On the radiation of a planar undulator with constant magnetic field on its axis taken into account

The intensity of undulator radiation, distortion of the spectrum, and the broadening of spectral lines of a planar undulator with a constant component of the magnetic field on its axis are studied using the technique of generalized special functions. Based on the obtained mathematical solutions, it is shown how the choice of certain values of the undulator parameters makes it possible to decrease the distortions of its radiation spectrum. The dependence of distortion of the spectral lines on the number of periods, the magnetic field, and other undulator parameters is determined analytically. The broadenings of the spectral lines caused by homogeneous and inhomogeneous effects produced by the constant-field components in undulators are compared. The possibility of the influence of the Earth’s magnetic field on the radiation of an undulator with a large number of periods is analyzed.     

A translational heat-bath model for foreign gas broadening of spectral lines—I. Variational methods

A new formalism of Green's functions is used for discussing foreign gas broadening of atomic spectral lines. In the present work, the translational degrees of freedom are separated from the internal degrees of freedom by a translational heat-bath model. The conditions of a heat bath, weak and binary collisions lead to a Lorentzian line shape in the center of the line and to a rapid decay of the line wings. For weak interaction potentials, a new explicit expression for line broadening, which demonstrates this behaviour, is obtained.     

Calculation of the self-broadening coefficients of water vapor absorption lines using an exact trajectory model

The broadening coefficients γ and δ of vibrational-rotational absorption lines of water vapor by self-pressure are calculated. The exact trajectory model is used, in terms of which the real and imaginary parts of the resonance wave functions are calculated. The reconstruction accuracy of the coefficients γ is considerably improved compared to the model of rectilinear trajectories.     

Effects of collision-broadening on apparent spectral absorption coefficients for dimers

The Mayer-Goody random model for the distribution of spectrum lines over an observational intervals is used in order to demonstrate that the apparent spectral absorption coefficient for pressure-broadened dimer-bands can depend quadratically on the total pressure, even in the non-transparent absorption regime. Therefore, reported data which were obtained under these conditions depend still on the parameters describing the particular experimental measurement system and the applicable effects of pressure broadening. This problem can be avoided if integrated band-absorption data are obtained in the non-transparent regime under conditions for which the spectral line features are sufficiently smoothed by collision broadening.     

The study of microwave pressure lineshifts

The results of experimental investigations of pressure shifts and broadening of spectral lines of polar molecules performed in the submillimeter region by a microwave spectrometer RAD are reported. About 30 measurements were made of self-shift and foreign gas shift parameters of the lines of NH₃, PH₃, AsH₃, and H₂O molecules including lineshifts in excited vibrational states, lineshifts of transitions connected by common levels, lines with various values of J and K quantum numbers, and the “forbidden” |ΔK| = 3 lines. On the basis of the data obtained in this work and data available in the literature, new experimental dependences of lineshifts on molecular parameters are found. The results are well described by a simple “Stark effect” model of lineshifts. Some new directions of investigations are outlined.     

Analysis of an Inhomogeneous Semitransparent Plasma by the Lines in the Emission Spectrum

Using the methods of numerical simulation, we have investigated the dependence of the intensity and parameters of the spectral line profiles in the radiation of semitransparent plasma on its optical thickness, the degree of inhomogeneity, and the parameter distribution. As a model, we used the equilibrium plasma of argon with a given temperature profile on the observation line. The calculation has been performed for the spectral lines of the argon atom characterized by different broadening constants. On the basis of the results obtained it has been shown that it is possible to diagnose the plasma and determine the degree of its inhomogeneity and reabsorption by the parameters of the self-reversed profiles of the spectral lines. To diagnose the plasma in the absence of self-reversal, we propose to use the line intensities in the emission spectra of the plasma, including those obtained by probing it by its self-radiation. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 3, pp. 404–411, May–June, 2005.     

Diode-laser measurements of O2, N2 and air-pressure broadening and shifting of NH3 in the 10 μm spectral region

Using a tunable diode-laser spectrometer, we have measured the O₂, N₂, air-shift and broadening coefficients for 5 lines of ammonia in the R branch of the ν₂ band. These lines are located in the spectral range 1030-1070 cm⁻¹. The pressure shift and broadening are obtained by fitting the measured shapes of these lines by a Voigt profile. The broadening parameters and shift coefficients are compared to the results of theoretical calculations based on the semiclassical Robert-Bonamy formalism (RB) in which the intermolecular potential includes electrostatic, induction, and dispersion energy contributions. The variation of these coefficients with rotational and vibrational quantum numbers is examined. The results are generally in satisfactory agreement with experimental data.     

Comparison between theoretical calculations and high-resolution measurements of pressure broadening for near-infrared water spectra

We report N₂ and air foreign pressure broadening coefficients of more than twenty rovibrational transitions of water vapor in the 935-nm spectral region, and these measurements are compared to new theoretical calculations. The data were obtained using the frequency-stabilized cavity ring-down spectroscopy method, yielding relative uncertainties for the broadening parameters in the range 0.4-2.2%. The sensitivity of measured broadening parameters to the choice of line shape functions is discussed, and systematic differences between experimentally determined collisional broadening coefficients are shown for the cases when the observed line narrowing is interpreted in terms of Dicke-narrowing or the speed-dependence of the collisional broadening and shifting. Theoretical models of pressure broadening for these transitions agree with the measurements to within 4% for most transitions with an average relative difference of 0.63%.     

Correlations in the plasma broadening of ion spectral lines

The results of a kinetic theory of spectral line broadening are applied to Stark broadening of ion lines in a unified classical path theory, paralleling existing results for neutral radiators. In the small plasma parameter limit, the radiator-electron interactions are screened by equilibrium electron correlation functions and a frequency-dependent dielectric function.     

Low rotational transitions of the CF3H molecule: The pressure-induced shift and broadening

Using a microwave spectrometer with a radioacoustic signal detection, the absorption profiles in the multiplets of the low rotational transitions J’?J = 2?1, 3?2, 4?3, and 5?4 of the ¹²CF₃H molecule in the ground vibrational state at pressures of pure gaseous CF₃H from 0.1 to 1.3 Torr when all the K components of the multiplets merge into a single spectral line are studied. The parameters of the pressure-induced shift and broadening of the observed lines are determined by comparing the theoretically modeled absorption signal and the experimental spectrum. The model used takes into account weak lines corresponding to the excited vibrational states v₃ and v₆ of the ¹³CHF₃ molecule and the instrumental features of the spectrometer. The observed multiplet is simulated as an isolated Lorentzian line and as a sum of the profiles of the K components with known unshifted positions and known amplitude ratio. The shift and broadening parameters obtained in both cases are shown to agree well with each other. The dependences of the shift and broadening parameters on the quantum number J are analyzed and compared with the previously obtained data for the lines J’?J = 1?0 and 2?1.     

Measurements of O2-broadening and -shifting parameters of water vapor spectral lines in the second hexad region

Oxygen pressure induced broadening and shifting coefficients for water vapor absorption lines in the 8600–9010 cm⁻¹ region have been measured and calculated. The spectra were recorded with a Bruker IFS 125HR spectrometer at a spectral resolution of 0.01 cm⁻¹ for lines with angular moment of the upper states up to 10. Calculations of line broadening and shifting coefficients are performed using a semi-empirical approach. The method is based on the impact theory of broadening, and includes the correction factors whose parameters can be determined by fitting the broadening or shifting coefficients to the experimental data. The comparison of our calculations with the experimental values argues that the semi-empirical method is quite acceptable for the determination of the water vapor absorption line profile parameters.     

Collisional line shifting and broadening in the fundamental P-branch of CO in Ar between 214 and 324 K

The collisional shifts and widths of several P-branch spectral lines in the fundamental band of CO-Ar have been measured at temperatures between 214 and 324 K and pressures between 0.025 and 1 atm. The widths have been determined using a line shape model based on the solution of the transport/relaxation equation for the appropriate off-diagonal element of the density matrix. The model uses a realistic molecular potential energy surface to calculate the speed dependence of the collisional broadening, and a rigid sphere potential to calculate the translational motion. It is found that both the shifting and broadening coefficients follow a power law dependence on the temperature. Additionally, it is demonstrated that studies have tended to overestimate the accuracy of collisional widths when the line shape model used to obtain the widths involves multiple fitted line shape parameters or fails to fit the measured spectra within the experimental noise.     

光谱线型函数的四种形式及其变换关系

从理论上研究了光谱线型函数的四种形式及其关系,以多普勒展宽导致的线型函数为例,分析了光子数、能量按频率及波长分布函数的最大值和半高全宽。结果表明,光子数、能量按频率的分布函数近似相等,光子数、能量按波长的分布函数也近似相等。通过对多普勒线型函数的分析,建立了根据两条光谱线的线型函数的最大值比值求得光子数比值的方法。     

Pressure broadening and shift in the millimeter-wave spectrum of formaldehyde

Helium, hydrogen, and self-broadening have been measured at room temperature for 12 lines of formaldehyde between 100 and 300 GHz. The self-broadening parameters ranged from 20 to 30 MHz/Torr, with typical accuracies of 0.5–0.8 MHz/Torr. For all measured lines the helium and hydrogen broadening parameters were 2.5 and 5.5 MHz/Torr, respectively, to within the experimental accuracy, typically 0.25 MHz/Torr. Pressure shifts of up to 2.5 MHz/Torr were observed in self-broadening, with estimated errors of 0.25–0.50 MHz/Torr. No significant lineshifts were seen in the foreign gas broadening measurements.The observed widths and shifts are compared with those calculated from three models of molecular collisions: Anderson's pressure broadening theory, a similar semiclassical theory of Rabitz and Gordon, and a hard-sphere, sudden approximation model of Thaddeus.     

Stark-Effekt-Verbreiterung von Kohlenstoff I-Linien im Bogenplasma

The half widths of Stark broadened C I spectral lines measured in a wall stabilized arc plasma were compared with theoretical half widths according toGriem. Within the errors of Griems line broadening calculations of about 20% there was agreement between experimental and theoretical half widths for all measured spectral lines with known calculated broadening parameters.     

Modeling of the absorption profile of the 60 GHz band of atmospheric oxygen using the memory function formalism

The profile of the oxygen absorption band centered at 60 GHz is modeled using the formalism of memory functions. The memory function determines the relation between the initial and final states of a molecule after its collision. The model profile takes into account the spectral exchange and contains two parameters, which depend on temperature and pressure. These parameters characterize the probabilities of spectral exchange between series of lines (branches) corresponding to molecular transitions of different types. To describe the absorption profile in the frequency range of 0–120 GHz in terms of the model proposed, the “+” and “?” branches of fine structure transitions and the series of nonresonance lines with frequencies on the order of 10^?3–10^?5 GHz are taken into account. The values of the parameters that take into account the spectral exchange are found from the condition of the best fit between the developed model profile and the profile calculated according to the millimeter-wave propagation model. The parameters found have physically substantiated and smooth temperature dependences, which confirms the adequacy of the model. The difference between these models does not exceed 2–3%, which corresponds to the declared uncertainty.     

Analytical representation of broadening coefficients of vibrational-rotational absorption lines of linear molecules

Analytical formulas are proposed for the coefficients that determine broadening of vibrational-rotational absorption lines of diatomic and linear molecules in the case when the broadening is caused by the pressure of buffer gases or linear molecules. The formulas are obtained by the parameterization of the semiclassical method relations with allowance for the predominant contribution related to polarization or dipole-quadrupole interaction. The parameters of the analytical formulas are determined for different vibrational bands of HCl and HF molecules in the case of argon, nitrogen, and air broadening, as well as for CO and CO₂ molecules in the case of broadening by collisions with CO, CO₂, N₂, O₂, and H₂O.     

Influence of spectral line broadening on the mode structure of He-Kr and He-Ar gas lasers

Using the semiclassical perturbation approach, Stark broadening parameters for Kr II 469.4 nm, Ar II 476.5 nm, and Ar II 480.6 nm spectral lines have been determined. The obtained results have been used for the investigation of the role of the Stark broadening mechanism on the mode properties of hollow cathode excited noble gas mixture lasers. It has been found that for the He-KrII 469.4 nm laser broadening by neutral atom collisions is large enough to explain the single-mode operation of this laser, as opposed to the He-ArII 476.5 nm laser where Stark broadening also has to be taken into account to explain this property. Published in Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 3, pp. 405–407, May–June, 2006.     

Broadening of absorption lines of the v2 band of the H2S molecule by the pressure of atmospheric gases

The broadening coefficients γ of absorption lines of the v₂ band of H₂S molecules due to the pressure of molecular gases H₂S (self-broadening), H₂O, N₂, O₂, H₂, D₂, and CO₂ have been calculated by the semiclassical methods. A satisfactory agreement with the experimental data available for some lines has been achieved. In all cases, the parameters of an analytical model allowing the reconstruction of the calculated and experimental values of γ have been determined. For the case of line self-broadening, the calculation has been performed for several temperatures in the range 296 K ≤ T ≤ 1300 K and the parameters determining the temperature dependence of γ have been obtained.