Light diffraction by a strong standing electromagnetic wave

The nonlinear quantum interaction of a linearly polarized x-ray probe beam with a focused intense standing laser wave is studied theoretically. Because of the tight focusing of the standing laser pulse, diffraction effects arise for the probe beam as opposed to the corresponding plane wave scenario. A quantitative estimate for realistic experimental conditions of the ellipticity and the rotation of the main polarization plane acquired by the x-ray probe after the interaction shows that the implementation of such vacuum effects is feasible with future X-ray Free Electron Laser light.     

Quantitative analysis of electronic properties of carbon nanotubes by scanning probe microscopy: from atomic to mesoscopic length scales

A new multiscale approach to the quantitative interpretation of scanning probe microscopy data in terms of the local electronic properties of 1D systems such as carbon nanotubes is presented. The interactions between a probe and the system are treated using a combination of first-principles density functional calculations and continuum electrostatics modeling. Realistic tip size effects are included using an image charge model. It is shown that the local potential at a nanotube on a substrate due to a probe can be calculated quantitatively, allowing experimental data to be analyzed in terms of the electronic structure of defects.     

Paramagnetic resonance of transition complexes as probes of motion during glass-to-rubber transitions in polymers

It is shown that motional averaging of the g and the A tensor of the electron paramagnetic resonance spectrum of such transition metal complexes as copper benzoyl acetonate (CuBA) and vanadyl acetonate (VAA) doped into polymers provides a sensitive probe of motion during the glass-to-rubber transition. Because of the larger and more anisotropic g and A tensors these probes are more sensitive to motional effects than the more commonly used nitroxide paramagnetic probes. The relationship between probe motion and intrinsic chain motion is examined.     

Miniaturized probe based on a microelectromechanical system mirror for multiphoton microscopy

A factor that limits the use of multiphoton microscopy (MPM) in clinical and preclinical studies is the lack of a compact and flexible probe. We report on a miniaturized MPM probe employing a microelectromechanical system (MEMS) scanning mirror and a double-clad photonic crystal fiber (DCPCF). The use of a MEMS mirror and a DCPCF provides many advantages, such as size reduction, rapid and precise scanning, efficient delivery of short pulses, and high collection efficiency of fluorescent signals. The completed probe was 1 cm in outer diameter and 14 cm in length. The developed probe was integrated into an MPM system and used to image fluorescent beads, paper, and biological specimens.     

High-resolution NMR probe for high pressure studies

Specialized design features of high-resolution, high-pressure NMR probe are discussed. A new design of the high-pressure NMR probe is presented. The achieved performance characteristics such as high resolution, high sensitivity, large sample volume, variable temperature, and wide range of pressures up to 1000 MPa make this instrumentation well suited for studies of biochemical systems.     

基于数据采集系统的等离子体Langmuir探针诊断实验

 采用Langmuir探针、扫描电源和微机数据采集系统相结合,实时获得了等离子体的伏安特性曲线及参数计算结果。本数据采集系统是一个虚拟仪器系统,包括数据采集、分析测试和结果显示三部分,用来采集Langmuir探针的电流电压信号,并加以分析处理。整个测试过程非常快,可以在ms级的时间内完成,相对于手动测试,基于数据采集系统的Langmuir探针诊断实验得到的数据更为精确,电压测试范围更大,并能去除因为等离子体电位漂移而产生的曲线失真。根据所得的伏安曲线,讨论了等离子体的电子温度,离子密度等参数的计算方法。进一步研究发现电子温度随真空室气压增大而变小,离子密度随气压增大而变大。     

2,6-Dansyl Azide as a Fluorescent Probe for Hydrogen Sulfide

A second-generation sulfonyl azide-based fluorescent probe, 2,6-DNS-Az, has been developed for the quantitative detection of H₂S in aqueous media such as phosphate buffer and bovine serum. Compare to the first-generation 1,5-DNS-Az probe, this probe shows both high sensitivity in phosphate buffer without the need for addition of surfactant and selectivity for sulfide over other anions and biomolecules, and thus can be used as a useful tool for detection of H₂S in the biological system.     

Interferometric measurement of injection nozzles using ultra-small fiber-optical probes

The measurement of boreholes with diameters smaller than 500 μm is a demanding task that cannot be performed using state-of-the-art production metrology. In this letter, a miniaturized fiber probe with a diameter of 80 μm is presented. A probe is used for low-coherence interferometry to conduct highly precise measurements of form deviations of small boreholes. Measurements conducted in nozzles are also presented. The results prove the potential of the fiber-optical sensor for quality inspection of high-precision parts, such as injection nozzles, for common-rail diesel engines.     

Spot focus size effect in spectroscopic ellipsometry of thin films

A focused as opposed to collimated light beam is typically used as probe in order to achieve a smaller as well as more intense light interrogation area in spectroscopic ellipsometry of thin films. In this work, we performed geometric ray analysis at the illumination and recording ends of such a system. The numerical results revealed substantial changes in (i) average optical path length and (ii) optical path length differences, which varied according to wavelength despite the film thickness remaining uniform. These results were able to consistently explain the anomalies found when different focus probe beam sizes were used in experimental spectroscopic ellipsometry measurements.     

Double resonance 1-D photonic crystal cavities for single-molecule mid-infrared photothermal spectroscopy: theory and design

We propose and theoretically examine a novel mid-infrared (mid-IR) photothermal spectroscopic sensing technique capable of detecting a single small molecule. Our conceptual design attains such high sensitivity by leveraging dramatically amplified photothermal effects in an optical nanocavity doubly resonant at both mid-IR pump and near-IR probe wavelengths. Unlike conventional mid-IR spectroscopy, the technique eliminates the need for cryogenically cooled mid-IR photodetectors, as optical detection is performed solely at the near-IR probe wavelength. A device design based on nested one-dimensional nanobeam photonic crystal cavities is numerically analyzed to demonstrate the technique's potential for single small gas molecule detection.     

All-optical logic gates with bacteriorhodopsin

All-optical logic gates with bacteriorhodopsin (bR) protein molecules have been demonstrated based on all-optical switching of a cw probe laser beam by multiple pulsed pump laser beams due to nonlinear intensity-induced excited-state absorption. A cw probe laser beam at 640 nm corresponding to the peak absorption of O-state in the bR photocycle is switched by a pulsed pump laser beam at 570 nm corresponding to the maximum initial B state absorption, at relatively low powers. The switching characteristics have been used to design all-optical NOT and the universal NOR and NAND logic gates and the effect of various parameters such as variation in pump pulse width, pump intensity, lifetime of O state and absorption cross-section of the B state at probe wavelength on the switching characteristics has been analyzed.     

Development of evanescent wave absorbance-based fibre-optic biosensor

Development of chemical and biochemical sensors is the current need of the society. In this report, we present our investigation on the development of a label-free fibre-optic biosensor based on evanescent wave absorbance to detect the presence of analytes such as bacteria, virus and some clinically important proteins. A simple UV-LED (280 nm) and photodetector combination along with a fibre probe was used for developing cost-effective, user-friendly and field applicable device. To improve the sensitivity of the detection technique, the probe design was modified and the U-bent probe was fabricated by simple procedure. Further, to overcome the problems for using UV light source in the fibre, the localized surface plasmon resonance of noble metal nanoparticles at visible wavelength was exploited as a sensing medium for the biochemical reactions. Our systematic studies in this regard presented in this communication may bring the excitement for developing the waterborne pathogen detection device for house-hold as well as field applications.     

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介绍了一种对等离子体边缘进行径向扫描的往复静电探针系统,该系统由高压气源、传输杆、光栅尺、探针组件构成。它在一次放电中能测量主等离子体边缘的温度、密度、悬浮电位、空间电位、离子饱和电流、极向电场、粒子通量等参数的径向分布以及电子温度和密度的衰减长度。测量结果表明,利用该系统测量的主等离子体边缘参数分布与JT-60U、TEXT、HT-7等装置上测量的结果一致。     

Fluctuational dissipative electromagnetic interaction between a nanoprobe and a surface

In the framework of fluctuational electromagnetic theory, analytical expressions are obtained for the dynamic dissipative damping forces acting on the probe of an atomic-force microscope (AFM), as well as between two plane surfaces at their contact. The contacts between materials typical of AFM, quartz-microbalance, and surface-force apparatus experiments are considered. The conditions for nondissipative slide are discussed. A comparison between the calculated oscillator quality factor associated with fluctuational dissipative forces and its values obtained in AFM experiments with a silicon probe and a mica sample shows that they are of the same order of magnitude; therefore, an experimental investigation of such forces is feasible.     

制备扫描近场光学显微镜光纤探针的自动化腐蚀方法

提出了一种制备扫描近场光学显微镜光纤探针的自动化腐蚀方案.该方案利用静态腐蚀过程中光纤所形成的特殊结构,及动态腐蚀过程中光纤在氢氟酸中的移动所带来的新月形弯液面在光纤表面接触位置的变化,通过合理控制腐蚀时间来制备尖端锐利、大锥角或多锥体角等各种结构的探针.设计方案采用计算机控制整个装置实现了探针制备过程的自动化,保持了腐蚀光纤探针实验条件的一致性.实验结果表明,采用此方案可以制备出尖端孔径小于100 nm且锥体角高达70°的光纤探针,且重复性高.此外,该方案的装置结构简单,实现容易.     

In a tradition of excellence

A laser-based security technique called Laser Surface Authentication (LSA) is described in which diffuse laser scattering is used as a probe of the naturally-occurring randomness present in virtually all surfaces. LSA brings the principles of biometric identification currently used in human fingerprint- or iris-recognition to the world of inanimate objects such as paper documents, plastic cards, high value branded products and a range of other things that are commonly counterfeited or smuggled.     

飞秒时间分辨实验中相关函数和时间零点的确定

结合飞秒激光在研究分子激发态弛豫动力学中的应用,介绍了几种飞秒时间分辨实验中确定泵浦激光脉冲与探测激光脉冲的相关函数和时间零点的方法.对于波长在可见波段的泵浦和探测激光脉冲,我们可以利用非线性光学的技术手段,探测泵浦光与探测光的和频光的强度随二者间的时间延迟的变化来确定相关函数和时间零点;对于波长在紫外甚至更短的波段的泵浦和探测激光脉冲,由于单脉冲能量比较低,目前还很难利用技术手段来测定泵浦激光与探测激光的相关函数及时间零点,可以利用某些原子气体(如Xe)或某些具有短寿命态的分子作平行实验进行间接测量.     

Characterization of a 20 kHz sonoreactor. Part II: analysis of chemical effects by classical and electrochemical methods

A new electrochemical redox probe has been investigated in order to characterize the local production of radicals during the cavitation events. The results have been compared with those obtained with Fe(CN)6(3-)/Fe(CN)6(4-) (electrochemical probe for local mechanical effects) and classical chemical methods such as iodide and Fricke dosimeters (chemical probes for global effects).     

Surface physics with radioactive ion beams

Nuclear methods using radiation detection are very well suited for surface and interface investigations, since they generally require only a small number of radioactive probe nuclei. Virtually isolated probe atoms can be investigated. The use of an isotope separator to solve the central problem in the application of radioactive atoms for the study of surfaces, the clean deposition of the probe nuclei, is described. First physics experiments include studies of desorption isochrones and characterization of adatom sites on flat and vicinal surfaces by PAC. A particularly complete picture could be obtained for Cd and In on the Pd(111) surface, where five different sites successively populated in the surface diffusion process were observed. Other nuclear methods suitable for a future extension of the surface investigations, such as Mössbauer spectroscopy, decay recoil angular distribution and emission channeling, are briefly discussed.     

Ultrasonic reflection mode imaging of the nonlinear parameter B/A. II: Signal processing

The nonlinear acoustic interaction between a reflected single-frequency sinusoid and a broadband pump waveform propagating in the opposite direction produces phase changes in the probe proportional to the nonlinear parameter B/A in the spatial region of interaction. The instantaneous phase change along the received probe can be expressed as the convolution of the pump waveform with the spatial distribution of B/A along the propagation path over which the pump and reflected probe interact. In theory, the phase modulated sinusoidal probe can be processed (phase detection and deconvolution) to produce an "A-mode" representation of B/A. If the pump is an intense unipolar impulse and the probe a swept-frequency sinusoid, then the pump interacts with the probe at each point along the propagation path at a unique frequency. Thus the phase modulation that carries information about the spatial distribution of B/A can be extracted from the phase spectrum by a simple Fourier transformation analogous to the space to frequency mapping so basic to magnetic resonance imaging. If the impulsive pump is replaced by another swept-frequency sinusoid, then the phase change in the probe due to B/A at a particular point along the propagation path will be spread out for the duration of the pump along the probe. Passage of the received signal through an appropriate matched filter restores spatial coherence to the phase information in the probe so that it can be processed as if the pump were a broadbanded impulse. This approach suggests a means of approaching the design of effective pump waveforms that can resolve a wide range of spatial frequencies in (B/A)(x).