Nonlinear optical behaviours in a silver nanoparticle array at different wavelengths

The optical nonlinearities of an Ag nanoparticle array are investigated by performing the Z-scan measurements at the selected wavelengths (400, 600, 650, and 800 nm). The nonlinear refraction index in the resonant region (around 400 nm) exhibits a significant enhancement by two orders compared with that in the off-resonant region (around 800 nm)), and exhibits an sign alternation of the resonant nonlinear absorption, which results in a negligible nonlinear absorption at a certain excitation intensity. Moreover, a low degree of nonlinear absorption was measured at the edges of the resonant region (600 and 650 nm), which is attributed to the competition of the saturated absorption and the two-photon absorption processes.     

Two-photon cross-section measurement of meso-tetra-hydroxyphenyl-chlorin using femtosecond laser pulses

Experiments were carried out using the femtosecond laser to compare the fluorescence amplitude produced by two-photon excitation at 800 nm and 400 nm (i.e. to the strong absorption band in mTHPC). Using an experimental arrangement where the fluorescence sampling geometry was kept unchanged between the two exposure wavelengths a value for the two-photon cross-section of mTHPC at 800 nm of ?1.8 × 10^?57 m⁴ s/molecule/photon was derived. This is larger than the value estimated using a simple theoretical model, probably because the calculation neglects ??resonant?? assistance provided by the real state at ??650 nm (S ₀). In terms of order of magnitude the values are in agreement with the two-photon cross-section for other organic species.     

绿黄色磷灰石热处理紫外可见光谱研究

绿蓝色磷灰石因其颜色和"帕拉伊巴"绿蓝色碧玺相似而为消费者所熟知。为了验证此种磷灰石颜色是否经过人工处理,将不同颜色的磷灰石样品分别置于空气气氛下进行400~800℃的热处理。结果表明绿黄色磷灰石经过650℃的热处理就可产生绿蓝色。根据热处理过程中样品的X射线粉末衍射数据,在热处理过程中并未发生相变。为了进一步研究热处理过程中样品颜色的变化行为和实验参数对热处理效果的影响,将绿黄色磷灰石样品分别置于空气和还原气氛下进行300~800℃的对比热处理实验。结果显示不同气氛下样品颜色的变化行为十分相似。因此这也表明绿黄色磷灰石颜色的改变和元素价态的变化没有直接关联。室温下样品的紫外可见吸收光谱(200~800 nm)主要表现在蓝紫区强烈吸收,红橙区有一宽缓的吸收带(620~720 nm),黄绿区透过,出现了515, 528, 578, 739和747 nm等一系列吸收峰。随着热处理温度的升高,样品在可见光范围内的吸收系数大幅降低颜色变浅,吸收截止边逐渐蓝移导致样品逐渐呈现蓝色。与此同时,随着温度升高至400℃, 620~720 nm吸收带中最强吸收峰位置会发生蓝移导致样品的黄色调减弱。当温度达到800℃时,样品褪色, 620~720 nm吸收带消失,但515, 528, 578, 739和747 nm等一系列吸收峰仍然存在。因此绿黄色磷灰石在热处理过程中颜色的变化主要和吸收截止边以及620~720 nm吸收带的变化有关。     

γ辐照对掺Er硅酸盐玻璃吸收和发光特性的影响

用传统的高温熔融法熔制了一系列掺Er硅酸盐玻璃, 并测试了这些样品经5 kGy γ 射线辐照前后紫外至近红外的吸收和荧光光谱. 实验结果表明, 辐致暗化效应使得玻璃材料中形成了大量色心, 导致在400 nm附近出现强吸收带, 其尾端延伸至近红外区. 辐照产生的新能带增加了基质与Er³⁺ 特定能级(如²H_11/2, ⁴S_3/2及⁴F_9/2等) 之间的能量传递, 从而使辐照后的样品荧光寿命减小, 且在相同激发条件下荧光强度下降. 室温下辐照样品在荧光测试过程中出现了漂白现象.     

热处理棕褐色电气石光谱学特征与颜色成因初探

电气石属三方晶系的硼铝硅酸盐,主要有铁电气石、锂电气石、镁电气石、钠-锰电气石等品种,因含不同的过渡元素或色心而呈绿、蓝、黄、红、粉、棕和黑色。选取棕褐色电气石样品在还原和中性气氛加热3 h,结果显示,600 ℃晶体出现大量裂隙;500和450 ℃棕褐色调减弱,透明度大大提升,500 ℃裂隙稍多;350 ℃加热,样品变绿黄棕色;250 ℃加热样品略微变浅,仍为棕褐色调;加热后∥c轴切面见明显绿色与棕色二色性,垂直c轴切面,即{0001}面,为棕色;综合显示,最佳变色温度在450~500 ℃。利用X射线荧光光谱(XRF)、红外吸收光谱(IR)和紫外-可见光吸收光谱(UV-Vis)对热处理前后样品进行分析,样品属于富Mn和Fe的锂电气石。样品中红外特征吸收峰在3 800~3 400,1 350~1 250,1 200~800与800 cm-1,近红外光谱有4 720,4 597,4 537,4 441,4 343,4 203和4 170 cm-1特征峰。热处理后,由M-OH(M为Al,Mg,Fe和Mn等)伸缩和弯曲振动所致的3 800~3 400 cm-1吸收峰减弱,600 ℃消失,与加热失水行为导致的结构水弯曲/伸缩振动减弱有关;近红外光谱4 170和4 720 cm-1吸收消失。棕褐色电气石在∥c轴切面的可见光范围内具有715,540和417 nm吸收带,依次为Fe2+ d-d(5T_2g→5E_g)跃迁、Fe2+→Fe3+(IVCT)、Fe2+→Ti4+(IVCT)所致。样品具有高的Mn含量,417 nm附近的吸收可能存在Mn2+ d-d (6A_1g→4A_1g, 4T_Eg)自旋禁阻跃迁产生的413/414 nm叠加。热处理使Mn3+还原成Mn2+,Mn2+增加导致414 nm吸收峰增强,因此417 nm附近吸收带变化不大。同时,热处理后与Mn3+有关的520 nm吸收也同时消失,520 nm吸收带的存在也可能是540 nm吸收带呈非对称吸收峰的原因。450 ℃以上热处理后,715和417 nm吸收带变化不大,位于绿光区的540 nm吸收带消失,分析认为加热使得部分Fe3+还原为Fe2+,导致Fe2+→Fe3+(IVCT)减少,在∥c轴切面上540 nm吸收显著减弱。540 nm吸收带在绿色光区域,其消失导致绿色光透过,样品呈绿色。     

Doping transition metal ions as a method for enhancement of ablation rate in femtosecond laser irradiation of silicate glass

We present a doping method to improve the femtosecond laser ablation rate and promote ablation selectivity. Doping transition metal ions, Co2＋ or Cu2＋, in silicate glass apparently change absorption spectroscopy and induce resonant absorption at wavelengths of 600 and 800 nm, respectively. Comparing with femtosecond laser processing of the same glass without doping, we find that the threshold fiuenee decreases and the ablation rate increases in resonant absorption in doped silicate glass. Resonant absorption effectively increases multiphoton ionization for seed-free electron generation, which in turn enhances avalanche ionization.     

Optical absorption properties of Ge-Sb-Te films

The optical properties of monolayer Ge2Sb2Te5 thin films with three different thicknesses prepared by dc magnetron sputtering method at the range of 400 - 800 nm were studied. The optical absorption coefficients and the optical energy gap (Eg) were calculated. The results gave values for the absorption coefficients in the range of (1.3 - 7.5) × 105 cm-1 which were in the high absorption wavelength region of 400 - 800 nm. The optical energy gaps were 0.684, 0.753 and 0.810 eV corresponding the films thicknesses of 57, 88 and 127 nm, respectively, showing the characteristic of increasing with the increase of the film thickness.     

Ge2Sb2Te5薄膜光学性能和短波长静态记录特性的研究

利用直流磁控溅射制备了单层Ge₂Sb₂Te₅薄膜,研究了薄膜在400～800 nm区域的反射、透过光谱,计算了它的吸收系数,发现薄膜在400～800 nm波长范围内具有较强的吸收.随着薄膜厚度的增加,相应的禁带宽度Eg也随之增加.对Ge2Sb2Te5薄膜光存储记录特性的研究发现,在514.5 nm波长激光辐照样品时,薄膜具有良好的写入对比度,擦除前后的反射率对比度在6%~18%范围内.对实验结果进行了分析.     

Optimization of locally resonant acoustic metamaterials on underwater sound absorption characteristics

The study of acoustic metamaterials, also known as locally resonant sonic materials, has recently focused on the topic of underwater sound absorption. The high absorption occurs only within a narrow frequency band around the locally resonant frequency. Nevertheless, this problem can be addressed through a combination of several acoustic metamaterial layers that have different resonant frequencies. In this paper, an optimization scheme, a genetic and a general nonlinear constrained algorithm, is utilized to enhance the low-frequency underwater sound absorption of an acoustic metamaterial slab with several layers. Both the physical and structural parameters of the acoustic metamaterial slab are optimized to enlarge the absorption band. In addition, the sound absorption mechanism of the acoustic metamaterial slab is also analyzed. The result shows that each layer is found to oscillate as a nearly independent unit at its corresponding resonant frequency. The theoretical and experimental results both demonstrate that the optimized metamaterial slab can achieve a broadband (800–2500 Hz) absorption of underwater sound, which is a helpful guidance on the design of anechoic coatings.     

Anomalous wavelength dependent effects in photoacoustic measurements of Nd3+ luminescence quantum efficiency in various laser materials

Values for the luminescence quantum efficiency of Nd³⁺ in phosphate glass, silicate glass and YAG have been obtained from measurement of the photoacoustic and optical absorption spectra. For the phosphate glass a quantum efficiency value of 0.31 ±0.10 was obtained for excitation in the wavelength range 350–750 nm, silicate glass gave a value of 0.72 ±0.10 for the range 350–600 nm. In both cases, anomalously high photoacoustic signals were obtained in the IR, around 800 nm, suggesting lower quantum efficiencies in this region. YAG gave a value of 0.95 ±0.10 for the excitation range 450–800 nm with smaller than expected PA signals in the UV (355 and 334 nm bands) suggesting the existence of an alternative decay mechanism following excitation in this region.     

Correlation between surface oxide and photoluminescence properties of Si nanoparticles prepared by pulsed laser ablation

Hydrogenated silicon nanoparticles were prepared by pulsed laser ablation (PLA) of Si target in hydrogen gas. We observed native oxidation process for 250 days by infrared (IR) absorption measurement and investigated correlation between native oxidation and photoluminescence (PL) properties. We found three PL peak regions, around 800 nm, 600–700 nm and 400–500 nm. These PL peak wavelengths depended on the Si-O bond density and remarkable correlation with composition of the oxide layer was not observed. The native oxidation is a passive method to modify the surface. We propose plasma surface treatment as an active method. The PL wavelength varied by the surface treatments due to suppression of native oxidation. The surface modification is an important technique to control PL peak wavelength of silicon nanoparticles. PACS 81.15.Fg; 81.07.Bc; 78.67.-n     

离子液体辅助N,S,F共掺杂纳米TiO2的制备与表征

以TiCl4、硫脲和离子液体([C6mim]+[BF4]-)为原料,采用微波催化水解法合成掺杂的纳米TiO2前驱体,在NH3/N2气氛中经程序升温煅烧处理制得N,S,F共掺杂TiO2光催化剂(N—S—F—TiO2)。采用X射线粉末衍射(XRD)、X射线光电子能谱(XPS)、紫外-可见漫反射光谱(UV-Vis/DRS)等对该光催化剂的结构和性能进行表征。结果表明,该光催化剂为锐钛矿晶型,具有较高的纯度和结晶度,掺杂在TiO2晶体中形成Ti—O—N键,Ti—O—S键,Ti—S键,而F以TiOF2形态掺杂。在可见光区400～550nm具有强吸收,且在600～800nm出现一个较强的吸收带。实验表明,使用[C6mim]+[BF4]-与H2O的体积比为5/95所制得的光催化剂对甲基橙降解的催化活性最高,可见光照射200min降解率达95%。多掺杂的协同效应使得N—S—F—TiO2具有对可见光的强烈吸收和较高的可见光催化活性。     

Investigation of optical nonlinearities in Pd(po)2 by Z-scan technique

With nanosecond scale at a 532 nm wavelength, we firstly measured the nonlinear optical absorption and refraction coefficients of Pd(po)₂ complex by using Z-scan technique, here Hpo=1-hydioxy-2-pyridone. We describe an empirical expression for the case when nonlinear refraction is accompanied by nonlinear absorption to separately evaluate the nonlinear refraction and the nonlinear absorption by performing straightforward measurements with the aperture removed. The nonlinear optical response of Pd(po)₂ was determined by the linear decreasing irradiance-dependence. The nonlinear absorption originates from the near resonant two-photon absorption while the mechanism of the nonlinear refraction is the near resonant two-photon absorption transition enhancement. The linear increasing dependences of the optical nonlinearities on the incident irradiance arise from the population redistribution due to the near resonant two-photon absorption.     

Electronic structure and optical properties of CdWO4 with oxygen vacancy studied from first principles

The electronic structures, dielectric functions and absorption coefficient of both perfect CdWO₄ crystal (CWO) and the CWO crystal containing oxygen vacancy (CWO: V _O) have been studied using the CASTEP code with the lattice structure optimized. The calculated total density of states (TDOS) of CWO: V _O indicates that the oxygen vacancy would introduce a new electronic state within the band gap compared with that of perfect CWO. The dielectric functions are calculated since the imaginary part of the dielectric function can reduce the optical absorption of a certain crystal, and then the absorption coefficient is calculated. The calculated absorption spectra show that CWO: V _O exhibits two absorption bands in the ultraviolet and visible region, peaking at about 3.0 eV (413 nm) and 3.5 eV (354 nm), respectively, which are in agreement with the experimental results showing that the yellow CWO has two optical absorption bands in this region peaking at around 350 nm and 400 nm respectively. It can be concluded that oxygen vacancy causes these two absorption bands. The calculations also indicate that the optical properties of CWO exhibit anisotropy, and can be explained by the anisotropy of the crystal lattice.     

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     

“爱迪生”珍珠及染色处理有核珍珠的谱学特征

颗粒大、圆度高并具有浓郁颜色的淡水有核养殖珍珠（商贸名称为“爱迪生”珍珠）为珍珠市场提供了更高的品质与价值,然而受利益的驱使,染色的有核养殖珍珠也逐渐流入市场,扰乱了消费者的健康消费,在一定程度上阻碍了“爱迪生”珍珠产业的良性发展。本文利用红外光谱仪、紫外-可见分光光度计和光致发光光谱仪对养殖和染色“爱迪生”珍珠进行了系统的谱学研究,并将其与海水珍珠、染色海水珍珠进行了比较。结果表明：（1）染色与养殖“爱迪生”珍珠在红外光谱上均显示1 445,882和725 cm-1处的文石振动峰,其中染色“爱迪生”珍珠在3 800 cm-1处均出现宽缓的弱吸收峰;（2）染色“爱迪生”珍珠的紫外可见光光谱中280 nm处的吸收峰明显弱于养殖“爱迪生”珍珠,染色后的“爱迪生”珍珠整体反射率降低,可能与染剂使珍珠中的蛋白质分子受损有关。染黄色“爱迪生”珍珠缺失养殖橙黄色“爱迪生”珍珠在360～380 nm处的吸收峰,而与染色海水金珠430 nm处的强吸收峰相似。染黑色“爱迪生”珍珠在425 nm处有吸收峰,染色海水黑珍珠在480和645 nm处有吸收峰,养殖海水黑珍珠在702 nm处有吸收峰,三者图谱的差异可能为各自的染料不同所致;（3）养殖“爱迪生”珍珠在光致发光光谱中450～550 nm范围内可见一组吸收峰,染色“爱迪生”珍珠的发光中心向红区偏移且在650 nm附近出现强度不等的与染色剂相关的吸收峰,染色海水金珠也在600 nm处有和染色剂有关的吸收峰。     

积雪与气溶胶粒子混合的光谱反照率模拟研究

积雪中的黑碳气溶胶粒子会导致积雪光谱反射率显著下降,进而引起的气候辐射变化会推迟或提前积雪融化时间,严重影响了干旱区地表径流特征、区域水循环过程,由此引起的干旱区生态水文问题也越来越受到关注。2018年1月在新疆北疆地区开展积雪中气溶胶粒子观测实验,借助ASD地物光谱仪、Snow Folk积雪特性仪与HR-1024外场分光辐射度计等仪器获取原始积雪光谱数据与其他积雪参数,应用Snow,Ice,and Aerosol Radiation model(SNICAR)模型模拟了不同雪粒径下、不同太阳天顶角、不同Black Carbon(BC)浓度下的积雪光谱反照率变化状况,讨论了BC、雪粒径在不同光谱范围内敏感性,结果表明:太阳天顶角对雪面光谱反照率的影响在近红外波段比其他波段表现得更明显,在积雪光谱曲线中太阳天顶角从0°变化到80°,可见光波段600 nm处光谱反照率升高了0.045,近红外波段1000,1200和1300 nm处光谱反照率分别升高了0.16,0.225和0.249;在天顶角为60°时,雪粒径从100μm增大到800μm,对应的光谱反照率减少量最大可达到0.15,且100~300μm范围内的雪粒径比400~800μm范围内的引起光谱反照率的下降量明显增大,雪粒径的增大能使吸光性颗粒物的光吸收效应增强;随着BC浓度的增加,积雪反照率会显著下降,且不同浓度的BC对积雪的反照率的差值不同,随着BC浓度的增加,反照率的差值量越来越小。不同的BC浓度在近红外波段对光谱反照率影响较小,影响较大的范围主要集中可见光波段,在光谱800和1100 nm处,5μg·g-1的BC浓度使光谱反照率减小了0.13和0.04,5μg·g-1的BC可使350与550 nm处的光谱反照率减小0.25与0.23;比较不同粒径下,BC浓度对积雪光谱宽波段反照率的减少情况可发现,在BC存在的情况下,雪粒径的增加会增大BC的光吸收效应,且浓度越高,吸收增加的越多;从光谱指数角度表明BC在可见光波段350~740 nm比较敏感,相关系数较高;雪粒径在近红外波段1100~1500 nm比较敏感,尤其在1000与1300 nm左右,BC与雪粒径在积雪光谱曲线中的敏感波段相关性都较高,R 2高达0.9以上;最后将模型模拟的积雪反照率与实测数据进行验证对比,R 2为0.738,模拟效果较好,可为干旱区积雪光谱反照率的研究奠定数据基础。     

玻璃中CdSeS纳米晶体的室温光致发光谱

对掺有过饱和的镉、硒和少量硫的玻璃在500～800℃分别退火4h,生长了不同尺寸的CdSe_1-xS_x纳米晶体。测量了纳米晶体的室温吸收光谱和光致发光(PL)光谱,550℃生长的样品在300～800nm的范围没有观察到吸收和发光峰,表明温度低于550℃玻璃中不能形成纳米晶体。生长温度在600～650℃,纳米晶体的PL光谱主要为两个宽的发光带,即带边激子发光带和通过表面态复合的发光带。随着生长温度的升高,带边复合发光的蓝移减小,通过表面态的发光逐渐消失,并出现了叠加于宽发光带上的一系列明显的弱发射峰。不同温度生长的样品中,叠加峰的能量相同。同一样品中叠加峰的能量不随激发光波长的变化而变化。     

便携式近红外光谱仪对涤/棉混纺织物的快速无损鉴别

利用便携式近红外光谱仪对376个涤/棉混纺织物进行研究,利用定量分析模型中的偏最小二乘法(partical least squares,PLS)作为校正方法,结合涤/棉混纺织物中涤、棉含量设定的定性鉴别系数,建立了涤/棉混纺织物的半定量-定性分析校正模型。该模型对涤/棉混纺织物进行定性鉴别的同时得出其相对含量,分析结果具有半定量性质。在建模过程中,采用Savitzky-Golay导数法,消除噪声和基线漂移对光谱的影响,并研究了波段选择和不同预处理方法对定性校正模型的影响。纯棉的主要吸收峰位于1 400~1 600 nm,纯涤的主要吸收峰位于1 600~1 800 nm,随着涤或棉含量的增加,其相应的吸收峰强度增强,因此,建模波段以涤、棉主要吸收峰区间为基本波段,进行双向扩展,得到最佳波长区间1 100~2 500 nm(相关系数0.6,波点数934)。利用所建校正模型对验证集样本进行预测,结果表明,在1 100~2 500 nm处,预处理方法为Savitzky-Golay导数、多元散射校正与均值中心化相结合时,该模型评价参数较佳,其中RC(校正集相关系数)0.978,RP(验证集相关系数)0.940,SEC(校正标准差)1.264,SEP(预测标准差)1.590,样品预测正确率达93.4%。表明该定性分析校正模型能够较好地对涤/棉混纺织物进行半定量-定性预测。     

Modeling and identification on nonlinear saturable and reverse-saturable absorptions of gold nanorods using femtosecond Z-scan technique

An improved Z-scan analysis approach is proposed by establishing and solving the saturable absorption (SA) and reverse-SA (RSA) models, respectively. Near-infrared femtosecond Z-scans are carried out on the synthesized gold nanorods (NRs) possessing the average length of 46 nm using a femtosecond laser operated at the wavelength of 800 nm, which is close to the peak position of longitudinal surface plasmon resonance (SPR) (710 nm) of gold NRs. At lower input intensity of less than 400 GW/cm2 , the normalized transmission exhibits only SA phenomenon; however, when it exceeds 400 GW/cm2 , both SA and RSA are observed. By using the presented Z-scan modeling and theory, the three-photon absorption (3PA) is identified in the material, and the 3PA cross-section is determined to be 1.58×1071 cm6s2 .