Resonant enhancement of dielectronic recombination by a microwave field

We have observed dielectronic recombination of Ba+ and e(-) from a continuum of finite bandwidth in the presence of microwave fields of frequencies 8.08 and 12.05 GHz and amplitudes of up to 2 V/cm. There are sharp resonant enhancements when the microwave frequency matches the Deltan = 1, 2, and 3 resonances of the intermediate autoionizing Rydberg states, and we attribute the enhancements to resonant microwave Stark l mixing. The microwave field provides a simple and powerful way to enhance the recombination rate for incident electrons of a specific energy.     

Resonant two-photon absorption in ZnSiP2

The complex of optical investigations into the intrinsic (I) and resonant (R) two-photon absorption (TPA) inZnSiP ₂ crystals of tetragonal modifications is performed by methods of amplitude laser-modulation spectroscopy. The ITPA of allowed-forbidden type and the two Lorentz spectral lines associated with coherent resonant two-photon transitions through impurity states of allowed-allowed type are found. The electron transverse relaxation time at the RTPA is determined, and the total absorption cross section of laser-radiation photons emitted at electron transitions between the valence band v, the conduction band c, and local centers that produce real states intermediate for the RTPA in the forbidden band is estimated. M. P. Dragomanov National Pedagogical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 36–43, February, 2000.     

Resonant Raman effect of I2 dissolved in solution

We report measurements of the visible absorption and Raman intensity dispersion of I₂ molecules dissolved in chloroform. The absorption spectrum is adequately by means of a simple model for the excited state vibrational wave function. The model gives relatively unsatisfactory fits to the Raman dispersion data but is used to discuss how more precise calculations might proceed.     

Resonant absorption and scattering in evanescent fields

Received: 14 July 1998     

Pressure-induced absorption of microwave radiation by the oxygen molecule

It has been known that microwave absorptions at 9, 23 and 60 GHz by high pressure oxygen gas are considerably greater than expected by conventional theory, except at 68.7 GHz. A reasonable explanation is the pressure-induced absorption, which enhances the well established magnetic dipole absorption at the 60 GHz region. A total of 4.3 p db/km (p in atmosphere) of peak intensity is proposed to be due to the pressure-induced absorption in the 60 GHz region, compared to 145 db/km due to magnetic dipole absorption.     

Dynamics of flux lines studied by modulated microwave absorption

The solution of the coupled differential equations of motion of a flux line in the pinning potential is obtained under the condition of a swept de field, modulation field and microwave field. It can explain the hysteresis which is observed when lock-in detected signal is recorded in forward and reverse field sweeps. The width of the hysteresis is proportional to the pinning potential. From the measurements in laser grown the films of YBa₂Cu₃O_7-δ, we have deduced field and temperature dependences of the pinning potential. The irreversibility line fits to the formB∞ (T _c-T)^β with β=2.3±0.3.     

Characterization of active layers in GaAs by microwave absorption

Free carrier electric microwave absorption is applied to the analysis of ion implanted and epitaxial active layers in GaAs. An improved version of a previously reported waveguide system is described. It allows a quick and nondestructive determination of the sheet resistance, carrier concentration and carrier mobility of active layers. The usefulness of the method for routine electric material characterization supporting a microelectronic device fabrication is demonstrated. Finally, some explorative microwave measurements of heterostructures and photo-induced effects are reported.     

Characterization of magnetic materials by low-field microwave absorption techniques

A low-field non-resonant microwave absorption has recently been observed in a variety of magnetically ordered materials at low DC fields (−1000 Oe H_DC+1000 Oe), which is known as low-field microwave absorption (LFA). It has been shown that LFA is essentially similar to giant magnetoimpedance (GMI), and clearly different from ferromagnetic resonance (FMR). LFA strongly depends on the anisotropy field of the sample. In contrast with FMR (which can be described as the homogeneous precession of spins in the saturated state), LFA can be thought as a spin rotation process occurring during the magnetic saturation. In this work, we present a detailed study of the basic features of LFA in several types of materials: ferrites and amorphous microwires and ribbons; in particular the effects sample shape, temperature up to the Curie transition, the influence of easy axis and the effects of annealings. These examples show that once LFA is fully understood, it can become a powerful characterization tool.     

Resonant and relaxation absorption of ultrasound by anisotropic Jahn-Teller centers in GaAs

The contribution of the Jahn-Teller effect to absorption of an ultrasonic wave by a GaAs crystal doped with copper has been investigated theoretically. The distinguishing feature of the problem under consideration is the existence of two holes in the state of the complex valence band. The magnitude of the tunneling splitting in Jahn-Teller centers has been determined. The theoretical values of the absorption coefficients for the resonant and relaxation types of absorption have been obtained. The magnitudes of these coefficients have been estimated.     

Resonant self-trapping and absorption of intense bessel beams

We report the observation of resonant self-trapping and enhanced laser-plasma heating resulting from propagation of high intensity Bessel beams in neutral gas. The enhancement in absorption and plasma heating is directly correlated to the spatial trapping of laser radiation.     

Multiferroic and enhanced microwave absorption induced by complex oxide interfaces

NiFe_2O_4(NFO)/ZnO composite nanoparticles with different ZnO components were investigated, which were prepared by a simple wet chemical route method. The magnetoelectric coupling between magnetostriction from NFO and piezoelectricity from ZnO was induced by the surface coating NFO nanoparticles of ZnO layer, NFO/ZnO composite showed ferroelectric properties and the remanent electric polarization reached 0.08 μC/cm. Moreover, the changes of resistance at different room temperatures reached about 2% under 3 T magnetic fields comparing with that of zero magnetic fields. Furthermore, multiferroic NFO/ZnO resulted in enhancement of microwave absorption due to magnetoelectric coupling.     

Resonant two-photon absorption in a tetragonal CdP2

Kinetic, spectral, intensity, angular, and polarization of resonant two-photon absorption (TPA) in β-CdP₂ has been investigated. Resonant TPA was observed for which the total energy of the two photons was 2.60 eV. It is shown that resonant TPA takes place via a real intermediate level d ₃ in the band gap at the depth E _c-0.86 eV. The electron transverse relaxation time for resonant TPA, the cross section for absorption of laser photons in d ₃→C transitions, the equilibrium population of d ₃ centers in a doped n-type sample, and the resonant TPA constant were determined as 4.3×10⁻¹⁴ s, 1.25×10⁻¹⁷ cm², 0.95, and 0.028 cm/MW, respectively. Fiz. Tverd. Tela (St. Petersburg) 40, 1252–1256 (July 1998)     

Resonant light absorption by the ordered structures of ions stored in a trap

Far-infrared laser action has been demonstrated in three previously unknown laser media. The substances used were: propargyl fluoride, 15-N cyanogen fluoride, and hydroxylamine. Assignments of the molecular transitions giving rise to the observed laser lines were made for the latter two compounds.New FIR laser lines were also observed with two substances, vinyl chloride and vinyl fluoride, which were already known as laser media by pumping with isotopic CO₂ and N₂O laser lines.The wavelengths of a total of 26 new FIR laser lines were determined together with the threshold pump power and an indication of the relative line strengths.