bluuebunny/crossref_metadata_2025 huggingface dataset:
Temporally and spectrally resolved optical imaging of normal and cancerous human breast tissues
Authors: Gayen S. K. , Alrubaiee M. , Zevallos M. E. , Alfano R. R.
Published: February 2023

Time-sliced and spectroscopic imaging approaches were used to obtain two-dimensional (2-D) transillumination images of a composite in vitro human breast tissue sample comprising cancerous and normal fibrous tissues, adipose tissues, and a lymph node. Time-sliced imaging approach used 800-nm, approximately 130-fs duration, 1 kHz repetition-rate pulses from a Ti:sapphire laser system to illuminate the sample, and a gated imaging system that provided a variable-position, ~80 ps-duration electronic gate to record time-sliced 2-D images. Images recorded with earlier temporal slices (approximately, first 100 ps) of the transmitted light highlighted the lymph node and cancerous tissues, while the later slices (later than 300 ps) accentuated the adipose and normal tissues. Spectroscopic imaging arrangement made use of 1225 - 1300 nm light from a chromium-doped forsterite laser for sample illumination, a Fourier space gate and a polarization gate to sort out a fraction of the image-bearing photons, and an InGaAs area camera for recording 2-D images. Marked enhancement of image contrast between the adipose tissue and other tissues in the specimen was observed when the wavelength of imaging light was near resonant with the 1203-nm optical absorption resonance of the adipose tissue. Wavelength-dependent differences in relative light transmission through the normal and cancerous tissues were observed.
Laser Fluorimetric Detection: Application to LC and Capillary Zone Electrophoresis
Authors: Zare Richard N.
Published: February 2023

The analysis of volatile compounds relies heavily upon gas chromatography (GC) or mass spectrometry (MS) or the combination of GC-MS. Nonvolatile compounds present a more severe challenge to the analyst who frequently relies on liquid chromatography (LC) and in some cases of notable biological importance electrophoresis. But both these resolution techniques are distinctly inferior to the resolution routinely achieved for volatile compounds. To overcome this handicap, much emphasis has been placed on increasing the theoretical plate number of these separation techniques - - in the case of LC by the use of long microcolumns - - and in the case of electrophoresis by using capillary columns which reduce the adverse effects of Joule heating. In both cases the results are rather spectacular with separation power exceeding one million. However, these accomplishments carry with them a penalty in terms of volume of eluent to be analyzed and amount of analyte to be detected - - a penalty which stresses our best instrumentation. This talk summarizes progress on one method to meet this challenge, namely, the use of laser fluoresence excitation as a detection scheme for the minute quantities of effluent associated with the use of LC microcolumns or of open-tube high-voltage capillary electrophoresis.
Laser Based Analytical Measurements In Liquids
Authors: Yeung Edward S.
Published: February 2023

The use of lasers for detection in liquid chromatography (LC) has been gaining in popularity. The reason is that unique properties of the laser beam fit well with many of the requirements in LC. Fluorescence is one of the widely used laser-based techniques. However, one is often limited by the availability of a fluorophore, the availability of the appropriate laser wavelength, and the poor intensity stability of lasers. A possible solution is to use indirect fluorometry. Because there is always a solvent present in LC, one can include a fluorescent probe in the solvent. There is then a large background fluorescence in the optical region at all times. When analytes elute from the chromatographic system, they can displace the probe molecules to cause a lower fluorescence signal. This then allows fluorometry to be used to detect non-fluorescing species. Since the choice of the fluorophore is governed by some broad guidelines, a convenient laser wavelength can be used. The stability of the laser intensity is critical to detection at low concentrations. Good stability can be achieved in a double-beam arrangement with modulation at high frequencies. To enhance detection, we make use of the competition between the probe molecule and the analyte either by ion exchange or by adsorption on the LC column. Good mass detectability is possible when microbore or open capillary LC columns are used.
Laser-Induced Thermal Decay of SERS as a Probe of Silver Surface Active Sites in Electrochemical Systems
Authors: Sobocinski Raymond L. , Pemberton Jeanne E.
Published: February 2023

The activation parameters for the temperature dependent irreversible loss of surface enhanced Raman scattered (SERS) intensity from pyridine and chloride adsorbed at silver surfaces in an electrochemical environment have been determined. Accurate laser-induced surface temperatures must be known for these experiments and are calculated from the Stokes and anti-Stokes intensities of adsorbed pyridine. The laser-induced heating method is used successfully to promote a first order reaction at the electrode surface. It is found that the kinetic data follow Arrhenius behavior for both pyridine and chloride as shown in the figures. The activation energies are 13 kcal/mole and 26 kcal/mole for pyridine at two different types of sites on the silver surface. Similarly, values for coadsorbed chloride are determined from the Ag-Cl vibration and are found to be 13 kcal/mole and 25 kcal/mole. These values are consistent with a surface reaction that involves the discharge of a positively charged Ag adatom or cluster.
Second Harmonic Generation and Differential Capacitance Studies of Silver Electrodes
Authors: Rojhantalab H. M. , Richmond G. L.
Published: February 2023

Detailed studies of factors influencing optical second harmonic generation (SHG) at the silver-aqueous electrolyte iterface have been performed and compared with simultneously obtained differential capacitance measurements.
Time-Resolved Fluorescence Using an Optical-Fiber Probe1
Authors: Vickers G. H. , Miller R. M. , Hieftje G. M.
Published: February 2023

Time-resolved fluorescence has found wide application in the study of excited-state lifetimes of both atoms and molecules. The information that is provided by time resolution can be used to characterize chemical systems; in addition, it can be very useful in analytical determinations where the information provided by steady-state fluorescence is insufficient. Some examples where this situation might occur include the presence of quenching agents in the sample, errors due to scattered radiation, and mixtures with spectral overlap.
Wavelength Dependent Fragmentation in Resonance Enhanced Multiphoton Ionization
Authors: Kinsel G. R. , Johnston M. V.
Published: February 2023

Resonance enhanced multiphoton ionization/fragmentation (REMPI/F) is a useful technique for the production of parent and fragment ions for analysis by mass spectrometry. It is well documented that the degree of fragmentation of a parent ion by REMPI/F can be varied by changing the laser intensity, and that either soft or hard ionization can be achieved. It is less well known that the relative abundance of the fragments produced from a particular parent ion can be strongly dependent on the wavelength of light used for ionization/fragmentation. This effect is independent of laser intensity and arises from the narrow internal energy distributions of the parent ions created by REMPI/F.
Absorption and Scattering: Thin Film Analogs of Classical Experiments
Authors: Stephens D.A. , Bohn P.W.
Published: February 2023

Absorption measurements in thin films made perpendicular to the film plane are hampered by the extremely short pathlength available for typical transmission based measurements. Analytical chemists have traditionally dealt with low absorbances such as those generated in thin film media in two ways: by increasing the pathlength or by increasing the intrinsic absorption cross section of the system being measured (1). Although the latter approach works well enough in solution where some transforming chemistry may be carried out, the possibilities for rendering thin film matrices more absorbing are not abundant. Thus one must concentrate on improving the sensitivity of the measurement or increasing the optical pathlength. Another problem squarely facing accurate absorption measurements in thin films is the separation of the scattering loss from true absorption (2-4). Any transmission based measurement has this problem, however it is particularly severe when there are no readily available methods for making scattering background corrections.
Applications of Linear and Nonlinear Site Selective Spectroscopy to Chemical Measurements
Authors: Wright John C.
Published: February 2023

Selectivity is a factor that limits practical chemical measurements in many analytically important situations either because the large number of components causes overlapping of distinguishing features or the features of any one component are broadened because of inhomogeneties within the sample. Site selective spectroscopy has been developed as a method for improving selectivity by reducing both types of problems. Fluorescence line narrowing was first developed by Szabo for eliminating inhomogeneous broadening in ruby crystals [1], it was extended to the elimination of inhomogeneous broadening in the spectra of polyaromatic hydrocarbons by Marchetti and coworkers [2], and it was adapted to analytical problems by Small and coworkers [3]. In this technique, a laser is tuned to a position within an inhomogeneously broadened band so that molecules in sites that are resonant with the laser are excited. The resulting fluorescence spectrum can be markedly sharpened because only a subset of the chromophores contribute and the inhomogeneous broadening can be eliminated.
Laser-Enhanced Ionization Spectrometry as an Ultra-Sensitive Method for Trace Element Analysis
Authors: Axner O. , Rubinsztein-Dunlop H.
Published: February 2023

In Laser-Enhanced Ionization spectrometry (LEI), the thermal ionization rate of an analyte atom in a flame or furnace is enhanced when the atom illuminated by light from a pulsed dye laser system, tuned to an absorption transition. The enhanced ionization rate which follows the excitation is detected non-optically by applying an electric field across the interaction region and measuring the current. Two-step LEI, where the atoms are simultaneously excited by the light from two dye lasers, gives an increase in both the sensitivity and selectivity of the method.
Analytical Applications Of Supercritical Fluid/Supersonic Beam Laser Ionization Mass Spectrometry
Authors: Lubman David M. , Sin Chung Hang , Pang Ho Ming
Published: February 2023

Supercritical fluids of CO2 and N2O are used as a means of solubilizing nonvolatile polynuclear aromatic hydrocarbons and small thermally labile biologicals for expansion into supersonic beams for mass spectrometry. The resulting expansion into vacuum results in internally ultracold molecules with sharp spectral features for unique identification in UV-VIS absorption spectroscopy. In this work laser resonant two-photon ionization is used as a means of selectively producing ions for detection in mass spectrometry where the first photon excites the molecule to a real resonant state and the second photon ionizes the molecule. Although ions are produced for mass spectrometry, the ionization cross section reflects the SO → S1 transition so that ionization spectroscopy can be used as a means of identifying molecules in a mass spectrometer. We have applied this method to detection of several PNAH's where supercritical fluid expansion was used to solubilize these molecules essentially at room temperature, i.e. without heating. In addition, small biological and pharmaceutical analogs have been examined and the effect of the supercritical fluid solvent is studied. Most recently supercritical ammonia has been investigated as a highly polar solvent for dissolving indoleamines, catecholamines and other polar biological species. The key to this experiment is a novel compact molecular beam apparatus for supercritical fluid injection which takes advantage of (a) efficient liquid N2 cryopumping of CO2 and (b) a special high-pressure pulsed valve. This valve is capable of operation up to 400 atm backpressure at 250°C. The combination of pulsed valve injection with cryopumping allows the use of a 150-200 μ orifice for high on-axis density and thus sensitivity. The resulting chamber pressure at 400 atm reservoir pressure is <2×10−5 torr so that the ions produced by R2PI can be detected and mass analyzed in a time-of-flight mass spectrometer. The future potential of this method is discussed and compared to the use of the laser desorption method for volatilizing labile compounds into jet expansions.
In Situ Elemental Analysis of Particulate Fuels Using Laser Spark Spectroscopy
Authors: Ottesen D. K. , Radziemski L. J.
Published: February 2023

One of the most challenging areas for coal combustion diagnostics is that of determining the composition of entrained coal, char, and mineral matter particles in the combustion zone. We are currently evaluating the potential of laser spark spectroscopy as a non-intrusive optical diagnostic for such studies. The technique uses a high power pulsed laser beam focused on a target to form a high temperature plasma which results in an intense emission spectrum. The spectral lines are then used for qualitative analysis of the sample. A brief review of various demonstration experiments is given by Schmieder (1).
Optical Remote Sensing of Atmospheric Pollutants
Authors: Edner H. , Galle B. , Sunesson A. , Svanberg S. , Unéus L. , Wallin S. , Wendt W.
Published: February 2023

The problems connected with atmospheric pollutants are being more and more widely recognized. Soil and lake acidification have been long discussed while reports on widespread damage to forests are more recent. Air pollutants constitute a threat to public health both directly through inhalation and indirectly through possible long-term influences on the atmospheric environment. The need for powerful actions and international cooperation is becoming evident. Clearly, remote sensing techniques utilizing laser / optical technology provide attractive possibilities for measurements on local, regional and global scales. Source emissions, ambient air quality, atmospheric chemical transformation and long-distance transport of pollutants are all areas receiving increasing attention. Whereas point monitors can provide reasonably reliable information at a specific location, much more representative values can be obtained with remote sensing techniques, which also provide unique means to study the dynamics of the atmospheric processes. A review of the optical and laser remote sensing field is provided by e.g. Refs. 1 and 2.
Laser-Based Ionization Analyses at Pacific Northwest Laboratory(*)
Authors: Whitaker Tom J. , Cannon Bret D. , Gerke Gretchen K. , Bushaw Bruce A.
Published: February 2023

Pacific Northwest Laboratory (PNL) has several projects dedicated to developing new resonance ionization techniques and the study of related basic processes. The two techniques described here differ from most resonance ionization experiments in that the lasers used for resonant excitation are not required to photoionize the excited state atom. This permits excellent sensitivity to be achieved even when relatively weak lasers are used for the resonance steps. In one case, continuous wave (cw) lasers provide isotopically selective resonant excitation and a medium intensity infrared laser ionizes the excited atoms. In the other case, pulsed lasers are used for resonant excitation, and collisions with an inert buffer gas produce ionization. The merits of these techniques are discussed.
CW Dye Laser with a Photorefractive Intracavity Mode Selector and Frequency Stabilizer
Authors: Whitten W. B. , Ramsey J. M.
Published: February 2023

We have recently performed some experiments with a standing-wave CW dye laser with a BaTiO3 crystal intracavity element. A holographic grating formed within the crystal by the counterpropagating waves in the laser cavity generates positive feedback that is strongly frequency selective. The laser has a narrow linewidth with unusual mode patterns that depend upon the position of the crystal along the cavity axis. The output frequency is unstable for most positions of the crystal but is exceptionally stable for a few regions. With the crystal at one of these locations, it is possible to scan the output frequency at high resolution over a range of several hundred wavenumbers without mode jumps. The frequency stability and scanning is interpreted in terms of static and dynamic phase shifts between the light that produces the holographic grating in the BaTiO3 crystal and the light reflected by the grating. The mode selection is due to a combination of mode competition in the gain medium and the variation of grating contrast with the different patterns of oscillating modes.
Studies of Gasdynamic Focusing in a Near Critically Choked Expansion
Authors: Muenchausen R. E. , Garcia A. R. , Keller R. A. , Nogar N. S.
Published: February 2023

We have developed a technique well suited for gaseous flow field visualization using laser induced fluorescence (LIF) coupled with an array detector which allows us to obtain real-time spatial profiles of fluorescence from iodine seeded gas jets. Furthermore, array detection provides signals that are linear in fluorescence intensity as well as producing data ammenable to digital signal processing.
Photothermal Diffraction for Background-Free Detection of Weak Absorption in Liquids
Authors: Harris Joel M. , McGraw Daniel J.
Published: February 2023

The introduction of lasers into spectroscopic instrumentation has produced outstanding gains in detection compared to conventional light sources. These improvements arise not only from the higher optical power output of the laser, but also from the unique coherence properties of laser radiation. A new class of sensitive, spectroscopic techniques has been developed in which the heat produced by nonradiative decay of excited species acts to perturb the optical path within the sample [1,2]. The spatial coherence of a laser beam probing the sample allows extremely small perturbations in optical path to be observed allowing the detection of very weakly absorbing samples.
Intracavity Photothermal Deflection Spectroscopy
Authors: Tran Chieu D.
Published: February 2023

Photothermal deflection has been demonstrated to be a suitable technique for low absorbance measurements of nonfluorescent molecular spieces such as atmospheric constituents.1-3 This technique involves the excitation of a sample by a modulated "pump-laser" beam. The heat generated from the absorption of light by the sample increases the temperature which changes the index of refraction, which in turn effects the optical beam of the "probe laser". Absorptivities in order of 10-6cm-1 have been measured using this technique1-3. Recent attempts to improve the photothermal measurements have utilized interferometric detection scheme4. In spite of their high sensitivity, interferometric photothermal apparatuses are not suitable for general analytical use because they are bulky and require strict accurate alignments.
Surface Enhanced and Unenhanced Raman Scattering of Alkanethiols Adsorbed on Silver and Gold Surfaces
Authors: Johnston Christopher R. , Bryant Mark A. , Pemberton Jeanne E.
Published: February 2023

Raman spectroscopy has been demonstrated to be a powerful tool with which to probe the orientation of bonding of molecules on metal surfaces. Surface enhanced Raman scattering (SERS) has been successfully used for this purpose, but suffers from the requirement for considerable surface roughness in order for the ehancement to be realized. A more desirable approach is the acquisition of Raman spectra of molecules on smooth metal surfaces. This is accomplished in our laboratory with charge-coupled device (CCD) detection which provides adequate sensitivity for the observation of monolayers of organic molecules. This detector is coupled to a triple spectrometer and used with Ar+-pumped dye laser excitation between ca. 600 and 720 nm. Excitation in the red region of the spectrum is essential for enhancement on Au surfaces. The high quantum efficiencies of extended-red CCDs in this region provide excellent sensitivity for these measurements.
CARS from Lift-Off to Re-Entry
Authors: Taran J.P.
Published: February 2023

Coherent Anti-Stokes Raman Scattering (CARS) has been particularly useful for making temperature measurements in flames. A majority of the CARS instruments is used in studies of small-scale burners, piston engines, and even furnaces and boilers of industrial size. Occasional investigations of species concentrations and rotational and vibrational temperatures in rarefied gases have also been conducted. In the area of aerospace research, one must tackle very delicate problems in all of these fields. For instance, it is particularly difficult to investigate cryogenic rocket motor combustion, hypersonic flight aerothermochemistry, or the elaboration of refractory materials by Chemical Vapor Deposition (CVD).
Quantitative CARS Spectroscopy of the ν1 Band of Water Vapour
Authors: Porter F.M. , Greenhalgh D.A. , Williams D.R.
Published: February 2023

Water vapour is of great relevance to heat transport in power plants and is the only non-polluting product of combustion. CARS spectroscopy is an established tool for thermometry in practical and industrial systems1. The accuracy of CARS thermometry depends on an accurate spectral model. In this paper we show that modelling of water vapour spectra has been significantly advanced so that for low pressure from 400 to 900K experimental CARS spectra may be accurately described by theoretical models. Accurate CARS thermometry of water vapour has now been demonstrated; over a large range of temperatures and pressures we have achieved temperature errors of order ±15K.
10.5 eV Photoionization Mass Spectroscopy
Authors: Van Bramer S.E. , Johnston M.V.
Published: February 2023

Laser ionization is becoming an increasingly powerful tool in mass spectroscopy. By frequency tripling the third harmonic of a Nd:YAG laser (355 nm) in a mixture of xenon and argon, it is possible to produce coherent vacuum ultraviolet (VUV) radiation at 118 nm (10.5 eV) for laser ionization mass spectroscopy. 10.5 eV photoionization is a potentially powerful tool for soft ionization. Since 10.5 eV is close to the ionization energy of most molecules, little fragmentation should be induced. Since no resonant intermediate state is required in a one photon process the ionization efficiency should be relatively high and consistent for most compounds when compared to multiphoton ionization. The 10.5 eV mass spectra of aliphatic C8 compounds with functional groups which induce extensive fragmentation will be discussed in this presentation.
Application of UV Lasers to Detection and Identification
Authors: Long S. Randolph
Published: February 2023

Principal processes occurring in molecules under the influence of focused UV laser radiation include fragmentation and ionization. These processes can facilitate substantially the detection and identification of molecular species.
Quantitative Fluorescence Determination of Impurities in Compound Semiconductors
Authors: Harris T. D. , Colonell J. I.
Published: February 2023

The electrical behavior of compound semiconductors is governed by the combined effects of the stoichiometry and impurities. The determination of impurity concentration in undoped samples is a largely unsolved problem. This deficiency results from the high purity routinely achieved in these materials, typically 1-20 ppb total impurity concentration, less than the detection limit of the applicable methods, such as SIMS. Progress toward quantitative impurity determination has been achieved by employing electronic Raman scattering, but this method is applicable only to acceptor concentration determination in bulk undoped semi-insulating GaAs. Low temperature luminescence methods have long been employed for impurity identification, but no attempt to quantify luminescence in direct gap semiconductors has been published, despite considerable success employing quantitative luminescence in Si.
Laser-Induced Ionization of Atoms in a Power-Modulated Inductively Coupled Plasma.
Authors: Turk Gregory C. , Yu LiJian , Watters Robert L. , Travis John C.
Published: February 2023

Laser-enhanced ionization (LEI) spectroscopy is presently being utilized for the analysis of trace metals in a variety of samples. The measurement is usually performed in the traditional analytical air-acetylene flame. This flame is well suited to LEI, serving not only as the source of sample atomization, but also as the source of collisional ionization of the excited analyte atoms produced by resonant laser excitation. However, the flame does have weaknesses which limit the usefulness of LEI. Many elements are not efficiently atomized, and a variety of chemical interferences, well known in conventional flame spectroscopy, occur in LEI as well. Interfering molecular spectra from flame molecules are also observed. Many analytical methodologies have largely abandoned the flame for higher temperature electrical plasmas, notably the atmospheric pressure argon inductively coupled plasma (ICP). The inert argon atmosphere and higher temperature of the ICP ensure a more complete atomization of most elements and a relative freedom from chemical interference. Such advantages would also benefit LEI measurements, if LEI could be performed in an ICP, but very high electron densities and radio-frequency (rf) interference from the plasma power source make sensitive detection of LEI in a conventional ICP impossible.
Time-Resolved Laser Calorimetry of Photoinitiated Processes
Authors: Harris J. M. , Poston P. E. , Stone P. , Zhu X. R.
Published: February 2023

Photothermal spectroscopy with pulsed laser sources is developing into
a powerful method for determining nonradiative, excited state quantum
yields and decay kinetics of molecules in solution. The measurement is
an example of photocalorimetry where the heat given off by the decay
of excited states and/or photoproducts is observed as an increase in
the sample temperature. Photoacoustic spectroscopy with a pulsed laser
and a high bandwidth piezo electric transducer allows the
time-dependence of the heat release from excited states to be measured
directly with submicrosecond time resolution. The instrument signature
on the heat signal for this method, however, is not ideal for
determining the photoreaction kinetics of the sample due to acoustic
resonances and lack of any low-frequency response.
Time Resolved Spectra of Lightning Simulation in Titan's Atmosphere
Authors: Lakkaraju H.S. , Jebens D.S. , Borucki W.J. , Mckay C.P.
Published: February 2023

We report, for the first time, time resolved spectroscopic measurements pertaining to the chemical evolution in a gas mixture reflecting the composition of Titan's atmosphere, under simulated lightning via Laser Induced Plasma (LIP)1.
High Sensitive Laser Spectroscopy For Detect Trace Rare Earth Impurities In YbF3 and CaF 2 : Y b 3 + Crystals
Authors: He-yi Zhang , Xuehua He , Hai Tang Sing
Published: February 2023

The upconversion fluorescence is an interest subject for many applications. But very few papers study the high sensitivity upconversion fluorescence and its application to analytical chemistry. The laser excited high sensitive upconversion fluorescence of YbF3 contain with trace

T
m

3
+

 and E

r

3
+

reported here for first time to our knowledge. Also high sensitive upconversion fluorescence of

CaF

2

:

Y
b

3
+

contain with trace

T
m

3
+

 and E

r

3
+

as impurities were studied.
Laser-Induced Sorption at Silicon Surface in Liquid
Authors: Beklemyshev V.I. , Petrov Yu.N. , Prokhorov A.M. , Pustovoy V.I.
Published: February 2023

The laser radiation action upon the surface of a solid gives rise to
different changes of both the system itself and the reactions running
with the surface participation. Among the most studied processes are
laser-induced catalytic reactions, alloying, etching, etc. To a less
extent is studied the influence of laser radiation upon the surface of
a semiconductor immersed into water.
Silicon Photopotential Relaxation In Different-Composition Electrolytes
Authors: Maslov A.P. , Petrov Yu. N. , Pustovoy V.I. , Prokhorov A.M.
Published: February 2023

Diagnostics of microimpurities, adsorbed ions, and particles at the
semiconductor surface can be based on the influence of these particles
upon the structure of the semiconductor surface levels and upon
relaxation processes through the levels. The most important dependence
of the surface recombination rate upon the surface state may be
determined by the time of the semiconductor photopotential relaxation
in different-composition electrolytes. This nondestructive technique
enables to control the surface state and observe the sorption dynamics
at the surface and, in particular, photosorption of metal ions and
complex compounds.
Laser-Based Imaging Diagnostics For Combustion
Authors: Hanson R. K. , Paul P. H. , Seitzman J. M. , Lee M. P. , McMillin B. K.
Published: February 2023

Laser-based combustion diagnostics which yield multi-dimensional data
sets (e.g., 2-D, 3-D or 2-D plus time) are currently under
.investigation in several laboratories. Work thus far has emphasized
Planar Laser-Induced Fluorescence (PLIF), owing particularly to its
signal strength and species sensitivity, but alternative sensing
strategies based on Rayleigh, Raman and degenerative four-wave mixing
(DFWM) concepts are also of interest. In all cases, significant
progress is being made owing to advances in laser systems, solid-state
camera technology and improved understanding of laser-gas
interactions, especially at high spectral intensities.
H Atom Concentration Measurement by Two-Photon LIF Near a Heated Filament in a Hydrogen Environment
Authors: Meier U. , Kohse-Höinghaus K. , Schäfer L. , Klages C.-P.
Published: February 2023

For the investigation of filament-assisted CVD diamond coating processes, the knowledge of the role of atomic hydrogen seems of crucial importance. It is therefore desirable to determine absolute hydrogen atom concentrations and the influence of parameters like temperature, pressure, flow conditions etc. on the hydrogen atom distribution under typical conditions for this process.
Lidar Measurements Of Stratospheric Ozone: Comparison With Balloon-Borne Electrochemical Cell (ECC) Measurements
Authors: Butler J. , Whiteman D. , Burris J. , Torres A. , Ferrare R. , McGee T. J. , Komhyr W. , Barnes R.
Published: February 2023

The NASA/Goddard Space Flight Center Stratospheric Ozone Lidar Trailer Experiment (STROZ LITE) participated in the stratospheric ozone measurement intercomparison campaigns in October-November 1988 and July-August 1989 at Table Mountain Observatory near Wrightwood, CA. As part of these campaigns ozone profiles between 20 and 35 obtained by the lidar were compared to profiles measured by Wallops Flight Facility electrochemical cell (ECC) sondes in Fall 1988 and Wallops and NOAA ECC sondes in Summer 1989.
Ultrasensitive Analysis Of Trace Atmospheric Species Using Diode Lasers: A Comparison Of High Frequency Modulation Techniques.
Authors: Bomse David S. , Silver Joel A. , Stanton Alan C.
Published: February 2023

Numerous frequency modulation techniques are now available to overcome the large excess noise inherent to diode laser operation at low frequencies. In some cases, shot noise limited laser performance has been obtained with measured absorbances as low as 10-7. Combination of these novel methods with the long (10-100 m) optical paths provided by multipass cells makes feasible sub-part-per-billion detectivities for many gaseous compounds.
Molecular rotation in organized media: surface monolayers, liquid crystals and micelles
Authors: Wirth Mary J. , Shiow-Hwa  , Burbage John
Published: February 2023

Molecular rotation in ordinary liquids is generally understood, albeit imperfectly. However, molecular rotation in more complicated and intriguing media, such as surface monolayers, liquid crystals and organized surfactants, is less understood. These media are structured, thus affecting the way a solute rotates. To study molecular rotation, the correlation of the orientations of 2 transition dipoles of a solute is measured as a function of time. The results are interpreted using the spherical harmonics to describe the decay of the correlation function. The keys to describing rotation in complicated media are 1) highly quantitative and sensitive measurements of the rotational correlation function and 2) development of mathematical models to describe hindered rotation. In this paper, the rotational behavior of solute probes in bonded chromatographic phases, micelles and liquid crystals is described and contrasted with rotational behavior in ordinary liquids.
Fluorescence Imaging of Large Molecules in the Gas Phase Generated by Laser Desorption
Authors: Yeung Edward S. , Kimbrell Sandra M. , Heise Theodore
Published: February 2023

Lasers have been used since 1962 to vaporize small amounts of solid inorganic material. More recently their use to vaporize (desorb) large thermally labile organic molecules has grown. The larger and more polar the molecule, the more difficult it is to volatilize it by traditional means without thermal degradation. Very promising is matrix assisted laser desorption, which can produce large gas-phase molecules without fragmentation. Analytical measurements can then be performed on large molecules in the gas phase.
Secondary Laser Emission from Underwater Plasma Induced by Laser Breakdown of Ultrafine Particle
Authors: Kitamori Takehiko , Nakamura Masato , Sawada Tsuguo
Published: February 2023

Laser breakdown spectroscopy for analyzing ultrafine particulates in liquids has been proposed.1) The laser breakdown of an ultrafine particle is induced by irradiation of a focused pulsed laser. Acoustic emission from plasma was applied for particle counting and plasma emission was used for elemental analysis.
Surface-enhanced resonance Raman scattering studies of photosynthetic systems
Authors: Cotton Therese M. , Chumanov George D. , Kim Jae-Ho , Gaul Dale
Published: February 2023

Surface-enhanced resonance Raman scattering (SERRS) spectroscopy is a powerful new technique for the study of membrane preparations containing chromophoric molecules. Photosynthetic reaction center and light harvesting complexes have been examined. The spatial location and redox state of the various components (chlorophylls, pheophytins, and cytochromes) can be ascertained from the spectra.
Laser Interferometric Measurement of Small Refractive Index Change in Fluids Within a Sub-Microliter Volume Capillary Tube
Authors: Bornhop Darryl J. , Neill Paul , Tarigan Hendra J.
Published: February 2023

Reflected (back scattered) laser light from a fluid filled Capillary Tube has been used to determine small refractive index changes in the fluid. The direction and magnitude of shift in the fringe pattern produced in the back scattered light is a function of the change in refractive index. The effect of temperature perturbation and orientation of the incident beam polarization on the sensitivity of the relative index measurement is also investigated. A linearly Polarized He-Ne Laser (P=1mW, Wavelenglh=632.8 run) is used as a beam source, an uncoated Fused Silica Capillary Tube (I.D.-530 um) is used as a Flow Cell (Cell Probed Volume=4.4x10-7 L), and a series of low concentration glycerol-water solutions are used as sample solutions. Detection limit of the detector is 9X10-7 change in refractive index.
Computer-Replicated Spectrograms By Ensemble Averaging and Normalization
Authors: Edwards Matthew E.
Published: February 2023

High resolution absorption bands, as produced by a tunable diode laser, are superimposed on a background that reflects both the variation of the laser-output power with frequency and the specificity of the spectrometer used to filter out unwanted cavity modes. Gross distortions of the absorption bands from these combined effects make the extraction of characteristic line data extremely tedious or error prone. To address these features, I measured high resolution infrared spectra in the 8.7 microns region using a tunable diode lasers spectrometer where the latter is interfaced -using the Labwindows' MC-MIO-16 interface board - to the IBM Model 70 PS/2 computer. The replicated computer enhanced spectrograms are free of random fluctuation noises that typifies analog chart recorder outputs. The production of the computer-replicated spectrograms occurs from a software program called the "horter.” I have addressed the problem of normalization of the spectrograms, using a second computer program. The overall outcome is a computer- replicated spectrogram having reduced spectra band distortions. These two improvements have implications for increasing the measurable of the line parameters, halfwidths, pressure broadening coefficients, and the line intensities. Measurements have been made for such gases as N2O, and SO2.
Photoacoustic, Photothermal Beam Deflection and Flash Photolytic- High Pressure Rate Studies Done with a Pulsed Nd:YAG Laser
Authors: Isak Stefan J. , Reddy K.B. , Hoffman Rüdiger , Konya Gabor , van Eldik Rudi , Eyring Edward M.
Published: February 2023

A combination of photoacoustic (PA), photothermal beam deflection (PBD) and fluorimetric spectroscopic measurements has been used to determine fluorescence quantum yields for cresyl violet perchlorate in methanolic and aqueous solutions. A concentration dependence of the fluorescence quantum yield is found to be significant. The same Quanta Ray DCR-2 Nd:YAG laser used in the PA and PBD experiments has been the flash photolysis light source at λ = 355 nm for a rate study of ring closure reactions of Mo(CO)5L complexes where L is one of several substituted 2,2'-bipyridine chelating ligands. The laser pulse creates the Mo(CO)5L species from Mo(CO)6/L dissolved in toluene. The sample liquid is in a compressible quartz pill-box cell housed in a steel autoclave that can be pressurized to 200 MPa. Values of the activation parameters ΔS# and ΔV# for the rate determining ring closure reaction are small and negative for two of the 2,2'-bipyridine ligands supporting the concept of an associative interchange mechanism for CO extrusion. For another, bulkier 2,2'-bipyridine type ligand ΔV# is small and positive suggesting a dissociative interchange mechanism. These results demonstrate a changeover in reaction mechanism with changes in steric hindrance.
Relaxation and Quenching of Excited States of Br2 in CC14 Studied by Photothermal Gratings Combined with Near-IR Fluorescence
Authors: Zhu X. R. , Harris J. M.
Published: February 2023

Relaxation and quenching of excited states of Br2 in CC14 is studied by time-resolved photothermal grating combined with near-IR fluorescence. A slow rise in diffraction transient signals from photothermal gratings, due to nonradiative relaxation of excited states, is observed for Br2 in CC14. Near-IR fluorescence measurement reveals that there are two decay components; the fast component has a lifetime about 6 ns, and the slower component has a lifetime around 20 ns, depending on Br2 concentration and oxygen content in the sample. The slower component is assigned to the decay of A' state. From the amplitudes of thermal grating, the quantum yield of the A' state formation is estimated to be 0.33+0.03. Stern-Volmer plot of the measured decay rate of A' state, including results obtained from both near-IR fluorescence and photothermal grating measurement, suggests that quenching of A' state proceeds initially at diffusion-limited rate at low concentration and reduces to nondiffusion-limited at higher concentration. Possible mechanisms for the observed decrease of quenching rate as concentration increases are also discussed.
Laser Based Refractive Index Detection in Capillary Tubes
Authors: Bruno Alfredo E.
Published: February 2023

Paper Not Available at time of printing
Multiphoton Ionization Spectra of SiH3 and SiCl3 Radicals
Authors: Hudgens J. W. , Johnson R. D. , Irikura K. K.
Published: February 2023

We will present electronic spectra of the SiH3 and SiCl3 transient free radicals which were observed using resonance enhanced multiphoton ionization (REMPI) spectroscopy. These free radicals are believed to play important roles during the chemical vapor deposition of silicon films from the feed gases SiH4 and SiHCl3. Prior to these studies, no electronic states of these radicals were known. The spectra reported here may form the bases of new optical detection methods for these species.
Four Wave Difference Mixing in Sodium Using CH4/Air Flame
Authors: Singh J.P. , Yueh F.Y.
Published: February 2023

Four-wave mixing (FWM) in Sodium (Na) vapor has drawn considerable attention in the past two decades.1 Most of the work on non-linear mixing processes was performed to generate the tunable laser in the infrared (IR) or ultraviolet (UV) region of the spectrum. Recently, the Four and higher order non-linear mixing processes have been observed using a Na seeded flame.2
Optical Spectroscopy Of Single Impurity Molecules In Solids
Authors: Moerner W. E. , Ambrose W. P. , Basché Th.
Published: February 2023

Recent advances in high-efficiency fluorescence excitation spectroscopy of pentacene in p-terphenyl crystals [1-3] have improved the signal to noise ratio for the detection of single molecular defects, thus confirming earlier single molecule detection in solids using absorption techniques[4]. Using 1-10 μm thick samples, tightly focused laser beams, and high collection efficiency, background emission noise is significantly reduced below the fluorescence emission rate of single molecular impurities at low (liquid helium) temperatures. To observe single molecules, the laser is tuned out into the wings of the inhomogeneously broadened 0-0 electronic transition until the number of defects per homogeneous linewidth is less than 1. This new regime of single molecule spectroscopy, in addition to representing optical detection at the ultimate 1/NA = 1.6 × 10−24 mole level, has also opened the door to the observation of a variety of new physical effects. With the improved detection sensitivity, we have observed two classes of pentacene defects present in both the red and blue wings of the inhomogeneous line in p-terphenyl crystals: class I defects are of stable, time-independent impurities with lifetime-limited Lorentzian homogeneous linewidths below 4 K, and class II defects, surprisingly, have time varying resonance frequencies. In recent work on perylene single molecular defects in the polymer poly(ethylene), controllable persistent spectral hole-burning of a single molecule has been observed in addition to spectral diffusion.
Laser Photodissociation Probe for Ion Tomography Studies in a Quadrupole Ion Trap Mass Spectrometer
Authors: Hemberger P. H. , Nogar N. S. , Williams J.
Published: February 2023

Operation of a quadrupole ion trap mass spectrometer depends intimately on the details of ion trajectories in the trapping field 1,2. Stable ion trajectories provide storage of ions for reactive3 and spectroscopic studies4-6 while unstable trajectories allow selective ejection of ions for mass analysis7. Clearly, the details of ion trajectories, including spatial and velocity distributions, and the effects of drive frequency, phase and amplitude, and gas pressure, are crucial to the performance of an ion trap mass spectrometer.
Laser-Based Spectroscopic Detection of Photolytic Rare Gas Complexes
Authors: Lemire G.W. , McQuaid M.J. , Sausa R.C.
Published: February 2023

In recent years there has been a renewed interest in laser-based spectroscopic studies of jet-cooled complexes.1,2 However, much of this work centered on rare-gas (RG) closed shell complexes. We have constructed an apparatus that will allow us to study supersonically cooled photolysis products including rare-gas open shelled complexes. The apparatus consists of a reflectron time-of-flight mass spectrometer with access to LIF diagnostics. As a test case, we have investigated jet-cooled NO-rare gas generated from the supersonic expansion of a NO/Ar mixture and the 193 nm photolysis of NO2/Ar in an extender channel off a pulsed nozzle. The complexes were detected by laser induced fluorescence (LIF) and by (1 + 1) resonance-multiphoton ionization (REMPI) via the A2E+ ← X2Π1/2,3/2 transition near 226 nm.
"Refractive Index Equalizer for HPLC"
Authors: Maystre Francois , Bruno Alfredo E.
Published: February 2023

Detection in High Performance Liquid Chromatography (HPLC) is most often done by optical methods1. The most popular detection modes, in order of importance are, absorption, fluorescence, refractive index (RID) or optical activity (OAD). It is known2 that the measured changes in those physical properties are always associated with changes in refractive index (Δn) in the mobile phase. This coupling of refractive index (RI) usually shows up in the response of detectors as non-linearity2, increased noise level or, even spurious response, which all have detrimental effects on the quantitative evaluation of chromatograms.
Study of the High Temperature Multiplex HCℓ CARS Spectrum
Authors: Kao W. , Singh J.P. , Yueh F.Y. , Cook R.L.
Published: February 2023

Coherent Anti-Stokes Raman Spectroscopy (CARS) is a laser based advanced combustion diagnostic technique and is being used to measure the temperature and major species concentration in a turbulent, harsh, high luminescence and reactive combustion environment.1 Recently, it has also been applied to a Coal Fired Flow Facility (CFFF), which is a unique practical combustion environment.2 Only a few CARS applications to chemical reaction have been reported. One of the important chemical reactions is a chlorination reaction. CH4 + Cℓ2 → CH3Cℓ + HCℓ. This is being used to manufacture the halogenated hydrocarbon. HCℓ is one of the product species in the reaction. So, there is a possibility to apply the multiplex HCℓ CARS spectrum for temperature measurements in a chemical reactor. This type of measurement should provide the information about mixing of CH4 and Cℓ2 and also the completion of the reaction.
Computation of Synthetic Diatomic Spectra
Authors: Hornkohl J. O. , Parigger C. , Lewis J. W. L.
Published: February 2023

Comparisons of measured spectra to synthetic spectra have become commonplace in both pure and applied spectroscopy. For example, the comparison might be made as part of the evaluation of the accuracy of the molecular parameters, or the comparison might be made for determination of the temperature or population density of the spectroscopically active molecule. Numerous computer programs have been written for the computation of synthetic diatomic spectra. Many of these apply only to a specific type of transition. Some apply only to specific bands of a certain molecule. One starting on a new molecule faces the task of writing a new computer program for computation of the synthetic spectra. The following describes a series of computer programs that can be applied to any diatomic molecule.
Zeeman Laser Interferometry for Detection and Chemical Analysis
Authors: Johnston Roger G.
Published: February 2023

Zeeman Laser Interferometry Zeeman laser interferometry [1-3] relies on use of a two-frequency, Zeeman effect laser. This helium-neon laser uses a carefully controlled magnetic field to cause a Zeeman energy level splitting inside the laser plasma tube. As a result, the laser emits two collinear laser lines with orthogonal linear polarizations. The two laser lines have a wavelength near λ = 632.8 nm, and differ by only 250 kHz in frequency.