高Q法布里-珀罗腔中二阶串级非线性相移

在高Q值法布里珀罗腔中研究了二阶串级非线性相移.结果表明,通过改变入射光强,可以全光学控制基频光束的透射率和它的相移.基频透射光束的非线性相移相对入射光强的变化率被提高了腔精细度的平方.这可用作光子学开关器件 关键词： 二阶串级效应 法布里珀罗腔 非线性相移     

光学测试 材料(物质)光学性能测试与设备

TB962007054775基于ABCD矩阵的Z-扫描理论=Z-scan theory based onABCDformalism[刊,中]/王超(西北大学光子学与光子技术研究所.陕西,西安(710069)),李渭龙…//光子学报.?2007,36(3).?444-447基于光学系统对傍轴激光束的传输与变换技术-ABCD定理,以非线性相移为研究对象,采用表征高斯光束特征的q参量在光束无像散近似假设下,分析了Z-扫描测量方法的理论基础,得到了表达简单的解析理论公式。在非线性相移|ΔФ0|<πrad时,所得模拟结果可以很好地与已知理论结果相吻合。对CS2和纳米碳管乙醇溶液的非线性测量及数据的拟合,证明了用此结…     

非线性相移对Z-scan曲线对称性的影响

 基于由光束传输的ABCD矩阵得出的Z-scan透过率的解析结果，分析了Z-scan实验曲线随非线性相移的变化规律。发现随着相移的增加，折射非线性相移比吸收非线性相移对Z-scan曲线对称性的影响更大。对于具有强饱和吸收和弱自聚焦特性的非线性介质，其Z-scan曲线随非线性折射相移的变小将失去典型的类色散特点。对于1μm厚的ZnCdSe-ZnSe多量子阱，扫描光源采用532 nm的基模高斯光束，采用透过率表达式来拟合所得的实验数据，在吸收非线性相移为0.9与耦合因子为-10条件下，推算出三阶非线性吸收系数为2×10^-3 cm/W，三阶非线性折射系数为 8.0×10^-8 cm²/W，这与J.Ma等人的结果吻合。最后对曲线特征参数随非线性相移变化进行了数值计算，得到的曲线所对应的非线性相移与曲线谷位置的乘积近似为一常量，值为0.166。     

基于衍射理论的大非线性相移Z扫描研究

以衍射理论为基础,建立了强非线性吸收下,非线性介质对高斯光束的衍射模型.数值计算表明,折射相移的增大使峰的透过率增强而谷的透过率趋于饱和;而吸收相移的增大使峰的透过率被抑制而谷的透过率增强.相移比值是决定谷-峰结构存在与否的关键.在一定的输入功率下,远场输出功率并不是完全随着非线性吸收系数的增大而增大.该理论的近似条件只要求是薄样品,具有更好的适用性.     

基于衍射模型的Z扫描理论

以菲涅耳－基尔霍夫衍射理论为基础，建立了非线性光学介质对高斯光束的衍射模型，从一种新的角度解释了Z扫描现象，这种理论不仅在小非线性相移的情况下与传播Z扫描理论的结果完全一致，而且还适用于大非线性相移的情况。数值计算表明，随着非线性相移的增大，原来近似对称的Z扫描曲线发生畸变，谷的透过率被饱和抑制而峰的透过率被增强。通过开孔的光功率随着入射激光功率的增加会出现振荡衰减现象。     

大非线性相移下光学非线性Z扫描特性的研究

采用高斯分解法(GD)对大非线性相移下的Z扫描特性进行了分析,通过对数值算法的优化,将GD推广到对脉冲入射激光下大非线性相移下的Z扫描理论分析.对不同条件下大非线性相移Z扫描曲线峰谷结构的比较,发现在大非线性相移的情况下,Z扫描曲线的峰和谷随透过光阑或入射光强变化表现出某些新的特性.随着透过光阑孔径的增加,Z扫描曲线峰的变化要明显快于谷的变化,而且在谷明显存在的情况下,峰很快消失.采用皮秒脉冲激光下的纯二硫化碳实验对理论结果加以验证,实验结果和理论分析相一致.我们的分析结果对大非线性相移下Z扫描测量有一定的指导性意义,避免在大非线性相移下对Z扫描结果产生错误的分析.     

非线性介质表面缺陷对激光光场的调制

以高斯光束为例,研究了非线性介质表面振幅调制型缺陷对光场的调制。基于广义惠更斯-菲涅尔衍射积分并采用泰勒级数展开方法,建立了高斯光束经过表面存在缺陷的非线性介质后的传输模型,得到了受缺陷调制光束经非线性介质后的光强分布解析式,研究了缺陷尺寸和光束在非线性介质中产生的附加相移大小对光强分布的影响,结果表明介质表面的缺陷尺寸越大,介质内产生的附加相移越大,光场受到的调制越严重。分别考虑了非线性折射率为正值和为负值的情况,研究发现相应的折射率值导致光束发生会聚或发散现象,并由于缺陷调制的作用,在光束传输过程中始终存在一光强极值点,且随着附加相移绝对值的增大光强极值点的峰值也随之增强。     

大非线性相移下光学非线性Z扫描特性的研究

采用高斯分解法(GD)对大非线性相移下的Z扫描特性进行了分析，通过对数值算法的优化，将GD推广到对脉冲入射激光下大非线性相移下的Z扫描理论分析.对不同条件下大非线性相移Z扫描曲线峰谷结构的比较，发现在大非线性相移的情况下，Z扫描曲线的峰和谷随透过光阑或入射光强变化表现出某些新的特性.随着透过光阑孔径的增加，Z扫描曲线峰的变化要明显快于谷的变化，而且在谷明显存在的情况下，峰很快消失.采用皮秒脉冲激光下的纯二硫化碳实验对理论结果加以验证，实验结果和理论分析相一致.我们的分析结果对大非线性相移下Z扫描测量有一定的指导性意义，避免在大非线性相移下对Z扫描结果产生错误的分析. 关键词： 大非线性相移 高斯分解法 Z扫描     

非线性介质F－P干涉仪光束输出特性的理论研究

本文对准直光束射入含有非线性介质的Ｆ－Ｐ干涉仪内的光场分布进行了研究．由于非线性介质与光的作用，从Ｆ－Ｐ干涉仪出射的光束截面上的相移随位置的改变呈一定的分布，进而引起了干涉仪的透射率和输出光束重新分布。当干涉仪两个面的反射系数较大时，输出光束截面出现光强和相移的跃变．这种现象与以前在平面波假设下所得的光强分布所得结论有较大的不同．     

非线性介质F—P干涉仪光束输出特性的理论研究

本文对准直光束射入含有非线性介质的Ｆ－Ｐ干涉仪内的光场分布进行了研究。由于非线性介质与光的作用，从Ｆ－Ｐ干涉仪出射的光束截面上的相移随位置的改变呈一定的分布，进而引起了干涉义的透射率和输出光束重新分布。当干涉仪两个面的反射系数较大时，输出光束截面出现光强和相移的跃变。这种现象与以前在平面波假设下所得的光强分布所得结论有较大的不同。     

Growth and optimization of optical traits of copper sulphate crystal exploiting L-ascorbic acid for photonic device applications

In current investigation organic ligand of _L-ascorbic acid (LAA) has been firstly exploited to tune the optical properties of copper sulphate (CuS) single crystal. The pure and LAA influenced CuS crystal has been grown from aqueous solution by slow evaporation process. The powder X-ray diffraction technique has been employed to identify the crystal planes and evaluate the structural parameters of grown crystals. The functional groups of LAA influenced CuS (LAA-CuS) crystal has been recognized by Fourier transform infrared analysis. The impact of LAA on optical transmittance of CuS crystal has been examined within 200-900 nm by means of UV-visible spectral analysis. The Z-scan technique has been employed to examine the third order nonlinear optical (TONLO) properties of pure and LAA-CuS crystal. The eye-catching effect of LAA in switching the nonlinear refraction behavior of CuS crystal from self-focusing to self-defocusing has been explored. The magnitude of TONLO refractive index (n₂), absorption coefficient (β) and susceptibility (χ³) of pristine and LAA-CuS crystal has been comparatively evaluated using the Z-scan transmittance data.     

Third order nonlinear optical properties of potassium dichromate single crystals by Z-scan technique

Single crystal of potassium dichromate (KDC) has been grown from aqueous solution by slow evaporation technique. The lattice parameters of the grown crystal were determined by X-ray diffraction analysis. The optical absorption studies reveal that the crystal has UV cut-off wavelength around 240 nm. Thermo gravimetric and differential thermal (TGA/DTA) studies revealed that the crystal thermally stable up to 397.1 °C. The mechanical strength of the grown crystal was carried out by Vickers micro hardness test. The crystal perfection was confirmed by etching studies. Third order nonlinear optical studies was performed using by single beam Z-scan technique using continuous Nd:YAG laser. Closed aperture Z-scan studies reveal the negative nonlinearity in the crystals and open aperture Z-scan reveals the saturation absorption. Also various parameters such as nonlinear refractive index n₂, absorption co-efficient β and nonlinear optical susceptibility χ⁽³⁾ were calculated for the grown crystal.     

Wavelength dependent resonant nonlinearities in a standard saturable absorber IR26 on picosecond time scale

Nonlinear optical properties of a standard dye IR26 have been studied by using the Z-scan technique to decipher the difference in the mechanism of nonlinear absorption on picosecond time scale at two wavelengths i.e. at 1064 nm and 532 nm. A prominent contribution of nonlinear absorption is observed in the Z-scan profiles at 1064 nm. The dye exhibits the mechanism of self-defocusing at 1064 nm in contrast to that of self-focusing at 532 nm. While the two photon absorption has been found to be the dominant mechanism of reverse saturable absorption at 1064 nm, the mechanism of excited state absorption is operating at 532 nm. Additionally, the optical phase conjugate geometry of degenerate four wave mixing (DFWM) technique has been used to measure the third order nonlinear susceptibility values at 532 nm to compare with those obtained from the Z-scan profiles.     

1维部分相干光束的Z扫描理论分析

 对使用高斯-谢尔模型光束的Z扫描做了理论分析，研究了光阑半径和空间相干度变化对Z扫描曲线的影响。研究发现：随着光阑半径的变大，Z扫描峰谷透过率之差逐渐减小直至为零，其作用效果与完全相干光一致；随着空间相干度的增加，峰谷透过率之差也逐渐增大，当空间相干度大于某一定值后，峰谷透过率之差达到饱和不变。部分相干光束的Z扫描实验为测量其空间相干度提供了一种可行的方法。     

A novel approach for analyzing open Z-scan experiments

In this work, a novel method for analyzing open Z-scan experiments is presented. It is based on the calculation of the nonlinear absorption parameter q directly from the transmittance measurements. Specifically, we have found an analytic formula describing the dependence of the parameter q on the normalized transmittance. The influence of noise has been studied and the method was proved robust even under conditions of relatively high noise. Extension to the general case of an elliptic Gaussian incident beam has also been realized. The technique has been experimentally tested by analyzing transmittance measurements obtained from a recently synthesized pyrylium salt, illuminated by a femtosecond laser system. The results are in very good agreement with those obtained by the standard Z-scan analysis, especially regarding the nonlinear absorption coefficient β.     

以衍射理论为基础考虑双光子吸收的Z-扫描理论

以菲涅尔-基尔霍夫衍射理论为基础,建立了非线性介质对高斯光束的衍射模型,对高斯光束通过非线性介质后的传输行为进行了详细的理论推导和数值计算,从一种新的角度解释了Z-扫描现象.理论推导出了考虑双光子吸收的闭孔和开孔Z-扫描曲线的统一公式,是计算非线性折射率和双光子吸收系数的一种新方法.数值模拟计算表明,对于考虑双光子吸收的闭孔Z-扫描曲线,其结果与经典的Z-扫描理论完全一致.而对于已给定的开孔Z-扫描曲线,用该理论计算出的双光子吸收系数是经典开孔Z-扫描理论计算值的1/3,其它结论与传统Z-扫描理论完全吻合.该理论的近似条件只要求薄样品和小非线性吸收,比传统理论具有更好的准确性.     

Enhanced sensitivity of Z-scan technique by use of flat-topped beam

Based on the Huygens–Fresnel diffraction integral method, we report a theoretical investigation on the closed-aperture Z-scan technique by using the flat-topped beam. The sensitivity of the flat-topped beam Z-scan technique, which can be enhanced with the increase of the flatness order N for the flat-topped beam, is greatly higher than of the Gaussian beam. Some salient characteristics of the flat-topped beam Z-scan traces are addressed. The flat-topped beam Z-scan technique for characterizing the instantaneous nonlinearity is also presented.     

激发态分子内质子转移有机分子HBT的三阶非线性光学特性

以532nm皮秒脉冲作抽运光,采用单光束Z-扫描技术对具有激发态分子内质子转移效应的有机分子2-(2′-羟基苯基)苯并噻唑(HBT)在其双光子吸收区的非线性光学特性进行了研究.实验结果表明,对532nm波长的光,HBT分子存在明显的双光子吸收.通过拟合开孔Z-扫描实验数据,求解了HBT分子在其双光子吸收区的非线性吸收系数,并探讨了抽运光强度对介质双光子吸收效应的影响.采用高斯分解法,通过拟合闭孔Z-扫描除以开孔Z-扫描数据,理论推导并计算了在介质对抽运光存在非线性吸收的情况下HBT分子的非线性折射率,以及不同入射光强度时HBT分子的三阶非线性极化率实部和虚部的值.计算结果表明,理论分析与实验结果较好地符合,这些结果为进一步研究和开发此类材料的应用提供了理论与实验依据.