基于内置电光晶体F P标准具的扫描滤波方法

基于内置电光晶体的F-P标准具,利用F-P多光束干涉原理和晶体的线性电光效应,提出了一种能有效提高啁啾脉冲信噪比的扫描滤波方法。给出了电光晶体加载电压的时变函数表达式,分析了影响信噪比提升效果的主要因素,并重点讨论了电光晶体的电压控制参数对信噪比提升效果和滤波器透过率的影响。研究结果表明,利用该扫描滤波方法可将啁啾脉冲激光信噪比提升约2个量级。     

基于光折变效应提升啁啾脉冲信噪比的光谱扫描滤波法

基于光谱扫描滤波原理,提出了一种利用光折变效应来提高啁啾脉冲信噪比的扫描滤波方法,并进行了理论分析。针对内置光折变晶体的Fabry-Perot (F-P)标准具光谱扫描滤波装置,定量分析了其透射谱特性,详细讨论了Fabry-Perot(F-P)标准具两平板的反射率、透射谱窗口带宽、外加场的控制参数以及信号光啁啾率变化等对啁啾脉冲信噪比的提升及其滤波透射率的影响。结果表明,F-P两平板的反射率越高,则透射谱越尖锐,透射窗口越窄,滤波效果也就越好。为了得到有效的信噪比提升,一般要求其反射率大于0.99;外加场的控制和信号光啁啾率的变化对扫描滤波的影响较大,在实际工作中,应尽量保证外加场和啁啾率的精确控制,以确保信号光和滤波函数的同步匹配。针对中心波长800 nm的啁啾信号脉冲,采用提出的光谱扫描滤波方法,对放大自发辐射(ASE)的随机噪声与预脉冲进行滤波,可得到近3个量级的信噪比提升效果。     

利用Mach-Zehnder干涉仪提升啁啾脉冲信噪比

基于内置电光晶体的Mach-Zehnder干涉仪,利用Mach-Zehnder干涉仪双光束干涉原理和晶体的线性电光效应,提出了一种新的能有效提高啁啾脉冲信噪比的扫描滤波方法。定量分析了其扫描滤波谱特性,探讨了预脉冲噪声延时对信噪比提升效果的影响,并讨论了电光晶体的电压控制参数对信噪比提升效果的影响。研究结果表明:预脉冲噪声的延时和控制电压的变化会对滤波效果产生较大影响,利用该扫描滤波方法可将啁啾脉冲激光信噪比提升约2个量级,且信号光透过率高达95%以上。     

光谱扫描滤波法提升超强飞秒激光相干信噪比分析

光谱调制所形成的预脉冲和后沿脉冲的时频谱图将等间距、 平行地分布于啁啾主脉冲时频谱图的两侧, 基于光谱调制啁啾光脉冲的这种时频谱特点, 采用扫描滤波方式来提升其对比度. 数值模拟分析了扫描滤波过程中时间抖动、 扫描率差异和通带宽度等因素对扫描滤波效果的影响, 结论表明, 在扫描轨迹与信号光频率相同的情况下, 控制通带宽度, 相干信噪比提升率接近0.41F²倍, 而啁啾信号光以超过90%的透光率通过光谱扫描滤波器. 关键词： 超快激光技术 相干信噪比 光谱扫描滤波 短时傅里叶变换法     

光谱扫描滤波法提升飞秒激光信噪比的理论分析

在时间--频率域中,啁啾脉冲被淹没在放大自发辐射等噪声中,且其瞬时频率线性分布,基于此,提出采用光谱扫描滤波的办法来提升高功率飞秒激光系统的信噪比,并以法布里--珀罗干涉仪作为光谱扫描滤波器,对该法提升信噪比的效果进行了详细的理论分析.采用短时傅里叶变换方法,研究了光谱扫描滤波器对自发辐射放大(ASE)的滤波效果,数值分析表明,在时间抖动为-2 ps到2 ps之间、光谱扫描滤波器的通带宽度为0.4 nm条件下,该法能将飞秒激光系统的信噪比提升2个量级,而啁啾信号光以超过90%的透光率通过光谱扫描滤波器;级联光谱扫描滤波方式能进一步提升飞秒激光信噪比.     

电光双折射扫描滤波法提高啁啾脉冲对比度

提出了一种通过扫描滤波来提高啁啾脉冲对比度的方法,并分析了该方法的原理。与传统的非线性滤波技术不同,扫描滤波方法消除预脉冲时,选通原理是基于光的频率而不是强度。以电光双折射扫描滤波器为例,说明了扫描滤波法的具体应用。通过数值模拟及实验研究,发现电光双折射扫描滤波法可以有效地消除主脉冲以前几百ps的预脉冲,并且主脉冲同时还能保证较高的透过率。     

啁啾匹配OPCPA方案用于消除超短激光脉冲的预脉冲

采用了一种利用啁啾匹配光参量啁啾脉冲放大（OPCPA）技术来消除泵浦脉冲时间窗口内的预脉冲的方法,并对该方法展开了数值模拟研究。分析了泵浦光脉冲形状、预脉冲提前时间等因素对预脉冲消除效果以及信噪比提升情况的影响。通过与传统的非共线OPCPA方案对比,发现啁啾匹配OPCPA方案可以消除掉离主脉冲更近的预脉冲,且它对预脉冲的消除效果受泵浦光脉冲形状的影响较小。     

啁啾脉冲堆积用于光脉冲整形

报道了一种利用100 ps啁啾脉冲堆积产生2．2 ns任意整形脉冲的脉冲整形系统。采用掺Yb~(3 )光纤锁模振荡器得到稳定的锁模光脉冲序列,将该锁模脉冲通过啁啾光纤光栅展宽并通过1 nm带宽的高斯形光谱滤波器滤波,得到标准的100 ps高斯形啁啾脉冲序列,将此脉冲选单经过光纤延迟线组成的32路脉冲堆积器,得到了精度为32 bit的重复频率为1 Hz的2．2 ns任意整形光脉冲。研究了堆积脉冲的特性,分析了宽带啁啾堆积整形脉冲的光谱时间扫描特性对激光驱动惯性约束聚变打靶束匀滑的优化作用。实验测得了该系统输出的2．2 ns整形光脉冲具有小于50 ps的上升沿,与100 ps啁啾脉冲的时间抖动小于4 ps。     

钽铌酸钾晶体的电控偏转色散特性

钽铌酸钾(KTN)晶体具有很高的二次电光系数,响应速度快,因此可以作为高速电光开关的材料,能在较低电压下快速产生大的光束偏转角。但是KTN晶体的色散问题制约了其作为电光开关在宽光谱范围内的应用。探讨了外加电压、温度及波长对偏转特性的影响,发现同时调节电压和温度的方法可以平衡光束偏转角和色散,为KTN晶体用于宽波段光束偏转提供参考。     

F-P滤波器对啁啾光脉冲脉宽的扩展和压缩

导出了啁啾光脉冲通过F P滤波器后输出脉冲光强的解析表达式。在此基础上 ,对啁啾光脉冲通过F P滤波器后其脉冲宽度的变化进行了研究。结果表明 ,对于一确定的滤波器 ,其对输入脉冲脉宽的影响与输出脉冲的宽度及啁啾因子的大小有关     

Structures and elastic properties of paraelectric and ferroelectric KTa0.5Nb0.5O3 from first-principles calculation

The structures, elastic properties and intrinsic hardness of B-O bonds of KTa_0.5Nb_0.5O₃ crystal in paraelectric and ferroelectric phase structures have been investigated by means of the density functional theory. Both structures are found to be elastically stable and in good agreement with available results. The elastic properties including the bulk modulus, shear modulus and Young’s modulus change largely during phase transition. The paraelectric KTa_0.5Nb_0.5O₃ crystal is more incompressible and harder than ferroelectric phase. The hardness of KTa_0.5Nb_0.5O₃ crystal is mostly determined by Nb-O bonds and the modifications of the bond strength affect the hardness of the crystal. Charge density contours indicate that the electronic distributions between B-O bonds play an important role in the formation of elastic properties.     

铁电钾钠铌酸锶钡薄膜电光性能的研究

采用溶胶-凝胶法在氧化镁单晶衬底上制备了符合化学计量比的完全填充型铁电钾钠铌酸锶钡(KNSBN)薄膜，通过X射线衍射，摇摆曲线，X射线Φ扫描，扫描电子显微镜等方法研究了薄膜的微结构，采用Adachi法研究了薄膜的电光特性. 实验发现，KNSBN薄膜在氧化镁(001)单晶衬底上沿c轴外延生长，K⁺，Na⁺的引入有效地提高了薄膜的横向电光系数r₅₁. 成分为K_0.2Na_0.2Sr_0.24Ba_0.56Nb₂O₆, K_0.2Na_0.2Sr_0.6Ba_0.2Nb₂O₆, K_0.2Na_0.2Sr_0.72Ba_0.08Nb₂O₆的三种KNSBN薄膜的r₅₁值分别为108.52pm/V, 119.98pm/V, 126.96pm/V，r₅₁的数值随Sr²⁺含量增加而增大. 关键词： 横向电光系数 钾钠铌酸锶钡 外延生长     

Coupled-optical-phonon-mode electron scattering in perovskite oxides

Conductivity and Hall effect measurements were made on KTa_1?xNb_xO₃(x= 0.00,0.04,0.11 and 0.16) in the intermediate temperature range (77–300 K). It was found that the temperatures dependence of the Hall mobility obeyed a semiempirical relationship of Wemple et al. in this temperature range. The main scattering mechanism is proposed to be longitudinal optical phonons which are coupled to the “soft” transverse optical phonons associated with ferroelectricity.     

KTa1-xNbxO3晶体生长固/液边界层结构的微区研究

测量了KTa_1－xNb_xO₃(KTN)晶体在常温和高温下的Raman光谱;实时测量了晶体生长过程中,固/液边界层内以及边界层两侧的晶体和熔体的高温显微Raman光谱.通过光谱分析获得了KTN晶体生长固/液边界层内的结构特征,以及晶体生长基元从熔体结构经边界层过渡到晶体结构的变化规律.研究表明,KTN熔体中的 结构基团进入到生长边界层后逐步转化为 八面体结构基团,已具有KTN单胞的一些特征.进而讨论了以 八     

A 2 by 2 wavelength tunable Fabry-Perot filter by using an electro-optic polymer film

A tunable Fabry-Perot (F-P) filter by using electro-optic polymer film is proposed. The electro-optic polymer is alkoxysilane dye (ASD)/SiO2-TiO2 hybrid material, whose electro-optic coefficient γ33 is about 5 pm/V. The wavelength tuning range of 3.8 nm under 400-V DC voltage and the nonlinear characteristic with the electric field have been obtained via electro-optical properties of polymer. Both of polymer film fabrication and F-P filter design have been introduced. The tunable F-P filter is designed for the application of two-input/two-output port wavelength-selective optical switch. Also, some problems have been discussed in this letter.     

Electro-optic characterization of tetragonal (1−x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 single crystals by a modified Sénarmont setup

The refractive indices of tetragonal (1−x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ (PMN-xPT) single crystals were measured with a prism coupler and their linear electro-optic (EO) properties were investigated from 20 to 80 °C by the automated scanning Sénarmont system with an ac field. The composition and temperature effect on the EO coefficients were also discussed. It has been found that their EO coefficients are much larger than that of widely used LiNbO₃ single crystal and the calculated half-wave voltages are also much lower, which enable the operation at lower voltages and the smaller device dimensions. Since the excellent EO properties are very stable and such high quality single crystals with large-size have been obtained, the PMN-xPT single crystals are a very promising candidate for EO modulation applications. By linking to the polarization-related quadratic EO coefficients, we find that the linear EO properties are related with the spontaneous polarization and dielectric constants.