bluuebunny/crossref_metadata_2025 huggingface dataset:
Laser Spectroscopic Diagnostics for CVD Diamond Growth
Authors: Shaw Robert W. , Whitten W. B. , Ramsey J. M.
Published: February 2023

Chemical vapor deposition (CVD) methods have become increasingly important for the manufacture of technologically-significant thin films. Numerous examples exist in the semiconductor and wear hardening coatings industries. The growth of polycrystalline diamond thin films from light hydrocarbons has recently received great interest, and several U. S. and foreign manufacturers have already begun to market products.
Optical and Laser Diagnostics for Molten Carbonate Fuel Cells
Authors: Palmer Byron A. , Funk David J. , Oldenborg Richard
Published: February 2023

Molten-carbonate fuel cells (MCFCs) operate at 650°C and 0.1-1 MPa. MCFCs generate electrical energy through the conversion of the fuel gas (either natural gas or coal gas) using an electrolyte of molten carbonate with nickel electrodes. Because of the heat and the corrosive nature of the carbonate and gases, traditional diagnostics are not applicable. We have developed several diagnostics that can be used in such cells for in-situ measurements. We demonstrated CARS as an in-situ detector for major species, especially CO2, in a MCFC. Measurements of CO2 concentrations over a cell give a spatial measure of the operation and efficiency of the cell. We have also demonstrated laser-induced breakdown spectroscopy and photo-fragment spectroscopy as viable techniques for studying the gaseous alkali halides and alkali hydroxides that form as a result of chlorine contamination in the feed gas. We will also talk about our work on a HC1 monitor for the feed lines.
Surface Raman Scattering as a Probe of Metal Surface Chemistry
Authors: Pemberton Jeanne E.
Published: February 2023

Raman scattering is an attractive probe of surface and interfacial chemistry at metals due to the high degree of molecular specificity inherent in the results. One aspect of Raman scattering that enhances its utility for the study of metal surfaces is the ability to deduce orientational information about molecules at these metal surfaces from the presence of oriented electric fields at these surfaces with which selective vibrational modes can couple. These "surface selection rules" have been both theoretically described and experimentally validated for a variety of metal surfaces. Given the wealth of information available from such studies, potential applications for surface Raman scattering span the range from electrochemical to catalytic systems. Thus, considerable effort has been expended in an attempt to develop Raman scattering for the study of surface and interfacial phenomena. These efforts have largely been focused on overcoming problems attendant to sensitivity and selectivity for the interface in the presence of the bulk environment.
Remote thermometry of evaporating water drops as an octadecanol monolayer changes phase
Authors: Seaver Mark , Peele J. R.
Published: February 2023

We have used laser-based luminescence measurements to follow the temperature of an evaporating waterdrop (~ 1 mm diameter) as it compresses a monolayer of octadecanol. Our results indicate that the specific resistance to evaporation (water accommodation coefficient) of the monolayer changes slowly over periods of minutes.
Laser Fragmentation/Laser Induced Fluorescence Detection Of Chlorinated Hydrocarbons*
Authors: Jeffries Jay B. , Raiche George A. , Jusinski Leonard E.
Published: February 2023

Chlorinated hydrocarbons (CHC) have a myriad of industrial applications including solvents, feedstocks, and the components of polymeric materials. The byproduct of these industrial uses is an enormous quantity of liquid waste. Incineration is an attractive treatment process for this hazardous waste, however, the current technology is costly and highly empirical. Better fundamental knowledge of incinerator chemistry and improved diagnostic techniques will improve incinerator design and help evaluate innovative CHC destruction schemes. The development of real-time monitors of the effluent stream is necessary to satisfy environmental concerns and insure compliance of emission regulations.
Comparison of Laser Raman Measurements and Fluid Dynamic Calculations in the Characterization of Atmospheric Pressure CVD Flow Reactor
Authors: Von Drasek William , Jurcik Benjamin , Jursich Gregory
Published: February 2023

Gas flow dynamic information is obtained on an atmospheric pressure flow reactor. Density spatial profiles have been both predicted by modeling and measured experimentally using spontaneous Raman spectroscopy.
Temperature Profiles of Low Pressure Hydrocarbon Flames Determined From the Doppler Linewidths of CO Transitions
Authors: Dayton D.C. , Sausa R.C. , Kotlar A.J. , Miziolek A.W.
Published: February 2023

Tunable diode lasers are an excellent source of narrow linewidth (< 0.001 cm-1) infrared radiation which can be rapidly scanned to perform fast, high resolution absorption spectroscopy. With the advantages of high sensitivity and high resolution, tunable diode laser spectroscopy is a potentially powerful diagnostic technique for probing infrared active flame species whenever a line-of-sight method is suitable. In the late 1970's, Hanson and co-workers introduced infrared diode laser spectroscopy as a combustion diagnostic technique. Quantitative CO [1,2] and NO [2,3] concentrations were determined from the absorption measurements and temperatures [4] were determined from the relative intensity of two closely spaced ro-vibrational transitions originating from different vibrational levels.
Spectroscopic Studies of Laser-Generated Microplasmas
Authors: Simeonsson Josef B. , Locke Randy J. , Morris Jeffrey B. , Forch Brad E. , Miziolek Andrzej W.
Published: February 2023

The ability of pulsed lasers to cause breakdown in gaseous media has been observed and studied nearly as long as lasers have been available. A breakdown microplasma is initiated at the focus of a laser when atomic and molecular species are ionized following the resonant and/or nonresonant absorption of laser radiation. Free electrons that are initially produced absorb laser radiation through a process known as inverse bremsstrahlung. After absorbing enough energy, the electrons collide with other species causing them to ionize and the process is repeated until a cascade ionization occurs. When the electron density is sufficiently high, the microplasma becomes opaque to the laser radiation which results in a very rapid heating of the plasma for the duration of the laser pulse. Temperatures in laser produced microplasmas have been estimated as high as 104 to 105 K with electron densities on the order of 1015 to 1019 per cm3. Studies of microplasmas produced using laser radiation from the ultraviolet to the far infra-red have shown that the intensity required for optical breakdown to occur (the breakdown threshold) generally decreases as the laser wavelength decreases (1-5). Similarly, the "rise time" of the microplasma, or the time it takes for the plasma emission intensity to reach a maximum value, has been found to decrease as the laser wavelength decreases.
Raman Spectroscopy Measurements of Single Reacting Aerosol Microparticles
Authors: Rassat Scot D. , Davis E. James
Published: February 2023

The chemical reaction between sorbent particles and sulfur dioxide (SO2) is used to remove SO2 from stack gases. The addition of powdered limestone to coal in the fluidized bed coal combustor generates calcium oxide (CaO) which reacts with the SO2 to form CaSO3 at low temperatures and CaSO4 at temperatures above 700 K. The utilization of the limestone is known to be low (about 20%) because the pores of the CaO plug as the product forms. This research was conducted to examine the reaction between CaO and SO2 to elucidate the rate-controlling processes, to generate CaO particles with a more open pore structure, and to develop techniques for single particle measurements at elevated temperatures.
Fundamental Investigations of the Mechanism of Laser Desorption and Ionization in Matrix Assisted Laser Desorption / Ionization
Authors: Kinsel Gary R. , Gillig Kent , Edmondson Ricky , Russell David H.
Published: February 2023

The recent development of Matrix Assisted Laser Desorption / Ionization (MALDI) has sparked a revolution in the field of high molecular weight mass spectrometry.1 Time-of-flight (TOF) mass spectra of proteins weighing up to 300,000 Da are now routinely produced and this achievement has fostered a variety of bioanalytical applications which were previously unapproachable using conventional mass spectrometric techniques. These successful applications have burgeoned in spite of a poor understanding of the mechanism of analyte desorption and ionization under MALDI conditions. An improved understanding of the MALDI mechanism should aid in overcoming a number of limitations of the current state-of-the-art and forms the motivation for the work described.
Cellular and Biological Applications of Laser Induced Fluorescence
Authors: Sklar Larry A. , Jones Gregory M. , Houghton Terri Gilbert
Published: February 2023

Lasers are widely used in biological applications to detect fluorescent molecules which probe the structure and activities of cells, cellular components, and biomolecules. Dye molecules used in biological systems are often referred to as “probe molecules” or “probes”. Lasers are often selected over other excitation sources such as arc lamps because of the power density, the increased intensity when imaging faint or dilute fluorophores and the advantages of monochromatic sources for reducing stray light from turbid biological samples. The applications introduced in this paper include observing molecules and cells in suspension by spectroscopy, flow cytometry, and microscopy.
Tunable Diode-Pumped Mid-infrared Lasers
Authors: Budni P.A. , Knights M.G. , Schunemann P.G. , McCarthy J.C. , Pollak T.M. , Chicklis E.P.
Published: February 2023

Recent advances in Mid-Infrared (MIR) tunable lasers open new possibilities for detection / analysis of chemical species in the laboratory and by the use of remote sensing techniques in the field. Lasers for these applications vary by system defined operating parameters such as: energy output, pulse repetition rate, spectral emission / tunability, linewidth, and compact reliable platform mounted architectures. Solid-state lasers comprising of optical parametric oscillators (OPO) using ZnGeP2 and AgGaSe2 non-linear optical crystals driven by 2-micron Tm2Ho:YLF pump lasers, are an attractive method for the generation of efficient tunable MIR radiation spanning the wavelength ranges of 2.6 to 12 microns. Providing systems which can operate at high repetition rates (4-20kHz), high average power (2.4W, 3-to-5 microns) [1], or low repetition rate (<60Hz) systems with capabilities of energy output in the 15mJ region (2 microns). We describe two MIR diode-end-pumped laser systems: one a high repetition rate OPO / 2-micron laser, and the other a laser-diode pulse-pumped 2-micron laser operating at low repetition rate / high peak power per pulse (60Hz / 1.25MW) designed to drive an OPO for >500KW of pulsed output.
Hook Spectroscopy as a Single-Shot OH Density and Temperature Diagnostic
Authors: Zerkle David K. , Sappey Andrew D.
Published: February 2023

Hook spectroscopy is being implemented to measure OH density and temperature in a premixed, CH4/air, atmospheric pressure flame on a single shot basis. The hook method makes use of the region of anomalous dispersion surrounding electronic transitions, typically in atomsl. In this region, the refractive index of the sample experiences dramatic shifts from its non-resonant values as shown in Figure 1. As seen in the figure, the solid curve has a minimum on the blue side of λ0, and a maximum to the red. The dashed curve represents the Sellmeier approximation to the refractivity which assumes that the linewidth is infinitely narrow. This approximation is normally quite valid in the wings of electronic transitions and is used to simplify the mathematics involved in determining number density from hook spectra.
Chemical Species from Tritium-Breeding Compacts by Raman Spectroscopy
Authors: Taylor David J , Steinkruger Fred J , Christiansen David E , Gettemy Donald J
Published: February 2023

The retention of tritium in reactor breeding compacts has been studied in these experiments at conditions simulating nuclear reactor accidents, and the experimental results have been used to determine New Production Reactor safety envelopes. The tritium-breeding compacts tested contain thousands of spherical particles within a carbonaceous matrix; each particle is fabricated as a kernel of lithium aluminate, enriched in 6Li for breeding tritium by (n,α) reaction, surrounded by consecutive shells of porous carbon, pyrolytic carbon, silicon carbide, and pyrolytic carbon to retain the tritium during breeding. The experiments demonstrated that in an accident with a sudden reactor temperature jump to 1300°C, more than 99% of the tritium would be retained within the compact for over 50 hours, which is ample time to bring such an accident under control. In these experiments, chemical species released from the compacts were measured by laser-Raman spectroscopy to enable design of chemical safety systems. Chemical species that were observed at intermediate temperatures, including H2O, H2, CO, and hydrocarbons, resulted from compact exposure to air, whereas species released at high temperatures, including HT and CO, originated within the particles. The Raman data identified the dominant tritiated species to be HT, at concentrations commensurate with measurements of total tritium using ion chambers and scintillation counter. These tests attained Raman detectability as low as 6.4 parts-per-million (ppm) for HT.
Potential Application of Three Laser-Based Bacteria Detection Techniques to The Meat Processing Plants - A Review
Authors: Chou Nee-Yin , Chen Yud-Ren
Published: February 2023

This review was prompted by the concerns of the recent serious incidence of bacterial contamination, especially in raw or partially cooked meat. There are 4 million cases of food poisoning reported annually, most of them are caused by bacteria. Recent GAO testimony on food safety stated that the meat inspection system has changed little since it was first instituted in 1906 and is not capable of addressing today's concerns about microbial contamination (1).
Fiber-Optic Sensor based on Porous Polymer doped by Dye: Detecting Ammonia in Liquid Media
Authors: Bondarenko D. B. , Dolotov S. M. , Koldunov M. F. , Ponomarenko E. P. , Sitnikov N. M. , Startsev A. V. , Tulaikova. T. V.
Published: February 2023

Fiber-optic sensors bave many attractive features i.e. (1) They are not subject to electrical interference. (2) They can be used in the active and explosive media. (3) Unlike electro-chemical sensors, they have not any reference electrodes.
Species Identification and Conversion Measurements in a Carbon Tetrachloride Radio Frequency Plasma Using Coherent Raman Techniques
Authors: Rodriguez R. , Wells F.V.
Published: February 2023

Radio frequency plasmas are used in the electronics industry in various phases of microcircuitry processing. Deposition and etching are two key areas where these types of plasmas are used. In recent past, carbon tetrachloride, CC14, has been used in the etching of metals such as aluminum. However, one of the problems associated with using this gas as an etchant is the formation of a glow polymer which coats the walls of the chamber and can interfere with the etching.
Laser-Induced Fluorescence Measurements of the Distribution of C3 in the Plume of a dc-Arcjet During Diamond Deposition
Authors: Raiche George A. , Jeffries Jay B.
Published: February 2023

Thin films of diamond phase carbon can be grown by a wide variety of
chemical vapor deposition techniques, including hydrocarbon
combustion and hydrogen rich hydrocarbon plasmas at atmospheric and
sub-atmospheric pressures. The excellent thermal conductivity and high
electrical resistance of diamond make it an attractive material for a
wide variety of thermal management applications. Low cost, uniform
deposition over large areas would make polycrystalline diamond an
ideal substrate for high speed electronic circuit packaging in
multi-chip modules. Thus, reactors which can rapidly deposit diamond
and can be scaled to large area deposition are most attractive for
these practical applications.
Raman Applications with All-Silica Fiberoptic Probe
Authors: Lee Yuan-Hsiang , Dai Sheng , Young Jack P.
Published: February 2023

We have developed a unique all-silica fiberoptic probe that has the advantages of being simple and inexpensive to fabricate. The probe is useful for Raman, fluorescence, absorption, reflectance analysis over a wide temperature/pressure range and in corrosive chemical environments. The all-silica probe comprises one light exciting and six signal collecting optical fibers that are fused into a quartz tube under reduced pressure. No epoxy materials are required in the fabrication of the probe. Thus constructed, the probe is essentially a SiO2rod that maintains the optic characteristics of the individual fibers and has the thermal and chemical properties of SiO2. We have evaluated the use of all-silica fiberoptic probe for normal Raman spectroscopy and investigated silver doped sol-gel films directly coated on the probe head for surface enhanced Raman scattering (SERS). The silver doped sol-gel films exhibit strong enhancement of Raman scattering from molecules adsorbed on the metal surface. We have applied the SERS-active films to both organic and inorganic analysis. In contrast to other silver surfaces, SERS response on our films develops rapidly and remains stable over long period of time (48 hours or more). We have also demonstrated analytical SERS enhancement for many inorganic ions, e.g.

UO

2

2
+

,

CO

3

2
−

,

NO

3
−

,

NO

2
−

,

SO

4

2
−

,

SO

3

2
−

. This presentation will describe and discuss our recent efforts toward the development of the all-silica fiberoptic probe, the fabrication of silver doped sol-gel films, and the analytical usefulness of both concepts.
Quantitative Surface Analysis Using Photoionization of Sputtered Neutrals
Authors: He Chun , Becker Christopher H.
Published: February 2023

Surface quantitative elemental composition information is a fundamental measurement of critical importance to the design and evaluation of materials and components. Secondary ion mass spectrometry (SIMS) and spectroscopic techniques based on secondary electron energy measurements, such as electron spectroscopy for chemical analysis (ESCA) and Auger spectroscopy, are well-established analytical tools used to meet such a requirement in the industry. SIMS is a highly sensitive technique, capable of detecting trace element at ppm level. However, based on detection of ionized materials ejected during sputtering, SIMS has difficulties in quantification at surfaces and interfaces due to its well-known matrix effect. On the other hand, ESCA and Auger spectroscopy have good quantification capability, but low sensitivity. The detection limit of ESCA or Auger spectroscopy is ≤ 0.1% of the total sample composition[1].
A new approach to laser-induced fluorescence detection of nitric oxide in high pressure flames
Authors: Schulz Christof , Sick Volker , Heinze Johannes , Stricker Winfried
Published: February 2023

Laser induced fluorescence of nitric oxide is commonly used for detection of this major pollutant in combustion processes. Mostly, excitation within the A-X (0,0) band is used next to excitation of the D-X (0,1) band. However, for real engine applications strong absorption of the laser beam prevents the application of these schemes. Exciting in the A-X(0,2) band circumvents these problems and allows the sensitive two-dimensional detection of nitric oxide in engines fueled with iso-octane or Diesel fuel.
Particle Sizing From Multi-Wavelength Frequency Domain Measurements of Photon Migration
Authors: Pierce Joseph E. , Sevick-Muraca Eva M.
Published: February 2023

Particle density and size distribution are critical process parameters in many of today's industrial processes that involve dispersed phase process streams. For example, granulation, crystallization, emulsion polymerization, and liquid-liquid extraction lack the appropriate monitoring techniques to facilitate process control and optimization. Optical sensors involving dynamic light scattering, turbidity, and backscatter have been proposed in the past. Yet these optical sensors are restricted to process streams that are either relatively non-scattering by industry standards, or require calibration to the process streams which they are intended to monitor. The latter is especially detrimental for successful implementation of optical sensors in the chemical based industries. When process disturbances occur, the optical sensor is intended to provide important and accurate information to the controller for corrective action. If the calibration of the sensor is invalidated due to changing process stream composition (as might happen during process disturbances), then the accuracy of the feedback signal may cause catastrophic results if actuation is based upon it. Thus, a robust, self-calibrating optical sensor is required for optimization of many processes in the chemical-based industries.
Particle Sizing Using Time-Domain Techniques of Photon Migration
Authors: Kao Jeffrey , Sevick-Muraca Eva
Published: February 2023

The objective of this research is to develop non-invasive, uncalibrated methods for measuring the particle size distributions within optically dense polydisperse media. Our work is subdivided into addressing two goals. First, we must measure isotropic scattering coefficients of polydisperse media and successfully compare them with values predicted by theory. Secondly, from multi-wavelength measurements of scattering coefficients, we must recover the particle size distribution. We describe these two steps as forward and inverse problems.
Four Wave Mixing Diagnostics of Atmospheric Regions with an Excess of Charged Aerosol Concentration
Authors: Boyarchuk K.A. , Lyakhov G.A. , Svirko Yu. P.
Published: February 2023

In this paper we address the phenomena of four-wave mixing and stimulated Brillouin scattering (SBS) in a medium containing free electric charges. Under SBS the hypersonic wave at the frequency of the Stokes shift Ω [1] gives rise to oscillation of the all particles of the medium near their equilibrium positions. In an electrically neutral medium equilibrium quantities of the positive and negative charged particles per unit volume are the same. However their mobilities are slightly different. Therefore, the magnitudes and phases of their oscillations near equilibrium positions are not equal to one another. This results in transient electric charge separation in acoustic field [2]. That is, under SBS the excitation of hypersonic wave in the medium with free electric charges leads to the generation of the electric charge density wave of the same frequency in the medium [3].
Nitrocompound Analysis by 226 nm Laser Photofragmentation/Fragment Detection
Authors: Pastel R.L. , Sausa R.C.
Published: February 2023

The development of fast and sensitive detectors for NOx
(NO+NO2) and nitrocompounds is important in many military
and civilian applications.2,3 Some applications include
environmental compliance to state and federal regulations, clean up of
ammunition sites, aviation security, and atmospheric monitoring.
Two Photon Resonant Detection of N2 Using Polarization Spectroscopy and Laser Induced Fluorescence
Authors: Kaminski C. , Löfstedt B. , Fritzon R. , Aldén M.
Published: February 2023

Molecular nitrogen, N2, is one of the most important molecules in combustion and environmental diagnostics since it constitutes the major species of our atmosphere. For temperature and concentration measurements N2 CARS has been developed into a highly robust and accurate tool. There are environments where N2 concentrations are too low for CARS to be applicable. In this case excitation schemes can be used which have been developed to allow direct access to electronic resonances of N2 via multi-photon transitions [1]. Almost all detection schemes of these techniques employ further resonant multi-photon steps to create N2+ ions and the resulting signal electrons are collected by electrodes (resonance enhanced multi-photon ionisation - REMPI) [2,3].
An In-Line Photoacoustic Sensor for Environmental Monitoring in Water
Authors: Freeborn S.S. , Hannigan J. , MacKenzie H.A. , Greig F.
Published: February 2023

During the operation of offshore production platforms, sea contamination occurs from leakage, spillage and from the overboard discharge of produced water. Produced water is the terminology applied to water which is obtained during oil production from two main sources. These are naturally from within the oil reservoirs and from sea water used in the oil recovery process. Legislative limits are set in the most of the major oil production regions world wide. These limits vary from region to region but are generally set between 15ppm and 40ppm for dispersed hydrocarbon concentration in water. The volumes of produced water are exceeding that of crude oil production in many offshore oil fields, such as in the North Sea fields to the north-east of the U.K. where in 1994 for a total crude oil production of 114.4 million tonnes, 147 million tonnes of water was produced, the majority of which was discharged back into the sea. The volumes of oil discharged within produced water are the single greatest source of oil contamination from oil production facilities in the North Sea and with similar situations replicated world wide represents a global concern to sensitive marine environments. The present methods for the detection of oil in produced water are based either on chemical analysis of intermittent samples or bypass pipelines with instrumentation to detect either dissolved or dispersed hydrocarbons by a variety of optical techniques including absorption, scattering and fluorescence. Tests in the U.K. on a range of commercially available instruments have shown that no single one entirely meets either the present needs or satisfies the requirements of the more stringent future legislation which is likely to be introduced in the atmosphere of growing concern for our environment. New instrumentation is required to meet these needs and will require a specification to include both in-line and on-line operation and sensitive measurements on dissolved and dispersed hydrocarbons. The requirement for in-line operation introduces further complexities to the specification due to the optical scattering which can be introduced by sand and other sediments which could not be filtered, and from the high sample flow rates and turbulence which is introduced by the flow rate of 1ms 1 typically encountered in the discharge pipes. To meet these needs a new generation of in-line systems for environmental monitoring are being developed based upon the Photoacoustic Spectroscopy technique. The instrumentation is being developed initially for the on­line monitoring of hydrocarbons in produced water but may also find application in the detection of oil and other pollutants in the open sea, rivers, lakes and sewage.
High-Speed Single Molecule Detection in Microdroplet Streams
Authors: Lermer N. , Barnes M. D. , Kung C-Y. , Whitten W. B. , Ramsey J. M.
Published: February 2023

The detection of individual fluorescent molecules in liquids has been of great interest in recent years. Various fluorescence-based techniques shown to provide single molecule sensitivities include confocal microscopy [1], flow cell techniques [2], and levitated microdroplets [3]. The application of the microdroplet technique to single molecule detection offers many advantages. First, fluoresence decay rates and total fluoresence yield have been shown to be enhanced in glycerol microdroplets [4]. Additionally, the droplet confines the single fluorophore to a small volume thereby removing difficulties arising from diffusion of the fluorophore. Furthermore, the discrete detection unit of the droplet is ideally suited to the application of digital molecular detection for the analysis of ultradilute solutions [5]. Previous liquid microdroplet work has exhibited single molecule detection with signal-to-noise ratios in the range of 10-40 [3]. In our previous work, an electrodynamic trap was employed to trap glycerol microdroplets for a period much longer than the average photochemical lifetime, thus obtaining the maximum possible signal from the analyte. However, the application of digital molecular analysis to real systems requires tens of thousands of droplet measurements [5]; the time required to trap (and to size) the droplet in a levitated system prohibits its application in a high-speed molecular counting technique. In addition, many biological applications of single molecule fluorescence detection require aqueous samples. The present work discusses the development of an instrument designed to permit single molecule detection in water microdroplets at count rates in the range of 10 - 1000 Hz.
Passively Q-Switched Microchip Lasers for Environmental Monitoring
Authors: Zayhowski J. J. , Johnson Bernadette
Published: February 2023

The need exists for sensors capable of measuring soil, groundwater, and airborne pollutants without laborious sample collection and analysis. Single-wavelength transmission, differential absorption, laser-induced fluorescence (LIF), stimulated Raman scattering, and laser-induced breakdown spectroscopy (LIBS) are all highly sensitive methods for providing quantitative values of concentrations of chemical species. These optical techniques have been proven to provide high sensitivity and chemical selectivity for a large number of the materials on the EPA’s priority pollutant list.
High Sensitivity Detection on Microchips
Authors: Fister J. C. , Davis L. M. , Jacobson S. C. , Ramsey J. M.
Published: February 2023

High efficiency separations coupled with rapid response times have been
demonstrated on capillary electrophoresis devices micromachined on
glass substrates. [1-3] Although detection of single
organic dyes has been achieved with fluorescence detection in
capillaries, [4] such detection limits have not yet
been demonstrated in micromachined channels. Efficient, single
molecule detection is desirable for many potential applications such
as rapid DNA sequencing. The structure of microfabricated separation
channels, however, does not readily facilitate a 90°
fluorescence excitation/collection geometry which has been used to
achieve high sensitivities in capillaries. [4] This
optical geometry allows efficient spatial rejection of scattering at
the capillary solution interfaces. Confocal detection in which the
excitation source is introduced through the collection optics provides
a means of achieving both high axial resolution and high collection
efficiency.
Modeling Fluorescence Collection from Single Molecules in Liquid Microspheres
Authors: Hill S. C. , Barnes M. D. , Whitten W. B. , Ramsey J. M.
Published: February 2023

Optimization of molecular detection efficiencies is of central importance in analytical applications involving single molecule detection.1 In addition to limitations imposed on the fraction of molecules which can be detected by the average signal-to-noise ratio, experimental factors such as excitation inhomogeneity and molecular diffusion conspire to further limit "molecular detectability." Recent single molecule detection experiments in microdroplets suggest that such experimental limitations can be significantly reduced primarily because the molecule cannot diffuse away from the excitation volume. However, unlike fluorescence detection from bulk streams where the fluorescence intensity is isotropic in space, the large refractive index change at the surface of microdroplets implies that the fluorescence intensity collected by a lens will be strongly dependent on the position of the molecule within the droplet. In addition, the same refractive index discontinuity at the droplet surface produces a complicated excitation intensity distribution within the droplet as a result of interference between refracted and totally-internally-reflected rays. Thus, issues such as whether molecules near the surface of the sphere can "hide" from the detector as a result of total internal reflection of emission near the droplet surface, or poor excitation efficiency due to the molecule being located in a "shadow" region of the droplet will have a potential effect on molecular detection efficiencies. These questions are nontrivial to address in a quantitative way. Here we discuss development of numerical tools for modeling the fluorescence collected from a single molecule within a microdroplet as a function of position, orientation, and detection geometry based on the semiclassical electrodynamics formalism developed by Chew2 for light scattering in dielectric microspheres. In addition we also examine effects of excitation inhomogeneity within the sphere, molecular diffusion, and transition rate modification in order to obtain a realistic model of molecular detection efficiencies in microdroplets.
Low Level Determinations of Uranium Hexafluoride Using Multiphoton Ionization Time-Of-Flight Mass Spectroscopy
Authors: Armstrong Donald P. , Harkins David A. , Compton Robert N.
Published: February 2023

The uranium enrichment enterprise in the United States uses the gaseous diffusion method to achieve the desired level of enrichment of the 235U isotope. The feedstock for this process is gaseous uranium hexafluoride (UF6). In addition to the current production facilities there are also facilities which have been idled due to programmatic reasons, but may still contain residual, low levels of (UF6). For the case of certain of these industrial processes or laboratory scale applications, the need to observe low levels of uranium hexafluoride (UF6), often in the presence of other gases, is an important, but difficult, problem. UF6 is a highly reactive gas particularly when acting as a fluorinating agent, and is very reactive with even trace levels of moisture. For these reasons, meticulous chemical drying techniques and containment vessels of suitable materials must be used. An accepted manner of analysis for the detection of UF6 is to use a Fourier-transform infrared (FTIR) spectrometer. These units work reasonably well for observing UF6 levels on the order of a few dozen ppm, but the reactive nature of the gas greatly limits the choice of infrared windows. The fundamental vibration of interest in UF6 is the v3 band at ~ 625 wavenumbers, but spectral interferences can occur from other gaseous species which may be mixed with the UF6 thereby complicating the analysis. We describe a laser technique which can provide sub-ppm levels of detection for UF6 in the presence of other gases using commonly available laser hardware.
Near field scanning optical microscope for biological applications
Authors: Baibyrin V. B. , Anisimov P.I. , Konnov N.P. , Shcherbakov A.A. , Volkov U.P.
Published: February 2023

In our biophysical laboratory systematic investigations of plague and choler microbes are carried out by different methods (conventional electron microscopy, scanning tunneling microscopy and atomic force microscopy). At present for the investigations we have develop a near field scanning optical microscope (NSOM).
Detection of Single Molecules in Microcavities
Authors: Lermer N. , Barnes M. D. , Kung C-Y. , Whitten W. B. , Ramsey J. M.
Published: February 2023

A significant limitation in the detection and spectroscopy of individual dye molecules in liquid room temperature samples is the loss of fluorescence signal through chromophore photobleaching. Although often considered a fundamental restriction on sensitivity, it has been shown that the probability per excitation cycle of photobleaching may be reduced by enhancing the spontaneous emission rate of the chromophore located inside a microdroplet, which acts as a optical cavity. Studies of glycerol microdroplets containing R6G dye molecules, and levitated in a three-dimensional electrodynamic trap, have demonstrated a significant enhancement of both the fluorescence decay rate [1] and the total fluorescence yield [2] of the chromophore. Modification of the emission rate is greatest for molecules located near the surface of small (< 10 μm) microdroplets, where the influence of the droplet cavity modes of the droplet is most significant. To exploit this surface sensitivity, surfactant forms of rhodamine dyes were recently studied [3]. Fluorescence emission of the dye molecules, constrained to the droplet surface and with fixed transition moments perpendicular to the surface normal, were shown to be significantly enhanced at small droplet sizes. Additionally, at larger droplet sizes corresponding to higher droplet Q’s, preferential emission into the cavity modes was observed, however the detection of fluorescence photons was delayed by the storage time of the cavity, which may be on the same order as the fluorescence lifetime. These measurements, performed on relatively concentrated dye solutions, suggest that microcavity effects may be exploited to greatly enhance single molecule detection sensitivity in glycerol microdroplets. Furthermore, the large cavity storage time of the high-Q droplets opens the possibility for re-excitation of the molecule following emission into the droplet resonance, and subsequent stimulated emission, that is, single-molecule lasing.
Environmental Monitoring with Fiber Optic Immunosensors and Compact Optoelectronics
Authors: Ives J.T. , Sullivan B.J. , Thamer J. , Bechtel J.H. , Thomas T.C.
Published: February 2023

Environmental hazards are often detected by gas chromatography, mass spectroscopy, or high performance liquid chromatography. These methods are well characterized, but they are expensive and usually not performed on-line. Antibody-based technologies are increasingly being applied due to the specificity of the antibodies, and the low cost of the detection kits. With the immunoassay kits, personnel collect samples, mix them with the kit components, and observe the results on-site.
Following the Dynamics of Single Oligonucleotide Molecules in Water
Authors: Sauer M. , Drexhage K. H. , Han K.-T. , Nord S. , Zander C.
Published: February 2023

The dynamic fluorescence characteristics of individual dye molecules in specific local environment are of particular interest for many biological applications.1,2 Furthermore, dye molecules that are influenced by the environment can act as molecular probes, i. e. they exhibit information about neighbouring groups and changes in the microenvironment. They also allow the direct observation of individual dynamic events such as conformational changes of a biological macromolecule if they are monitored on the single-molecule level. In addition, measurements on individual molecules are well suited for the study of complex systems in which it is not known whether all molecules exhibit the same characteristics or each molecule contributes with its individual characteristics to the observed behaviour.
Degenerate Four-Wave Mixing Spectroscopy: Multistate Resonances and Multimode Laser Effects
Authors: Reichardt Thomas A. , Giancola William C. , Lucht Robert P.
Published: February 2023

Degenerate four-wave mixing (DFWM) spectroscopy is a promising diagnostic technique [1-3], but significant questions remain regarding its application for quantitative concentration measurements in combustion environments with typical laser systems. In this paper we present a summary of two numerical investigations with the goal of quantifying the measurement technique for common experimental situations. Specifically, we investigate both (1) probing a degenerate-level (multistate) resonance with a single-mode laser and (2) probing a two-state resonance with a multimode laser. DFWM signal levels are calculated by solving the time-dependent density matrix equations using direct numerical integration (DNI) [4, 5] for a two or more level system interacting with three laser beams.
Polarization Spectroscopy: Calculation of Lineshapes and Saturation Effects
Authors: Reichardt Thomas A. , Lucht Robert P.
Published: February 2023

In recent years there have been several experimental demonstrations of
the application of polarization spectroscopy (PS) as a combustion
diagnostic technique.1-3 However, there have been very few theoretical
investigations of the technique since the work of Teets et al.4 in
1977. Teets et al.4 investigated the low-laser-power limit where
saturation effects are small. In this paper we present the initial
results of a theoretical investigation of polarization spectroscopy
using the method of direct numerical integration (DNI) of the
time-dependent density matrix equations to analyze the process. The
application of this numerical method allows us to include saturation
effects, Doppler effects, non-steady-state effects associated with the
finite pulse length of the pump and probe lasers, and will enable us
to investigate in great detail the effects of different kinds of
collisions.
Trace Gas Monitoring with Antimonide Diode Lasers
Authors: Oh Daniel B. , Stanton Alan C. , Nicolas Jean-Christophe
Published: February 2023

Semiconductor diode lasers, including lead salt lasers operating at wavelengths beyond 3 μm and InGaAlP, GaAlAs, or InGaAsP lasers operating at wavelengths less than 2 μm, have been used extensively for measurement of trace gases by optical absorption.1 The inherently narrow linewidths of these light sources, combined with high sensitivity detection techniques such as wavelength modulation spectroscopy2 or frequency modulation spectroscopy,3 provides a capability for the highly selective and sensitive measurement of a wide range of species important in atmospheric and combustion research, environmental monitoring, and process monitoring. The lead salt lasers, accessing vibrational fundamental bands, generally permit the highest detection sensitivity. However, development of commercial diode laser-based instrumentation for environmental or industrial application has focused on the use of the near-infrared wavelength devices due to their characteristics of room temperature operation, compatibility with silica optical fibers, and availability of single mode operating devices.
Microanalysis of solids by laser ablation with one shot
Authors: Bauer H. E. , Niemax K.
Published: February 2023

Sampling by pulsed lasers (LA: laser ablation) is a fast and simple method which, in principle, can be used for all types of solid samples. The technique is well established in combination with the inductively coupled plasma (ICP) and is also commercially available. Optical emission spectrometry (OES) of the laser produced plasma, called LIBS (laser induced breakdown spectrometry), is the more direct method. However, LIBS is still regarded as the less accurate technique in comparison with LA-ICP-OES or -MS, because the analytical data are strongly dependent on the parameters of the laser produced plasma which can change dramatically from laser shot to laser shot if the matrix composition and the ambient conditions vary. One way to compensate for the variation of the plasma is the simultaneous spectroscopic measurement of the analyte lines and all relevant plasma parameters. This requires simultaneous and time gated measurements of the total emission spectrum of the laser spark.
Application of LIBS to Monitor Compositions for Plant Control
Authors: DEGUCHI Yoshihiro , IWASAKI Seiji , ISHIBASHI Naohiko
Published: February 2023

It has become more and more important to monitor the condition of material to cope with environmental disruption and improve the efficiency of industrial plants. As the situation now stands, the on-line monitoring techniques of plant controlling factors are necessary to enhance the control ability of the overall operation of industrial plants.
Near -Infrared Tunable Diode Laser Diagnostics in Laboratory and Real-Scale Inhibited Flames
Authors: McNesby Kevin L. , Daniel Robert G. , Skaggs R. Reed , Miziolek Andrzej W. , Miser Craig S.
Published: February 2023

The goal of this research project is to develop and demonstrate/validate new laser-based instrumentation for the measurement of concentrations of candidate suppressants, oxygen, fuels, and combustion byproducts during suppression of flames and explosions. Time resolved measurement of concentrations of suppressants, oxygen, fuels, and combustion byproducts serve as a check on the repeatability of the tests and help determine why a suppressant is behaving well or poorly in a given full-scale suppression test.
Characterisation of surfaces using reflectance and optical rotation measurement methods
Authors: Prakash O. , Lal Mohan
Published: February 2023

In order to characterise new materials being exploited for development of newer devices, in some of the cases, the materials are prepared in the form of thin films or wafers. In order to characterise thin films or wafers of the materials, a simple method has been deviced. In this method reflectance of the samples is measured at nearly normal incidence on a home made reflectometer. Also the optical rotation of incident light beam on reflection from the sample at nearly 45 deg. is measured on home made polarimeter. With the help of a graph drawn between reflectance and optical rotation, if value of reflectance of a sample can be measured, the value of its optical rotation can be approximated and vicei-versa. The main advantage of the method is that the samples of diffused nature whose reflectance cannot be measured, it can be characterised with the polarimeter. The methods are non-destructive.
Simultaneous PLIF and Stereo PIV measurements of a Turbulent Non-Premixed Flame
Authors: Harvey A.P. , Hult J. , Kaminski C.F. , Stonestreet P.
Published: February 2023

Stereo PIV and time sequenced PLIF were performed simultaneously on the TECFLAM turbulent, non-premixed international reference flame to investigate local flame extinction phenomena. The results show, for the first time, effects due to the out-of-plane component of the velocity.
The moon illusion and relevant perceptual mechanisms
Authors: Leibowitz H.W. , Owens D.A.
Published: February 2023

The larger apparent size of the moon when viewed near the horizon as compared to its appearance at higher altitudes is perhaps the oldest perceptual phenomenon in the literature. The earliest known reference is associated with the Assyrian king Assurbanipal (668-626 B.C.). In modern times, it has been a challenging phenomenon for behavioral as well as optical scientists. A recent book illustrates the diverse approaches to this challenging phenomenon (Hershenson, 1989).
Behavioral Implications of Civil Twilight
Authors: Leibowitz H.W. , Owens D.A.
Published: February 2023

Civil twilight, when the sun is six degrees below the horizon, has been described as a period when all normal daylight activities can be carried out without supplementary illumination. While this was an appropriate description during the previous centuries when this definition was formulated, the nature of visual demands accompanying the introduction of modern technology in this century suggests that this criterion should be reexamined. Figure 1 presents the relation between visual acuity and luminance (1). This function is typical of a number of visual functions including resolution, vernier, single line and stereoscopic acuities, oculomotor responsiveness, contrast sensitivity and reaction time. It should be noted that performance begins to decline at about 10 millilamberts and that at .01 millilambert, foveal vision is no longer possible.
The Sylvanshine
Authors: Fraser Alistair B. , Beatty George H.
Published: February 2023

Most of the phenomena of meteorological optics have been known for centuries, many of them since antiquity. While understanding of these phenomena has increased markedly in the last century or so, during that time the discovery of new phenomena has largely taken the form of making distinctions within an already known phenomenon. Thus, a subclass of the Fata Morgana is relabeled as the Fata Bromosa, or the Parry arcs are split into suncave and sunvex groups. Indeed, as the hallmark of meteorological optics is naked-eye observations, there is no good reason to suspect that after millennia of weather watching there would be anything other than nuances remaining to be discovered.