Taking into account physical and instrumental parameters in atomic absorption spectroscopy with a continuous radiation source

We present a detailed analysis of the dependences of the absorption contours and concentration curves on various parameters in atomic absorption spectrometry with a continuous radiation source. We have developed a multifunctional application software package allowing us to calculate the emission and absorption line profiles for different elements under different physical conditions. We take into account Doppler and collisional broadening of the absorption lines, which have a complex structure as a result of the isotopic shift, hyperfine splitting of the components, and also instrumental distortion of these lines. We consider two different procedures for calculating the absorbance and do a comparative analysis of the two procedures. For all the listed cases, we can plot concentration curves and find the absorbance within the classical definition and plot the concentration curve using only a portion of the spectral width of the profile rather than the entire width. We have modeled the instrumental distortions of the spectral profile due to spectral selection, and we have analyzed their effect on the shape of the absorption contour. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 3, pp. 285–289, May–June, 2006.     

Measurement and computations for temperature dependences of self-broadened carbon dioxide transitions in the 30012←00001 and 30013←00001 bands

Using a Fourier transform spectrometer setup we have measured the self-broadened half width, pressure shift, and line asymmetry coefficients for transitions in the 30012←00001 and 30013←00001 vibrational bands of carbon dioxide for four different temperatures. A total of 46 pure CO₂ spectra were recorded at 0.008 and 0.009 cm⁻¹ resolution and at pressures varying from a few Torr to nearly an atmosphere. The individual spectral line profiles have been fitted by a Voigt profile and a speed-dependent Voigt profile, to which we have added dispersion profiles to account for weak line mixing. A comparison of the sets of results obtained for each band showed no vibrational dependence of the broadening coefficients. The self-broadening and self-shift coefficients are compared to semiclassical calculations based on the Robert-Bonamy formalism and were found to be in good agreement. The line asymmetry results are compared to line mixing calculations based on the Energy Corrected Sudden (ECS) and Exponential Power Gap models.     

仪器展宽对大气压等离子体电子密度测量的影响

实验使用两台不同的单色仪,采用光谱线型法测量了大气压氩气介质阻挡放电中的电子密度.诊断结果表明,由于不同的单色仪其仪器加宽不同,仪器加宽对总的光谱线型有较大影响.通过考虑等离子体中的各种加宽机制,采用卷积和反卷积的方法对氩原子发射谱线线型进行了分析,从整个光谱线型中分离出Stark线型,排除了仪器加宽对最终诊断结果的影响.从而最终测量了大气压氩气介质阻挡放电中的电子密度.测量得到在大气压氩气介质阻挡放电中单个放电丝存在时,电子温度为10000K时,电子密度约为3.05-3.26×1021 m-3.此方法不仅可以应用在大气压介质阻挡放电中,还可以用于测量其它大气压等离子体电子密度.     

Diode laser measurements of the first overtone HF lineshape broadened by Ar,Xe, Kr and N2

A high-resolution spectroscopy study of the HF first overtone vibrational–rotational 0–2 R(0) line profile was carried out in Ar, Xe, Kr and N₂ gas mixtures using near-IR tunable diode laser. The HF 0–2 R(0) analytical line is known as the most appropriate for laser detection of HF molecules in the atmosphere. Highly accurate collisional broadening, shift and “narrowing” coefficients were determined from the direct spectroscopic fit employing traditional Voigt, Rautian and Galatry symmetric profiles and using an asymmetric speed-dependent Voigt profile. These data make the information of modern spectroscopic databases, e.g., HITRAN2012, much more exact. A noticeable line shape asymmetry was investigated in detail. In this paper, the validity of the use of model profiles in spectroscopic fitting is severely discussed. For the first time, we draw attention to the need for physically realistic line shape models to avoid systematic errors in retrieved gas concentrations. We stress that in the case of HF, all considered model profiles serve only as ad hoc models; they may conceal the true physics of spectral line formation.     

Measurement of molybdenum ion density for L-mode and H-mode plasma discharges in the EAST tokamak

We report the measurement of total molybdenum ion density for L-mode and H-mode plasmas on EAST using spectral lines observation and calculation based on an impurity transport code. A flat-filed extreme ultraviolet spectrometer with some spatial resolution is used to obtain the radial profiles of molybdenum spectral line emissions. The absolute calibration for the extreme ultraviolet spectrometer is finished by comparing the calculated bremsstrahlung intensity with the readings of CCD detector. Molybdenum ion transport study is performed using the radial ion density profiles and one-dimensional impurity transport code STRAHL. The total molybdenum density profiles are determined from the transport analysis. The molybdenum density during L-mode and H-mode phases are obtained, which are about 3 and 4 orders of magnitude smaller than the electron density, respectively. An inward pinch is found during the H-mode phase that leads to the peaked profile of molybdenum density.     

Resonance line transfer and transport of excited atoms—III. Self-consistent solutions (2)

In this last part of our study on non-LTE line transfer with convective transport of excited atoms, we present self-consistent solutions of the radiative transfer equation and the kinetic equation of the excited two-level atoms when the excited atoms undergo elastic velocity-changing collisions. We assume pure Doppler broadening of the spectral line and investigate reflecting and destroying boundaries for the excited atoms. Concerning elastic collisions of the excited atoms, our study covers all cases, from a collisionless gas (free particle streaming) discussed in Part II of this series of papers to a collision- dominated gas with the limiting case of complete redistribution. We present arguments that the streaming pattern of the gas of excited atoms does not depend critically on the shape of the line profile. Therefore, our results for a pure Doppler profile may also be used for other line profiles (Voigt, Lorentz) in first approximation, at least when the streaming parameter η is not too large.     

Theoretical basis for the quantitative characterization of impurities in n-type III–V compound semiconductors by photoelectromagnetic spectroscopy

Theoretical results are described for the quantitative characterization of impurities by photoelectromagnetic spectroscopy. The diagnostics is based on a study of profiles of spectral lines. Line broadening is caused mainly by the influence of electric fields of charged impurities on neutral donors, in which optical transitions occur. The profile of the spectral line for the intradonor transition between 1s and 2p₀ states is calculated taking into account Coulomb correlations in the distribution of charged impurities in space at low temperatures. Calculations were carried out by computer simulation of the impurity system over a wide range of compensation degrees. This parameter can be found by a study of line profile evolution with an increase of temperature. The concentration of donors can then be found by a comparison of the experimental curve with the theoretical line profile for the corresponding degree of compensation. For low compensations an analytical theory is developed for the evolution of line profile with temperature.     

Influence of the thermal motion on the line shape and position of resonances in collinear fast beam laser spectroscopy

We derive the spectral line shape for collinear fast beam laser spectroscopy. As initial condition we take a thermally distributed ensemble into account. While the thermal velocity distribution of the fast ensemble has an asymmetric structure due to the acceleration by the electrostatic field, under typical experimental conditions the convolution with the natural line shape preserves the Lorentz profile with negligible broadening. However, the spectral line as a whole experiences a small shift depending on the temperature of the source and the acceleration . PACS 32.70.Jz     

Periodic surface profiles under the influence of anisotropic surface energy: A steady-state solution

The steady-state shape of surface profiles under the influence of anisotropic surface energy was calculated. All shape changes were assumed to occur by surface self-diffusion at elevated temperature. The orientation-dependent surface energy γ(θ) was allowed to contain a local minimum of very high curvature (cusp). The orientation of this cusp was equal to the macroscopic-orientation of a single crystal surface. No assumptions were made about the shape of the original profile. Only boundary conditions concerning the amplitude of the profile and several derivatives entered the calculation for the integration of the differential equations. The resulting profiles showed nearly flat regions centered at the cusp orientation. These results agree well with experiments and with previously published profile shapes which had been calculated dynamically. A big advantage of the steady-state calculation were short computing times, even in the case of very high curvature in γ(θ). Hence it could be shown that the profile shape converged towards a limit with increasing curvature of γ(θ). The anisotropy of γ(θ) can be evaluated from experimental shape data of faceted profiles.     

A new approach to determination of the asymmetry parameter of Stark-broadened isolated spectral lines

A new approach to evaluation of asymmetry parameters of Stark-broadened isolated spectral lines is presented. The procedure is discussed on the example of the N I line at λ = 9822.75 Å. Line shape measurements were performed using a wall-stabilized arc, operated at atmospheric pressure. The radiation of the plasma, emitted from homogeneous plasma layers in end-on direction, was measured using a grating spectrometer equipped with a two-dimensional CCD detector. Griem-like profiles, convoluted with the corresponding Doppler and apparatus profiles, were fitted to experimental data. In this way the Stark broadening parameters (electron impact widths, shifts and asymmetry) have been determined. Detailed analysis of the line shapes shows that the standard Griem-like profile does not explain the observed line asymmetry satisfactorily. The results of preliminary studies indicate that including collision-duration effects in profile calculations provides a better agreement between experiment and calculations. PACS. 32.70.Jz Line shapes, width, and shift – 52.70.Kz Optical (ultraviolet, visible, infrared) measurements.     

Spectral power density calculations for pulsed Doppler

Range-gated pulsed Doppler can be used to make localized velocity measurements within a blood vessel. A spectral flow profile can be created by stepping a sufficiently small sample volume across the lumen, but no set of spectra will correspond directly to the true velocity profile. Spectral flow profiles are affected by a complex interplay between different sources of spectral broadening. In this study we developed a systematic theoretical method which allows spectral power density functions to be calculated under a very wide range of conditions, and used it to obtain simulated flow spectra. The model was formulated analytically. It is based on the weighted-volume approach and incorporates, through the concept of a spread function, the intrinsic spectral broadening associated with a focused transducer. It can be applied for arbitrary values of the spread parameter; for non-uniform beam profiles; with maximal (continuous wave-type) or minimal (pulse wave-type) range-gated sample volumes; and for beams that intersect the flow tube axis, or are off centre. Results are presented for a Gaussian beam and parabolic flow. Simulated spectral flow profiles are given which illustrate how a profile's appearance can be altered by the different sources of spectral broadening.     

温度和压强的变化对谱线线型峰值的影响

谱线线型是用于气体浓度测量中的一个重要参数。本文基于温度(压强)变化会引起相应压强(温度)的变化这一点,考虑温度和压强同时变化对气体线型峰值的影响。通过分析氟化氢的吸收谱线,发现可用Lorentzian线型来计算峰值吸收系数的温度和压强范围都扩大,而Gaussian线型在绝大数情况下不能用来计算峰值吸收系数;在一定的温度范围和压强范围内,如果只考虑压强或温度的变化,由此计算的三种线型峰值(Gaussian,Lorentzian和Voigt)的相对误差大于0.1。因此,在计算线型峰值时,需考虑压强和温度同时变化对线型峰值的影响。最后分别讨论了甲烷、二氧化碳、一氧化碳及一氧化氮,得到与氟化氢结论相似的结论,结论的不完全相同是由于每种气体在波数、压力展宽系数、相对分子质量及温度系数上的不同而导致。     

The static approximation in the interpretation of collision broadening

The validity of the static approximation for analyses of spectral line profiles is considered. The Fourier transform of the profile of an isolated line is compared for representative cases with the unified theory, and it is shown that the simple static approximation can be used effectively to interpret low spectral resolution experiments. This result applies to the entire profile in the limit of high density, but it also applies at low density if the instrumental line width is sufficiently large. Furthermore, in the absence of turning points in the interatomic potential, the unified and static theories produce almost identical line-wing profiles. Easily evaluated criteria are provided to guide application of the straightforward static theory to the interpretation of interatomic potentials.     

土壤有机质和母质特征对典型水稻土时间序列VNIR漫反射光谱的影响与解析

为研究水稻土的光谱特征及其对不同土壤组分的响应规律,研究采集江西省发育于红粘土(RC)和红砂岩(RS)的两个水稻土时间序列为研究对象。以水稻土时间序列为研究对象的优势在于,样本有相同的土地管理背景,母质和种稻时间成为土壤发育过程中的两个主导差异因素,进而能够对土壤有机质(SOM)和母质特征在光谱上的响应特征进行研究。使用Cary 5000分光光度计采集样品在350～2 500 nm波段的漫反射光谱信息,并从土壤层次、成土时间和成土母质三个方面,论述了在VNIR波段水稻土中的主要有机质和无机矿物组成的光谱响应特征和规律。实验结果表明：对于单一母质的时间序列土壤样品而言,SOM增加是人为水耕条件下土壤演变的重要趋势之一,用PC_1 Score表征的整体反射率与SOM含量间可建立精度较高的模型(R2_RC=0.91,R2_RS=0.79),且在SOM含量低值区也能保证较高精度;1 400,1 900和2 200 nm三个波段处的吸收强度主要与母质中的矿物有关,在土壤剖面中下层土壤受人为作用较弱、土层吸收强度较大,且相同母质的土壤光谱,在这三个波段有相同的吸收峰强度比值,可作为判断母质同质的依据;母质成分的差异会显著影响土壤光谱的波形以及吸收强度,在建模中充分考虑母质因素将使模型更具解释性。     

The effect of rate of stimulation on perception of spectral shape by cochlear implantees

The effect of rate of stimulation on spectral shape perception was measured in six users of the Nucleus CI24 cochlear implant. Three spectral shapes were created by using three profiles of current across seven electrode positions. Each current profile was replicated in three stimuli that interleaved stimulus pulses across the seven electrodes with cycle rates (rate per electrode) of 450, 900, and 1800 Hz. The stimulus space resulting from a multidimensional scaling experiment showed a clear dimension related to the rate of stimulation that was orthogonal to the dimension related to the spectral shapes. A second experiment was performed with the same subjects to investigate whether the perceptual dimension related to rate in Experiment 1 could be attributed to different perceptual flatness of the profiles at different rates. In Experiment 2, the rate of stimulation was fixed at 900 Hz and three profiles were created for each spectral shape that differed in flatness. This experiment did not, however, result in an independent perceptual dimension related to the flatness of the profile. In conclusion, rate of stimulation provided an independent perceptual dimension in the multiple-electrode stimuli, in spite of the rates being not discriminable or barely discriminable in single-electrode stimulation.     

Correction of self-absorption spectral line and ratios of transition probabilities for homogeneous and LTE plasma

Expressions for fundamental spectral line parameters are reported for Gaussian and Lorentzian shape profiles for homogeneous plasma at equilibrium in presence of the self-absorption. These expressions for Lorentzian profiles are applied to the determination of the ratios of transition probabilities and the ratios of optical thicknesses by a new method that we propose in this article. The self-absorption is computed by spectral line profiles with a Simplex algorithm program fitting. Applications to some experimental lines illustrate the appropriate corrections.     

Stark broadening of the overlapping 4471.48 Å HeI line in a plasma. II. Nonmarkovian and ion dynamic effects

The inclusion of a frequency-dependent collision operator in the line shape expression is investigated quantitatively for the 4471 Å overlapping HeI line. We compare at several electron densities frequency-independent (markovian) profiles with frequency-dependent (nonmarkovian) profiles taking into account incomplete electron-atom collisions. No significant discrepancies appear in the domain of validity of the impact approximations (|Δω| ? ωp_e), whereas for the far wings important differences may be found. At the extrema (two peaks, one dip) the nonmarkovian intensities prove to be the higher ones. For a modest electron density, the inclusion of ion dynamic shielding introduces more modifications then nonmarkovian effects. In the blue wing, the frequency-dependent profile lies below the frequency-independant profile in accord with the hydrogenic behavior for that part of the line shape in the presence of a large perturber density.     

Rapid and accurate calculation of the Voigt function

Two general techniques significantly improve both the accuracy and speed of spectral line shapes that use only the complex Voigt function. Such line shape functions include the Voigt line profile, which is closely related to the real part of this function. The first technique is a new algorithm, which trades a small amount of RAM (at most 1.49 megabytes) for a considerable gain in speed and accuracy. The accuracy is one part in 10⁶ of the function itself. In addition, the derivatives of the function with respect to x and y are returned with an accuracy of 0.5%. The algorithm is up to nine times faster than the Drayson or Humlí?ek algorithms and about two orders of magnitude more accurate. A second independent improvement is a set of simple criteria to decide when an evaluation is required and when a value of zero can be assumed. This section alone can reduce the computation time by three orders of magnitude or more and it can be applied to algorithms using any Voigt approximation.     

Principle of temperature,velocity and pressure of upper atmospheric wind measurement for the Voigt profile

Using the accurate expression of the Fourier transform of the pure Voigt spectral line profile, we present the principle of the passive optical method to measure temperature, velocity, and pressure of atmospheric wind for the Voigt profile. Through discussion, from the Gaussian, Lorentzian and Voigt profiles, we find that velocity will not be affected, pressure can be derived for Lorentzian and Voigt profiles, and temperature will be affected greatly. By simulation and comparison, we find that temperature derived from the Voigt profile is greater than that from the Gaussian profile, and it is less than that from the Lorentzian profile. This discussion will be significant in accurate upper atmospheric wind measurement.     

全频域下窄线宽激光器光谱线宽的分析

窄线宽激光器的线宽表征方式通常采用延时自外差法测量技术。该技术是通过延时光纤差拍产生一个与待测激光线宽相关的洛伦兹频谱,因此该频谱只具有单一的线宽表现形式。为了能够观察到激光器的线宽和频率噪声在其傅里叶频率分布下的完整特性,报道了一种基于β算法计算窄线宽激光器线宽的方法。该方法是结合频率噪声中的白噪声和1/f噪声分别诱导不同激光线型的理论,从而确定激光线宽。首先,对β算法的基本原理进行了详细的分析说明。通过基于维纳-辛钦定理,分析了窄线宽激光器不同频率范围内的频率噪声和激光线宽的依赖关系。阐明了在截止频率趋于0和无穷大的两个范围条件时,激光频谱特性从高斯线型向洛伦兹线型演变。同时推导出使两种线型转换的截止频率表达式,并将其转换为频率噪声函数,该函数定义为β分子线。此时频率噪声分量中高斯线型的总和即为激光线宽计算公式;其次,对窄线宽激光器的频率噪声和激光线型进行数值仿真。将通过OEwaves公司的OE4000互相关零差相位/频率噪声自动测试系统测得的频率噪声谱密度,带入β算法理论公式中。结果显示：1/f噪声导致激光呈现高斯线型,线宽随截止频率的增加而增大。而白噪声将导致洛伦兹线型,线宽不再随截止频率而改变。此外,在低频区域,频率噪声电平远大于其傅里叶频率,噪声调制系数较高,该部分噪声可以决定线宽大小。因此,高斯线型区域对应的频率噪声的积分,即为待测激光器的线宽;在高频区域,频率噪声电平与其傅里叶频率相差较小,频率波动较快,噪声对线宽影响可以忽略。并且频率带宽在截止频率范围内,计算的线宽误差较小。最后,实验上运用β算法对RIO公司的1 550 nm低噪声窄线宽激光器的频率噪声功率谱密度进行积分计算,成功获得了其不同傅里叶频率分布下对应的激光线宽值。其中β分子线将频率噪声中的白噪声和1/f噪声分隔两部分：当频率噪声谱密度大于β分子线时,激光即为高斯线型,线宽随频率积分带宽的增加而减少;而频率噪声谱密度小于β分子线时,激光呈现洛伦兹线型,线宽为定值不再改变。同时为了对β算法进行实验验证,搭建了延迟光纤为50 km、移频频率为60 MHz的延时自外差法测量系统。对注入电流为110 mA的RIO 1 550 nm低噪声窄线宽激光器的线宽进行实验测量,测量结果表明激光线宽为1.8 kHz,与上述β算法中2.8 kHz的频率带宽积分结果一致。充分证明了此算法的准确性。β算法可以对任意类型的窄线宽激光器进行线宽表征,对窄线宽激光器的研究具有重要意义。