Two series of MgxZn1-xO/ZnO multiple quantum wells with 18 at.% and 27 at.% of magnesium content in barrier layers and well width Lw from 1 nm to 20 have been grown by pulsed laser deposition method. The stimulated emission is observed in photoluminescence spectra excited by pulsed laser (λexc=248 nm). The pump density threshold of stimulated emission nonmonotonously depends on the well width that is associated with an increase of the internal quantum efficiency of two-dimensional structures caused by a reduction of radiative lifetime of excitons at decreasing of the well width as it has been shown by the time-resolved photoluminescence spectra analysis. The minimum value of a lifetime τr=355 ps was obtained for the Mg0.27Zn0.73O/ZnO MQW with the well width Lw=2.6 nm.
The formation of laser-induced structures on the multicrystalline silicon surface has been investigated. Optimum
performances of the surface structurization have been explored. A cardinal decrease in reflectance from modified
surface has been discovered in a wide spectral range in comparison with the samples of chemically texturized
monocrystalline silicon. The influence of subsequent chemical etching on the reflection spectra of the texturized
samples surface has been analyzed.
The Mg0.27Zn0.73O/ZnO multiple quantum wells with different well width Lw have been grown by pulsed laser
deposition method. The interface roughness of quantum wells was inherited from the bottom one and did not exceed 1
nm. The quantum confinement effect has been observed. The exciton binding energy of the two-dimensional
Mg0.27Zn0.73O/ZnO structures was two times higher in comparison with the bulk ZnO. A sharp increase of exciton peak
intensity in the photoluminescence spectra at well width reduction was observed. The optical excited stimulated
emission in quantum wells Mg 0.27Zn0.73O/ZnO with an excitation threshold ~210 kW/cm2 has been demonstrated.
O. Novodvorsky, V. Panchenko, V. Sokolov, O. Khramova, L. Gorbatenko, Ye. Cherebilo, G. Batishev, C. Wenzel, J. Bartha, H. Hiemann, V. Bublik, K. Chtcherbatchev
The thin films of zinc oxide have been produced at various levels of doping with gallium. The dependence of the ZnO film crystallographic parameters on the deposition process parameters has been established. The dependence of the photoluminescence spectra of films on the conditions of deposition has been investigated. A study has been made of the intensity, emission band width, and the value of Stokes shift of ZnO films.
The ZnO films have been produced on the monocrystalline sapphite substrates (0001) by the pulsed laser deposition method. The photoluminescence spectra of these films have been obtained. The dependence of ZnO films transmission on the gallium admixture concentration has been determined for the spectral region of 200 to 3200 nm. it has been ascertained that the increase in gallium admixture is responsible for the shift of fundamental absorption band edge to the blue, and for the reduction in ZnO films transparency in the IR region. The dependence of the crystallographic parameters (lattice constant C) on the gallium admixture concentration and on the deposition parameters has been found.
On irradiation of metallic targets from niobium and tantalum with excimer XeCl laser (308 nm) in vacuum the UV and visible spectra of erosion plume were obtained. The erosion plume after ablation of copper, niobium and tantalum targets was studied using Langmuir probe. The ion and electron probe currents were obtained in the range from 0.2 to 2.2 J/cm-2 of energy densities at the target with probe-to-target separations from 10 to 133 mm. Multimodal distributions of ions by scatter velocities have been revealed. The spatial and temporal dependencies of electron probe currents were obtained in real time. The electron temperature of different plume regions was determined from a series of I-U characteristics taken at different distances between probe and copper or tantalum target. It was established that the plume electron temperature is non-uniform and has a maximum value in front of the plume. The acceleration of tantalum ions on plume irradiation with cw CO2 laser recorded. The increase in ions energy from 25 to 50 eV was observed. The emission optical spectra were used in studying the plume qualitative composition. The velocities of atom and ion scatter were measured by the time-of-flight method from the emission optical spectra.
The time-of-flight probe method was used in investigations of erosion plume in ablation of copper with 308 nm radiation of excimer XeCl laser in vacuum. The time-of-flight curves of electron and ion currents at the probe were obtained in the range from 0.2 to 2.2 J/cm-2 of energy densities at the target with probe-to-target separations from 10 to 133 mm. Multimodal distributions of ions by scatter velocities have been revealed. The voltage-current curves of probe current have been constructed in the range of probe potentials +/- 18 V. The electron temperature has been calculated for different plume regions. It has been revealed that the plume electron temperature is nonuniform.
On irradiation of metallic targets from niobium and tantalum with excimer XeCl laser (308 nm) the spectra of erosion plume were obtained. These spectra were used in studying the plume qualitative composition. The velocities of atom and ion scatter were measured by the time-of-flight method. Plasma electron temperature was found by continuous spectrum of plume radiation. The results obtained were compared with the outcomes of the previously performed probe measurements of electron temperature and ion scatter velocities.
The erosion plume resulting from an ablation of tantalum target in vacuum with excimer laser radiation (308 nm) was studied using Langmuir probe. The spatial and temporal dependencies of electron probe currents were obtained in real time. The electron temperature of different plume regions was determined from a series of I-U characteristics taken at different distances between probe and target. It was established that the plume electron temperature is nonuniform and has a maximum value in front of the plume. The acceleration of ions on plume irradiation with CW CO2 laser recorded. The increase in ions energy from 25 to 50 eV was observed.
The Langmuir probe was used to study erosion plume resulting from ablation of a tantalum target in vacuum with excimer laser (308 nm) radiation. The spatial and temporal dependencies of electron and ion probe currents were obtained in real time. Relying upon a series of dependencies of electron probe currents on the value of probe potential, electron temperature of different plume regions was taken at various distances from the target. It was established that the plume electron temperature is non-uniform. The ion concentration in the plume determined at various distances from the target.
The ablation of metallic targets from Al, Cu, Nb, Ta has been studied under irradiation with 308 nm excimer XeCl laser. A single-wire electron Langmuir probe has been used in time-of-flight measurements of velocity of plume ions scatter. An investigation has been pursued of the dependence of ion current shape at the probe both on laser radiation flux in the range from 0.2 to 2 J/cm2 and on the probe- to-target interval 23 to 113 nm. The velocities of ions scatter and their energy spectrum have been found with regard for the time of charge reaching the probe. The dynamics of energy spectrum of the plume ions has been studied. Multimode distributions of ions by scatter velocities have been revealed. The dependence of amplitudes of plume energy components on plume scatter time and on radiation flux has been investigated. The experimental time- of-flight data have been compared with Maxwell distribution by velocities, and a good agreement has been obtained. The threshold values of laser radiation flux have been determined for different modes of ion energy spectrum. Measurements have been taken of ion energy spectrum dependence upon scatter angle in the planes of orthogonal cross-sections of radiation focused spot on the target.
The paper reviews the results of experimental study of punching channels in glass samples by radiation of a single- mode CO2 laser in the intensity range from 4 104-1 106 W/cm2. The effect of pressure of the air flow following in the same direction upon punching velocity has been studied. The threshold conditions of channel formation have been determined by radiation intensity and surplus pressure of the air. The dependence of glass surface tension coefficient on radiation intensity has been estimated. The variation of the surface modulation period by the channel depth has been qualitatively explained on the basis of the model of thermocapillary instability.
Variation of the angular spectrum of the laser beam transmitted through the hole formed by it in the glass plate 2 mm thick located in the vicinity of focus of the lens placed into the beam, has been experimentally studied. It has been established that this hole manifests itself as a focusing device and possesses the properties of a short waveguide. The dependence of radiation divergence on the relation between the transverse sizes of the hole and the beam at the inlet has been studied.
The dynamics of motion of the channel side walls has been studied in the process of narrow holes formation in glass plates (channel depth to diameter ratio exceeds 4) under the action of pulse-periodical CO2 laser radiation at 4 (DOT) 104 divided by 1 (DOT) 106 W/cm2 intensity. The conditions of relief formation on the channel walls and dependence of relief characteristics on radiation intensity and modulation frequency have been investigated.
The theoretical model of hole punching by laser radiation is submitted. It takes into account the basic laws of radiation absorption by the walls of the channel. This model describes the dynamics of the form and depth of the channel, as well as presents the known and obtained experimental data on hole punching in metals and dielectrics.
The influence of the following on running air flow upon the velocity of hole punching in glass has been investigated under the action of pulse-periodical carbon-dioxide laser radiation over the intensity range from 40 to 300 kW/cm2. The power density range has been determined that is favorable to the penetration regime.
The process of channel formation during hole punching in glass by pulse-periodic radiation of carbon-dioxide laser has been experimentally investigated with due account of modulation of radiation that passed through the keyhole under deep penetration conditions (ratio between hole depth and diameter was 3 divided by 10). The frequencies of keyhole walls vibrations in the course of punching and velocities of channel radius variation have been measured. In the experiment, the phenomenon of periodic structure formation on the channel walls under the action of carbon- dioxide laser pulse-periodic radiation has been revealed.
An investigation of energy, temporal and spatial characteristics of industrial carbon-dioxide laser beam with 1.5 kW average power has been undertaken under modulation of the resonator output mirror transmittance. The use of a mirror, based on Fabry-Perot interferometer for intracavity modulation permitted us to achieve pulse-periodical generation in the 0.1 - 2 kHz range of pulse repetition rate with pulse duration from 0.2 to 5 ms. The beam modulation depth was adjusted by control voltage amplitude and could reach 100%.
An investigation into the process of hole formation in 1 to 5 mm thick silicate glass has been undertaken with radiation of the continuous-wave carbon-dioxide-laser operated in pulse- periodical regime. Punching velocity, time of hole formation and heat-affected zone have been determined in accordance with sample thickness, beam and gas flow parameters.
Wavefront aberrations and Gaussian beam profile distortions have been experimentally studied in the amplifier using carbon-dioxide:N2:He mixture as the active medium, with transverse flowing and about 5 kW power. As a pumping generator a laser with single-mode stable resonator and beam power close to 1 kW was used. The obtained experimental data were correlated with the estimated values of beam power and wavefront distortions caused by thermal deformations of reflection mirrors and optical nonuniformities in active medium. It has been shown that the amplifying scheme enables us to improve the beam quality with retention of industrial carbon-dioxide-laser high power, provided there exists the agreement between the amplified beam and amplifier parameters.
The solution method of a diffraction problem for a multilayer diffraction structure enabling us to analyze the diffraction coupler (DC) with an efficiency of 80% in the first order is discussed. The DC of 62% efficiency in the first order has been manufactured by the photolithography method in conjunction with ion-beam surface treatment. A resonator with DC as an output mirror has been investigated experimentally. The beam output has been performed through the zero order of DC. The stepped change in generation in the range from 9.18 to 10.82 mm has been obtained. A condition for concurrent generation on several neighboring lines has been investigated.
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