The temperature dependence of the Rayleigh line wing and depolarized combinational scattering line widths in critical mixtures

It has been experimentally found that at approaching the critical temperature of the exfoliating mixture carbon-disulfide-ethanol the widths of the Rayleigh line wing and the depolarized combinational scattering line drastically decrease. The same phenomenon was observed for 3 nitrobenzene combinational line scattering in a nitrobenzene—n-hexane mixture.     

A shell-model calculation in the continuum for the reaction N15(n,n′) N15

Using the shell-model approach to nuclear reactions, the Lippmann-Schwinger equation for elastic and inelastic nucléon scattering is solved numerically. The procedure is based upon an adaptation of a method due toWeinberg. The differential and total elastic and inelastic cross-sections and the asymmetry of the scattering of a transversally polarised beam of neutrons are calculated. The positions (energies and total widths) and residues (partial widths) of the scattering matrix in the complex plane are determined. The results are discussed and compared with previous treatments.     

Information content of a planetary spectrum

The information content of equivalent widths and line profiles is investigated when all of the pressure-broadened lines belong to a unique spectrum. The parameters which can be derived without a priori knowledge of the planetary atmosphere are emphasized. In general, the analysis of equivalent widths alone does not allow one to distinguish between different atmospheric models. A scattering indicator, which is a dimensionless number derived from the shape of line wings, is found to determine the influence of scattering in the absorption process.     

The effect of diatom-diatom collisions on depolarized light scattering linewidths : I. General theory

With the use of an appropriately generalized Waldmann-Snider collision (super-) operator, a unified kinetic theory treatment of depolarized light scattering (both depolarized Rayleigh and rotational Raman) and their related linewidths is presented for gases of rigid rotor molecules. Explicit expressions are given, both exactly and within a distorted wave Born approximation, for the various state-to-state (i.e. rotational quantum number dependent) collision processes which can contribute to any observed linewidths due to diatom-diatom collisions. The results of this paper are employed in the calculation of the depolarized linewidths for the hydrogen isotopes in the following article.     

Data pulse distortion induced by a slow-light tunable delay line in optical fiber

We experimentally demonstrate an all-optical tunable delay line based on slow light induced by stimulated Brillouin scattering in a highly nonlinear fiber (HNLF) and study the distortion of data pulses with different pulse widths and the induced pattern-dependent distortion on non-return-to-zero data in slow-light systems.     

Resonant coupling of free quantum rotors in inclusion compounds

NH3 groups in certain Hofmann clathrates form almost free one-dimensional quantum rotors with energy levels E(n) = n(2)B and angular momentum n (planck constant), where n = 0, +/-1, +/-2,.... Recent neutron scattering experiments revealed a surprising temperature dependence for the linewidths of the n = 0 <--> 1, 0 <--> 2, and 1 <--> 2 transitions. We propose a novel line broadening mechanism based on rotor-rotor coupling and obtain a simple analytic expression for the widths that depends on the rotor level occupation and on the 3-proton spin degeneracies of initial and final states. Our model provides, without adjustable parameters, a good fit both to the temperature dependence of the observed widths and to their relative magnitude.     

Coherent rayleigh scattering

The spectrum of coherent scattering induced by electrostriction in gases has been analyzed in the previously unexplored, free-molecule limit by solving Boltzmann's equation with a periodic force due to the optical fields. Calculated and measured spectra of several gases at rarefied conditions are nearly Gaussian with widths approximately 10% wider than the spontaneous Rayleigh widths. Our results are the first spectrally resolved measurements of coherent Rayleigh scattering in the free-molecule limit, where the hydrodynamic analysis of stimulated Rayleigh-Brillouin scattering does not apply.     

Raman spectrum and cross sections of n-C3F7I. Implications for a large-scale atomic iodine laser

The Raman spectrum of gaseous n-C₃F₇I has been recorded.Raman cross sections, depolarization ratios, and line widths were measured for the four strongest Raman-active modes. Using the measured values for the 280 cm^-1 mode, the stimulated-Raman gain for a large-scale iodine laser was calculated. The results indicate that losses due to stimulated-Raman scattering will be negligible for a fusion-driver iodine laser.     

Spontaneous Raman scattering spectra of ADP and DADP crystals in different polarization schemes

Spontaneous Raman-scattering spectra of light in ADP and DADP crystals were obtained in four polarization schemes, the widths of some Raman lines were measured. The presence of a strong and sharp Raman line corresponding to the totally symmetric vibration of the phosphate group and a strong diffuse Raman satellite corresponding to the totally symmetric vibration of the ammonium group in the spontaneous scattering spectra of both (ADP and DADP) crystals was observed. According to the theory, such lines are preferable for the stimulated Raman scattering.     

Electron-phonon interaction in superconducting Nb

Acoustic phonon damping in Nb due to superconductivity is accurately measured by the inelastic neutron scattering technique. The phonon line widths can be characterized by the reduced parameters $\text{h}\text{?}\text{ω}{}_{\mathrm{p}}\text{/2Δ(0)}$ and T/T_c, and are in good qualitative agreement with the calculation by Bobetic based on the BCS theory.     

Water vapor line width and shift calculations with accurate vibration-rotation wave functions

Calculations of H₂¹⁶O rotation-vibration line broadening and shifting due to N₂ pressure effects are performed using a semi-empirical approach. The calculations are based on impact theory modified by introducing additional parameters to extend the use of empirical data. These model parameters are determined by fitting the broadening and shifting coefficients to experimental data. The method is further developed by using anharmonic wavefunctions in the estimates of the line profiles. The main feature of the present calculation is the use of a complete set of high-accuracy vibration-rotation dipole transition moments calculated for all possible transitions using wavefunctions determined from variational nuclear motion calculations and an ab initio dipole moment surface. This approach explicitly takes into account all scattering channels induced by collisions. Results of these calculations clearly demonstrate improved agreement between observed and calculated parameters for both the line widths and the line shifts.     

Two-photon resonant Raman and luminescence of excitonic molecules in CuCl

Two-photon resonant Raman scattering via excitonic molecule in CuCl is studied with using dye laser excitation of different band widths. The yield of the Raman scattering is found to drop remarkably at resonant excitation and luminescence line of 0.3 meV half-width comes out. The predominance of the Raman or luminescence or their coexistence depends on the intensity and energy band width of excitation light.     

Raman scattering investigations of KY3F10

Single crystals of the fluoride compound KY₃F₁₀ (O_h⁵) were studied by Raman scattering from 40 to 950 K. Group theory analysis predicts 3A_1g + 4E_g + 6F_2g Raman-active modes, but the experimental spectra show two F_2g modes missing. Over the whole temperature range the frequency shifts are negligible whereas the line widths show a strong increase with temperature. Both reversible and irreversible line width behaviour are exhibited for different temperature runs, indicating a complex microscopic phenomenon underlying the creation of defects responsible for these line widths and their interaction with the different phonon modes. An approximate activation energy for defect creation of ΔE ≈︁ 0.3 eV can be obtained from the temperature behaviour of the line widths. This activation energy may be connected with the high-temperature ionic conduction mentioned previously for this crystal.     

Experimental evidence for a diffusionally broadened mountain line of a polyatomic gas

After briefly recalling the theories that have been developed for Rayleigh-Brillouin scattering in polyatomic gases in the hydrodynamic regime and which lead to various line widths for the Mountain line, experiments are described on SF₆ where the central component of the scattered line is found not to be lorentzian, and to fit well with the translational hydrodynamics predictions concerning the width of the Mountain line which is dominated by diffusion.     

Study of Be δ-doped GaAs/AlAs multiple quantum wells by the surface photovoltage spectroscopy

We report a surface photovoltage and differential surface photovoltage (DSPV) study of Be δ-doped GaAs/AlAs multiple quantum wells (QWs) with widths ranging from 3 to 20 nm and sheet doping densities from 2 × 10¹⁰ to 2.5 × 10¹² cm⁻² per well aiming to characterize their electronic properties and structural quality. From a line shape analysis of room temperature DSPV spectra the interband excitonic transition energies and broadening parameters for a large number of QW-related subbands have been established. A study of well-width and quantum number dependencies of the excitonic linewidths allowed us to evaluate the various broadening contributions to the spectral line shapes in QWs of different design. It was found that an average half monolayer well-width fluctuations are the dominant broadening mechanism of the excitonic line for QWs thinner than 10 nm. In QWs thicker than 10 nm, the spectral line broadening originates mainly from thermal broadening as well as Stark broadening due to random electric fields of ionized impurities and exciton scattering by free holes.     

Neutron scattering from intinerant ferromagnets just above Tc

Neutron scattering from itinerant ferromagnets at and just above T_c is studied on the basis of a simple band model with no short range order. Results are found for scattering line widths for small momentum and energy transfers which are substantially independent of band parameters. Some comparison with experiment is attempted.     

The influence of finite line widths on parity mixing in muonic atoms

The parity mixing due to parity-violating neutral currents in muonic atoms is discussed in the case where the line widths of two mixing states are comparable with or larger than their energy difference. It is shown that the line widths give rise to a considerable reduction of the parity mixing effects.     

CIV共振谱线的电子碰撞展宽的理论计算

 使用R-矩阵方法,利用碰撞近似和密耦理论,计算了确定CIV 2s²S-2p²P⁰共振谱线的碰撞参数,并由此得到了在电子密度为10¹⁷cm^-3 的条件下,共振谱线的线宽和线移随温度的变化关系。计算得到的线宽与半经典的理论计算值符合得比较好,但大约只有实验线宽的一半。     

Application of pressure broadening theory to the calculation of atmospheric oxygen and water vapor microwave absorption

The problem of the pressure broadening of spectral lines is investigated with respect to the microwave absorption of two terrestrial atmospheric gases, oxygen and water vapor. A formalism and accompanying computational procedures under the impact approximation and using the Liouville (line) Space concept introduced by Baranger and elaborated by Fano are employed. It is desired that the theory would obviate the necessity for specific line shapes, provide a means of computing line widths and account for line overlapping effects from first principles. The present approach is found to be generally adequate for the treatment of O₂ absorption on comparison with experimental data for line widths, absorption coefficients and zenity opacities. While H₂O line widths are satisfactorily predicted, estimated resonance overlapping effects are found to be far from sufficient (accounting for at most ~ 5%) to explain the theoretically controversial anomalous absorption.