Some aspects of the silicon behaviour under femtosecond pulsed laser field evaporation

Three dimension atom probe analysis of semiconductor materials requires the ability to bring high electric field at the specimen apex to remove atoms. It is shown that, if voltage pulses are used to evaporate doped silicon, the resistivity of the material has to be lower than about 10(2) Omega cm. To overcome this problem, voltage pulses have been replaced by femtosecond laser pulses. The laser pulses give rise to field evaporation by two processes. Both thermal and optical field evaporation have been observed. Thermal evaporation takes place at high laser intensities and with short wavelengths while the evaporation is assisted by the rectification of the optical field for lower intensities and in the infrared domain. Using the optical field evaporation, reproducible and good analyses in term of spatial and mass resolutions could be conducted.     

Application of a diffraction grating and position sensitive detectors to the measurement of error motion and angular indexing of an indexing table

In this paper, two systems for the measurement of the error motion and angular indexing of a rotary indexing table have been developed. A laser diode, a laser holder and a position sensitive detector (PSD) are integrated as a simple measuring device for the measurement of the rotary error without using a precision reference artifact (a cylinder or a sphere), multiple probes or error separation methods. The laser diode is assembled in the laser holder and fixed on the rotary table. The PSD is set up above the laser holder to detect the position of an incident laser beam from the laser diode. When the rotary table rotates, the rotary error changes the direction of the incident beam and also the position of the spot on the PSD. For the measurement of the angular indexing, a reflective diffraction grating and two PSDs are integrated as a high-resolution angle measuring device without using an autocollimator or a laser interferometer system. The diffraction grating is set at the center of the rotary table and reflects an incident laser beam into several diffractive rays. Two PSDs were set up for detecting the positions of ±1st-order diffraction rays. A simple algebraic method is used to solve the angular indexing through an optical analysis. The experimental results showed the feasibility of the proposed test devices.     

Separation of emission lines of multiply charged ions against background of a very noisy spectrum of femtosecond laser plasma

At high intensities of interaction of femtosecond laser pulses with various targets, numerous high-energy particles emitted from plasma in all directions lead to the appearance of parasitic peaks in the X-ray spectra of femtosecond laser plasma (FLP) during detection of these peaks with a detector based on a charge-coupled device (CCD). The algorithm proposed in this study allows identification of parasitic peaks in a series of experimental spectra, which are recorded for each pixel of the CCD detector independently of other pixels, and removal of these peaks. The algorithm is able to detect peaks in the presence of both variations in the intensities of spectral lines and very intense noise. The efficiency of the algorithm has been confirmed via testing with the use of a series of model spectra and spectra of Fe and Al ions recorded in experiments devoted to studies of the interaction of ultrahigh-intensity and ultrashort laser pulses with solid targets.     

Holographic Vector Wave Femtosecond Laser Processing

Parallel femtosecond laser processing using a computer-generated hologram (CGH) displayed on a spatial light modulator (SLM), called holographic femtosecond laser processing, provides the advantages of high throughput and high energy-use efficiency. Use of a light wave with spatially controlled polarization fields, called a vector wave, also offers novel properties in various applications. In this study, we demonstrated holographic femtosecond laser processing with a vector wave by using a pair of SLMs. In particular, we performed three-dimensional reconstruction with multifocal radial beams. We also realized simultaneous reconstruction with two different types of vector beams by using a novel design method of a CGH composed of multiple small CGHs. To our knowledge, this is the first demonstration of its kind. The polarization fields of the multifocal vector beams at the sample plane were analyzed from the orientations of periodic nanostructures fabricated with femtosecond laser light.     

Calibration of a Thomson parabola ion spectrometer and Fujifilm imaging plate detectors for protons, deuterons, and alpha particles

A Thomson parabola ion spectrometer has been designed for use at the Multiterawatt (MTW) laser facility at the Laboratory for Laser Energetics (LLE) at the University of Rochester. This device uses parallel electric and magnetic fields to deflect particles of a given mass-to-charge ratio onto parabolic curves on the detector plane. Once calibrated, the position of the ions on the detector plane can be used to determine the particle energy. The position dispersion of both the electric and magnetic fields of the Thomson parabola was measured using monoenergetic proton and alpha particle beams from the SUNY Geneseo 1.7 MV tandem Pelletron accelerator. The sensitivity of Fujifilm BAS-TR imaging plates, used as a detector in the Thomson parabola, was also measured as a function of the incident particle energy over the range from 0.6 MeV to 3.4 MeV for protons and deuterons and from 0.9 MeV to 5.4 MeV for alpha particles. The device was used to measure the energy spectrum of laser-produced protons at MTW.     

Measurement and analysis of the flow field in a pulsatile ventricularassist device

A pneumatically driven ventricular assist device (VAD) of unconventional geometry, designed to mitigate adverse haemostatic phenomena by optimization of flow patterns, was investigated using two-component laser Doppler anemometry (LDA). Data were taken on a rectilinear grid over two orthogonal traverses, allowing synthesis of three-dimensional velocity vectors over most of the grid. The resulting data were examined by two-dimensional and three-dimensional static and animated computer graphic visualizations of the time-varying vector fields. This analysis revealed illuminating and previously unobserved features of the complex flow fields within pulsatile VADs and identified design considerations that bear upon minimization of turbulence and of flow recirculation and stasis. The findings of this study suggest that, while total abolition of undesirable flow phenomena in a diaphragm-type blood pump is probably impossible, comprehensive investigation in vitro can engender considerable improvements in the efficacy of a device.     

Versatile single-molecule multi-color excitation and detection fluorescence setup for studying biomolecular dynamics

Single-molecule fluorescence imaging is at the forefront of tools applied to study biomolecular dynamics both in vitro and in vivo. The ability of the single-molecule fluorescence microscope to conduct simultaneous multi-color excitation and detection is a key experimental feature that is under continuous development. In this paper, we describe in detail the design and the construction of a sophisticated and versatile multi-color excitation and emission fluorescence instrument for studying biomolecular dynamics at the single-molecule level. The setup is novel, economical and compact, where two inverted microscopes share a laser combiner module with six individual laser sources that extend from 400 to 640 nm. Nonetheless, each microscope can independently and in a flexible manner select the combinations, sequences, and intensities of the excitation wavelengths. This high flexibility is achieved by the replacement of conventional mechanical shutters with acousto-optic tunable filter (AOTF). The use of AOTF provides major advancement by controlling the intensities, duration, and selection of up to eight different wavelengths with microsecond alternation time in a transparent and easy manner for the end user. To our knowledge this is the first time AOTF is applied to wide-field total internal reflection fluorescence (TIRF) microscopy even though it has been commonly used in multi-wavelength confocal microscopy. The laser outputs from the combiner module are coupled to the microscopes by two sets of four single-mode optic fibers in order to allow for the optimization of the TIRF angle for each wavelength independently. The emission is split into two or four spectral channels to allow for the simultaneous detection of up to four different fluorophores of wide selection and using many possible excitation and photoactivation schemes. We demonstrate the performance of this new setup by conducting two-color alternating excitation single-molecule fluorescence resonance energy transfer (FRET) and a technically challenging four-color FRET experiments on doubly labeled duplex DNA and quadruple-labeled Holliday junction, respectively.     

Air-borne laser induced fluorescence system for measuring OH and other trace gases in the parts-per-quadrillion to parts-per-trillion range

Described in detail is a laser induced fluorescence system which has been successfully interfaced with two aircraft sampling platforms (i.e., Sabreliner jet and an L-188C Electra). This system, which has been under development for four years, presently consists of the following major components: (1) a Nd-Yag laser driven oscillator-amplifier dye laser; (2) a sampling manifold with associated fluorescence detection optics; (3) an OH calibration chamber; (4) a laser beam steering assembly; and (5) sampling electronics and data processing hardware. During the last three years, this system has been flown some 50 000 air miles making tropospheric OH radical measurements over the latitude range of 70 degrees N to 57 degrees S. OH concentrations measured during these flights have ranged from 30 parts-per-quadrillion (3.7x10(5) molecules/cm(3)) at altitudes of 6 km to 0.8 parts-per-trillion (2.0x10(7) molecules/cm(3)) at 0.5 km. Computations have been completed which indicate that the existing aircraft system with modest modifications should also be capable of detecting natural tropospheric levels of NO, SO(2), CH(2)O, NO(2), HNO(2), NO(3), H(2)O(2), and CS(2) by using both conventional laser-induced fluorescence methodology and multiphoton techniques.     

Two‐dimensional profiling of carriers in terahertz quantum cascade lasers using calibrated scanning spreading resistance microscopy and scanning capacitance microscopy

The distribution of charge carriers inside the active region of a terahertz (THz) quantum cascade laser (QCL) has been measured with scanning spreading resistance microscopy (SSRM) and scanning capacitance microscopy (SCM). Individual quantum well‐barrier modules with a 35.7‐nm single module thickness in the active region of the device have been resolved for the first time using high‐resolution SSRM and SCM techniques at room temperature. SSRM and SCM measurements on the quantum well‐barrier structure were calibrated utilizing known GaAs dopant staircase samples. Doping concentrations derived from SSRM and SCM measurements were found to be in quantitative agreement with the designed average doping values of the n‐type active region in the terahertz quantum cascade laser. The secondary ion mass spectroscopy provides a partial picture of internal device parameters, and we have demonstrated with our results the efficacy of uniting calibrated SSRM and SCM to delineate quantitatively the transverse cross‐sectional structure of complex two‐dimensional terahertz quantum cascade laser devices.     

Comparison under controlled conditions between multi-frequency ADCPs and LISST-SL for investigating suspended sand in rivers

This paper aims to investigate the possibility and limits of using the laser device LISST-SL to calibrate and validate the multi-frequency acoustic method for assessing the concentration and grain size of suspended sand in rivers by using Acoustic Doppler Current Profilers (ADCPs). Over the last few decades, the methods for investigating suspended sediment using Acoustic Backscattering (ABS) have been gaining increasing acceptance for riverine applications. ABS allows indirect quantification of the suspended sediment using non-intrusive measurements with high temporal and spatial resolution from a moving boat, with a range of several metres. Despite the advancement of these techniques, the use of ABS usually implies calibration and validation in the field, which can be performed by comparing echo recording by ADCP to data from water samples. Sampling and analysis of water samples noticeably increase the campaign cost and limits the reliability of the calibration because of the time and spatial averaging involved in physical sampling. In the present work, the LISST-SL suited to river applications was tested to provide matching data in one point for the validation of ADCP methods in future field work. To this end, laboratory tests were conducted utilising two ADCPs working at 1200 and 600 kHz frequencies and studying the same water volume that was concurrently being analysed by the laser device. Rapid injections of sand (median grain size: 130–250 μm) produced average concentrations of 100–1000 mg/L in a 0.25-m/s-fast and 1.7-m-deep flow. Echo records at the two frequencies were compared to the mean grain size and concentration measured via laser diffraction. Although noticeable differences between the acoustic and laser assessments of concentration were due to (1) inappropriate sampling of LISST-SL at low flow velocity and (2) investigation scarce resolution with respect to actual gradients, the corresponding mean sizes were well correlated.     

An alternative illumination source based on LEDs for PIV measurements on human swimmers—A feasibility study

Methods for flow visualization help to investigate the motion of fluids that are normally invisible. Especially, Particle Image Velocimetry (PIV) – with a laser as light source – has been established in the field of engineering and partly in biology. Since the standard measuring equipment applying a laser system is very sensitive with respect to transport, temperature, humidity as well as laser safety requirements have to be adhered, the observation and classification of flow pattern around human swimmers in swimming pools has been rarely applied. There is a need for a simple, powerful, affordable, robust, and portable illumination source which shall not harm the swimmer by exceeding the permitted maximum radiation for human skin and eyes. As a result, this technical note demonstrates an alternative light source system based on LEDs which enables PIV measurements around human swimmers similar to experiments with a (traditional) laser system. As an example, the flow fields of two different swimmers with a similar movement and phase are compared using both illumination methods laser and LED. Furthermore, a series of sequential velocity fields, produced by the motion of a monofin swimmer, generate a vortex pair with an inverse Karman vortex street which is typically seen in fish and marine mammal locomotion. Consequently, this LED illumination source is show to provide a sufficient suitable light intensity as well as light quality enabling the measurement of the flow field around swimmers.     

Absolute calorimeter for measuring low-energy outputs from CO2 lasers

This paper describes the construction of a calibrated energy measuring device for pulsed CO(2) lasers of low output energy. An aluminium disk of low thermal capacity has been used for the detection of laser radiation. An Al(2)O(3) layer has been electrolytically deposited on the aluminium disks. It is used as a highly absorbing surface (> 95% for wavelengths between 8.5 and 11.0 microm), thus eliminating the need for calibration. The laser output energy is calculated from the measured increase of temperature of a calorimeter disk of known thermal capacity. Calculations and measurements have shown that this device is capable of measuring the energy of a single pulse of the order of 1 mJ, and in a set of 10 pulses even to 0.1 mJ, for pulses as short as 1 ps.     

Elemental mapping using the Ga 3d and In 4d transitions in the epsilon2 absorption spectra derived from EELS

It is proposed that by using the valence-band states in electron energy loss spectroscopy, high-spatial resolution maps of quantitative elemental composition may be acquired with high acquisition rates. Further, it is shown that by using the epsilon(2) spectrum instead of single scattering data, the noise in the observed transitions and associated maps is significantly reduced. The epsilon(2) spectra are derived through a Kramers-Kronig transformation from electron energy loss spectra obtained in a scanning transmission electron microscope. Using transitions that occur in the epsilon(2) absorption spectrum (<40eV), quantitative elemental maps for III-V device structures have been produced. An example is provided using the Ga 3d transition to map a GaInNAs/GaAs laser structure. Weaker transitions such as In 4d have also been used to verify the Ga elemental distribution.     

基于单目视觉的激光光束方向标定研究

在由激光位移传感器组成的测量系统中,激光光束的方向是一个关键参数.方位角和俯仰角对于一条激光光束是最为重要的两个参数.本文中提出一种基于单目视觉的激光光束方向测量方法.首先,将CCD相机放置于基础平面上方,保持相机光轴与基础平面接近于垂直状态,并利用误差为10μm的圆孔型标定板建立单目定位模型.然后将激光光束发生装置放置在基础平面上并保持位置固定,同时在基础平面上放置特制靶块,使激光光束可以投射到靶块斜面上并形成一个激光光斑.在基础平面上方放置的CCD相机可以清晰的采集到激光光斑、靶块斜面的图像,应用相关算法提取出光斑质心的二维图像坐标.沿激光光束方向以相等间距移动靶块,通过CCD相机采集每移动一次靶块在当前位置下的光斑、靶块图像.利用相关的转换公式,结合靶块本身固有参数,将光斑质心图像二维坐标转换为基础平面下的空间三维坐标.由于靶块的移动,会得到靶块不同位置下激光光斑质心的三维坐标,将这些三维坐标拟合成空间直线表征待测激光光束.拟合直线得俯仰角即为待测激光光束的俯仰角.实验中,应用高精度仪器对靶块参数进行测定,并使用高精度标定板标定相机内外参数建立相应的定位模型.测量精度主要通过单目视觉定位精度、光斑重心提取精度来保证.结果显示,待测光束的俯角最大误差达到0.02°,光束间夹角的最大误差为0.04°.     

Spectroscopic comparison between 1200 grooves/mm ruled and holographic gratings of a flat-field spectrometer and its absolute sensitivity calibration using bremsstrahlung continuum

A flat-field extreme ultraviolet (EUV) spectrometer with a varied line spacing groove grating (1200 grooves/mm at grating center) has been developed to study the emission spectra from highly ionized medium Z impurities in large helical device (LHD). It covers a wavelength range of 50-500 A using a mechanically ruled grating, which was later replaced by a newly developed laminar-type holographic grating for comparative studies. Differences in spectral resolution, intensities of higher order spectra, and sensitivities of the spectrometer were studied between the two gratings by observing the emission spectra of LHD plasmas. Although the achieved resolution was alike between them, i.e., deltalambda approximately 0.24 A at 200 A, the holographic grating was much superior in suppressing the higher order light than the ruled grating. The relative sensitivity between the two gratings was evaluated using continuum radiation from LHD plasmas. As a result, it was found that the holographic grating has a flat response in the full wavelength range, but the sensitivity of the ruled grating drops sharply below 200 A. A new technique for the absolute calibration of the EUV holographic grating spectrometer was tried by combining the continuum radiation with a branching ratio of C IV lines (3p-3s: 5800 A/3p-2s: 312 A), and an accurate absolute sensitivity has been successfully obtained.     

基于高场非对称离子迁移谱的糖类异构体分离研究

本工作研发了一款配套滤波算法及重叠峰分离算法、可独立使用的平板型高场非对称离子迁移谱(FAIMS)系统,能够在分离不同离子、有效滤噪的同时,从重叠峰中准确、快速提取分析物峰,由此实现物质的精准定性分析。通过评估该FAIMS装置对糖类异构体的分离效果,发现FAIMS能有效分离出蔗糖离子的2种结构,证明其对离子结构差异更加敏感。采用氮气、氦气的混合气体作为载气,可进一步提高FAIMS的分辨力。当氦气比例达到40%时,蔗糖峰和麦芽糖峰的重合度由纯氮气时的77%降低至50%。本研究表明,该FAIMS系统可为同分异构体的定性分析提供一种新方法。     

同轴度同步旋转测量的空间投影解析

研究了国际上同轴度准直测量的专利发展状况。在这些专利材料研究的基础上,对2轴三维空间准直测量建立数学模型,用三维空间的思想来描述一个运动的准直激光在一个同步旋转轴的垂直二维平面位置测量装置上的投影,解决同轴度测量空间解析问题。通过试验检测同轴测量空间坐标的位置变化。原来的激光光斑在从动轴垂直平面中为椭圆曲线,在位置检测器件坐标中曲线也发生了改变,并且展示了角偏差变化和轴心的位置变化对曲线的影响。     

Near-field scanning optical microscopy and near-field induced photocurrent investigations of buried heterostructure multiquantum well lasers

Buried heterostructure multiquantum well laser devices are investigated utilizing a near-field scanning optical microscope to characterize and correlate the surface topography, optical output and electronic properties of the device. Near-field photocurrent imaging has been used to accurately measure the unbiased buried heterostructure multiquantum well device in cross-section, successfully revealing the distribution of pn-junctions and their associated fields. Moreover, this has been accurately correlated with the physical structure of the device determined by simultaneous shear-force imaging of the surface. Topographic structure is manifested as a result of strain relaxation (∼10⁻¹⁰ m) of the cleaved cross-section. These imaging modes are similarly correlated with the optical output of the operational device mapped with 50 nm lateral resolution. The collection-mode measurements detected electroluminescence external to the active region, highlighting the existence of carrier recombination away from the multiquantum well device region. The combination and correlation of different near-field scanning optical microscope imaging modes proved powerful in the analysis of the buried heterostructure multiquantum well device, and was shown to assist in the identification of current leakage pathways within the structure.     

液晶空间光调制器的纯相位调制特性研究

介绍了液晶空间光调制器的纯相位调制原理,采用泰曼-格林干涉系统对液晶纯相位特性进测试。测量了BNS(Boulder Nonlinear Systems)公司的专利产品-256256像素纯相位空间光调制器的相位与电压(灰度)的响应曲线。 给出了对任意图形进行相位恢复的优化算法流程,利用纯相位调制方法对光束进行方向和强度的快速程序控制。设计了实验装置,实际产生了二维任意衍射图形,图形产生时间小于200 ms。本研究对空间目标进行扫描跟踪,具有精确、响应快、无机械惰性等特点,在激光寻的、制导以及多目标威胁预警和反击中有着重要的研究价值。     

High coherent bi-chromatic laser with gigahertz splitting produced by the high diffraction orders of acousto-optic modulator used for coherent population trapping experiments

To prepare the coherent population trapping (CPT) states with rubidium and cesium, the commonly used atoms in CPT studies, a coherent bi-chromatic light field with frequency difference of several GHz is a basic requirement. With a 200 MHz center frequency acousto-optic modulator (AOM), we have realized bi-chromatic laser fields with several GHz frequency splits through high diffraction orders. We have experimentally studied the coherence between two frequency components of a bi-chromatic laser beam, which is composed of ±6 orders with frequency split of 3 GHz diffracted from the same laser beam, and the measured residual phase noise is Δφ(2)<0.019 rad(2). The bi-chromatic laser fields were used to prepare CPT states with (85)Rb and (87)Rb atoms, and high contrast CPT signals were obtained. For CPT states preparation, our study result shows that it is a feasible approach to generate the bi-chromatic light field with larger frequency splits through high diffraction orders of AOM.