Low-coherence doppler lidar with multiple time coherence of reference and probe waves

The notion of multiple time coherence of optical beams is introduced and mathematically analyzed for the first time. Mathematical simulation is used to demonstrate the possibility of the generation of multiple fiber pulses (MFPs), which exhibit multiple time coherence, and the possibility of their application for the laser Doppler anemometry of spatially separated scattering objects (including the realization of wind coherent Doppler lidars). A method to obtain MFPs of a given duration with the means of fiber-optic commutation is proposed. The method is based on nanosecond lasers with a limited coherence length realized in a set of fiber topologies. The concept of a low-coherence Doppler lidar with the multiple time coherence of the reference and probe waves is formulated. The energy parameters of the lidar are mathematically simulated for one of the topologies of the MFP device.     

<Superscript>13</Superscript>C NMR studies of isomerization of <Emphasis Type="SmallCaps">D</Emphasis>-glucose in an aqueous solution of Ca(OH)<Subscript>2</Subscript>. The effect of molecular oxygen

Isomerization of D-glucose to fructose and mannose in aqueous solutions of Ca(OH)₂ with the initial pH 11.4 in a temperature interval of 20–90 °C was studied by ¹³C NMR spectroscopy in the presence and absence of dissolved oxygen. In the presence of oxygen, the apparent equilibrium isomerization constant is much lower than that in the absence of oxygen. This is related to the oxidation of monosaccharides to formic and aldonic acids, a decrease in the pH of solutions, and cessation of isomerization at pH < 9. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1909–1913, August, 2005.     

The arithmetic of distributions in free probability theory

We give an analytical approach to the definition of additive and multiplicative free convolutions which is based on the theory of Nevanlinna and Schur functions. We consider the set of probability distributions as a semigroup M equipped with the operation of free convolution and prove a Khintchine type theorem for the factorization of elements of this semigroup. An element of M contains either indecomposable (“prime”) factors or it belongs to a class, say I ₀, of distributions without indecomposable factors. In contrast to the classical convolution semigroup, in the free additive and multiplicative convolution semigroups the class I ₀ consists of units (i.e. Dirac measures) only. Furthermore we show that the set of indecomposable elements is dense in M.     

Properties of calcium phosphate coatings deposited by high-power ion beam ablation plasma

Biocompatible hydroxyapatite coatings (Ca₁₀(PO₄)₆(OH)₂) are used in stomatology and orthopedic surgery as an original structure for production of medical materials. These coatings have been deposited on Si, Ti and VT15-alloy substrates from ablation plasma formed under the impact of pulsed high-power ion beams on a calcium phosphate ceramic target. The nanohardness, Young’s modulus, elastic recovery, adhesion of coatings to substrates, friction constant, and surface roughness were measured.     

Stress-strain State of Dispersion-hardened Aluminum Tube Under External and Internal Pressure

Russian Physics Journal - The paper presents research into the stress-strain state of a heavy-walled aluminum alloy tube strengthened by incoherent nanoparticles, subjected to the external and...     

Reabsorption of laser-induced fluorescence in a plant canopy: Stochastic model

This paper continues the series of publications on the statistical simulation of transspectral processes. A system of interrelated radiative transfer equations is proposed. This system gives a formal basis for a numerical analysis of a wider range of spectroscopic effects that accompanies the propagation of laser radiation in the environment, such as the reabsorption of fluorescence in dense disperse media containing two and more fluorophores. As applied to the problem of lidar monitoring of the state of a plant canopy, an optical model is developed in which a leaf is not treated as an individual scattering element, but rather as a local volume of a multiphase medium with a complex polydisperse structure. The Monte Carlo algorithms have been modified so that they have achieved the simulation of fluorescence and reabsorption processes. Test calculations have demonstrated the adequacy of the proposed approach.     

Basic principles of pulsed-wind Doppler lidars with multitime coherence

A concept of multitime coherence (MTC) of optical beams is proposed. Two versions of fiber multiplicator topologies are presented, which are intended for the generation of multiple fiber pulses (MFP) possessing the MTC property. The fiber multiplicators may be a useful tool for Doppler laser anemometry of spatially separated scattering objects. Moreover, their use makes feasible the implementation of low-coherence wind Doppler lidars on the base of laser sources having a limited-time coherence (from one to a few tens of nanoseconds) and a high-velocity measurement resolution. Different lidar systems that feature a ring-fiber resonator (RFR) for reference wave generation are proposed. Two systems are also considered: (i) one based on a multimode fiber topology, which provides for the sensing ns-pulse generation and for the reference and probe wave multiplication; (ii) one based on a single-mode fiber topology, which provides for ns-pulse sensing and for the signal and reference wave multiplication. The concept of a low-coherence Doppler lidar system intended for atmospheric-sensing applications, which makes use of reference and signal waves possessing the MTC properties, is formulated for the first time.