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.     

Stochastic resonance between the limiting cycles of precession dynamics

A new type of stochastic resonance that arises between two precession modes under dynamic bistability conditions and is excited by an alternating magnetic field, including a harmonic signal and a white noise, has been studied using a numerical analysis of the uniform magnetization precession in a thin film. The spectrum of the steady-state dynamics of the system at stochastic resonance has been investigated, and its distinctive features have been revealed for the longitudinal and transverse orientations of the additional alternating field.     

Excitation hierarchy of the quantum sine-gordon spin chain in a strong magnetic field

The magnetic excitation spectrum of copper pyrimidine dinitrate, a material containing S = 1 / 2 antiferromagnetic chains with alternating g tensor and the Dzyaloshinskii-Moriya interaction and exhibiting a field-induced spin gap, is probed using submillimeter wave electron spin resonance spectroscopy. Ten excitation modes are resolved in the low-temperature spectrum, and their frequency-field diagram is systematically studied in magnetic fields up to 25 T. The experimental data are sufficiently detailed to make a very accurate comparison with predictions based on the quantum sine-Gordon field theory. Signatures of three breather branches and a soliton, as well as those of several multiparticle excitation modes, are identified.     

Stochastic motion of a charged particle in a magnetic field: I Classical treatment

We study the dissipative, classical dynamics of a charged particle in the presence of a magnetic field. Two stochastic models are employed, and a comparative analysis is made, one based on diffusion processes and the other on jump processes. In the literature on collision-broadening of spectral lines, these processes go under the epithet of weak-collision model and Boltzmann-Lorentz model, respectively. We apply our model calculation to investigate the effect of magnetic field on the collision-broadened spectral lines, when the emitter carries an electrical charge. The spectral lines show narrowing as the magnetic field is increased, the narrowing being sharper in the Boltzmann-Lorentz model than in the weak collision model.     

High-amplitude precession and dynamic unsusceptibility of magnetic moments of a two-layer film

The precession motion of magnetization in a longitudinal alternating magnetic field for a system of two antiferromagnetically coupled magnetoactive layers is studied. New dynamic modes characterized by large precession amplitudes and doubling of the period are found. The modes can be efficiently controlled using an external magnetic bias field. A new effect consisting in the unsusceptibility of a magnetic subsystem to excitation by an alternating field has been revealed.     

Brillouin light scattering investigation of FeSm/FeTaN trilayer

The static and dynamic magnetic properties of a FeTaN/FeSm/FeTaN trilayer are investigated by alternating gradient field magnetometry and Brillouin light scattering. Evidence is given for a strong in-plane uniaxial anisotropy induced by a magnetic field applied during deposition. The spin-wave spectrum consists of different modes, with either surface or bulk character. A nonreciprocal behavior of the spin-wave frequency due to the exchange field exerted on the FeTaN layer at the FeSm interface is observed.     

A Mössbauer study on the surface hyperfine field of uniform hematite particles

A Mössbauer spectroscopic study was performed on uniform spherical hematite particles (99±9 nm, Sample I) and those enriched with⁵⁷Fe on the surface (Sample II). A striking difference was found between the spectra of these two samples, in that Sample I showed a spectrum with nearly symmetrical resonant absorption lines, while Sample II showed a spectrum with the lines broadened toward the central peaks asymmetrically. But after the⁵⁷Fe-enriched sample was heated to 623 K, the spectral lines became narrower due to the diffusion of the surface⁵⁷Fe-ions into the bulk. The above results showed that the centripetal broadening of the spectral lines for small uniform hematite particles resulted from a surface effect. The surface exhibited a hyperfine field about 5.2% lower than that for the bulk. The wider distribution of the surface hyperfine field was explained by structural inhomogeneity of the surface.     

Optical decoherence times and spectral diffusion in an Er-doped optical fiber measured by two-pulse echoes, stimulated photon echoes, and spectral hole burning

Two-pulse and stimulated photon echoes and spectral hole burning were measured on the transition from the lowest component of the ⁴I_15/2 manifold to the lowest component of ⁴I_13/2 of Er³⁺ in a silicate optical fiber at 1.6 K. The two-pulse echo decays gave decoherence times as long as 230 ns for magnetic fields above 2 T. A large field dependent contribution to the homogeneous line width of >2 MHz was found and interpreted in terms of coupling to magnetic tunneling modes (TLS) in the glass. The stimulated echoes measured at 2 T showed spectral diffusion of 0.8 MHz/decade of time between 0.4 and 500 μs. Spectral diffusion in this high field region is attributed to coupling to elastic TLS modes which have a distribution of flip rates in glasses. Time-resolved spectral hole burning at very low field showed stronger spectral diffusion of 5.7 MHz/decade of time, attributed to coupling to magnetic spin-elastic TLS modes.     

Weakly nonlinear analysis of the magnetorotational instability in a model channel flow

We show by means of a perturbative weakly nonlinear analysis that the axisymmetric magnetorotational instability (MRI) of a viscous, resistive, incompressible rotating shear flow subject to a background vertical magnetic field in a thin channel gives rise to a Ginzburg-Landau equation for the disturbance amplitude. For small magnetic Prandtl number (P(m)), the saturation amplitude is proportional square root P(m) and the resulting momentum transport scales as R(-1), where R is the hydrodynamic Reynolds number. Simplifying assumptions, such as linear shear base flow, mathematically expedient boundary conditions, and continuous spectrum of the vertical linear modes, are used to facilitate this analysis. The asymptotic results are shown to comply with numerical calculations using a spectral code. They suggest that the transport due to the nonlinearly developed MRI may be very small in experimental setups with P(m)<1.     

Determination of the gradient magnetic field above a sunspot based on observations of the HeI and FeI infrared lines

The magnetic field strength above 36 sunspots was studied using the spectra of the HeI λ 1083.030 nm and FeI 1082.837 nm magnetosensitive lines. The value of the field was determined directly by Zeeman splitting of the lines. The advantages of our observations are as follows: (a) in the IR region, the Zeeman splitting exceeds the similar splitting in the visible region by several times, (b) both studied lines are in the same spectrum in close proximity to each other, (c) the instrumental scattering in the IR region is lower, d) the measurements are conducted close to the true continuum of intensity between the spectral lines. The relationship between magnetic field strength and residual intensity in both spectral lines is nonlinear. The gradient of the magnetic field above sunspots at heights from the photosphere to the upper chromosphere varies within 0.1–0.7 G/km for all the studied sunspots.     

The possibility of measuring linear and quadratic magnetooptical effects in magnetic field under conditions of magnetomechanical resonance

We have considered the possibility of measuring the linear and quadratic (in magnetic field) magnetooptical effects in magnetooptical crystals that are simultaneously exposed to a constant (polarizing) magnetic field and to an alternating magnetic field under conditions of magnetomechanical resonance. The use of a Mueller polarimeter in combination with spectral analysis of the intensity of the light wave at the output of the polarimeter makes it possible to selectively determine elements of the Mueller matrix and minimize the amount of measurements. We have shown that there is a possibility of solving the inverse problem on finding two components of the alternating magnetic field in which a magnetooptical crystal is placed.     

Observation of molecular migration in porous media using 2D exchange spectroscopy in the inhomogeneous magnetic field

We present a new method for observing fluid diffusion in a porous medium. The method employs 2D exchange spectroscopy for molecules diffusing in the presence of local magnetic field inhomogeneities, in our case distilled water in various sized glass bead packs. Our experiment involves an acquisition and evolution time domain with the two Fourier domains corresponding to the spectral distribution of local fields. We show that exchange in the internal magnetic field can be seen in a 2D spectrum with a characteristic time on the order of that required to diffuse 0.15 sphere diameters with similar behavior found for computer simulations. The method is potentially useful for studying the internal migrations in more complicated systems such as sandstones or other porous media.     

Studying the regime of complete decoupling of the bond between the electron and nuclear moments at the <Emphasis Type="Italic">D</Emphasis><Subscript>1</Subscript>-line of the <Superscript>39</Superscript>K potassium isotope using a spectroscopic microcell

Atomic transitions of the ³⁹K potassium isotope in strong (up to 1 kG) longitudinal and transverse magnetic fields have been studied with a high spectral resolution. It has been shown that crossover resonances are almost absent in the saturated absorption spectrum of potassium vapors in a 30-μm-thick microcell. This, together with the small spectral width of atomic transitions (~30 MHz), allows one to use the saturated absorption spectrum for determining frequencies and probabilities of individual transitions. Among the alkali metals, potassium atoms have the smallest magnitude of the hyperfine splitting of the lower level. This allows one to observe the break of the coupling between the electronic and nuclear angular momentums at comparatively low magnetic fields B > 500 G, i.e., to implement the hyperfine Paschen–Back regime (HPB). In the HPB regime, four equidistantly positioned transitions with the same amplitude are detected in circularly polarized light (σ⁺). In linearly polarized light (π) at the transverse orientation of the magnetic field, the spectrum consists of eight lines which are grouped in two groups each of which consists of four lines. Each group has a special distinguished G-transition and the transition that is forbidden in the zero magnetic field. In the HPB regime, the probabilities of transitions in a group and derivatives of their frequency shifts with respect to the magnetic field asymptotically tend to magnitudes that are typical for the aforesaid distinguished G-transition. Some practical applications for the used microcell are mentioned.     

Laser Microspectral Analysts in a Magnetic Field

A series of possibilities are shown of increasing the sensitivity of laser microspectral analytical determinations of impurities in minerals, Steels, and aluminium alloys. When the excitation of the spectrum of the laser beam evaporated substance is transferred to a magnetic field, a considerable increase in the intensity of certain spectral lines of the basic and admixed components and a certain decrease in the intensity of the background, are observed. The intensification factor depends on the regime of the laser and the additional impulse discharge, the intensity of the magnetic field, and the utilized spectral lines.     

Effect of spectral diffusion on saturation kinetics of dilute ruby samples

We report experimental evidence of the effectiveness of spectral diffusion in the inhomogeneous resonance lines of dilute ruby crystals in high magnetic fields (∥c axis). The value of the spectral diffusion rate is inferred from the experimental data. The relationship to recent experiments on narrow optical hole recovery is also examined.     

EAST多道运动斯塔克效应诊断光谱分析

通过对多道运动斯塔克(MSE)系统测得的EAST等离子体中Dα谱线的拟合，获得了Stark分裂谱分量的间距，从而得到等离子体的磁场强度分布，并与线圈电流产生的磁场进行了比较，偏差约为5%。     

Stabilization effect of Weibel modes due to inverse bremsstrahlung absorption in laser fusion plasma using Krook collisions model

In this work, the Weibel instability due to inverse bremsstrahlung absorption in laser fusion plasma has been investigated. The stabilization effect due to the coupling of the self-generated magnetic field by Weibel instability with the laser wave field is explicitly showed. The main result obtained in this work is that the inclusion of self-generated magnetic field due to Weibel instability to the inverse bremsstrahlung absorption causes a stabilizing effect of excited Weibel modes. We found a decrease in the spectral range of Weibel unstable modes. This decrease is accompanied by a reduction of two orders in the growth rate of instability or even stabilization of these modes. It has been shown that the previous analyses of the Weibel instability due to inverse bremsstrahlung have overestimated the values of the generated magnetic fields. Therefore, the generation of magnetic fields by the Weibel instability due to inverse bremsstrahlung should not affect the experiences of an inertial confinement fusion.     

Quantum interference effect on spontaneous emission spectrum in a doubly driven M-type atom

An M-type atomic system with two closely spaced upper levels interacting with the same modes of the vacuum radiation field exhibits the interference effect between the spontaneous decay channels. The phenomenon of this decay-interference along with the dynamically induced quantum interference created in the system by two coherent fields can change significantly the spontaneous emission spectrum. Our results highlight large enhancement of ultranarrow spectral components within the spontaneous emission line shape in various conditions. We have shown the occurrence of two contradistinctive phenomena: compression of two spectral lines towards their mid-position and the spreading of two lines away from each other under different dynamic conditions. The phenomenon of suppression of spectral line and the quenching of spontaneous emission have also been focused.     

Dynamics of the lattice of magnetic nanodipoles with cubic anisotropy

The 5 × 5 square lattices of magnetic dipoles with cubic crystallographic anisotropy were investigated by the computer simulation method. The conditions for implementing the random orientation of lattice configurations, each of which are characterized by a certain response to the influence of an external magnetic pulse, as well as by the established regime of the oscillation of the total magnetic moment under the influence of an alternating field, are revealed. Regular vibration modes with a doubled frequency and quasi-periodic and chaotic modes are detected. The dependence of the system response on the parameters of the magnetic field pulse is studied.