CO的第二泛频(3←0)跃迁谱线线形强度测量研究

CO分子是监测大气污染气体的优异示踪气体,要实现对CO分子实时监控就需要做到对气体浓度的精确快速测量。气体分子浓度测量可以利用测量吸收光谱和谱线线形强度得到,CO的(3←0)泛频谱带是吸收较弱的跃迁波段,利用以干空气为缓冲气体的200μmol/mol的CO混合物,基于稳频的光腔衰荡装置测量了在温度293K、压力13~93kPa下的CO分子R支3条跃迁谱线的吸收光谱。HTP(Hartmann-Tran profile)线形被用来获得这些谱线的线形强度,测量结果的相对标准不确定度优于1%,与国际HITRAN、HITEMP和GEISA光谱数据库比较,相对偏差小于4%。     

Actively controllable EIT-like resonance between localized and propagating surface plasmons for optical switching

We theoretically investigate the plasmonic interaction between radiative localized surface plasmon resonances and subradiative propagating surface plasmon modes in a nanostructure consisting of a periodic array of gold nanobars and an optically thick gold film, separated by a silica dielectric spacer layer. A controllable transparency window within the broad dipole resonance profile is observed clearly in the reflectance spectra via tailoring the length of the bar, the periodicity of the nanoparticle array, or the incident angle of applied field, respectively, a classic analog of electromagnetically induced transparency (EIT). We believe that the last excitation configuration is particularly beneficial for the realization of active manipulation of plasmonic optical switching without using coupling/control fields required in the conventional EIT scheme.     

Manipulating the focal shift in a medium with electromagnetically induced transparency

By approximating the index distribution of a medium with electromagnetically induced transparency (EIT) as a gradient index (GRIN), propagation laws in the medium with EIT can be obtained. Transmission properties in an optical system with an EIT medium are analyzed. The results show that, unlike the case in the ordinary GRIN medium, the refractive index of EIT medium has the better controllability. Consequently, discussions are focused on how to conveniently manipulate the focal shift of the input in the EIT by means of controlling the index of the medium. Additionally, the speckle radius on the location of the actual focus can be diminished by adjusting some parameters in the EIT medium.     

Experimental evaluation of 3D electrical impedance tomography with total variation prior

In electrical impedance tomography (EIT), two- or three-dimensional (2D or 3D) distribution of the electrical conductivity is reconstructed based on potential measurements from the surface of the object. In many industrial and medical applications of EIT, the conductivity distribution is discontinuous – due to, e.g. phase or tissue boundaries. Previous studies have shown that such features in the conductivity can be preserved by using total variation (TV) prior model in the EIT image reconstruction. Recently, both 2D and 3D TV models have been utilized in EIT simulation studies. This far, however, EIT reconstructions with TV models have been evaluated experimentally only in 2D cases or translationally invariant 3D cases. In this paper, an experimental study of EIT with a TV prior in a 3D geometry is presented. In addition, we propose the selection of the prior parameters in the TV model based on the prior information of materials in the target, and their conductivity ranges. The results demonstrate the robustness of the proposed parameter selection strategy, and verify that the use of the TV prior yields sharp reconstructions in 3D EIT.     

Inclusion boundary reconstruction and sensitivity analysis in electrical impedance tomography

Reconstruction of conductive inclusions in a homogeneous background medium is commonly seen in electrical impedance tomography (EIT). One of the methods to deal with the inclusion reconstruction problems is the shape-based method. With prior knowledge of conductivity of target inclusions, the boundary of inclusions is parameterized by several shape coefficients and recovered from EIT measurements. This paper presents a shape-based inclusion reconstruction method and its numerical implementation with boundary element method (BEM). A shape perturbation method (SPM) is proposed to calculate the shape sensitivity in EIT. To evaluate the accuracy of the presented method, a series of numerical tests are conducted. The characteristics of EIT shape sensitivity are analysed. Some factors influencing the reconstruction performance are discussed.     

Application of pulsed buffer gas jets for the signal enhancement of laser-induced breakdown spectroscopy

We report a new simple method for the signal enhancement of laser-induced breakdown spectroscopy using a pulsed buffer gas jet. The signal is enhanced up to more than 10 fold by using argon gas jets, which are injected through a pulsed nozzle onto the sample area to be analyzed. By synchronizing the buffer gas pulse with the laser pulse and optimizing the spatial arrangements between the gas jet and the sample surface, we have successfully exploited the useful properties of the buffer gas in open atmosphere. The signal-enhancement mechanism in our buffer gas jet has been discussed. Also, applications to various samples (metal, glass, and paper) have been demonstrated.     

Atomic coherence induced Kerr nonlinearity enhancement in Rb vapour

The Kerr nonlinear index of refraction for rubidium atoms is measured by using an optical ring cavity with and without electromagnetically induced transparency (EIT). Significant enhancement and inhibition of the Kerr nonlinear index is observed near resonance with EIT. The nonlinear index of refraction is measured as functions of probe and coupling frequency detunings, respectively, with and without the presence of EIT. A simple theoretical calculation including Doppler broadening is presented and is found to be in good qualitative agreement with the experimentally measured results.     

Electromagnetically induced transparency and steady-state propagation characteristics in Doppler broadened diamond systems

We explore the feasibility of attaining simultaneous electromagnetically induced transparency (EIT) and efficient nonlinear generation in different configurations of Doppler broadened diamond (double-cascade) systems such as, the frequency up-conversion, nearly degenerate and degenerate scheme. We show that EIT and nonlinear generation efficiency depend critically on the type of residual Doppler broadening present in each of the two cascade subsystems constituting the diamond system. Furthermore, it is observed that nonlinear generation with perfect EIT simultaneously in both subsystems is not possible as the process of nonlinear generation actually tends to oppose EIT. Yet in an extended medium, on resonance field propagation under matched conditions for probe and generated signal can occur when a balance (equilibrium) is established between these two competing processes.     

EIT信号对CPT磁力仪弱磁测量性能的影响

针对现有磁力仪测量数百纳特斯拉弱磁场存在精度低和便携性差等问题,提出一种通过压窄CPT磁力仪EIT信号线宽来实现弱磁场测量的方法.该方法是根据EIT信号磁场测量仿真模型,采用相敏检波二阶微分信号获得磁力仪灵敏度系数,并根据最佳灵敏度系数分析得出EIT信号分离条件及其线宽对弱磁场测量性能的影响.仿真和试验结果表明:具有窄...     

Multinozzle gas-dynamic molecular-beam source

The results of an experimental investigation of a multinozzle gas-dynamic molecular-beam source, in which the working material is introduced directly into a supersonic jet of a buffer gas, are presented. The source is designed to create slow cold beams of atoms and molecules. Time-of-flight profiles of the beams of the N₂ buffer gas and the working material SF₆ formed by a source with six nozzles are presented. The measured parameters of the flow field of the buffer gas are compared with the results of calculations for an axisymmetric nozzle with an inner body having an annular critical cross section. The results obtained show that multinozzle designs can be used, in principle, in molecular-beam sources instead of axisymmetric nozzles with an inner body. This permits relaxation of the requirements placed on the accuracy needed in fabricating such sources, reduction of the buffer gas flow rate, and the employment of fairly simple schemes for recycling the buffer gas. Pis’ma Zh. Tekh. Fiz. 23, 47–54 (October 26, 1997)     

The Scanning Data Collection Strategy for Enhancing the Quality of Electrical Impedance Tomography

This paper addresses a scanning data collection strategy in electrical impedance tomography (EIT) to enhance the quality of an impedance image by expanding the electrode number. This scanning EIT (SEIT) system rotates the electrode pairs at a small angle, and then, the measurement electrodes can scan around the circumference of a phantom tank. The numerical simulations examine the reconstructed result by using a cylindrical model with two conductivity varieties. The experimental results illustrate the reconstruction images with and without the SEIT from 2-D real measurement data. Compared with conventional EIT images, the images reconstructed from the scanning data collection strategy exhibit high resolution and are clearer. This paper provides a feasible configuration to reduce the noise and improve the resolution of the impedance image.     

Influence of saline media on the fluorescence emission of Bacillus spores

Single-particle levitation in conjunction with 264.3-nm laser excitation is used to measure the fluorescence emission of individual particles of Bacillus globigii spores. With precise humidity control, the fluorescence emission of wetted and desiccated Bacillus spore particles is measured from 300 to 450 nm. Comparison of spectra for Bacillus spores suspended in a standard buffer aqueous solution and for a desiccated 10-mum-diameter aggregate Bacillus spore particle shows that the spectra is virtually indistinguishable. However, at 85% relative humidity, corresponding to a 4.5M sodium chloride solution, the spore spectra redshifts by approximately 25 nm. It is postulated that the spectra redshifting is a result of specific interactions between the tyrosine fluorophore of the Bacillus spore and the phosphate moieties in the buffer solution.     

Effect of argon buffer and the UV preionization regime on the electric-discharge XeCl laser parameters

The gas discharge and output radiation parameters were studied in XeCl lasers with various buffer gas compositions (argon vs. neon) and different types of excitation regimes (fast vs. quasi-stationary) in the preionization source. The intervals of specific energy for the neon-and argon-based buffer gas mixtures are 10–125 and 45–360 J/(l atm), respectively. The specific parameters of radiation in the neon-and argon-based buffer gas mixtures depend on the energy required for the UV preionization. For high-power UV preionization sources, the output parameters of lasers using argon-based gas mixtures may exceed those obtained with neonbased mixtures.     

Ion sputtering of cathode surface in a hollow cathode discharge

In this paper, ion sputtering of cathode material in a specific type of glow discharge—hollow cathode discharge (HCD)—is analyzed. To estimate both real sputtering yield and screening effect of the buffer gas, two different methods—combination of experimental and analytical approach (applicable for Ar buffer gas only) and use of Monte Carlo simulations—are used. The latter, which is introduced for the first time here, can be used for any buffer gas. Real sputtering yield S_k is estimated by Monte Carlo simulations for several commercial HCD lamps with Ne buffer gas: Ne-Li (0.046), Ne-As (0.862), Ne-Ca (0.337) and Ne-Cd (1.069).     

基于导模共振效应的多通道窄带滤光片的设计

基于导模共振效应设计了几种多通道窄带滤光片,并利用严格耦合波法分析其光谱特性。在设计的单层滤光片的基础上增加第一层高折射率缓冲层,当厚度为523.8 nm和689.2 nm时,得到双通道和三通道的反射峰,在此基础上增加第二层厚度为768 nm的低折射率缓冲层,得到四通道的反射峰。另外,通过调节单层滤光片的入射角度得到对称的双通道反射峰。     

Constrained image reconstruction for magnetic detection electrical impedance tomography

Magnetic detection electrical impedance tomography (MD‐EIT) produces images of conductivity from magnetic field measurements taken around the body. The ill‐conditioned nature of the MD‐EIT inverse problem is improved by limiting the number of unknowns to be solved. In this article, a method of iterative grid refinement for MD‐EIT, which produces images significantly better than unconstrained solutions, is described. © 2008 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 17, 379–382, 2007     

Image reconstruction using simulated annealing in electrical impedance tomography: a new approach

Image reconstruction in electrical impedance tomography (EIT) deals with an ill-posed and non-linear inverse problem. It has the objective of minimizing the difference between simulated (virtual) object data and electric voltage measurements performed on a non-simulated (real) object. In this paper, a new approach to the simulated annealing method applied to the reconstruction of EIT images is described. The main advantage of this approach is that all conductivity parameters are updated simultaneously. Most methods that employ simulated annealing to the problem of EIT usually evaluate each conductivity parameter individually resulting in high computational cost. The algorithm was tested both with computationally generated data and with measurements performed on a physical tank. In both cases, the method was able to make data inversion, determining the position, the dimensions and the conductivity of materials in an opaque object plane.     

Using phase dynamics in EIT to probe ground state relaxation in rubidium vapor

We have studied a time response of electromagnetically induced transparency (EIT) in a rubidium vapor to a rapid variation of optical phase. We have observed a very fast growth of the absorption when the phase of the optical field has been abruptly changed, followed by a slow return to the level of steady-state absorption. The recovery time decreases with increasing optical power. A simple theoretical analysis shows that under our experimental conditions the low power limit of the recovery time is determined by the ground relaxation time. In our case it is defined by a time-of-flight of rubidium atoms through laser beam. The obtained value of the ground state relaxation time is in a good agreement with result of direct measurements by ‘relaxation in the dark’ method. Our technique based on phase dynamics in EIT can be used for investigation of the ground state relaxation and the fast control of EIT.     

大型活塞式压缩机性能试验装置中缓冲器的应用研究

一般采用气体流量计前加装缓冲器消除压缩机性能试验装置中气流脉动对测量精度的影响。本文分析2种适用于大型活塞式压缩机性能试验装置的缓冲器容积的计算方法,认为针对压缩机性能试验装置中的微小脉动气流,德国BORSIG的计算方法更加适合。搭建大型活塞式压缩机性能试验装置,利用经理论计算设计的缓冲器进行试验,发现即使在最大测试流量的情况下,缓冲器仍然可以很好地削减气流脉动的影响,从而大大提高压缩机试验装置的试验精度。     

Phase time delay and Hartman effect in a one-dimensional photonic crystal with four-level atomic defect layer

The Hartman effect is revisited using a Gaussian beam incident on a one-dimensional photonic crystal (1DPC) having a defect layer doped with four-level atoms. It is considered that each atom of the defect layer interacts with three driving fields, whereas a Gaussian beam of width w is used as a probe light to study Hartman effect. The atom–field interaction inside the defect layer exhibits electromagnetically induced transparency (EIT). The 1DPC acts as positive index material (PIM) and negative index material (NIM) corresponding to the normal and anomalous dispersion of the defect layer, respectively, via control of the phase associated with the driving fields and probe detuning. The positive and negative Hartman effects are noticed for PIM and NIM, respectively, via control of the relative phase corresponding to the driving fields and probe detuning. The advantage of using four-level EIT system is that a much smaller absorption of the transmitted beam occurs as compared to three-level EIT system corresponding to the anomalous dispersion, leading to negative Hartman effect.