硒化铅量子点聚乙烯醇薄膜的三阶非线性光学特性

通过湿化学方法制备了具有三阶非线性光学性质的硒化铅/聚乙烯醇复合物薄膜.采用透射电镜和扫描电镜对硒化铅量子点的尺寸和薄膜的形貌进行表征.运用Z扫描方法,研究了薄膜在波长为532nm,脉冲宽度为38ps条件下的三阶非线性光学性质.实验结果表明:合成的硒化铅量子点尺寸在10nm左右,属于强量子受限,制备的薄膜表面粗糙度比较好;薄膜在皮秒脉冲激光作用下呈现负的非线性折射效应和反饱和吸收性质,其三阶非线性极化率χ(3)为3.6×10-11 esu.     

生物大分子杂化处理的CdSe/ZnS核/壳量子点多层膜的超快三阶非线性研究

利用静电自组装技术，以生物大分子材料壳聚糖杂化处理具有稳定结构的CdSe/ZnS核/壳量子点，形成复合多层薄膜. 与薄膜的吸收谱线比较，在375nm飞秒激光激发下测量的量子点的光致发光谱存在Stokes位移. 采用Z扫描技术，利用790nm飞秒激光研究了其三阶非线性吸收和折射特性，发现饱和吸收信号来自CdSe/ZnS量子点，而自聚焦的折射信号则部分来自壳聚糖. 测出多层膜的三阶非线性系数分别是β＝6.5×10^-6cm/W，n₂＝1.5×10^-10cm²/W. 关键词： CdSe/ZnS量子点 非线性性能 光致发光谱     

CdSe量子点的线性和非线性光学特性

主要从实验和理论两个方面,探讨了强受限尺寸区域内不同尺寸对CdSe量子点线性和非线性光学性质的影响.用吸收光谱研究了量子点尺寸与吸收峰之间的关系,用皮秒Z扫描技术研究了共振和非共振情况下(激发光波长分别为532和1064nm),尺寸与三阶非线性极化率之间的关系.基于电子能量状态理论和局域场增强理论对量子点进行分析,得到了CdSe不同尺寸的三阶非线性效应,研究了尺寸对量子点非线性光学性质的影响.结果表明,由激发态粒子数布局改变和纳米颗粒增大引起的非线性共振增强效应相当,二者共同作用使得三阶极化率增强20倍左右,且用532nm的共振频率激发4.3nm CdSe量子点时,χ⁽³⁾具有最大值2.0×10^-11esu. 关键词： CdSe量子点 三阶非线性 Z扫描')" href="#">Z扫描 量子限域效应     

CdSeS量子点的光学非线性特性

以脉冲宽度为35 ps,基频为1064 nm的Nd:YAG锁模激光器二倍频532 nm的激光作激发,利用Z-扫描技术研究了CdSeS量子点的光学非线件特性.实验结果表明CdSeS量子点在532 nm光激发下具有很大的非线性吸收效应,该吸收效应来自于光学三阶效应引起的双光子吸收.在不同的入射光强下观测了CdSeS量子点的Z-扫描曲线,实验表明,CdSeS具有大的非线性折射率1.9×10-8esu和大的双光子吸收截面25283 GM,比现在使用的ZnS量子点高出近2个数量级.     

不同激光脉冲宽度下甲苯的光学非线性特性的研究

在不同激光脉冲激发下,用Z 扫描法测量了甲苯的三阶光学非线性,发现其非线性折射率随着脉冲宽度增加而增大（从150 fs时的3.7×10－16 cm2/W到4 ns时的2.6×10－14 cm2/W）.在波长532 nm、光强4.73×1014 W/m2 和21 ps的脉冲作用下,甲苯溶液呈现反饱和吸收现象.结果表明,该吸收效应主要来自于导致该分子中苯环结构π－π电子跃迁的双光子吸收的贡献.     

水溶性CdTe:Mn量子点的双光子吸收

采用激发波长800 nm、脉宽50 fs、重复频率1 kHz的Ti:sapphire放大飞秒激光器作为激发光源,利用开孔Z扫描技术研究了不同粒径的CdTe:Mn量子点的非线性吸收性质。理论计算结果表明,同一生长时间CdTe:Mn量子点的双光子吸收系数是CdTe量子点的1.1倍,其双光子吸收系数随量子点尺寸的减小而增大,这是由于CdTe:Mn量子点非线性吸收属于反饱和吸收,掺杂了Mn元素,减小了表面缺陷浓度,表明掺杂量子点具有很好的双光子吸收现象。     

CuO薄膜的三阶非线性光学特性研究

采用脉冲激光沉积技术在Si(100)和熔石英基片上制备了单相的CuO薄膜.通过X射线衍射仪,拉曼光谱仪,场发射扫描电镜和紫外可见光光度计对薄膜的结构,表面形貌和光学性质进行了表征. 场发射扫描电镜结果表明CuO薄膜中晶粒排列致密且分布均匀,其尺寸约为45nm.结合飞秒激光(800nm,50fs)和Z扫描方法测量了薄膜的三阶非线性光学特性,结果表明CuO薄膜具有超快的非线性光学响应且非线性折射率和非线性吸收系数均为负值,其大小分别为-3.96×10^-17 m^{2< 关键词： CuO薄膜 Z-扫描')" href="#">Z-扫描 三阶光学非线性}     

Au纳米颗粒阵列中双光子吸收的饱和过程

采用纳米球蚀刻法制备了Au纳米颗粒阵列.并通过扫描电子显微镜观测了其表面形貌,表明三角形的Au纳米颗粒呈阵列状分布.采用Z扫描方法(800 nm, 50 fs)测量了Au纳米颗粒阵列的三阶非线性光学特性.在较小的激发功率下,结果呈现出双光子吸收效应,随着激发功率不断增加,出现了双光子吸收饱和的过程;非线性折射则呈现出自散焦效应.这种高效率的非线性响应机理使得该种Au纳米颗粒阵列在高速全光开关中有潜在的应用价值. 关键词： 纳米球蚀刻技术 Au纳米颗粒 三阶光学非线性     

一新型金属有机化合物在皮秒激光下的三阶非线性光学性质研究

利用皮秒激光光源,采用z扫描技术研究了一种新型金属有机化合物的三阶非线性光学性质以及光限幅特性.z扫描研究结果表明,这种化合物在1064 nm波长激光激发下的三阶非线性极化率χ(3)为3.8×１０-14 esu,并且存在双光子吸收.光限幅实验结果显示双光子吸收和非线性折射两种不同机制决定了该化合物的光限幅特性.     

低强度飞秒激光激发下CdTe和CdTe/CdS核壳量子点的荧光上转换研究

利用400 nm和800 nm不同波长的低强度飞秒激光,对CdTe和CdTe/CdS核壳量子点溶胶进行激发,研究其稳态和时间分辨荧光性质.800 nm飞秒激光激发下,CdTe和CdTe/CdS核壳量子点产生上转换发光现象,上转换荧光峰与400 nm激发下的荧光峰相比蓝移最多达15 nm,而且蓝移值与荧光量子产率有关.变功率激发确认激发光功率与上转换荧光强度间满足二次方关系,时间分辨荧光的研究表明荧光动力学曲线服从双e指数衰减.提出表面态辅助的双光子吸收模型是低激发强度上转换发光的主要机理.CdTe和CdT 关键词： CdTe量子点 CdTe/CdS核壳量子点 时间分辨荧光 上转换荧光     

Enhancement of Kerr nonlinearity at long wavelength in a quantum dot nanostructure

The giant Kerr nonlinearity with reduced linear and nonlinear absorption in a four-level quantum dot by employing the tunnel coupling is investigated. It is shown that by enhancement of tunnel coupling value the Kerr nonlinearity increases and at the same time linear and nonlinear absorption reduces at the long wavelength which is very important for communicational applications. Enhanced of Kerr nonlinearity in a double quantum dots is investigated. It is found that the electron tunneling has an essential role to reducing the linear absorption and increasing the Kerr nonlinearity at long wavelength.     

Quantum confinement effects of CdTe nanocrystals sequestered in TiO2 matrix: effect of oxygen incorporation

Thin films of TiO₂ with high volume fraction (40–55%) and crystallite size (6–40 nm) of CdTe nanoparticles had been prepared by rf magnetron sputtering from a composite TiO₂:CdTe target at room temperature and 373 K. A detailed optical properties of nanocrystalline CdTe:TiO₂ films as-deposited and after thermal treatment (300 °C) are studied. The absorbance of the TiO₂ films with CdTe nanocrystallite dispersions depends both on the nanocrystallite size and volume fraction. The blue-shifts of the optical absorption edge concurrent with the CdTe nanocystal size reduction for as-deposited and after thermal treatment of nanocrystalline CdTe:TiO₂ thin films with respect to the bulk semiconductor agrees quite well with the strong quantum confinement theory. A slight deviation in absorption edge values than the predicted values from the strong quantum confinement model can be attributed to change in interplanar distance due to oxygen incorporation and inhomogeneous size distribution of CdTe nanocrystallites in these films.     

边界对石墨烯量子点非线性光学性质的影响

石墨烯作为一种新型非线性光学材料,在光子学领域具有重要的应用前景,引起研究人员的极大兴趣.本文运用量子化学计算方法研究了边界引入碳碳双键(C=C)和掺杂环硼氮烷(B₃N₃)环对石墨烯量子点非线性光学性质和紫外-可见吸收光谱的影响.研究发现,扶手椅边界上引入C=C双键后,六角形石墨烯量子点分子结构对称性降低,电荷分布对称性发生破缺,导致分子二阶非线性光学活性增强.石墨烯量子点在从扶手椅型边界向锯齿型边界过渡的过程中,随着边界C=C双键数目的增加,六角形石墨烯量子点和B3N3掺杂六角形石墨烯量子点的极化率和第二超极化率分别呈线性增加.此外,边界对石墨烯量子点的吸收光谱也有重要影响.无论是石墨烯量子点还是B₃N₃掺杂石墨烯量子点,扶手椅型边界上引入C=C双键导致最高占据分子轨道能级升高,最低未占分子轨道能级的降低,前线分子轨道能级差减小,因而最大吸收波长发生了红移.中心掺杂B₃N₃环后会增大石墨烯量子点的分子前线轨道能级差,导致B3N3掺杂后的石墨烯量子点紫外-可见吸收光谱发生蓝移.本文研究为边界修饰调控石墨烯量子点非线性光学响应提供了一定的理论指导.     

PbTe/CdTe量子点的光学增益

PbTe/CdTe量子点是一类新型异系低维结构材料,实验发现具有强的室温中红外光致发光现象.为研究这一材料体系的发光特性,建立了理论模型,计算了PbTe/CdTe量子点的光学跃迁和增益.模型基于k·p包络波函数方法并考虑了PbTe能带结构的各向异性.分析了量子点光学增益与量子点尺寸、注入载流子浓度的关系.结果表明,当注入载流子浓度在(0.3—3)×10¹⁸cm^-3范围时,尺寸为15—20nm的量子点可以产生 关键词： PbTe/CdTe量子点 光学增益 铅盐矿半导体     

Induced Birefringence in CdSe Quantum Dots in Phosphate Glass Matrix

Optics and Spectroscopy - Light-induced anisotropy (optical Kerr optical) caused by the third-order nonlinear susceptibility χ(3) in a nanocomposite material consisting of CdSe quantum dots in...     

CdTe量子点的光谱特性及其应用

研究了水相CdTe量子点的共振散射光谱、荧光光谱和吸收光谱特性。结果表明,随着量子点粒径(d)的增大,CdTe量子点的荧光峰(λ_F)发生红移,吸收峰也发生红移,且吸收峰(λ_A)的峰形变宽、吸光度(A)降低,λ与ln(d)均存在较好的线性关系。其函数关系为λ_A =126.74 ln(d)+395.92和λ_F=155.01 ln(d) +415.5。共振散射光谱研究表明, 共振散射波长λ_R与CdTe量子点粒径（3.8～8.6 nm）的对数存在较好的线性关系,线性回归方程为λ_R=148.37 ln(d)+418.08, 相关系数为0.995 2,而且同一粒径的CdTe量子点,共振散射强度与CdTe量子点的浓度也存在良好的线性关系,粒径为3.8 nm的CdTe量子点在波长597 nm处的线性范围,回归方程,相关系数分别为：22.5～180.0 μmol·L-1;I_{597 nm}=0.572 1c+5.884,0.997 5。共振散射光谱法作为检测CdTe量子点粒径的一种新方法,具有简便快速及较好的应用价值。     

The third-order optical nonlinearity and upconversion luminescence of CdTe quantum dots under femtosecond laser excitation

The aqueous CdTe quantum dots (QDs) were synthesized by the electrostatic reaction method. The optical properties of CdTe QDs were investigated by femtosecond Z-scan and time-resolved luminescence technique in nonresonant spectral region. The nonlinear absorption and refraction are ascribed to two-photon absorption, and time-resolved upconversion photoluminescence produces biexponential decay pattern at infrared femtosecond laser excitation. Upconversion luminescence is composed of a band-edge excitonic state and a photoinduced trapping state. The short-lived band-edge excitonic emission is independent of the detection wavelengths, and long-lived species becomes even longer with the increase of detection wavelengths, which indicates the size dependence of surface excitonic emission. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Absorption Spectra and Refractive Index Changes of an Exciton in a Core/Shell Quantum Dot

The absorption spectra and the refractive index changes are calculated theoretically for an exciton in a core/shell quantum dot. The advantage of our methodology is that one can investigate the influence of the repulsive core by varying two parameters in the confinement potential. The dimensionality effect of exciton quantum dots on the optical absorptions has been studied. It has been found that in the same regime, the optical absorption intensities of excitons are much smaller for the core/shell quantum dots than for the two-dimensional quantum rings. The linear and the nonlinear optical absorption coefficients and refractive index changes have been examined with the change of the confinement potential. The results show that the optical absorptions and the refractive index changes are strongly affected by the repulsive core of core/shell quantum dots. Moreover, the calculated results also reveal that as the inner radius increases, the peak values of the absorption coefficients and the refractive index changes of an exciton will show the optical Aharonov–Bohm oscillation in core/shell quantum dots.     

Defects related emission and nanosecond optical power limiting in CuS quantum dots

We report optical and nonlinear optical properties of CuS quantum dots and nanoparticles prepared through a nontoxic, green, one-pot synthesis method. The presence of surface states and defects in the quantum dots are evident from the luminescent behavior and enhanced nonlinear optical properties measured using the open aperture Z-scan, employing 5 ns laser pulses at 532 nm. The quantum dots exhibit large effective third order nonlinear optical coefficients with a relatively lower optical limiting threshold of 2.3 J cm⁻², and the optical nonlinearity arises largely from absorption saturation and excited state absorption. Results suggest that these materials are potential candidates for designing efficient optical limiters with applications in laser safety devices.