Decelerated molecular beams for high-resolution spectroscopy

Ultimately, the resolution of any spectroscopic experiment is limited by the interaction time between the particles that are to be examined and the measuring device. The obtainable spectroscopic resolution in a molecular beam experiment can be considerably improved using samples of slow molecules, as produced, for example, in a Stark-decelerator. This is demonstrated here by measuring the inversion tunneling spectrum of using a pulsed molecular beam that has been decelerated to about 52 m/s. Hyperfine resolved inversion transitions in in the state (around 1.43 GHz) are induced in a microwave region, and molecules that have undergone the transition are subsequently detected using a UV-laser based ionization detection scheme. To increase the signal intensity, the decelerated molecular beam is both transversally and longitudinally focused into the laser detection region. The observed spectral width of individual hyperfine transitions in the fully resolved spectrum is about 1 kHz, and the standard deviation of the best fit is 62 Hz.Received: 7 September 2004, Published online: 23 November 2004PACS: 33.15.Pw Fine and hyperfine structure - 33.20.Bx Radio-frequency and microwave spectra - 33.40. + f Multiple resonances - 33.70.Jg Line and band widths, shapes, and shifts - 39.10. + j Atomic and molecular beam sources and techniques     

Verification of X-ray line coincidences by high-resolution spectroscopy

Photo-resonant pumping of X-ray lasers requires close coincidence of a strong emission line with a suitable absorbing transition. We use a high-resolution crystal spectrometer to verify five coincidences, one of which has apparently not yet appeared in published work. All but one of the coincidences are found to lie within one linewidth. With respect to X-ray laser photo-pumping three of the five coincidences seem to be promising candidates.     

Automated line search in molecular spectra based on nonparametric statistical methods: Regularization in estimating parameters of spectral lines

The application of pattern-recognition methods to automated processing of spectroscopic information is described. Model shapes of spectral lines are fitted by the least squares method with a regularizing addition. Some additional ways of increasing the stability of the fitting process are described. The results can be interesting for specialists who solve problems of spectroscopy and pattern recognition and construct expert and developmental support information systems.     

高分辨率电子能量损失谱在材料科学中的应用

简要介绍了FEI Titan80—300STEM扫描透射电镜中装配的Wien-filter型能量单色器(monochromator).文章特别指出,装配有能量单色器的FEI Titan80—300STEM扫描透射电镜,可以直接给出高能量分辨率（~0.1eV）的电子能量损失谱.利用高分辨电子能量损失谱,在高能损失区,对于K或L能级自然宽度(natural width of energy level)小于0.5eV的元素,可以获得更细致的的近限精细结构（energy-loss near-edge structure）,更有利于解析其电子结构;在低能损失区,可以用于精确地确定半导体材料的带隙（bandgap）以及p型掺杂引起的带隙能的变化.     

Proposed search for small violations of bose statistics in molecular spectra

Summary I discuss the possibility of performing a test of the symmetrization postulate for bosons by high-sensitivity spectroscopy of¹⁶O₂. I show that the sensitivity required to give significant information can be easily achieved by well-developed spectroscopic methods. The author of this paper has agreed to not receive the proofs for correction     

Application of pressure-tuned diode lasers to high-resolution spectroscopy

The application of the high-pressure chamber with a pressure transmitting medium (liquid at room temperature) to diode-laser tuning was found to be a useful method for high-resolution spectroscopy. Ammonia absorbtion spectra in the 10 μm region were recorded with a resolution approaching the Doppler limit.     

Temperature-compensated,high-resolution infrared absorption spectroscopy: Application to carbon monoxide

The analytic basis is presented for an optical absorption technique on CO suitable for a single line-of-sight determination of average gaseous species number density in the presence of concentration, pressure and temperature gradients and of particulate loading. The technique depends on the use of high-resolution IR (tunable diode laser) spectroscopy. The method requires the construction of functions of molecular line strengths that are nearly temperature independent. A method for constructing these functions is described.     

A hollow cathode for high-resolution optogalvanic spectroscopy: Application to uranium

Summary We report the design criteria and performance characteristics of a hollow-cathode tube developed especially for high-resolution Doppler-free laser spectroscopy. It is simple to construct and is easily demountable. Narrow homogeneous line widths of refractory and highly reactive-element transitions have been observed by applying intermodulated detection scheme. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

Chirped laser dispersion spectroscopy with harmonic detection of molecular spectra

Chirped laser dispersion spectroscopy (CLaDS) has been introduced recently as a technique that performs molecular detection based on measurement of optical dispersion. In this paper, a new detection scheme based on chirp modulation (CM) and subsequent phase-sensitive detection is described. CM-CLaDS inherits the full advantages of conventional CLaDS and additionally overcomes some of its limitations. A prototype CM-CLaDS instrument has been developed and characterized in laboratory conditions. The system is based on a distributed feedback quantum cascade laser which operates around 4.52???m and can probe the most intense nitrous oxide (N₂O) ro-vibrational transitions. Preliminary performance tests are presented and provide a path/bandwidth normalized minimum N₂O detection limit below 100?ppbv?m/Hz^1/2.     

Application of the strip-transmission line in submillimetre spectroscopy

We demonstrate theoretically that in ‘electro-’ and ‘magneto-spectroscopy’ using submillimetre radiation the actual structure of the strip-line mode has a great influence on the resultant strip-line transmission, in agreement with experimental results.     

Measurement of N2O line strengths from high-resolution Fourier transform spectra

The absolute line strengths in four bands of nitrous oxide N₂O have been measured by means of the high information Fourier transform interferometer at the Laboratoire d'Infrarouge (apodized resolution: 5.4 × 10^?3 cm^?1). The investigated transitions were the 2ν₁ and ν₁ + 2ν₂ near 4 μm, and the ν₁ and 2ν₂ near 8 μm, which are all used for atmospheric detection. Conditions for extracting accurate line parameters are discussed. Reproducibility of measurements is better than 3% while absolute precision on both line and band intensities is shown to be currently better than 5%. Band intensity values compare well with the most recent determinations whereas the line strengths were never measured previously.     

表征超声衰减谱粒度的改进和声搜索算法

针对超声衰减谱法颗粒粒径测量,提出一种改进和声搜索算法,在和声搜索算法迭代达到200次时,加入拟牛顿算法,调节和声搜索算法全局和局部搜索能力,提高算法的收敛精度.对服从3种典型粒径分布函数颗粒系进行数值模拟,改进算法反演得出罗辛-拉姆勒(Rosin-Rammler)分布参数值相对误差小于8％,正态分布参数值相对误差小于...     

Frequency comb Vernier spectroscopy for broadband, high-resolution, high-sensitivity absorption and dispersion spectra

A femtosecond frequency comb provides a vast number of equidistantly spaced narrow band laser modes that can be simultaneously tuned and frequency calibrated with 15 digit accuracy. Our Vernier spectrometer utilizes all of theses modes in a massively parallel manner to rapidly record both absorption and dispersion spectra with a sensitivity that is provided by a high finesse broadband optical resonator and a resolution that is only limited by the frequency comb line width while keeping the required setup simple.     

玉米近红外光谱在仿生模式识别中的特征提取方法研究

近红外光谱特征提取是近红外光谱定性分析的关键步骤,其质量直接影响定性分析结果。采用漫透射方法测量8个玉米品种的近红外光谱,经预处理后,分别采用PCA,ICA,PLS-DA和小波分解四种方法对光谱进行特征提取,并使用仿生模式识别方法建立了8个玉米品种识别模型,最后使用测试集数据进行模型测试。结论如下:使用PLS-DA方法进行特征提取后建立的模型正确识别率优于使用PCA,ICA和小波分解特征提取后建立的模型。     

功率谱在高分辨率遥感相机检调焦中的应用

检调焦是高分辨力遥感相机得到高质量图像的关键技术之一。线阵CCD遥感相机在推扫过程中地面景物不断变化,而一般的图像清晰度评价函数只能在相同的图像内容下作比较来判断系统是否合焦。在介绍了遥感相机离焦原因及常用检调焦方法的基础上,用遥感图像验证了图像的功率谱对自然景物具有一定的不变性,分析了将其用于相机检调焦的可行性。实验表明,在系统合焦时,不同图像的功率谱值基本相同;而系统离焦时,功率谱值随着离焦程度的增加而逐渐减小,以此提出了以两幅不同图像功率谱的比值作为CCD遥感相机调焦的评价函数。     

Theory of line shape of optical absorption and emission spectra in molecular crystals

We solve the equations of the coupled coherent and incoherent motion of excitons in molecular crystals and determine the optical line shapes and positions including Davydov splitting.     

Comparison of pattern recognition methods in classifying high-resolution BOLD signals obtained at high magnetic field in monkeys

Pattern recognition methods have shown that functional magnetic resonance imaging (fMRI) data can reveal significant information about brain activity. For example, in the debate of how object categories are represented in the brain, multivariate analysis has been used to provide evidence of a distributed encoding scheme [Science 293:5539 (2001) 2425–2430]. Many follow-up studies have employed different methods to analyze human fMRI data with varying degrees of success [Nature reviews 7:7 (2006) 523–534]. In this study, we compare four popular pattern recognition methods: correlation analysis, support-vector machines (SVM), linear discriminant analysis (LDA) and Gaussian naïve Bayes (GNB), using data collected at high field (7 Tesla) with higher resolution than usual fMRI studies. We investigate prediction performance on single trials and for averages across varying numbers of stimulus presentations. The performance of the various algorithms depends on the nature of the brain activity being categorized: for several tasks, many of the methods work well, whereas for others, no method performs above chance level. An important factor in overall classification performance is careful preprocessing of the data, including dimensionality reduction, voxel selection and outlier elimination.