Investigation of third-order nonlinear optical properties of two azo-nickel chelate compounds

This paper investigates the third-order nonlinear optical properties of two azo-nickel chelate compounds by the optical Kerr gate method at 830 nm wavelength with pulse duration of 120 fs. Both of the two compounds exhibited large third-order optical nonlinearity. The second-order hyperpolarizability,γ, of Compound 1 is of 1.0 × 10^-31 esu. Due to the charge transfer, the γ of Compound 2 with electron donor and acceptor group is 4.9 × 10^-31 esu, which is a four-time enhancement in comparison with Compound i. The absorption spectra show that the electron push-pull effect, which induces intramolecular charge transfer, leads to the increased optical nonlinearity.     

蒽二酮类化合物的合成及结构-非线性光学性能关系的研究

设计合成了6个新的蒽二酮类化合物,用紫外可见吸收光谱、傅里叶变换红外光谱、1H 核磁共振和元素分析表征了结构.采用飞秒激光,运用简并四波混频法,研究了化合物在非共振状态下的三阶非线性光学性能.它们的三阶非线性光学极化率χ(3)为2.62～3.55×10－13 esu,非线性折射率n2为4.82～6.52×10－12 esu,分子二阶超极化率γ为2.57～3.25×10－31 esu,响应时间τ为91～116 fs.探索了化合物的分子结构对三阶非线性光学性能的影响.增长共轭链,形成供吸供构型,增大取代基的供电子能力,提高共轭体系的共平面程度等因素有利于获得较大的三阶非线性光学性能.     

Enhancement of second-order optical nonlinearity in photo-darkened Ge25Sb10S65 chalcogenide glass by femtosecond laser light

The second-order optical nonlinearity of poled Ge₂₅Sb₁₀S₆₅ chalcogenide glass was found to be 40-50% larger after femtosecond laser irradiation. The highest χ⁽²⁾ was 11.4 pm/V. Raman spectral change indicated that centrosymmetric defects were created by fs light. These defects promoted the third-order optical nonlinearity of the glass and as a result, its second-order nonlinearity was also enhanced. The study shows that fs laser modification is an effective method of increasing the optical nonlinearity of photonic materials.     

聚芳香杂环甲烯的三阶非线性光学效应与时间分辨光克尔效应

合成了一系列聚芳香杂环甲烯,包括聚吡咯甲烯和聚噻吩甲烯.采用四波混频法研究材料的共振三阶非线性光学效应(λ＝532nm),其共振二阶超分子极化率γ三阶非线性光学系数分别达到10^-30esu和10^-8esu.选择具有良好溶解性、成膜性的聚吡咯对二甲氨基苯甲烯(PPDMAB),采用飞秒时间分辨光克尔效应方法研究材料的非共振三阶非线性光学效应(λ=790nm).实验表明,翠绿亚胺碱溶液的光克尔信号仅表现一超快响应的成分,归功于π电子云扭转产生的非共振激发.PPDMAB的非共振二阶超分子极化率γ三阶非线性光学系数分别达到γ=5.78×10^-32esu和χ⁽³⁾=1.26×10^-10esu.     

DR1掺杂复合凝胶玻璃光学二阶非线性效应的研究

对分散红1(disperse red 1,缩写为DR1)掺杂聚甲基丙烯酸甲酯(PMMA)/凝胶玻璃复合材料的光学二阶非线性及其热稳定性进行了研究.分析了实时极化二次谐波产生(SHG)的动态过程及影响光学二阶非线性的因素.同时对影响DR1掺杂复合凝胶玻璃材料的光学二阶非线性强度的因素进行了分析. 关键词：     

束缚电荷对玻璃材料二阶光学非线性的影响

对电场极化后薄膜材料与体材料二阶光学非线性的比较研究表明,二者具有相同的极化和弛豫特性．分析了束缚电荷的形成及其对二阶光学非线性的影响,定性地从理论上指出,由束缚电荷产生的电场对薄膜及体材料的极化和弛豫过程起了决定作用． 关键词： 二阶非线性 玻璃 极化 束缚电荷     

Three-dimensional second-harmonic generation imaging with femtosecond laser pulses

A three-dimensional reflectance scanning optical microscope based on the nonlinear optical phenomenon of second-harmonic generation is presented. A mode-locked Ti:sapphire laser producing <90-fs pulses at ~790nm was used, and the images were constructed by scanning of an object, which possessed local second-order nonlinearity, relative to a focused spot from the laser. The second-harmonic light at ~395nm generated by the specimen was separated from the fundamental beam by use of dichroic and interference filters and was detected by a photodiode. The technique was then used to characterize the distribution of second-order nonlinearity and microstructure of the nonlinear material lithium triborate.     

Interaction of two light beams with different polarizations in TGS

By ellipsometric measurements we have observed the polarization variations of the primary light beam, with wavelength λ₁=5145 ?, interacting with the secondary light beam of controlled variable polarization, transmitted through a TGS crystal layer. We present a theoretical explanation based on the second-order optical nonlinearity of TGS. Received: 4 December 2001 / Revised version: 28 May 2002 / Published online: 25 October 2002 RID="*" ID="*"Corresponding author. Fax: +48-22/660-5447, E-mail: petyk@if.pw.edu.pl     

Photophysical properties of a crown ether-bearing [60]fulleropyrrolidine

The photophysical properties of the first crown ether-bearing [60]fulleropyrrolidine (CFP) have been studied. The absorption and fluorescence spectra are hypsochromically shifted by metal ions complexation via intramolecular electron transfer which is confirmed by AMI computation. The third-order optical nonlinearity of CFP is measured by time-resolved degenerate four-wave-mixing experiment. The third-order optical susceptibility χ⁽³⁾ of CFP is 8.97×10⁻¹⁴ esu. The nonlinear optical temporal response is second-order exponential, the fast process is determined as 120 ps. Received: 24 March 1999 / Revised version: 11 May 1999 / Published online: 25 August 1999     

Postcompensation for nonlinearity of Mach-Zehnder modulator in radio-over-fiber system based on second-order optical sideband processing

A postcompensation technique for nonlinearity of a Mach-Zehnder modulator in a radio-over-fiber (ROF) system is proposed and experimentally demonstrated based on second-order optical sideband processing and optical carrier band attenuation. The phase of the second-order optical sideband is shifted to suppress the third-order intermodulation distortion (IMD3) in a direct detection ROF link. The optical carrier band is attenuated to make two kinds of origins of IMD3 have equal intensity and cancel each other out. A spurious-free dynamic range of 124.8 dB·Hz(2/3) is achieved, which is about 25 dB more than that without compensation.     

Spatial temporal wave mixing for space time conversion

A nonlinear optical processor that is capable of true real-time conversion of spatial-domain images to ultrafast time-domain optical waveforms is presented. The method is based on four-wave mixing between the optical waves of spectrally decomposed ultrashort pulses and spatially Fourier-transformed quasi-monochromatic images. To achieve efficient wave mixing at a femtosecond rate we utilize a cascaded second-order nonlinearity arrangement in a beta-barium borate crystal with type II phase matching. We use this ultrafast technique to experimentally generate several complex-amplitude temporal waveforms, with efficiency as high as 10%, by virtue of the cascaded nonlinearity arrangement.     

Large optical second-order nonlinearity of poled WO3-TeO2 glass

Second-harmonic generation, one of the second-order nonlinear optical properties of thermally and electrically poled WO>(3)-TeO>(2) glasses, has been examined. We poled glass samples with two thicknesses (0.60 and 0.86 mm) at various temperatures to explore the effects of external electric field strength and poling temperature on second-order nonlinearity. The dependence of second-harmonic intensity on the poling temperature is maximum at a specific poling temperature. A second-order nonlinear susceptibility of 2.1 pm/V was attained for the 0.60-mm-thick glass poled at 250 degrees C. This value is fairly large compared with those for poled silica and tellurite glasses reported thus far. We speculate that the large third-order nonlinear susceptibility of WO>(3)- TeO>(2) glasses gives rise to the large second-order nonlinearity by means of a X((2)) = 3X((3)) E(dc) process.     

Enhancement of the second harmonic generation from monolayer WS2 coupled with a silica microsphere

Monolayer transition metal dichalcogenides (TMDs) are widely used for integrated optical and photoelectric devices. Owing to their broken inversion symmetry, monolayer TMDs have a large second-order optical nonlinearity. However, the optical second-order nonlinear conversion efficiency of monolayer TMDs is still limited by the interaction length. In this work, we theoretically study the second harmonic generation (SHG) from monolayer tungsten sulfide (WS₂) enhanced by a silica microsphere cavity. By tuning the position, size, and crystal orientation of the material, second-order nonlinear coupling can occur between the fundamental pump mode and different second harmonic cavity modes, and we obtain an optimal SHG conversion efficiency with orders of magnitude enhancement. Our work demonstrates that the microsphere cavity can significantly enhance SHG from monolayer 2D materials under flexible conditions.     

Towards integrated semiconductor optical parametric oscillators

Microelectronic grade semiconductors display excellent figure of merits for second-order optical nonlinearity effects. However, most of them are not birefringent and cannot be properly phase-matched for efficient optical frequency conversion. This paper describes the different phase-matching scenarios which are currently developed in different laboratories to solve this problem. If successful, this field of research will open the way to future complete integrated optical parametric oscillators.     

高阶色散和指数饱和非线性光纤的调制不稳定性

采用线性稳定性分析法,解析和计算了指数饱和非线性和高阶色散光纤中的调制不稳定条件和增益谱。结果表明:当二阶和四阶色散同为负时,随着参数的不同,增益谱可能只有一个谱区,也可能出现两个分离的谱区;当二阶和四阶色散分别为正和负时,无调制不稳定性;在其它色散区,则只有一个谱区。指数饱和非线性可能使各谱区的谱宽、峰值增益随入纤功率的增大呈现出先增大后减小的特点,即出现两个不同的输入功率对应同一个不稳定增益峰值和谱宽的情形。在其它参数相同时,指数饱和非线性下增益谱的谱宽和峰值增益随入纤功率的变化速度将比传统饱和非线性更快。     

Simultaneous process of embossing and poling at elevated temperatures: a simple technique for nonlinear grating formation in polymer films

A simple technique for fabrication of nonlinear gratings in polymer films, based on simultaneous embossing and poling, is proposed and demonstrated. A master grating consisting of a metal electrode with a dielectric die was fabricated and used for repeated embossing of the grating structures into nonlinear optical polymers at elevated temperatures. At the same time, we applied high voltage to the polymer films to induce second-order nonlinearity. The grating profile and the nonlinearity were estimated, as well as the mass productivity of nonlinear gratings.     

Redox and photoisomerisation switching the second-order nonlinear optical properties of a tetrathiafulvalene derivative across ten stable states: a DFT study

A molecular switch having large contrast on the second-order nonlinear optical (NLO) properties has been studied based on tetrathiafulvalene (TTF)-π-polynitrofluorene (PTF) molecule. It can afford to switch second-order NLO response across 10 stable states by an effective combination of its photoisomerisation and redox properties. According to density functional theory (DFT) finite field calculations (BHandHLYP/CAM-B3LYP/LC-BLYP/6-31g(d)), the redox-active TTF, TCNQ (7,7′,8,8′-tetracyano-p-quinodimethane) units, and a photoisomerised chromophore (thiophene derivative of perfluorocyclopentene) act as the tuning centre to switch second-order NLO responses. Meanwhile, time-dependent DFT method has been employed to calculate excited-state nature for getting more insights of the second-order NLO responses.     

交叉克尔非线性对二阶非线性诱导透明的影响

考虑耦合介质存在交叉克尔非线性的情形下,研究了交叉克尔效应对耦合双谐振腔中二阶非线性诱导透明的影响.首先给出了描述体系理论模型的哈密顿量,再通过对海森堡-朗之万方程进行线性化,得到了探测场的透射率,进而得出系统的吸收和色散关系.研究结果表明,在交叉克尔非线性强度较小时,可忽略其对诱导透明的影响;随着交叉克尔非线性强度的增大,诱导透明窗口宽度随之快速变窄.此外,吸收曲线中还出现了双吸收峰.进一步增强交叉克尔非线性,导致原本出现的诱导透明消失,并在新吸收峰处产生了新的诱导透明,新的诱导透明的吸收零点位置随着交叉克尔非线性增加而向左偏移.这些结果可能在不透明介质的窄窗口光传输和提高光学腔的性能方面提供一些参考.     

噻二唑衍生物的三阶非线性光学性能与合成

设计合成了7个新的噻二唑衍生物,用UV、IR1、H NMR和元素分析进行了表征。采用飞秒激光,运用简并四波混频法,研究了衍生物在非共振状态下的三阶非线性光学性能。它们的三阶非线性光学极化率χ(3)为3.75~4.18×10-13esu,非线性折射率n2为6.90~7.68×10-12esu,分子二阶超极化率γ为3.75~4.26×10-31esu,响应时间为101~115 fs。探索了衍生物的分子结构对三阶非线性光学性能的影响。引入离域能小的芳杂环,增长共轭链,形成吸供构型,增大取代基的供电子能力,提高共轭体系的共平面程度等因素有利于获得较大的三阶非线性光学性能。     

Transient sum-frequency mixing with temporally tailored laser pulses

We discuss the possibility of using temporally tailored pump laser pulses to control the temporal width and shape of optical pulses generated in a process of transient sum-frequency mixing in crystals with second-order nonlinearity. Specific calculations performed in a model crystal in the case of fifth-harmonic generation are presented.