bluuebunny/crossref_metadata_2025_split huggingface dataset:
Interspecific and Geographical Variation of the Chromium Sensitivity of Algae
Authors: Riedel GF 
Published: February 2009

The toxic effect of hexavalent chromium on the growth rate of ten species of estuarine phytoplankton was examined in a defined growth medium. The concentration causing 50% inhibition of growth rate varied by a factor of more than 50 among the species. Three possible causes of interspecific variation in the sensitivity were examined: detoxification by extracellular reduction, interspecific differences in growth rate, and interspecific differences in chromium (VI) uptake. Results indicate that none of these hypotheses explains the interspecific variation in chromium sensitivity.
The chromium (VI) sensitivity of each algal species was also tested at two different sulfate concentrations. In every case, the toxicity of chromium (VI) was greater in the medium with lower sulfate concentrations. This confirms and extends previous results showing that chromate sensitivity in algae is closely correlated to the sulfate concentration of the growth medium.
Stress Intensity Factors Caused by Residual Stress Fields in Autofrettaged Tubing
Authors: Stacey A , Webster GA 
Published: February 2009

The influence of residual stress distributions on the stress intensity factors developed in thick-walled cylinders containing line cracks is quantified. A stress intensity factor caused by the residual stress field, Kres, is evaluated using the superposition principle. This can then be superposed on the stress intensity factor associated with the applied loading to give an effective stress intensity factor controlling crack growth.
Boundary integral equation and weight function methods are applied to determine Kres as a function of crack depth for internally and externally flawed as-received and autofrettaged cylinders with a diameter ratio of 2.07. Good agreement is obtained between the two approaches over the range of normalized crack depth 0 ≤ a/W ≤ 0.7 (a = crack length, W = specimen width). Actual measured residual stress distributions, as well as analytical residual stress fields for autofrettaged tubing obtained assuming elastic-perfectly plastic behavior and the von Mises and Tresca yield criteria, are investigated. The Kres caused by autofrettage residual hoop stresses is essentially negative for internal cracks and positive for external cracks. The Kres solutions for the experimentally measured and von Mises distributions compare very favorably. The results for the Tresca distribution are approximately twice as large and are considered to be too conservative.
Increased Pressure Vessel Fatigue Life Caused by Decreased Autofrettage
Authors: Brown BB 
Published: February 2009

Pressure vessels, while gaining fatigue life at interior surfaces caused by autofrettage residual stresses, suffer a decreased life when fatigue cracking initiates at the exterior. This situation may result in a less than optimum vessel life if maximum autofrettage is applied. A series of controlled experiments have been performed along with analyses to maximize the life of a pressure vessel by optimizing the level of autofrettage.
The experiments used specimens with an outer diameter of 284 mm, a 64-mm wall thickness, and an exterior groove. Autofrettage overstrain levels were varied incrementally from 100 to 50% with fatigue life increases over 100%. Normally, pressure vessels would experience a decrease in fatigue lives with decreasing overstrains of this range. In this experiment, because of the exterior stress concentration of the groove, fatigue lives increased with the reduced overstrains. The work has been subsequently applied to operating pressure vessels with fatigue test data taken on these vessels.
LIMA in Damage Diagnostics
Authors: Laidler I , Edge GJ , Emmony DC , Temple PA 
Published: February 2009

LIMA (laser induced mass analysis) has been used as a damage testing facility incorporating damage detection and analysis of all ionic species generated by breakdown and plasma formation on a surface.
The laser radiation is frequency quadrupled Nd-YAG at 266 nm, enabling studies in the UV near to the most important KrF emission.
Preliminary qualitative results give an insight into damage mechanisms and coating weaknesses.
Two prototype coatings, an A.R. and an H.R., have been studied above and below the 50% damage fluence. The state of coating cleanliness is immediately obvious and it is possible to conclude the sources of sub-threshold damage and the extent of coating disruption. The ready availability of this information should led to forthcoming improvements from coating manufacturers.
Mechanical Stability and Absorptance of Metal Films
Authors: McGuirk M , Perkin-Elmer  
Published: February 2009

The absorptance of gold films deposited under a variety of conditions was measured to an accuracy of.0002 with an HF Laser Calorimeter. The absorptance was observed to vary from.0107 to.0091, which is an 18% change.
The specimens were analyzed with a Perkin-Elmer PHI Auger spectrometer and the absorptance was found to be directly correlated with the impurity content.
The impurities were determined to originate in the residual gas in the chamber. A Dycor residual gas analyzer was used to locate and eliminate the sources of the impurities.
Films deposited at the same rates and temperatures, but with essentially no impurities were found to have absorptance ten times greater than the original films. These films have a dramatically different structure. They have been commonly observed, and are generally described as “recrystallized.”
Impurities were intentionally added to produce an absorptance of approximately.0095. The doped films were observed to be substantially more stable than un-doped films under thermal cycling between room temperature and 225°C. The dopant atoms are believed to pin the grain boundaries. While no quantitative hardness measurements were made. The doped films are also expected to be harder.
Similar results were observed for silver. Partial recrystallization is hypothosized to explain the reflectance degradation of siver based EHR coatings reported by Dr. Don Decker in 1982.
Highly Damage Resistant Anti-reflection Coating on the Chemically Etched Surface for High Power Lasers
Authors: Yoshida K , Yoshida H , Kato Y , Yamanaka C , Ohtani M 
Published: February 2009

When the surface of BK-7 glass is conventionally polished by CeO2 as polishing compound, the polishing compound is buried into the substrate. The buried compound can not be removed by standard optical cleaning techniques. Therefore, when the polished surface is anti-reflection (AR) coated and exposed to the focussed laser beam, the surface ionization occurs due to absorption at the isolated sites, leading to laser induced damages in the AR coating.
In order to improve the damage threshold, we have prepared the BK-7 substrate which was chemically etched after polishing. The damage threshold of the AR coating on the etched surface showed 1.5∼2 times improvement compared with that of un-etched surface, at the laser wavelength of 1.06 &m and 1 ns pulse width. Due to the special etching technique, the surface roughness of the etched surface was 10∼15 Årms, which was close to the surface roughness before etching (7∼12 Årms).
An Investigation of Laser Processing of Thin Film Coatings
Authors: Weber AJ , Stewart AF , Exarhos GJ 
Published: February 2009

An initial set of experiments has been conducted to determine the practicality of laser processing of thin film coatings. A high average power CO2 laser was used to flood load the entire surface of each test sample. Thin film coatings of HfO2 and MgF2 on fused silica substrates were irradiated with power densities between 25 and 125 W/cm2.
Extensive pre- and post-test characterization revealed that some changes in the microstructure were observed, the coating optical thickness was reduced and short wavelength transmission was improved.
Laser Induced Damage of Dielectric Phase Retardation Mirrors at 1.064 Microns
Authors: Ristau D , Akhtar SMJ , Ebert J 
Published: February 2009

Dielectric phase retarders are frequently used in high power laser systems for cutting and welding. The phase shift is commonly achieved by total reflection or optical tunneling.
In this paper laser induced damage thresholds of plane phase retardation mirrors are measured using single 14 ns Nd-YAG laser pulses. The results are compared to the properties of the corresponding nonshifting deflectors. We investigated in stacks of Titania, Tantala, Hafnia and Zirconia in conjunction with Silica designed for retardation angles of 45° and 90°. Laser induced damage thresholds are related to the field strength distribution in the layers.
Correlation of Damage Levels at 1.06μm Varying Modal Content and Irradiance History on Representative Coated Laser Optics
Authors: Arenberg JW , Frink ME , Mordaunt DW , Lee G , Seitel SC , Teppo EA 
Published: February 2009

This paper reports on efforts to correlate two commercially oriented laser damage tests. The two test facilities are located at Hughes Aircraft Company and Montana Laser Optics.
A variety of coated laser optics have been tested under different test conditions and the damage levels compared. The test parameters varied were transverse modal content, spot size, sample conditioning history and, to a lesser degree, pulsewidth. The accumulated results were correlated by ascertaining the existence of a high probability functional relationship (linear fit) between pairs of damage levels for the same optics under different test conditions. A strong correlation was found between samples tested with the same irradiance history, regardless of the modal content and pulsewidth. Comparison of the samples of different irradiance conditioning history were found not to correlate in general.
Fabrication of Fluoride Thin Films Using Ultra-High Vacuum Techniques
Authors: Lewis KL , Pitt AM , Chew NG , Cullis AG , Wyatt-Davies TJ , Charlwood L , Dosser OD , Muirhead IT 
Published: February 2009

Previous papers at this meeting have highlighted the potential afforded by molecular beam techniques in producing optical thin film structures with a high resistance to laser induced damage. These techniques have been recently applied to the growth of polycrystalline thin films of candidate fluoride materials suitable for use over a wide range of laser wavelengths. Here the chief materials of interest have been barium and lead fluoride. Despite sharing a common vaporisation process, significant differences exist in the behaviour of the two molecules on condensation. In the case of barium fluoride, the surface morphology is rough in films produced at room temperature and it is necessary to deposit at significantly elevated temperatures to obtain smooth fi1ms even in UHV. In comparison, lead fluoride films have an exceptionally smooth morphology, even when produced at ambient temperatures. Such factors have an important influence on the laser damage thresholds of the films.
In multilayer designs, some control of columnar microstructure is also possible by a stratification technique where two differing component materials are used to prevent microstructure propagation. The coating is built up by alternating the materials throughout the coating until the desired thickness is achieved. By continuously varying the relative thicknesses of the individual laminations, it is possible to produce graded index coating designs. These allow the exploration of interface effects, hitherto difficult using optical techniques.
Photon Induced Desorption and Emission from Thin Film Dielectric Surfaces
Authors: Kardach JA , Stewart AF , Guenther AH , McIver JK 
Published: February 2009

Results from 1-on-1 and N-on-1 laser induced damage experiments, together with associated charged particle emission from 22 dielectric thin films on fused silica, sapphire, and calcium fluoride substrates are reported. A Q-switched Nd:YAG laser (1.06 microns, 5 nsec (FWHM), 500 microns 1/e2 diameter) was used to irradiate the half wave (at 1.06 microns) thin films. The experiments were performed in a UHV vacuum chamber with a base pressure of 10-8 Torr, and were computer controlled.Preliminary analysis indicates that the damage threshold for dielectric thin films increases with the substrates thermal conductivity, even for these very short laser pulses. Laser damage thresholds and charge emission curves are presented and characterized as a function of the incident laser energy density.
The Effect of Layer Thickness Errors in the Design of Coatings with Reduced Electric Field Intensity
Authors: Keller GL 
Published: February 2009

Many papers have been written on the design of laser-damage-resistant high reflectors. Usually, reduction in the peak electric-field intensity in the outermost layers of a multilayer stack is studied.
In this work, the effect of random and systematic errors in the quarter-wave stack below the enhanced layers is investigated. Also, optical monitoring errors in the optimized layers and their relation to the standing-wave electric field through the multilayer stack are discussed.
Impact of Thermal Blooming on Laser Damage Measurement Accuracy
Authors: Newnam BE 
Published: February 2009

The presence of thermal blooming in laser damage experiments conducted in air frequently goes unnoticed. For certain conditions, however, this effect can result in significant errors in determining the magnitude of damage thresholds.
Thermal blooming of a laser beam is a direct result of nonuniform heating of the transmitting medium (air) across the laser beam diameter. The resultant changes in refractive index cause the laser beam to diverge. In a laser damage experiment the test sample is often placed in the focal plane of a positive lens. With thermal blooming, however, the actual focus of the high-intensity laser beam can occur significantly in front of the sample, resulting in overestimates of the damage threshold.
Using the formulation of Skinner for a focused Gaussian beam, we calculate the magnitude of possible errors for damage thresholds of surfaces and thin films measured in air with various wavelengths. Measurements reported by several laboratories fall in the parameter space for which corrections for the effects of thermal blooming are recommended.
An Investigation of Laser Processing of Silica Surfaces
Authors: Weber AJ , Stewart AF , Exarhos GJ , Stowell WK 
Published: February 2009

An initial set of experiments has been conducted to determine the practicality of laser processing of optical substrates. In contrast to earlier work, a high average power CO2 laser was used to flood load the entire surface of each test sample. Fused silica substrates were laser polished on both surfaces at power densities ranging from 150 to 350 W/cm2. During each test sequence sample surface temperatures were recorded using a thermal imaging system.
Extensive pre- and post-test characterization revealed that surface roughness and scattering of bare silica surfaces were reduced while internal stress increased. Laser damage thresholds were found to increase only for certain conditions. Changes in the microstructure were observed. These preliminary experiments have demonstrated that laser processing can dramatically improve the optical properties of fused silica substrates. Optimization of processing parameters will be the subject of future work.
Damage Morphologies and Cumulative Behavior of Laser Damage on Single Crystal Metal Surfaces
Authors: Jee Y , Becker MF , Walser RM 
Published: February 2009

We have observed laser induced damage morphologies and the accumulation dependence of damage on single crystal metal surfaces under Q-switched Nd:YAG laser irradiation (1064 nm, 10 nsec pulses with a 240 μm spot diameter). The samples were chemically-polished copper and electro-polished aluminum of several crystallographic orientations.
Several different damage morphologies have been observed: slip-line formation, ripple patterns, flat-melting, and boiling. Damage probability versus fluence curves and accumulation curves were plotted to investigate damage behavior as it correlates with morphology. Flat-melting damage was observed near the 50% damage fluence on chemically polished copper surfaces, and slip-lines were found near the 50% damage fluence on electropolished aluminum surfaces. Surface defects produced during sample preparation greatly influenced the damage threshold of copper because of its high melting threshold. The influence of surface defects on copper decreased with increasing numbers of laser pulses. Accumulation curves show different damage behavior for crystals of different orientation. Accumulation was the largest on (111) Cu and Al surfaces, and the single shot damage threshold of these surfaces was less than the other crystal orientations for both Cu and Al.
Some Comments On: Temperature Dependent Effects In Laser Induced Damage
Authors: Lange MR , McIver JK , Guenther AH 
Published: February 2009

The temperature dependence of various processes can be extremely important in laser induced damage mechanisms. This has been well known since study in this field began. The ways in which temperature plays a role are both varied and many. However, one must be careful not to attribute too much of the responsibility for damage to temperature effects alone. Its specific roles must be carefully characterized and quantified.
On more than one occasion, there have been suggestions of temperature dependent absorption as an important pulsed laser damage mechanism in dielectrics. Similarly, there have been a collection of works supporting theories which do not significantly involve temperature. A comparison of both macroscopic and microscopic scales indicate that, in general, damage must consist of a natural series of evolutionary events that generally involve both temperature independent effects combined with those that are temperature dependent. The series of events that dominate in any process leading to damage depends critically upon the structure and state of the material involved and the photon energy that is incident, to name but the two most obvious. Thus, they must be tediously reconstructed for each given interaction, though certain cases, e.g., classes of material, may be generalized to some extent.
Recent works by the present authors have suggested the level of absorption involved in damage of certain optical films. Subsequently, some of the mechanisms for absorption were assumed and analyzed. In the present work some perspective is placed upon the role temperature plays in the steps leading up to damage.
Laser Induced Damage Threshold Derived from Chaotic Electron Dynamics
Authors: Becker W , McIver JK , Guenther AH 
Published: February 2009

An important stage in the laser induced damage of a dielectric material is a mechanism-initiated triggering by the presence of sufficient electrons in the conduction band. When these electrons are subsequently accelerated by the laser field under photon assistance, they can lead to an electron avalanche, and, in turn, may initiate visible damage.
We have investigated the precondition or presetting of the electron model, i.e. the initial creation of electrons in the conduction band. We assume the presence of small metallic inclusions (r ∼10 to 100 Å) in the dielectric which we model by infinitely deep one-dimensional square well potentials. The dynamics of this model are known to be chaotic if the laser field exceeds a certain threshold value. Under these conditions the electrons can gain enough energy to bridge the gap between the valence band and the conduction band.
The model yields threshold fields of the order of 1010 W/cm2. However, the dependence on the wave length is complicated.
Influence of Impurities and Defects on 1064 nm and 532 nm Damage in Quartz
Authors: Merkle LD , Bandyopadhyay PK 
Published: February 2009

It is axiomatic that even low concentrations of defects or impurities can control the damage behavior of transparent solids. Following the observation, reported in the 1985 Symposium, of strikingly different damage properties in two apparently similar samples of crystalline quartz, a study of several grades of quartz has been made to determine the influence of impurities and structural defects on their damage resistance. Data were taken at 1064 nm and 532 nm using a Q-switched YAG laser.
It has been found that considerable differences in single and multiple pulse damage “thresholds” exist among quartz samples of varying quality. These variations do not correlate with the concentrations of the most common impurities, Al and OH, but they appear to correlate with the density of coarsely spaced defects such as inclusions or etch channels (dislocations). These results tend to rule out damage mechanisms involving point-like defects, emphasizing instead the importance of larger impurities, even if submicroscopic.
Digital Fluence Profiling System and Software
Authors: Seitel SC , Rypma RL 
Published: February 2009

An advanced digital fluence profiling system based on a windowless GE TN2502 or TN2509 silicon array camera and Poynting Products 505RM frame grabber is described. The camera array is located precisely in the target plane or equivalent, and synchronized to the pulsed laser source with a flashlamp radiation sensor circuit. Data acquired by the frame grabber are transferred to an HP Series 200 computer for analysis.
Analysis is performed with BEAMCODE 2.0 software which permits near real time extraction of the peak fluence to total energy ratio in a single pulse to better than 20 percent. When corrected to camera nonuniformity and compared to large-aperture calorimetry, accuracy exceeds 10 percent. Other functions include measurement of pointing stability (beam wander) and divergence, fit-to-gaussian, and graphics data displays in contour and pseudo-3D formats.
Investigation of Optical Damage via Resonance Ionization Mass Spectrometry
Authors: Estler RC , Nogar NS 
Published: February 2009

Resonance ionization mass spectrometry (RIMS) has been used as a diagnostic for interrogating optical damage events. RIMS involves multistep laser photoionization, generally through real intermediate states, followed by mass separation and detection. It is a sensitive and selective means of detection, and has the potential for detection of ultratrace inclusions in substrates and/or coatings.
In initial experiments, damage on uncoated CaF2 substrates was initiated by pulses of 1.06-μm light from a Q-switched Nd+3:YAG laser. Interrogation of the spalled plume revealed CaF radicals only when damage events occurred. No Ca atoms were observed, and no attempt was made to detect F atoms or CaF2. In subsequent experiments conducted at laser intensities below the damage threshold, we observed the presence of surface adsorbents and a correlation between the presence of the adsorbents and the occurrence of optical damage.
Design and Construction of a Single Polarizer Infrared Ellipsometer/Reflectometer for Characterization of Highly Curved Surfaces
Authors: Stubbs JB , Loomis JS , Leonard TA 
Published: February 2009

The University of Dayton has designed and built an Infrared Ellipsometer/ Reflectometer (E/R) to characterize curved surfaces in support of the ALPHA Laser Program. The instrument is tunable in wavelength and angle of incidence, is remotely controlled by a dedicated microcomputer, is positioned and scanned by a six-degree-of-freedom translation stage, and makes simultaneous measurements of Rp, Rs, Ψ, and Δ.
A return path configuration was chosen to provide the versatility necessary for the variety of curved surfaces to be used in the ALPHA laser. This E/R is capable of measuring Rp and Rs to 0.1% accuracy and Delta to better than 0.1° accuracy on curved surfaces to 1.0 centimeter radius of curvature.
The optical design and theory of operation as well as automatic alignment and focusing features are discussed. Data taken with this instrument are presented.