Laser induced lasing in CS2 vapor

When CS₂, contained in a tube at pressures ranging from 350 to 450 mTorr, was optically excited by a pulsed laser at a wavelength of 343.6 nm to the J=29, v=(0, 10, 0), R ³ B ₂ state (i.e., the =0 component of the a ³ A ₂ state), six coherent emissions were observed along the same axis from both ends of the tube. These emissions possess the characteristics of the pump laser, such as linewidth, pulse duration and polarization, but do not need a cavity to gain amplification. The emissions terminate on the high vibrational states of the ground electronic state. A time delay between the pump laser and the emissions was observed. The emission intensity depends non-linearly on the CS₂ pressure and exhibits a third order power dependence. A cooperative stimulated emission model is proposed to explain this phenomenon.     

Atomic scale conductance induced by single impurity charging

A scanning tunneling microscope was used to probe electron transport through an alkali doped C(60) monolayer crystal on Al(2)O(3) grown by the oxidation of NiAl(110). Each individual alkali atom forms a localized complex with the neighboring C(60) molecules. Charging of the complex induces a substantial rise in the current that persists outside the physical dimensions of the complex. This induction of the current rise is characterized by spatially resolved spectroscopy and mapping of the differential conductance (dI/dV) in the vicinity of the complex.     

Localization of optically excited states by self-trapping

We discuss the localization of the surface exciton at the Si(111)- (2x1) surface due to self-trapping, which leads to a characteristic temperature-dependent linewidth of the optical response and to a significant Stokes shift of the luminescence. Self-trapping results in this case from a structural relaxation in the excited state, caused by the interplay between electronic and geometric degrees of freedom. The most significant contribution to this effect comes from one single geometric deformation mode which is driven by the internal electronic charge transfer in the self-trapped exciton.     

Atomic absorption spectra induced by NaRb in sodium-rubidium vapour

Six atomic spectral lines induced by NaRb molecules in the absorption spectrum of sodium-rubidium vapour have been observed in the wavelength range 611–641 nm. For sodium-rubidium vapour, the laser induced fluorescence spectra at laser wavelengths 616.04 and 615.81 nm and the excitation spectra at sodiumD-lines with the laser scanning in the range 613.9–616.9 nm have also been measured. The possible mechanisms for the appearance of these absorption lines are discussed.     

The discrete self-trapping equation

A simple system of ordinary differential equations is introduced which has applications to the dynamics of small molecules, molecular crystals, self-trapping in amorphous semiconductors, and globular proteins. Analytical, numerical and perturbation methods are used to study the properties of stationary solutions. General solution trajectories can be either sinusoidal, periodic, quasiperiodic or chaotic.     

Atomic K-shell ionization induced by 20–50 MeV protons

By varying the energy of fast protons incident on gold, europium, silver, ribidium and copper targets, it has been possible to produce several self consistent sets of relative K-shell ionization cross sections covering the region from below to above the velocity matching peak.     

Jahn-Teller effect at exciton self-trapping

In the adiabatic approximation two limiting cases of exciton self-trapping have been considered for a degenerate atomic term creating the bands of Frenkel excitons, which interact with all crystal deformations admitted by symmetry: a case of a large radius excitation on the self-trapping barrier and a small-radius case. In the first case wave functions and deformations have been found which correspond to the barrier, in the second case the adiabatic surface of self-trapping excitons have been obtained. It is shown that the interaction with non-totally symmetric deformations leads to a lowering of the crystal point symmetry in a state corresponding to the lowest self-trapping barrier, that is the manifestation of the Jahn-Teller effect applied to a self-trapping exciton.     

Removal of single-atom optical bistability by quantum fluctuations

The dynamics of the quantum-statistical properties of the radiation of an atom in a cavity interacting with an external coherent field is investigated. A high level of quantum fluctuations of the field in the cavity is shown to destroy optical bistability in the multiatom case. Photon-number fluctuations and the spectral dispersion of the canonically conjugate quadratures of the field inside and outside a cavity are calculated. It is found that in contrast to the multiatom case quadrature squeezing and squeezing of the radiation intensity of a single atom are negligible inside and outside the cavity. Zh. éksp. Teor. Fiz. 115, 2001–2013 (June 1999)     

Single-photon and three-photon absorption induced whispering-gallery mode lasing in ZnO micronails

The ZnO micronails were synthesized by the vapor phase transport method. The heads of the micronails show hexagonal disk structure which is suitable for the whispering-gallery mode lasing microcavity. Under the excitation of a nanosecond pulse at 355 nm, the single-photon absorption induced lasing was stimulated in the micronail with the head diameter of 3.0 μm, the whispering gallery mode and Fabry-Pérot mode lasing were investigated. Under the excitation of femtosecond laser pulses at 804 nm, the second harmonic generation and the three-photon absorption induced photoluminescence were observed from a bulk of micronails, then an individual micronail with the diameter of 9.1 μm was employed to realize the three-photon absorption induced whispering-gallery mode lasing.     

Adiabatic surface of self-trapping excitons

The problem of the self-trapping of the Frenkel exciton interacting with phonons is considered in the adiabatic approximation. The self-trapping is assumed to take place at a single site. The exciton scattering by phonons at this site and the nearest neighbouring sites is taken into account. Analytical expressions for the adiabatic surface of self-trapping excitons, in particular, for the barrier height separating almost free and self-trapped states, are found. The condition for the applicability of the model to the describing of the self-trapping barrier is determined. The adiabatic surface is shown to have several minima separated by a barrier, i.e. the coexistence of several types of self-trapped excitons is possible.Dedicated to Professor Miroslav Trlifaj on the occasion of his sixtieth birthday.     

Threshold properties of quasi-one-dimensional self-trapping

Excitons in a molecular chain, incorporated into a solid matrix, are considered. Self-trapping phenomena in such a system involve one-dimensional electronic motion and three-dimensional lattice deformation. It is shown that self-trapping in such a quasi-one-dimensional system (contrary to a true one-dimensional system with linear exciton-lattice coupling) is of a complicate threshold character. This entails non-trivial consequences. In particular, the usual relation between the self-trapped state radius and energy shift is violated. The results qualitatively explain anomalous features of the luminescence spectrum and kinetics recently observed by Yu.V. Malyukin et al. [Pis'ma JETP 58 (1993) 385; JETP 107 (1995) 812] for self-trapped states in molecular chains (J-aggregates) incorporated in an organic matrix.     

Significance of self-trapping on hydrogen diffusion

The diffusion rate of hydrogen in Nb was calculated using ab?initio molecular dynamics simulations. At low temperatures the hydrogen is strongly trapped in a local strain field which is caused by the elastic response of the lattice. At elevated temperatures, the residence time (τ) of hydrogen in an interstitial site is not sufficient for fully developing the local strain field. This unbinding of the interstitial hydrogen and the strain field increases the hopping rate (1/τ) at elevated temperatures (>400 K). These results call for a revision of the conceptual framework of diffusion of hydrogen in transition metals at elevated temperatures.