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c—切MgO:LiNbO3质子交换平板波导中切伦科夫倍频的理论分析 总被引:1,自引:0,他引:1
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. 相似文献
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LiNbO3波导中切伦科夫辐射型的倍频 总被引:1,自引:1,他引:0
对条波导中切伦科夫辐射型的倍频作了简要分析,着重分析了产生切伦科夫辐射倍频的,工从实验上实现了条波导中1.06μm红外光到0.531m绿光的倍频辐射,转换效率为的0.9%,对应的输入光功率为10mW。 相似文献
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针对现有核素治疗中内照射剂量测量缺乏简单、高效方法的问题,基于内照射剂量与切伦科夫辐射之间的关系,提出一种基于切伦科夫辐射的核素治疗内照射剂量测量的新方法。利用蒙特卡罗计算程序Geant4,模拟放射性核素131I在水体模型和甲状腺模型中产生切伦科夫辐射与剂量沉积的分布情况,并定量分析切伦科夫光子数与剂量之间的关系。计算结果表明:在水体模的半径方向上切伦科夫光子数与剂量之间有着相同的变化趋势,且两者有着相同的二维分布规律;核素131I在介质中产生的切伦科夫光子数与剂量两者之间存在一定的线性关系,且这种线性关系与核素的分布情况无关。研究结果证实,将这种放射性核素在介质中产生的切伦科夫辐射应用于内照射剂量学具有非常大的研究潜力和价值。 相似文献
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研究了两维光学超晶格光波导中的准相位匹配切连科夫(Cerenkov)倍频与和频效应,利用光学超晶格的不同倒格矢实现了多组准相位匹配切连科夫倍频与和频的同时输出,从理论和实验两个方面探讨了光学微结构材料中非线性切连科夫辐射产生的机制、效应和可能的应用. 相似文献
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针对直接测量16.7 MeV进行烧氚历史诊断所需聚变产额高的情况,模拟研究了利用14 MeV中子与副靶作用产生的非弹伽马进行烧氚历史诊断的情况,计算了几种材料14 MeV中子作用产生的次级伽马能谱以及切伦科夫辐射阈能之上的非弹伽马数目,对副靶材料和厚度进行了选择。计算了14 MeV中子产生的切伦科夫光子时间谱,分析了光电转换器件处伽马、电子以及正电子等噪声信号,分析了气体切伦科夫系统测量统计涨落与聚变中子产额之间的关系,确定了气体切伦科夫系统所适用的最低聚变中子产额,通过测量14 MeV中子与副靶产生的非弹伽马进行烧氚历史诊断较直接测量16.7 MeV伽马可将测量所需聚变中子产额降低2个量级。 相似文献
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《Optics Communications》2002,201(1-3):179-190
The coupled-mode equation in dissipative waveguides in Cherenkov configuration has been detailedly discussed for the first time, to our knowledge. Based on this equation, Cherenkov second harmonic generation (SHG) and Cherenkov nonlinear phase shift (NPS) caused by Cherenkov cascading second order nonlinear (CSON) effects have been analyzed and optimized comprehensively and systematically by an analytical method, taking into account both the conversion depletion and the waveguide loss, and the analytical expressions for Cherenkov SHG and NPS has been presented. The dependence of the NPS and the conversion efficiency on varied parameters, such as the waveguide thickness, the fundamental wavelength, the input fundamental power and the temperature, has been discussed completely. The results show that a large enough NPS (>10π) can be attained for nondissipative waveguides with a very small depletion of the fundamental power, at the same time, this Cherenkov CSON configuration has some advantages over the quasi-phase matching CSON configuration, e.g., the much looser tolerances of the waveguide parameters and the noncollinear feature of the fundamental wave and the second harmonic wave, these characteristics make the Cherenkov CSON configuration a promising direction to realize all-optical devices. 相似文献
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We examine the effect of wiggler magnetic field on pulse slippage of short pulse laser-induced third harmonic generation in plasma. The process of third harmonic generation of an intense short pulse laser in plasma is resonantly enhanced by the application of a magnetic wiggler. The laser exerts a ponderomotive force at second harmonic driving density oscillations. The second harmonic oscillations coupled with electron velocity at the laser frequency, produces a non-linear current, driving the third harmonic. Third harmonic pulse generates in the fundamental pulse domain. However, the group velocity of the third harmonic wave is greater than the fundamental wave. Hence, the third harmonic pulse saturates strongly and moves forward from the fundamental pulse at shorter distance than the second harmonic pulse. 相似文献
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为了提高超短脉冲二倍频的转换效率和改善出射倍频光的脉冲形状,对超短脉冲倍频中三阶非线性效应的影响进行了理论分析和数值模拟,并采用初始相位失配的方法来补偿三阶非线性效应的影响。结果表明:用KDP晶体二倍频中心波长为800 nm的超短脉冲,当入射功率密度大于100 GW/cm2时,三阶非线性效应是倍频转换效率的主要影响因素。对脉宽为50 fs,入射功率密度为250 GW/cm2的超短脉冲在KDP晶体(2 mm)中的二次谐波变换,当初始相位失谐0.9 mrad时,转换效率提高了10%,同时由三阶非线性效应引起的强度调制得到明显抑制,出射基频光和倍频光的脉冲形状得到明显改善。 相似文献
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Vasudevarao A Kumar A Tian L Haeni JH Li YL Eklund CJ Jia QX Uecker R Reiche P Rabe KM Chen LQ Schlom DG Gopalan V 《Physical review letters》2006,97(25):257602
Multiferroicity can be induced in strontium titanate by applying biaxial strain. Using optical second harmonic generation, we report a transition from 4/mmm to the ferroelectric mm2 phase, followed by a transition to a ferroelastic-ferroelectric mm2 phase in a strontium titanate thin film. Piezoelectric force microscopy is used to study ferroelectric domain switching. Second harmonic generation, combined with phase-field modeling, is used to reveal the mechanism of coupled ferroelectric-ferroelastic domain wall motion. These studies have relevance to multiferroics with coupled polar and axial phenomena. 相似文献
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C. Deng J. W. Haus A. Sarangan A. Mahfoud C. Sibilia M. Scalora A. Zheltikov 《Laser Physics》2006,16(6):927-947
Enhanced second-harmonic generation (SHG) conversion efficiency was theoretically predicted in waveguide geometry with coupling to a one-dimensional grating photonic band gap (PBG). We report a series of experiments using samples made with lithium niobate. A waveguide was fabricated near the surface by applying the proton-exchange technique. The characteristics of waveguide modes were determined by several techniques: prism coupling, diffraction, and Cherenkov radiation. The WKB method was used to analyze the results. Ultraviolet laser lithography was applied to make PBG gratings on the sample. We further investigated Cherenkov second-harmonic generation (CSHG), i.e., SHG radiated into the substrate, under the condition of a band-edge PBG resonance in the waveguides. The SHG inside planar waveguides was also experimentally investigated. We fabricated waveguides with multiple pump modes and found that the second mode was more efficient in enhancing the second harmonic signal. This result is explained by our model. Several samples were investigated in detail; the highest conversion efficiency of CSHG with a PBG was enhanced around 50 times above the CSHG signal without a PBG. A numerical model was constructed with parameters calculated from our sample characterization data to interpret the experimental results. 相似文献
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The second harmonic generation behavior of a contacting interface has been evaluated experimentally and discussed theoretically in the light of a nonlinear interface model. Two aluminum blocks were mated together to constitute a contact interface and subjected to normal compressive loading. A 5 MHz longitudinal toneburst wave was sent to the interface in the normal direction and the transmitted wave was recorded, from which the fundamental and the second harmonic components were extracted. A nonlinearity parameter was obtained as the ratio of the second harmonic amplitude to the squared fundamental amplitude. From the measured contact pressure dependence of the transmitted fundamental amplitude, the linear and the second-order interfacial stiffness parameters were identified, which enabled the evaluation of the nonlinearity parameter based on the theoretical model. The theoretical contact pressure dependence of the nonlinearity parameter was found to be in good qualitative agreement with the experimental results. 相似文献
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K. Kalinowski V. Roppo T. ?ukasiewicz M. ?wirkowicz Y. Sheng W. Krolikowski 《Applied physics. B, Lasers and optics》2012,109(4):557-566
We theoretically study the parametric wave interaction in nonlinear optical media with randomized distribution of the quadratic nonlinearity $\chi ^{(2)}$ . In particular, we discuss the properties of second and cascaded third harmonic generation. We derive analytical formulas describing emission properties of such harmonics in the presence of $\chi ^{(2)}$ disorder and show that the latter process is governed by the characteristics of the constituent processes, i.e. second harmonic generation and sum frequency mixing. We demonstrate the role of randomness on various second and third harmonic generation regimes such as Raman?CNath and ?erenkov nonlinear diffraction. We show that the randomness-induced incoherence in the wave interaction leads to deterioration of conversion efficiency and angular spreading of harmonic generated in the processes relying on transverse phase matching such as Raman?CNath interaction. On the other hand, the ?erenkov frequency generation is basically insensitive to the domain randomness. 相似文献
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We theoretically investigate the evolvement of dark spatial soliton with
cascading quadratic nonlinearity in quasi-phase-matched second harmonic
generation. It is shown that the dark solitary wave can propagate stably
when background intensity is large enough, in which diffraction of beam can
be balanced by the cascading quadratic nonlinearity. We also analyze the
influence of phase-mismatch on the stability of dark soliton propagation. 相似文献
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The formation of the dark spatial solitary wave in cascaded second harmonic generation processes is numerically studied based on the nonlinear-coupled equations. It is shown that the solitary wave exists when the effective three-order nonlinearity induced by cascaded second-order nonlinearity is negative. 相似文献