Phonon linewidths in YNi<Subscript>2</Subscript>B<Subscript>2</Subscript>C

Phonons in a metal interact with conduction electrons which give rise to a finite linewidth. In the normal state, this leads to a Lorentzian shape of the phonon line. Density functional theory is able to predict the phonon linewidths as a function of wave vector for each branch of the phonon dispersion. An experimental verification of such predictions is feasible only for compounds with very strong electron-phonon coupling. YN₂B₂C was chosen as a test example because it is a conventional superconductor with a fairly high T _c (15.2 K). Inelastic neutron scattering experiments did largely confirm the theoretical predictions. Moreover, they revealed a strong temperature dependence of the linewidths of some phonons with particularly strong electron-phonon coupling which can as yet only qualitatively be accounted for by theory. For such phonons, marked changes of the phonon frequencies and linewidths were observed from room temperature down to 15 K. Further changes were observed on entering into the superconducting state. These changes can, however, not be described simply by a change of the phonon linewidth.      

The temperature broadening of purely electronic lines by the hole burning technique

The hole burning method has been employed for measuring the homogeneous contours of the purely electronic line in the luminescence of the H₂-tetra-4-tert-butylphtalocyanine molecule in solid tetradecane. A near-quadratic temperature dependence of the linewidth in the region of 6–30 K has been obtained and is interpreted as the result of electron—vibrational coupling with a pseudolocal vibration of 36 cm^?1.     

An analytical derivation of a popular approximation of the Voigt function for quantification of NMR spectra

The approximation of the Voigt line shape by the linear summation of Lorentzian and Gaussian line shapes of equal width is well documented and has proved to be a useful function for modeling in vivo (1)H NMR spectra. We show that the error in determining peak areas is less than 0.72% over a range of simulated Voigt line shapes. Previous work has concentrated on empirical analysis of the Voigt function, yielding accurate expressions for recovering the intrinsic Lorentzian component of simulated line shapes. In this work, an analytical approach to the approximation is presented which is valid for the range of Voigt line shapes in which either the Lorentzian or Gaussian component is dominant. With an empirical analysis of the approximation, the direct recovery of T(2) values from simulated line shapes is also discussed.     

Fano lineshape and phonon softening in single isolated metallic carbon nanotubes

Evolution of G-band modes of single metallic carbon nanotubes with the Fermi level shift is examined by simultaneous Raman and electron transport studies. Narrow Lorentzian line shape and upshifted frequencies are observed near the van Hove singularities. However, all G modes soften and broaden at the band crossing point. The concurrent appearance of an asymmetric Fano line shape at this point indicates that phonon-continuum coupling is intrinsic to single metallic tubes. The apparent Lorentzian line shapes of as-synthesized metallic tubes are induced by O2 adsorption causing the Fermi level shift.     

Superradiance regime of laser cooling in extended solids

The kinetics of the extended crystal doped by rare-earth ions in the regime of anti-Stokes laser cooling has been considered taking into account the collective radiation effects. The system of Markovian equations for impurities and pseudolocal phonons has been obtained. As would be expected, the collective radiation effects cause an acceleration in relaxation depletion of the phonon mode and, therefore, an increase in crystal cooling efficiency. The text was submitted by the author in English.     

Dipolar broadening and exchange narrowing of EPR lines from the paramagnetic centers distributed on a solid surface

Experiments with char samples provide support for the theory of EPR line shape in a system of surface paramagnetic centers with dipole-dipole interactions. It is also demonstrated that, if a strong Heisenberg exchange dominates over the dipole-dipole interactions, the EPR line of a two-dimensional system narrows and acquires Lorentzian shape, similar to the three-dimensional case.     

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.     

Spectroscopy of molecules in helium droplets

The work reviewed in the talk explores the possibilities of using molecules immersed in liquid helium as probes to study superfluidity on the microscopic level. For this purpose liquid ⁴He, ³He and mixed ⁴He/³He droplets consisting of 10³–10⁵ atoms have been doped with single molecules or a small defined number of molecules which form clusters in the droplet interior. The dopants were investigated with high-resolution optical spectroscopy. The electronic and rovibrational spectra show unusually sharp spectral lines and unexpected features such as a distinct gap between the zero phonon line and the phonon wing as well as the free rotations of single molecules. Both are not observed in colder nonsuperfluid ³He droplets and therefore are considered to be new microscopic manifestations of superfluidity. Spectroscopic studies of small p-H₂ and o-D₂ clusters surrounding a single chromophore molecule formed in the interior of the He droplets are also reported.     

NMR line shape in one-dimensional magnet in the finite temperature region

The NMR line width is calculated for the one-dimensional ferro- and antiferro-magnets in the finite temperature region. The NMR line shape turns out to have a structure with double peaks which is quite different from the Lorentzian and the Gaussian type.     

Overtone spectroscopy of water molecules based on room temperature diode laser emitting in the NIR range

The measurement of very weak overtone spectroscopic line shape of water molecule is performed using wavelength modulation spectroscopy (WMS). In this work a high resolution near infrared diode laser spectrometer is used to record first derivative (1f) signal of buffer gas Helium and Carbon dioxide broadened water vapour transitions around 820 nm wavelength region. The effect of collision due to perturber pressure on signal to noise ratio (SNR) is discussed. The Lorentzian HWHM of observed 1f signal is calculated. The comparison is made between collisional broadening of water vapour transition broadened by inert gas Helium and high quadrupole moment active gas Carbon dioxide.     

Emission and absorption of phonons by rotons in superfluid helium

The roton spectrum of superfluid helium apparently has a threshold for phonon emission and absorption processes. We calculate the roton spectral function near the threshold for phonon emission in order to determine the effect of the phonon emission process on the roton line width. The spectral function develops a line shape anomaly due to a strong energy dependence of the roton self-energy. The line width is generally smaller than the sum of the phonon emission rate and the roton-roton collision rate. We also derive the ultrasonic attenuation due to the absorption of phonons by thermal rotons above the threshold.     

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。     

EPR of Radicals in Primitive Organic Matter: A Tool for the Search of Biosignatures of the Most Ancient Traces of Life

In this paper we report on electron paramagnetic resonance (EPR) of paramagnetic centers in the carbonaceous matter of primitive siliceous rocks, known to contain the most ancient traces of life. The EPR lines observed are attributed to π-radicals stabilized by the aromatic structure of this matter. It is found that the line widths and the line shapes vary continuously during geological periods and show a progressive pattern evolution from Gaussian–Lorentzian (recent) to purely Lorentzian (ca. 2000 million years [Myr]), and to supra-Lorentzian (ca. 3500 Myr). Artificial ageing experiments allowed us to define four stages of maturation of the organic matter according to the evolution of g-factors, EPR intensity, peak-to-peak line width and line shape. We suggest that the peculiar supra-Lorentzian line shape observed for organic matter older than 2000 Myr should be related to a low-dimensional (two- or one-dimensional) spatial distribution of electron spins. From these results, we derive a relationship between the line shape and the age of the organic matter, valid for ages ranging from about 600 Myr to about 3500 Myr. Authors' address: Didier Gourier, Ecole Nationale Supérieure de Chimie de Paris, 11 rue Pierre et Marie Curie, 75231 Paris cedex 05, France     

Line strength and halfwidth measurements from far infrared absorption spectra: Carbon monoxide

A method for deriving Lorentzian line shape parameters (line strengths and halfwidths) from absorption spectra taken at two different path lengths is discussed. Far i.r. absorption spectra of carbon monoxide are analysed to yield line strengths and halfwidths for the rotational transitions J″ = 3 through J>″ = 9. Experimental errors are discussed, and the value for the dipole moment derived from the line strengths, 0·108±0·005 D, is in agreement with the microwave value within experimental uncertainty. The Lorentzian halfwidths are compared, where appropriate, with two recent determinations of these quantities. Lorentzian halfwidths are also derived from absorption spectra taken at long path length using theoretical line strengths based upon μ_co = 0·112D.     

高层大气风场洛伦兹光谱线型粒子辐射率探测研究

以高层大气中的极光谱线为被探测源,提出了一种高层大气(80—300km)风场洛伦兹光谱线型的粒子辐射率被动探测的新原理.采用该原理不仅可获得高层大气风场的速度、温度和压强信息,更重要的是还能同时探测到高层大气中辐射粒子体辐射率,解决了目前高层大气风场研究中只能探测高层大气风场速度、温度和压强却不能获知粒子的体辐射率的问题.给出了基于洛伦兹光谱线型的辐射源粒子体辐射率、大气风场速度、温度和压强的理论计算公式.采用计算机模拟对探测误差进行了分析,给出了体辐射率、风场速度、温度、压强的误差分布规律,为进一步丰富和完善高层大气风场探测提供了理论依据和实验基础,对航空航天、空间探测、环境保护、国家安全和国民经济建设都具有重要的科学意义和广阔的应用前景.     

A theory of the bion in a one-dimensional sine-Gordon system: II. AC conductivity

A linear response theory is developed for the ac conductivity due to one-dimensional sine-Gordon bions within a semiclassical approximation. As a damping mechanism we consider the diffusive motion of the phase of the internal motion of the bion due to collisions with other bions. The line shape is either Lorentzian or asymmetric Lorentzian with a lower frequency tail. The lower frequency tail has its origin in the bion to bion transition accompanying one-photon annihilation; a new process other than one-bion creation from the vacuum. The effect of an extrinsic damping is also examined, which, in some cases, results in an asymmetric Lorentzian with a higher frequency tail. The results of the far infrared reflection experiments on quasi-one-dimensional conductors TTF-TCNQ and KCP are reanalyzed in the light of the present theory.     

Interaction of optical phonons with anisotropic imperfections

Inelastic (Raman) light scattering by phonons interacting with anisotropic imperfections is investigated. Three different kind of disorder-induced defects (point, linear and planar) have been considered. The optical phonon width and line shape are found to depend importantly on the dimension of the imperfections. There is a close correspondence between the scale of the imperfection and the phonon line shape observed in the Raman scattering experiments. The dependence of the phonon frequency shift and width on the defect concentrations is calculated, and the critical concentrations at which the optical phonon can no longer be observed are determined. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 12, 817–822 (25 December 1997) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Intensity correlations in filtered phase-diffusing light

Light undergoing phase diffusion displays a Lorentzian line shape: Here, electrical filtering techniques are used to examine the correlations among different spectral regions under this line shape. The experiment involves delayed self-heterodyne measurements of the output from a single-mode semiconductor laser. Two filters are tuned to isolate the signal contributions from opposite wings of the spectrum, and the transmitted intensities are shown to be strongly correlated in some regimes and strongly anticorrelated in others.     

On the NMR line shape in one- and two-dimensional ferromagnets

For the one- and two-dimensional Heisenberg ferromagnets it is shown the NMR line shape has a double peak structure and is different from the Lorentzian and the Gaussian type. The corresponding selfconsistent calculation scheme must be true only at elevated temperatures.     

The Features of Mössbauer Spectra of Hemoglobins: Approximation by Superposition of Quadrupole Doublets or by Quadrupole Splitting Distribution?

Mössbauer spectra of hemoglobins have some features in the range of liquid nitrogen temperature: a non-Lorentzian asymmetric line shape for oxyhemoglobins and symmetric Lorentzian line shape for deoxyhemoglobins. A comparison of the approximation of the hemoglobin Mössbauer spectra by a superposition of two quadrupole doublets and by a distribution of the quadrupole splitting demonstrates that a superposition of two quadrupole doublets is more reliable and may reflect the non-equivalent iron electronic structure and the stereochemistry in the α- and β-subunits of hemoglobin tetramers.