Lubrication oil is a vital component of heavy rotating machinery defining the machine's health, operational safety and effectiveness. Recently, the focus has been on developing sensors that provide real-time/online monitoring of oil condition/lubricity. Industrial practices and standards for assessing oil condition involve various analytical methods. Most these techniques are unsuitable for online applications. The paper presents the results of studying degradation of antioxidant additives in machinery lubricants using Fluorescence Excitation-Emission Matrix (EEM) Spectroscopy and Machine Learning techniques. EEM Spectroscopy is capable of rapid and even standoff sensing; it is potentially applicable to real-time online monitoring.
Optical free-space communications involving moving parties require precise beam pointing and mutual tracking of communicating transceivers. The existing variety of tracking techniques is still the major limiting factor in free-space laser communications. Here we propose a technique for optical beam tracking that utilizes nonlinear optical properties of materials. In our proof-of-concept experiment, a thin layer of a nematic liquid crystal (NLC) with high thermal nonlinearity was used to produce a thermal lens induced by the incoming optical beam. That beam modulated the NLC refractive index. As the transmitted optical beam passed through the same layer, the beam intensity was modulated in the far field. A sharp intensity maximum was formed at the distant communicating party position. This tracking capability has been demonstrated for angular disturbances at a subkilohertz frequency. This tracking mechanism also offers adaptive capability of compensation of strong aberrations. Such compensation has been demonstrated experimentally; numerical modeling performed with the Fresnel integral technique showed very good agreement with the experiment.
KEYWORDS: LIDAR, Vegetation, 3D modeling, Solar radiation models, Instrument modeling, Transmittance, Atmospheric propagation, Optical filters, Sensors, Signal to noise ratio
Structural and biophysical parameters of vegetation canopies, such as tree heights, biomass, vertical and horizontal
heterogeneity are important factors affecting flows of energy, water, carbon and trace gases through terrestrial systems.
Knowing such parameters is required to model processes associated with photosynthesis, energy transfer, and
evapotranspiration at local and global scales. Monitoring vegetation canopies has long been one of the main tasks of
several proposed and launched space missions. Lidar instruments have demonstrated the best potential to provide
estimates of vegetation height, cover, and canopy vertical structural profiles. A spaceborne lidar would deliver such data
on global scale producing the total land biomass value with the accuracy demanded by carbon-cycle and global-change
modelers.
This paper presents the preliminary results of a numerical model simulating signal returns of a spaceborne lidar for the
assessment of land-vegetation canopy biomass. It is a part of work with the overall purpose to develop a trade-off
analysis tool for a spaceborne lidar system as a payload of a land-vegetation observation space mission. An end-to-end
propagation of a spaceborne lidar sensing pulse through vegetation canopies is considered by the model. It consists of
the modules characterizing the laser and the receiver optical systems, satellite's orbit, atmosphere, vegetation canopies,
optical filtering, and detectors. This tool can be used to evaluate the effects of instrument configurations on the retrieval
of vegetation structures, and to carry out trade-off studies in the instrument design.
Optical free-space communications involving moving parties require precise beam pointing and mutual tracking of
communicating transceivers. The existing variety of tracking techniques is still the major limiting factor in free-space
laser communications. Here we propose a technique for optical beam tracking and shaping that utilize nonlinear optical
properties of materials. In our proof-of-concept experiment a thin layer of a nematic liquid crystal (NLC) with high
thermal nonlinearity was used to produce a thermal lens induced by the incoming optical beam. That beam modulated
the NLC refractive index. As the transmitted optical beam passed through the same layer the beam intensity was
modulated in the far field. A sharp intensity maximum was formed at the distant communicating party position proving
the device's tracking capability. Numerical modeling showed very good agreement with the experiment. The technique
offers - many advantages and is simple to implement.
Double phase conjugation (DPC) of two nearly opposite light waves has been theoretically and experimentally studied in a nematic liquid crystal with thermal optical nonlinearity. A model for wave coupling in the material with thermal nonlinearity has been analyzed for the DPC threshold conditions. DPC of two mutually incoherent laser beams has been demonstrated in a nematic liquid crystal (NLC) multilayer structure in good agreement with the model. An all-optical beam tracker consisting of such a structure has been built and demonstrated to compensate for beam/reflector jitter.
High-speed free-space communications have been increasingly studied for applications ranging from short-distance ground-to-ground transmissions to inter-spacecraft links. Optical communications involving moving parties, especially at extra-long distances, require precise beam pointing and mutual tracking of communicating transceivers. The design concept and preliminary test results of a free-space communicator incorporating novel nonlinear optical tracking subsystem are presented. The development goal is to demonstrate a cost-effective terminal for Gbps optical links at a distance of up to 5 km. The tracking system consists of three subsystems: the coarse tracker (a 10.5 cm-diameter motorized Maksutov telescope); the electro-optical tracker (a voice-coil and a Si-based position detector); and the nonlinear optical fine tracker (a nonlinear cell with an IR-sensitive liquid crystal). Three-stage tracking allows for link budget improvement and maintaining a microradian pointing precision.
We report the concept and preliminary test results of development of a three-stage beam tracking system for demonstration of a Gbps free-space laser communicator. The development goal has been high-speed optical inter-satellite communications. The tracking system consists of three sub-systems: the coarse tracker (a 10.5 cm-diameter motorized Maksutov telescope with acquisition sensor); the intermediate electro-optical tracker (a voice-coil and a Si-based position detector), and the nonlinear optical fine tracker (a nonlinear cell with a liquid crystal). Three-stage tracking allows for efficient compensation of jitter of up to kHz while maintaining a sub-microradian pointing precision. A combination of the tracking system with a signal feed / modulation unit has been designed to demonstrate a 2.5-10 Gbps-level performance at distances of about 5-7 km.
The paper presents the results of experimental study of an optical-beam tracking concept involving two systems based on different principles. One is all-optical tracking, which utilizes a nonlinear optical material providing automatic fine-tracking feature. Another is traditional opto-mechanical technology using a quadrant avalanche detector, a voice coil-mirror actuator, control electronics, and computer interface. The possibility of establishing automatic mutual tracking between two communicating parties without involving computer-aided beam addressing has been experimentally proven. Capabilities and limitations of both systems are described. The all-optical system performs better than the traditional one when it tracking laser beam angular disturbances of magnitude of a few mrad and the jitter frequency is high (≥100 Hz). The traditional opto-mechanical system shows higher efficiency at lower jitter frequencies. A combination of an all-optical fine-tracking module and an opto-mechanical coarse tracking module is suggested for applications where using our originally proposed all-optical approach for both coarse and fine beam steering / tracking would be less efficient.
High bit-rate laser communications have been increasingly studied for applications ranging from short-distance transmissions to inter-spacecraft links. Optical communications involving moving parties require precise beam pointing and mutual tracking of communicating transceivers. Current approaches based on electro-mechanical beam steering are limited by the need for large volumes of beam-addressing computing and difficulties in providing automatic tracking/pointing capabilities to compensate for rapid changes in directivity patterns, transmitters’ relative misplacement and jitter [1].
An all-optical adaptive beam-tracking approach, proposed by some of the authors earlier, is based on the double phase conjugation effect (DPC) [2]. No mechanical steering, positioning or addressing computing are needed for fine tracking in such a bi-directional optical link. The approach efficiency strongly depends on non-linear properties of the used optical materials, which have been thoroughly studied [3].
This paper presents the results of theoretical analysis and further experimental studies of the DPC all-optical tracking technology. In the experiment, two optical terminals were linked with a modulated laser signal at a telecommunication wavelength. A DPC-mirror was a multi-layer liquid-crystal stack with a giant optical nonlinearity. The tracking and communication capabilities were simultaneously demonstrated in a range of angles, transmission rates and laser power levels. The experiment was in good agreement with the theoretical model.
REFERENCES
1. E Lerner, Laser Focus World 36 11 2000
2. A Dudelzak, A Kuzhelev, A Novikov, G Pasmanik, Patent Application 12346-US-Prov 2002
3. A Kuzhelev, A Dudelzak, J Opt A: Pure and App Opt 5 L5 2003
Results of in-vitro studies of bactericidal effects of ultraviolet (UV) irradiation on strains causing drug-resistant endo-cavital infections (Enterococcus, Staphylococcus aureus, Pseudomonas aeruginosa, and others) are presented. An original technique to measure effects of UV-irradiation on bacterial growth at different wavelengths has been developed. Spectral dependences of the bactericidal effect have been observed, and spectral maxima of bactericidal efficiency have been found. Applications to curative treatments of wounds, post-surgical intra-abdominal abscesses and other diseases are discussed.
The study of thermally induced holographic gratings written in NLC by the laser beams at telecommunication wavelength of 1500 nm is presented. Thermally induced gratings are especially interesting as having at least one order of magnitude faster response time than orientational gratings. However, their formation in the range 1300-1600 nm is limited due to small absorption of NLCs and absence of effective doping. The formation of thermal grating in our cell is initiated by absorption in the cell walls coating. The tuning of liquid crystal temperature and orientational enhancement of thermal grating allowed us to reach 3% level of diffraction efficiency at low writing beams intensity (23 Wcm-2) and small thickness of material (0.02 mm). Holographic liquid crystal devices can be used in all-optical switching, beam routing, automatic wave front correction, phase conjugation etc.
The paper presents the results of a study of the spatial structure of Si-containing [poly(ethynediyl-arylene-ethynediyl-silylene)] composites in the nanometer scale, as well as of an optical study of photorefractive effects in the visible and near-infrared ranges in these composites. The compositions have been examined using transmission/diffraction electron microscopy. The results suggest the existence of an extraordinary self-organisation in conjugated silicon organometallic polymers (nano-structured layers with a spatial period of several nanometers and the length of more than 100 nm). The most probable mechanism of the structure formation is π-stacking of the aromatic groups with the poly(phenylsilsesquioxane) matrix as a template. The observed self-organisation is very important for the understanding of the infrared photorefractive effect in the organometallic polymer compositions. Two-wave mixings in the Raman-Nath and Bragg modes were used to study non-linear optical properties in the visible (632 nm) and near-infrared (1500 nm) spectral ranges. Both local and non-local types of refractive index gratings have been observed.
The paper overviews capabilities of a multi-wavelength laser remote sensing technique in real-time analytical monitoring of aquatic and terrestrial targets. The conceptual design of the Fluorescent Lidar Spectrometer (FLS) - a compact, multipurpose analytical lidar - is described. Its modular architecture allows efficient research and routine monitoring applications from small boats or aircraft. Depending on the application requirements, the FLS analytical performance can be optimized with features such as variable excitation wavelengths and high-speed, gated hyper-spectral detection. The Spectral Fluorescent Signature (SFS) concept, which forms the background for the FLS functioning, has been successful in the detection and identification of trace organics in various environmental, industrial and other mixtures.
FLS-lidars have been used in a variety of applications ranging from detecting chemical pollution in water and on soil to classifying marine dissolved organic matter (DOM) and mapping spatial distributions of phytoplankton in the Baltic, North and Norwegian seas. The presented field data obtained with shipborne and airborne FLS illustrate the approachs potential for real-time monitoring of marine, coastal and inland-water environments. Future developments are discussed.
Polymeric photorefractive materials have attracted much attention over the past decade due to their potential applications, especially for optical information processing. However, their practical use has until now been limited, the available photosensitizers being efficient only in the visible range. Here, the chemical development and optical investigations of a photorefractive polymeric material active at 1500 nm are described. To our knowledge, this is the first such material to be reported. A conjugated poly[(ethynediyl)(arylene)(ethynediyl)silylene] acts as both an optical chromophore, as well as charge generator and conductor. Its absorption band tails into the near-IR hence providing charge generation at the 1500 nm excitation. The photoconductivity of the composite samples was measured with a dc-method using a 1500 nm diode laser source. The electro-optical coefficient was measured with a simple reflection technique. The photorefractive response was investigated with a two-beam coupling technique. The gain of the probe beam intensity, delivered from the pumping beam, reached 40 cm-1 at the electric field strength of 650 kVcm-1 thus confirming the photorefractive nature of the grating. The gain exceeded the absorption (30 cm-1) that showed a good potential of this material for applications.
This paper is presented to give a general description of the ORACLE project and of the technology development results obtained to date. ORACLE is a feasibility study of a fully automated differential absorption lidar for global measurements of tropospheric and stratospheric ozone and aerosols with high vertical and horizontal resolution. The proposed program includes both novel technology demonstrations and obtaining scientific data from spacecraft. These data are needed to address key issues in atmospheric research including the depletion of stratospheric ozone, global warming, atmospheric transport and dynamics, tropospheric ozone budgets, atmospheric chemistry, and the atmospheric impact of hazards. Only a space-based lidar system can provide the required spatial resolution for ozone and aerosols in both the stratosphere and the troposphere on a global scale at all required altitudes. To deliver these data, the most novel technologies such as all-solid-state lasers, photon-counting detectors and ultra-lightweight deployable telescopes must be employed in the mission payload.
Field measurements of the spatial distribution of phytoplankton by tunable lidar on board a research vessel are reported. The possibility of applying laser remote sensing to the diagnostics of hydrophysical processes in the upper layers of the sea is discussed. Twelve tracks in different directions were sensed. Marked periodical structures were observed when the vessel was moving at small angles in the direction of a swell. The frequencies of periodic structures correlated with the angle between the vessel's motion and swell directions. When this angle was increased, the frequency increased proportionally. At a right angle, the periodic structures disappeared. The results do not contradict the hypothesis of the influence of internal waves on the spatial distribution of phytoplankton.
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