Second harmonic generation in inhomogeneous MgO:LiNbO3 waveguides

A fibre laser at 1111.6 nm is frequency doubled by two inhomogeneous MgO:LiNbO3 waveguides and the output powers of 85 mW and 49 mW at 555.8 nm have been generated with the conversion efficiencies of 47% and 27% respectively. By analysing the second harmonic generation temperature tuning curves, we investigate the influence of the optical inhomogeneities upon the conversion efficiency. The final result shows that the efficiency difference is mainly affected by the optical inhomogeneities in our case.     

Second harmonic generation in periodically poled LiNbO3 waveguides formed by oxygen‐ion implantation

Planar and channel waveguides were fabricatied in periodically poled lithium niobate crystals by 6 MeV O‐ion implantation. Single‐pass second harmonic generation was carried out. A conversion efficiency of 34.5%/(W · cm²) was achieved in the channel waveguide, and 1.11 mW second harmonic light at 492.5 nm was generated. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

飞秒脉冲的二次谐波理论和实验研究

本文分析了小信号情况下飞秒脉冲的倍频特性,在非耗尽近似下,得出了飞秒脉冲二次谐波波形及效率的解析解,在时间域内,对一般条件的耦合波方程进行了数值解,分析了相位失配对飞秒脉冲倍频波形及效率的影响。 用0.5mm厚的一类匹配LBO晶体对碰撞锁模激光器产生的80fs超短脉冲进行了腔外倍频实验,实验结果与理论计算符合得很好。     

Phase-matched second-harmonic generation in hybrid polymer-LN waveguides

Here we propose a hybrid polymer-LN waveguide for achieving phase-matched second-harmonic generation (SHG). From the aspect of super-mode theory, the geometric parameters of the hybrid semi-nonlinear waveguide were optimized to utilize both symmetric (even) and antisymmetric (odd) modes of the pump and SHG waves so as to facilitate phase matching with large modal overlap. Phase matching between a fundamental even (TE₀₀-like) mode at 1320 nm and a fundamental odd (TE₀₁-like) mode at 660 nm was found with a calculated modal overlap integral of 0.299, while utilizing the largest nonlinear coefficient d₃₃, and achieving an efficient calculated normalized conversion efficiency of 148% W^-1·cm^-2. Considering the fabrication feasibility of such hybrid waveguide with features including etchless, large dimension, and low structural sensitivity, we believe our findings would provide a useful reference for future on-chip efficient nonlinear conversion devices.     

应用级联倍频方法提高倍频系统输出稳定性研究

提出应用级联倍频方法提高倍频系统输出稳定性,并就该方法的有效性进行了理论分析和模拟计算.分析和计算结果不但证明级联倍频方法能实现倍频系统稳定输出,而且还表明可以通过仔细调节第一块倍频晶体中波矢方向 k 与光轴间夹角、两块倍频晶体间的间隔,能调节改变实现倍频系统最稳输出时所需第二块晶体的理论计算长度,使之与第二块倍频晶体的实际加工长度一致,最终实现系统稳定倍频输出.级联倍频方法在实现高输出稳定性的同时能实现高的倍频转换效率,对应用于光参量啁啾脉冲放大系统的高稳定抽运源系统的设计建造具有重要参考意义. 关键词： 级联倍频 稳定倍频输出 光参量啁啾脉冲放大     

Second harmonic generation from closed packed hexagonal structure of nano-nickel arrays

A closed packed hexagonal structure of nickel nanoparticles was fabricated by deposition of thin nickel films on self-assembled polystyrene micron spheres, which were made of nanospherical lithography in conjunction with left-off the micro spheres. The optical second harmonic generation from these periodically arrayed nickel nanoparticles reveals intensity with a value much larger than that generated from a uniform nickel-film of the same thickness. Quasi phase matching contributed from Bragg wave vectors of the periodic arrayed nickel nanoparticles can satisfactorily express this enhancement.     

二维不可压缩流体Kelvin-Helmholtz不稳定性的二次谐波产生

推导了Kelvin-Helmholtz(KH)不稳定性二次谐波产生的理论公式,利用该公式得到的二次谐波增长的弱非线性结果与LARED-S程序的模拟结果符合.二维模拟定出了KH不稳定性单模非线性增长的阈值. 关键词： Kelvin-Helmholtz不稳定性 二次谐波产生 非线性阈值     

Second harmonic generation of metal nanoparticles under tightly focused illumination

The near-field and far-field second harmonic(SH) responses of a metal spherical nanoparticle placed in the focal region of a highly focused beam are investigated by using the calculation model based on three-dimensional finite-difference time-domain(FDTD) method. The results show that off-axis backward-propagating SH response can be reinforced by tightly focusing, due to the increase of the relative magnitude of the longitudinal field component and the phase shift along the propagation direction.     

用激活性非线性介质Nd：MgO：LiNbO3产生二次谐波

以Nd:MgO:LiNbO_3同时兼作激活介质和非线性光学材料,研究自倍频激光器。用小型氙灯泵浦,在室温下获得二次谐波激光(0.547μm) 阈值小于4.8'J,最大输出400μJ/shot,工作温度范围大于20℃～45℃,无光损伤。     

二倍频晶体温升分布对输出光场分布的影响

利用分步快速傅里叶变换和四阶龙格-库塔法,对具有一定温升分布的倍频晶体的二次谐波转换过程进行了研究。综合考虑了谐波转换过程中的离散、衍射、二阶、三阶非线性等效应,着重讨论了倍频晶体吸收光能后,晶体内温升分布对晶体内o光和e光的折射率分布的影响,定量分析了温度分布引起的相位失配量、输出光场分布、二次谐波转换效率随倍频晶体温度分布变化的规律。结果表明:在高功率倍频系统中,倍频晶体温升分布引起基频光、倍频光的相位失配,相位失配导致输出光场光强分布的变化以及谐波转换效率的降低。     

KNbO_3高效倍频产生427～470nm蓝紫光

厚1.5 mm的KNbO_ 3晶体在室温下角度相位匹配倍频脉冲参量激光获得427～470nm蓝紫光,能量转换效率超过40％,输出单脉冲蓝紫光的峰功率达60kW.对相位匹配曲线、倍频效率与基波光强的关系和相应匹配角允差作了计算和讨论.     

c—切MgO：LiNbO3质子交换平板波导中切伦科夫倍频的理论分析

从耦合模方程出发,推导了切伦科夫倍频转换效率公式,并得出该效率主要是由交叠积分决定的结论;通过对交叠积分的计算找到了进一步提高该效率的有效方法;最后用Nd:YAG激光器进行了切伦科夫倍频实验,得到了接近1%的转换效率,增加包层折射率可以使该效率增加到1.3%,实验结果证实了理论分析.     

组装L-B膜光学二次谐波的实验研究

一种分子形成的多层L-B膜由于相邻层的分子取向相反而使非线性极化抵消,总的X~(2)=0.本文用光学二次谐波方法确定了带有不同极性基团的L-B单分子层的有效非线性系数的大小和符号,对有效非线性系数符号相反的两种单分子层交替组装,使相邻单分子层的非线性极化相互叠加,得到了具有较大二阶非线性系数的组装L-B膜.     

Effect of fundamental radiation wave front astigmatism on the process of second optical harmonic generation in uniaxial crystals

Nonlinear processes of conversion of radiation with wave front astigmatism in nonlinear crystals of 6 and 3m symmetry are theoretically analyzed. Spatial-angular and energy structures of the second optical harmonic in lithium niobate and iodate crystals are investigated theoretically and experimentally. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 72–75, November, 2008.     

增益介质位置对腔外倍频效率的影响

采用MgO掺杂的周期性极化铌酸锂晶体作为非线性晶体,搭建了线性平-凹腔结构的外腔式倍频系统,分析了增益介质和输入耦合镜之间的距离对二次谐波转换效率的影响。实验中,使用光纤耦合二极管泵浦Nd: YVO₄激光器作为基频光源,通过改变增益介质和输入耦合镜的间距,测量了激光器的纵模数量、锁模脉冲稳定性、基频光线宽以及光-光转换效率。实验结果显示,增加增益介质和输入耦合镜之间的距离,可以在一定程度上提升自锁模脉冲的稳定性并有效减小基频光线宽。当泵浦功率较高时,适当增加该间距可以有效提升二次谐波转换效率。     

Pulse shape analysis of second harmonic and difference-frequency generation

A computer model has been used to investigate the pulse shape evolution of interacting waves during second harmonic generation and difference-frequency generation processes. Using general assumption and coupled equations theory we describe in detail the back and forth energy transfer in connection with pulse shape. Two type of phase-match (modal phase-match and quasi-phase-match) with experimental relevance are discussed. In the case of quasi-phase-match uniform and chirped grating are discussed. The connection of the model with material properties and non-linear optical (NLO) strength is presented. The proposed model have allowed us to derive the essential feature of pulse shaping and compressing that rely on NLO process only.     

高功率半导体激光器倍频实现紫外光输出

采用中心波长780 nm、线宽0.13 nm的体布拉格光栅外腔半导体激光作为基频光,基于Ⅰ类相位匹配的三硼酸锂晶体(LBO),获得了中心波长为390 nm的倍频光输出,输出功率30 μW,转换效率0.01%,为高功率紫外光束的实现提供了新的技术路线。     

On the efficiency of the second harmonic generation in optical waveguides: TM case

In this paper we analyse the second harmonic generation of TM polarisation in a planar waveguide with a non-linear anisotropic substrate using the coupled mode theory under the non-depleted pump approximation. It is an extention of our previous paper in which we treated TE polarisation. Moreover, both guided waves and erenkov radiation are now taken into account simultaneously. It is shown both analytically and numerically that the erenkov efficiency peak follows the L ^3/2 dependence on the interaction length L also for TM polarisation. In an anisotropic KTP/Si₃N₄/SiO₂ waveguide, higher maximum attainable second harmonic generation (SHG) efficiency was calculated for the TM polarisation than for the optimum TE case.     

Second harmonic generation by cold-deposited silver films

The second harmonic generation (SHG) of light diffusely scattered by cold-deposited silver films is negligible with respect to the specular intensities. Therefore, a cold-deposited silver film is well approximated by a homogeneous effective medium. The intensities of SHG at 1.06 μm and the optical absorption at 0.53 μm depend on both the square of the internal effective field at 0.53 μm and a change in the same way when annealing the film. This can be understood by the assumption that SHG is also mainly following the electric field within the metal phase and surface contributions to SHG interfere destructively. This is corroborated by the observation that the SHG intensity does not show the ‘chemical first layer effects’ seen by surface-enhanced Raman scattering (SERS).