Magnetic resonance line shape

The long-time asymptote of the magnetization correlation function and its distribution are investigated with slow motion of the spin and molecular subsystem taken into account the most. The influence of molecular drift in the field of the thermal hydrodynamic fluctuations on the magnetic resonance line shape is examined.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 118–121, May, 1976.     

The microwave resonance line shape in ferromagnetic cubic FeGe

The ferromagnetic resonance as well as the antiresonance in cubic FeGe have been studied in the temperature range 77–300 K using the frequencies 9·5 and 35 GHz. The observed line broadening was found to be due to the shape of the samples. Experimentally determined values are given for saturation magnetizations, g-factors and demagnetization factors. The latter differ considerably from those calculated in the ellipsoidal approximation. The g-factor increases from 2·07 at 35 GHz to 2·18 at 9·5 GHz. The line shape of the magnetic resonances has been calculated for an external magnetic field parallel as well as perpendicular to the plane of a disc-shaped sample. The calculations are outlined in the paper and the results are presented in the form of the derivatives of the calculated spectra. The latter are found to be in excellent agreement with experimental results. Exchange and spin pinning turned out to have negligible influence on the lines. The theoretical results have been obtained from the perturbation theory of Lax and Button which was modified by augmenting the dynamic susceptibility with a constant in order to account for the behavior of the cavity fields at the walls.     

The shape of the giant dipole resonance for light nuclei

A complete spectrum of the giant dipole resonance is calculated taking into account the finite depth of the single particle potential. The mixing of the one particle-one hole excitations because of residual interactions is treated in the time-dependent Hartree-Fock approximation. If the interaction is approximated by a separable potential a general formula can be derived, which gives the total dipole excitation cross section σ(E) in terms of the simple shell-model cross section σ₀(E). Numerical results are given for O¹⁶ and C¹² by evaluating σ₀(E) in a square well potential.     

Generic shape of multichromatic resonance peaks

The European Physical Journal B - Recent experiments with ultracold atoms in an optical lattice have realized cavity-mediated long-range interaction and observed the emergence of a supersolid phase...     

The 1P shape resonance in electron-hydrogen scattering

The shape resonance in the ¹P channel in electron-hydrogen scattering which occurs just above the n = 2 threshold has been studied by variational calculations employing a pseudostate basis. Its parameters are E_R = 0.7512 (Ry), Γ = 0.0015 (Ry).     

The line shape of Coherent Antistokes Raman Scattering excited under resonance conditions

If Coherent Antistokes Raman Scattering (CARS) is excited by a biharmonic pump in resonance with one photon molecular transition, the Raman line shape is significantly changed compared to the case of nonresonant excitation. This is due to an essential alteration of the 3rd order susceptibility responsible for CARS. Aside from a considerable enhancement of the Raman signal (which makes it possible to detect dissolved molecules in concentration lower than 10^-4 mole/l) the most marked effects are a reversal of the spectral sequence of the Raman maximum and minimum in the CARS-spectrum and for a specially chosen concentration an enhanced contrast of the signal. The factors determining the CARS line shape are discussed theoretically and preliminary experimental results concerning resonance CARS spectra are reported.     

The shape of collision broadened lines from resonance to the far wings

A line shape for collision-broadened lines applicable from the resonance region to the far wings is developed. An empirical correlation function is used to represent the known short and long time behavior of the true correlation function and to interpolate the unknown intermediate time regime. The resulting spectral shape is a simple analytic function which reduces to essentially the Van Vleck-Weisskopf equation when |ω?ω₀|τ₂?1, but which smoothly assumes an exponential behavior in the far wings where |ω?ω₀|τ₂?1. The time parameter, τ₂, is a measure of the duration of collision and is related to the mean squared torque produced in bimolecular collisions. The effect of overlapping lines, also variations in the model correlation function on the line shape are considered. The theory is applied to the absorption in the high-frequency far wing of the 4.3υ band in CO₂.     

Theory of ferromagnetic resonance line shape in insulators

The paper discusses the absorption of the energy of a high-frequency field by a magnetic sample from the point of view of the interaction of spin waves with photons and spin waves amongst themselves. A general expression for the form of the absorption curve is derived, using the method known from the quantum theory of radiation and assuming very weak fields.

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The author thanks S. Krupika, Candidate of Sciences, for the exceptional interest taken in this work, for advice and a number of helpful and critical remarks.     

On the theories of cyclotron resonance line shape

A recent claim by Choi and Chung that the Argyres-Sigel theory of cyclotron resonance line shape is invalid is shown to be erroneous.     

The shape of saturated absorption resonance in atoms with degenerate levels and light pressure effect

Anomalous behavior of the shape of saturated absorption resonance on the transition 1s₅→ 2p₈ (J=2→J=2) in the Ne atom is experimentally observed. The shape of the saturation resonance on transitions with degenerate excited states of atoms is analyzed numerically and the reasons for the anomalous behavior of the resonance shape and the formation of its doublet spectral structure are established. The effect of the resonance light pressure on the amplitude and frequency properties of resonance is investigated. It is shown that the asymmetry of the doublet splitting of the resonance is associated with the effect of resonance light pressure.     

Analysis of magnetic resonance line shape under slow molecular motions

A new approach is considered to the analysis of the magnetic resonance line shape under slow molecular motions. The essence of the approach consists in calculating the coefficientsa _n in the Taylor expansion G(t). A straightforward procedure has been developed for calculating the coefficientsa _n for molecular motions described by random Markov processes.Translated from Izvestiya Vysshikh Uchebnyh Zavedenii, Fizika, No. 7, pp. 48–52, July, 1982.     

The experimental investigation of the spin packet line shape in an inhomogeneous magnetic resonance line

It is shown that the saturation transient of an inhomogeneous spin system is strongly affected not only by the width but also by the shape of the spin packets. In two cases of main interest, Lorentzian and Gaussian packets, we report approximate analytical expressions of χ(t) during the saturation transient, with which the experimental results may be compared. By this method we give experimental evidence that the packet profile in dilute ruby samples has a Gaussian shape.     

Validity of perturbative expansions in theories of cyclotron resonance line shape

A recent claim by Choi, Yi and Chung that the Argyres-Sigel theory of cyclotron resonance line shape is invalid is proved to be wrong.     

Influence of inhomogeneities in magnetic crystal on ferromagnetic resonance line shape

The general theory of the preceding paper is applied to a concrete case. The spin wave interaction operator, ^s , is derived by quantizing a phenomenological expression, which expresses the contribution to the energy of the magnetic sample, caused by fluctuations in the anisotropic and exchange interaction. The influence of thermally excited spin waves on the absorption of energy from a high-frequency field and the justification for the application of the general results of the preceding paper are discussed on the basis of the form of the operator ^s . The interaction operator of the magnetic sample with the h-f field is also determined, and it is used to give a definite form to the expression for the resonance curve of the imaginary part of the susceptibility '. Using the matrix elements of the operator ^s we calculate the quantitiy, which formally corresponds to the width of the resonance -curve. The magnitude of is estimated numerically and our results are compared with those obtained by A. M. Clogston et al. and E. Schlömann for the line width in monocrystals and the shape of the resonance curve in polycrystals respectively. The expression obtained on the basis of the theory of the preceding paper for the frequency shift diverges in our case. The way in which to avoid this divergence is indicated.

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The author would like to thank S. Krupika for advice and remarks during the work, J. Duek, V. Syneek, and J. ternberk for valuable discussions and F. Zounová for help in the numerical calculations.     

Quantum state control via trap-induced shape resonance in ultracold atomic collisions

We investigate controlled collisions between trapped but separated ultracold atoms. The interaction between atoms is treated self-consistently using an energy-dependent delta-function pseudopotential model, whose validity we establish. At a critical separation, a "trap-induced shape resonance" between molecular bound states and a vibrational eigenstate of the trap can occur. This resonance leads to an avoided crossing in the eigenspectrum as a function of separation. We investigate how this new resonance can be employed for quantum control.     

Influence of resonance tube geometry shape on performance of thermoacoustic engine

Based on the linear thermoacoustics, a symmetrical standing-wave thermoacoustic engine is simulated with a cylindrical tube and a tapered one as the resonance tube, respectively. The experiments with both cylindrical and tapered tubes are carried out. The suppression of nonlinear effects due to tapered tube as the resonance tube is discussed. Both simulation and experimental results show that the performance of the tapered tube is better than cylindrical one as the resonance tube.     

The oscillator strength of the πg shape resonance in the absorption K-spectrum of a nitrogen molecule

Magnitudes of the absorption cross sections of a nitrogen molecule are measured by the transmission method near the ionization K-threshold. Based on these data, the partial absorption NK cross sections are obtained and the oscillator strength of the π_g shape resonance is determined. It is found that the oscillator strength of the π_g-resonance increases as the optical density of nitrogen decreases. This phenomenon is interpreted as a result of the instrumental distortion effect (the thickness effect). By extrapolating to zero pressure, the oscillator strength of the π_g shape resonance is determined to be 0.29.