Influence of a static magnetic field on the detected atomic velocity distribution in an optically pumped cesium beam frequency standard

Irregularities of the microwave Ramsey patterns in an optically pumped cesium atomic beam frequency standards with a sharp angle incidence detecting laser beam have been diagnosed. They arise from a separated two-peak detected velocity distribution, which is caused by static magnetic fields. Experimentally measured results and theoretical analysis of this phenomenon are presented in this paper.     

Nondegenerate parametric down conversion in coherently prepared two-level atomic gas

We describe the parametric down conversion process in a two-level atomic gas, where the atoms are in a superposition state of relevant energy levels. This superposition results in splitting of the phase matching condition into three different conditions. Another, more important, peculiarity of the system under discussion is the nonsaturability of amplification coefficients with increasing pump wave intensity, under ‘sideband’ generation conditions.     

Talbot effect of selective reflection from a homogeneous atomic vapour

In the present work, the Talbot effect of selective reflection (SR) modified by the coupling fields is examined. It is shown that SR Talbot (SRT) patterns can be dramatically modified by the detuning, the strength and the incident angles of the coupling fields. SRT patterns at the integer and the half integer planes are similar to conventional Talbot images. However, the manifest change in fractional SRT patterns can be observed at several planes, e.g. at the quarter and the three quarters planes, the spatial frequency of those patterns is doubled comparing to that of the original output plane, and the carpets become blurring with an increasing asymmetry as the coupling fields are detuned away from the resonant transition of atoms, or as its strength increases. These peculiar Talbot patterns are mainly from a combined contribution of real and imaginary parts of source SR field modified by the coupling light. The SRT images may have potential applications in the detection of atom–surface interactionsand the processing of optical information.     

On velocity profiles of an inhomogeneous vibrofluidized grain bed on a shaker

Consideration has been given to the dynamics of a vibrofluidized bed of grain mixture on an inclined shaker with a vibration viscosity that is a linear function of the transverse coordinate. The flow-velocity distribution over the cross section of the bed has been represented as a series in Bessel and Struve functions. The convergence of the solution has been analyzed. Calculations of the velocity profiles have been carried out, and the estimates of the maximum value of this kinematic characteristic have been given.     

Acoustic channels and lenses in a medium with inhomogeneous velocity field

A homogeneous moving medium can feature waveguide propagation of acoustic oscillations, provided that the velocity of medium is inhomogeneous. A waveguide of a finite length is equivalent to a lens. The waveguides and lenses are nonreciprocal, whereby their characteristics are significantly different for the acoustic waves propagating in opposite directions. Estimates are obtained and the possible applications are discussed.     

Three-photon electromagnetically induced absorption and transparency in an inhomogeneously broadened atomic vapour

We study both theoretically and experimentally three-photon electromagnetically induced transparency and electromagnetically induced absorption resonances in inhomogeneously broadened 85 Rb atomic vapour driven by probe and drive laser radiations. We observe narrow Doppler-free absorption as well as transmission resonances for the probe field when the driving laser field is redshifted from the D₁ or D₂ lines of ⁸⁵Rb; the frequency difference between the drive and probe fields is equal to the hyperfine splitting of the ground state of the atoms, and the probe field is tuned to the centre of the Doppler broadened atomic transition. We theoretically study the spectroscopic effect in both homogeneously and inhomogeneously broadened media. Our numerical simulations are in good agreement with the experimental results.     

Treatment of inhomogeneous radiation broadening in quantum dot heterostructures described within the framework of the superradiation model

Based on the simplest expressions of the theory of superradiation for a two-level system, a model is suggested to describe inhomogeneously broadened spectra of radiation from heterostructures with quantum dot. A 98% agreement between predicted and experimental spectra is demonstrated in the entire wavelength range for an InGaAs/AlGaAs/GaAs heterostructure with quantum dots. Estimates of inhomogeneous broadening and characteristic time of superradiation are given.     

Coupling between the crack propagation velocity and the vapour diffusion in concrete

In this study, it is shown that the toughness of concrete calculated using the classical compliance method is not an intrinsic property of the material, since it depends on the loading rate even in the quasi-static condition. It would seem that this toughness is a decreasing linear function of the crack propagation velocity, at least in the range of crack propagation velocities obtained in the test presented. It is proposed that the propagation of a crack in concrete may be investigated from the standpoint of the propagation of a crack under conditions of confined viscoelasticity; a possible physical explanation of this confined viscoelasticity (this is an hypothesis) is coupling between the microcracking at the end of the propagating macrocrack and water vapour diffusion.     

Growth of calcium carbonate by the atomic layer chemical vapour deposition technique

Thin films of CaCO₃ (calcite) have been grown with the atomic layer chemical vapour deposition (ALCVD) technique, using Ca(thd)₂ (Hthd=2,2,6,6-tetramethylheptan-3,5-dione), CO₂, and ozone as precursors. Pulse parameters for the ALCVD-type growth are found and self-limiting reaction conditions are established between 200 and 400 °C. Calcium carbonate films have been deposited on soda-lime glass, Si(100), -Al₂O₃(001), -Al₂O₃(012), -SiO₂(001), and MgO(100) substrates. The observed textures were: in-plane oriented films with [100](001)CaCO₃ [100](001)Al₂O₃ and [100](001)CaCO₃[110](001)Al₂O₃ on -Al₂O₃(001), amorphous films on -Al₂O₃(012) when grown at 250 °C, and columnar oriented films on soda-lime glass, Si(001), -SiO₂(001), and MgO(100) substrates with (00l) and (104) parallel to the substrate plane at 250 and 350 °C, respectively. The film topography was studied by atomic force microscopy and AC impedance characteristics were measured on as-deposited films at room temperature. The films were found to be insulating with a dielectric constant (_r) typically approximately 8. Thin films of CaO were obtained by heat treatment of the carbonate films at 670 °C in a CO₂-free atmosphere, but the thermal decomposition led to a significant increase in surface roughness.     

Effect of piezoelectric polarization on phonon group velocity in nitride wurtzites

We have investigated the effect of piezoelectric (PZ) polarization property on group velocity of phonons in binary as well as in ternary wurtzite nitrides. It is found that with the presence of PZ polarization property, the phonon group velocity is modified. The change in phonon group velocity due to PZ polarization effect directly depends on piezoelectric tensor value. Using different piezoelectric tensor values recommended by different workers in the literature, percent change in group velocities of phonons has been estimated. The Debye temperatures and frequencies of binary nitrides GaN, AlN, and InN are also calculated using the modified group velocities. For ternary nitrides Al _x Ga_(1−x)N, In _x Ga_(1−x)N, and In _x Al_(1−x)N, the phonon group velocities have been calculated as a functions of composition. A small positive bowing is observed in phonon group velocities of ternary alloys. Percent variations in phonon group velocities are also calculated for a straightforward comparison among ternary nitrides. The results are expected to show a change in phonon relaxation rates and thermal conductivity of III-nitrides when piezoelectric polarization property is taken into account.     

Influence of spectral broadening on femtosecond wavelength conversion based on four-wave mixing in silicon waveguides

Femtosecond wavelength conversion in the telecommunication bands via four-wave mixing in a 1.5 mm long silicon rib waveguide is theoretically investigated. Compared with picosecond pulses, the spectra are greatly broadened for the femtosecond pulses due to self-phase modulation and cross-phase modulation in the four-wave mixing process, and it is difficult to achieve a wavelength converter when the pump and signal pulse widths are close to or less than 100 fs in the telecommunication bands because of the spectral overlap. The influence of the spectral broadening on the conversion efficiency is also investigated. The conversion bandwidth of 220 nm and peak conversion efficiency of -8 dB are demonstrated by using 500 fs pulses with higher efficiency than the picosecond pulse-pumped efficiency when the repetition rate is 100 GHz.     

Diffusion in an inhomogeneous velocity field in the presence of a first-order homogeneous chemical reaction

Upon taking the average of the local transport equation with a homogeneous first-order chemical reaction, a differential equation is obtained for the mean concentration over the channel section in the form of an infinite asymptotic series. Estimates are executed showing that we can limit ourselves to terms of third order or even second order for not-too-high reaction rates in the averaged transport equation; however, additional connective and source-like terms appear here in the equations. The theory is confirmed by an experiment in a 3.4-m operating chemical reactor.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 60, No. 1, pp. 77–88, January, 1991.     

Direct observation of inhomogeneous solid electrolyte interphase on MnO anode with atomic force microscopy and spectroscopy

Solid electrolyte interphase (SEI) is an in situ formed thin coating on lithium ion battery (LIB) electrodes. The mechanical property of SEI largely defines the cycling performance and the safety of LIBs but has been rarely investigated. Here, we report quantitatively the Young's modulus of SEI films on MnO anodes. The inhomogeneity of SEI film in morphology, structure, and mechanical properties provides new insights to the evolution of SEI on electrodes. Furthermore, the quantitative methodology established in this study opens a new approach to direct investigation of SEI properties in various electrode materials systems.     

Tailoring of group velocity dispersion in dual-core chiral nihility waveguide

The article focuses on an approach to overcome the dispersion present in optical communication systems. The group velocity dispersion (GVD) remains an important issue in this context. The approach presented in this paper is based on the use of chiral nihility mediums with different chirality parameters in dual-core planar optical waveguide. It is found that the two cores can be resonantly coupled in the guide, and also, the waveguide would yield high GVD by choosing suitable design parameters. For the analytical investigation, transfer matrix method is used and the dispersion relation is derived by implementing appropriate boundary conditions. Excitation of supermodes in the guide may be achieved through the coupling of two particular core modes, which would ultimately result in giant GVD. This essentially demonstrates that the structure may find applications in dispersion compensating systems.     

Influence of inhomogeneous electric and magnetic fields on internal mass transfer in capillary-porous bodies

Equations are derived for mass transfer in inhomogeneous electric and magnetic fields. Experimental results are given in support of the theoretical conclusions.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 35, No. 7, pp. 93–100, July, 1978.     

Influence of deposition pressure on texture of pyrolytic graphite during chemical vapour deposition

To investigate the influence of deposition pressure on the texture of pyrolytic graphite, a series of experiments were carried out. The pyrolytic graphites were fabricated at 2000°C with propylene as the carbon source and nitrogen as the carrier gas in a system pressure from 1·1 to 1·8 kPa. Results show that lowering the deposition pressure will increase the density and thin the growth cones. The reduce of deposition pressure will also cause an increasing in the degree of graphitisation extracted from X-ray diffraction patterns and the value of (I_G/I_D) in Raman spectra. Therefore, lower deposition pressure is more inclined to yield high texture pyrolytic graphite. Finally, the deposition mechanism was discussed.