Light emitted from a liquid that flows in a narrow channel as triboluminescence

The flow of a liquid through a narrow channel under a high pressure (on the order of tens of atmospheres) can be accompanied by emission of light, which has been termed hydroluminescence. We have shown that this light emission takes place both from the gas and from the liquid phase, with each type of emission being characterized by its own radiation spectrum. The spectra of hydroluminescence are similar to the spectra of photoluminescence obtained upon UV irradiation of a liquid under study. Therefore, the hydroluminescence of a liquid is not a light emission of a specific type; the flow through the narrow channel is only one of the ways of excitation of the light emission, which, in this case, is caused by friction. In other words, hydrodynamic luminescence can be referred to a wider class of phenomena—triboluminescence.     

Two-color ionization of hydrogen by short intense pulses

Photoelectron energy spectra resulting by the interaction of hydrogen with two short pulses having carrier frequencies, respectively, in the range of the infrared and XUV regions have been calculated. The effects of the pulse duration and timing of the X-ray pulse on the photoelectron energy spectra are discussed. Analysis of the spectra obtained for very long pulses show that certain features may be explained in terms of quantum interferences in the time domain. It is found that, depending on the duration of the X-ray pulse, ripples in the energy spectra separated by the infrared photon energy may appear. Moreover, the temporal shape of the low frequency radiation field may be inferred by the breadth of the photoelectron energy spectra.     

Energy and emission characteristics of superlattice quantum-cascade structures

Energy levels, wave functions, and matrix elements of optical dipole transitions have been numerically calculated for superlattice quantum-cascade structures. An expression for the gain has been obtained with regard to the complete set of energy levels in different models of spectral-line broadening. A universal relation between the gain and emission spectra for unipolar laser structures has been proposed. The effect of spectral broadening on the shape of emission spectra is estimated. The electroluminescence spectra are compared with the calculated spontaneous recombination spectra and good agreement between the results is shown.     

Renormalization of the energy spectrum of quantum dots under vibrational resonance conditions: Persistent hole burning spectroscopy

A theory of photophysical burning of spectral holes in an inhomogeneously broadened light absorption profile of spherical quantum dots under vibrational resonance conditions is developed. The energy spectrum and the eigenfunctions of polaron-like excitations that arise in a quantum dot when the energy of an optical phonon is close to the energy gap between some pair of levels of the quantum dot electron subsystem are found by the method of canonical transformations. Expressions describing the difference light absorption spectra of quantum dots in the regimes of strong and weak confinement are obtained within a simple kinetic model.     

High resolution X-ray spherically bent crystal spectrometer for laser-produced plasma diagnostics

A new high spectral resolution crystal spectrometer is designed to measure very low emissive X-ray spectra of laser-produced plasma in 0.5-0.9 nm range. A large open aperture （30 ×20 （mm）） mica （002） spherically bent crystal with curvature radius R = 380 mm is used as dispersive and focusing element. The imaging plate is employed to obtain high spectral resolution with effective area of 30 × 80 （mm）. The long designed path of the X-ray spectrometer beam is 980 mm from the source to the detector via the crystal. Experiment is carried out at a 20-J laser facility. X-ray spectra in an absolute intensity scale is obtained from Al laserproduced plasmas created by laser energy of 6.78 J. Samples of spectra obtained with spectral resolution of up to E/△E - 1500 are presented. The results clearly show that the device is good to diagnose laser high-density plasmas.     

水体细菌微生物多波长透射光谱特征分析研究

多波长透射光谱能够反映出样品细胞大小、形状、内部结构和化学组分等丰富而独特的信息,是微生物快速、实时、在线检测与识别的有利工具。将多波长透射光谱技术应用于水体致病性细菌微生物的快速有效检测对控制水体细菌微生物污染及保护饮用水源水质安全具有重要的现实意义。为了建立及发展基于多波长透射光谱技术的水体致病性细菌微生物快速有效的检测方法,采用紫外-可见分光光度计获取了多种水体致病性细菌微生物(如： 肺炎克雷伯氏菌、鼠伤寒沙门氏菌、金黄色葡萄球菌和大肠杆菌)在200～900 nm波段的多波长透射光谱,对比分析了不同细菌及同种细菌在不同浓度时的多波长透射光谱特征。结果表明： 对于同种细菌,当细菌浓度发生变化时,400～900 nm波段透射光谱形状较为一致,并且在400,450,500和550 nm波长处的光密度值与浓度具有很好的线性关系,该波段由细菌体的散射起主要作用;但在200～400 nm波段范围内,细菌透射光谱的形状随细菌浓度的变化而变化,在200,258,300和350 nm波长处的光密度值与细菌浓度分别具有很好的二次多项式关系。根据微粒的Mie散射理论,采用Levenberg-Marquardt非线性最小二乘方法对测得的四种细菌透射光谱进行了散射光谱和吸收光谱拟合,并对比分析了不同细菌散射光谱特征和吸收光谱特征,结果表明： 四种细菌散射光谱的特征峰均在245 nm波长处,但该波长处的光密度值具有明显差异性,这与不同细菌外部结构及内部结构细胞器的大小、形状等不同有关;而四种细菌吸收光谱特征峰均在260 nm波长处,且不同细菌在240～400 nm波段内吸收光谱也具有明显差异性,这与不同细菌细胞内的核酸、蛋白质等化学组分含量不同有关。该研究表明对于不同种细菌及具有不同浓度的同种细菌,测得的多波长透射光谱及计算出的散射光谱和吸收光谱特征都具有明显的不同,通过多波长透射光谱解析可以获得细菌多种特征参数,多波长透射光谱可以被用于快速有效检测水体中的致病性细菌微生物。该研究为发展水体细菌微生物快速在线监测仪提供了重要依据。     

调控空间非均匀啁啾场获得孤立阿秒脉冲

通过调节二阶啁啾参数和空间非均匀效应对高次谐波光谱进行了优化.结果表明：在长脉宽负向啁啾和负向非均匀效应组合下,谐波光谱截止能量和强度得到最佳增大,并获得X射线范围内的光谱连续区.最后,通过叠加光谱连续区上的部分谐波可获得一个脉宽仅为23 as的孤立脉冲.     

Z箍缩诊断中椭圆晶体谱仪测量数据的处理

以氖气喷气Z箍缩的实验结果为例,详细讨论了椭圆晶体谱仪测量数据的处理方法,包括使用标定结果将胶片黑密度转换为X光强度,根据已知谱线的能量和扫描点序号对测量能谱的能点进行定标,以及使用Henke给出的考虑谱仪非均匀色散效应、晶体积分反射率和X光滤片透过率后的公式对测量能谱的强度进行修正,给出了最终的解谱结果。并使用Lorentz线型函数拟合谱线轮廓,求出了Hα,Heα和Heβ等K壳层谱线的相对强度,对处理后能谱强度的误差进行了简单分析。     

Silicon nanoclusters formed through self-assembly on CaF2 substrates: morphology and optical properties

We studied the influence of the size and shape of silicon nanoclusters on their optical response. For this purpose, clusters were prepared by deposition, and subsequent diffusion and nucleation, of Si atoms on CaF₂ substrate surfaces. By varying the growth parameters, oblate aggregates with sizes of between 5 and 30 nm and axial ratios between almost unity and 0.1 were generated. We found that the substrate temperature during growth predominantly influences the diameter and number density of the particles, whereas the coverage and deposition rate determine the axial ratio. Optical extinction was measured in the photon energy range between 1.0-6.0 eV and compared to model calculations. The mean size of the Si clusters mainly determines the absolute magnitude of the optical extinction. In contrast, the axial ratio drastically affects the overall structure of the spectra and the relative importance of three identified maxima. The most essential and interesting reason for the pronounced influence of the particle shape on the optical properties is a shift of the valence band plasmon in the silicon nanoparticles from an energy of above 9.0 eV for spherical clusters into the ultraviolet spectral range to about 5 eV for axial ratios below 0.3.     

Band-reject-filtering X-ray spectra by mosaic structures of pyrolytic graphite

The possibility of effective band-reject filtration of intense spectral lines in X-ray spectra and the creation of deep spectral valleys in the continuous spectrum by diffraction extinction was shown. Optimum material for band-reject filters in the energy range E > 6 keV is highly oriented pyrolytic graphite (HOPG). The filtering scheme in the form of an echelon arrangement of HOPG films is proposed, which suppresses the negative effect of multiple reflections due to diffraction extinction. The full width at half minimum of the spectral valleys can vary from tens of electronvolt to several kiloelectron volt depending on the HOPG mosaic spread, HOPG filters arrangement, and rejected energy region. At the energy range E of ~10 keV, the spectral density attenuation value may be of order 10⁻³ and lower. The obtained results can be used in various fields of X-ray spectrometry, as well as in static energy dispersive diffractometry and reflectometry.     

Characterization of attosecond XUV pulses from photoelectron spectra of atoms

A method to characterize attosecond extreme ultra violet (XUV) pulses from photoelectron spectra of atoms is presented. A pump pulse prepares a coherent superposition of two atomic bound states, from which photoionization takes place after variable time delays by the attosecond XUV pulse. Information on the spectral phase of the attosecond XUV pulse is extracted from the analysis of photoelectron spectra as a function of photoelectron energy and time delay. Together with information on the spectral intensity obtained from a separate optical measurement, a temporal shape of the attosecond XUV pulse can be precisely reconstructed. After the theoretical formulation of the problem, we present numerical examples for H atom and show that, depending on the choice of energy separation of two bound states, a different accuracy is reached to characterize attosecond XUV pulses.     

Specific features of the magneto-optical properties of α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> in the IR region

The spectra of reflection and magnetoreflection of light from the crystalline insulator α-Al₂O₃ in the IR spectral region (λ = 2.5–25 μm) are investigated. Some features in the magnetoreflection spectra in the wavelength range corresponding to the excitation of optical phonon modes in α-Al₂O₃ are found. A significant increase in magnetoreflection is observed near these wavelengths. The amplitude and shape of the magnetore-flection spectra for the p and s polarizations of probe light are determined. It is shown that the optical and magneto-optical properties of α-Al₂O₃ in the IR region can be described on the basis of the theory of polaron excitation. A satisfactory correlation between the theoretical and experimental spectra is obtained, which indicates that polarons play an important role in determining the optical characteristics of nonmagnetic insulators and make the dominant contribution to the magnetoreflection spectra.     

Determination of SWCNT diameters from the Raman response of the radial breathing mode

We report on the evaluation of the distribution of diameters for nanotube samples with a wide variation of mean diameters. Such results were obtained from a detailed analysis of the radial breathing mode Raman response and compared to results obtained from an evaluation of optical spectra and X-ray diffraction pattern. The evaluation of the Raman data needs a well refined analysis as the experimental analysis exhibits a rather complicated and oscillating relation between response and exciting laser. Both, an exact calculation where the density of states was considered explicitly and an approximate calculation were applied. Both models used for the analysis are able to explain several unexpected results from the experiment such as the oscillating behavior of the spectral moments, unusual discontinuities in the first moments of the Raman response for excitation in the IR, a fine structure for the response in optics and Raman, and an up shift of the RBM frequency as compared to qualified ab initio calculations. In detail the first moment and the variance of the spectra were used for the evaluation of the diameter distribution. To obtain good results between experimental and theoretical oscillation pattern the transition energy between the first two van Hove singularities had to be scaled up which is considered as a result from coulomb interaction of the electrons in the tubular material. On the other hand the analysis does not only allow to determine the mean value and the width of the diameter distribution but yields also a value for the average bundle diameters or, alternatively, the strength of the tube-tube interaction. The model used for the analysis of the Raman data is also appropriate to analyze the optical response, at least for the spectral range from 0.5 eV to 3.5 eV. The fine structure in the response for the transitions between the three lowest van Hove singularities is well reproduced and the mean tube diameters and their distribution is obtained in very good agreement with the results from the Raman analysis. From the X-ray analysis the same mean values and comparable distributions for the tube diameters were received whereas the bundle diameters could not be retained with high precision in this case. Received 18 February 2001 and Received in final form 3 April 2001     

Simple method for estimating shape functions of optical spectra

A simple method for estimating shape functions of optical spectra is proposed, based on the numerical correlation with an assumed optical spectrum composed of a central main rectangular component and two right-angled triangular wings on either side of the main component. The degrees of correlation between observed and assumed spectra were examined using spectral and coherence widths of those spectra and pulsewidths of Fourier-transform-limited pulses calculated from those spectra. By using this method, shape functions of output spectra from superluminescent diodes and a self-pulsating laser diode were evaluated in detail over a relatively wide injection current range beyond their rated currents.     

铝合金焊前激光清洗的等离子体光谱在线检测

铝合金焊接技术在工业生产、制造和维修等领域有广泛的应用,焊缝内存在气孔导致焊接质量降低是铝合金焊接技术的常见问题。由于铝合金表面金属氧化物是导致气孔生成的主要来源,对激光清洗过程进行在线检测,不但可以实时分析表面氧化物的清洗状态,而且可以避免基体表面因为过度清洗造成损伤或二次氧化。提出采用激光诱导等离子体光谱(LIBS)在线检测铝合金焊前激光清洗过程,表征清洗后铝合金基体的表面状态。LIBS技术可以对多元素成分同时检测,拥有较低的检出限和较高的准确性。搭建基于Andor Mechelle 5000光谱仪的铝合金焊前激光清洗在线检测系统,剔除空气环境对实验结果的影响,测试6061铝合金表面氧化物和铝合金基体的LIBS光谱,分析两者独特的元素特征谱线,采用X射线能谱(EDS)测试结果验证元素特征谱线的准确性,并探讨激光清洗过程LIBS技术在线检测的可行性。实验测试等离子体光谱谱线强度与激光能量密度之间的关系,获得单次脉冲激光去除铝合金表面氧化物的损伤阈值,结合X射线能谱的检测结果研究激光损伤阈值的成因及影响。研究激光清洗过程等离子体光谱特征谱线与脉冲次数之间的关系,提出基于O/Al特征谱线强度比值作为在线检测清洗效果及二次氧化损伤的评判依据。为验证该评判依据的准确性,将O/Al特征谱线强度比值随清洗次数的变化趋势与X射线能谱测试获得的氧元素原子百分比变化趋势进行对比。实验结果表明:采用200~700 nm范围内激光诱导等离子体谱线特征分析激光清洗状态,可以剔除空气环境的影响;氧元素和铝元素特征谱线准确反映出表面氧化膜与铝合金基体的成分差异;X射线能谱检测元素成分和含量表明氧元素含量随着激光清洗能量密度先减后增,单次清洗铝合金的二次氧化损伤的激光能量阈值为11.46 J·cm-2,小于损伤阈值的激光能量密度对铝合金基体的多次清洗未造成损伤,等离子体光谱特征谱线强度与表面清洗状态相关, 656.5 nm(OⅡ)/396.2 nm(AlⅠ)谱线强度比值≤1.5%为激光清洗干净的依据。研究结果有利于铝合金的激光清洗实时控制技术和焊接装置集成化。     

Generation of doublet spectral lines at self-seeded X-ray FELs

Self-seeding schemes, consisting of two undulators with a monochromator in between, aim to reduce the bandwidth of SASE X-ray FELs. We recently proposed to use a new method of monochromatization exploiting a single crystal in Bragg transmission geometry for self-seeding in the hard X-ray range. The obvious and technically possible extension is to use such kind of monochromator setup with two (or more) crystals arranged in a series to spectrally filter the SASE radiation at two (or more) closely-spaced wavelengths within the FEL gain band. This allows for the production of doublet (or multiplet) spectral lines. Exploitations of such mode of operation involve any situation where there is a large change in cross-section over a narrow wavelength range. In this paper we consider the simultaneous operation of the LCLS hard X-ray FEL at two closely spaced wavelengths. We present simulation results for the LCLS baseline, and we show that this method can produce fully coherent radiation shared between two longitudinal modes. Mode spacing can be easily tuned within the FEL gain band, i.e. within 10 eV. An interesting aspect of the proposed scheme is a way of modulating the electron bunch at optical frequencies without a seed quantum laser. In fact, the XFEL output intensity contains an oscillating “mode-beat” component whose frequency is related to the frequency difference between the pair of longitudinal modes considered. Thus, at saturation one obtains FEL-induced modulations of energy loss and energy spread in the electron bunch at optical frequency. These modulations can be converted into density modulation at the same optical frequency with the help of a weak chicane installed behind the baseline undulator. Powerful coherent radiation can then be generated with the help of an optical transition radiation (OTR) station, which have important applications. In this paper we briefly consider how the doublet structure of the XFEL generation spectra can be monitored by an optical spectrometer. Furthermore, the OTR coherent radiation pulse is naturally synchronized with the X-ray pulses, and can be used for timing the XFEL to high power conventional lasers with femtosecond accuracy for pump-probe applications.     

Light emission from Ag cluster films excited by conduction current

The light emission spectra obtained for a silver cluster film, excited by the passage of electrical current through it, were measured by the charge‐coupled device (CCD) combined with a monochromator in the spectral range 200 ≑ 1050 nm (6.2 ≑ 1.18 eV). This film is a two‐dimensional ensemble of Ag clusters linked by tunneling on a dielectric substrate. It was shown that the light emission spectra had a number of features, and the shape of spectrum depends on a voltage applied to the film. With increasing the voltage the spectrum starts to extend to high energies. The light emission in the visible spectral region was observed already at 1 V applied to the film, i.e., the photon energy can exceed the excitation energy. It means that this phenomenon is not trivial. In order to explain these results, an assumption about the electron gas heating in metal clusters may be used.     

Broadband spectral attenuation measurements on optical fibres: an interlaboratory comparison by members of COST 208

Comparative loss measurements on optical fibres are being performed by members of COST 208, and in this paper some preliminary results are reported. Full spectral attenuation measurements have been made, covering the range from 700 to 1800 nm, on graded-index and single-mode fibres. In the multimode fibre the measured loss depends on the energy distribution launched into the fibre. By ensuring similar energy distributions the deviations between loss spectra have been maintained to within about ± 5%. In single-mode fibre the launched power is very small so the transmitted intensity was closer to the noise limit of the detector. Differences between loss spectra amounted to about ± 8% in the low-loss ranges.     

三五阶非线性下啁啾超高斯脉冲的啁啾和频谱

利用三五阶非线性效应下的扩展非线性薛定谔方程,在忽略光纤色散的情况下,计算模拟了以二阶情形为例的啁啾超高斯光脉冲的啁啾和频谱。结果表明,脉冲无预啁啾时,正五阶非线性增大啁啾量,负五阶非线性在减小啁啾量的同时还改变啁啾曲线的形状。当预啁啾与五阶非线性系数同(异)号时,总啁啾增加(减小)。随着超高斯脉冲阶次的增大,总啁啾量增大,脉冲中心附近无啁啾的范围变宽,整个有啁啾的范围变小,总啁啾中预啁啾所占比重增大。脉冲无预啁啾时,正负五阶非线性分别可以增大和减小频谱展宽。预啁啾若增强非线性所致啁啾,则可能使频谱峰值结构加强,谱峰数目增多。当超高斯光脉冲的阶次或最大非线性相移增大时,在某些宽大的频谱峰上还可能出现许多精细谱峰。     

Centrality dependence of charged-hadron transverse-momentum spectra in d+Au collisions at sqrt[s(NN)]=200 GeV

We have measured transverse momentum distributions of charged hadrons produced in d+Au collisions at sqrt[s(NN)]=200 GeV. The spectra were obtained for transverse momenta 0.25相似文献