Optical properties of indium phosphide in the 50-200 Å wavelength region using a reflectivity technique

The optical constants of indium phosphide (InP) in the soft x-ray region of 50-200 ? are determined from angle-dependent reflectivity measurements. The measurements are carried out using the reflectivity beam line at the Indus-1 synchrotron source. The derived optical constants are compared with tabulated values of Henke et al. [At. Data Nucl. Data Tables 54, 181 (1993)]. Experimental values of δ and β are in close agreement with the tabulated values in the lower wavelength region of 50-120 ?. The experimental value indicates an edge shift of 0.4 ? toward the lower wavelength side from the phosphorous L-edge value of 92 ?. However, above the 120 ? region, where the indium N(2) edge falls at 160.7 ?, there is a huge difference between experimental and tabulated values. Both delta and beta values are significantly higher. In contrast to tabulated values of the β/δ ratio, which is more than 1 above the 140 ? region, the experimental measured ratio is found to be less than 1. This study presents the first reported experimental values of optical constants for InP in this wavelength range, to the best of our knowledge.     

Optical design of a compact long-range thermal imaging camera in the 3–5 μm wave band

In this work, the design study of a fixed focus thermal imaging system for 3–5?µm using infrared focal plane array is presented. The system is designed to have possible minimum weight and length in order to achieve the best operational characteristics. The system is designed as an objective relay combination to have 100% cold shield efficiency. In this way, the objective and relay are designed as short as possible. The objective is designed as a Schmidth–Cassegrain type mirror and the relay is a triplet type with one lens far from the others to guarantee the minimum distance to the intermediate image.     

Subsecond measurements of optical properties in the spectral range 0.4–1.1μm in the vicinity of high-temperature phase transitions of refractory oxides

A new dynamic method is proposed for measuring the spectral hemispherical-directional reflection coefficients within the spectral range 0.4–1.1m in vicinity of high-temperature phase transformations of refractory oxides. Diffuse polychromatic irradiation of the tested sample makes it possible to exclude the effect of a sharp change of the indicatrix of reflection in the case of phase transformations and to obtain a large bulk of data for exact determination of the temperatures of phase transitions. The methodical error in determination of the spectral hemispherical-directional reflection coefficients does not exceed 2% within the investigated temperature range.Physicotechnical Institute, Scientific Production Association Physics-Sun, Tashkent, Uzbekistan. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 65, No. 2, pp. 223–228, August, 1993.     

Tribological properties and structural features of pseudoalloys of the aluminum–tin system

We have studied the influence of alloying of aluminum with tin (2–15 mass %) on its wear resistance in a pair with a copper antibody under conditions of friction without lubrication. We have established that, with increase in the tin content in alloys, their wear is reduced to one-sixth to one-fourth. Alloying with tin over 10% leads to the appearance of liquations.     

AlGaAsSb lasers emitting in the 1.6 μm region

AlGaAsSb lasers with different Al concentrations in the active and confinement regions are fabricated and investigated. The structures lase in the region ∼1.6 μm. The AlGaAsSb solid solution in the active region is a direct-gap material with a small energy separation (∼56 meV) between the direct-gap Γ minimum and the indirect-gap L minimum of the conduction band. The lasers have a single-mode spectrum with a predominant longitudinal mode in the spatial distribution of the emission. The lasers operate at room temperature in a pulsed mode. Pis’ma Zh. Tekh. Fiz. 25, 35–41 (May 26, 1999)     

Modulation Transfer Function Measurement of Optical Systems in the Visible and Infra-red (5 to 20 μm) Range

The ACOFAM combines an optical method of frequency analysis with electronic data unit and display to obtain a fast and accurate measurement of the Modulation Transfer Function of lenses and complete systems in the visible range. Some extra devices are described in order to convert the standard ACOFAM to the infra-red spectral range (5–20 μm). Results of measurements on a 50 mm F/1 developed by the Optical Division of Engins MATRA are shown.     

Accuracy of LOWTRAN 7 and MODTRAN in the 2.0-5.5-µm region

LowTRAN 7 and MODTRAN were evaluated in the 2.0-5.5-μm region against field-collection data at high zenith angles and long path lengths to determine the degree of uncertainty associated with these models under these conditions. Matching data sets were developed with data from the U.S. Air Force Geophysics Laboratory's Flying Infrared Signatures Technology Aircraft (FISTA) as the field reference. The percent difference between the model and the field data was determined. Agreement between the model and the field data was found to be better than 97% for most cases. Median percent difference was within 10% for zenith angles less than 90°.     

The optical properties of hot-pressed magnesium fluoride and single-crystal magnesium fluoride in the 0.1 to 9.0 μm range

A polycrystalline high-density magnesium fluoride, fabricated into plates or shapes by hot-pressing, exhibits high in-line transmittance from 2.5 to 6.0 m, and single-crystal magnesium fluoride extends from 0.1 to 6.0 m. The ultimate and practical transmittance of hot-pressed magnesium fluoride using intrinsic and extrinsic reflectance, absorptance and scattering mechanisms, are investigated. The intrinsic scattering mechanism due to the polycrystalline structure is basically responsible for the tremendous difference in transmittance in the short wavelength region of the spectrum. The in-line transmittance of polycrystalline and singlecrystal MgF₂ is discussed in terms of sample thickness.     

Coupled-cavity concept applied to a highly compact single-frequency laser operating in the 2 μm spectral region

We present a highly compact and cost-efficient Tm:YAP laser setup supporting single-frequency operation at a significantly high efficiency. The coupled-cavity concept was used to design a single-frequency laser operating at 1990 nm. Single-frequency output power of 784 mW was obtained when the absorbed pumping power was 2.4 W. The optical-to-optical efficiency was 33%, and the slope efficiency was 52%.     

2 μm emission properties and hydroxy groups quenching of Tm3+ in germanate-tellurite glass

Tm³⁺ activated germanate-tellurite glasses with good thermal stability and anti-crystallization ability were prepared. Efficient 2 μm fluorescence was observed in the optimal concentration Tm³⁺ doped glass and the corresponding radiative properties were investigated. For Tm³⁺: ³F₄ → ³H₆ transition, high spontaneous radiative transition probability (260.75 s⁻¹) and large emission cross section (7.66 × 10⁻²¹ cm²) were obtained from the prepared glass. According to Dexter's and Forster's theory, energy transfer microscopic parameters were computed to elucidate the observed 2 μm emissions in detail. Besides, the effect of hydroxy groups quenching was also quantificationally investigated based on simplified rate equations. Results demonstrate that the optimal concentration Tm³⁺ doped germanate-tellurite glass possessing excellent spectroscopic properties might be an attractive candidate for 2 μm laser or amplifier.     

Optical properties of O2 − centres in KCl∶NaCl mixed crystals

The optical properties of O₂ ^– centres in KClNaCl mixed crystals were investigated. The timeresolved spectra and the fluorescence decay time are shown. From the measurements of the radiative decay time, the oscillator strength of the absorption,f _ab=0.045, the oscillator strength of the fluorescence,f _fluo=0.019, and the activation energy E=0.22 eV for the O₂ ^– centre in KClNaCl were determined.     

The effect of molybdenum on optical properties of ZnO nanoparticles in Ultraviolet–Visible region

Zn_1?xMo_xO (x = 0.0, 0.01, 0.03, and 0.05) nanoparticles (NPs) are synthesized by using gelatin, via the sol-gel method. A calcination temperature of 600 °C is maintained for 2 h. The influence of molybdenum concentration on the structural and optical properties of these NPs is demonstrated. Synthesized NPs are characterized using X-ray diffraction (XRD), UV–vis spectroscopy, and transmission electron microscopy (TEM). XRD patterns reveal the crystallite nature of samples that exist in the hexagonal wurtzite phase. TEM images manifest the existence of nearly spherically-shaped NPs. The UV–vis spectroscopy results showed that the absorption edge of ZnO nanoparticles is red-shifted by adding molybdenum. Finally, the optical parameters of the refractive index and permittivity of the synthesized samples were calculated using Kramers-Kronig relations using the UV–vis spectra.     

Does the higher citation of collaborative research differ from region to region? A case study of Economics

Many studies have found that collaborative research is, in general, more highly cited than non-collaborative research. This paper describes an investigation into the extent to which the association between high citation and collaboration for Economics articles published in 2000 varies from region to region and depends on the choice of indicator of citation level. Using data from the Social Science Citation Index (SSCI) for 18 countries, 17 American states and four indicators of citation level the citation levels of the collaborative articles are compared with the citation levels of the non-collaborative articles. The main findings are that: (a) for every country and every indicator the mean citation level of the collaborative articles was at least as high as that for the non-collaborative articles, but for five US states and for at least one other indicator the citation level of collaborative articles was lower than that of non-collaborative articles, and (b) the extent to which collaborative articles were more highly cited varied considerably from country to country, from state to state, and from indicator to indicator. This indicates the importance of using multiple indicators when investigating citation advantage since the choice of indicator can change the results.     

Ion-nitriding behaviour of Fe-Ti alloys in theα-phase region

The ion-nitriding behaviour of four iron alloys containing between 0.11 and 1.48 wt% titanium was investigated in the-phase region to discuss kinetics of the growth of the nitriding layer. The ion-nitriding experiments have been made at 823 K. Two nitriding layers were observed: a thin surface layer which mainly consists of Fe₄N; an internal nitriding layer beneath the surface layer, where the nitride formed was found to be TiN. The growth of the internal nitriding layer is controlled by a diffusion process of nitrogen in the matrix metal. The apparent diffusion coefficient of nitrogen in the nitriding layer, evaluated using the rate equation proposed for internal oxidation, increases linearly with the volume fraction of titanium nitride. Furthermore, by excluding the effect of the titanium nitride from the apparent diffusion coefficient, the diffusion coefficient of nitrogen in-iron was calculated, being in good agreement with that reported so far. In addition, the increase in hardness in the internal nitriding layer has been discussed.     

Subsecond measurements of the optical properties in the spectral range 0.4–1.1 μm near high-temperature transformations of samarium oxide

A new dynamic method is described for measuring the spectral directional-hemispherical reflectivity in the spectral range 0.4–1.1 m near high-temperature phase transformations of refractory materials. The use of diffuse sample irradiation enables one to exclude the influence of an abrupt variation of the angular reflection distribution of sample surface at the phase transitions. The experimental results on samarium oxide showed that light pulses are emitted by the sample during the high-temperature transformations.Paper presented at the Third Workshop on Subsecond Thermophysics, September 17–18, 1992, Graz, Austria.     

High-Power Quantum-Cascade Lasers Emitting in the 8-μm Wavelength Range

Technical Physics Letters - Molecular beam epitaxy techniques were used to grow a quantum-cascade laser (QCL) heterostructure based on an In0.53Ga0.47As/Al0.48In0.52As heteropair lattice-matched...     

Graphene-GaAs-graphene stacked layers for the improvement of the transmission at the wavelength of 1.55 μm

Transmission filter operating at the wavelength of 1.55 μm and based on stacked graphene-GaAs-graphene layers separated by air gaps is presented. By using the transfer matrix method (TMM), we show that the addition of a graphene layer at each interface of a GaAs-based stratified structure, which initially exhibit only 30% transmission at 1.55 μm, allows the active control of the transmission by the adjustment of the graphene chemical potential. Transmission of almost 100% at the wavelength of 1.55 μm is achieved after addition of graphene layers. These results show the potential role of stacked graphene-GaAs-graphene layers in the development of new optical active communications devices.     

Polarization strategies to improve the emission of Si-based light sources emitting at 1.55 μm

We present a electroluminescence (EL) study of the Si-rich silicon oxide (SRSO) LEDs with and without Er³⁺ ions under different polarization schemes: direct current (DC) and pulsed voltage (PV). The power efficiency of the devices and their main optical limitations are presented. We show that under PV polarization scheme, the devices achieve one order of magnitude superior performance in comparison with DC. Time-resolved measurements have shown that this enhancement is met only for active layers in which annealing temperature is high enough (>1000 °C) for silicon nanocrystal (Si-nc) formation. Modeling of the system with rate equations has been done and excitation cross-sections for both Si-nc and Er³⁺ ions have been extracted.     

A Study of the Spatial-Emission Characteristics of Quantum-Cascade Lasers for the 8-μm Spectral Range

Technical Physics Letters - Near- and far-fields of quantum-cascade lasers emitting in the spectral range near 8 μm have been studied. For all laser samples with a ridge width of 20 and 50...     

The Use of Simple Relationships between Wavefront Aberration and Wavelength to Approximate the Polychromatic Optical Transfer Functions of 8 to 12 µm Thermal Imaging Lenses

Abstract

Two methods are described which can be used to predict polychromatic optical transfer functions (OTFs) of thermal imaging lenses to good accuracy from only one finite ray trace. These methods offer some saving in calculation time and could be used to predict polychromatic OTFs from monochromatic test data provided suitable paraxial data and spectral details are available.