Optical Absorption Levels Research Articles

Оптимизация оптического поглощения в спинтронных терагерцовых излучателях с использованием брэгговских отражателей

An optimized design of a spintronic terahertz emitter has been developed, based on a bilayer Co/Pt structure with an integrated distributed Bragg reflector. The incorporation of the Bragg mirror between the Co/Pt structure and the silicon substrate enhances optical absorption in the ferromagnetic layer, thereby amplifying spin current generation and, consequently, THz signal. A model was developed for calculating the optical absorption in the ferromagnetic layer of the spintronic emitter, taking into account the parameters of the Bragg mirror (layer thicknesses, period) based on the superlattice structure [TiO2/SiO2]N. This model is grounded on the solution of Maxwell's equations for electromagnetic waves using the COMSOL Multiphysics software. The effect of anti-reflective dielectric coatings on the level of optical absorption in the ferromagnetic layer was also analyzed. The study confirmed that using the optimized Bragg mirror is sufficient for achieving optimal absorption.

Dynamic changes in adenosine monophosphate-activated protein kinase in neonatal rats with hypoxic ischemic encephalopathy

Objective To determine the dynamic changes in adenosine monophosphate-activated protein kinase (AMPK) in neurons of neonatal rats suffering from hypoxic ischemic brain injury. Methods Twenty-four-hour old and seven-day old neonatal rats were used in this study. A classic primary cortical neuron oxygen glucose deprivation (OGD) model and neonatal rat hypoxic ischemic encephalopathy (HIE) model were employed. Lactic dehydrogenase (LDH) and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) were used to evaluate neuron viability and damage. The expression of phosphorylated adenosine monophosphate-activated protein kinase (P-AMPK), phosphorylated activated protein kinase (P-Akt) and Cleaved Caspase-3 in neurons and brain tissue was measured by Western blot at different time points after OGD or HIE. The Student-t test was used for statistical analysis. Results (1) Compared with the control group, LDH levels at 2, 4, 8 and 24 h after OGD were higher (all P<0.05) and optical absorption levels of MTT were lower (all P<0.05). (2) Levels of P-AMPK in the OGD group were higher than those in the control group, and showed a time-dependent increase at 30 min and 2, 4, 8 and 24 h (all P<0.05). The expression levels of P-AMPK in the HIE group were higher than those in the control group (0.345±0.038, 0.387±0.112 and 0.618±0.075 at 1, 3 and 7 days after HIE, and 0.132±0.032 in the control group, all P<0.05). (3) The levels of P-Akt increased above the control levels at 30 min (0.991±0.134 vs 0.304±0.050), reached a maximum level at 2 h (1.183±0.107), and then gradually declined, whereas the levels of Cleaved Caspase-3 started to increase at 30 min, and remained elevated at 24 h (all P<0.05). Conclusion Following hypoxic ischemic brain damage, the expression of P-AMPK is significantly increased in both in vivo and in vitro studies in a time-dependent manner. Key words: Hypoxia-ischemia, brain; AMP-activated protein kinases; Animals, newborn; Rats

Study of optical absorption in thin films of a-As2Se3 by photocapacitance spectroscopy

Photocapacitive spectroscopy is used for the first time to study optical absorption in thin films of a-As2Se3 for optical photons with energies below the gap width. Photocapacitance spectra are obtained over energies of 0.83–1.94 eV and used to characterize the density of localized states in the tail of the valence band and in deep states of charged defects. Aging and illumination of the film are found to affect the level of optical absorption by deep centers.

Analysis of ion implanted diamond

Abstract Ion implantation allows controlled introduction of impurities into diamond. A basic problem is to determine if the implanted layers are dominated by substitutional doping or radiation damage effects. Optical and electrical measurements on the implanted diamonds revealed (1) a degradation of the band-gap and sample coloration, (2) no optical absorption levels which would be characteristic of hydrogenic ionization levels, (3) resistivity activation energies of 0.2 to 0.3 eV independent of the ion specie, and (4) no measurable Hall Effect. Phosphorous implanted layers in diamond were analyzed by means of the channeling technique. It was shown that (1) the diamond retained the implanted phosphorous atoms during a vacuum anneal at 950°C which restored crystalline order, (2) the implanted phosphorous atoms did not assume either substitutional or tetrahedral interstitial sites, (3) the measured projected range for 70 keV phosphorous in diamond of 450 ± 115 A was consistent with theoretical range calcula...