Z-scan分析CdS纳米晶掺杂玻璃的光学非线性

利用溶胶-凝胶方法合成了CdS纳米晶掺杂Na2O-B2O3-SiO2玻璃。通过透射电镜(TEM)以及附带的扫描模式透射(STEM),X射线能量散射谱(EDX)和高分辨透射电镜(HRTEM)分析CdS颗粒的形貌、微结构以及组成。结果显示,在钠硼硅玻璃先驱体中生成了CdS纳米晶,其晶相结构为六方相结构,颗粒尺寸在10～20 nm。此外,利用Z-scan技术在波长为770 nm研究该玻璃的三阶非线性光学性质。结果表明:该玻璃的三阶光学非线性折射率γ,三阶非线性吸收系数β以及三阶非线性磁化率χ(3)分别为-2.16×10-16 m2W-1,6.32×10-11 mW-1和7.32×10-10 esu,优于此前一些关于CdS纳米晶掺杂在不同基体中所得到的三阶非线性光学性质的结果。

Z-scan的理论及技术研究进展

本文在介绍传统Z scan的基础上介绍双色光Z scan(TwocolorZ scan)、双光束时间分辨率Z scan(Time resolvedZ scan)、遮挡Z scan(EclipsingZ scan)、反射Z scan(ReflectionZ scan)等改进的Z扫描技术。分析了各种Z scan技术的特点及应用。综述了Z扫描理论与技术的发展。

用Z-scan法研究推拉型偶氮化合物的非线性光学性质

利用Z－scan法，对掺有以偶氮苯作为母体的一个系列推拉型偶氮化合物的有机聚合物薄膜的非线性光学系数进行了测量，实验结果的分析表明，材料的非线性折射率来源于共轭π电子效应．

用双色Z-SCAN法研究热效应的弛豫过程

用双色Z－SCAN法研究了热效应的弛豫过程，首次给出了为得到最大的测量灵敏度所满足的泵浦光束和参考光束的几何条件．在实验上对偶氮染料有机物热弛豫时间进行了测量。

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2×10-3cm/W,三阶非线性折射系数为8.0×10-8cm2/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。

用Z-scan法研究非线性介质中的热效应

从热传导方程出发，研究了脉冲激光作用下因样品线性和非线性吸收引起热效应而产生的折射率变化．从理论分析得出，当仅存在线性吸收时，非线性折射率的概念在通常情况下并不适合于由热效应产生的非线性，但在所用的激光脉冲很短的情况下，类似于其它非线性的各种效应，对热效应也可定义时间平均非线性折射率，并可用Z－scan法对这两类吸收感生的不同非线性折射率进行测量．所得结论符合实验结果．

Z─scan方法测量介质非线性折射的研究

本文用衍射理论研究了薄介质情况下的Ｚ—ｓｃａｎ法，分析了通常所用Ｚ—ｓｃａｎ法的适用范围，研究结果对在实际测量中如何使用Ｚ—ｓｃａｎ法具有一定的指导意义，另外对介质中五阶非线性效应较强情况下及介质存在饱和非线性折射率情况下的Ｚ—ｓｃａｎ法进行了研究，给出了非线性折射率及其它非线性光学系数的测量方法。

Z-scan的基础理论及技术回顾(英文)

由Sheik-Bahae于1989年提出的Z-scan技术已经成为在非线性光学和材料科学领域里的一项非常有用的测量方法,它能简单而灵敏地测量非线性光折射率和吸收率。本文概要地讨论了Z-scan技术并介绍了它的最新进展,其中着重讨论了高斯分解法对此项技术的理论研究。

基于LabVIEW与MATLAB混合编程的Z-Scan测量系统设计

针对Z扫描实验系统数据量大、稳定性要求高以及数据处理的实际需要,设计了一种基于LabVIEW和MATLAB混合编程的全自动激光Z-scan测量系统,用以表征样品非线性光学特性。运用LabVIEW2012开发平台,实现对实验系统测量的全自动控制,通过在LabVIEW环境中的MATLAB Script节点直接调用MATLAB数值分析程序,实现对实验数据的自动拟合,从而直接得到非线性光学系数。通过标准样品CS2的定标测试,测得三阶非线性折射率系数与已报道数据相符,且测量过程迅速。实验表明,该系统利用LabVIEW和MATLAB软件的优势互补,简化了繁琐的手动操作,成功实现了Z-scan系统的自动测量和数据处理的整合,提高了测量的准确性和效率。

飞秒Z—scan法测量有机溶液的双光子吸收截面

按照单光束Z—scan法，利用飞秒激光脉冲对Rb甲醇溶液进行了测量研究，详细研究了光强大小对实验结果的影响，通过对样品池和溶剂进行Z扫描，排除了样品池和溶剂发生非线性吸收带来的误差，利用薄样品理论对测量数据进行计算处理，所得结果与其他方法测得的结果相吻合，证明了此实验方法对有机溶液的测量和处理方法的合理性和有效性．

用Z—Scan法高精度测量非线性折射率

介绍了一种简单而灵敏的单光束测量非线性折射率ｎ２大小和符号的实验方法（Ｚ—Ｓｃａｎ）。样品在聚焦的高斯光束ｚ方向上移动，得到远场通过小孔后的透射率曲线，由该曲线很容易计算出ｎ２。使用ＣＷＣＯ２激光器对ＩｎＳｂ样品进行测量，得到该样品相对１０．６μｍ波长的非线性折射率为１．８０×１０－４ｅｓｕ。

Role of the aperture in Z-scan experiments: A parametric study

In close-aperture Z-scan experiments, a small aperture is conventionally located in the far-field thereby enabling the detection of slight changes in the laser beam profile due to the Kerr-lensing effect. In this work, by numerically solving the Fresnel-Kirchhoff diffraction integrals, the amount of transmitted power through apertures has been evaluated and a parametric study on the role of the various parameters that can influence this transmitted power has been done. In order to perform a comprehensive analysis, we have used a nonlinear phase shift optimized for nonlocal nonlinear media in our calculations. Our results show that apertures will result in the formation of symmetrical fluctuations on the wings of Z-scan transmittance curves. It is further shown that the appearance of these fluctuations can be ascribed to the natural diffraction of the Gaussian beam as it propagates up to the aperture plane. Our calculations reveal that the nonlocal parameter variations can shift the position of fluctuations along the optical axis, whereas their magnitude depends on the largeness of the induced nonlinear phase shift. It is concluded that since the mentioned fluctuations are produced by the natural diffraction of the Gaussian beam itself, one must take care not to mistakenly interpret them as noise and should not expect to eliminate them from experimental Z-scan transmittance curves by using apertures with different sizes.

Nonlinear optical properties in double-sided nonlinear media with Z-scan technique based on the Huygens-Fresnel principle

We present a theoretical model to analyse the propagation of a Gaussian laser beam through double-sided nonlinear media. This model is based on the Huygens-Fresnel diffraction integral method. This theoretical model is not only consistent with the cascade structure model for a small nonlinear phase-shift but also can be used for a large nonlinear phase-shift. It has been verified that it is suitable to characterize the double-sided nonlinear media compared with the cascade structure model. A good agreement between the experimental data and the results from the theoretical model is obtained. It will be useful for the design of multi-sided nonlinear materials.

Nonlinear optical properties of [（CH3）4N]Au（dmit）2 using Z-scan technique

The third-order optical nonlinearities of [（CH3）4N]Au（dmit）2 （dmit = 4,5-dithiolate-1,3-dithiole-2-thione） at 532 nm and 1064 nm are investigated using the Z-scan technique with pulses of picoseconds duration. The Z-scan spectra reveal a strong nonlinear absorption （reverse saturable absorption） and a negative nonlinear refraction at 532 nm. No nonlinear absorption is observed at 1064 nm. The molecular second-order hyperpolarizability γ for the [（CH3）4N]Au（dmit）2 molecule at 532nm is estimated to be as high as （2.1 ±0.1） × 10^-31 esu, which is nearly three times larger than that at 1064 nm. The mechanism responsible for the difference between the results is analysed. Nonlinear transmission measurements suggest that this material has potential applications in optical limiting.

Ultrafast Nonlinear Optical and Optical Limiting Properties of Phthalocyanine Thin Films Studied Using Z-Scan

We have investigated the nonlinear optical properties, optical limiting thresholds, and figures of merits for five different phthalocyanine thin films, achieved through doping in PMMA polymer, using the Z-scan technique at 800 nm with 2 ps laser pulse excitation. From the open-aperture Z-scan data we derived that these molecules exhibit strong two photon absorption (2PA) with the nonlinear coefficients in the range of 15 - 200 cm/GW. We have also estimated the sign and magnitude of real part of third order nonlinearity through the closed aperture data. Preliminary femtosecond pump-probe data suggests that the lifetimes of excited states are in the sub-100 ps regime for all the molecules in film form. Our studies provide concrete evidence that these phthalocyanines are prospective candidates for multi-photon imaging and optical limiting applications.

Z-scan analysis of high-order nonlinear refraction effect induced by using elliptic Gaussian beam

The irradiance of an elliptic Gaussian beam that is high enough to excite high-order nonlinear refraction effect is used to calculate the normalized on-axis transmittance function in the z-scan technique by introducing complex beam parameters which make the calculation simpler. The transmittance formula is applied to the first-, first two-, and first three-order nonlinearities. Numerical evaluation shows that the symmetry no longer holds when using an elliptic Gaussian beam instead of a circular Gaussian beam. A distortion is observed in the central part of the curve, which decreases as ellipticity increases. Moreover, the variation of the normalized peak-valley difference decreases as ellipticity decreases.

Theory of Z-scan technique using Gaussian-Bessel beams with a phase object

This paper reports the theoretical study of combining Z-scan technique with Gauss-Bessel （GB） beams beside a phase object （PO） to measure the third-order nonlinear susceptibility components. By using this method, the sign of refractive index which depends on the shape of the close aperture Z-scan curve can be easily determined. Meanwhile, the magnitude of nonlinear coefficients can also be deduced by theoretical fit. The proposed method is advantageous for high sensitivity and imposes a lower stress in the cases of fragile materials, since small pulse energy is enough for the measurement of nonlinear coefficients. Predictions of the models are compared with Gaussian Z-scan measurement and GB Z-scan measurement. By using GB beams with a PO, the sensitivity of Z-scan measurements is found to be a factor of over 60 times greater than for Gaussian beams and 2 times greater than for Gaussian-Bessel beams.

Nonlinear optical characterization of phosphate glasses based on ZnO using the Z-scan technique

The nonlinear optical properties of a phosphate vitreous system [（ZnO）x-（MgO）30-x-（P2O5）70], where x=8, 10, 15, 18, and 20 mol% synthesized through the melt-quenching technique have been investigated by using the Z-scan technique. In the experiment, a continuous-wave laser with a wavelength of 405 nm was utilized to determine the sign and value of the nonlinear refractive （NLR） index and the absorption coefficient with closed and opened apertures of the Z-scan setup. The NLR index was found to increase with the ZnO concentration in the glass samples by an order of 10-10 cm2·W-1. The real and imaginary parts of the third-order nonlinear susceptibility were calculated by referring to the NLR index （n2） and absorption coefficient （β） of the samples. The value of the third-order nonlinear susceptibility was presented by nonlinear refractive or absorptive behavior of phosphate glasses for proper utilization in nonlinear optical devices. Based on the measurement, the positive sign of the NLR index shows a self-focusing phenomenon. The figures of merit for each sample were calculated to judge the potential of phosphate glasses for application in optical switching.

Z-Scan technique: To measure the total protein and albumin in blood

Z-scan technique is an effective tool for measuring the optical nonlinearity of the materials. By using this technique the measurement was made for total protein and albumin. The nonlinear refractive index of the total protein and albumin were found to vary linearly with concentration. Hence by calculating the nonlinear refractive index it is possible to measure their concentration in the sample. The values measured thus are found in equivalence with conventional colorimetric method.

Nonlinear Coefficient Determination of Au/Pd Bimetallic Nanoparticles Using Z-Scan

In this paper we present the nonlinear optical characterization of Au/Pd nanoparticles in order to obtain the nonlinear refractive indices using the Z-scan technique. The experiments were performed using a 514 nm laser beam Ar+, with 14 Hz of modulation frequency, as excitation source. By using a lens the excitation beam was focused to a small spot and the sample was moved across the focal region along the z-axis by a motorized translation stage. Seven samples with different concentration ratio of Au/Pd nanoparticles were prepared by simultaneous reduction of gold and palladium ions in presence of poly (N-vinyl-2-pirrolidone) (PVP) using ethanol as a reducing agent. In this work, we report the application of the Z-scan technique, to generate optical transmission of laser light as a function of the z position for solutions containing bimetallic nanoparticles of Au (core)/Pd (shell) with average sizes ranging from 3 to 5 nm. The magnitude of the obtained nonlinear refractive index was in the order of 10?8 cm2/W. Our results show that the nonlinear refractive index has a nonlinear behavior when the (Au/Pd) ratio was increased.