Natural electron oscillations in granular indium films deposited on rough surfaces of NaCl and KCl single crystals

Two plasma resonance bands were simultaneously observed in granular indium films deposited on rough surfaces of NaCl and KCl single crystals; one of them is caused by a combined action of the light-wave field and of the field created by the dipole grains, and the other, by the light-wave field alone with the frequency of natural electron oscillations ω₀ in the grains. The indium plasma frequency, calculated from the measured frequencies ω₀ and known dielectric constants of NaCl and KCl, agrees well with the known plasma frequency of bulk indium. An anisotropy in the plasma resonance band of granular indium films deposited on a rough NaCl surface was found and interpreted.     

Plasma resonance in granular silver films deposited on rough surfaces of NaCl and KCl single crystals

Granular silver films deposited on rough NaCl and KCl single-crystal surfaces exhibit, besides the low-frequency plasma-resonance band induced by the light-wave field and the field generated by the grain dipoles, a second, high-frequency plasma-resonance band, which is excited only by the light-wave field at the frequency ω₀ of the natural electron vibrations in the grains. The dielectric constant due to interband transitions was calculated from the known plasma frequency and the dielectric constant of the medium surrounding thegrains, the plasma frequency ω_p of the granular films, and the measured frequency of the maximum of surface plasmon vibrations in solid films. The results obtained agree with the data quoted by other authors.     

Natural electron oscillations in granular aluminum films deposited on rough surfaces of NaCl and KCl single crystals

Granular aluminum films deposited on rough surfaces of NaCl and KCl single crystals form a two-layer coating. In the lower layer, a low-frequency band of plasma resonance is excited due to the joint action of a light-wave field and a field induced by granules-dipoles. In a small amount of granules of the upper layer isolated from each other, a high-frequency band with a frequency ω₀ of natural electron oscillations in the granules is excited. Using the measured frequencies ω₀ and the known dielectric constants of NaCl and KCl, a plasma frequency of aluminum is calculated that agrees well with the known plasma frequency of solid samples. Kharkov State University, 4 Svoboda Sq., Kharkov, 310077, Ukraine. Translated from Zhurnal Prikladnoid Spektroskopii, Vol. 66, No. 6, pp. 853–856, November–December, 1999.     

Observations of ferromagnetic resonance modes on FeCo-based nanocrystalline alloys

Uniform and symmetric resonance modes (known as Aharoni’s exchange resonance modes) are derived from micromagnetic equilibrium condition in the linear approximation. To investigate the uniform and symmetric resonance modes in ferromagnetic nanoscale grains, the microwave permeability of FeCo-based nanocrystalline alloy particles/paraffin composites was measured and calculated in the range 0.5-18 GHz. The measured dynamic permeability curves exhibit a broad resonance band at 4-6 GHz; some curves also exhibit a narrow resonance band at 13 GHz. The former behavior is in qualitative agreement with the uniform mode, and the latter is attributed to the first eigenvalue mode of the symmetric resonance modes excited in nanocrystalline monodomain grains in FeCo-based alloys. The difference value (Δω₁₁) between the uniform resonance frequency and the first frequency eigenvalue of the symmetric resonance modes shows good agreement with experiment.     

Band gap engineering at surfaces of insulating films by adsorption of organic molecules

Adsorption of simple organic molecules on wide band gap insulators is a versatile tool to introduce unoccupied electronic states in the band gap at the surface. Relative energetic positions, varied also by intra-molecular interactions of functional side groups, determine the effective band gap. Specific examples used here are adsorbed molecules of benzoic acid and of its OH-substituted derivates (salicylic acid, etc.) on NaCl, KCl and on MgSO₄ · H₂O. These acids are mainly physisorbed on NaCl and KCl, whereas on MgSO₄ · H₂O chemical bond formation is found. Ab initio and semi-empirical calculations are used in order to identify mechanisms of surface-molecule as well as intra-molecular interactions.     

低温氮化硅薄膜的介电性能研究

研究了微波电子回旋共振等离子体化学汽相沉积低温氮化硅薄膜在5—10⁶Hz频率范围内的介电性能．由于低温氮化硅薄膜为具有分形结构的纳米非晶薄膜，致使氮化硅薄膜的介电谱、损耗谱在低频区和高频区具有两种不同的分布规律．在低频区介电谱具有ε′∝ω^n－1₁的关系，ｎ₁在0.82—0.88之间，是电子跳跃导电的结果；在高频区介电谱具有ε′∝ω^n-1₂的关系，n₂在0 关键词：     

Nonlinear and multiquantum effects in dual-frequency EPR experiment: the intensities of sideband resonances

Two microwave frequencies ω₁ and ω₂ simultaneously exciting a paramagnetic spin probe near the resonance condition ω₁ = γB ₀ effect a pattern of resonances occurring at multiples of the difference frequency δ = ω₂ ? ω₁. Their intensities, measured in the absorption or dispersion mode in the magnetic field-sweep experiment, decrease rapidly as the distance from the centerband increases. Numerically solved Bloch equations are used to discuss the intensities of the transverse components of magnetization up to seven, harmonics of the frequency difference δ. In conclusion, it is suggested that the experimental investigation of these patterns can be used for the purpose of a continuous-wave monitoring the relaxation rates of spin probes.     

Effect of the Bloch-Siegert shift on the frequency responses of Rabi oscillations in the case of nutation resonance

The dynamics of a two-level spin system dressed by bichromatic radiation is studied under the conditions of double resonance when the frequency of one (microwave) field is equal to the Larmor frequency of the spin system and the frequency of the other (radio-frequency) field ω_rf is close to the Rabi frequency ω₁ in a microwave field. It is shown theoretically that Rabi oscillations between dressed-spin states with the frequency ? are accompanied by higher-frequency oscillations at frequencies nω_rf and nω_rf ± ?, where n = 1, 2,.... The most intense among these are the signals corresponding to n = 1. The counter-rotating (antiresonance) components of the RF field give rise to a shift of the dressed-state energy, i.e., to a frequency shift similar to the Bloch-Siegert shift. In particular, this shift is manifested as the dependence of the Rabi-oscillation frequency ? on the sign of the detuning ω₁ ? ω_rf from resonance. In the case of double resonance, the oscillation amplitude is asymmetric; i.e., the amplitude at the sum frequency ω_rf + ? increases, while the amplitude at the difference frequency ω_rf ? ? decreases. The predicted effects are confirmed by observations of the nutation signals of the electron paramagnetic resonance (EPR) of E′₁ centers in quartz and should be taken into account to realize qubits with a low Rabi frequency in solids.     

Double resonance in the system of coupled Josephson junctions

The effect of LC shunting on the phase dynamics of coupled Josephson junctions has been examined. It has been shown that additional (rc) branches appear in the current-voltage characteristics of the junctions when the Josephson frequency ω_J is equal to the natural frequency of the formed resonance circuit ω_rc. The effect of the parameters of the system on its characteristics has been studied. Double resonance has been revealed in the system at ω_J = ω_rc = 2ω_LPW, where ω_LPW is the frequency of a longitudinal plasma wave appearing under the parametric-resonance conditions. In this case, electric charge appears in superconducting layers in the interval of the bias current corresponding to the rc branch. The charge magnitude is determined by the accuracy with which the double resonance condition is satisfied. The possibility of the experimental implementation of the effects under study has been estimated.     

Resonances of orientation and alignment of atoms in the case of inclined optical pumping

It is shown that, with pumping inclined relative to a constant magnetic field H₀, the radio-frequency (RF) magnetic field rotating at frequency Ω induces new resonances ω₀ = γ H ₀ and 2Ω for the Fourier components of orientation and ω₀ = ?Ω, Ω/2, 3Ω/2, 2Ω, and 3Ω for the components of alignment. New resonances excited by the oscillating RF field are also considered.     

Parametric Excitation of Plasma instabilities by two Monochromatic Pump waves

The dispersion characteristics of a plasma in a pump field ??(t) = ?? sub ω₀t + ??₁ sin ω₁t are considered. Firstly we assume, that the second wave is weak (|??₁| ? |??₀|) and the frequency ω₁ is near sω₀(ω₁ = sω₀ + Ω,Ω ? ω₀). We obtain the dispersion equation, describing the parametric coupling of the waves driven by the strong field ??₀ sin ω₀t under the resonance condition ω₀ ≈ ω_Le/P and derive the expressions for the growth rates (ω_Le is the electron LANGMUIR frequency; s, p are integers). In the second part it is shown, that a strong field ??₁ with a frequency ω₁ much larger than ω _Le(ω _Le ≈ pω₀) stabilizes the plasma; the growth rates are reduced and the frequency region of the parametric instability is contracted.     

Effect of two-photon saturation on ordinary Raman scattering

The excitation profile of ordinary Raman scattering under steady-state excitation conditions and the time-resolved emission spectrum of ordinary Raman scattering under transient excitation conditions undergo considerable changes when the excitation frequency ω approaches $\text{1}\text{2}$ ω_mn, where ω_mn is the resonance frequency of a two-photon transition from the ground state |n to an excited state |m of a molecule. The appearance of ghost peaks, dips or dispersion-like features centred at ω ? $\text{1}\text{2}$ ω_mn in the excitation profile and of coherence effects such as Rabi nutations with unusual time-dependence in the time-resolved spectrum are predicted.     

高频引力波对环形波导中电磁波的调制作用

讨论了垂直入射的、频率为ω_g的平面高频引力波对环形波导管中频率为ω_e的电磁波的调制作用．一般情况下，在波导管中与引力波传播方向垂直的对称平面附近，电磁波的能流密度会出现三种新的频率成分（2ω_e±ω_g）和ω_g．在ω_g》ω_e时，能流密度振幅的相对调制量与引力波的无量纲振幅h₀数量级相同．特别是当ω_g，ω_e和电磁波绕波导传播的绕行频率ω₀满足关系ω_g＝2ω_e》ω₀时，由于类似于共振的机制，能流密度会出现比h₀大几个数量级的振幅相对调制量．这个结果不会由于参数的微小改变而消失，这对于探测极微弱的引力辐射信号将是十分重要的 关键词：     

Mode competition and frequency locking

A theoretical study is presented of frequency locking to be observed in lasers with broad homogeneous emission lines, when the cavity losses are reduced, at a certain frequency ω₀, by placing inside the cavity a suitable element (e.g., a selectively reflecting “mirror”). Two kinds of locking effects are analyzed: i) When tuning the center frequency of the laser output ω_f towards ω₀, by means of a filter or a grating, the laser frequency becomes locked to ω₀, when |ω_f ? ω₀| reaches a critical value. ii) In the absence of frequency-selective elements, the laser oscillates only in a narrow spectral range centered at ω₀. Special emphasis is given to the role played by mode competition in these locking phenomena.     

超导弱连接中的Josephson电流在一个磁通量子内的振荡(Ⅰ)——Josephson结

本文指出如果Josephson结处在Q值足够高的谐振腔内,当Josephson频率ω=(2eV₀)/h与谐振腔的本征频率ω_r发生谐振时,谐振的电磁场对Josephson结自身的反馈作用将导致超流电流在一个磁通量子内随磁场的小周期振荡。 关键词：     

Change in the shape of a symmetric light pulse passing through a quantum well

A theory for the response of a 2D two-level system to irradiation by a symmetric light pulse is developed. Under certain conditions, such an electron system approximates an ideal solitary quantum well in a zero field or a strong magnetic field H perpendicular to the plane of the well. One of the energy levels is the ground state of the system, while the other is a discrete excited state with energy ?ω₀, which may be an exciton level for H=0 or any level in a strong magnetic field. It is assumed that the effect of other energy levels and the interaction of light with the lattice can be ignored. General formulas are derived for the time dependence of the dimensionless “coefficients” of the reflection ?(t), absorption A(t), and transmission ?(t) for a symmetric light pulse. It is shown that the ?(t), A(t), and ?(t) time dependences have singular points of three types. At points t ₀ of the first type, A(t ₀)=T(t ₀)=0 and total reflection takes place. It is shown that for γ_r?γ, where γ_r and γ are the radiative and nonradiative reciprocal lifetimes, respectively, for the upper energy level of the two-level system, the amplitude and shape of the transmitted pulse can change significantly under the resonance ω_l=ω₀. In the case of a long pulse, when γ_l<γ_r, the pulse is reflected almost completely. (The quantity γ_l characterizes the duration of the exciting pulse.) In the case of an intermediate pulse duration γ_l?γ_r, the reflection, absorption, and transmission are comparable in value and the shape of the transmitted pulse differs considerably from the shape of the exciting pulse: the transmitted pulse has two peaks due to the existence of the point t ₀ of total reflection, at which the transmission is zero. If the carrier frequency ω_l of light differs from the resonance frequency ω₀, the oscillating ?(t), A(t), and ?(t) time dependences are observed at the frequency Δω=ωl?ω₀. Oscillations can be observed most conveniently for Δω?γ_l. The position of the singular points of total absorption, reflection, and transparency is studied for the case when ω_l differs from the resonance frequency.     

Study of the precipitation behavior of NaCl:Pb and KCl:Pb by optical spectroscopy2

The aggregation and precipitation behavior of lead in NaCl and KCl crystals has been systematically investigated by absorption and luminescence spectroscopy. For NaCl, absorption bands at 265 and 285 nm have been identified which correspond to intermediate stages in the formation of a double band (262–266 nm) associated with PbCl₂ precipitates. The kinetics of growth during ageing as well as the thermal annihilation behavior have been obtained for all bands. The emission spectra for excitation at those absorption bands have also been determined. For KCl, absorption bands at 265 and 280 nm develop during ageing at 160 and 200°C and their growth-rate is markedly enhanced by plastic straining. Their emission spectra involve a main band at $\text{\$}\text{?}$550 nm. In contrast to NaCl, no stage has been found where those absorption bands feed into a final band, which could be associated with PbCl₂ precipitates.     

Far-infrared shifted cyclotron resonance in a charge-density-wave system,NbSe3

Cyclotron resonance studies on the charge-density-wave metal NbSe₃ at 2 Kelvin reveal two types of free carriers (with effective mass 0³.18m₀ and 0.71 m₀ respectively.) The measured lifetimes agree with earlier estimates of the dc mobility. An unexplained shift of the resonance field of the form ω₀² + ω_c² is observed when the laser electric field is polarized perpendicular to the chain direction.     

Nonlinear Raman scattering of photons by a channeled particle

Channeled particles are characterized by the discrete spectrum of bound transverse motion. The interaction of photons with channeled particles in single crystals can be accompanied by energy transitions between the levels of transverse motion of the channeled particle. The Raman scattering of photons at a quasibound channeled particle leads to the appearance of a combination of frequencies: the incident radiation frequency ω₀ and the frequency Δω_{m, n}, i.e., ω = ω₀ ± Δω_m,n where Δω_m,n = 2Δε_m,nγ²; Δε_{m, n} is the energy of the transition between quantum states (m and n) of the transverse motion of the channeled particle; and γ = E/mc² is the Lorentz factor of the channeled particle. The appearance of a violet satellite (the anti-Stokes component) in the Raman scattering spectrum is analyzed. The three-photon Raman-type transition, which is the process of the simultaneous absorption of two photons with the frequency ω₀ with the emission of a photon with the frequency ωs = 2ω₀ ± 2Δε_m,nγ², is considered. The conditions for resonance observation during the formation of the second harmonic (ω = 2ω₀) are discussed.