Study of High-Order Harmonic at VUV/XUV

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真空紫外和极紫外相干光源的研究及进展

本文简明扼要地介绍和评论了真空紫外和极紫外波段相干光源研究的现状和发展前景 ,重点包括 :真空紫外和极紫外波段相干光源的产生机制 ,理论描述 ,实验方法 ,以及一些典型的实验结果。最后对该领域的发展前景做了简要的评述。     

Generation of the wavelength-tunable XUV pulse using the two-color and three-color infrared pulses

We present an efficient method to generate an ultrashort wavelength-tunable XUV pulse by using the harmonic selec- tive enhancement scheme. The results show that by properly controlling the delay times of a two-color field or a three-color field, selective enhancement of the harmonics with photon energies between 80 eV and 315 eV can be obtained. Fur- ther, a wavelength-tunable and bandwidth-controllable XUV radiation can be obtained by Fourier transformation of these enhanced harmonics.     

HL-2A真空紫外光谱空间分布测量及绝对标定

A vacuum ultraviolet VUV spectrometer with spatial and temporal resolutions was presented in this paper. The sensitivity of the spectrometer has been calibrated in situ by using the VUV bremsstrahlung continuum radiation of the HL-2A plasma. The sensitivity coefficients of two gratings were given. The absolute density profile of carbon radiation was thus obtained based on the absolutely radial profile measurement of carbon radiation.     

Developing VUV spectroscopy for protein folding and material luminescence on beamline 4B8 at the Beijing Synchrotron Radiation Facility

The new 4B8 beamline provides UV–VUV light in the wavelength range from 360 to 120 nm. It uniquely enables two kinds of spectroscopy measurements: synchrotron radiation circular dichroism spectroscopy and VUV excited fluorescence spectroscopy. The former is mainly used in protein secondary structure studies, and the latter in VUV excited luminescent materials research. Remote access to fluorescence measurement has been realised and users can collect data online. Besides steady‐state measurements, fluorescence lifetime measurements have been established using the time domain method, while a laser‐induced temperature jump is under development for protein folding dynamics using circular dichroism as a probe.     

VUV synchrotron radiation: a new activation technique for tandem mass spectrometry

A novel experimental technique for tandem mass spectrometry and ion spectroscopy of electrosprayed ions using vacuum‐ultraviolet (VUV) synchrotron radiation is presented. Photon activation of trapped precursor ions has been performed by coupling a commercial linear quadrupole ion trap (Thermo scientific LTQ XL), equipped with the electrosprayed ions source, to the DESIRS beamline at the SOLEIL synchrotron radiation facility. The obtained results include, for the first time on biopolymers, photodetachment spectroscopy using monochromated synchrotron radiation of multi‐charged anions and the single photon ionization of large charge‐selected polycations. The high efficiency and signal‐to‐noise ratio achieved by the present set‐up open up possibilities of using synchrotron light as a new controllable activation method in tandem mass spectrometry of biopolymers and VUV‐photon spectroscopy of large biological ions.     

Recent progress on sum-frequency spectroscopy

Second harmonic generation (SHG) and sum frequency spectroscopy (SFS) have provided unique opportunities to probe surfaces and interfaces. They have found broad applications in many disciplines of science and technology. In recent years, there has been significant progress in the development of SHG/SFS technology that has significantly broadened the applications of SHG and SFS. In this article, we review the recent progress of the field with emphasis on SFS.     

脉冲形状和静电场对电离率和高次谐波的影响

采用数值方法研究静电场和不同的激光脉冲对氢原子的电离率和高次谐波的影响.结果表明脉冲形状和电离率之间有着确定的关系,电离率反过来又影响了谐波谱的性质;另外,随着所加的静电场强度的增大,电离率呈上升的趋势,而谐波谱出现一个双平台的结构.     

Thermal radiative properties of carbon materials under high temperature and vacuum ultra-violet (VUV) radiation for the heat shield of the Solar Probe Plus mission

The Solar Probe Plus (SP+) mission will approach the Sun as close as 9.5 solar radii in order to understand the origin of the solar corona heating and the acceleration of the solar wind. Submitted to such extreme environmental conditions, a thermal protection system is considered to protect the payload of the SP+ spacecraft. Carbon-based materials are good candidate to fulfill this role and critical point remains the equilibrium temperature reached at perihelion by the heat shield. In this paper, experimental results obtained for the solar absorptivity α, the total hemispherical emissivity ? and its ratio α/?, conditioning the equilibrium temperature of the thermal protection system, are presented for different kinds of carbon materials heated at high temperatures with or without vacuum-UV (100 < λ < 200 nm) radiation. The synergistic effect of ion bombardment is also presented for one kind of material.     

紫外-真空紫外漫反射板的研究

选用在紫外－真空紫外波段反射率较高的铝作基底材料,通过光学研磨加工和光学镀膜处理制成漫反射板;建立了紫外－真空紫外波段漫反射特性测试研究装置,利用该系统进行漫 反射板余弦特性、双向反射比分布函数的测试。结果表明,该漫反射板反射比ρ（ｏ／ｄ）在３１５ｎｍ处为４９％;在正入射情况下,双向反射比分布函数在１５℃￣４０℃范围内偏差优于１１％。     

DESIRS: a state‐of‐the‐art VUV beamline featuring high resolution and variable polarization for spectroscopy and dichroism at SOLEIL

DESIRS is a new undulator‐based VUV beamline on the 2.75 GeV storage ring SOLEIL (France) optimized for gas‐phase studies of molecular and electronic structures, reactivity and polarization‐dependent photodynamics on model or actual systems encountered in the universe, atmosphere and biosphere. It is equipped with two dedicated endstations: a VUV Fourier‐transform spectrometer (FTS) for ultra‐high‐resolution absorption spectroscopy (resolving power up to 10⁶) and an electron/ion imaging coincidence spectrometer. The photon characteristics necessary to fulfill its scientific mission are: high flux in the 5–40 eV range, high spectral purity, high resolution, and variable and well calibrated polarizations. The photon source is a 10 m‐long pure electromagnetic variable‐polarization undulator producing light from the very near UV up to 40 eV on the fundamental emission with tailored elliptical polarization allowing fully calibrated quasi‐perfect horizontal, vertical and circular polarizations, as measured with an in situ VUV polarimeter with absolute polarization rates close to unity, to be obtained at the sample location. The optical design includes a beam waist allowing the implementation of a gas filter to suppress the undulator high harmonics. This harmonic‐free radiation can be steered toward the FTS for absorption experiments, or go through a highly efficient pre‐focusing optical system, based on a toroidal mirror and a reflective corrector plate similar to a Schmidt plate. The synchrotron radiation then enters a 6.65 m Eagle off‐plane normal‐incidence monochromator equipped with four gratings with different groove densities, from 200 to 4300 lines mm^?1, allowing the flux‐to‐resolution trade‐off to be smoothly adjusted. The measured ultimate instrumental resolving powers are 124000 (174 µeV) around 21 eV and 250000 (54 µeV) around 13 eV, while the typical measured flux is in the 10¹⁰–10¹¹ photons s^?1 range in a 1/50000 bandwidth, and 10¹²–10¹³ photons s^?1 in a 1/1000 bandwidth, which is very satisfactory although slightly below optical simulations. All of these features make DESIRS a state‐of‐the‐art VUV beamline for spectroscopy and dichroism open to a broad scientific community.     

Attosecond spectroscopy for filming the ultrafast movies of atoms,molecules and solids

Three decades ago, a highly nonlinear nonpertubative phenomenon, now well-known as the high harmonic generation (HHG), was discovered when intense laser irradiates gaseous atoms. As the HHG produces broadband coherent radiation, it becomes the most promising source to obtain attosecond pulses. The door to the attosecond science was opened ever since. In this review, we will revisit the incredible adventure to the attoworld. Firstly, the progress of attosecond pulse generation is outlined. Then, we introduce the efforts on imaging the structures or filming the ultrafast dynamics of nuclei and electrons with unprecedented attosecond temporal and Angstrom spatial resolutions, utilizing the obtained attosecond pulses as well as the high harmonic spectrum itself.     

氦,氢,氮空心阴极放电的真空紫外辐射特性

介绍了一种水冷、陶瓷封接结构的空心阴极放电装置.研究了He、H_2、N_2在120nm～20Onm范围内该装置的真空紫外辐射特性,获得了100～600mA电流范围内的辐射强度与放电电流的关系,以及充气气压变化对它的影响.实验表明:在实验条件下,主要发射谱线为氮的原子线和氦的离子线;辐射谱线强度在0.03～0.72mW·cm~(-2);气压改变时,N_2、H_2辐射强度有一极大值,而He的离子线辐射强度则出现二个极大;在He/H_2混合气体放电时,随着He的加入,氢分子带光谱有明显下降.     

用光电子能谱相位确定法同时测量阿秒超紫外线XUV脉冲的频率和强度时间分布

介绍阿秒超紫外线(XUV)激发惰性气体原子产生光电子并在强激光电场中运动的半经典近似 方法，以及同时、直接、全面地测量阿秒XUV脉冲频率和强度时间分布的光电子能谱相位确定法. 采用飞秒超短脉冲激光和XUV间的交叉关联技术，从不同激光强度下、与激光线性极化方向成0°或180°方向上测得的光电子能量积分谱，可以重建XUV的频率和强度时间分布. XUV脉冲时间宽度的测量范围从1／4到1／2激光振荡周期，时间分辨率取决于激光束和XUV脉冲之间的相对延时控制精度和光路抖动时间. 所述方法可用于在阿秒尺度上的超快速测量，以及有关电子在原子和分子中运动的超快速动力学过程研究. 关键词： 阿秒测量 光电子能谱 相位确定法 超紫外线 频率和强度时间分布     

Fast and slow light generated simultaneously for up-down-link frequency converter applications

We firstly propose a new system for simultaneous fast and slow light generation using a soliton pulse propagating within the nonlinear micro-ring resonators. The nonlinear Kerr effect induces the spreading frequency bands within the micro-ring device, where the chaotic filtering characteristics can be employed using the appropriate micro-ring parameters. Results obtained have shown that the wide spreading of frequency bands can be generated and selected to form the optical wireless communication links. In this work, the selected down-link and up-link frequency bands are 500 MHz and 2 GHz, respectively. The proposed system can be implemented within the mobile telephone hand set, where the two different frequency carriers within the same frequency bands can be selected to form the up-down-link converters, which means that the frequency converter can be performed within a single system.     

Simultaneous Raman micro–spectroscopy of optically trapped and stacked cells

The combination of Raman spectroscopy and optical trapping holds great promise for single‐cell studies and is an emergent theme in microfluidic environments. Here, the evolution of the Raman signal intensity with an axial increment of the mass of the substance of interest inside a specific Raman excitation volume is investigated. Whilst Raman spectroscopy may be applied to tissue samples, solutions and single cells, there are no easily available methods to rapidly acquire signals from small cell populations. We show a simple but powerful method to record the Raman intensity signal simultaneously from a small number of trapped cells or colloidal particles using the technique of optical stacking. The Raman spectra of stacks of red blood cells and yeast cells show that this method can be applied to biological systems. We demonstrate how we may reveal biochemical fingerprints that would otherwise require long integration times for each single cell or averaging over many sequentially acquired cell spectra. There is potential to apply this method to directly attain Raman spectra from sorted sub‐populations of normal, abnormal and tumour cell lines. Copyright © 2007 John Wiley & Sons, Ltd.     

Development of an experimental set‐up for low‐temperature spectroscopic studies of matrix‐isolated molecules and molecular ices using synchrotron radiation

An experimental set‐up for studying photophysics and photochemistry of molecules in an inert gas medium (matrix‐isolated) and in the ice phase at low temperatures has been developed and commissioned at the Photophysics beamline, Indus‐1 synchrotron radiation source. This end‐station uses an in‐house‐developed closed‐cycle cryostat for achieving cryo‐temperatures (～10 K). Synchrotron radiation from the Photophysics beamline is used as the source of UV–VUV photons and the system is equipped with a Fourier transform infrared spectrometer for characterization of the molecular species formed at low temperature. Various individual components of the end‐station like closed‐cycle cryostat, experimental chamber, gas mixing and deposition systems are tested to ascertain that the desired performance criteria are satisfied. The performance of the composite system after integration with the Photophysics beamline is evaluated by recording IR and UV–VUV photoabsorption spectra of sulfur dioxide at low temperatures (10 K), both in the ice phase as well as isolated in argon matrices. Results obtained are in good agreement with earlier literature, thus validating the satisfactory performance of the system. As an off‐shoot of the study, the VUV absorption spectrum of matrix‐isolated SO₂ in argon matrix up to 10.2 eV is reported here for the first time. This experimental end‐station will provide new opportunities to study photon‐induced reactions in molecules of environmental, astrochemical and industrial importance. Details of the design, development and initial experimental results obtained are presented.     

Determination of radiative lifetimes of neutral sulphur by time-resolved three-photon VUV laser spectroscopy

Radiative lifetimes of the highly exited states s and d of neutral sulphur have been measured using time-resolved laser-induced fluorescence. The sulphur atoms were generated in a laser-produced plasma. The investigated states were populated through a two-step process involving a two-photon excitation to the lowest excited triplet state of even parity , followed by a one-photon excitation to the investigated state. We obtained ns and ns. These values are much longer than theoretically predicted ones and much shorter than those indirectely inferred from astronomical data. Received: 9 February 1998 / Accepted: 24 February 1998     

高温高压下方解石相转变的拉曼光谱原位实验研究

用热液金刚石压腔装置结合拉曼光谱技术研究了高温高压下方解石的相变过程及拉曼光谱特征。结果表明:常温条件下,体系压力增至1 666和2 127 MPa时,方解石的拉曼特征峰155cm-1消失,1 087cm-1峰分裂为1 083和1 090cm-1两个谱峰、282cm-1峰突然降至231cm-1,证明其转变为方解石-Ⅱ和方解石-Ⅲ。在起始压力为2 761MPa和低于171℃的升温过程中,方解石-Ⅲ的拉曼散射的各个特征振动峰没有变化。当温度达到171℃,方解石晶体完全变成不透明状,其对称伸缩振动峰1 087cm-1、面内弯曲振动峰713cm-1和晶格振动峰155和282cm-1均发生突变,说明方解石-Ⅲ相变生成一种碳酸钙新相。体系降至常温,该新相一直保持稳定不变,表明高温高压下方解石向碳酸钙新相的转变过程是不可逆的。方解石-Ⅲ与碳酸钙新相之间的相变线方程为P(MPa)=9.09.T(℃)+1 880。碳酸钙新相的对称伸缩振动峰(ν1 087)随压力、温度的变化率分别为dν/dP=5.1(cm-1.GPa-1),dν/dT=-0.055 3(cm-1.℃-1)。     

Emission spectroscopy of atmospheric pressure plasmas for bio-medical and environmental applications

The paper demonstrates several ways of use of the UV-vis optical emission spectroscopy of medium resolution for the diagnostics of atmospheric pressure air and nitrogen plasmas relevant to bio-medical and environmental applications. Plasmas generated by DC discharges (streamer corona, transient spark, and glow discharge), AC microdischarges in porous ceramics, and microwave plasma were investigated. Molecular (OH, NO, CN) and atomic (H, O, N) radicals, and other active species, e.g. N₂ (C, B, A), (B), were identified. The composition of the emission spectra gives insight in the ongoing plasma chemistry. Rotational, i.e. gas, and vibrational temperatures were evaluated by fitting experimental with simulated spectra. Streamer corona, transient spark and microdischarges generate cold, strongly non-equilibrium plasmas (300-550 K), glow discharge plasma is hotter, yet non-equilibrium (1900 K), and microwave plasma is very hot and thermal (∼3000-4000 K). Electronic excitation temperature and OH radical concentration were estimated in the glow discharge assuming the chemical equilibrium and Boltzmann distribution (9800 K, 3 × 10¹⁶ cm⁻³). Optical emission also provided the measurement of the active plasma size of the glow discharge, and enabled calculating its electron number density (10¹² cm⁻³).