bluuebunny/crossref_metadata_2025 huggingface dataset:
Concepts for Future Meteorological Earth Observing Sensors
Authors: Glackin David L.
Published: February 2023

The Aerospace Corporation is currently surveying advanced sensor concepts for environmental monitoring from space in the late 1990's and beyond. The parameters to be measured include a wide variety of atmospheric, terrestrial, and oceanographic items. The specific sensor concepts to be described apply to the measurement of clouds, winds, temperature, and humidity. Special emphasis in this presentation will be placed on the subject of clouds. The sensor concepts include: 1) a scanning radiometer for low Earth orbit cloud observation, 2) a meter-class telescope for geosynchronous altitude cloud observation, 3) a millimeter wave radar for cloud top, layer, and base sensing, 4) a stereo imager with a lidar sounder for cloud top sensing, 5) a lidar wind sensor, and 6) a differential absorption lidar (DIAL) for temperature and humidity profiling.
A Compact Wide-Field Sensor for Remote Sensing of Ocean Phenomena
Authors: Pagano Thomas S. , Woody Loren M.
Published: February 2023

A low-cost, high-performance sensor design for low-earth-orbit ocean-color remote sensing is presented with system tradeoffs and performance estimates.
Optimum Local Oscillator Levels for Coherent Detection Using Photoconductors
Authors: Hunt John M. , Holmes J. Fred , Amzajerdian Farzin
Published: February 2023

Photoconductors can be used as optical heterodyne detectors and they have the advantage of lower cost and larger size. Much literature is available for the perfect case where the circuit connected to the detector has no effect on the response of the detector. For direct detection when the signal is very small these results may be satisfactory. However, application of an optical local oscillator in the milliwatt range to the photoconductor modifies its conductance sufficiently to have a considerable effect on both the responsivity of the detector and its interaction with the signal processing circuitry. Penin et al. [1] recognized that there was a local oscillator induced interaction with the circuit and derived a formulation for the noise factor of a photoconductive detector as a function of local oscillator power. Unfortunately, they did not recognize that the equivalent source term is also modified by the local oscillator; and consequently, their result is not correct. In this paper, the signal to noise ratio (S/N) is derived for a photoconductive detector as a function of local oscillator power and includes both effects. It will be found that there is a finite level of local oscillator power for which the S/N is a maximum.
Radiance Ratio Classification of Earth Surface Features—A Spaceborne Shuttle Experiment
Authors: Sivertson W. E.
Published: February 2023

New spaceborne technology is being developed for autonomously detecting and classifying four primary Earth features—water, vegetation, and bare land, and a cloud-snow-ice class. Using this technology, a space-based remote imaging system could provide automatic pretransmission screening and selection of remotely sensed information. Classification is based on camera output radiance ratio values. The hardware is relatively small and could be operated in concert with other spaceborne sensors to remotely monitor Earth resources. This paper discusses the technology concept and spaceborne Shuttle test flight results.
Laser-Excited Optical Filters: Laser Power Requirements
Authors: Shay T. M.
Published: February 2023

Narrow bandwidth optical sources are readily available. However, tunable narrow bandwidth, wide field-of-view optical filters are not available. The laser-excited optical filters (LEOF) presented here are in principle tunable narrow bandwidth, wide field-of-view optical filters. These filters can simultaneously provide high resolution (0.001 nm), wide field-of-view (2π), high quantum efficiency, and electrically tunable optical filtering. Narrow bandwidth operation of laser-pumped atomic vapor filters were first demonstrated by Gelbwachs et al1., by Marling et al.2, and recently by Chung et al.3 The first electrical tuning of these devices was demonstrated by Gelbwachs et. al.4 In addition, alkali vapor based LEOFs can operate on 130 transitions between 921 and 474 nm. LEOFs are ideally suited for extracting weak narrow bandwidth signals buried in strong nonresonant optical background radiation. Potential applications of these filters include laser radar, laser communications, detection of Raman radiation, atomic spectroscopy, etc.
Laser Requirements for Wind Shear Detection from Aircraft
Authors: Moody Stephen E. , Byron Stanley R. , Lawrence T. Rhidian , Targ Russell
Published: February 2023

Wind shear events that are threatening to aircraft safety can potentially be detected directly from the aircraft by Doppler lidar techniques. The main requirements for such a system are sufficient range and reliability under realistic conditions to provide advance warning of shear conditions. With remote wind sensing from the aircraft, it should be possible to significantly improve aircraft safety by allowing pilots to better respond to, or even avoid, wind shear events.
Electrooptic Phase Modulation Gas Correlation Spectroradiometry
Authors: Rider David M. , Schofield John T. , McCleese Daniel J.
Published: February 2023

Recent work[1] has demonstrated a new type of gas correlation spectroscopy where electrooptic phase modulation of a molecular spectrum together with selective absorption by a reference gas is used to quantify the abundance of a gas phase species selectively. The use of electrooptic phase modulation for gas correlation measurements is a significant enhancement of the gas correlation technique because it provides a means for remotely measuring winds as well as atmospheric species abundances and temperature in the stratosphere and mesosphere[2,3].
Polychromatic Holographic Correlation Techniques for Enhancing Resolution in Remote Sensing Applications
Authors: Sambasivan R.
Published: February 2023

In optical remote sensing by photo-reconnaissance satellites or in ground-observation by orbiting space telescopes, the diffraction-limited theoretical resolution possible, is degraded by accidental & vibratory motion of the imaging camera, defocussing, atmospheric turbulence effects on satellite-pictures transmitted, etc. For instance, an orbiting space telescope (height,

h
′

=
275
 
km

above earth) with an effective focal length, f = 57.6m and equipped with a CCD camera with pixel, d = 15 microns, has a theoretical resolution:

R
=

(

h
′

d

/
f

)

→
=
7.16
 
cm
(
!
)

on ground; however, in practice due to image-degradation, the feasible resolution is of 10-15m only(which can be improved with rigid satellite attitude-control, to 1-2m).
Atmospheric Correction Algorithm of Real and Simulated Space Imagery Using Radiative Transfer Code
Authors: Kim Hongsuk H.
Published: February 2023

An image processing algorithm which can be used not only to simulate satellite mulitispectral imagery but also to derive surface reflectance from satellite imagery is being developed. In essence, the algorithm is a pixel by pixel modelling of the atmospheric radiance which can be either added to a simulated ground scene or subtracted from space data.
Focal Plane Array Technology for Optical Remote Sensing
Authors: Cutts James A. , Leipold Martin H.
Published: February 2023

Progress in the development of solid-state self-scanned imaging arrays for remote sensing in the infrared region highlighting recent developments is reviewed.
Dual Alexandrite Laser for Autonomous Lidar Applications
Authors: Degnan John J.
Published: February 2023

NASA's Lidar Atmospheric Sensing Experiment (LASE), a joint effort of the Langley Research Center and the Goddard Space Flight Center, is a first step toward the realization of the agency's goal of developing autonomous Differential Absorption Lidar (DIAL) instruments for future airborne and spaceborne remote sensing applications. The scientific goal of the first phase of the LASE program is to measure water vapor, aerosol, and cloud profiles from a high altitude ER-2 (extended range U-2) aircraft. The science motivation and overall system concept has been presented previously [1]. The present paper will discuss the design and performance characteristics of the Tunable Laser Subsystem (TLS) being developed at the Goddard Space Flight Center.
Progress in Solid State Lasers for Remote Sensing
Authors: Mooradian Aram
Published: February 2023

Summary not available.
Sources and Technology for Coherant Lidar Wind Measurement
Authors: Vaughan Michael
Published: February 2023

The required characteristics of laser sources, both pulsed and cw, are described and illustrated. Technology questions in attaining quantum limited system performance are briefly outlined.
Laser-Excited Optical Filter: Experiments In Rb Vapor
Authors: Shay T. M. , Dobbins J. D. , Chung Y. C.
Published: February 2023

Narrow bandwidth optical sources are readily available; however, tunable narrow-bandwidth, wide field-of-view optical filters are not available. Laser-excited optical filters (LEOFs) are in principle, tunable narrow-bandwidth, wide field-of-view optical filters. LEOFs can simultaneously provide high resolution (0.001 nm), wide field of-view (2π), and high quantum efficiency. These devices are ideally suited for extracting weak narrow bandwidth signals buried in strong nonresonant optical background radiation. Potential applications of these filters include remote sensing, laser communications, laser radar, detection of Raman radiation, atomic spectroscopy, etc.
An Airborne Polarization Lidar for Sounding Clouds and Underlying Surface
Authors: Abramochkin A.I. , Burkov V.V. , Zuev V.E. , Samokhvalov I.V. , Shamanaev V.I.
Published: February 2023

The information on the scattering coefficient of clouds and their phase state, as well as on the presence of oriented particles can be obtained, and the classification of an underlying surface can be made based on the analysis of lidar-return polarization.
Design Concepts for An Advanced Airborne Meteorological Lidar (LASE II)
Authors: Schwemmer Geary
Published: February 2023

The use of differential absorption lidar (DIAL) instruments in high altitude aircraft platforms for mesoscale meteorological applications dictates requirements on the instrument systems which approximate or approach spacecraft platform requirements. Unattended automated operation, power, mass, volume, and data rate may be constrained to some extent. The ability to utilize such a platform provides a good opportunity to demonstrate technology developments which will enhance the possibility of developing spaceborne lidar atmospheric sounders. This paper describes the investigation of techniques to increase alexandrite laser efficiency and frequency stability, and the use of Fabry-Perot etalons in a double narrow-passband receiver filter.
A Rapid Tuning Device for a CO2 LIDAR
Authors: Klein V. , Endemann M.
Published: February 2023

A rapid tuning device for a TEA CO2 laser has been developed for multispectral DIAL measurements in the atmosphere. This equipment is part of a LIDAR experiment for the remote detection, identification and quantification of several atmospheric pollutants within a range of 2 km.
Angular Distribution of Photoelectrons from Above-Threshold-Ionization (ATI) of Xenon Atoms
Authors: Feldmann D.
Published: February 2023

The range of angular momenta of continuum states involved in ATI has been determined at the four harmonic wavelengths of a Nd-YAG laser.
Study of ponderomotive forces and above-threshold multiphoton ionization by angle resolved photoelectron spectroscopy
Authors: Bucksbaum P. H. , Freeman R. R. , McIlrath T. J. , Bashkansky M.
Published: February 2023

In investigations of above-threshold ionization (ATI)1, we have shown that ponderomotive forces dominate photoelectron angular distributions at high laser intensities. The experiments employ 1064 nm 100 psec laser pulses or their harmonics, to ionize xenon and other rare gases, with peak intensities up to 1014 w/cm2.
Quantum Optical Approaches to the Problem of Atoms and Electrons in Intense Fields
Authors: Eberly J. H.
Published: February 2023

The principles of quantum optics suggest certain points of view in problems involving the interaction of intense radiation with atoms and electrons. These principles can frequently be used as a guide regarding the value of perturbation theory, the utility of dressed-state or Floquet methods, the presence or absence of significant electron-photon correlations, the relevance of Fermi's Golden Rule, and so on. They can also point to the existence of possible scaling relationships and assist in the qualitative interpretation of diverse data. We will attempt to show how an application of these principles leads to some tentative conclusions regarding the behavior of atoms and electrons in intense radiation fields.
A Pair Description of Two-Electron States
Authors: Rau A. R. P.
Published: February 2023

Two electron states may be divided into two classes. Those in which only one electron is excited, or in which when both are excited they have very different degrees of excitation, form a group distinct from those in which both electrons share comparable amounts of excitation. Particularly for the latter, an appropriate description is one which views the pair of electrons as a single entity from the start. Such states have been called "ridge states" and may be distinguished from the other group of states with disparate excitation by using the term "planetary states" for the latter. In this contribution, we take further steps in the evolving description of a basis for two-electron states in terms of the pair. Thereby we have a complementary description and basis to the independent particle picture.
Novel motions in highly excited two-electron atoms
Authors: Klar Hubert
Published: February 2023

Novel attracting motions consisting of periodic, quasiperiodic and chaotic components predict a new resonance formation in doubly excited atoms. Also double escape correlations are analysed.
Time Dependent Hartree Fock Theory of Multiphoton Ionization
Authors: Kulander Kenneth C.
Published: February 2023

The theory of multiphoton ionization for single electron atoms (or pseudo-one electron atoms such as sodium and cesium) is relatively well established from the standpoint of the knowing the relevant equations to be solved and interpreting the results. There is still some debate about the above threshold effects, but ionization rates have been calculated for high order processes, and the results agree well with experiment. This is not the case for multi-electron systems. In the limit of laser fields which are very strong compared to the Coulombic interactions, collective motion should be expected. At lower laser intensities, linear response theory or perturbation theory has proven to be adequate to model the absorption processes. In this regime, the inter-electronic forces are stronger than the photon-electron interaction so that the perturbation series is convergent. For the intermediate regime, say >1014W/cm2, these two kinds of interactions should be treated on the same footing. A complete, exact, many body calculation for this problem is not possible so that several approximations have been considered. Independent particle models seem to be the most reasonable, with time dependent Hartree Fock being able to include most of the important physical effects, particularly as the number of electrons increases. The major approximation of this approach is that the state of the system is represented by a single, determinantal wave function for all time. This constraint limits the kinds of information which can be obtained from the calculations to averaged quantities. It has the merit, however, of including the effects of the time evolution of the electronic charge density on the absorption process. The redistribution of absorbed energy between all the system's electrons, and the rate at which this occurs is part and parcel of the calculations. This energy exchange is done self consistently so that an understanding of the total absorption dynamics is possible. This seems a minimum requirement in order to investigate any collective effects.
Multiphoton Ionization of Beryllium
Authors: Wen J. , Travis J. C. , Lucatorto T. B. , Clark C. W.
Published: February 2023

We have utilized resonance ionization mass spectrometry (RIMS) to investigate the spectroscopy and dynamics of multiphoton absorption in Be. This work is directed towards developing methods for selective laser ionization of the isotope 10Be, a long-lived radionuclide (τ1/2 = 1.6 × 106 a) used for geological dating purposes. Since Be is the simplest “two - electron” atom that can be excited by absorption of a few photons at convenient laser wavelengths, these studies may also contribute to understanding the nonlinear interaction of radiation with many-electron systems.
Inverse Half-Bremsstrahlung in Multiphoton Ionization of Atoms in Intense Light Beams
Authors: Kupersztych Joseph
Published: February 2023

It is shown that absorption of the minimum number of photons needed to ionize an atom in a light beam of moderate intensity is no longer energetically possible when the external field is strong. However, subsequent absorption of a large number of photons by the "emerging" electron in the field of its parent ion can occur via multiphoton inverse "half-Bremsstrahlung" and ionization is possible again. This new theory leads to a simple interpretation of the appearance of a large number of peaks in the electron spectrum together with the disappearance of the low-energy peaks. The roles played by the laser intensity and wavelength are singled out, and quantitative agreement is found between the conclusions of the present theory and existing experimental data. Furthermore, using an argument developped in a recent paper (Phys. Rev. Lett., 54, 1385 (1985)), it is demonstrated that the ponderomotive force does not contribute to any modification of the energy of the electron when it leaves the laser beam. An intuitive physical explanation of this fact is given.
Model of Two-Electron Ionization Based on Semi-Classical Phase Space Averaging
Authors: Mostowski Jan , Trippenbach Marek , Van Cao Long
Published: February 2023

In this work the two electron ionization of helium is studied with a mixture of quantum and classsical theories.
Multiphoton Excitation and Ionization of Atoms
Authors: Jara H. , Johann U. , Luk T. S. , McIntyre I. A. , McPherson A. , Schwarzenbach A. P. , Boyer K. , Rhodes C. K.
Published: February 2023

It has been conjectured that atomic motions fundamentally different from those presently observed may be driven under extreme conditions of irradiation. Indeed, it has been suggested1-4 that ordered many-electron motions of outer-shell electrons could lead to enhanced rates of coupling from the radiation field to an atom. In order to study the conditions necessary for new atomic responses to occur and to determine the influence of possible damping mechanisms, the properties of ion charge state distributions,5 electron energy spectra,6 and harmonic radiation7 produced by irradiation of atoms with ultra-violet radiation with different pulse lengths, wavelengths, and intensities have been investigated.
Simple Demonstrations of Meteorological Optical Phenomena
Authors: Bohren Craig F.
Published: February 2023

It may be trite to say that seeing is believing, but this is nowhere more true than in meteorological optics. Yet optical phenomena of the atmosphere are sometimes rare, and even if common they are usually ephemeral. Unlike laboratory experiments they cannot be arranged to occur at the convenience of the observer. They neither can be reproduced at will nor controlled so that their workings are more readily discernible. For these reasons demonstrations of meteorological optical phenomena are highly desirable, particularly for classroom use or as accompaniments to popular lectures. In the following paragraphs five such demonstrations are briefly described. The common thread linking them is that they require no more than a few items found in any home or school. Except for the projectors, it would be difficult to spend more than a few dollars on all of them taken together.
Assessing the Value that Observers Place on Good Visual Air Quality
Authors: Malm William C.
Published: February 2023

Good visibility has long been recognized as an important value in our National Parks. Congress in the National Park Service Act of 1916 directed the Service to manage the parks to "conserve the scenery and natural and historic objects … and to provide for the enjoyment of the same in such a manner and by such means as will leave them unimpaired for the enjoyment" of visitors1. In order to effectively carry out its Congressional mandate the National Park Service (NPS) needs to be able to determine how scenic landscape features effect a visitor's experience and enjoyment of a park and must assess how these scenic values will be affected by changes in air quality. With this information the decision maker can better judge the adversity of potential changes in air quality.
The Apparent Compression of Distance with Distance
Authors: Fraser Alistair B.
Published: February 2023

The incremental change in apparent distance varies inversely with distance squared. This has implications for both meteorological visibility and the appearance of mirages.
The Colors of Snow
Authors: Bohren Craig F.
Published: February 2023

No one needs to be convinced that snow is white. But those who have observed white snow on countless occasions may never have noticed that holes in snow are sometimes deep blue. So also are crevasses in glaciers blue. And sometimes the bubbly ice of frozen waterfalls may have a bluish-green hue. The purpose of this paper is to discuss these observations in the light of a simple theory (Bohren and Barkstrom, 1974), which has been critically discussed by van de Hulst (1980) and by Warren (1982).
Droplet Sizes in an Irregular Lunar Corona
Authors: Peterson Alan W.
Published: February 2023

Near midnight on March 30-31, 1980 a large, irregular, rapidly changing lunar corona was noted in a thin altocumulus sheet moving to the southeast. Eight Kodachrome 25 photographs of varying exposure were taken. On 10 and 12 sec exposures three red rings are clearly seen, and a partial fourth red ring can be detected on the original slides. The display ended shortly after midnight when the sky cleared. The moon was within 8 hr of being full.
The Landscape as Viewed in the 320 - 390 nm Ultra-Violet
Authors: Livingston W.
Published: February 2023

Our perception of the landscape depends on the product of the spectral irradiance of the sun, the transmission and scattering of the earth's atmosphere, and the spectral sensitivity of our eyes. Although this last factor, the human eye, is reasonably matched through evolution to the available energy (400-700 nm), appreciable information is unavailable to us in the infrared (λ 700-1000 nm) and in the near ultra violet (λ 320-400 nm). While the infrared landscape has received much attention, hardly anything is known about the ultraviolet. The UV is of special interest in meteorological optics because water is perfectly transparent at these wavelengths and because all refractive phenomena are enhanced at short wavelengths. Here is a new domain worthy of exploration.
Use of Optical Limiting Atmospheric Conditions to Assess Historical Changes in Air Pollution
Authors: Changnon Stanley A.
Published: February 2023

Efforts to evaluate the success of the U.S. air pollution regulatory program, begun in the 1970’s, has been limited since systematic measurements of most pollutants such as ozone, SOx, and NOx are minimal prior to 1970 with none prior to 1955. Inevitable questions that arise, as one inspects and tries to interpret the temporal fluctuations of various pollutants since 1970, is whether the fluctuations are due to weather (climatic) shifts in the 70's, and whether the values differ from those that occurred during the prior 70 years when the nation became heavily industrialized, changed fossil fuels, and when gasoline-burning vehicles came into use.
Why do the Supernumeraries of Secondary Rainbows Never Show up in Rainshowers?
Authors: Können G.P.
Published: February 2023

At the last Topical Meeting, Fraser 1) offered an explanation for the paradoxical fact that supernumeraries of the primary rainbow are regularly visible in rainshowers, although the obvious broad droplet-size distribution should prevent such. The reason of their appearance is the flattened shape of falling drops, which causes the rainbow angle to increase with increasing (equivalent) drop-radius r, at least for solar heights h between 0 and 42°. Since therefore the positions of the Airy maxima as a function of r have a minimum, the supernumeraries still show up in rainshowers. However, the angular spacing between then contains hardly information about the drop-sizes in the showers any more, as they are determined by the places of these minima: if the drop-size distribution is broad enough, the separation between the first and second supernumerary is fixed at 0.7°.
Computer Simulation of Rainbows, Glory and Corona Phenomena including Multiple Scattering.
Authors: Tränkle E.
Published: February 2023

The primary and secondary rainbow, as well as the glory, are well known phenomena, whereas the corona is scarcely known. These phenomena are produced by the scattering of light at water droplets; the main features can be explained by light scattering at a single water droplet. In the framework of geometrical optics the primary and secondary rainbows are described as a limiting angle effect of rays with one and two internal reflections, respectively /1/. Glory and corona phenomena are interference effects at small water droplets being approximately desribed by diffraction scattering at a plane disk /2/.
The Heiligenschein as Diagnostic Tool in Satellite Remote Sensing
Authors: Gerstl S. A. W. , Simmer C.
Published: February 2023

When remote sensing of the Earth's surface from high-altitude airplanes or satellites is considered, scattering and absorption effects of the atmosphere must be taken into account. Although these atmospheric effects constitute in most cases undesirable perturbations to the observed surface features, it is sometimes possible to use these effects to diagnose atmospheric conditions. Similarly, certain unique surface reflectance characteristics may also be useful as a surface feature identifier in addition to pattern recognition. Such a potential diagnostic tool may be available by observing the Heiligenschein over structured surfaces. However, atmospheric perturbations must be minimized or eliminated by atmospheric correction formalisms, and confusion with other retro-reflection effects, such as the glory, must be avoided.
Carbon Dioxide Ice Halos on Mars; A Prediction from Crystal Growth Experiments
Authors: Doherty Paul , Bennett Clarence
Published: February 2023

Some of the clouds observed on Mars are composed of carbon dioxide ice and appear as uniform thin layers1. On Earth, similar layers of water ice clouds produce a 22 degree halo and associated parhelia, known as sundogs. Will the CO2 ice clouds of Mars produce halos and sundogs? If so, at what angles? To calculate the angles at which halos might appear, the shape of CO2 ice crystals on Mars and their index of refraction are needed. Crystals of CO2 ice were grown in a laboratory chamber under Martian atmospheric conditions; atmospheric pressure2 of 0.73 kPa, and CO2 sublimation temperature3 of 148 K. A literature search produced an estimate of the index of refraction of CO2 ice under these same conditions. Angles of CO2 ice crystal halos were then calculated to be 26±3 and 38±5 degrees from the sun.
Ion Enhanced Processes in Etching of Silicon
Authors: Mayer T. M. , Ameen M. S. , Barish E. L. , Vitkavage D. J. , Mizutani T.
Published: February 2023

A case study of the ion-assisted etching of silicon by chlorine is presented as a prototype of a class of ion-assisted etching processes. In contrast to the more well studied Si-F system, and other F atom etching reactions, Cl etching processes are much more dependent on energetic ion impact of the surface. We will examine aspects of chlorine adsorption to silicon, sputtering of adsorbed chlorine atoms, incorporation fo chlorine into the silicon crystal lattice, and formation and removal of SiClx etch products. In-situ SIMS, ISS, and modulated beam mass spectrometric measurements, and post etch RBS and XPS analysis of the altered surface are used to examine the dynamics of the etching process and the state of the altered surface layer produced by ion bombardment.
Surface Coherent Raman Spectroscopy
Authors: Hetherington W. M. , Van Wyck N. E. , Koenig E. W. , Ho Z. Z. , Stegeman G. I. , Fortenberry R. M. , Moshrefzadi R.
Published: February 2023

Surface coherent Raman scattering (SCRS) is a powerful technique for obtaining vibrational Raman spectra of surface species with submonolayer sensitivity. This sensitivity is achieved by using incident and scattered fields in the form of guided waves. A planar optical waveguid (1 µm) of a transparent oxide is deposited upon a silica substrate. Dye laser beams of frequencies ω1 and ω2 are coupled into the waveguide via coupling prisms in optical contact with the surface. The allowed TE and TM modes (electric field and magnetic field in the plane of the surface, respectively) for guided waves are characterized by a discrete set of wavevectors which depend upon the indices of refraction and the film thickness. The guided wave fields extend beyond the film into the surrounding media, and hence nonlinear interactions such as coherent anti-Stokes Raman Scattering (CARS) can occur on the surface of a waveguide. The field distribution functions exhibit an exponentially decaying evanescent tail outside the film.
Photophysical Studies of DAQ on Silica and Aluminum Oxides. A Molecular Probe of Surface Heterogeneity
Authors: Drake J. M.
Published: February 2023

The optical features of organic molecules adsorbed to the surface of oxides, such as silica and alumina, can be strongly perturbed by the chemical properties of the surface adsorption sites. The topography of the surface as it relates to the fractal dimension and its relation to the nature and distribution of surface sites is important information if we are to be able to understand the photophysics and photochemistry of surface bound molecules. The work we report here is for the molecule 1,4 dihydroxyanthraquinone (DAQ, Quinizarin). This molecule provides striking evidence of how the surface of silica gel modifies the optical features of DAQ in different ways depending on the nature of the surface adsorption site.
Time Resolved Kinetic Studies of Molecular Decomposition on Ni(100) using Laser Induced Desorption
Authors: Bares S. J. , Hall R. B.
Published: February 2023

Laser induced desorption (LID) of surface bound species is rapidly developing into an important technique for studying the dynamics of the adsorbate-substrate bond. We report here the first application of this new technique to time resolved studies of reaction kinetics on a clean metal surface. In particular, measurements of decomposition rates of methanol to form the methoxy intermediate and hydrogen are described. Surprisingly, the decomposition curves cannot be interpreted assuming a simple first order rate expression; rather, a pseudo-second order rate law is invoked to explain the data. Additional insight into the methanol decomposition reaction is obtained from studies of the reaction rate dependence on the initial concentration of methanol. Preliminary results using this technique to study the decomposition of ethylene on Ni(100) will also be discussed and compared to the methanol results.
Characterization of Photochemical Processing
Authors: Hirose Masatake
Published: February 2023

Photochemical etching processes of SiO2 in NF3 plus H2 gas and GaAs in Cl2 using ArF excimer laser by in-situ x-ray photo-electron spectroscopy.
Laser–induced Selective Deposition of Micron-size Structures on Silicon by Surface Reduction of Tungsten Hexafluoride
Authors: Liu Y.S. , Yakymyshyn C.P. , Philipp H.R. , Cole H.C. , Levinson L.M.
Published: February 2023

Selective deposition of refractory metal and metal sicilide on silicon induced by a focussed Argon laser beam is reported. Micron-size lines with extremely good surface smoothness were observed at a writing speed of 7 cm/sec. Deposition mechanism and properties of fine structures are discussed.
Diffusion and Reaction in Tortuous Structures as Modelled by Fractals
Authors: Klafter J. , Drake J. M.
Published: February 2023

It has been recently suggested that many structures in nature have fractal geometries: polymers1, diffusion limited aggregates2, sandstones3, Vycor glasses4 and various irregular surfaces
5
. Avnir et al.5,6 have demonstrated that for porous surfaces the concept of surface area is not meaningful. The area as measured by molecular adsorption changes with the size of the adsorbate molecules (the yardsticks). It has been proposed5,6 that many porous surfaces are characterized by their fractal dimension d̅ in a way which relates the number of adsorbed molecules to their cross sectional areas (yardstick sizes), σ, There have been only a few works7-9 which study the dynamics of molecules adsorbed in Vycor glasses and on porous silica gels. However no attempt has been made to relate the observations to a geometrical parameter. Interestingly enough both porous Vycor and porous silica gel have been proposed as fractal systems.4,5
Large Modification of the Surface Enhanced Raman Scattering of Pyridine on Ag Surfaces by Pd Submonolayers.
Authors: Lopez-Ríos T. , Gao Y.
Published: February 2023

It is known that SERS is partially due to localized surface plasmons and consequently can be only observed on metals supporting this electromagnetic excitation. It is also known that the surface chemical bonding of the molecule involved on the Raman process is relevant for SERS.
UV-Laser Photodeposition of Patterned Catalyst Films from Adsorbate Mixtures*
Authors: Ehrlich D. J. , Tsao J. Y.
Published: February 2023

It has been demonstrated in recent studies that laser-induced photochemical modifications of surface properties can be used in combination with nonlinear kinetics and interfacial chemistry for maskless patterning of thin films by selected-area growth.1-3 With one exception,3 these new techniques have relied on photochemical lowering of surface-tension barriers to physical condensation, e.g., prenucleation; laser-modification of chemical surface properties will have practical advantages over the use of physical barriers, particularly on surfaces with previously defined structures and crystalline defects.1 In this paper we describe a study in which chemical catalysts have been prepared by local photochemical reaction under UV-laser irradiation. Thin (monolayer) films of these laser-deposited surface agents are shown to predispose surfaces to "spontaneous" polymerization of ethylene or acetylene on exposure to these monomer vapors. The UV-laser deposition reaction for preparation of these catalysts involves a greater-than-unity-order reaction in a mixed-component adsorbed layer of TiCl4 and Al2(CH3)6. The method is far more efficient than direct radiation-driven polymerization, and is of particular interest as a method for the patterning of easily oxidized polymers, many of which are difficult or impossible to pattern by lithographic methods.
Laser-Stimulated Vibrational Excitation of an Adspecies Studied by a Generalized Master Equation.
Authors: Beri A. C. , George Thomas F.
Published: February 2023

Recent attempts to clearly demarcate selective and nonselective effects in the IR-laser-stimulated vibrational excitation of an atom or molecule adsorbed on a solid surface1 have included a number of model studies2 and a few that have examined the detailed nature of the individual quantum states of the adsorption potential.3,4 The presence of at least four time scales in such dynamical studies (experiment, laser, phonon, adbond) leads to difficulties in applying approximations such as the Markovian approximation (MA) which neglects memory effects in the generalized master equation (GME) describing the excitation. Use of the MA leads to the Pauli master equation (PME) which is easier to solve than the exact GME, and is therefore almost universally employed, but to our knowledge no realistic comparison has been made of the GME and the PME. We present below our results of the exact GME and the PME and find that for the few cases considered the two are drastically different in an (arbitrary) time range related to a time parameter τ necessary to force the MA in the first place. In the asymptotic (long time) limit the solutions can be made to converge. We also present the results of an approximation which gives results (for any time range) which are almost as good as those of the exact GME, but which are as easy to obtain as those of the PME.
Effects of Optical Properties on Wet Etching of Semiconductors
Authors: Podlesnik D.V. , Gilgen H.H. , Chen C.J. , Osgood R.M.
Published: February 2023

Many laser microchemical processes, for example, metal photodeposition and semiconductor annealing, are influenced by a surface electromagnetic field which results from the interaction of the incident light with the surface. This effect has not been extensively documented in laser etching of semiconductors. In this talk, we will show that such effects can play an important role in determining the etch profile and surface structure obtained from wet etching of semiconductors. In particular, the formation of surface ripples and the fabrication of high-aspect-ratio via holes will be discussed.
Transient Nonlinear Laser Heating and Deposition: A Comparison of Theory and Experiment
Authors: Goldstone J. A. , Allen S. D.
Published: February 2023

The deposition rate and deposit resolution in laser chemical vapor deposition (LCVD) and other laser induced chemical processes at surfaces are a function of a large number of variables including: the laser generated surface temperature profile, the local reactant concentration distribution, the substrate and deposited film characteristics and the reaction kinetics. Most laser generated temperature profile calculations to date nave assumed steady state behavior and/or neglected the nonlinear temperature dependent thermal properties of the substrate. In addition, most theoretical models neglect the changing surface reflectivity as the film is deposited. Equilibrium calculations, while useful for high thermal conductivity materials such as Si and metals, are inadequate for low thermal conductivity materials such as fused quartz where characteristic reaction times are considerably shorter than the time necessary to reach thermal equilibrium.
Photofragmentation and Desorption of CH2I2 from Sapphire and Silver Surfaces by a UV Laser
Authors: Domen K. , Chuang T. J.
Published: February 2023

Lasers have been extensively used in recent years to induce gas-surface photochemistry. There exist, however, relatively few mechanistic studies on well characterized surfaces involving electronic excitation of adsorbed molecules. We have recently investigated the electronic excitation effect of CH2I2 molecules adsorbed on a sapphire crystal and silver surfaces with a XeCl laser. The molecule is chosen because it is readily activated by the 308 nm light pulses into its first and antibonding state. The excited molecules can dissociate into CH2I radicals and I atoms with a unit quantum yield in the gas phase.
Excited-Atom Production by Electron Bombardment of Alkali-Halides
Authors: Walkup R. E. , Avouris Ph. , Ghosh A. P.
Published: February 2023

Bombardment of solids by energetic beams of electrons, photons, or ions is generally accompanied by the ejection of particles from the surface. The ejected particles include ground-state neutral atoms and molecules, electronically excited atoms, and ionic species. We have performed a variety of experiments on the bombardment of alkali-halides by electron and ion beams. These experiments suggest a new mechanism for the formation of excited atoms and positive ions due to electron bombardment of alkali-halides. Additional measurements provide an interesting contrast between excited atom production by the bombardment of alkali-halides with ion vs. electron beams.
Mechanisms for the Production of Chemiluminescence from F and XeF2 Etching of Silicon Wafera)
Authors: Suto M. , Mitchell M. J. , Lee L. C. , Chuang T. J.
Published: February 2023

We have investigated the ultraviolet and visible chemiluminescence accompanying the etching of silicon by XeF2 and atomic fluorine. The spectra obtained exhibit many similarities, but also have differences. The chemiluminescence spectrum generated by etching with atomic fluorine has one broad, unresolvable peak spanning wavelengths from 210 to 800 nm. The chemiluminescence spectrum generated by etching with XeF2 has three bands. One band from 215 to 280 nm is presently unassigned. A second band is sharp and intense, and centered at 354 nm. We identify this band as arising from the XeF (B → X) emission. The third band arising from the reaction of XeF2 with silicon is a broad continuum similar to that arising from the atomic fluorine reaction, which has been suggested to come from the excited SiF3*.
Radical-Surface Interaction and Its In-Situ Monitoring on GaAs and AlGaAs Surfaces in an Ultrahigh-Vacuum Etching and Cleaning System
Authors: Asakawa K. , Sugata S. , Takado N.
Published: February 2023

Interaction between a plasma-excited radical beam and a GaAs surface has been studied for establishing plasma-assisted surface cleaning by using an enclosed ultrahigh-vacuum RIBE (Reactive Ion Beam Etching)1) and RBC (Radical Beam Cleaning)2) system.
Direct Observation of Excimer Laser Photoablation Products by Picosecond-UV-Laser Mass Spectroscopy
Authors: Stuke M. , Larciprete R.
Published: February 2023

Since the first demonstration of the photoetching of polymers by excimer laser radiation [1, 2], the ability to produce sharp structures with submicrometer accuracy and well-defined depth has stimulated a series of investigations of this process. It is now well established, that this process works for a series of polymers and tissue material and for a range of laser wavelengths between 193 nm and 351 nm. We shall describe the direct observation of excimer laser (248 nm) photoablation products from PMMA, polystyrene, Kapton and Teflon using picosecond (ps) laser mass spectroscopy. By this technique, the abundance of the parent molecular ion P+ in the mass spectrum can be enhanced dramatically [3, ref.].
Surface CARS Spectroscopy with Optical Waveguides
Authors: Hetherington W. M. , Ho Z. Z. , Wijekoon W. M. K. P. , Koenig E. W.
Published: February 2023

Using the planar optical waveguide geometry, coherent anti-Stokes Raman scattering becomes a very sensitive type of vibrational spectroscopy for the study of surface structure and chemistry. The waveguide structure consists of a film (about one micron thick) of a material such as ZnO on a fused silica substrate. Laser fields can be constrained by total internal reflection such that they propagate through the film as guided waves. The concept is to perform CARS using the evanescent fields extending above the waveguide surface. The key to making this a very attractive form of surface spectroscopy is the establishment of an interference condition within the film, thereby eliminating the contribution from the vibrationally resonant or nonresonant third order susceptibility of the film itself. The remaining signal consists mainly of the signal from the surface and any surface adsorbates. With this technique, the Raman spectrum of interfacial species can be observed over the 0 to 4000 cm-1 range under environments ranging from UHV to condensed phases.
Laser Etching and Evaporation of CaF2 Studied by Mass Spectrometry
Authors: Estler R. C. , Apel E. C. , Nogar N. S.
Published: February 2023

In this work we describe the interaction of relatively high-fluence laser pulses (ϕ≥10 J/cm2) with polished CaF2 substrates. Both electron impact- and laser ionization-mass spectrometry have been used to probe the material spalled by the fundamental(1.06μ) and harmonic (355 nm and 266 nm) outputs from a Q-switched Nd:YAG laser. Primary ions produced in the source region of a quadrupole mass spectrometer were detected by turning off the eletron impact ionizer, while survey electron impact mass spectra were typically acquired at an energy of 75 eV. A time-of-flight mass spectrometer was modified to permit optical access by both the etching and interrogation laser beams1. This latter apparatus was used to measure velocity distributions, and to provide optical spectroscopic identification of the ion precursors.
Surface Second Harmonic Generation Spectroscopy of Oxide Surfaces
Authors: Hetherington W. M. , Padma Bandu G. G. , Mazely T. L. , Ho Z. Z. , Wijekoon W. M. K. P.
Published: February 2023

Second harmonic generation has been established recently as a specific probe of interfacial species. On dielectric surfaces, it has been used to detect the presence, the electronic states and the average orientation of interfacial species.
Imaging of Surface Atoms and Their Wavefunctions with the Scanning Tunneling Microscope
Authors: Demuth J. E. , Hamers R. J. , Tromp R. M.
Published: February 2023

Recent advances in scanning tunneling microscopy are described which permit energy-resolved imaging of filled and empty surface states and allow state selective, chemical imaging of surfaces with atomic scale resolution.
Pulsed-Laser Field Ion Microscope Study of Solid Surfaces
Authors: Tsong T. T.
Published: February 2023

By combining a ps to ns pulsed-laser heating and excitation technique to the atomic resolution field ion microscope and the single atom detection sensitivity atom-probe FIM, we are now able to study in detail the atomic structures and the atomic steps in surface reconstruction, gas-surface interactions, and many other field ion emission phenomena with atomic spatial resolution and ns to fs time resolution. In this talk an over view of this new development will be described, but I will emphasize two specific subjects where the uniqueness of the technique can be clearly visualized. They are the atomic reconstruction of Pt and Ir(001) and (110) planes, and dissociation of compound ions in high electric field by an atomic tunneling effect.
Combined Optical Second-Harmonic Generation and Surface Science Studies: Ag Layer and 3-D Cluster Growth on Cu(110)
Authors: Hoffbauer Mark A. , Muenchausen Ross E.
Published: February 2023

Optical surface second harmonic generation (SHG) has been used in conjunction with conventional surface science techniques to investigate the Cu(110) surface and the Ag/Cu(110) interface under UHV conditions. Surface SHG is found to provide detailed information on the well-characterized, clean Cu(110) single-crystal surface. It is also shown to be a sensitive real-time probe of both the growth of uniform monolayer thick Ag layers and the nucleation and growth of three-dimensional Ag nano-clusters (<10 monolayers thick) on the Cu(110) substrate.
Desorption Induced by Sub-picosecond Laser Pulses: NO/Pd (111)
Authors: Prybyla J.A. , Heinz T.F. , Misewich J.A. , Loy M.M.T. , Glownia J.H.
Published: February 2023

The possibility of desorption of atomic or molecular species from surfaces occurring by non-thermal means has recently attracted considerable interest.1 One of the most intriguing cases is that of desorption from the surface of a metal substrate, for which the lifetimes of excited, non-equilibrium states in both the bulk and surface region are expected to be extremely short. In this paper, we report results on the desorption of NO from chemisorbed states on a Pd (111) surface induced by exposing the surface to laser radiation of 2-eV photons in a 200 fsec pulse. Analysis of these results in conjunction with our earlier study of NO desorption from Pd (111) by nanosecond laser pulses2 indicates that by depositing energy into the surface on a sub-picosecond timescale we are able to observe a non-thermal desorption mechanism. Here we outline the nature of our experiment and present data concerning the yield and vibrational energy distribution for the desorbed NO molecules.