Faraday-Active Fabry-Perot Resonator: Transmission, Reflection, and Emissivity

The propagation of light within a semiconductor Faraday-active Fabry-Perot resonator (FAFR) is investigated theoretically and experimentally. It is shown that an external magnetic field radically changes the angular and spectral characteristics of transmission, reflection and emissivity of the resonator not only for polarized, but also for unpolarized light. Suppression of interference patterns and phase inversion of the interference extrema were observed in both monochromatic and polychromatic light. The investigations were carried out for the plane-parallel plates of n-InAs in the spectral range of free charge carrier absorption. The results can be used to create new controllable optical and spectroscopic devices for investigation of Faraday-active material properties and for control of parameters of plane-parallel layers and structures

Role of mechanical stresses at ion implantation of CdHgTe solid solutions

Представлено результати систематичних дослiджень структурних, оптичних та електричних властивостей напiвпровiдникових гетероструктур nCdxHg1xTe/CdZnTe (x 0,223) до та пiсля опромiнення iонами B+ та Ag+ (100 кeВ, доза iмплантацiї Q = 3 1013 см2). Здiйснено математичне моделювання процесу iонної iмплантацiї iз застосуванням програмного пакета TRIM_2008. Встановлено, що в результатi опромiнення на поверхнi дослiджуваних зразкiв вiдбувається утворення характерного рельєфу, а в приповерхневiй областi – шару з вiдмiнними вiд матрицi оптичними характеристиками. В результатi iмплантацiї епiтаксiйних шарiв CdxHg1xTe iонами бору та срiбла з однаковою енергiєю та дозою утворюється суттєво вiдмiнний за характером пошкодження та товщиною порушений шар з максимальними механiчними напруженнями, що вiдрiзняються на два порядки величини. Отримано значення коефiцiєнта стискання кристалiчної ґратки та механiчних напружень макс в областi радiацiйного розупорядкування твердого розчину. Обговорюється роль механiчних напружень легованого шару у перерозподiлi дефектiв i формуваннi постiмплантацiйних властивостей Cd0;223Hg0;777TeПредставлены результаты систематических исследований структурных, оптических и электрических свойств полупроводниковых гетероструктур n-CdxHg1xTe/CdZnTe (x 0;223) до и после облучения ионами B+ и Ag+(100 кeВ, доза имплантации Q = 3 1013 см2). Произведено математическое моделирование процесса ионной имплантации с использованием программного пакета TRIM_2008. Установлено, что в результате облучения на поверхности исследованных образцов происходит образование характерного рельефа, а в приповерхностной области – слоя с отличными от матрицы оптическими характеристиками. В результате имплантации ионами бора и серебра с одинаковой энергией и дозой эпитаксиальных слоев CdxHg1xTe образуется существенно отличный по характеру нарушений разупорядоченный по толщине слой с максимальными механическими напряжениями, которые отличаются на два порядка величины. Получены значения коэффициентов сжатия кристаллической решетки и механических напряжений макс в области радиационного разупорядочения твердого раствора. Обсуждается роль механических напряжений легированного слоя в формировании постимплантационных свойств Cd0;223Hg0;777TeThe properties of n-CdxHg1xTe/CdZnTe (x 0.223) structures implanted with B+ and Ag+ ions with an energy of 100 keV to a dose of 3 1013 cm2 are studied. The software package TRIM 2008 was applied to simulate the ion implantation process. The surface morphology of heterostructures and their optical, mechanical and electrical properties are studied. It is found that the ion irradiation of specimens gives rise to the formation of a characteristic relief on their surface, as well as a layer in the near-surface region, where the optical parameters differ from those in the matrix. The implantation of CdxHg1xTe epitaxial layers with boron and silver ions with the same energy and to the same dose brings about the formation of a damaged layer, substantially non-uniform by the thickness and the damage character, with maximum mechanical stresses that differ by two orders of magnitude. The values of the crystal lattice contraction coefficient and the mechanical stresses max in the region of radiation-induced disordering in the solid solution are determined. The influence of mechanical stresses in the doped layer on the defect redistribution and the formation of properties of Cd0:223Hg0:777Te after the implantation is discusse

Formation of helium spectrum in solar quiescent prominences

We present new non-LTE modelling of the helium spectrum emitted by quiescent solar prominences. The calculations are made in the frame of a one-dimensional plane-parallel slab. The physical parameters of our models are the electron temperature, the gas pressure, the slab width, the microturbulent velocity and the height above the solar surface. In this paper, we present isothermal isobaric models for a large range of temperature and pressure values. This work brings considerable improvements over the calculations of Heasley and co-workers (Heasley et al. 1974, Heasley and Milkey 1976, 1978, 1983) with the inclusion in our calculations of partial redistribution effects in the formation of the HI Lyα, Lyβ, HeI λ 584 Å and HeII λ 304 Å lines. In addition we consider detailed incident profiles for the principal transitions. The statistical equilibrium equations are solved for a 33 bound levels (HeI and HeII) plus continuum atom, and the radiative transfer equations are solved by the Feautrier method with variable Eddington factors. In this way we obtain the helium level populations and the emergent line profiles. We discuss the influence of the physical parameters on the helium level populations and on the main helium spectral lines. The effect of helium abundance in the prominence plasma is also studied. Some relations between singlet and triplet lines are given, as well as between optically thin or thick lines, HeI and HeII lines, and between the HeI λ 5876 Å and HI λ 4863 Å lines. In a future work this numerical code will be used for the diagnostic of the prominence plasma by comparing the results with SUMER observations

Long slit Spectropolarimetry of Jupiter and Saturn

We present ground-based limb polarization measurements of Jupiter and Saturn consisting of full disk imaging polarimetry for the wavelength 7300 A and spatially resolved (long slit) spectropolarimetry covering the wavelength range 5200 to 9350 A. For the polar region of Jupiter we find for wl=6000 A a very strong radial polarization with a seeing corrected maximum of about +11.5% in the South and +10.0% in the North. Our model calculations demonstrate that the high limb polarization can be explained by strongly polarizing (p~1.0), high albedo (omega~0.98) haze particles with a scattering asymmetry parameter of g~0.6 as expected for aggregate particles. The deduced particle parameters are distinctively different when compared to lower latitude regions. The spectropolarimetry of Jupiter shows a decrease in the polar limb polarization towards longer wavelengths and a significantly enhanced polarization in strong methane bands when compared to the adjacent continuum. For lower latitudes the fractional polarization is small, negative, and it depends only little on wavelength except for the strong CH4-band at 8870 A. The South pole of Saturn shows a lower polarization (p~1.0-1.5%) than the poles of Jupiter. The spectropolarimetric signal for Saturn decrease rapidly with wavelength and shows no significant enhancements in the fractional polarization in the absorption bands. These properties can be explained by a vertically extended stratospheric haze region composed of small particles <100nm. In addition we find a previously not observed strong polarization feature (p=1.5-2.0%) near the equator of Saturn. The origin of this polarization signal is unclear but it could be related to a seasonal effect.Comment: Accepted for publication in ICARU

Magnetic Fields via Polarimetry: Progress of Grain Alignment Theory

Most astrophysical systems, e.g. stellar winds, the diffuse interstellar medium, molecular clouds, are magnetized with magnetic fields that influence almost all of their properties. One of the most informative techniques of magnetic field studies is based on the use of starlight polarization and polarized emission arising from aligned dust. How reliable the interpretation of the polarization maps in terms of magnetic fields is the issue that the grain alignment theory addresses. Although grain alignment is a problem of half a century standing, recent progress achieved in the field makes us believe that we are approaching the solution of this mystery. I review basic physical processes involved in grain alignment and discuss the niches for different alignment mechanisms. I show why mechanisms that were favored for decades do not look so promising right now, while the radiative torque mechanism ignored for more than 20 years looks so attractive. I define the observational tests and outline the circumstances when grain alignment theory predicts that new yet untapped information of magnetic field structure is available through polarimetry. In particular, I touch upon mapping magnetic fields in circumstellar regions, interplanetary space and in comet comae.Comment: 30 pages, 1 figure, accepted to Journal of Quantitative Spectroscopy and Radiative Transfe

Circular polarization in comets: Observations of Comet C/1999 S4 (LINEAR) and tentative interpretation

Comet C/1999 S4 (LINEAR) was exceptional in many respects. Its nucleus underwent multiple fragmentations culminating in the complete disruption around July 20, 2000. We present circular polarization measurements along the cuts through the coma and nucleus of the comet during three separate observing runs, in June 28 - July 2, July 8 - 9, and July 21 - 22, 2000. The circular polarization was detected at a rather high level, up to 0.8%. The left-handed as well as right-handed polarization was observed over the coma with the left circularly polarized light systematically observed in the sunward part of the coma. During our observations the phase angle of the comet varied from 61 up to 122 deg., which allowed us to reveal variations of circular polarization with the phase angle. Correlation between the degree of circular polarization, visual magnitude, water production rate, and linear polarization of Comet C/1999 S4 (LINEAR) during its final fragmentation in July 2000 was found. The mechanisms that may produce circular polarization in comets and specifically in Comet C/1999 S4 (LINEAR) are discussed and some tentative interpretation is presented

HYDRO2GEN: Non-thermal hydrogen Balmer and Paschen emission in solar flares generated by electron beams

Aims. Sharp rises of hard X-ray (HXR) emission accompanied by H↵ line profiles with strong red-shifts up to 4 Å from the central wavelength, often observed at the onset of flares with the Specola Solare Ticinese Telescope (STT) and the Swedish Solar Telescope (SST), are not fully explained by existing radiative models. Moreover, observations of white light (WL) and Balmer continuum emission with the Interface Region Imaging Spectrograph (IRIS) reveal strong co-temporal enhancements and are often nearly cospatial with HXR emission. These effects indicate a fast effective source of excitation and ionisation of hydrogen atoms in flaring atmospheres associated with HXR emission. In this paper we investigate electron beams as the agents accounting for the observed hydrogen line and continuum emission. Methods. Flaring atmospheres are considered to be produced by a 1D hydrodynamic response to the injection of an electron beam defining their kinetic temperatures, densities, and macro velocities. We simulated a radiative response in these atmospheres using a fully non-local thermodynamic equilibrium (NLTE) approach for a 5-level plus continuum hydrogen atom model, considering its excitation and ionisation by spontaneous, external, and internal diffusive radiation and by inelastic collisions with thermal and beam electrons. Simultaneous steady-state and integral radiative transfer equations in all optically thick transitions (Lyman and Balmer series) were solved iteratively for all the transitions to define their source functions with the relative accuracy of 105. The solutions of the radiative transfer equations were found using the L2 approximation. Resulting intensities of hydrogen line and continuum emission were also calculated for Balmer and Paschen series. Results. We find that inelastic collisions with beam electrons strongly increase excitation and ionisation of hydrogen atoms from the chromosphere to photosphere. This leads to an increase in Lyman continuum radiation, which has high optical thickness, and after the beam is off it governs hydrogen ionisation and leads to the long lasting order of magnitude enhancement of emission in Balmer and Paschen continua. The ratio of Balmer-to-other-continuum head intensities are found to be correlated with the initial flux of the beam. The height distribution of contribution functions for Paschen continuum emission indicate a close correlation with the observations of heights of WL and HXR emission reported for limb flares. This process also leads to a strong increase of wing emission (Stark’s wings) in Balmer and Paschen lines, which is superimposed on large red-shifted enhancements of H↵-H line emission resulting from a downward motion by hydrodynamic shocks. The simulated line profiles are shown to fit the observations for various flaring events closely