Transient energy density distribution of a rod under high-frequency excitation

Energy finite element analysis (EFEA) is an efficient way to solve high-frequency structural dynamics response problems. Up to now, EFEA has been used to deal with time-independent vibration problems. However, it is still necessary to understand the time dependent details of energy density distribution of a structure. To study the transient response of a rod under high-frequency sinusoidal excitation, the transient energy density governing equation for a rod is presented. The governing equation is solved, and the solution is verified using an analytical method. Example application to a rod is presented to illustrate the feasibility.     

Transient sloshing in half-full horizontal elliptical tanks under lateral excitation

A semi-analytical mathematical model is developed to study the transient liquid sloshing characteristics in half-full horizontal cylindrical containers of elliptical cross section subjected to arbitrary lateral external acceleration. The problem solution is achieved by employing the linear potential theory in conjunction with conformal mapping, resulting in linear systems of ordinary differential equations which are truncated and then solved numerically by implementing Laplace transform technique followed by Durbin's numerical inversion scheme. A ramp-step function is used to simulate the lateral acceleration excitation during an idealized turning maneuver. The effects of tank aspect ratio, excitation input time, and baffle configuration on the resultant sloshing characteristics are examined. Limiting cases are considered and good agreements with available analytic and numerical solutions as well as experimental data are obtained.     

Two-Photon Raman scattering and high excitation luminescence in ZnTe

Two-Photon-Raman Scattering (TPRS) and the luminescence of ZnTe are investigated when the samples are highly excited with a tunable narrow-band dye-laser. In luminescence, one observes emission bands due to the well-known inelastic exciton-exciton scattering at intermediate excitation intensities, and the recombination radiation of an electronhole plasma (EHP) at the highest excitation levels. For the first time, TPRS is reported in ZnTe. From the change in the TPRS lines in magnetic fields up to 10T we deduce a diamagnetic shift of 1.2°10^–2 meV/T² of the free longitudinal exciton. This value is in good agreement with results obtained by other authors from reflection spectroscopy.     

Anti-stokes photon replica emission in GaS under two photon excitation

Experimental evidence of light emission due to an anti-stokes photon replica in the extrinsic photoluminescence spectrum of GaS is reported.This non-linear effect has been observed utilizing a high power pulsed ruby laser both for two photon excitation and to provide the electric field for controlling the elementary luminescence event. The experimental result is interpreted on the basis of existing theoretical predictions.     

Two-Photon Raman scattering and high excitation luminescence in ZnTe

Two-Photon-Raman Scattering (TPRS) and the luminescence of ZnTe are investigated when the samples are highly excited with a tunable narrow-band dye-laser. In luminescence, one observes emission bands due to the well-known inelastic exciton-exciton scattering at intermediate excitation intensities, and the recombination radiation of an electronhole plasma (EHP) at the highest excitation levels. For the first time, TPRS is reported in ZnTe. From the change in the TPRS lines in magnetic fields up to 10T we deduce a diamagnetic shift of 1.2°10^?2 meV/T² of the free longitudinal exciton. This value is in good agreement with results obtained by other authors from reflection spectroscopy.     

Stimulated emission of GaN under high one and two quantum excitation

Stimulated emission at 3.435 eV in GaN at 80 K is reported. This emission is attributed to a cooperative excitonic process and is observed only in undoped samples. One and two photon optical pumping has been used and optical gain of about 10³ cm^-1 has been measured.     

Temperature dependence of photoluminescence intensity of self-assembled CdTe quantum dots in the ZnTe matrix under different excitation conditions

The temperature dependence of the integrated photoluminescence intensity of nanometer-sized ZnTe/CdTe/ZnTe quantum wells has been investigated under different excitation conditions. It has been shown that the character of thermal decay of the luminescence intensity depends on the frequency of the exciting light and, under the above-barrier excitation, strongly depends on the optical excitation power density. It has been found that an increase in the excitation intensity leads to a saturation of thermal quenching of the luminescence in the low-temperature range. The conclusion has been drawn that this behavior reflects the saturation of nonradiative recombination centers with photoexcited carriers.     

A new emission band under high density excitation in alkali halides

A new emission band has been found in alkali halides under high density excitation produced by heavy ion bombardments and is suggested to be arised from the recombination of bi-excitons.     

THz coherent emission from quantized metallic films under ultrafast IR excitation

2 laser is studied theoretically. The consideration is based on the second-order perturbation for the density matrix under the collisionless regime. The numerical results for the response in the THz spectral region as a function of the pump frequency and the pulse duration demonstrate the possibility of efficient excitation of the THz emission from the quantized metallic films. Received: 20 September 1998 / Revised version: 27 January 1999     

Absorption and emission dynamics in concentrated optical ensembles under laser excitation

A new theoretical model describing the emission and absorption dynamics in an ensemble of molecules under intense coherent pulsed pumping is developed on the basis of the concepts of cooperative light-induced luminescence (CLIL). The CLIL development is described within the framework of formalism of the system density matrix in the space of photon wave functions. It is shown that the fast growth of CLIL relates to the development of coherent states of the quantum field in the area of efficient cooperative interactions of molecules (coherence volume). A system of equations for the calculation of CLIL energy, population of excited states, and optical absorption of the system in dependence on the laser pump energy density is solved. The theoretical results obtained are in good agreement with the experimental data.     

Ultrafast dynamics of thermionic emission on Au film under femtosecond laser excitation

A high-fidelity numerical model for investigations of the ultrafast heating is highly desirable for simulating the pulsed laser damage and the ultrafast electron emission characteristics. However, realization of accurate predictions of thermal dynamics and thermionic electron emission remains challenging due to the high non-equilibrium state, in which the equilibrium heating parameters are invalid. Here, we report an axisymmetric two-dimensional (2-D) high-fidelity numerical model for predictions of the thermionic emission with respect to the temperature-dependent dynamics parameters. The spatio-temporal temperature evolution dynamics and the thermionic emission rate characteristics on Au film target are demonstrated, whose credibility is approved by the Au film ablation threshold experiments.     

Selective excitation of surface-enhanced secondary emission from biomolecules by substrates based on thin golden films

Thin (5–30 nm) golden films have been derived by vacuum deposition of gold onto dielectric substrates and subsequent annealing at temperatures of 200–350°C. These films allow selective detection of the desired component (fluorescence or Raman scattering) of the surface-enhanced secondary emission from the same resonantly driven molecule.     

Vacuum ultraviolet 178.7 nm emission in sodium vapour under two-photon resonance excitation

We have observed a fixed wavelength emission at 178.7 nm in sodium vapour under 578.7 nm two-photon resonance excitation. The proposed non-linear wave mixing scheme is described by _{178.7 nm} = 2_L + _{465.7 nm}; where _178.7 is the 178.7 nm photon frequency, _L is the laser-photon frequency, and _465.7 is the 465.7 nm photon frequency. This 465.7 nm emission comes from another six-wave mixing process involving two hyper-electronic Raman scattering photons. The excitation spectrum of the 178.7 nm emission has a typical multiwave mixing pattern with a competing effect appearing at higher temperatures under two-photon resonance excitation. Numerical analysis indicates that this vacuum ultraviolet emission has a poor phase-match condition that will depress the emission intensity to a certain extent. This makes the observation more difficult compared with other reported four-wave mixing generated emissions. Fortunately, on the one hand, it is enhanced by quasi-auto-ionization resonance when the 3s–5s transition is coupled to the sodium continuum by a 330.2 nm photon. On the other hand, its wavelength sits so close to the sodium Cooper minimum that weak absorption will not suppress this vacuum ultraviolet emission further.