the gain expression of the Stokes wave. The expression is theoretically analyzed to find the relationship between the pump threshold and the parameters of the resonant cavity.     

Simulation of parametric oscillation in the submillimeter range at pumping of the ZnGeP2 crystal by a train of 100-ps high-power pulses

Analysis is given for a possibility of singly resonant parametric oscillation in the submillimeter range at synchronous pumping of the ZnGeP₂ crystal by a train of 100-ps second-harmonic pulses from the CO₂ laser with the radiation energy 1.0 J. The calculation shows that using the ZnGeP₂ crystal and the second harmonic of the CO₂ laser with the energy density 1.8 J cm⁻², one can get the peak submillimeter radiation power from 3.6 to 12 MW in the range from 95 to 300 μm (1.0–3.3 THz). The expected peak power values are larger than the experimental ones obtained by other nonlinear optics methods.     

基于钽酸锂晶体的太赫兹波参量振荡器运转特性的研究

基于晶格振动模受激电磁耦子散射过程的基本原理,对由LiTaO₃（LT）晶体组成的太赫兹波参量振荡器（TPO）的输出调谐特性、增益和吸收损耗特性,以及基于硅棱镜阵列耦合装置的THz波输出特性等方面进行了详细的理论研究和分析.研究结果表明,基于LiTaO₃晶体A₁对称性晶格振动的特点以及自身优异的非线性光学特性,通过利用短波长抽运光、适当提高抽运能量以及缩短TPO谐振腔腔长等方法,完全可以实现LT-TPO的高性能运转,证明了LiTaO₃晶体是一种性能优良的TPO工作介质.理论计算结果及方法为以后的LT-TPO实验工作提供了详实的理论依据和实验指导. 关键词： 非线性光学 THz辐射 3晶体')" href="#">LiTaO₃晶体 电磁耦子     

Analysis of THz-wave surface-emitted difference-frequency generation in periodically poled lithium niobate waveguide

It was shown that the periodically poled LiNbO₃-waveguide with period of poling λ≈λ/n_g (λ is the wavelength of emitted THz-wave, n_g is a refractive index corresponding to optical group velocity) emits THz-wave difference-frequency generation (DFG) in the direction normal to the surface of the planar waveguide. The 5% distinction between the manufactured and required periods of gratings results only in a small deflection (∼6°) of the output THz-beam from the normal direction. The dependence of DFG efficiency on mode size is analyzed. The output THz power at λ=150 μm is estimated as 2 mW, taking into account imperfections in coupling incident beams with guided modes. It was shown that the efficiency of THz-wave DFG in surface-emitting geometry is more than for collinear geometry in bulk crystal, especially in the high-absorption wavelength region. Received: 16 May 2001 / Revised version: 13 August 2001 / Published online: 2 November 2001     

Widely tunable broadband terahertz radiation generation using a configurationally locked polyene 2-[3-(4-hydroxystyryl)-5,5-dimethylcyclohex-2-enylidene] malononitrile crystal via difference frequency generation

Widely tunable terahertz (THz) waves were successfully generated from 0.5 to 10 THz via difference frequency generation (DFG) in a configurationally locked polyene 2-[3-(4-hydroxystyryl)-5,5-dimethylcyclohex-2-enylidene] malononitrile (OH1) crystal. Potassium titanium oxide phosphate optical parametric oscillator pumped by nanosecond Q-switched Nd:YAG laser was used to generate two waves, which were then used to irradiate OH1 crystal. The maximum energy of the generated THz wave was about 461 pJ/pulse. We investigated the dependency of generated THz energy to the excitation pump power density and OH1 crystal thickness. In addition, we compared the THz energy generated by OH1 crystal to 4-N,N-dimethylamino-4′-N′-methyl-4-stilbazolium tosylate (DAST) crystal using DFG, and we achieved 560 times higher energy using OH1 crystal than DAST crystal at around 1.1 THz.