Determination of the temperature corrections to the readings of measuring instruments under dynamic temperature conditions

A method of obtaining the temperature corrections to readings of measuring instruments, taking their thermal inertia into account, when the temperature of the medium changes is proposed. The procedure was tested under laboratory conditions on static nonthermostated gravimeters. The results of the investigations, which confirm the effectiveness of the proposed procedure, are presented. __________ Translated from Izmeritel’naya Tekhnika, No. 1, pp. 50–52, January, 2007.     

Laser-induced reaction in Cu---In---Se systems

Laser-induced synthesis of CuInSe₂ has been investigated at various laser fluences by using electron diffraction and Raman spectroscopy techniques. The analysis of the products of irradiation shows that different phases of Cu---In---Se are formed according to the incident power of the radiation. When the laser power is lower than the threshold value (164 W cm⁻²), several binary phases are obtained. At threshold power, however, almost all binary phases are absent and reasonably good quality CuInSe₂ thin films are obtained.     

Diffusive-to-ballistic transition in dynamic light transmission through thin scattering slabs: a radiative transfer approach

We study the deviation from diffusion theory that occurs in the dynamic transport of light through thin scattering slabs. Solving numerically the time-dependent radiative transfer equation, we obtain the decay time and the effective diffusion coefficient Deff. We observe a nondiffusive behavior for systems whose thickness L is smaller than 8l(tr), where l(tr) is the transport mean free path. We introduce a simple model that yields the position of the transition between the diffusive and the nondiffusive regimes. The size dependence of Deff in the nondiffusive region is strongly affected by internal reflections. We show that the reduction of approximately 50% of Deff that was observed experimentally [Phys. Rev. Lett. 79, 4369 (1997)] can be reproduced by the radiative transfer approach. We demonstrate that the radiative transfer equation is an appropriate tool for studying dynamic light transport in thin scattering systems when coherent effects play no significant role.     

Laser-induced damage studies in silicon and silicon-based photodetectors

Laser-induced damage studies have been carried out on single-crystal silicon and silicon-based photodetectors, FND 100 P-I-N photodiodes, and C30954E avalanche photodiodes as a function of repetition frequency for a 1064-nm wavelength. It has been observed that the damage threshold decreases significantly when the samples are irradiated with a large number of pulses. However, this effect is evident only when the repetition frequency is greater than 1 Hz. The results are discussed in light of various existing theories.     

激光诱导击穿光谱及其在元素分析中的应用

激光诱导击穿光谱是一种新的元素分析方法,但仍处于不断完善之中。利用它可以分析不同形态样品的成分,因此在成分分析和微量元素检测方面具有重要的应用前景。本文阐述了激光击穿诱导光谱仪的基本原理和激光诱导击穿光谱在多个领域中的应用,研究内容涉及固体样品、液体样品、气体样品、微量杂质分析和成分深度剖析等,并分析了基体效应、自吸收效应、测量时间、环境气体、激光参数等对激光诱导击穿光谱分析结果的影响。     

Laser-induced processes in the IR range in nanocomposites with fullerenes and carbon nanotubes

Laser-induced processes in the IR spectral range, which are related to manifestations of the optical limiting in composite systems containing fullerenes and carbon nanotubes (CNTs), have been studied. Organic materials based on polyimides (PIs), 2-cyclooctylamine-5-nitropyridine (COANP), polyanilines, and dispersed liquid crystal (LC) structures were used as nanoparticle-sensitized matrices. Manifestations of optical limiting in the IR range at 1047, 1080, 1315, and 2940 nm are demonstrated and the position of composites studied among other systems used for optical limiting in the IR range is determined. The optical limiting at 1080 nm in CNT-containing solutions and LC cells was studied and the levels of limiting in thin-film PI-based nanocomposites with CNTs are established. A microscopic examination of thin PI films with CNTs revealed the structure of quasi-photonic crystals formed in these systems.     

球面波散射因子对光电子全息的影响

用于研究物质结构的光电子全息 ,其物理机制是光电子波在固体中的散射。在电子能量为 5 0～ 2 0 0eV的中低能量下 ,不能用通常的平面波近似方法加以研究 ,必须考虑到光电子波的球面波本质。即使在电子能量大于 5 0 0eV的高能情况下 ,用平面波近似的方法也应对前向散射进行修正。本文以铜单晶薄膜为例 ,利用单重散射模型讨论了球面波近似模型下校正因子对光电子全息函数的影响 ,并与平面波近似作了比较。结果表明 ,对能量低于 2 0 0eV的光电子全息来说 ,球面波近似校正因子对前向散射和背向散射的振幅和相位都有较明显的修正。而在高能条件下 ,球面波近似校正因子主要影响光电子的前向散射 ,对背向散射的影响较小。进一步研究发现 ,球面波近似校正可以提高光电子全息的重现图的质量。     

Floquet stability analysis of the longitudinal dynamics of two hovering model insects

Because of the periodically varying aerodynamic and inertial forces of the flapping wings, a hovering or constant-speed flying insect is a cyclically forcing system, and, generally, the flight is not in a fixed-point equilibrium, but in a cyclic-motion equilibrium. Current stability theory of insect flight is based on the averaged model and treats the flight as a fixed-point equilibrium. In the present study, we treated the flight as a cyclic-motion equilibrium and used the Floquet theory to analyse the longitudinal stability of insect flight. Two hovering model insects were considered—a dronefly and a hawkmoth. The former had relatively high wingbeat frequency and small wing-mass to body-mass ratio, and hence very small amplitude of body oscillation; while the latter had relatively low wingbeat frequency and large wing-mass to body-mass ratio, and hence relatively large amplitude of body oscillation. For comparison, analysis using the averaged-model theory (fixed-point stability analysis) was also made. Results of both the cyclic-motion stability analysis and the fixed-point stability analysis were tested by numerical simulation using complete equations of motion coupled with the Navier–Stokes equations. The Floquet theory (cyclic-motion stability analysis) agreed well with the simulation for both the model dronefly and the model hawkmoth; but the averaged-model theory gave good results only for the dronefly. Thus, for an insect with relatively large body oscillation at wingbeat frequency, cyclic-motion stability analysis is required, and for their control analysis, the existing well-developed control theories for systems of fixed-point equilibrium are no longer applicable and new methods that take the cyclic variation of the flight dynamics into account are needed.     

Active galaxies and radiative heating

There is abundant evidence that heating processes in the central regions of elliptical galaxies have both prevented large-scale cooling flows and assisted in the expulsion of metal rich gas. We now know that each such spheroidal system harbours in its core a massive black hole weighing ca. 0.13% of the mass in stars and also know that energy was emitted by each of these black holes with an efficiency exceeding 10% of its rest mass. Since, if only 0.5% of that radiant energy were intercepted by the ambient gas, its thermal state would be drastically altered, it is worth examining in detail the interaction between the out-flowing radiation and the equilibrium or inflowing gas. On the basis of detailed hydrodynamic computations we find that relaxation oscillations are to be expected with the radiative feedback quite capable of regulating both the growth of the central black hole and also the density and thermal state of the gas in the galaxy. Mechanical input of energy by jets may assist or dominate over these radiative effects. We propose specific observational tests to identify systems which have experienced strong bursts of radiative heating from their central black holes.     

Bistability in radiative heat exchange

The possibility of a bistable regime in systems with radiative heat exchange is theoretically demonstrated for the first time. The transfer characteristics of a radiation-closed stationary system have been calculated, in which the radiator is a blackbody and the absorber is made of a material with the absorptivity sharply increasing in a certain temperature interval. The radiator and absorber are separated by a vacuum gap. The heat exchange between the system and the environment is controlled by varying the flow rate of a heat-transfer agent cooling the absorber. The output parameter of a bistable system is the absorber temperature, while the input parameter can be either the radiator temperature or the heat-transfer agent flow rate. Depending on the choice of the input parameter, the transfer characteristic of the system is either represented by a usual S-like curve or has an inverted shape.     

Measuring radiative losses in the globus-M spherical tokamak

We report on the first measurement of the absolute values of radiative losses in the Globus-M spherical tokamak. Measured by a wide-aperture pyroelectric bolometer, the radiative losses amount to about 30% of the total power deposited in the discharge, which is indicative of a sufficiently high purity of plasma in the experimental setup. Radiative losses on such a level have to be taken into account in determining the energy confinement time of the tokamak plasma. A new method is proposed for calibrating the bolometer using the data of other diagnostic techniques for the current ramp up stage, which provides for a coincidence up to within 15% with the calibration data obtained on a test bench.     

Comparison of the Gauss-Seidel spherical polarized radiative transfer code with other radiative transfer codes

Calculations that use the Gauss-Seidel method are presented of the diffusely scattered light in a spherical atmosphere with polarization fully included. Comparisons are made between this method and the Monte Carlo calculations of other researchers for spherical geometry in a pure Rayleigh atmosphere. Comparisons with plane-parallel atmospheres are also presented. Single-scatter intensity comparisons with spherical geometry show excellent agreement. When all orders of scattering are included, comparisons of polarization parameters I, Q and U as well as the plane of polarization show good agreement when allowances are made for the statistical variability inherent in the Monte Carlo method.     

Laser-induced synthesis,deposition and etching of materials

The field of laser-induced synthesis, deposition and etching of materials is reviewed with an emphasis on the emerging trends and novel adaptations of the basic laser processing concepts. A number of examples are cited to illustrate the issues involved. These include rapid synthesis of titanium nitride by pulsed laser induced reactive quenching at Ti:liquid NH₃ interface, laser deposition of good quality thin films of such materials as hot oxide superconductors, zinc ferrite, iron oxide, stainless steel, etc. and laser etching of superconductor films.     

Relationship between the Kubelka-Munk scattering and radiative transfer coefficients

The relationship between the Kubelka-Munk (K-M) and the transport scattering coefficient is obtained through a semi-empirical approach. This approach gives the same result as that given by Gate [Appl. Opt.13, 236 (1974)] when the incident beam is diffuse. This result and those given by Star et al. [Phys. Med. Biol.33, 437 (1988)] and Brinkworth [Appl. Opt.11, 1434 (1972)] are compared with the exact solution of the radiative transfer equation over a large range of optical properties. It is found that the latter expressions, which include an absorption component, do not give accurate results over the range considered. Using the semi-empirical approach, the relationship between the K-M and the transport scattering coefficient is derived for the case where the incident light is collimated. It is shown that although the K-M equation is derived based on diffuse incident light, it can also represent very well the reflectance from a slab of infinite thickness when the incident light is collimated. However, in this case the relationship between the coefficients has to include a function that is dependent on the anisotropy factor. Analysis indicates that the K-M transform achieves the objective of obtaining a measure that gives the ratio of absorption to scattering effects for both diffuse and collimated incident beams over a large range of optical properties.     

Light scattering described in the mode picture

A system of orthonormal functions representing the eigenmodes of an optical resonator with perfectly spherical mirror surfaces has been described in the literature. In real experiments, however, the wave front of the passing beam will be deformed by surface irregularities or index inhomogeneities inside components traversed by the beam. We describe quantitatively the relative power transferred out of the fundamental mode into higher-order modes by these irregularities.     

Laser-induced breakdown spectroscopy at high temperatures in industrial boilers and furnaces

Laser-induced breakdown spectroscopy (LIBS) was applied (1) near the superheater of an electric power generation boiler burning biomass, coal, or both; (2) at the exit of a glass-melting furnace burning natural gas and oxygen; and (3) near the nose arches of two paper mill recovery boilers burning black liquor. Difficulties associated with the high temperatures and high particle loadings in these environments were surmounted by use of novel LIBS probes. Echelle and linear spectrometers coupled to intensified CCD cameras were used individually and sometimes simultaneously. Elements detected include Na, K, Ca, Mg, C, B, Si, Mn, Al, Fe, Rb, Cl, and Ti.