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.     

光学测试 材料光学性能测试与设备

TB96 2006043578大非线性相移下光学非线性Z扫描特性的研究=Study onZ-scan characteristics for large optical nonlinear phase shift[刊,中]/陈树琪(南开大学物理科学学院光子学中心.天津(300071)) ,刘智波…∥物理学报.—2006 , 55(3) .—1211-1217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…     

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。     

基于衍射理论的Z扫描技术分析与数值模拟

以菲涅耳-基尔霍夫衍射理论为基础,对通过非线性介质的高斯光束传输行为进行理论分析,分别给出了强吸收、无吸收情况下开孔、闭孔Z扫描曲线公式;对不同条件下非线性介质的归一化透过率进行数值模拟计算,发现Z扫描曲线透射峰和透射谷表现出3种新的特性:随着入射激光峰值光强的增加,Z扫描曲线透射峰的高度受到抑制,而透射谷则加强变得更深;非线性相移的增加对Z扫描曲线透射峰和透射谷均有增高和加深的作用;激光束束腰半径越大,Z扫描曲线的峰谷特征越明显。     

利用Z扫描技术确定非局域非线性介质的非线性折射率

采用高斯分解法,分析并讨论了非局域非线性介质的Z扫描特性.基于介质的非线性响应函数为高斯型,给出了用于确定非局域非线性介质的非线性折射率系数的透过率表达式,分析了非局域非线性介质的非局域程度对透过率曲线的影响,得到了计算非局域非线性介质的非线性折射率系数以及非局域程度的方法,讨论了由于非局域性条件所带来的对实验上的一些参数的调整,提出了测量介质非局域程度的可行的实验方法并说明了其他注意事项.同时还数值模拟了在介质的响应函数为双曲正割型情况下通过薄样品的远场Z扫描曲线,并与高斯响应情况下的结果进行了比较.     

利用Z扫描技术确定非局域非线性介质的非线性折射率

采用高斯分解法，分析并讨论了非局域非线性介质的Z扫描特性.基于介质的非线性响应函数为高斯型，给出了用于确定非局域非线性介质的非线性折射率系数的透过率表达式，分析了非局域非线性介质的非局域程度对透过率曲线的影响,得到了计算非局域非线性介质的非线性折射率系数以及非局域程度的方法，讨论了由于非局域性条件所带来的对实验上的一些参数的调整，提出了测量介质非局域程度的可行的实验方法并说明了其他注意事项.同时还数值模拟了在介质的响应函数为双曲正割型情况下通过薄样品的远场Z扫描曲线，并与高斯响应情况下的结果进行了比较. 关键词： 非局域程度 薄介质 远场条件 Z扫描曲线')" href="#">Z扫描曲线     

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。     

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.     

Z-扫描参量对薄膜材料三阶非线性光学特性的影响

采用数值计算方法对薄膜材料的Z-扫描参量进行研究.对不同激光脉宽下Z-扫描的三阶非线性折射系数和吸收系数进行分析,结果显示不同等级的脉宽激光器对计算结果的数量级影响很大.对不同小孔光阑半径的Z-扫描闭孔曲线进行仿真,结果显示光阑小孔越小,获得特征曲线的峰谷值越明显.对不同光阑离透镜焦点的距离值进行Z-扫描闭孔曲线仿真,...     

光阑对非线性折射光限幅效果影响的理论研究

分析和计算了光阑在两种典型光路系统的光限幅中对限幅效果的影响,包括光阑的大小和位置.两种典型系统分别为理想望远系统和理想聚焦系统.计算模型基于Z扫描理论及其改进公式,限幅机理为非线性折射.对每种情况下光阑的影响进行了定性分析和计算,并取得了相应的理论曲线.研究结果对于光限幅结构中光阑的选取和优化有重要的参考意义.     

Analyses and computations of asymmetric Z-scan for large phase shift from diffraction theory

Based on Presnel-Kirchhoff diffraction theory, we set up a diffraction model of nonlinear optical media to Gaussian beam, which can interpret the Z-scan phenomenon from a new way. This theory is not only well consistent with the conventional Z-scan theory in the case of small nonlinear phase shift, but also can fit for the lager nonlinear phase shift. Numeric computations indicate the shape of the .Z-scan curve is greatly affected by the value of the nonlinear phase shift. The symmetric dispersion-like Z-scan curve is only valid for small nonlinear phase shift (|Δφ0| < π), but with increasing the nonlinear phase shift, the valley of the transmittance is severely suppressed and the peak is greatly enhanced. Further calculations show some new interesting results.     

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.     

克尔介质中瞬态热光非线性效应的作用

研究了介质中瞬态热光非线性效应对于克尔效应Z扫描测量结果的影响，观察到了Z扫描峰谷特性的转变，相应的数值模拟结果与实验结果很好地吻合.实验也发现，克尔效应和瞬态热光非线性效应相互抵消时Z扫描曲线呈现出新奇的单峰或平台状曲线.对于用纳秒脉冲激光进行的Z扫描测量结果的正确分析具有重要意义. 关键词： 瞬态热光非线性效应 克尔效应 Z扫描     

Z-扫描参量对薄膜材料三阶非线性光学特性的影响

采用数值计算方法对薄膜材料的Z-扫描参量进行研究.对不同激光脉宽下Z-扫描的三阶非线性折射系数和吸收系数进行分析,结果显示不同等级的脉宽激光器对计算结果的数量级影响很大.对不同小孔光阑半径的Z-扫描闭孔曲线进行仿真,结果显示光阑小孔越小,获得特征曲线的峰谷值越明显.对不同光阑离透镜焦点的距离值进行Z-扫描闭孔曲线仿真,结果显示距离为1/2透镜焦距值时闭孔Z-扫描曲线能得到相对较大的峰谷差值.数值分析结果与相关文献报道的实验结果基本一致.     

The third order nonlinear optical characteristics of amorphous vanadium oxide thin film

We studied the nonlinear absorptive characteristics (saturation intensity threshold and effective nonlinear absorption coefficients) and nonlinear refraction in a 50-nm-thick VO _x thin amorphous film prepared by pulsed DC magnetron reactive sputtering. The absorptive and refractive nonlinearities were investigated by pump–probe and Z-scan techniques. The closed-aperture Z-scan results reveal self-defocussing characteristics of the amorphous VO _x thin film for both nanosecond and picosecond pulse durations. Experimental results show that a phase transition does not occur in the range of intensities used for the experiments and the investigated sample can be treated as an amorphous semiconductor structure. The open-aperture Z-scan curves with nanosecond pulses exhibit saturable absorption for all input intensities. On the other hand, the open-aperture Z-scan curves with picosecond pulses exhibit nonlinear absorption/saturable absorption for low/high input intensities, respectively. Saturation intensity thresholds were found to be 15.3 MW/cm² for 4-ns pulse duration and 586 MW/cm² for 65-ps pulse duration.     

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。     

Large optical nonlinearity in CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> thin films

CaCu₃Ti₄O₁₂ (CCTO) thin films were successfully prepared on LaAlO₃ substrates by pulsed laser deposition technique. We measured the nonlinear optical susceptibility of the thin films using Z-scan method at a wavelength of 532 nm with pulse durations of 25 ps and 7 ns. The large values of the third-order nonlinear optical susceptibility, χ ⁽³⁾, of the CCTO film were obtained to be 2.79×10⁻⁸ esu and 3.30×10⁻⁶ esu in picosecond and nanosecond time regimes, respectively, which are among the best results of some representative nonlinear optical materials. The origin of optical nonlinearity of CCTO films was discussed. The results indicate that the CCTO films on LaAlO₃ substrates are promising candidate materials for applications in nonlinear optical devices.     

The effect of concentration on the thermo-optical properties of colloidal silver nanoparticles

The thermo-optical properties of colloidal silver nanoparticles (AgNPs) are investigated under a low power laser irradiation at 532 nm. Colloidal AgNPs are synthesized by nanosecond pulsed laser ablation of a pure silver plate in distilled water. The morphology and size of the AgNPs are determined by transmission electron microscopy. Closed Z-scan measurements reveal that nonlocal thermo-optic process is responsible for the nonlinear refractive index of colloid containing different concentrations of silver nanoparticles. The Z-scan behavior of the nanoparticle samples has been investigated based on a nonlocal thermo-optic process and it is shown that the aberrant thermal lens model is in excellent agreement with the experimental results. Z-scan measurement fits have allowed the values of nonlinear refractive index (n₂) and thermo-optic coefficients (dn/dt) to be determined at different concentrations of silver nanoparticles. Large enhancement factors were measured for values of n₂ and dn/dt of the colloids at higher silver nanoparticle volume fraction. Our results suggest that nonlocal thermal nonlinear processes will play an important role in the development of photonic applications involving metal nanoparticle colloids.     

Pseudo-nonlinear and athermal lensing effects on transverse properties of Cr based solid-state lasers

Several experiments (time-resolved Z-scan experiments based on pulsed and CW pump lasers, time-resolved divergence diagnostics) have been performed to examine and clarify the question of the converging or diverging population lensing effect occurring in a Cr^3 +:Al₂O₃ ruby laser. The dynamics of the laser far-field divergence of such a laser indeed indicated initially a diverging effect while Z-scan measurements conclude to a converging one. The origin of this discrepancy is thus analysed and elucidated here by introducing the general concept of correlation collapse between the centre and the wings of a laser beam having some clipping.