Influence of the 61 S 0–63 P 1 resonance on continuous Lyman-α generation in mercury

Continuous coherent radiation in the vacuum ultraviolet at 122 nm (Lyman-α) can be generated using sum-frequency mixing of three fundamental laser beams in mercury vapor. One of the fundamental beams is at 254 nm wavelength, which is close to the 6¹ S ₀–6³ P ₁ resonance in mercury. Experiments have been performed to investigate the effect of this one-photon resonance on phase-matching, absorption and the nonlinear yield. The efficiency of continuous Lyman-α generation has been improved by a factor of 4.5.     

High-power Lyman-alpha source generated with an ArF excimer laser

We report high-power vacuum-ultraviolet (vuv) generation at the Lyman- alpha wavelength of 121.6nm , using a simple experimental system. vuv radiation is produced through two-photon-resonant difference-frequency mixing with a tunable ArF excimer laser and a Nd:YAG-pumped dye laser. Using phase-matched mixtures of Kr and Ar at a total pressure of 650 mbar, we produced 7-microJ energies at Lyman- alpha in approximately 5ns (1.3kW) , as measured directly with a pyroelectric energy probe. Measurements indicate that higher powers are possible with system optimization. A tuning range of 0.1nm was achieved for a fixed gas mole fraction at a total pressure of 650 mbar. Qualitative agreement is found between measured tuning profiles and theoretical predictions.     

Absolute cross section measurement of Lyman-α radiation production

An absolute cross section has been determined for Lyman-α radiation production during collision of a low-energy atomic hydrogen ion and laser-excited sodium vapor.     

Lyman- alpha(1) decay in hydrogenlike ions: interference between the E1 and M2 transition amplitudes

For the Lyman- alpha(1) transition (2p(3/2)-->1s(1/2)) in hydrogenlike ions an interference between the leading E1 decay channel and the much weaker M2 multipole transition gives rise to a remarkable modified angular distribution of the emitted photons from aligned ions. This effect is most pronounced for the heaviest elements but results in a still sizable correction for medium- Z ions. For the particular case of hydrogenlike uranium where the angular distribution of the Lyman- alpha(1) x rays following radiative electron capture has been measured, the former variance with theoretical findings is removed when this E1-M2 interference is taken into account.     

A new method of Lyman-α radiation generation

An efficient method of Lyman-α generation has been demonstrated and involves collisions of hydrogen ions and laser-excited sodium vapor. About 80% enhancement in the Lyman-α production rate during collisions of atomic hydrogen ions with excited sodium Na₂ has been observed to occur at about 7 eV kinetic energy in the laboratory frame of reference.     

Generation of narrowband tunable VUV radiation at the Lyman-α wavelength

Tunable narrowband VUV radiation has been generated at the Lyman-α wavelength $\text{λ =}\text{1216}\text{\&}\text{A}\text{ring}$; by frequency tripling in krypton the frequency-doubled output of a powerful dye laser system which is excited with the second harmonic of a Nd-YAG laser. 5 ns long UV dye laser pulses ($\text{λ =}\text{3646}\text{A}\text{?}$) of 1.8 MW peak power yielded VUV light pulses of 2.2 W (5.4 × 19⁹ photons/pulse). The bandwidth of the dye laser radiation could be narrowed to 8.7 × 10^-3cm^-1 (4.6 × 10^-3 Å). The expected bandwidth of the VUV is less than 5.2 × 10^-2cm^-1 (7 × 10^-4 Å). The tunable VUV radiation is used for the recording of the absorption spectra of the Lyman-α resonance transitions in atomic hydrogen and deuterium with doppler-limited resolution.     

Asymmetry of the natural line profile for the hydrogen atom

The asymmetry of the natural line profile for transitions in hydrogenlike atoms is evaluated within a QED framework. For the Lyman- alpha 1s-2p absorption transition in neutral hydrogen this asymmetry results in an additional energy shift of 2.929 856 Hz. For the 2s(1/2)-2p(3/2) transition it amounts to -1.512 674 Hz. As a new feature this correction turns out to be process dependent. The quoted numbers refer to the Compton-scattering process.     

Mechanisms of the destruction of micron conductors by an electromagnetic pulse with a subnanosecond front

The results of the experiments on the destruction of micron-diameter conductors by an electromagnetic pulse, which is generated in an inhomogeneous coaxial line by a high-voltage power source and has a subnanosecond front, are reported. The role of electrodynamic processes in the surface layer of microconductors and in environment in the formation of the spatial structure of the plasma channel and in the transformation of the energy of the source to the energy of radiation has been revealed. The spectral characteristics of the radiation of the plasma channel have been analyzed. It has been shown that the radiation spectrum at the time of the formation of the plasma corona is continuous. The most intense spectral lines of copper (510.554, 515.324, 521.82 nm) appear at ∼3 ns after the formation of the plasma corona. The temperature has been estimated from the ratio of the intensities of the spectral lines as T _e ∼ 0.7 eV.     

Earth-based gravitational wave detection from pulsars

The main features of continuous gravitational radiation bathing the Earth has been evaluated for a set of 558 pulsars. In particular, the maximum gravitational wave background and the maximum gravitational wave emission have been evaluated for each source and compared with the projected sensitivities of the planned Earth based very long baseline interferometric antennas for gravitational wave detection, like VIRGO and LIGO. This study shows that such detectors have a good chance of detecting gravitational waves emitted from this class of astrophysical sources.     

一种新型微束斑X射线源的研究

采用高效长寿命的LaB6单晶阴极电子枪作为电子束发射系统、轻便的等径双圆筒静电系统作为聚焦系统等技术研究了一种新型台式微束斑X射线源.通过在综合测试仪上的初步实验研究,表明该微束斑X射线源不仅可以连续辐射,而且可以脉冲辐射X射线,输出X射线束斑小、亮度高.此外,该台式X射线源具有体积小、重量轻,使用寿命长、造价低,可灵活移动等优点.     

1s lamb shift in hydrogenlike uranium measured on cooled, decelerated ion beams

The Lyman- alpha transitions of hydrogenlike uranium associated with electron capture were measured in collisions of stored bare U (92+) ions with gaseous targets at the storage ring ESR. By applying the deceleration technique, the experiment was performed at slow collision energies in order to reduce the uncertainties associated with Doppler corrections. From the measured centroid energies, a ground state Lamb shift of 468 eV+/-13 eV is deduced which gives the most precise test of quantum electrodynamics for a single electron system in the strong field regime. In particular, the technique applied paves the way towards the 1 eV precision regime.     

Spektraluntersuchungen im Gebiet um 1mm Wellenlänge

Based on the mass-oscillator principle, a pulsed radiation source has been developed which emits a continuous spectrum at the long wavelength end of the infrared region. In order to fully utilize the short radiation pulses, this generator is used in conjunction with a crystal rectifier, responding to the instantaneous value of the radiation power, and a pulse-lock-in demodulator. At wavelengths ?-1.5 mm this combination-as compared to the high pressure Hg arc-yields an increase of the spectroscopic information flux rate of the recorded spectra by more than an order of magnitude. The limited reproducability of the basic mass-oscillator spectra necessitates the alternating recording of the two spectra which are to be compared.     

舰船辐射噪声模拟发射系统的设计研究

本文依据典型舰船噪声的频谱特性规律,设计研制了一套舰船辐射噪声发射系统实验样机,包括信号结构设计、换能器选择配置、系统构成设计等,本噪声模拟发射系统具有100Hz～16kHz频带噪声的模拟发射功能,包括线谱、连续谱成分,频谱分配和谱线形式可调可控,信号总声源级动态范围达60dB。     

Cosmological magnetic fields

Magnetic fields are observed not only in stars, but in galaxies, clusters, and even high redshift Lyman-α systems. In principle, these fields could play an important role in structure formation and also affect the anisotropies in the cosmic microwave background radiation (CMB). The study of cosmological magnetic fields aims not only to quantify these effects on large-scale structure and the CMB, but also to answer one of the outstanding puzzles of modern cosmology: when and how do magnetic fields originate? They are either primoridial, i.e. created before the onset of structure formation, or they are generated during the process of structure formation itself.     

Predictive estimation of vacuum ultraviolet emission intensity in a low-pressure inductively coupled hydrogen plasma based on the branching ratio technique

Vacuum ultraviolet (VUV) emission has recently attracted attention in low pressure processing plasmas because of the possibility of high-energy photon damages on the substrates. To quantify the VUV induced damages during the plasma processes, it is need to use of a VUV spectrometer equipped with vacuum systems not readily available in industries. In this work, therefore, we report a simple method to estimate the VUV emission intensity of hydrogen plasmas utilizing a conventional visible spectrometer widely used in plasma processes. From the measurement of hydrogen emission spectra in the visible wavelength region, the VUV emission line (Lyman-β) was calculated using the branching ratio technique and enabled the estimation of Lyman-α emission intensity based on the Boltzmann relation with given plasma parameters. In addition, it was found that the method could also predict the VUV emission intensity for high density hydrogen plasma cases by considering the self-absorption effect by hydrogen atoms.     

Shrinking Orbital Radii–An Ellipsoid Theory Requisite

The ellipsoid theory of electromagnetic radiation from a moving source is consistent with the observed reduction in atomic frequencies if, and only if, orbital radii also shrink by the alpha factor.     

Coherent excitation of then=3 level of hydrogen in a field free region

The theory of coherent excitation of then=3 level of atomic hydrogen by electron impact is studied using density matrix techniques. A set of multipole parameters is defined which allows to characterise coherently excited states with different angular momenta. Numerical results of these parameters, calculated in first order Born approximation, are tabulated for several energies and angles. Angular distribution and polarization of Balmer-α radiation are expressed in terms of the initial multipole parameters for the case that scattered electrons and emitted photons are detected in coincidence. The theory of cascade effects is briefly considered and applied to the case where scattered electrons and Lyman-α photons are detected in coincidence, generalising earlier formulations. Most of the formulas presented here are quite general and can be applied, for example, to an analysis of light emitted by beam foil excited hydrogenic levels.     

Start current and gain measurements for a Smith-Purcell free-electron laser

Coherent Smith-Purcell radiation is a promising source of coherent emission in the THz domain. Although it has been observed in several experiments, some physical quantities related to the bunching of an initially continuous beam had not yet been studied experimentally. Among them, the gain as function of beam current, together with the value of the start current, needed to be addressed. We report here their measurements in a microwave experiment using a sheet beam. A start current of about 20 A/m was found. Two-dimensional simulations with a very thin beam agree well with our results.     

Brilliant,coherent far-infrared (THz) synchrotron radiation

A new technology for generating steady state, brilliant, broadband, coherent, far-infrared (FIR) radiation in electron storage rings is presented, suitable for FIR spectroscopy. An FIR power increase of up to 100 000 compared to the normal, incoherent synchrotron radiation in the range of approximately 5 to approximately 40 cm(-1) could be achieved. The source is up to 1000 times more brillant compared to a standard Hg arc lamp. The coherent synchrotron radiation is produced in a "low alpha" optics mode of the synchrotron light source BESSY, by bunch shortening and non-Gaussian bunch deformation.     

低本底α/β仪测量饮用水中总 α放射性活度的实验室质量控制

总α放射性活度检测可避免繁琐的低水平放射性核素鉴定,是饮用水放射性水平的初筛监测手段之一。近年调查显示：我国饮用水总α放射性活度稳定保持在较低水平。低水平的α放射性活度检测需要高质量实验室质量控制,以保证检测结果的准确度。实验采用低本底α/β仪,以α闪烁体为探测器,吸收样品核辐射α粒子能量,使有机闪烁体分子ZnS(Ag)发射荧光,通过统计单位时间内的闪烁体发射荧光数目正比于核衰变数目,由此感应有效厚度样品层辐射的α粒子计数信号,对饮用水中总α放射性活度浓度检测。首先,实验以表面α粒子发射率为2～20粒子数/s(2π 方向)的电镀源测定本底α计数效率(CPS)。然后,在最优化的本底值、工作源效率、串道率等参数条件下,运用标准曲线法测定标准源α计数效率(ε)。最后,结合CPS和ε代值计算质控样总α体积活度、计数平均值(或总体积活度平均值)和标准偏差s,并以±s为上辅助线(upper auxiliary limit, UAL)和下辅助线(lower auxiliary limit, LAL),以±2s为上警告线(upper warning limit, UWL)和下警告线(lower warning limit, LWL),以±3s为上控制线(upper control limit, UCL)和下控制线(lower control limit, LCL),绘制本底α计数、标准源α计数和质控水样总α体积活度的均数质量控制图,以考察CPS和ε对质控水样总α体积活度测量质量控制的影响。数据结果显示,以电镀239Pu为工作源,以241Am为标准源,样品放置时间24 h,测量时间60 min,铺样厚度4 mg·cm-2时,本底α计数率CPS=0.000 37 s-1,工作源探测效率η=94.35%,α→β串道率Fα=0.41%,标准源计数效率ε=7.25%(Y=1.323X-5.285,R2=0.991 5)。统计结果显示：40份空盘本底α计数的受控范围为-1.61~5.82,33个点落在UAL与LAL范围内,2个点落在UWL与UAL范围内,3个点落在LWL与LAL范围内,2个点落在UWL与UCL之间,本底测量受控良好;24份标准源α计数的受控范围523.7~644.3,14个点落在UAL与LAL范围内,5个点落在UWL与UAL范围内,5个点落在LWL与LAL范围内,标准源测量受控良好;20份质控水样总α体积活度受控范围为0.007 91~0.057 86 Bq·L-1,11个点在UAL与LAL范围内,5个点在UWL与UAL范围内,3 个点在LWL与LAL范围内,1个点在LWL与LCL之间,质控水样测量实验室质量控制良好。因此,以α闪烁探测器对低水平α放射性计数测量时,控制α本底计数和标准源计数效率,这两个α统计计数中的主要不确定度来源,可以实现水样中总α放射性活度检测的有效实验室质量控制。