NASA multipurpose airborne DIAL system and measurements of ozone and aerosol profiles

An airborne differential absorption lidar (DIAL) system has been developed for the remote measurement of gas and aerosol profiles in the troposphere and lower stratosphere. The multipurpose DIAL system can operate from 280 to 1064 nm for measurements of ozone, sulfur dioxide, nitrogen dioxide, water vapor, temperature,pressure, and aerosol backscattering. The laser transmitter consists of two narrow linewidth Nd: YAG pumped dye lasers with automatic wavelength control. The DIAL wavelengths are transmitted with a 00-,usec temporal separation to reduce receiver system complexity. A coaxial receiver system is used to collect and optically separate the DIAL and aerosol lidar returns. Photomultiplier tubes detect the backscattered laser returns after optical filtering, and the analog signals from three tubes are digitized and stored on high-speed magnetic tape. Real-time gas concentration profiles or aerosol backscatter distributions are calculated and displayed for experiment control. Operational parameters for the airborne DIAL system are presented for measurements of ozone, water vapor, and aerosols in the 290-, 720-, and 600-nm wavelength regions, respectively. The first ozone profile measurements from an aircraft using the DIAL technique are discussed in this paper. Comparisons between DIAL and in situ ozone measurements show agreement to within +/-5 ppbv in the lower troposphere. Lidar aerosol data obtained simultaneously with DIAL ozone measurements are presented for a flight over Virginia and the Chesapeake Bay. DIAL system performance for profiling ozone in a tropopause folding experiment is evaluated, and the applications of the DIAL system to regional and global-scale tropospheric investigations are discussed.     

Reconstruction of spatially inhomogeneous dielectric tensors through optical tomography

A method to reconstruct weakly anisotropic inhomogeneous dielectric tensors inside a transparent medium is proposed. The mathematical theory of integral geometry is cast into a workable framework that allows the full determination of dielectric tensor fields by scalar Radon inversions of the polarization transformation data obtained from six planar tomographic scanning cycles. Furthermore, a careful derivation of the usual equations of integrated photoelasticity in terms of heuristic length scales of the material inhomogeneity and anisotropy is provided, resulting in a self-contained account about the reconstruction of arbitrary three-dimensional, weakly anisotropic dielectric tensor fields.     

Chamber lidar measurements of biological aerosols

In order to determine the performance of standoff sensors against agents, there is a need to develop methods to characterize the optical properties of biological warfare agents. The goal of this work is to develop a methodology that would allow the characterization of agent optical cross sections from the UV to the longwave IR. The present work demonstrates an optical measurement architecture based on lidar technology, allowing the measurement of backscatter and depolarization ratio from biological aerosols (either simulants or agents) released in a refereed, 1m³ chamber. Measured results on simulant materials are calibrated and compared to theoretical simulations of the cross sections.     

Error analysis of DIAL measurements of ozone by a Shuttle excimer lidar

An error analysis of DIAL (differential absorption lidar) measurements of stratospheric ozone from the Space Shuttle is discussed. A transmitter system consisting of a KrF excimer laser pumping gas cells of H2 or D2 producing output wavelengths in the near UV is shown to be useful for the measurement of ozone in a 15-50-km altitude range.     

Linear stability criteria in a reaction-diffusion equation with spatially inhomogeneous delay

Time delays play an important role in many biological and ecological systems. However, they are usually incorporated into mathematical models in a way not explicitly dependent on space, even though the delay may be modelling some environmental aspect of the system. In this paper we study a scalar reaction-diffusion equation with a spatially inhomogeneous delay, taken for simplicity in the form of a step function of the spatial coordinate. We derive the dispersion relation from which analytical results on the stability or instability of the uniform steady states can be determined. We confirm and extended these results by numerical simulations which confirm the possibility of qualitatively different types of behaviour on different parts of the spatial domain.     

Optical properties of tropospheric aerosols determined by lidar and spectrophotometric measurements (Photochemical Activity and Solar Ultraviolet Radiation campaign)

We present the results of the aerosol measurements carried out over the Aegean Sea during the Photochemical Activity and Solar Ultraviolet Radiation campaign held in Greece during June 1996. Simultaneous observations performed with a lidar and a double-monochromator spectrophotometer allowed us to retrieve the optical depth, the Angstr?m coefficient, and the backscatter-to-extinction ratio. The Sun photometric data can be used to improve quantitative aerosol measurements by lidar in the Planetary Boundary Layer. Systematic errors could arise otherwise, because the value of the backscatter-to-extinction ratio has to be supplied. Instead this ratio can be retrieved experimentally by use of an iterative solution of the lidar equation.     

Generation of an extreme ultraviolet supercontinuum in a two-color spatially inhomogeneous field

We theoretically investigate the high-order harmonic generation from the helium ion in a two-color spatially inhomogeneous laser field. The numerical calculations show that this spatiotemporally synthesized laser field can not only significantly extend the harmonic cut-off, but also generate an ultrabroad extreme ultraviolet supercontinuum with a 1737 eV bandwidth. In addition, the spatiotemporal combination can eliminate the long quantum path and select the short one, and then an ultrashort isolated 12.3 as pulse with a bandwidth of 310.2 eV is obtained directly. Further, the dependences of the harmonic spectrum on the parameters including spatial inhomogeneity, time delay, carrier-envelope phase, and intensity are further discussed.     

Theoretical investigation of Josephson tunnel junctions with spatially inhomogeneous superconducting electrodes

The microscopic theory of the Josephson effect in tunnel structures with electrodes having spatially inhomogeneous superconducting properties is formulated. Two mechanisms of inhomogeneity are considered. The first is associated with the presence of a thin transition normal layer located near the tunnel barrier, which is relevant for junctions based on refractory superconductors. The second case is the trapping of Abrikosov vortices by junction electrodes. The tunnel current components are calculated numerically in the whole temperature range 0<T<T _c and magnetic field range 0<H<H _c2. It is shown that the tunnel current is extremely sensitive to the type of smearing of the singularities of the classical tunnel theory ateV=2. The results allow experimental determination of the characteristics of real tunnel junctions.     

Numerical modeling of thermomechanical processes in absorption of laser radiation in spatially inhomogeneous media

A numerical model making it possible to consider, with exhaustive completeness, processes that occur in the absorbing spatially inhomogeneous liquid medium on exposure to pulsed laser radiation has been presented. Numerical experiments have shown the efficiency of the presented procedure of calculation in a wide range of pulse durations (from micro- to femtosecond ones) and for typical energy parameters of laser systems.     

A numerical solution algorithm for the spatially inhomogeneous equations of kinetic breakdown

A computational algorithm is described, based on the total approximation method. The discussion is centered on the example of the model problem of laser break-down of high-pressure atomic nitrogen near a metallic surface.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 55, No. 4, pp. 629–638, October, 1988.     

Reduced accuracy in infrared measurements in the presence of industrial aerosols

Translated from Izmeritel'naya Tekhnika, No. 12, pp. 52–53, December, 1992.     

Ultraviolet upconversion fluorescence of Er3+ in Yb3+/Er3+-codoped Gd2O3 nanotubes

Under 980 nm excitation, room-temperature ultraviolet (UV) upconversion (UC) emissions of Er3+ from the 4G(9/2), 2K(13/2), and 2P(3/2) states were observed in Gd2O3:Yb3+/Er3+ nanotubes, which were synthesized via a simple wet-chemical route at low temperature and ambient pressure followed by a subsequent heat treatment at 800 degrees C. The experimental results exhibited that these UV emissions came from four-photon UC processes. In the Gd2O3:Yb3+/Er3+ nanocrystals, the energy transfers (ETs) from Yb3+ to Er3+ played important roles in populating the high-energy states of Er3+ ions. This material provides a possible candidate for building UV compact solid-state lasers or fiber lasers.     

Elastostatic interaction of multiple arbitrarily shaped cracks in plane inhomogeneous regions

A numerical technique has been developed for the determination of stress fields associated with multiple arbitrarily shaped cracks in plane inhomogeneous regions. The procedure allows the elastostatic analysis of cracks interacting with one or more straight bimaterial interfaces; of cracks located near, or emanating from, circular inclusions; and of cracks that emanate from single or multiple origins. The cracks may be branched or blunted, and may be subjected to arbitrarily applied stresses. The technique employs an efficient surface integral method, using distributions of edge dislocations to represent the cracks. The resulting singular integral equations are solved using a Gauss-Chebyshev integration formula; appropriate conditions are developed for closing the set of equations governing cracks intersecting inhomogeneity boundaries, based on a consideration of the stresses and displacements at the points of intersection. Crack-tip stress intensity factor results are presented for several crack configurations. The overall scheme provides a more general, direct, and convenient approach than other available schemes. A computer program has been developed to implement the various formulations in a single framework.     

Reconstruction of refractive indices from spectral measurements of monodisperse aerosols

For the investigation of two-component aerosols, one needs to know the refractive indices of the two aerosol components. One problem is that they depend on temperature and pressure, so one needs for their determination a robust measurement instrument such as the FASP device, which can cope with rigid environmental conditions. In this article, we show that the FASP device is capable of measuring the needed refractive indices, if monodisperse aerosols of the pure components are provided. We determine the particle radii of the monodisperse aerosols needed for this task and investigate how accurate the measurements have to be in order to retrieve refractive indices in a sufficient quality, such that they are suitable for investigations of two-component aerosols.     

The detection of transient-like signals in the presence of a spatially inhomogeneous,nonstationary noise field

We will consider the problem of detecting transient-like signals by means of a spatially distributed array of sensors embedded in an inhomogeneous, nonstationary noise field. If each element of the array has an independent, uncorrupted reference sensor to estimate the noise statistics, then conventional adaptive noise cancellation algorithms can be used to improve the detection process. However, because of practical real-world constraints, independent, uncorrupted reference sensors for the noise might not be available. Thus, the applicability of conventional adaptive noise cancellation techniques is in question. This paper will discuss the development of a knowledge-based signal-processing system that uses Artificial Intelligence (Al) methodologies to adaptively cancel inhomogeneous, nonstationary noise from a distributed array of passive sensors that is constrained to have no noise-reference sensors.     

Orbital and spin parts of energy currents for electromagnetic waves through spatially inhomogeneous media

We investigate electromagnetic waves propagating through non-magnetic and loss-free dielectric media, but with spatially inhomogeneous refractive indices. We derive hence a set of analytic formulae for conservation laws and energy-current (Poynting) vector. As a result, we deduce that the energy-current vector cannot be neatly separated into its orbital and spin parts in contrast to the cases with spatially homogeneous media. In addition, we present physical interpretations of the two additional terms due to spatial material inhomogeneity.