Engineered Second Harmonic Generation in Photonic‐Crystal Slabs Consisting of Centrosymmetric Materials

Second harmonic generation (SHG) based on a quadrupole effect in photonic‐crystal slabs (PCSs) consisting of centrosymmetric materials is presented. The results show that SHG occurs when the pump mode with an asymmetric electromagnetic field distribution is coupled with the eigenmode of the PCS. Theoretical and experimental studies also show that the phase match condition can be achieved without resorting to birefringence or a quasi‐phase‐match condition when two conditions coincide: the fundamental mode and the second harmonic mode are the eigenmodes of the PCS, and they can be excited simultaneously by tuning the dispersion curves so that they cross by changing the thickness of the waveguide layer. The concept of the asymmetry of the electromagnetic field spatial mode can be used in a microcavity to obtain harmonic generation.     

Optically Tunable Nonlinearities in Polymers Based on Photoisomerizable Metal‐Based Coordination Complexes

The bottom‐up design of polymer films exhibiting quadratic nonlinear optical properties that can be tuned optically and chemically is described. The polymer matrices are doped with metal‐containing chromophores built around a Zn^II core and photoisomerizable ligands with two different geometries. These molecules possess specifically designed photophysical and nonlinear optical properties to be used towards all‐optical poling, an interference process between one‐ and two‐photon excitations that locally induces macroscopic second‐order effects in polymer films. It is shown that grafting the molecules onto the polymer chains improves the stability of the macroscopic photoinduced nonlinearity in the films.     

铒镱共掺光纤二次谐波的产生

报道了一种在光纤中激发二次谐波振荡(SHG)的简单方法：利用紫外脉冲激光在载氢后的高浓度铒、镱共掺的光纤上刻制布拉格光栅。从而打破了石英光纤二阶极化率为零的固有限制，形成了极大的永久的二阶极化率，周期性的结构辅助实现了相位的匹配。在实验中，利用波长为980nm的半导体激光器(LD)抽运该光纤光栅，在只有几毫瓦的抽运功率下，便观察到了显著的蓝绿光辐射，而且强度随抽运功率的增加而增加。在显微镜下对光纤光栅发光现象进行了观测并拍摄了数码相片，在相片中观测到光纤光栅纤芯处的蓝绿光辐射，而非光栅区没有发光现象，同时观测到了紫外光辐射。     

二次谐波细胞成像的研究进展

由于二次谐波(Second harmonic generation, SHG)技术具有探测深度深,对生物体的损伤小,时间空间分辨率高以及对结构的对称性敏感等特性,SHG成像成为近年来生物成像领域的研究热点.介绍了SHG成像技术的原理及其在细胞成像中的应用,重点介绍了基于染料标记的成像技术,特别是利用电压敏感染料,手性材料和金属纳米粒子作为标记的几种SHG细胞成像技术,最后展望了该技术在生物成像领域的应用前景.     

Directed Growth and Electrical‐ Transport Properties of Carbon Nanotube Architectures on Indium Tin Oxide Films on Silicon‐Based Substrates

Growing aligned carbon nanotubes (CNTs) on electrically conducting and/or optically transparent materials is potentially useful for accessing CNT properties through electrical and optical stimuli. Here, we report a new approach to growing aligned bundles of multiwalled CNTs on a porous back contact of optically transparent and electrically conducting indium tin oxide (ITO) films on silicon and silica substrates without the use of a predeposited catalyst. CNTs grow from a xylene/ferrocene mixture, which traverses through the pores in the thin ITO film, and decomposes on an interfacial silica layer formed via the reaction between ITO and the Si substrate. The CNTs inherit the topography of the silica substrate, enabling back‐contact formation for CNTs grown in any predetermined orientation. These features can be harnessed to form CNT contacts with other substrate materials which, upon reduction by Si, results in a conducting interfacial layer. The ITO‐contacted CNTs exhibit thermally activated ohmic behavior across a 100 ± 10 meV barrier at electric fields below ～ 100 V cm^–1 due to carrier transport through the outermost shells of the CNTs. At higher electric fields, we observe superlinear behavior due to carrier tunneling and transport through the inner graphene shells. Our findings open up new possibilities for integrating CNTs with Si‐based device technologies.     

基于级联倍频+差频效应的宽带波长转换过程

利用阶梯分段准相位匹配结构实现了基于级联倍频+差频效应的单通/双通宽带波长转换.对于固定的晶体长度,通过增加阶梯段数并合理设计准相位匹配结构参数,可以同时获得高转换效率、大转换带宽和高平坦性.当晶体长度为3 cm时,在保证平坦度低于0.2 dB的前提下,单通构型波长转换器的转换带宽和最大转换效率可分别达到177 nm和-9.94 dB,而双通构型的分别为170 nm和-4.15 dB.最后对基于阶梯分段准相位匹配结构的波长转换器与基于正弦啁啾光学超晶格和分段光栅结构的波长转换器的特性进行了对比分析,结果显示阶梯分段结构具有良好的综合特性.     

周期极化钽酸锂晶体腔内倍频实验研究

报道了基于准相位匹配(QPM)应用的周期性极化钽酸锂(PPSLT)晶体进行腔内倍频非线性光学变换实验研究.分析比对了不同长度(3.5 mm,5 mm,10 mm)晶体倍频过程.利用3.5 mm PPSLT晶体在2500 mW808 nm激光抽运下产生1445 mW 1064 nm基频光输出,经过倍频可以得到760 mW的绿光输出.同时对于制约倍频效果和效率提高的系统温度控制等问题进行了分析.