Mode selection in InAs quantum dot microdisk lasers using focused ion beam technique
Optically pumped InAs quantum dot microdisk lasers with grooves etched on their surface by a focused ion beam are studied. It is shown that the radial grooves, depending on their length, suppress the lasing of specific radial modes of the microdisk. Total suppression of all radial modes, except for the fundamental radial one, is also demonstrated. The comparison of laser spectra measured at 78 K before and after ion beam etching for a microdisk of 8 μm in diameter shows a sixfold increase of mode spacing, from 2.5 to 15.5 nm, without a significant decrease of the dominant mode quality factor. Numerical simulations are in good agreement with experimental results.
We have examined conditions and parameters of irradiation of materials perspective for use in the mainstream nuclear fusion facilities for two devices of the Dense Plasma Focus (DPF) type (PF-6 and PF-1000) with a number of diagnostics in comparison with conditions expected in the first-wall materials in Iter and NIF. It is found that a so-called “damage factor” helps in modelling of the fusion reactor conditions. Optical microscopy, SEM, Atomic Emission Spectroscopy, images in secondary electrons and in characteristic X-ray luminescence of different elements, and X-ray elemental analysis, present results for a number of materials including low-activated ferritic and austenitic stainless steels, β-alloy of Ti, as well as the double-forged W (candidate material for divertor in Iter). With an increase of the power flux density of hot plasma and fast ion streams irradiating the surface, its morphology changes from a weak wave-like structure of the surface to the strongly developed one for the same material. It was melted with the appearance of the fracturing pattern – first along the borders of grains and then with the intergranular net of microcracks. At the highest values of power flux densities multiple blisters appeared. Besides, in this last case cracks develop because of microstresses at the solidification of melt. Presence of deuterium within the surface nanolayers of irradiated ferritic steel is explained by capture of deuterons in lattice defects of the types of impurity atoms, pores and oxycarbonitride particles presented in the material.
We discuss the effect of self-heating on performance of injection microdisk lasers operating in continuous-wave (CW) regime at room and elevated temperature. A model is developed that allows one to obtain analytical expressions for the peak optical power limited by the thermal rollover effect, the corresponding injection current and excess temperature of the device. The model predicts, there exists the maximum temperature of microlaser operation in CW regime and the minimum mircrodisk diameter, at which CW lasing is possible. The model allows one to determine the dependence of the device characteristics on its diameter and the inherent parameters, such as thermal resistance, electrical resistance, non-radiative recombination and characteristic temperature of the threshold current. It is found that a rapid growth of the threshold current density with decreasing the diameter (which takes place even in the absence of the self-heating effect) is the main internal reason leading to the dependence of the temperature characteristics of the mirodisk laser on its size. In the calculations, we used a set of parameters extracted from experiments with InGaAs quantum dot microdisk lasers. The simulation results (in particular, the light-current curve and the dependence of the minimum microdisk diameter on ambient temperature) comply well with the measured dependences.
We study characteristics of ion and electron beams observed during 101 crossings of the near-separatrix region by Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) spacecraft in the magnetotail. We found that accelerated ion beams are observed under any level of geomagnetic activity. A duration of earthward moving ion beams is statistically longer (≤ 10 min) than a duration of tailward ion beams (≤ 4 min), which can be due to the transient character of ion acceleration in the vicinity of the near-Earth neutral line (NENL). Energetic characteristics of earthward and tailward ion beams are similar indicating similar acceleration conditions at ion kinetic scales at both sides of an X line independently of its location. Conversely, electron velocity distributions observed near magnetic separatrix earthward of the distant neutral line (DNL) differ from those observed tailward of the NENL. Earthward of the DNL a scattered and thermalized electron population without energetic field-aligned beams is observed near the separatrix. On the contrary, tailward of the NENL field-aligned electron beams accelerated to a few kiloelectron volts are detected. These observations show that near DNL the electron scattering and thermalization dominate over the direct acceleration, whereas stronger electric fields in the NENL produce substantial population of field-aligned kiloelectron volt electrons.
The fresh surfaces formation provided by materials destruction or cleavage often leads to surfaces charging and strong electric fields generation. These fields can create the high energy electrons beams and Bremsstrahlung radiation. For example the destruction of quartz and granite is accomplished by low intensity relativistic electron fluxes creation. However the adhesive tapes peeling is accomplished by significantly more intensive electron beams creation. These beams can provide hard irradiation of skin and other layers of biological tissues during the adhesive tapes separation. We will estimate this irradiation using the generalized diffusion model for non-relativistic electrons.
This work is aimed at studying the possibility of using antennas of different polarization, in particular linear and circular, to develop an antenna unit that will be used in RFID systems that perform identification and determine the location of objects marked with tags in space. Research and development of the antenna module will allow you to identify objects in space using a smaller number of antennas compared to the number of zones in which marked objects are located.
The dynamics of a two-component Davydov-Scott (DS) soliton with a small mismatch of the initial location or velocity of the high-frequency (HF) component was investigated within the framework of the Zakharov-type system of two coupled equations for the HF and low-frequency (LF) fields. In this system, the HF field is described by the linear Schrödinger equation with the potential generated by the LF component varying in time and space. The LF component in this system is described by the Korteweg-de Vries equation with a term of quadratic influence of the HF field on the LF field. The frequency of the DS soliton`s component oscillation was found analytically using the balance equation. The perturbed DS soliton was shown to be stable. The analytical results were confirmed by numerical simulations.
Radiation conditions are described for various space regions, radiation-induced effects in spacecraft materials and equipment components are considered and information on theoretical, computational, and experimental methods for studying radiation effects are presented. The peculiarities of radiation effects on nanostructures and some problems related to modeling and radiation testing of such structures are considered.
Let G be a semisimple algebraic group whose decomposition into the product of simple components does not contain simple groups of type A, and P⊆G be a parabolic subgroup. Extending the results of Popov , we enumerate all triples (G, P, n) such that (a) there exists an open G-orbit on the multiple flag variety G/P × G/P × . . . × G/P (n factors), (b) the number of G-orbits on the multiple flag variety is finite.
I give the explicit formula for the (set-theoretical) system of Resultants of m+1 homogeneous polynomials in n+1 variables