Collisionless bounce resonance heating in dual-frequency capacitively coupled plasmas

We present the experimental evidence of the collisionless electron bounce resonance heating (BRH) in low-pressure dual-frequency capacitively coupled plasmas. In capacitively coupled plasmas at low pressures when the discharge frequency and gap satisfy a certain resonant condition, the high energy beamlike electrons can be generated by fast sheath expansion, and heated by the two sheaths coherently, thus the BRH occurs. By using a combined measurement of a floating double probe and optical emission spectroscopy, we demonstrate the effect of BRH on plasma properties, such as plasma density and light emission, especially in dual-frequency discharges.     

Collisionless intraband absorption in a system of one-dimensional massless Dirac electrons

It has been shown that the Landau-damping-induced absorption of a modulated high-frequency electric field in a two-dimensional system of particles with a linear spectrum is absent up to the momentum of the field equal to the Fermi momentum of particles. This property qualitatively distinguishes such a system from the system of particles with a parabolic dispersion law, where the mentioned damping exists at any modulation period of an incident wave.     

Collisionless absorption in an overdense plasma with anisotropic electron distribution function

Collisionless absorption of linearly polarized electromagnetic wave in a plasma with anisotropic bi-Maxwellian electron velocity distribution is investigated. Due to the wave magnetic field influence on the electron kinetics in the skin layer, the wave absorption is found to significantly depend on the degree of the electron temperature anisotropy. Depending on the value of the skin layer anomaly parameter, and on the electron temperature anisotropy degree, the conditions are found when a significant decrease or increase of the collisionless absorption is expected. Received 25 January 2002     

Quantum limit cyclotron resonance in p-GaAs

Electron scattering by neutral acceptors has been studied through far infrared (λ=172 μm) cyclotron resonance on p-GaAs at 4.2 K. It is found that (1) The inverse relaxation time is considerably smaller in the quantum limit than that predicted by D.C. transport theory in the absence of a magnetic field. (2) The same increase linearly with neutral acceptor concentration. (3) The electron momentum transfer cross section by neutral acceptor is by more than an order of magnitude smaller than that by neutral donor even in the quantum limit.     

Distortion-free magnetic resonance imaging in the zero-field limit

MRI is a powerful technique for clinical diagnosis and materials characterization. Images are acquired in a homogeneous static magnetic field much higher than the fields generated across the field of view by the spatially encoding field gradients. Without such a high field, the concomitant components of the field gradient dictated by Maxwell’s equations lead to severe distortions that make imaging impossible with conventional MRI encoding. In this paper, we present a distortion-free image of a phantom acquired with a fundamentally different methodology in which the applied static field approaches zero. Our technique involves encoding with pulses of uniform and gradient field, and acquiring the magnetic field signals with a SQUID. The method can be extended to weak ambient fields, potentially enabling imaging in the Earth’s field without cancellation coils or shielding. Other potential applications include quantum information processing and fundamental studies of long-range ferromagnetic interactions.     

Transverse susceptibility as the low-frequency limit of ferromagnetic resonance

A new theory of transverse susceptibility (TS) based on magnetization vector dynamics, as described by the Landau–Lifshitz equation of motion, is given. It is shown that the traditional TS experiment is, in fact, the zero-frequency limit of the ferromagnetic resonance (FMR). The importance of these results resides in the generality of the approach which allows one to find the TS for virtually any magnetic system if an expression for the magnetic free-energy density is known. Moreover, the effect of the frequency of excitatory AC field on the TS experiments and the effect of energy dissipation through the imaginary part of TS emerge coherently from the new TS model.     

Pion absorption in the resonance region

Pion absorption in the resonance region is studied microscopically in terms of the elementary coupling of mesons to nucleons and isobars. Particular emphasis is put on calculating the contribution from genuine two-body absorption and three-body absorption. At low energies the two-body absorption is the most important channel, but around resonance and beyond the three-body absorption becomes important and can account for about 50% of the total absorption cross section. Genuine multiparticle absorption by more than three particles is estimated to be a small fraction of the total. Comparison with the experimental data is made and good agreement with experiment is found for different nuclei and different energies.     

Nuclear acoustic resonance absorption and dispersion

A generalized form of the “Kubo susceptibility” is presented correlating NAR absorption and NAR dispersion with the sound induced perturbation Hamiltonian h(t).To illustrate the advantage of NAR susceptibility, we give the first quantum theoretical treatment of dipole NAR in metals whose results are in agreement with experiment.     

Collisionless radiation in closed cosmologies

An outline is given of some new results for collisionless radiation in Bianchi type IX cosmologies. An interesting new effect is displayed which distorts the pattern of any microwave temperature anisotropy from the quadrupole + dipole shape previously predicted in these models.     

Collisionless relaxation in non-neutral plasmas

A theoretical framework is presented which allows us to quantitatively predict the final stationary state achieved by a non-neutral plasma during a process of collisionless relaxation. As a specific application, the theory is used to study relaxation of charged-particle beams. It is shown that a fully matched beam relaxes to the Lynden-Bell distribution. However, when a mismatch is present and the beam oscillates, parametric resonances lead to a core-halo phase separation. The approach developed accounts for both the density and the velocity distributions in the final stationary state.     

Total light absorption in plasmon resonance nanostructures

The effect of total light absorption in metal nanostructures of different type is described within the model of an equivalent oscillating electrical circuit. The condition for total light absorption is found, which, independent of the nanostructure type, is reduced to the condition of optical impedance matching on the nanostructure surface at the plasmon resonance frequency.     

Collisionless infrared energy deposition in OCS

We report experiments which show that OCS does not undergo collisionless infrared multiphoton dissociation at high fluences (250 J/cm²) and intensities (3 x 10¹¹ W/cm²), at variance with previously published results at lower fluence and intensity. Under these same conditions optoacoustic measurements, furthermore, show that an average of less than one photon per molecule is absorbed.     

Photoacoustic investigation of resonance absorption on corrugated surfaces

The PhotoAcoustic (PA) method has been used to study the optical resonance absorptions on corrugated surfaces. The resonance absorptions due to the excitations of surface plasmons and guide-waves of corrugated surfaces have been measured experimentally, and the effects of the groove depth and period of the corrugated surface on the absorption curve have been observed. Moreover, the differential method based on the rigorous use of electromagnetic theory is used to calculate the parameters of the grooves and the optical absorptivities of the samples. The theoretical results on the resonance absorption peaks are in good agreement with those of the PA experiments. Then, the parameters of the grooves can be estimated by the PA investigations.