64 research outputs found
Spatio-temporal dynamics in vertical cavity surface emitting lasers excited by fast electrical pulses
Includes bibliographical references (pages 320-321).We have measured the time average spatial intensity distribution and the spatio-temporal evolution of the spectrally resolved radiation emitted from broad-area vertical cavity surface emitting lasers (VCSEL) when pumped by a fast current pulse. We show that an intrinsic symmetry break exists due to geometrical asymmetry of the device structure and that the frequency separation between different modes allows the evaluation of the asymmetry factor. The space-time behavior shows the appearance of higher-order modes coexisting or alternating in time. The dynamical behavior shows a chirping infrequency
Temporal dynamics of semiconductor lasers with optical feedback
We measure the temporal evolution of the intensity of an edge emitting semiconductor laser with delayed optical feedback for time spans ranging from 4.5 to 65 ns with a time resolution from 16 to 230 ps, respectively. Spectrally resolved streak camera measurements show that the fast pulsing of the total intensity is a consequence of the time delay and multimode operation of the laser. We experimentally observe that the instabilities at low frequency are generated by the interaction among different modes of the laser.We acknowledge support of the European Community TMR program, the NSF Optoelectronic Computing System Center, the NSF (ECS 95-02888), CICYT Project No. TIC95-0563, and DGICYT Project No. SAB95-0674.Peer Reviewe
Temporal dynamics of semiconductor lasers with optical feedback
Includes bibliographical references (page 5539).We measure the temporal evolution of the intensity of an edge emitting semiconductor laser with delayed optical feedback for time spans ranging from 4.5 to 65 ns with a time resolution from 16to 230 ps, respectively. Spectrally resolved streak camera measurements show that the fast pulsing of the total intensity is a consequence of the time delay and multimode operation of the laser. We experimentally observe that the instabilities at low frequency are generated by the interaction among different modes of the laser
Mechanism of Deep-focus Earthquakes Anomalous Statistics
Analyzing the NEIC-data we have shown that the spatial deep-focus earthquake
distribution in the Earth interior over the 1993-2006 is characterized by the
clearly defined periodical fine discrete structure with period L=50 km, which
is solely generated by earthquakes with magnitude M 3.9 to 5.3 and only on the
convergent boundary of plates. To describe the formation of this structure we
used the model of complex systems by A. Volynskii and S. Bazhenov. The key
property of this model consists in the presence of a rigid coating on a soft
substratum. It is shown that in subduction processes the role of a rigid
coating plays the slab substance (lithosphere) and the upper mantle acts as a
soft substratum. Within the framework of this model we have obtained the
estimation of average values of stress in the upper mantle and Young's modulus
for the oceanic slab (lithosphere) and upper mantle.Comment: 9 pages, 7 figure
Nanometer-scale ablation with a table-top soft x-ray laser
Includes bibliographical references (page 3617).Ablation of holes with diameters as small as 82 nm and very clean walls was obtained in poly(methyl methacrylate) focusing pulses from a Ne-like Ar 46.9 nm compact capillary-discharge laser with a freestanding Fresnel zone plate diffracting into third order. These results demonstrate the feasibility of using focused soft x-ray laser beams for the direct nanoscale patterning of materials and the development of new nanoprobes
Damage to extreme-ultraviolet Sc/Si multilayer mirrors exposed to intense 46.9-nm laser pulses
Includes bibliographical references (page 622).The damage threshold and damage mechanism of extreme-ultraviolet Sc/Si multilayer mirror coatings are investigated with focused nanosecond pulses at 46.9-nm radiation from a compact capillary-discharge laser. Damage threshold fluences of ~0.08 J/cm2 are measured for coatings deposited on both borosilicate glass and Si substrates. The use of scanning and transmission electron microscopy and small-angle x-ray diffraction techniques reveals the thermal nature of the damage mechanism. The results are relevant to the use of newly developed high-flux extreme-ultraviolet sources in applications
Nanoimaging with a compact extreme-ultraviolet laser
Includes bibliographical references (page 2097).Images with a spatial resolution of 120-150 nm were obtained with 46.9 nm light from a compact capillary-discharge laser by use of the combination of a Sc-Si multilayer-coated Schwarzschild condenser and a freestanding imaging zone plate. The results are relevant to the development of compact extreme-ultraviolet laser-based imaging tools for nanoscience and nanotechnology
The peculiarities of cross-correlation between two secondary precursors - radon and magnetic field variations, induced by stress transfer changes
A model of precursor manifestation mechanisms, stimulated by tectonic
activity and some peculiarities of observer strategy, whose main task is the
effective measurement of precursors in the spatial area of their occurrence on
the Earth's daylight, are considered. In particular, the applicability of
Dobrovolsky's approximation is analyzed, when an unperturbed medium
(characterized by the simple shear state) and the area of tectonic activity
(local inhomogeneity caused by the change only of shear modulus) are linearly
elastic, and perturbation, in particular, surface displacement is calculated as
a difference of the solutions of two independent static problems of the theory
of elasticity with the same boundary condition on the surface. Within the
framework of this approximation a formula for the spatial distribution (of
first component) of magnetic field variations caused by piezomagnetic effect in
the case of perturbed regular medium, which is in simple shear state is
derived. Cogent arguments in favor of linear dependence between the radon
spatial distribution and conditional deformation are obtained.
Changes in magnetic field strength and radon concentrations were measured
along a tectonomagnetic profile of the total length of 11 km in the
surroundings of the "Academician Vernadsky" Station on the Antarctic Peninsula
(W 64{\deg}16', S 65{\deg}15'). Results showed a positive correlation between
the annual surface radon concentration and annual changes of magnetic field
relative to a base point, and also the good coincidence with theoretical
calculation.Comment: 27 pages, 11 figures, 3 tables (a substantially revised and extended
edition; v3 -- some analysis of recent publications added
Structural transformations in Sc/Si multilayers irradiated by EUVlasers
Multilayer mirrors for the extreme ultraviolet (EUV) are keyelements for numerous applications of coherent EUV sources such as newtabletop lasers and free-electron lasers. However the field ofapplications is limited by the radiation and thermal stability of themultilayers. Taking into account the growing power of EUV sources thestability of the optics becomes crucial. To overcome this problem it isnecessary to study the degradation of multilayers and try to increasetheir temporal and thermal stability. In this paper we report the resultsof detailed study of structural changes in Sc/Simultilayers when exposedto intense EUV laser pulses. Various types of surface damage such asmelting, boiling, shockwave creation and ablation were observed asirradiation fluencies increase. Cross-sectional TEM study revealed thatthe layer structure was completely destroyed in the upper part ofmultilayer, but still survived below. The layers adjacent tothe substrateremained intact even through the multilayer surface melted down, thoughthe structure of the layers beneath the molten zone was noticeablychanged. The layer structure in this thermally affected zone is similarto that of isothermally annealed samples. All stages of scandium silicideformation such as interdiffusion, solid-state amorphization, silicidecrystallization, etc., are present in the thermally affected zone. Itindicates a thermal nature of the damage mechanism. The tungstendiffusion barriers were applied to the scandium/silicon interfaces. Itwas shown that the barriers inhibited interdiffusion and increased thethermal stability of Sc/Si mirrors
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