bluuebunny/crossref_metadata_2025 huggingface dataset:
Excimer Laser Photofragmentation/Ionization for Chemical Detection
Authors: Long S. Randolph , Miziolek Andrzej W.
Published: February 2023

Many molecules are difficult to detect and identify spectroscopically due to the absence of well-defined rotational structure in their infrared absorption bands and to the lack of structured or any absorption in the convenient ultraviolet-visible spectral region. As a means of detection and class identification of such molecules, we are pursuing an approach based on the observation of numerous studies over the past few years that focused excimer laser radiation can lead to substantial fragmentation of a parent compound. (A partial list of representative studies is provided in Ref. 1.) The photofragments typically include di- and triatomics (as well as atoms), which do generally have structured, readily identifiable transition systems in the ultraviolet-visible spectral region. These fragments may be detected by their prompt emission, if formed in electronically excited states, or by probe techniques such as laser-induced fluorescence (LIF) or laser multiphoton ionization (MPI). Detection of distinctive photofragments can lead to identification of the parent. In particular, strongly bound moieties characteristic of a class of compounds may be anticipated to survive the focused laser photolysis.
Ultratrace Solids Analyses Using Resonance Ionization Spectroscopy
Authors: Parks J.E. , Moore L.J. , Spaar M.T. , Beekman D.W. , Taylor E.H.
Published: February 2023

Sputter initiated resonance ionization spectroscopy (SIRIS) is a new, ultrasensitive analytical technique for solids analysis, particularly in the fields of semiconductors, geophysics, biology, medicine, health physics, and basic science. SIRIS uses sputtering to atomize a solid sample and tunable dye lasers to selectively excite and ionize a selected element with the use of resonance ionization spectroscopy (RIS). The RIS process provides good sensitivity and allows interference-free measurements. The sensitivity is sufficiently high that analyses can be performed with a pulsed ion beam which does not sputter away more than an equivalent monolayer of the sample during an analysis. Thus, it is inherently a technique for surface analysis and for the analysis of very thin samples. For bulk analysis or for depth profiling, material can be removed by sputtering with a dc ion beam. The RIS technique is reviewed and the SIRIS technique is described along with the apparatus used at Atom Sciences. Applications for SIRIS are discussed and the results of measurements illustrating these applications are presented. For bulk analysis of gallium in silicon, a sensitivity of 2 ppb has been demonstrated. Depth profiles of silicon in gallium arsenide were made and recent results are presented. In a medical application, blood serum has been analyzed for trace amounts of copper and molybdenum. SIRIS allows the analysis of small, less than 0.1 ml, samples and is calibrated by the use of isotope dilution. Sensitivities of 20 pg are reported for molybdenum.
Doppler-Free Resonance Ionization Mass Spectrometry of Beryllium
Authors: Travis J.C. , Lucatorto T.B. , Wen J. , Fassett J.D. , Clark C.W.
Published: February 2023

As originally conceived, resonance ionization mass spectrometry (RIMS) combined the elemental selectivity of resonance ionization (1) with the isotopic selectivity of mass spectrometry to improve the accuracy and sensitivity of conventional mass spectrometry (2). For many applications, especially quantitation by isotope dilution (3) , it is important that no isotopic selectivity accompany the resonance ionization process. This condition is easily met for all but a few elements of the periodic table (4), since the great majority of optical isotope shifts are small with respect to typical dye laser bandwidths and Doppler-broadened linewidths in common atom reservoirs. However, another class of problem exists for which it is desirable to achieve isotopically selective resonance ionization. These applications involve the detection of extremely, rare stable or radioactive isotopes in the presence of the major isotopic species of an element. Miller et al. (5) have explored the optical isotopic selectivity of the isotopes of Lu using a RIMS spectrometer equipped with a high-resolution (single-mode) continuous-wave (cw) laser. Cannon et al. (6) have measured an optical selectivity (defined below) of 800 for isotopes of Ba, using a RIMS spectrometer with two cw lasers. We have proposed the use of pulsed, two-photon, Doppler-free resonance ionization to extend the capability of conventional mass spectrometers to measure isotope ratios in excess of 1012 (7). Initial experimental results using this approach, for the isotopes 9Be and 10Be, are reported here.
Applications of Resonance Ionization Mass Spectrometry in Analytical Spectroscopy
Authors: Nogar N. S. , Apel E. C. , Miller C. M. , Estler R. C.
Published: February 2023

RIMS is a powerful tool for elemental and isotopic analysis. This multistep laser photoionization process, when coupled with conventional mass analysis, can provide exceptional performance in detectivity, dynamic range, and discrimination against interfering species.1,2 These properties can be used to great advantage both in the analysis of conventional analytical materials3 and in the interrogation of interfacial phenomenae4. In this report we will discuss the use of laser desorption/ablation in combination with RIMS analysis.
Recent Advances in New Laser Sources
Authors: Baer Thomas M.
Published: February 2023

The application of laser sources to various areas of the natural sciences has had tremendous impact on the experimental methodology of the various disciplines. One of the areas most profoundly impacted has been analytical chemistry. For example, laser sources have provided the means for single atom detection, remote sensing of trace elements over large distances, and high sensistivity 2-dimensional mapping of free radical species in flames. For the most part these experimental techniques would not be possible without the laser sources.
Atomic Vapor Density Monitor*
Authors: Sewall N. , Harris W. , Beeler R. , Wooldridge J. , Chen H.
Published: February 2023

The atomic vapor density monitor (AVDM) system measures absorption of light from a swept-wavelength laser that passes through an atomic vapor stream. This vapor stream is above the surface of a crucible-contained melt in an atomic-vapor generator.
Two-Dimensional Detector Arrays and Their Applications to Imaging Diagnostics
Authors: Hanson Ronald K.
Published: February 2023

The availability of two-dimensional detector arrays has led to a new class of diagnostic techniques for probing gaseous flowfields. These techniques utilize sheet lighting of the flowfield with tunable laser sources and detection of scattered light from the illuminated plane with the 2-d detector. The intensity of scattered light recorded at each detector pixel can be related to relevant flowfield properties at the point in the illumination plane imaged by that pixel, so that the overall recording may be viewed as a 2-d image of the flowfield property studied. Thus far, flowfield imaging has been carried out using Mie scattering from particles or droplets and using molecular scattering based on laser-induced fluorescence, Rayleigh and Raman scattering.
Raman Spectroscopy of Molecules Adsorbed on Solid Surfaces
Authors: Campion Alan
Published: February 2023

Raman spectroscopy is an exceptionally powerful probe of the structures and reactions of molecules on surfaces with applications in catalysis, corrosion, electrochemistry and electronic materials. Recent advances in technology have resulted in submonolayer sensitivity for a wide variety of molecules adsorbed on low surface area single crystal substrates which may be metals, semiconductors or dielectrics. This sensitivity, which does not require any source of either surface or resonance enhancement, has been achieved through an understanding of the underlying physics and careful implementation of the experimental design. The physics of surface Raman scattering will be discussed as it determines both the experimental geometries and surface selection rules. As an example of the chemical utility of the technique, the adsorption and reaction of pyromellitic dianhydride and oxydianiline to form polyimide will be discussed. Finally, special considerations relevant to electrochemistry will be described and a few comments will be made on the chemical mechanism of surface-enhanced Raman scattering.
Adsorbates at Interfaces studied by Nonlinear Optics
Authors: Vogel Viola , Xiao Xu-dong , Mullin C.S. , Shen Y.R.
Published: February 2023

Second-order nonlinear optical techniques have been demonstrated to be highly surface specific. The adsorption of monolayers at various interfaces, e.g., metal/vacuum, glass/water or water/air, etc., can be probed with a submonolayer sensitivity. Detailed molecular information, such as the mean orientational distribution of the surface molecules, the surface concentration of adsorbates, the nonlinearity of adsorbates, and so on, can be deduced from the measurements.
Waveguide Dichroism and Depolarization Measurements for Molecular Orientation
Authors: Walls D.J. , Cropek D.M. , Hughes K.D. , Olinger J.M. , Bohn P.W.
Published: February 2023

Modern surface science is now emerging into a regime in which understanding the relationship betweeen structure and function will occupy an ever more prominent role. To this end one important piece of information concerns the three dimensional orientation of complex adsorbates at an interface. We have been using total internal reflection excited surface Raman scattering and waveguide mediated linear dichroism to measure the tilt angles of molecules adsorbed under realistic conditions (i.e. at the solid-liquid interface). These efforts will be described and compared.
Biological Applications of UV Raman Spectroscopy: Static and Dynamical Studies
Authors: Asher Sanford A.
Published: February 2023

The recent development of UV Raman spectroscopy has led to careful studies of the enhancement mechanism of vibrational modes for both small molecules such as amides, small aromatic molecules such as substituted benzene derivatives and also larger molecules such as polycyclic aromatic hydrocarbons, DNA and proteins The objective of the small molecule studies is to characterize the resonance Raman enhancement mechanisms to examine molecular excited state structure. These studies also clarify the resonance Raman enhancement mechanisms which clarify the dependence of Raman enhancement upon molecular environment. We will present an overview of this work as it relates to ongoing UV resonance Raman studies of the heme protein structure and function and the investigation of the details of the hemoglobin cooperativity mechanism.
Second Harmonic Detection of Sinusoidally Modulated Two-Photon Excited Fluorescence
Authors: Gilliland Donald L. , Freeman R. Griffith , Lytle Fred E.
Published: February 2023

Three interrelated problems that are routinely encountered in the taking of two-photon excitation spectra are inherently low signal levels, interferences arising from one-photon interactions such as scatter (Mie, Rayleigh, Raman) and absorption, and the need to correct the source for intensity and pulse width fluctuations. As a means of separating the quadratic signal of interest from linear interferences our group has traditionally used a linear regression method (1). This approach, though effective, suffers in two areas. The primary limitation is that it requires at least five measurements in order to yield meaningful results. This entails the attenuation of an already weak signal. A secondary concern is that the regression is performed at each wavelength resulting in excessively long data collection time; typically 6 to 8 hours for a single spectrum.
High Sensitivity Fluorescence Detection of Biological Molecules
Authors: Dovichi Norman J. , Wu Shade , Chen Da Yung
Published: February 2023

Fluorescein is a good fluorescent label for high sensitivity analysis.
The molecule has high molar absorptivity, 5 × 104 L
mol-1 cm-1 at 488 nm and near unit fluorescence
quantum yield in the pH range of 8 to 10. Unfortunately, the molecule
is not photostable undergoing irreversible photobleaching after
absorbance of about 8,000 photons. Fluorescein may be used to label
amino groups in amino acids, peptides, and proteins through the
isothiocyanate derivative. Under basic conditions, the thiocarbamoyl
derivative is formed, with relatively good stability. The reaction
between amino acids and fluorescein isothiocyanate is first order in
bod the concentration of amino acid and derivative, with an activation
energy of about 16 kcal/mol. Under acidic conditions, the cyclic
thiohydantoin derivative is formed, cleaving the terminal amino acid
from proteins and peptides. This thiohydantoin derivative possesses
greater photostability than the thiocarbamoyl derivative, decomposing
after absorbance of about 12,000 photons. The
thiocarbamoyl-thiohydantoin derivative series is the basis of an Edmon
degradation scheme for protein sequencing. In addition to amino acid
labeling, fluorescein may be used to label thiols through the
bromobimane derivatives; a high sensitivity DNA analysis is based on
this compound. Last, succinylfluorescein labeled chain terminating
dideoxynucleotides are used in DNA sequencing, these molecules have
similar spectral properties as fluorescein.
High-Sensitivity Single-Molecule Fluorescence Detection in Theory and Practice
Authors: Mathies Richard A. , Peck Konan , Stryer Lubert
Published: February 2023

The number of emitted photons that can be obtained from a fluorophore increases with the incident light intensity and the duration of illumination. However, saturation of the absorption transition and photodestruction place natural limits on the ultimate signal-to-noise ratio that can be obtained. Equations have been derived to describe the fluorescence-to-background-noise ratio in the presence of saturating light intensities and photodestruction.1 The fluorescence lifetime and the photodestruction quantum yield are the key parameters that determine the optimum light intensity and exposure time. To test this theory we have performed single molecule detection of phycoerythrin (PE). The laser power was selected to give a mean time between absorptions approximately equal to the fluorescence decay time. The transit time was selected to be nearly equal to the photodestruction time of ~600 μs. Under these conditions the photon count distribution function, the photon count autocorrelation function, and the concentration dependence clearly show that we are detecting bursts of fluorescence from individual fluorophores as they pass through the laser beam. A hard-wired version of this single-molecule detection system was used to measure the concentration of PE down to 10-15 M.2 This single-molecule counter is three orders-of-magnitude more sensitive than conventional fluorescence detection systems. The approach presented here should be useful in the optimization of fluorescence-detected DNA sequencing gels and in HPLC and capillary electrophoresis detectors.
Laser-Induced Fluorescence and Laser-Induced Photo-Dissociation in Two-Step Graphite Furnace
Authors: Sjöström Sten , Norberg Madelen
Published: February 2023

Laser-Induced Fluorescence (LIF) Spectroscopy performed in an electrothermal atomizer has shown to be an extremely sensitive and selective method for detecting traces in solid, liquid and gaseous samples with detection limits in the femtogram region reported.1-4
Analysis of Ag/Au Alloy by Sputter Initiated Laser Ionization Spectrometry and Secondary Ion Mass Spectrometry
Authors: Havrilla George J. , Nicholas Mark , Bryan Scott R. , Pruett J. Gary
Published: February 2023

Quantitative surface analysis has been the goal of several research
groups using ion beam sputtering followed by laser photoionization.
Published work has demonstrated trace level detection limits using
both resonance and non-resonance ionization schemes.(1-4)
Quantification of surface layers by SIMS requires that the standards
be matrix matched to the unknowns. The reason for this is that in
SIMS, the ionization process is intimately tied to the sputtering
process. Resonance ionization requires calibration standards, however
since the sputtering and ionization steps are separated, calibrations
can be obtained that cover a wide range of matrices. Non-resonance on
the other hand can use internal ratios to the matrix elements to
provide rapid survey analyses. This work compares resonance and
nonresonance ionization methods with SIMS for a silver/gold alloy
system.
"Use of Refractive Index Matching Fluids in a Laser Based Detector for Capillary Chromatography"
Authors: Bruno Alfredo E. , Bornhop Darryl J.
Published: February 2023

The diffraction pattern from side illuminated capillary tubes has been exploited to develop a refractive index detector of universal character suitable for HPLC and CE. A two-fold benefit is obtained by surrounding the capillary with a RI matching fluid. The fringe pattern is simplified and thermal drift is reduced.
Lidar Measurements of Stratospheric Ozone: Inter-Comparisons and Validation.
Authors: McDermid I. Stuart , Walsh T. Daniel
Published: February 2023

A high-power, differential absorption lidar system for measuring
stratospheric (20 - 50 km) ozone concentration profiles, has been in
operation at the JPL Table Mountain Observatory since January 1988.
Validation of the results obtained from this system has been provided
through two extensive inter-comparison campaigns carried out in
October/November 1988 and in July/August 1989. Many instruments were
involved in these campaigns, including the GSFC mobile DIAL system,
the SAGE II satellite instrument, ROCOZ-A rocket sondes and ECC
balloon sondes, microwave radiometers, and both Dobson and Brewer
column measuring spectro-photometers. The results have shown that the
lidars are capable of providing high quality, long-term data and will
play an important role in monitoring the stratosphere and providing
correlative and ground-truth measurements for future space-based
instruments such as UARS and Eos.
Molecular Oxygen Detection Using Frequency Modulation Diode Laser Spectroscopy
Authors: Wang Liang-guo , Sachse Glen
Published: February 2023

There are a variety of industrial and research applications for molecular oxygen (O2) sensors. Most existing oxygen sensors, however, are either intrusive and have slow response (e.g. electrochemical methods and mass spectrometry) or are expensive (e.g. UV laser-induced fluorescence). An attractive method for detecting O2 that is both non-intrusive and relatively inexpensive was first demonstrated by Kroll et al1 and involves the use of wavelength modulation (at 5 KHz) spectroscopy techniques with a GaAlAs diode laser. In this paper we extend this earlier work by making spectroscopic measurements of O2 using high frequency (≈1 GHz) modulation of GaAlAs lasers. This so-called frequency modulation spectroscopy (FMS) technique has the potential for achieving near quantum noise limited sensitivity and time response on the order of microseconds.
Applications Of Fourier Transform Raman Spectroscopy To Polymeric Systems
Authors: Rabolt John F.
Published: February 2023

Raman spectroscopy is an extremely sensitive technique used to characterize structure and local order in polymeric systems. Unfortunately it has never attained the routine analytical utility which other techniques such as infrared spectroscopy have due to the presence, in most long chain polymers, of trace amounts of impurities (chemical initiators, catalyst residues, stabilizers, etc.). These impurities give rise to strong fluorescence in the visible which interferes with the recording of a Raman spectrum in this region. Recently, however, with the advent of cw Nd:YAG lasers and low temperature InGaAs detectors, Raman spectroscopy in the near infrared has become possible. Near infrared photons do not give rise to fluorescence and hence Raman scattering from polymeric materials containing chromophores either as an inherent part of their molecular structure or as an impurity can be routinely obtained. The spectral distribution of the scattered light is obtained using a commercially available Fourier transform IR (FTIR) spectrometer thus giving name to the technique. Since the inception of this technique in 1985, Fourier transform Raman spectroscopy has been utilized to investigate the structure of biomolecules, the nature of order-disorder transitions in polysilanes and the orientation of side chain chromophores in carbon backbone polymers useful for nonlinear optical applications. Several examples will be used to explicitly illustrate the utility of this new spectroscopic technique.
Measurement of the Elements of χ(3) for Degenerate Four-Wave Mixing in OH*
Authors: Rahn Larry A. , Brown Michael S.
Published: February 2023

The sensitivity and coherent nature of the degenerate four-wave mixing (DFWM) signal from molecular gases has motivated a number of investigations into its application as diagnostic for combustion and chemical physics measurements. The degeneracy of molecular energy levels and thermal washout of contributions from counter-propagating pump and probe beams lead to interesting predictions of the polarization properties of DFWM that allow us to test our understanding of the responsible nonlinear mechanisms.
Applications of Laser Sampling Inductively Coupled Plasma Mass Spectrometry
Authors: Fredeen Kenneth J.
Published: February 2023

Laser sampling inductively coupled plasma mass spectrometry (LS-ICP-MS) is a increasingly popular technique for the direct determination of trace elements in solid materials. In this technique, a high-power pulsed laser is used to vaporize a portion of a solid specimen. The sample vapor is then swept into an ICP discharge, which ionizes the vapor before it is subsequently sampled by a mass spectrometer.
Laser Desorption/Ionization Mass Spectrometry of Biological Materials
Authors: Long S. Randolph , Chou Chih-Cong
Published: February 2023

The detection, identification, and analysis of biological materials in "real time" is of significant current interest in a number of fields. As with chemical materials, mass spectrometry holds great promise for such applications. We are presently engaged in a study of approaches to mass spectrometric analysis of biological materials, utilizing laser desorption/vaporization/ionization in conjunction with Fourier transform mass spectrometry. In this presentation, we focus on laser desorption/ionization applied to peptides. Although laser desorption can generate mass spectra with reasonably abundant molecular ion for relatively small peptides in the pure state, use of matrix-enhanced desorption techniques facilitates greatly the generation of molecular ion, We demonstrate this using examples of 248 nm laser desorption mass spectra of polypeptides. The nature of the substrate from which ions are desorbed is found also to be an important factor in the desorption/fragmentation processes through a study of a range of metallic supports. Thermal conductivity of the substrate appears to be the key parameter.
An Ultrasensitive Laser Microprobe for Detection of Surface Contamination
Authors: Duignan Michael T. , Christensen C. Paul
Published: February 2023

Increasingly, modem industrial processes demand strict control of potential interferences from contaminants on substrate surfaces. Direct detection of such small amounts of contamination presents a challenging technical task, particularly if detection is to be carried out in areas that are difficult to access. We report on a new laser-based detection method for nonvolatile residue on component surfaces.
Laser-Induced Fluorescence Measurements For Combustion Chemistry
Authors: Crosley David R.
Published: February 2023

Chemical kinetic processes form the governing factor in several key problems in combustion. Classic examples include ignition and inhibition phenomena, the formation of pollutants such as NOX, SOX and soot, and the emission of radiation in the ultraviolet and visible regions of the spectrum. A proper description of these processes is a complex network embodying a large number of reactive species and chemical reactions, with initiation and propagation steps generally depending on the concentrations of trace intermediate species.
CARS as a spectroscopic probe of a methyl chloride-air flat flame
Authors: Funk David J. , Palmer Byron A. , Oldenborg Richard
Published: February 2023

Spectroscopic characterization of methane-air and methyl chloride-air flat flames are carried out in the 600-900-cm-1 region using folded polarization BOXCARS.
Raman Lidar Measurements of Atmospheric Water Vapor: Development of a Daytime-Optimized System
Authors: Goldsmith J. E. M. , Whiteman D. N. , Bisson S. E. , Ferrare R. A. , Lapp M. , Melfi S. H.
Published: February 2023

This paper describes our research program on development of a Raman lidar system for measuring daytime profiles of atmospheric water vapor. The Raman lidar technique is a leading candidate for providing the high-resolution, day-night profiling of water vapor that is critical to programs in global climate change research. Because of the crucial role that water vapor plays directly in the earth’s radiation budget as an absorber, as well as its role in cloud formation and optical phenomenology, accurate, three-dimensional measurements of water-vapor concentration are an essential part of the experimental capability that is anticipated to be required for climate-change research.
Raman Spectroscopic Analysis of Electrochemically Oxidized Pyrite and Galena
Authors: Turcotte S. B. , Benner R. E. , Riley A. M. , Li J. , Wadsworth M.E.
Published: February 2023

Iron pyrite is a common constituent of coal and its presence during combustion leads to the production of sulfur dioxide and acid rain. Consequently, there is a large research effort dedicated to improving the methods of separating pyrite from coal. One method of separation is to utilize the natural hydrophobicity of many sulfide ores. It has been observed that under the correct conditions of pH and electropotential that sulfide minerals are sufficiently hydrophobic that they can be readily floated. This has been attributed this to the formation of elemental sulfur on the surface of the sulfide minerals [1]. Therefore, there is an interest in identifying the conditions that give rise to sulfur formation on the pyrite surface. In this study Raman spectroscopy is used to evaluate the pyrite surface in situ for various applied potentials. As a source of comparison, the surface products of galena (PbS) and electrodeposited sulfur on platinum are also given.
Structure Matters: Detection of Difluoromethyl and Difluoroethyl Radicals by Resonance Enhanced Multiphoton Ionization Spectroscopy
Authors: Hudgens Jeffrey W. , Brum Jeffrey L. , Johnson Russell D. , Dearden David V.
Published: February 2023

The link between anthropogenic chlorofluorocarbon (CFC) release and stratospheric ozone depletion now appears well established. Several fluorinated methanes and ethanes are among the hydrofluorocarbons (HFCs) currently being investigated as replacements for the chlorine containing congeners that have traditionally found use as refrigerants, fire extinguishers, and in more specialized applications. In recent years significant effort has focused on the tropospheric degradation pathways available to HFCs initiated by H atom abstraction by a hydroxyl radical. For alternate CFC's the generic initiating reactions are: Although an impressive amount of mechanistic and kinetic information concerning these pathways has been gathered recently, much remains to be learned about the fluorinated methyl and ethyl radicals which represent the first intermediates of the degradation process.
A 30 Hz CARS System for Concentration and Temperature Measurements in Supersonic, Turbulent, H2/Air Combustion
Authors: Smith M. W. , Cutler A. D. , Millard M.W. , Northam G. B.
Published: February 2023

CARS has become perhaps the most common non-intrusive laser diagnostic
technique used for the analysis of reacting gas flows.1-4
This paper describes the design and calibration of a dual broadband
CARS system assembled to measure single-point, single-shot,
temperature and species concentration in a simulated hydrogen-fueled
scramjet (Supersonic Combustion RamJET) engine model. No scramjet data
are included in this paper. However, the optical system design
features driven by the scramjet engine test environment are discussed.
During calibration, temperatures and relative concentrations of
N2 were derived by fitting single-shot CARS spectra
acquired at 30 Hz. This optical system was derived in part from a
previous 10 Hz system designed for thermometry only5. Since
N2 concentrations were found by spectral fitting, they were
not subject to problems of beam steering, or beam attenuation. These
problems, common in situations with high turbulence levels and
windows, interfere with concentration measurement strategies that
depend on acquiring absolute CARS signal intensities. In fuel-rich
conditions, single-shot temperatures were also found independently by
fitting H2 CARS spectra.
Chemical Analysis of Single Aerosol Particles Using Laser Ionization
Authors: Murphy D. M.
Published: February 2023

Aerosol particles are known to be extremely important for both radiative climate forcing and atmospheric chemistry. A basic requirement for understanding aerosol effects is knowledge of the composition of particles. Both heterogeneous chemistry and cloud condensation properties depends on the composition. Aerosol composition also provides essential information on the sources of particles.
Morphological Resonances for Multicomponent Immunoassays
Authors: Whitten W. B. , Shapiro M. J. , Ramsey J. M. , Bronk B. V.
Published: February 2023

We are developing a multicomponent immunoassay technique in which a small sample can ne simultaneously analyzed for a large number of species of microorganisms. Sensitivity is sufficient for the detection and identification of individual organisms. While the present scheme requires manipulation and visual observation by the analyst, the technique could be readily automated.
Spatially and Temporally Resolved Electron Number Densities in a Decaying Laser-Induced Hydrogen Plasma
Authors: Parigger Christian , Plemmons David H. , Lewis J. W. L.
Published: February 2023

Measurements of the widths of Stark broadened hydrogen Balmer Series lines can be used to infer electron number densities of optically created plasmas. A typical optical breakdown plasma is transient and shows spatial structure. For example, self-focusing effects may induce density variations which may be measured using diffraction techniques.1 The expanding plasma induces number density variations that in fact may form a light pipe for high intensity laser pulses.2
Vacuum Ultra-Violet Photoionization Time-of-Flight Mass Spectrometry for the Investigation of Products of Benzene Oxidation
Authors: Bermudez German , Pfefferle Lisa
Published: February 2023

A serious limitation for direct, routine mass spectrometric analysis of complex mixtures arises from the destructive nature of electron ionization methods employed in commercial instrumentation.
Trace Organic Chemical Detection Using an Ultraviolet Excitation Molecular Beam Fluorometer
Authors: Preppernau B.L. , Hargis P.J.
Published: February 2023

Detection of air-borne environmental contaminants, such as organic solvents, requires unambiguous compound identification and sensitivity to concentrations below those permitted by regulating agencies. One promising detection approach uses a pulsed supersonic molecular beam vacuum expansion in combination with fluorescence signal spectral analysis to identify species in a chemical mixture. Expanding a contaminated atmospheric sample through a supersonic molecular beam expansion acts to cool the sample and greatly reduce the spectral density in a fluorescence or photoionization spectrum. Most organic contaminants of interest have electronic transitions in the ultraviolet with near-featureless broad band fluorescence spectra when recorded at atmospheric pressure and room temperature. By using a supersonic vacuum expansion, cooling to within a few degrees of absolute zero can reduce the effective rotational and translational temperatures of the sample molecules and provide a sharply defined spectra which can be used to unambiguously identify specific molecules and their concentrations.
Absorption Spectra of Propylene at Carbon Dioxide (CO2) Laser Wavelengths
Authors: Rob Mohammad A. , Mack Larry H.
Published: February 2023

Laser remote sensing techniques for detecting trace level atmospheric pollutants have made rapid advances in the past several years.1,2 Molecular CO2 lasers play an important role in atmospheric pollution monitoring, because its emission spectrum in the 9-11 μn range falls within the largest atmospheric window and which overlap with the absorption spectra of a large number of molecules of environmental concern.2 The primary pollutants that are emitted to the atmosphere by natural and anthropogenic processes are, hydrocarbons (HC), carbon oxides (CO, CO2), nitric oxides (NO, NO2), ammonia (NH3), sulfur dioxide (SO2), and etc.3 The primary pollutants also go through complex chemical reactions among themselves or with the natural atmospheric constituents, to form a variety of secondary pollutants.2,3 An understanding of the atmospheric chemical processes requires fast detection of primary and secondary pollutants while they reside in the atmosphere. Laser remote sensing techniques are suitable for the detection of these pollutants.
Multichannel Time-Resolved Raman Spectroscopy for Photophysical and Photochemical Studies
Authors: Fister Julius C. , Harris Joel M.
Published: February 2023

CCD-detected Raman spectroscopy has been used to study intermediates and nanosecond kinetics in photoinitiated reactions. Multidimensional analysis techniques are used to isolate spectra of individual transient species from those of ground state initiators, photoproducts, reactants and solvent (Fig 1). These methods address several challenges facing Raman analysis of chemical reactions. Overlap in spectra of complex mixtures complicates band assignment and intensity analysis. Raman bands of transient species created in photoinitiated reactions may be difficult to separate from other bands. Multidimensional analysis allows bands to be resolved from spectra in which background subtraction is not feasible. Furthermore, kinetic and spectral information may be simultaneously extracted from the data.
Advances in Tunable Semiconductor Diode Lasers
Authors: Mehuys David G.
Published: February 2023

Semiconductor diode lasers are capable of generating tunable radiation with any of narrow-linewidth, high-power, or short-pulse output. Fundamental concepts, laser characteristics, and applications will be discussed.
Differential Absorption Lidar Measurements of Tropospheric Ozone
Authors: Langford Andrew O. , Proffitt Michael H.
Published: February 2023

Ozone is one of the most important trace species in the atmosphere and the focus of several important environmental issues. Most ozone resides in the stratosphere where it plays a critical role in protecting the biosphere from harmful solar ultraviolet radiation. A variety of observations indicate that ozone in this region is decreasing due to heterogeneous processes involving anthropogenic chlorine. In contrast, ozone is increasing at the surface due to photochemical reactions between man-made nitrogen oxides and hydrocarbons. This elevated ozone adversely affects human health and vegetation and can be transported across regional and international boundaries. Finally, ozone is the only radiatively important trace gas that absorbs both incoming ultraviolet radiation and outgoing infrared radiation. The net effect of atmospheric ozone changes on the surface radiation budget will depend on where the vertical profile changes, particularly in the upper troposphere and lower stratosphere.
Laser Diagnostics by Electrostrictive Gratings in the Gas Phase
Authors: Stampanoni-Panariello A. , Hubschmid W. , Hemmerling B.
Published: February 2023

Over the past two decades laser induced gratings (LIGs) have been widely used to study various properties of optical media. Refractive index changes are induced by optical fields through resonant and nonresonant mechanisms, respectively. Depending on the physical mechanism which is responsible for the formation of LIGs, this technique is suited for studying different processes in the solid, liquid, and gas phase. Resonant LIGs have been used for the detection of excited state absorption in the gas phase [1] and for the measurement of ultrafast phenomena [2], Furthermore, LIGs have been applied for the measurement of flame temperature [3] and for the study of fast combustion processes [4]. Recently, two-color laser- induced gratings have been proposed as a new spectroscopic method for detecting rovibronic transitions of excited molecules in the gas phase [5,6] and for the detection of atomic hydrogen in low pressure H2/O2 flames [7].
Investigation of Stagnation-Flow Diamond-Forming Flames Using Advanced Laser Diagnostics
Authors: Bertagnolli Kenneth E. , Lucht Robert P.
Published: February 2023

The deposition of polycrystalline diamond films has been demonstrated for a wide variety of flames and plasmas. Uniform diamond deposition was demonstrated recently in a rich H2/C2H2/O2 flat flame stabilized in the stagnation region of the deposition substrate [1,2]. Continued development of this technology depends strongly on increased understanding of the diamond growth process through experimental and theoretical studies [3].
Trace NOx Analysis by Laser Resonance-Enhanced Multiphoton Ionization Photoacoustic Spectroscopy near 454 nm
Authors: Sausa R.C. , Pastel R.L.
Published: February 2023

There is a growing interest in laser-based analytical techniques for
remote or in situ trace detection of NOx
(NO+NO2) pollutants.3 Much of this interest
stems from concerns related to health and the environment. The
detection of these species is also important in
photofragmentation/fragment detection techniques being developed for
the chemical analysis of energetic materials.4,5
Laser-Induced Chemistry within Clusters
Authors: Martin M. Z. , Desai S. R. , Feigerle C. S. , Miller J. C.
Published: February 2023

Clusters comprise an interesting environment for the study of chemical reactions. Binary cluster complexes can be produced which combine a variety of potential reactant partners in various proportions in an intimate, yet controlled arrangement. Molecules or ions within such a cluster (i.e. solvated) have properties which are intermediate between those of isolated species and of species in solution or in bulk. Furthermore as the cluster size increases their properties may smoothly change until the condensed-phase regime is reached. But, since clusters are generated and interrogated in the gas phase, powerful techniques such as mass spectrometry may be used for characterization. Such clusters may then represent model environments which simulate real world situations such as aerosols or cells. Similarly, the chemistry of such clusters may also differ in significant ways from that of the isolated species.
Applications of acousto-optic tunable filters in environmental sensors
Authors: Wang Xiaolu
Published: February 2023

Acousto-optic tunable filters (AOTFs) are electronically addressable optical filters that provide rapid, random wavelength access, broad spectral coverage and moderately high spectral resolution. They are based on acousto-optic diffraction of light in an anisotropic medium. A piezoelectric transducer bonded to a birefringent crystal generates a traveling acoustic wave through the crystal, whenever it is excited by an applied RF signal. This acoustic wave establishes a periodic modulation of the index of refraction and generates a moving grating which allows diffraction of the incident light beam. For a given acousto-optic frequency, only a small wavelength band will satisfy the phase-matching condition and will be cumulatively diffracted. Varying the RF frequency has the resulting effect of changing the center of the optical bandpass. In addition, applying multiple RF frequencies simultaneously, result in multiple wavelength bandpasses.
Resonant Laser Ablation: Applications and Mechanistic Aspects
Authors: Anderson J. E. , Garrett A. W. , Gill C. G. , Hemberger P. H. , Nogar N. S. , Allen T. M. , Kelly P. B.
Published: February 2023

Ever since the first report of laser action, it has been recognized that laser ablation (evaporation/volatilization) may provide a useful sampling mechanism for chemical analysis. In particular, laser ablation is rapidly gaining popularity as a method of sample introduction for mass spectrometry. Since its original description, numerous research papers and review articles have appeared on various aspects of laser mass spectrometry. While most laser ablation/mass spectrometry has been performed with fixed frequency lasers operating at relatively high intensities/fluences (≥108 W/cm2, ≥1 J/cm2), there has been some recent interest in the use of low-power tunable lasers to ablate and resonantly ionize selected components in the ablation plume. This process has been termed resonant laser ablation (RLA).1 Potential advantages of RLA include: 1) simplification of the mass spectrum, by enhancement of signal from the analyte of interest; 2) improvement of the absolute detection limits by improving the ionization efficiency, and 3) improvement in relative sensitivity by reduction of spurious signal in the detection channel of interest (due to bleed through from adjascent mass channels or from isobaric interferences).
Ground-Based and Airborne Measurements of Atmospheric Constituents Using Tunable Diode Lasers: An Overview and Recent Measurements
Authors: Fried Alan , Sewell Scott , Henry Bruce , Wert Bryan , Drummond James R.
Published: February 2023

The application of tunable diode laser absorption spectroscopy (TDLAS)
for studying the chemistry of the atmosphere on various platforms is
well documented. This technique, for example, has been employed in
laboratory kinetics and spectroscopic studies, in ground-based
measurements, in measurements on conventional as well as high flying
aircraft, and on balloon- borne payloads. The present talk will give a
brief overview of these capabilities, detailing some of the
atmospheric gases studied, the sensitivities achieved, and the current
limitations of the technique. This will be followed by a discussion of
a ground-based TDLAS system developed at the National Center for
Atmospheric Research (NCAR) for studying various constituents,
including the important reactive intermediate formaldehyde (HCHO).
This system has recently been modified for aircraft operation and this
will also be described.
UV Laser Absorption Measurements of Tropospheric Hydroxyl on a 21-km Atmospheric Long Path
Authors: Mount George H.
Published: February 2023

The hydroxyl radical (OH) plays a central role in the chemistry of the Earth's lower and middle atmosphere. The determination of its concentration is essential to an understanding of the chemistry of the lower atmosphere since this molecule controls the lifetimes, and therefore the concentrations, of many chemical species under both clean and polluted conditions. Predicted midlatitude tropospheric concentrations of OH range approximately from 0.1 pptv at the noontime maximum in the winter to several tenths pptv at noontime in the summer. These low values are extremely difficult to measure; sensitivity at least a decade smaller is essential to measure the daily growth and decay inorder to understand the photochemical variation of OH.
Remote Spectroscopy over Optical Fibers for In Situ Measurement of Contaminants in Soil
Authors: Lieberman Steve , Knowles David S. , Theriault Greg A. , Davey Michele
Published: February 2023

Fiber optic-based sensor probes have been developed that can be pushed up to 50 meters into the soil for remote, real-time detection of petroleum hydrocarbons using laser-induced fluorescence (LIF) and metals via laser-induced breakdown spectroscopy (LIBS).
Raman Techniques for Detection of Explosive Materials
Authors: Gilbert Brian D. , Janni James , Moss David , Field R.W. , Steinfeld Jeffrey I. , Mercado Alvaro
Published: February 2023

A key requirement for prevailing against terrorist threats to both transportation systems and stationary structures [1,2], as well as for facilitating the massive cleanup efforts required at decommissioned military bases [3,4], is the ability to detect trace quantities of explosive materials in the presence of a wide variety of interfering species. Numerous analytical techniques are being investigated for this problem, among which laser-based spectroscopic methods show enormous potential. Methods under investigation [1,2] include absorption spectroscopy of explosive vapors detected by photothermal or modulation techniques, detection of decomposition fragments by chemiluminescence, frequency-modulation spectroscopy, or modulated magnetic rotation spectroscopy [5], and resonance-enhanced multiphoton ionization spectroscopy.
Raman Spectroscopy of Explosives and Propellants During Heating
Authors: Fell N.F. , McNesby K.L
Published: February 2023

In this paper we report Raman spectra of nitramine and nitrocellulose
based explosives and propellants measured during heating of the
sample. Raman spectra are measured using a Fourier transform
spectrometer employing 1064 nm laser radiation as the scattering
source, and using a dispersive system employing 514.5 nm laser
radiation as the scattering source. For most explosives and
propellants, the longer wavelength radiation (1064 nm) measures
scatter from the bulk sample during heating, while the shorter
wavelength, visible radiation (514.5 nm) is used to measure changes in
the surface of the sample during heating.
Application of Laser Induced Fluorescence and Spontaneous Raman Scattering to Technically Applied Combustion Systems: Four Cylinder Spark Ignition Engine and Oil Burning Furnace
Authors: Beushausen V. , Knapp M. , Luczak A. , Eisenberg S. , Andresen Peter
Published: February 2023

In this paper the successful application of spontaneous vibrational Raman scattering (VRS) and laser induced (predissociative) fluorescence (LIPF) to technical applied combustion systems like a mass production internal combustion engine and a commercial oil burning furnace - both are modified for optical access - is described. It will be shown that these techniques can be used as a tool for design and optimization purposes as well as for fundamental research.