bluuebunny/crossref_metadata_2025 huggingface dataset:
Wavelength Modulation Spectroscopy of Oxygen A Band Transitions for Non-Intrusive Concentration Measurements
Authors: Jackson A. D. , Dharamsi A. N. , Chaturvedi S. K.
Published: February 2023

The technique of Frequency Modulation (FM) and Wavelength Modulation Spectroscopy has been used [1] very successfully recently to perform several different types of measurements, with the applications of this technique growing as advances in semiconductor technology result in the availability of reliable, tunable single-mode semiconductor diode lasers in parts of the electromagnetic spectrum which were previously inaccessible this way.
Suppression of scattering resonances in inhomogeneous microdroplets
Authors: Ngo Dat , Pinnick R.G.
Published: February 2023

Resonance structure in elastic scattering from microdroplets was first observed more than 15 years ago by Ashkin and Dziedzic1, who measured the time evolution of scattering from slowly evaporating optically levitated silicon oil droplets. On the heels of this discovery, Chylek et al2 identified the observed peaks in Ashkin’s data with predicted resonances in the Mie partial wave scattering amplitudes. Resonances were characterized as either transverse electric (TE1n) or transverse magnetic (TM1n) , having a mode number n and mode order 1 corresponding to the 1th resonance in the nth partial wave scattering amplitude. Since these early advances, the importance of these resonances (commonly called morphology dependent resonances or MDR’s) has been recognized not only in elastic scattering, but also in inelastic scattering processes3.
A New Field Tunable Diode Laser Absorption Spectrometer For Highly Sensitive Measurements of Atmospheric Gases
Authors: Fried Alan , Sewell Scott , Henry Bruce , Drummond James R.
Published: February 2023

The technique of tunable diode laser absorption spectroscopy (TDLAS) has been employed in a number of field investigations for studying the chemistry of both the lower atmosphere (the troposphere) as well as the middle atmosphere (the stratosphere) over the past several years.1 This technique offers many advantages in such studies including: high sensitivity, high selectivity, high precision, fast response, and versatility. The present paper describes a new field TDLAS system, which has been developed at the National Center for Atmospheric Research (NCAR), for furthering our understanding of tropospheric chemistry using this spectroscopic technique. Several novel features have been incorporated in the present system such as a new commercially-available astigmatic Herriott cell and digital signal processing electronics to further improve system performance and versatility. These aspects will be discussed in the present paper along with recent measurements of formaldehyde employing this system at a remote sampling site in Colorado.
Wavelength Modulation Atomic Absorption Spectrometry With Semiconductor Diode Lasers
Authors: Niemax K. , Schnürer-Patschan C. , Zybin A. , Groll H. , Kuritsyn Y.
Published: February 2023

Commercial semiconductor laser diodes of the AlGaAs and AlGaInP types are small, long-lived devices with excellent spectroscopic properties [1]. They are easy to operate and have low power consumption. These are the requirements for the arrangement of many independently operating laser diodes in compact instruments for simultaneous multielement analysis [2]. The main drawback of atomic diode laser spectroscopy is the limited wavelength range of commercially available laser diodes (625-950 nm). It will be extended to shorter wavelengths in the short and medium run. However, if low radiation powers can be used in experiment, it can be overcome by second harmonic generation (SHG) in non-linear crystals. Depending on the fundamental power of the laser diodes and on the efficiency of the crystal used, extracavity SHG-powers in the nW and μW can be generated easily in the range 315-500 nm. Such powers are sufficiently high for laser atomic absorption spectroscopy (LA AS). A list including more than 50 elements which can be measured by LA AS with fundamental and SHG radiation is given in a recent review paper [3].
Raman Lidar Profiling of Atmospheric Water Vapor
Authors: Goldsmith J. E. M. , Bisson Scott E.
Published: February 2023

Detailed measurements of the distribution of water vapor in the atmosphere are needed for a variety of scientific inquiries, including global climate change and related issues in radiative processes (water vapor is the major greenhouse gas in the atmosphere), and studies of a variety of atmospheric processes such as cloud formation and atmospheric circulation. The Raman lidar is a leading candidate for an instrument capable of the detailed, time- and space-resolved measurements required by these and other studies.
Fluorescence Lifetime Measurements in a Flow Cytometer by Amplitude Demodulation Using Digital Data Acquisition Technique
Authors: Deka C. , Stemkamp J.A. , Sklar Larry A.
Published: February 2023

In this paper we demonstrate, for the first time, fluorescence lifetime measurements by amplitude demodulation from fluorescence signals with time dependent amplitudes in a flow cytometer using digital data acquisition techniques. The lifetime measurements in the flow cytometer have been compared to standard fluorescent lifetime measurements in bulk suspensions. The present technique provides a method for analyzing chemical and biological species based upon their individual excited state lifetime. We also discuss the factors influencing the accuracy of the measurements by this method and the possible solutions to those problems.
Multiplex Degenerate Four Wave Mixing Thermometry of the C2 Radical
Authors: Lloyd G.M. , Kaminski C.F. , Hughes I.G. , Ewart P.
Published: February 2023

In recent years an increasing use has been made of laser based techniques for non-intrusive temperature measurements and analysis of combustion and other hostile environments. Degenerate four-wave mixing (DFWM) is a single photon resonant process producing a collimated signal which enables spatial discrimination of background and scattered light. Scanning DFWM has been used for detection of several radical species including OH [1] and C2[2] and for thermometry [3]. Of particular use for diagnostics, however, are single-shot temperature measurements, especially for studying rapidly varying environments. The feasibility of single-shot multiplex DFWM thermometry of the hydroxyl radical has been demonstrated[4,5].
Degenerate Four-Wave Mixing Spectroscopy using Picosecond Lasers: Theoretical Analysis
Authors: Reichardt Thomas A. , Lucht Robert P.
Published: February 2023

Degenerate four-wave mixing (DFWM) has emerged in recent years as a potentially powerful technique for quantitative measurement of minor species in gas-phase media.1,2 However, a complicated collision-rate dependence of the DFWM signal is observed when lasers with pulse lengths of several nanoseconds are used.3,5 On the other hand, picosecond lasers possess pulse widths shorter than the typical collisional time in atmospheric gas-phase media, and use of such lasers for DFWM measurements6 could reduce the sensitivity of the technique to the collision rate.2,7 While pulsed lasers are usually utilized to perform gas-phase DFWM measurements, DFWM analytical models are generally limited to the assumption of continuous wave (cw) laser inputs. These cw models have been applied successfully to modeling gas-phase DFWM with nanosecond-pulse lasers, where the pulse length (~10 nsec) is much longer than the typical collisional time (~100 psec) in atmospheric-pressure flames. In this paper, we use direct numerical integration (DNI) of the density matrix to investigate theoretically the use of lasers with pulse lengths (τ
L
) much shorter than characteristic collision times (τ
C
) for quantitative DFWM spectroscopy in gas-phase media. Both purely homogeneously broadened resonances and resonances that are both collision- and Doppler-broadened are considered.
Laser-Induced Gratings in the Red System of Molecular Oxygen
Authors: Hubschmid W. , Bombach R. , Hemmerling B.
Published: February 2023

Energy transfer processes involving singlet states of O2 are of great and continuous interest in atmospheric and biological research. Due to the low excitation energies the states 1Δg, and

1

Σ
g
+

are studied most extensively. The forbidden nature of optical transitions to the ground state makes the singlet molecules metastable. Thus, quite slow nonradiative processes can be studied. The singlet states of oxygen offer therefore a good possibility to analyse different contributions to laser-induced gratings. On the other hand, the analysis of the temporal evolution of the laser-induced gratings may prove to be a powerful method to study energy transfer processes.
Extinction, Absorption, and Backscatter Cross Sections for Homogenous and Coated Fibrous Aerosols at Millimeter Wavelengths
Authors: Gurton K.P. , Bruce C.W. , Jelinek A.V.
Published: February 2023

Analytic techniques describing the electromagnet behavior, even of
simple straight fibers of finite conductivity, have been developed
only recently. The electromagnetic modeling of fiber-like particles
formed (for example) in the process of burning hydrocarbons, i.e.
soot, is very difficult. Although several analytic and numeric
techniques are available, good experimental analogs have been lacking
and the few that do exist are restricted to scattering only.
Diagnostics of Boundary Layer Chemistry in an Atmospheric Pressure Plasma
Authors: Owano Thomas G. , Wahl Edward H. , Kruger Charles H. , Zare Richard N.
Published: February 2023

It can be quite difficult to probe the harsh and potentially nonequilibrium environment of atmospheric pressure Plasma-Assisted Chemical Vapor Deposition (PACVD) reactors [1]. Sensitive measurement of temperature and trace radical concentrations within the reacting substrate boundary layer is a challenging problem in atmospheric pressure reactors due to the highly luminous environment, small spatial scales, and steep thermal and concentration gradients. It is in this environment where the application of sensitive, nonlinear, laser based diagnostic techniques can complement the abilities of more conventional diagnostic techniques such as optical emission spectroscopy (OES) and laser-induced fluorescence (LIF), and allow the detailed measurement of temperature and trace radical concentrations to be made, and compared to models of the deposition environment. The application of a powerful nonlinear laser spectroscopy, degenerate four wave mixing (DFWM), as a gas-phase optical diagnostic has opened the door for significant advancement in the area of atmospheric pressure plasma chemistry, since it can provide high sensitivity and spatial resolution with a coherent, phase conjugate signal which can be readily discriminated against the plasma luminosity [2],
Laser Ignition of Gaseous Ammonia-Oxygen Mixtures
Authors: Plemmons David H. , Parigger C. , Lewis J. W. L.
Published: February 2023

Laser ignition of combustible gas mixtures has been studied by numerous investigators.1–10 We are interested in laser sparks resulting from nonresonant laser-induced breakdown generated by focusing Nd:YAG 1.064 μm, 4.5 ns full width at half maximum (FWHM) pulses into combustible ammonia-oxygen gaseous mixtures. The temporal and spatial evolution of the optical breakdown plasma into an ignition kernel, and subsequently into a propagating flame, is monitored using planar laser-induced fluorescence (PLIF) and shadowgraph imaging.
Nitric Oxide Optical Breakdown Spectra and Analysis by the Use of the Program NEQAIR
Authors: Parigger Christian , Lewis J. W. L. , Plemmons D. H. , Hornkohl J. O.
Published: February 2023

Optical breakdown air plasmas are generated by focused Nd:YAG ir laser radiation of 1012 to 1014 W/cm2 intensity, and rich emission spectra result. Time-resolved spectroscopy techniques are applied to characterize the decaying laser-induced plasma. Recombination spectra that are dominated by nitric oxide are measured and analyzed with the objective of obtaining temperature and species density information.
Light Scattering from a Pair of Osculating Spheres
Authors: Ngo Dat , Videen Gorden , Hart Matthew B. , Dalling Robert H.
Published: February 2023

Scattering and absorption of electromagnetic radiation by systems composed of individual spheres in close proximity1-5 or from subsystems completely enclosed by and arbitrarily located within a larger spherical system6,7 has been the subject of a great deal of research. In this paper we examine a system composed of two spheres which overlap as shown in Figure 1. The first sphere of radius a1 and refractive index m1 is centered on the x1,y1,z1 coordinate system; the second sphere of radius a2 and refractive index m2 is centered on the x2,y2,z2 coordinate system at a position x1 = 0, y1 = 0, z1 = d. The incident radiation is a plane wave traveling in the x-z plane, oriented at angle α with respect to the z axis.
Doubly Tunable Femtosecond Pulses Generated in the Visible using Optical Parametric Amplifiers for Time-resolved Spectroscopy
Authors: Matousek P. , Parker A.W. , Taday P.F. , Toner W.T. , Towrie M.
Published: February 2023

Many time-resolved spectroscopy techniques require two broadly and independently tunable, synchronised light pulses. This requirement can be met by optical parametric oscillators (OPOs) [1] and travelling wave optical parametric amplifiers (OPAs) [2, 3, 4, 5]. The latter capable of providing higher pulse energies. Our aim was to develop a multikilohertz repetition rate OPA system capable of providing femtosecond/picosecond, synchronised and independently tunable pump and probe pulses in the visible part of the spectrum for time-resolved absorption and resonance Raman spectroscopies.
Confinement, Detection, and Manipulation of Individual Molecules in Attoliter Volumes
Authors: Kung C-Y. , Barnes M. D. , Lermer N. , Whitten W. B. , Ramsey J. M.
Published: February 2023

We report observation of fluorescence from individual rhodamine 6G molecules in streams of charged 1-μm diameter water droplets. With this approach, probe volumes comparable to diffraction-limited fluorescence microscopy1 techniques (≤ 500 attoliters) are achieved, resulting in similarly high contrast between single molecule fluorescence signals and nonfluorescent background. However, since the fluorescent molecules are confined to electrically charged droplets, in situ electrodynamic manipulation can be accomplished in a straightforward manner, allowing experimental control over both the delivery of molecules of interest to the observation region and the laser-molecule interaction time.
Progress towards a Chip Based Detector for Explosives
Authors: Bailey Christopher G. , Arnold Don W. , Rakestraw David J.
Published: February 2023

The need for rapid, accurate detection of chemical species in the
environment has prompted much interest in the development of chemical
detectors. A number of considerations must be taken into account in
the design of a successful sensor such as low false alarm rates, low
levels of detection, ease of use and reliability. Moreover, the ideal
device would be compact and have low power requirements. Recent
progress in chip based chemical analysis offers great promise toward
the development of such a detector.1 Chip based devices offer a number
of advantages such as speed, reproducibility, and the need for low
sample volume. An example of a class of compounds that demands rapid
and accurate detection are the nitroaromatic and nitramine explosives.
Prompt, reliable detection of explosives amidst a complex background
is important in a number applications such as mine detection,
anti-terrorism measures, environmental remediation, forensics, and
health and safety concerns. Here we present results on the separation
of explosive compounds using microcapillary electrokinetic
chromatography and their detection using indirect laser-induced
fluorescence. These techniques are readily amenable toward
miniaturization and integration into a single chip based device.
Diode-Laser-Difference Frequency Spectrometer for Carbon Monoxide Detection
Authors: Blanke Torsten , Willer Ulrike , Kracht Dietmar , Schade Wolfgang
Published: February 2023

The application of laser absorption spectroscopy for remote sensing of environmental pollutants in the mid-infrared spectral range (MIR) is of fundamental interest, because most of the relevant molecules have strong vibrational transitions in this spectral region that can be used as “fingerprint” for a sensitive detection in complex environments, as air, water or soil. However, there is still a lack in simple, compact, portable and rugged MIR laser sources. In this context, diode-lasers and difference frequency generation recently have drawn considerable interest [1-3]. New and efficient nonlinear crystals, as e.g. AgGaS2 or GaAsSe, and recent progress in the fabrication of fiber optics for the MIR make it possible to set up compact MIR laser spectrometers with the option of evanescent field spectroscopy. The latter one is of essential advantage when a detection of pollutants in optical thick media, e.g. soil, is required.
Remote Radiation Sensing Using a Fiber-Coupled, Optically Stimulated Luminescence Dosimeter
Authors: Huston Alan L. , Justus Brian L.
Published: February 2023

Fiberoptic-based, radiation measurement methods provide a convenient approach for remotely monitoring hazardous or difficult-to-access areas such as nuclear waste sites or sampling wells for in situ ground water monitoring. Fiberoptic systems are attractive for these applications because of their small size, mechanical flexibility and optical, as opposed to electrical, signal transmission. In this paper, we describe a new, optically stimulated luminescent (OSL) glass dosimeter that can be attached directly to commercial optical fibers for remote radiation sensing applications. The OSL glass is optically transparent and can be manufactured to any desired length to provide the necessary sensitivity required for a specific application.
Influence Of The Non-Linear Characteristic Of The Laser Source On Detected Signals In Derivative Spectroscopy For Gas Analysis
Authors: Morante M. A. , Stewart G. , Culshaw B. , López-Higuera J. M.
Published: February 2023

Derivative spectroscopy, or wavelength modulation spectroscopy (WMS), consists in obtaining the concentration of a molecular absorbent by modulating the output wavelength of the optical source and detecting at one of the harmonics of the modulation frequency. The first and second harmonic signals are proportional to the first and second derivatives of the absorption feature, respectively, for small WM amplitude. The maximum gradient of the first and the absolute maximum of the second harmonic signal, which are located at the absorption line center, are directly proportional to the species concentration. [1-3]. In practice, the output power/current characteristic of the laser has a slight degree of nonlinearity which influences the form of the recovered signal. As a result, the detected derivative trace displays a non-constant baseline that degrades the absorption signal. Furthermore, such baseline does not remain unchanged over the operating period of the source, because it is influenced by environmental factors and aging. In this work we analyze the effect of the mentioned nonlinear laser characteristic on the detected harmonic signal, and we propose a simple post-detection processing method to capture the baseline from the demodulated signal in real time.
High Resolution Hole Burning Spectroscopy of Aluminum Phthalocyanine Tetrasulfonate in MCF-10F Human Breast Epithelial Cells
Authors: Milanovich N. , Reinot T. , Small G. J. , Hayes J. M.
Published: February 2023

Biological samples when subjected to cryogenic temperatures display an
inherent disorder which gives these samples glass-like properties.
Thus the high resolution optical techniques such as fluorescence line
narrowing (FLN) [1] and hole burning
[2] which have been developed to probe into the
inhomogeneously broadened absorption spectra of impurity molecules in
glasses are increasingly being used to investigate biological samples.
FLN, for example, has been used to study DNA-carcinogen complexes at
physiological damage levels [3,4] and
protein-chromophore interactions [5]. Hole burning has
been used extensively to study electron and energy transfer processes
in photosynthetic systems [6,7]. Because the band
widths obtained by these techniques are so narrow compared with room
temperature absorption widths, Stark shifts and broadening and
pressure effects on the spectra can be accurately measured.
Laser Induced Fluorescence of Aromatic Hydrocarbons in diesel oil laminar premixed flames
Authors: Cignoli F. , Benecchi S. , De luliis S. , Zizak G.
Published: February 2023

Because of the planned limitations on pollutants it is becoming more and more stringent to reduce IC engines emissions. In particular, for diesel oil engines, the reduction of soot emission is mandatory. It is well known that aromatic compounds play an important role in the mechanisms of soot production. It is possible that the different classes of aromatics naturally present in the Diesel fuel lead to the formation of different amounts of soot. For this work a set of seven fuels with calibrated composition of different blend of mono-, di- and tri-aromatics but with total aromatic content of about 27% was made available by ELF (Solaize, France). Soot and aromatic hydrocarbons profiles have been detected on the axis of rich premixed flames in order to find possible correlations.
Single-Frequency Semiconductor Diode Lasers for Gas Sensing
Authors: Martinelli Ramon U.
Published: February 2023

Building upon the substantial laser technology of telecomminications, Sarnoff has developed single-frequency, distributed-feedback (DFB) semiconductor diode lasers with emission wavelengths of 760 to 2000 nm. These devices are ideal sources for trace-gas monitoring systems employing laser absorption spectroscopy. The devices emitting at 760 to 1000 nm are made from AlGaAs/GaAs compounds, and those emitting from about 1300 to 2000 nm are based on the InGaAsP/InP materials system.
Applications of Surface Nonlinear Optical Spectroscopy
Authors: Shen Y. R.
Published: February 2023

Second-order nonlinear optical processes are forbidden in bulks with inversion symmetry, but necessarily allowed at surfaces and interfaces. This intrinsic surface specificity has rendered second harmonic generations (SHG) and sum frequency generation (SFG) exceptionally useful as surface probes. SFG in particular has been developed into an extremely powerful surface spectroscopic tool. It is applicable to all interfaces accessible by light and therefore has provided new research opportunities in many areas of surface science.
A Laser Desorption Mass Spectrometer Microprobe for Surface Mapping of Lithium
Authors: Bickel Grant A. , Adams Harry M.
Published: February 2023

A laser desorption mass spectrometer microprobe has been utilized to
map Li distributions in CANDU® nuclear reactor
components. Lithium is present in the Heat Transport System (HTS) of
the reactor and can be used as a tracer of HTS leakage. Leakage (in
the form of both liquid D2O and steam) into component
crevices, introduces uncontrolled and unknown chemistry within the
crevices. One such area is the rolled joint, where the zirconium
pressure tube is rolled into the stainless steel end fitting hub. HTS
leakage, occurring through cracks and crevices under the rolled joint,
may lead to deuterium ingress into the Zr pressure tube and
subsequently to pressure tube embrittlement. It is hoped that the
results from the laser desorption microprobe, can be used to correlate
the HTS leakage through the cracks and crevices under the rolled joint
with the deuterium profile in the pressure tube. The laser desorption
technique was found to be very sensitive and could provide
semi-quantitative Li distributions either at low spatial resolution
(the length of the 20 cm hub section) or high spatial resolution
(revealing Li in micron sized cracks). Other traditional surface
science techniques like SAM and XPS are not sensitive to Li, and
commercial SIMS instruments cannot accommodate the large hub samples
nor allow for profiling over the hub length.
Isotope-Selective Analysis by Diode Laser Spectrometry
Authors: Wizemann H. D. , Niemax K.
Published: February 2023

Single-mode laser diodes of the etalon-type generate radiation of very narrow bandwidth, typically 0.04 nm, in the red and near-infrared wavelength range [1]. The linewidth of such diodes is considerably narrower than the line widths of free atoms in thermal atomizers, analytical flames, or plasmas. Therefore, these laser diodes are proper tools for analytical high-resolution laser spectroscopy. The necessary condition for high-resolution measurements is the atomization of the samples in low-pressure atmospheres (≤ 10 hPa), where pressure broadening of the analyte lines is small and line broadening is dominated by the Doppler effect. If the shifts of spectral lines by the isotope effect are larger than the Doppler-widths of the individual components, the isotope composition of the elements can be measured by Doppler-limited laser spectroscopy. This is often sufficient for light and heavy elements, where large isotope line shifts occur due to the classical Bohr mass shift or due to the volume or field shift, respectively. For medium heavy elements the dominating contribution to isotope shift is the relatively small specific mass shift. This means in general, that for these elements Doppler-free spectroscopic methods are required, such as saturation spectroscopy or Doppler-free two photon excitation [2].
Feasibility Study of On-line Detection of Sulphuric Acid Aerosols in the Atmosphere by Laser Photofragmentation and Plasma Spectroscopy
Authors: Nuñez M. Hidalgo , Cavalli P. , Petrucci G. A. , Omenetto N.
Published: February 2023

A major interest of our Institute lies in the study of the atmospheric sulphur cycle and in the oxidation mechanism(s) of Dimethylsulfide (DMS) in air. DMS originates from the ocean biota and its crucial role in the formation of atmospheric aerosols is well-documented (1,2). When DMS is oxidized, it generates SO2 that can be further oxidized to H2SO4, inducing the production and growth of new aerosol particles that can act as cloud condensation nuclei and affect the Earth’s albedo (2). The possibility of detecting sulphuric acid aerosols with laser excitation has been discussed, to the best of our knowledge, only in one paper (3), where the aerosols generated by mixing SO3 and H2O were addressed with laser photons at 193 nm. The resulting broadband emission was attributed to sulphuric acid and was similar to the emission spectrum of gaseous SO2.
Real Time, in Situ Measurement of Aerosol Light Absorption with a New Photoacoustic Instrument: Quantification of Black and Elemental Carbon Aerosol
Authors: Moosmüller Hans , Arnott W. Patrick , Rogers C. Fred
Published: February 2023

A photoacoustic instrument has been developed to measure in situ light absorption by aerosol. The current lower detection limit for light absorption is 0.4 Mm−1 which corresponds to an elemental carbon mass density of ≈ 40 ng/m3 assuming an efficiency for light absorption of 10 m2/g. Calibration is performed using simple theory for the instrument along with use of a calibrated microphone and laser. Two compact, efficient lasers were used during instrument evaluation performed in the North Front Range Air Quality Study (Colorado, 1996/97). Laser wavelengths were 532 run and 685 nm, and corresponding average powers were 60 mW and 87 mW. Nearby measurements of black and elemental carbon aerosol show good correlation with the photoacoustic measurement of aerosol light absorption and shed further light on the question of absorption efficiencies of black and elemental carbon aerosol.
Intracavity Laser Spectral Analysis of Trace Elements in Environmental Samples
Authors: Burakov V. S. , Misakov P. Ya. , Raikov S. N.
Published: February 2023

Laser spectroscopic techniques have significantly enhanced the performance of atomic spectrometry [1,2]. Despite the impressive detection power of laser methods, they are as a rule still far from being practically applied in routine analyses especially of complex natural samples of environmental interest. The main reason for this situation hitherto remains the comparatively higher complexity and cost of tunable lasers and their power supplies excluding low-power semiconductor laser diodes, that have excelent potential spectroscopic and operational properties for spectral analysis [3]. Of course, these laser sources of radiation at present also have some specific disadvantages, that restrains their wide practical application. On the other hand, the common tunable dye laser-based instruments can compete with established analytical techniques and have a chance to be routinely used for the direct elemental analysis espesially at trace levels or for solving some narrowly specific problems.
On Step Brightness Changes of Distant Mountain Ridges and their Perception
Authors: Lynch David K.
Published: February 2023

Minnaert (1939) remarks on the appearance of undulating moors and other sources of step brightness changes. He correctly notes that adjacent to the dark-bright step change at the top of the nearer moor, an optical illusion occurs. The nearer moor, being darker either by virtue of less intervening airtight than the more distant one or by the circumstances of the moors’ illumination, appears to have a dark band at its top bordering the more distant moor. Similarly, the more distant moor seems to have a bright band adjacent to the top of the nearer (darker) moor.
Pyramidal Ice Crystals and Odd Radius Halos
Authors: Tape Walter
Published: February 2023

The halo literature contains many reports of circular halos having radii other than the usual values of 22° and 46°.1 Such odd radius halos are supposed to form by refraction and reflection of sunlight in pyramidal ice crystals, that is, in crystals having pyramidal faces instead of, or in addition to, the usual prism and basal faces. In this talk I will review some photographic evidence for the existence of odd radius halos and pyramidal crystals, and I will use computer simulations to reexamine the classical explanation of odd radius halos. I find no doubt regarding the existence of odd radius halos and pyramidal crystals. And the basic model of refraction and reflection in pyramidal crystals seems entirely justified, but classical predictions are significantly qualified and extended by the results of the simulations.
The Sky in Science and Art
Authors: Gedzelman Stanley David
Published: February 2023

The present sharp division lines drawn between the arts and sciences represent an historical anomaly. For centuries, artists were among the premier observers of nature and, as in the case of Leonardo da Vinci, were sometimes also scientists or engineers themselves. The range of artists' observations is impressive and includes the overall climatic environment, the colors of the sky, many of the atmospheric optical phenomena, cloud forms, and even indications of changing weather situations (Gedzelman, 1989). There are numerous cases in which artists depicted atmospheric phenomena long before they were identified by scientists.
All That’s Best of Light and Dark
Authors: Bohren Craig
Published: February 2023

A talk about brightness variation in nature and their perceptual and physical origins.
The Color of Refracted Light: Prisms, Rainbows, and the 'Disappearance of Yellow'
Authors: Kidder John N.
Published: February 2023

It has long since been recognized that Isaac Newton's analysis of the refraction of light by a prism was essentially correct, if understandably incomplete.
Disputing Viking Navigation by Polarized Skylight
Authors: Roslund Curt , Beckman Claes
Published: February 2023

Viking exploits in the North Atlantic have aroused people's imagination to a height where responsible judgement of extraordinary claims often seems to be suspended. The controversy over the alleged authenticity of the Minnesota Kensington runestone is a famous case in point*. The uncritical acceptance by a large section of the scientific community of the theory that the Vikings utilized polarized skylight for navigational purposes, is another.
Mirages with Atmospheric Gravity Waves
Authors: Lehn Waldemar H. , Silvester Wayne K. , Fraser David M.
Published: February 2023

Mirages observed over an interval of time occasionally display slow variations that seem to be periodic.
Glare points in the refracted-wave scattering by icicles and other tilted dielectric cylinders and the caustic-merging transition
Authors: Mount Catherine M. , Marston Philip L.
Published: February 2023

Naturally produced icicles can be approximately symmetrical about a vertical axis. Some icicles are only weakly tapered so that approximating the icicle as a circular cylinder gives insight into ray optics of die scattering. Several features of the scattering are evident when viewing a sunlit icicle with the unaided eye. These include (i) the specular reflection and (ii) the merging and disappearance of the two-chord "rainbow rays" as the scattering angle to the observer's eye is varied. As described below, other information about the scattering process is manifested by viewing the scattering through a camera focused on the farfield scattering. The dominant direction of the incident wave vector ki is ordinarily tilted by a angle γ relative to a plane perpendicular to the symmetry axis z of the icicle. Consequently the ray evolution differs from the well known case of a circular cylinder at normal incidence. An analysis summarized here shows how the conditions for the Airy caustic evolves with γ such that the Airy caustics from opposite sides of the cylinder merge and disappear at a critical tilt angle γc. These phenomena were simulated in laboratory observations of scattering by a clear tilted PMMA polymer fiber illuminated by a laser beam as summarized below. While our observations and analysis are intended to give insight into naturally occurring processes, the problem of the ray-optics of tilted dielectric cylinders may also be of general interest [1,2]. Furthermore, the Airy caustic features of laser-illuminated fibers at normal incidence have been used in the testing of optical fibers (for communication applications) so that is reasonable to inquire how the rainbow features evolve with tilt [3]. During the course of this investigation, we became aware of a closely related investigation by Lock et al. [4,5] of the ray optics of a large glass cylinder.
Bravais and Wegener Coordinates for Halos
Authors: Tape Walter
Published: February 2023

Bravais and Wegener coordinates, to be described below, provide a natural setting for classical halo theory. They give insights into many halos and especially into symmetries among halos.
The nonoccurance of haloes in ice clouds: implications from a laboratory study
Authors: Nelson Jon
Published: February 2023

Although there have been many laboratory studies of ice crystal growth shapes, few studies of evaporation have been reported. There have not been any evaporation measurements of single, solitary ice crystals surrounded by stagnant air.
Long Range Superior Mirages
Authors: Lehn Waldemar H. , Legal Thomas L.
Published: February 2023

We have observed numerous superior mirages at great distances, ranging from 70 to 100 km. Such mirages are well known and immediately recognised, because they do not look significantly different from short range mirages; but it appears that no one has published an analysis that actually identifies the appropriate atmospheric conditions. Three models developed1 to reproduce an observation will be presented here for comparison and discussion. Only one of them seems reasonable.
The Influence of the Multiple Light Scattering on the Aureole
Authors: Kokhanovsky Alex A.
Published: February 2023

The influence of the multiple light scattering on the aureole is studied. To solve the problem, the small angle approximation of the radiative transfer theory is used.
Origins of Skin Optical Properties and the Opportunities for Optical Diagnostics in Dermatology
Authors: Jacques Steven L.
Published: February 2023

The origins of scattering and absorption in skin and their interaction with skin architecture suggest opportunities for optical diagnostics using contrast based on optical properties.
Optical Methods—Fluorescence Spectroscopy as an Aid in Diagnosis of Skin Tumors
Authors: Kollias Nik
Published: February 2023

Summary not available.
Birefringence Measurements of Biological Tissue with Low Coherence Optical Tomography and its Application to Human Skin
Authors: de Boer J.F. , Milner T.E. , van Gemert M.C. , Nelson J.S.
Published: February 2023

High-resolution two-dimensional images of optical birefringence in biological tissue as a function of depth are shown. The application to human skin is discussed.
Laser Tattoo Removal
Authors: Zelickson Brian D.
Published: February 2023

Lasers have been employed in the removal of tattoos for the past three decades. During this time period, advances in the procedure allow ″lightening″ of tattoos with minimal risk of scarring. The most important development was the concept of selective phothermolysis. This concept lead investigators to examine the effects of employing very short pulsed or q-switched lasers with different wavelengths in treating small tattoo pigment particles.
Nonablative Laser Treatment of Facial Rhytides
Authors: Lask Gary , Lee Patrick K. , Seyfzadeh Manouchehr , Nelson J. Stuart , Milner Thomas E. , Anvari Bahman , Dave Digant , Geronemus Roy G. , Bernstein Leonard , Mittelman Harry , White Connie , Coulson Walter F. , O'Connell Jerome , Hennings David , Sand Bruce , Baumgarder Jon , Menefee Richard , Berry Michael
Published: February 2023

The purpose of this study is to evaluate the safety and effectiveness of nonablative laser treatment of facial rhytides (e.g., periorbital wrinkles) using the New Star Model 130 Nd:YAG laser system. Previous ablative laser skin resurfacing (LSR) using, for example, a pulsed or scanned CO2 laser has been accompanied by complications such as persistent erythema, dyspigmentation, scarring, and infection. A nonablative laser modality may be effective in reducing both the severity of wrinkles and the incidence of morbidity presently associated with LSR.
Laser-Induced Modulated Reflectance in Semiconductor Materials Analysis
Authors: Rosencwaig Allan
Published: February 2023

During the past few years, thermal wave physics has been successfully applied to studies of semiconductor materials and microelectronic devices. Previously, we described how these materials and devices might be examined with thermal wave imaging.1 This imaging is performed in a scanning electron microscope with a thermoelastic technique for thermal wave detection. Although this technique is a very sensitive detection method for thermal waves,2 it has limited applicability for integrated circuit process control and inspection because it requires contact to a transducer and thus is potentially contaminating. Furthermore the results are often strongly dependent on difficult to control acoustic variables such as sample geometry and sample/detector coupling. To overcome these problems we have developed a noncontact thermal wave technique that can be used at the high modulation frequencies required for micron-scale resolution.3–5
Characterization of Optically Induced Periodic Structures on Semiconductor Surfaces
Authors: Podlesnik Dragan V.
Published: February 2023

Increasing applications are being found for laser and optical techniques in the fabrication of semiconductor devices and in the diagnostics of processing steps such as etching or metal deposition. For example, by using two interfering laser beams to initiate localized chemical reactions, spatially periodic structures can be produced on semiconductor surfaces. Practically, such structures are of interest because of the potential for utility in a variety of electrooptical and electronic applications.1 An important aspect of this processing is that the structure growth can be monitored in real time by observing the diffraction of the writing beams, thus allowing a precise control over the feature depth. In addition, because the structures can have a high spatial frequency, the process of their fabrication becomes a method of studying the wavelength-scale physical processes which influence the structure growth. These processes may involve, for example, the diffusion of photoexcited species or the magnification of the optical fields at the illuminated surfaces.
Laser Microprobe Mass Spectrometry and Its Relationship to Other Microanalytical Techniques
Authors: Evans Charles A.
Published: February 2023

There are a variety of techniques employed for the microanalysis of materials. The majority of these techniques employ focused ions or electron beams to probe the materials. In recent years, a technique called Laser Microprobe Mass Spectrometry has been developed to provide a unique and complementary characterization capability. This paper will deal with the basic phenomena involved, instrumentation and illustrations of the technique's utility with a variety of applications.
Optical Methods for the Study of Explosive Chemistry
Authors: Trott Wayne M. , Renlund Anita M.
Published: February 2023

An understanding of the reaction zone in a detonating high explosive (HE) requires characterization of both the mechanical response of the material and the chemical reaction mechanisms that control the rate at which the HE is consumed. Moreover, the detailed chemistry is clearly a contributing factor in the shock-initiation of energetic materials. Although a considerable body of empirical knowledge on shock sensitivity and explosive performance is presently available, practically no information exists regarding the important microscopic physical and chemical processes. Much additional insight into these processes is needed for the development of predictive capabilities in the areas of initiation and performance. In this paper, we discuss the application of several optical diagnostic methods for the study of explosive chemistry. We have emphasized techniques which provide good spatial and temporal resolution and are applicable to "single-shot" measurements on pressed, polycrystalline samples of widely used HEs. These techniques include electronic fast-framing photography, time-resolved emission spectroscopy, single-pulse Raman scattering and time-resolved infrared spectral photography (TRISP).
Laser Diagnostics of Radio Frequency Discharges
Authors: Gottscho Richard A.
Published: February 2023

Recent applications of laser spectroscopy to the study of plasma and plasma-surface processes are reviewed. Using laser-induced fluorescence and optogalvanic spectroscopy, measurements of concentration gradients, reaction probabilities, electric fields, and process end-points have helped to elucidate plasma-chemical mechanisms.
DIAL Measurements of Atmospheric Water Vapor, HCl, and CH4 Using a Continuously Tunable 1.7 μm Co:MgF2 Laser*
Authors: Killinger Dennis K. , Menyuk Norman
Published: February 2023

There is a need for the development of new, tunable high-power lasers in the near-to-middle IR to serve as sources in lidar systems for remote sensing of the atmosphere. We report on the development and use of a new solid-state, cobalt-doped magnesium fluoride laser (Co:MgF2), which is continuously tunable from 1.5 to 2.3 μm, and describe the use of this laser in a DIAL system to measure water vapor, HCl, and CH4 in the atmosphere. Both path-averaged and range-resolved DIAL measurements have been made at ranges up to 6 km and 3 km, respectively.
High Altitude Lidar Observations of Marine Stratocumulus Clouds
Authors: Boers Reinout , Spinhirne James D. , Hart William D.
Published: February 2023

The present study describes the cloud top structure of an East Pacific marine stratocumulus cloud layer as observed from a downward-pointing lidar system aboard the NASA ER-2 aircraft. The lidar observations were coordinated with in situ observations of cloud parameters. These data are applied to study important statistical properties of the stratus clouds. The study of cloud top structures is highly relevant for detailed radiation budget calculations. Because large gradients in temperature and humidity exist near the cloud top, cloud top emmitted radiation varies significantly in the vertical. Precise knowledge of cloud top location allows for a precise determination of cloud top cooling and thus determines an important loss/gain in the atmospheric thermodynamic energy budget. Cloud top topography and periodic structures influence the solar reflectance and therefore the albedo of the clouds.
Airborne Sodium Lidar Measurements of Mesospheric Gravity Wave Horizontal Structure over the Rocky Mountains and Great Plains
Authors: Kwon Kevin , Senft Dan , Gardner Chet
Published: February 2023

In November 1986 an airborne lidar campaign was conducted to study the horizontal structure of the sodium layer. The campaign was based in Denver, CO, and 14 hours of data were collected during three flights over a total baseline of 7,500 km. The aircraft was a Lockheed-Electra operated by the NCAR RAF.
Aerosols and Humidity Profiles Recorded Using the Alexandrite Laser: Preliminary Results and System Tests
Authors: Cahen Claude
Published: February 2023

Since 1983 we were developing fully mobile new DIAL system to monitor the major meteorological parameters (humidity, temperature, aerosols) using the alexandrite laser as the transmitter.
Instrumental and Atmospheric Considerations in the Development and Application of an Airborne/Spaceborne Water Vapor DIAL System
Authors: Browell Edward V. , Ismail Syed
Published: February 2023

The Differential Absorption Lidar (DIAL) technique can be used to measure concentration profiles of many atmospheric gases1. Atmospheric water vapor (H2O) has been measured with the DIAL technique from ground-based2-4 and airborne systems5. In the DIAL technique, two laser wavelengths are transmitted near simultaneously, one "on" the peak of the H2O absorption line and another away from, or "off" the peak. In the range resolved DIAL measurement, H2O concentration between two ranges is calculated using the well known DIAL equation1, which is a function of the on and off signals at the two ranges and the effective H2O differential, absorption cross section. Random errors due to noise in the detected signal and systematic errors due to uncertainties in the knowledge of the effective cross section, Δσ, contribute to inaccuracy in the DIAL measurements. The development of a DIAL system must give full consideration to these two sources of error and any known systematic offsets can be at least partially compensated for in the DIAL data analysis phase. A brief discussion of these effects is given in this paper, and a more detailed description of these effects is given in Ismail and Browell6.
Improvement of laser Doppler anemometer results by simultaneous backscatter measurements
Authors: Köpp Friedrich
Published: February 2023

Infrared Doppler lidar systems have proven very efficient for remote measurements of atmospheric wind and turbulence. During the last five years the cw CO2 laser Doppler anemometer (LDA) from DFVLR has been successfully used for different routine applications, for example, the measurement of vertical wind profiles up to 750 m altitude or wind profiles close to the sea surface. Another type of applications covers the investigation of turbulence structures, especially the detection and tracking of aircraft wake vortices. Despite all the accurate results gained during these and additional field experiments, some difficulties became evident which can influence the LDA measurements in unfavourable cases. One of those cases is the presence of strongly scattering layers like fog or low clouds within or nearby the sensing volume. This paper describes the possibilities which arise by simultaneous measurements of aerosol profiles and cloud heights using a backscatter lidar and a ceilometer.