bluuebunny/crossref_metadata_2025 huggingface dataset:
Chapter 1—Reference Bases for Accurate Measurement
Authors: Yolken HT
Published: March 2009

Most measurements are made to communicate information on properties of material things in a purposeful way to accomplish useful goals. Communications can be effective or ineffective. In parallel, measurements can be meaningful or not meaningful. Meaningful measurements allow us to make decisions on a solid, objective basis. For example, the measurement of a patient's temperature is likely to cause little controversy because instruments and scales are available to determine temperature well within the required tolerance. On the other hand, measurements of the quality of wine on a scale of desirability are still highly subjective, and decisions based on results of “experts” using the taste test are subject to controversy.
Chapter 12—A Broad View of Needs in Standards Development in the Medical Field
Authors: Caceres CA , Hanlin DC , Schick JW
Published: March 2009

Development of standards and test methods is a time consuming and potentially costly activity. The value of the results, a standard or test method, is often unclear. “Cost” is a generally well understood concept, but the benefit in relationship to costs, or “value,” can be misunderstood.
Chapter 13—Determination of Information and Communication Needs: Computers in Medicine
Authors: Devey GB
Published: March 2009

The use of computers in medical technology and in medical information systems has become widespread and will continue to grow. Currently, large computerized information management systems are used in hospitals, small microprocessors are in pacemakers, and research is progressing toward artificial intelligence to help improve diagnostics, just to name a few of the computer uses. However, two basic problems must be surmounted: incompatibility of computerized instrumentation and inadequate medical specifications for developing reference bases for computer applications.
Chapter 15—Quality Assurance Implementation: Diagnostic Instrumentation
Authors: Lewis AD , Podolsky L , Anbar M
Published: March 2009

What methods are currently utilized for determining diagnostic equipment requirements? Who should be responsible for validating purchased instruments against approved standards?
Impurity Incorporation in Czochralski Silicon Grown for VLSI
Authors: Murgai A
Published: March 2009

Tight control of oxygen concentration (within ±0.3 ppma) is attained with a new method in the Czochralski growth of large-diameter silicon (86 to 125 mm). Programmed variation in growth parameters is employed during growth to compensate for the normal decrease in oxygen concentration otherwise present. The presence of A1 and B impurities in vendor-supplied silica crucibles (up to 100 and 1 ppm by weight, respectively) is shown to significantly alter the apparent dopant segregation coefficient. The nondetection limits of various other metallic impurities, such as Mo, V, Ti, etc., being large (∼5 ppm by weight) in the silica crucibles, the concentrations of these impurities can easily exceed undesirable levels in the crystal (up to 1012 atoms/cm3). Fluctuations in growth parameters can raise the concentrations of these impurities further (by approximately two times) over microscopic regions of growth.
Defects and High-Pressure Steam Oxidation of Silicon
Authors: Katz LE
Published: March 2009

Recently high-pressure oxidation has been successfully applied to both bipolar and metal-oxide-semiconductor (MOS) technologies. This paper reviews those aspects of high-pressure oxidation, from a perfection standpoint, which are necessary to qualify this technique for incorporation into device processing.

Oxidation-induced stacking faults, which are known to degrade junctions, are shown to be reduced with high-pressure oxidation when compared with conventional wet oxidation at atmospheric pressure. Models are discussed which correlate well with this observation.

Impurity levels, as measured by defect state concentration measurements and neutron activation, have values equal to or lower than those for wafers oxidized by conventional techniques. A review of oxide charges present, as observed by several authors on various equipment including commercial pyrogenic and water-injected systems, shows values comparable to one atmosphere control. Additionally, process parameters affecting stress in the growing oxide film are discussed.

Overall, the high-pressure oxidation technique appears to grow high-quality oxides comparable to those grown in qualified conventional systems.
Computerized Electron-Beam Linewidth Measuring and Inspection: A New Tool
Authors: Pomposo TF , Coates VJ
Published: March 2009

This paper describes a field emission linewidth measuring and inspection instrument. The low-voltage operation, which allows nondestructive measurement of critical dimensions on photoresist with good precision, is described. The effect on photoresist of nonpenetrating electrons in the low-voltage mode versus penetrating electrons in the high-voltage mode is discussed.
Measurement of Ion Implantation Doses in Silicon by Ellipsometry and Spectral Reflectance
Authors: Hochberg AK
Published: March 2009

Results of ellipsometric measurements are presented for arsenic implants in silicon at doses from 2 × 1013 to 8 × 1015 cm−2 and energies from 30 to 180 keV. For implanters which mechanically scan wafers through the ion beam, it is possible to construct curves relating ellipsometric parameters to implant parameters. Reproducible ellipsometric results are strongly dependent on wafer preparation and precise setting and control of implant energies. Spectral reflectance measurements of implanted samples show that this method may be also used for implant monitoring.
Some Salient Features of the Tearing Instability Theory
Authors: Ernst HA
Published: March 2009

In this work the problem of the stability of a system deformed under displacement and load-controlled conditions is examined. The instability conditions are found from the load versus displacements, P-δ, characteristics of the system and the stiffness of the structure, KM, on a completely general basis. The analysis is performed for the system in series with a spring under displacement control and for the system in parallel with the spring under load-controlled conditions.

In addition it is shown that the conditions for instability found for both situations using the tearing instability theory are in complete agreement with those obtained under a completely general basis. As a result the tearing instability theory is proven to be always valid in the sense that instability will occur if and only if Tapp > Tmat.

Finally, a small experimental program on a nickel-chromium-molybdenum-vanadium rotor steel was conducted in order to prove that structures can be designed to assure stable crack growth under load-controlled conditions beyond maximum load.
Validation of a Deformation Plasticity Failure Assessment Diagram Approach to Flaw Evaluation
Authors: Bloom JM
Published: March 2009

This paper is based upon work done to establish the validity of a simple engineering approach to assess ductile fracture. The approach is based upon the ideas of the British Central Electricity Generating Board's (CEGB) R-6 Failure Assessment Diagram (FAD) and the deformation plasticity solutions developed by General Electric. The FAD approach is an easy way to visualize a complex elastic-plastic analysis of a specimen or structure. The FAD is a safety/failure plane defined by the stress-intensity factor/fracture toughness ratio, Kr, as the ordinate and the applied stress/plastic collapse ratio, Sr, as the abscissa. For a particular stress level and flaw size, the coordinates (Sr′, Kr′) are determined. If the assessment point (Sr′, Kr′) lies on or outside of the failure assessment curve (FAC), the structure will fail. Design loads or margins of safety are readily determined graphically due to the unique linear proportionality of the diagram's axes. The FAC is constructed by taking the fully plastic solution results of deformation plasticity developed by Shih and Kumar along with Shih's estimation scheme to derive a curve in terms of (Sr, Kr) coordinates of the FAD. The validation of the deformation plasticity FAD was based upon the use of a Babcock & Wilcox-modified version of the incremental plasticity finite-element computer program ADINA (Automatic Dynamic Incremental Nonlinear Analysis). Since the FAC's are based upon the deformation plasticity J-integral, the validation of these curves is also a validation of the J-integral. Compact, center-cracked plate, double-edge-cracked plate, and single-edge-cracked plates were among the fracture configurations which were evaluated using the ADINA computer program. The additional validation of the FAD approach from experimental data of five test programs is also a validation of the elastic-plastic J-integral/J-resistance curve approach. These test programs included six different materials and five different test configurations. Based upon the assessment results the deformation plasticity failure assessment approach and the elastic-plastic J-integral/J-resistance curve approach appear to provide an excellent predictive method for determining specimen load behavior.
Ductile Crack Growth Analysis Within the Ductile-Brittle Transition Regime: Predicting the Permissible Extent of Ductile Crack Growth
Authors: Milne I , Curry DA
Published: March 2009

The ductile-brittle transition in ferritic steels is reviewed using data from pressure vessel steels A533B, A508, BS1501-271, and their associated weld metals and heat-affected zones in a variety of conditions. A schematic model is presented which provides a rational basis for understanding the phenomenon and making predictions. This model, which is consistent with the predictions obtained from physical models of cleavage fracture, contains the following important features. 1. If in the transition regime, KIc is defined as the fracture toughness at the onset of the brittle mode of fracture and KIJ is defined as the fracture toughness at the onset of ductile crack growth, then KIc > KIJ. 2. The ductile crack extension obtained between the initiation of ductile crack growth and the onset of brittle fracture is defined by the elastic-plastic crack growth resistance curve. 3. KIc cannot be reached without generating the appropriate amount of ductile crack extension.

It follows that, when performing a failure analysis in this temperature regime, the choice of KIJ as a failure criterion is unnecessarily pessimistic and inconsistant with the choice of KIc as a failure criterion below these temperatures. A procedure is presented which allows the permissible extent of crack growth to be obtained.
An Evaluation of the JR-Curve Method for Fracture Toughness Characterization
Authors: McCabe DE , Landes JD , Ernst HA
Published: March 2009

This program involved the testing of compact specimens made from A508 Class 2A tube plate material. The objective of the program was to study specimen size and plan view dimension effects on the upper-shelf [204°C(400°F)] JR-curve toughness behavior. Low upper-shelf Charpy toughness relative to typical reactor vessel materials was preferred.

The basis material was a 330-cm-diameter (130 in.) by 61-cm-thick (24 in.) slab of tube plate that had been rejected from service after ultrasonic inspection. There was some unwanted variability in strength and toughness properties and a careful specimen sampling plan did not entirely eliminate material variability from the test matrix. Therefore, a dimensional analysis in the form of key curves was used to categorize the material before attempting to decipher specimen geometry effects on the JR-curve behavior. It was then possible to show that specimens of all sizes from 1T to 10T that had equal conditions of constraint would develop the same JR-curve. The principal limitation on small specimens was that they simply lacked sufficient ligament size to sustain crack growth for full JR-curve development.

The omega (ω) criterion was evaluated with the hope of identifying when J—Δap data from specimens with short ligaments could be expected to depart from the specimen-size-independent JR-curve. This was not successful herein from the standpoint that few specimens had sufficiently small ligaments to display this deviation. When deviation did in fact occur, it was not distinctly associated with a given value of ω.

A comparison was made between the load-displacement behavior of two 1T compact specimens having equal Charpy (CVN) toughness and JR-curves but unequal strength properties (88 RB versus 99 RB). This was possible because of uniquely variable metallurgical conditions. The high-hardness specimen showed 40 percent greater load-bearing capacity. This was a good demonstration of why more than just JR-curve behavior should be used to judge the suitability of materials for given applications. Material strength properties are contained in crack drive representations which are curves that are compared with JR-curves. From such comparisons it is possible to predict load versus displacement and crack instability in untested configurations. Hence, part of the material flow property effect is not considered when comparing just JR-curves.
Thickness Effects on the Choice of Fracture Criteria
Authors: Liu HW , Hu W , Kuo AS
Published: March 2009

The stresses and strains in a cracked solid are in a complicated three-dimensional state. There are three two-dimensional limiting cases: plane strain, plane stress, and Dugdale's strip yielding case. The thickness of a plate relative to crack tip plastic zone size determines which one of these three limiting cases is predominant. The characteristics of the plane-stress and the Dugdale strip yielding crack-tip fields were investigated with the moire method together with the finite-element calculations. The state of the crack-tip stress and strain fields approaches that of plane strain for very thick plates. For a very thin plate with a very large crack-tip plastic zone, the Dugdale strip yielding model is applicable, and the crack opening displacement, crack-tip opening displacement, and thickness contraction are related to K or J and they can be used for fracture toughness measurements. When a plate thickness is in between these two extremes, there exists a characteristic plane stress crack-tip field. The correspondence of the planestress crack-tip fields in small-scale yielding and in general yielding was established, and the J value of a small specimen in general yielding can be obtained from the established correspondence. The value of the applied J-field of a small specimen in general yielding can be measured in terms of the applied stress and the specimen elongation.
J-R Curve Characterization of Irradiated Low-Shelf Nuclear Vessel Steels
Authors: Loss FJ , Menke BH , Hiser AL , Watson HE
Published: March 2009

The J-R curve behavior of irradiated nuclear pressure vessel steels is characterized in the ductile upper-shelf regime in order to provide a materials basis with which to assess the margin of safety against fracture for water reactor vessels exhibiting a low upper-shelf CV energy. With the single specimen compliance technique, the R-curve is shown to follow a power-law behavior for small crack extension, and this phenomenon has led to a proposed new indexing procedure forJIc. In addition, a specimen size dependence of the R-curve has been suggested by the results of similar compact tension specimens up to 100 mm thick and which have sufficiently deep side grooves to produce a straight crack-front extension.

R-curve data are presented in terms of a J versus T instability diagram which couples material and structural parameters, thereby permitting an analysis to be made of the margin against failure in terms of J. Also, a correlation has been suggested between the R-curve parameters and CV shelf energy; this could enhance the structural significance of CV reactor surveillance data.
Photoacoustic Spectroscopy of Adsorbed Surface Impurities on Alkali-Halide Laser Windows
Authors: McDavid JM , Yee SS
Published: March 2009

Significant infrared absorption can arise from vapors adsorbed on laser window surfaces during exposure to the atmosphere, during exposure to low-vapor-pressure system components, and during surface passivation or stabilization treatments. The photoacoustic effect has proved to be useful quantitative technique for the measurement of surface optical absorption and, when using a carbon dioxide laser source, provides a sensitivity of a few percent of one monolayer for vapor molecules chemisorbed on highly transparent substrates.

The work reported here involves an application of photoacoustic spectroscopy to surface absorption studies of high power laser window materials. Results are presented for the time dependence of surface absorption during controlled vapor exposure and for the wavelength dependence of surface absorption, in the 9–11 μm range, following atmospheric contamination. The application of these techniques to the determination of adsorption rate constants, activation energies, and the chemical identification of surface impurities is discussed.
Development of Forging Processes for Large-Scale Deformation of Lithium Fluoride
Authors: Vora H , Ready JF
Published: March 2009

Development of forging processes that would permit large-scale deformation of LiF without degradation of its optical properties is required for potential application of this material as an optical element in laser systems generating short intense pulses in the ultraviolet to heat targets for laser fusion. This paper describes forging processes that permit deformation of nearly 90% without introducing internal cloudiness in LiF. Mechanical and optical properties of LiF forged using these processes are also discussed, including the microyield and microcreep at room temperature and the residual absorption in the visible and ultraviolet.
Survey of 1.3 μm Window Materials
Authors: Fernelius NC , Dempsey DV , Walsh DA , O'Quinn DB , Knecht WL
Published: March 2009

The purpose of this work is to screen candidate materials for use in the iodine laser which operates at 1.315 μm. Most of the results presented here are the effective optical absorption, βeff, measured by laser rate calorimetry using a Quantronix Nd:YAG laser modified to operate at 1.319 μm. Spectral transmission scans using the Beckman UV 5270 and Perkin-Elmer 180 spectrophotometers are presented on the less common materials. In the beginning we measured β on materials obtained for CO2, CO and HF-DF laser studies. These included NaCl, KCl, LiF, CaF2, SrF2, Al2O3 (sapphire), ZnSe, Si and GGG (Gd3Ga5O12). At 1.3 μm a number of oxides which were too absorbing to use at the longer wavelengths can be considered. We present results on a variety of commercially available fused silicas, SiO2. Additional results on BaF2, Raytran ZnS, spinels (xMgO·Al2O3), MgO, Barr and Stroud BS37A and BS39B calcium aluminate glasses, CORTRAN 9753 and 9754 glasses, ZBT glass, undoped YLF (LiYF4) and As2S3 will be presented.
Ultrafine Finishing of Ceramics and Metals by Float Polishing
Authors: Namba Y , Tsuwa H
Published: March 2009

This paper deals with a method of finishing ceramics and metals to obtain a high degree of smoothness, and also deals with geometrical, crystallographic, magnetic, optical and chemical properties of finished surfaces. Float polishing is developed to polish many electronic and optical materials ultrafinely without deformed layers. Samples were mechanically polished on a tin lap having fine grooves of concentric circles while in a polishing fluid mixed with the pure water and fine powder. The samples were suspended in the polishing fluid by hydrodynamic phenomena due to the specially shaped tin lap. Very good flatness, excellent retention of edge geometry and extremely small surface roughness of 10ARz were obtained on the finished surfaces of amorphous materials and single crystals. The surface roughness of 20ÅRz were obtained on polycrystalline materials by float polishing using special techniques in order to reduce crystallographic anisotropy.
1.06 μm Laser-Induced Breakdown of CO2-Laser-Polished Fused SiO2
Authors: Temple PA , Soileau MJ
Published: March 2009

Fused silica surfaces have been treated with continuous wave CO2-laser radiation in an improved raster technique. Laser damage data for 1.06-μm, 9-nsec, small-spot irradiation are presented. It is shown that a reasonably sharp transition from laser damage prone to laser damage resistant surfaces takes place over a small CO2-laser power range. The transition to high damage resistance takes place at a silica surface temperature where material flow begins to take place, as evidenced by the onset of residual strain in the CO2-processed part. These data are taken as evidence that microcrack healing is an important mechanism in increased damage resistance in CO2-polished parts. Also presented are data which show that CO2-treated surfaces have a small-spot damage threshold at least as high as the bulk damage threshold of SiO2. In addition, these treated parts show no obvious change in surface appearance, as seen in total internal reflection microscopy. They also show little change in transmissive figure. It is suggested that uniform preheating be used to eliminate the strain presently seen in CO2-treated parts.
Wavelength and Temperature Dependence of the Absolute Reflectance of Metals at Visible and Infrared Wavelengths
Authors: Decker DL , Hodgkin VA
Published: March 2009

This paper presents the wavelength dependence of Ag, Cu, and Al from 4000 Å to 10 μm wavelength. An intercomparison of data is made for surfaces prepared with a variety of techniques, including vacuum evaporation and diamond single-point machining. Briefly described, also, are experimental techniques and apparatus developed at the Naval Weapons Center for measuring temperature-dependent changes in the near-normal incidence reflectance of a sample to a precision of a few parts in 105. Reflectance results obtained from this instrument are presented for films and bulk material over the same wavelength range as above at temperatures from 270 to 450 K. The sample and reference surfaces were protected in ultrahigh vacuum for these measurements.

A theoretical interpretation of results is presented, including both inter- and intraband electron transition effects, as well as extrinsic surface roughness effects. Of much practical interest for laser mirror applications, especially for pulsed mode operation, is the behavior of many metals upon temperature cycling, including hysteresis and time-dependent “annealing” behavior. Similar effects are also observed in both transport and thermal properties and are generally described under the name “premelting effects.”

The data presented in this paper are of immediate engineering value in computing the performance of optical systems whose components necessarily operate at temperatures other than room temperature. It is also hoped that it will stimulate theoretical interest in examining some of the subtle and poorly understood dispersion effects such as those seen in the near-infrared in silver.
Dependence of Metal Mirror Damage Thresholds on Wavelength, Material, Pulse Length, and Preparation Method
Authors: Porteus JO , Decker DL , Seitel SC , Soileau MJ
Published: March 2009

Multithreshold pulsed laser-damage characteristics of precision diamond-machined Cu, Ag, and Au mirrors have been determined at 10.6, 3.8, 2.7, and 1.06 μm. The effect of pulse length has been examined at 10.6 μm by comparing previously reported results obtained using a 100-nsec TEA laser pulse with new results using a 2-μsec pulse from a hybrid TEA laser. The pulse lengths at 3.8 and 2.7 μm are nominally 100 nsec, while that at 1.06 μm is 9 nsec. Spatial intensity distributions are very nearly Gaussian at all wavelengths with e−2 focal spot diameters ranging approximately from 200 μm at 10.6 μm wavelength to 50 μm at the shorter wavelengths. Melt thresholds were calculated from one-dimensional heat flow considerations with a correction for finite focal spot size. Laser waveforms are accurately modeled, and temperature-dependent absorption based on Drude theory is used. Calculated values for Ag are in excellent agreement with experiment, except at 1.06 μm, while calculated values for Cu and Au are in good agreement at 10.6 μm only. An unusually large discrepancy at 3.8 μm suggests a non-Drude-like absorption mechanism that is enhanced by the multipeaked nature of the waveform at this wavelength. Defect-related damage at submelting fluences has also been studied at the longer 10.6-μm pulse length on Cu mirrors representing a variety of preparation methods. Comparative evaluation of damage characteristics has resulted in identification of two new approaches to improving resistance to defect damage.
Epitaxial Regrowth and Defects in Laser Irradiated Single Crystal Ni
Authors: Draper CW , Buene L , Jacobson DC , Poate JM , Nakahara S
Published: March 2009

We have used Q-switched Nd:YAG irradiation to melt surface layers of metallic single crystal nickel. The quality of the epitaxially regrown layers has been determined by Rutherford backscattering and channeling as well as by TEM. TEM shows a high density of extended defects (dislocation tangles and walls). We have also observed significant differences between irradiated <100> and <111> crystals cut from the same Ni boule. One explanation for the orientation dependence is that slip occurs more easily in 111 planes of fcc structures and consequently there is a higher density of defect nucleation centers for 111 liquid phase regrowth.
Optical Damage Limitations for Copper Mirrors Used in CO2-ICF Laser Systems
Authors: Thomas SJ , Phipps CR , Harrison RF
Published: March 2009

Because copper optics for CO2-ICF system applications will be highly stressed, the single-shot damage thresholds which have been reported [1,2], provide only part of the information needed for accurate performance predictions. We report here a performance comparison for copper mirrors finished by different techniques, including single-point diamond turning (SPDT), showing for the first time the relative decrease in 10-μm damage thresholds corresponding to multiple shots, and the loss of reflected beam brightness arising at high fluence levels. We also report the intensity and energy loss due to plasma formation when Cu mirrors are used in air.
Absorption Calorimetry and Laser Induced Damage Threshold Measurements on Germanium and Zinc Selenide
Authors: Foley J , Sharma SK , Wood RM
Published: March 2009

It has been shown that the absorptance of coated and uncoated germanium samples varies with surface state and ambient atmosphere. Absorption measurements made in air are up to 50% higher than identical measurements made under vacuum. The removable surface absorption on germanium has been shown to be due to both hydrocarbon and water layers, depending on the previous cleaning and ambient conditions. The residual surface absorption depends on the surface polishing procedure. Bulk absorption levels as low as 0.007 cm−1 have been measured for freshly cleaned samples. Correlation between the surface condition and the laser induced damage thresholds at 10.6 μm indicates that the damage threshold should be significantly higher in vacuum.

Absorption and laser induced damage threshold measurements have been made on a range of CVD grown ZnSe substrates. Correlation has been shown between the grain size and the direction of measurement and the bulk absorption coefficient.
Insensitivity of the Catastrophic Damage Threshold of Laser Optics to Dust and other Surface Defects
Authors: Bennett HE
Published: March 2009

When laser optics are exposed to continuous radiation or to pulse lengths long enough so that the damage level is determined simply by thermal heating, the mechanisms causing catastrophic damage are fairly clear. In particular, the role of surface defects should be predictable from an analysis of the standing wave pattern at the surface, the optical properties and shape of the defects, and simple heat transfer calculations. The conclusion drawn from such an analysis is that although dust and other surface defects may cause small isolated damage sites to occur, these sites will not grow under continued irradiation and produce catastrophic damage unless the defects exceed a critical diameter or are so closely spaced that they significantly affect the average absorption of the surface. Experimental evidence supports this hypothesis. Dust and other small surface defects are thus acceptable in reasonable concentrations on high power continuous wave laser optics provided that they do not exceed the critical size.
Survey of Damage Thresholds at 532 NM for Production-RUN optical Components
Authors: Deaton TF , Rainer F , Milam D , Smith WL
Published: March 2009

We report the results of a survey of 532-nm, 0.7-ns damage thresholds for a variety of optical components. The optics were all samples from current production runs, which included high-reflector and anti-reflector films, beam dumps, leached AR surfaces, and multiwavelength AR and HR films.

The experiment was similar to the usual 1064-nm damage measurement. The green light pulses were produced by frequency-doubling 1-ns pulses from a Nd:glass laser. The 532-nm beam was then focused to a spot size of about 2 mm diameter at the sample. Beam profiles were recorded on a vidicon and on 1-Z photographic plates.

Thresholds for the AR and HR films were typically 2–5 J/cm2, somehwat lower than might have been expected. Some of the beam dumps damaged at 2 J/cm2. Bare and graded-index surface thresholds were found to be comparable to 1-ns, 1064-nm thresholds.
Laser-Induced Damage in Antireflection Coatings for LiNbO3 Crystals
Authors: Soileau MJ
Published: March 2009

Substrate preparation before coating and coating cleanliness are the dominant factors affecting laser-induced damage to antireflection-coated LiNbO3. Careful control of these factors resulted in an order-of-magnitude improvement in the laser-induced damage threshold.
Multithreshold HF/DF Pulsed Laser Damage Measurements on Evaporated and Sputtered Silicon Films
Authors: Donovan TM , Porteus JO , Seitel SC , Kraatz P
Published: March 2009

Previously, we reported a comparison of damage resistance of various coating materials deposited by vacuum evaporation and measured at 2.7 and 3.8 μm. It was found that Si films fail by a thermal process and, in agreement with other studies, that high-index materials, such as Si, tend to have lower thresholds than low-index dielectric materials, such as NaF, Al2O3, and SiOx, which by comparison are relatively outstanding performers. In this paper, we report results of tests which show that the thresholds of magnetron-deposited sputtered Si films are enhanced over those deposited by vacuum evaporation. The sputtering process leads to lower hydrogen impurity content (100 ppm vs 200 ppm), lower absorption (20 cm−1 vs 40 cm−1), and a factor of two or more enhancement in damage threshold over vacuum-evaporated Si films. Further improvement may be possible by optimization of the sputter-deposition parameters.
Design and Construction of Three Infrared Ellipsometers for Thin-Film Research
Authors: Leonard TA , Loomis J , Harding KG , Scott M
Published: March 2009

The University of Dayton Research Institute (UDRI) has designed and is building three infrared ellipsometers in support of the Air Force high-energy laser program. One of these instruments is a conventional null type elliposmeter for operation in the 3.39 to 4.00 μm wavelength range. Ellipsometric parameters are determined with a precision of 0.01° at any angle of incidence from 20° to 85°. Repeatability and absolute accuracy also approach 0.01° which yields optical constants accurate to 0.1 percent in some cases. All components are mounted on removable carriers for easy interchange, although operation is normally in the PCSA (Polarizer, Compensator, Sample, Analyzer) configuration.

The system software has special provisions for the second instrument which is also a null type ellipsometer dedicated to monitoring vacuum deposited coatings in real time at 3.39 μm. The software can model non-ideal components in the optical path using Jones or Mueller matrices and provide completely corrected data with a single zone measurement after the instrument is characterized. The third instrument is a rotating polarizer, automated ellipsometer tunable from 1 to 12 μm. A dedicated computer operates the instrument and reduces data.
Multilayer Thickness Uniformities Required to Meet Wave Front Error Tolerances in Laser Mirrors
Authors: Bennett HE , Burge DK
Published: March 2009

The wave front error tolerance per mirror in typical laser optical trains is quite severe. Expressed in terms of an equivalent figure error in the visible region, values of an eighth wave are not uncommon for mirrors in infrared systems, and values of one hundredth of a wave have been suggested for mirrors in some ultraviolet laser optical trains. The effect of figure error, i.e., error in the geometrical shape of the mirror, is well known and for a metal-coated mirror is the only one of significance. However, if the mirror has a multilayer dielectric coating, an additional apparent figure error may be introduced by the physical thickness and phase change differences produced by coating thickness nonuniformities. This source of wave front error has been largely unrecognized but can be significant. For example, a 2% variation in thickness uniformity for a typical infrared multilayer coating may create a wave front error at the operating wavelength equal to that produced by a mirror whose optical figure is in error by an eighth wave in the visible. The entire wave front error tolerance for the mirror may thus be used up by a slightly nonuniform coating. Such wave front errors usually cannot be determined unambiguously by interferometric measurements made in the visible region. If multilayer dielectric mirrors are used, the wave front error should thus ideally be measured at the operating wavelength, often a difficult task. A discussion is given of thickness uniformity requirements for dielectric multilayer films and possible ways to achieve this uniformity.
Pulse-Width and Focal-Volume Dependence of Laser-Induced Breakdown
Authors: Van Stryland EW , Soileau MJ , Smirl AL , Williams WE
Published: March 2009

The laser-induced breakdown fields at 1.06 μm of fused SiO2, single-crystal NaCl, and air were measured as a function of focal volume and laser pulse width while keeping all other parameters, including the specimen, constant. The laser pulse width was varied from 40 psec to 31 nsec, and the focal volume was varied by over two orders of magnitude. The dependence of the breakdown field for NaCl and SiO2 on the laser pulse width tp and the focal folume V was empirically determined to be EB = AV−1tp−1/4 + C and the dependence for air to be EB = (AV−1 + C) tp−1/4, where A and C are material-dependent constants. Current theories of laser-induced breakdown are carefully compared with these present measurements and are found to be inconsistent.
Deformation of Intense Laser Beams Tightly Focused Inside NaCl: A Comparison of the Multiphoton-Polaron and Avalanche Models of Optical Breakdown
Authors: Kelly P , Ritchie D , Braunlich P , Schmid A , Bryant GW
Published: March 2009

Computer simulations of the interaction of intense picosecond laser pulses (λ = 532 nm) with NaCl in the focal volume of a 2.54 cm focal length aberration-free lens indicate that severe beam deformation may take place at photon fluxes corresponding to the single-shot damage threshold measured under these experimental conditions. This deformation is the result of a change in the dielectric function which, in turn, is caused by free carriers generated via multiphoton-assisted avalanche ionization and/or multiphoton absorption. Strong self-defocusing prevents local photon fluxes from reaching values required to raise the lattice temperature sufficiently for damage to occur. We conclude that either both the avalanche ionization as well as the multiphoton-polaron absorption mechanisms of laser breakdown are invalid in their present form or that the experimentally determined damage thresholds do not pertain to the intrinsic properties of NaCl.
A Correlation of Laser Damage Vestige Structure and Spherical Aberrations
Authors: Braunlich P , Bryant G , Schmid A
Published: March 2009

Model calculations of spherical aberration effects on Gaussian beam propagation yield spatial intensity variations along the beam propagation direction. These intensity oscillations are compared with experimentally observed damage vestige sequences.
The Role of Laser-Induced Primary Defect Formation in Optical Breakdown of NaCl
Authors: Bräunlich P , Brost G , Schmid A , Kelly P
Published: March 2009

Rapid and efficient formation of primary defects (Vk-, F-1, and H-centers, self-trapped excitons) influences the kinetic processes involved in laser-induced optical breakdown in alkali halides. These processes have been studied for the case of NaCl exposed to short (30 psec to 30 nsec) laser pulses at λ = 532 nm wavelength.

Rapid defect formation acts as a drain on the free electrons and holes, produced by multiphoton absorption in the laser photon field. As a consequence, the rate of temperature increase of the lattice by free or “dressed” carrier absorption is reduced and, thus the damage threshold is increased. This effect is compensated by additional channels of energy deposition to the lattice which are provided by formation of and photon absorption by the generated primary defects.

The net effect of the photochemical processes of primary defect formation is a slight reduction in the damage threshold and a marked decrease of the free carrier densities required for damage to occur. Beam deformation, caused by free-carrier induced changes of the dielectric function, should therefore be less pronounced than that predicted by model calculations of laser damage in the absence of primary defect formation.
Interactions of Intense 2.7 μm Picosecond Laser Pulses with Germanium
Authors: Bryant GW , Schmid A , Braunlich P , Kelly P , Ritchie D
Published: March 2009

Computer simulations of the generation and temporal evolution of hot plasmas in germanium during the passage of intense picosecond laser pulses have been begun. At 2.7μ two-photon absorption is the generating mechanism for carriers. Carrier heating from free-carrier absorption and energy transfer to the lattice through phonon-carrier collisions are described with an electron-hole band model similar to one previously used to describe plasma dynamics in germanium driven by one-photon absorption. Details of this model will be presented and the results available to date will be discussed.
Two-Photon Absorption in Direct-Gap Crystals—An Addendum
Authors: Vaidyanathan A , Guenther AH , Mitra SS
Published: March 2009

An error made in an earlier paper by the authors regarding the appropriate effective masses to be used in calculations employing the Basov formulation is corrected. The new results for two-photon absorption coefficient obtained from the Basov formula now agree quite well with those computed using Keldysh's treatment. Furthermore, it is shown that improved agreement between theoretical and experimental two-photon absorption coefficients is obtained by including non-parabolocity and degeneracy of the energy bands in the calculations.
Three-Photon Absorption in Direct-Gap Crystals
Authors: Judell N , Mitra SS , Vaidyanathan A , Guenther AH
Published: March 2009

Third-order time dependent perturbation theory is used to calculate the three-photon absorption coefficients of several direct-gap crystals. Both parabolic and nonparabolic energy band structures are employed. The intermediate states used in these calculations are the higher energy bands obtained from band structure calculations. The resulting three-photon absorption coefficients have the following frequency dependence. Initially the absorption coefficients increase with increasing energy, until a maximum is reached at a relatively low energy. On further increasing the photon energy the absorption coefficients decrease significantly. The behavior is qualitatively similar to the prediction of the Keldyoh formula, even though the magnitudes of the three-photon absorption coefficients obtained from the two calculations are different. The theoretical results for CdS at 1.06 μm agree well with the experimental data.
Environmentally Affected Near-Threshold Fatigue Crack Growth in Steels
Authors: Suresh S , Toplosky J , Ritchie RO
Published: March 2009

Environmentally affected fatigue crack propagation in steels is described for ultralow growth rates (below 10−6 mm/cycle) in terms of the role of crack surface corrosion debris in promoting crack closure. It is shown that the reported effects of gaseous and aqueous environments (air, water, hydrogen, helium, etc.) on near-threshold crack growth in lower strength steels are consistent primarily with an oxide-induced crack closure mechanism. Moist atmospheres, such as humid air and water, are shown to promote the formation of oxide deposits within the crack, which at low load ratios are thickened by fretting-assisted oxidation to maximum thicknesses comparable with cracktip opening displacements. Using ultrasonic techniques, this is shown to increase closure loads and to lower effective alternating stress intensities at the crack tip. Observations that near-threshold growth in dry helium is similar to that in dry hydrogen gas and faster than in air, are shown to be consistent with such concepts since both environments provide a dry atmosphere limiting oxide formation. Extensive data on near-threshold corrosion-fatigue crack growth in ultrahigh-strength (300-M) and lower-strength (2¼Cr-1Mo and SA516) steels are examined in the context of this mechanism, and it is found that the threshold for no crack growth (ΔKo) is consistent with a maximum excess oxide thickness approximately equal to the pulsating crack-tip displacement (ΔCTOD). The implications of this and other microscopic mechanisms of closure are discussed in the light of microstructural and environmental influences on near-threshold fatigue.
Survey of 1.3 μm Window Materials Continued
Authors: Fernelius NC , Dempsey DV , O'Quinn DB , Gangl ME , Knecht WL
Published: March 2009

The purpose of this work is to screen candidate materials for use in the iodine laser which operates at 1.315 μm. The results presented here are the effective optical absorption coefficient, βeff, measured by laser rate calorimetry using a Quantronix Nd:YAG laser modified to operate at 1.319 μm. Here we extend the measurements reported last year to new materials. These include MgF2, MgO, Kigre Q-98 phosphate glass, YAG (Y3Al5O12), water clear ZnS, CdTe, Schott IRG-N6 CaAl silicate, IRG-7 lead silicate, IRG-9 fluorophosphate glasses, and Hughes HBL glass. Spectral transmission scans using a Beckman 5270 and a Perkin-Elmer 180 spectrophotometer are presented for some of the less common materials. We also take this opportunity to report remeasured absorption values for data reported last year.
Laser Damage of Crystalline Silicon by Multiple 1.06μm, Picosecond Pulses
Authors: Walser RM , Becker MF , Sheng DY
Published: March 2009

Recent studies [1] have shown that the iso-intensity damage kinetics of crystalline silicon irradiated by picosecond 1.06μm pulses could be fit to the equations of classical nucleation and growth. These results suggested that laser damage be viewed as a non-equilibrium phase transition in which the threshold intensity produced excursions across a first order phase boundary into a metastable region of the material phase diagram.

In the present work we discuss a simplified electronic phase diagram for silicon that we believe is relevant to the picosecond damage experiments. The physics of the metastable region are as yet uncertain, but its presence requires that the statistics of laser damage be determined by the activated nucleation of embryos (charge density fluctuations) to near liquid phase charge densities.

The thermodynamic perspective suggests a new laser damage mechanism in which incident photons are resonantly absorbed by the collective electronic oscillations (surface plasmons) of critical embryos. Evidence supporting this mechanism has been obtained from high resolution SEM studies of the damage morphology showing that a coherent radiative interaction occurred between resonant surface plasmon embryos on adjacent sites just prior to liquid-like phase nucleation. Calculations show that the surface plasmon of a spherical embryo with a near liquid charge density of ∼2 × 1022/cm3 is resonantly coupled to the laser photons.
Instrumentation of a Variable Angle Scatterometer
Authors: Stowell WK , Orzio FD , Silva RM
Published: March 2009

The problem of light scatter from optical surfaces is amplified to a critical level for the optics used in Ring Laser Gyros (RLG). Preparation of these optics is slow, laborious and very expensive. Further, the resulting surfaces are very fragile and extremely difficult to handle without damage. These concerns have led to the development of a scatterometer at the RLG Lab, Wright-Patterson AFB, which can detect light scatter from the so-called “supersmooth” optics used in RLG's without first overcoating with metals. A HeNe laser is used to illuminate a 0.5mm diameter spot on the surface of the test mirror or mirror substrate. The incident angle can be varied to accommodate different mirror designs. The test piece can be maneuvered with five degrees of freedom, four of which are computer controlled to facilitate scanning. Scatter measurements are made with a photomultiplier detection system which has a sensitivity of ten parts per billion per steradian. For these optics the standard process for determining substrate surface quality prior to applying the dielectric coatings is to coat the surface with silver and make a scatter measurement. The silver is then removed by etching and the dielectric coatings are applied. Using the scatterometer we have been able to measure surface scatter without first coating the surface with silver. This equipment has yielded evidence that virtually all the techniques now used to characterize these surfaces damage them, including the technique of coating with silver. Subjecting these optics to vibration, thermal cycling, multiple cleaning steps of almost any type and some classes of shipping containers, all seem to attack the Beilby layer in a way that increases the scatter substantially.
Multiple-Shot Ultraviolet Laser Damage Resistance of Nonquarterwave Reflector Designs for 248 nm
Authors: Newnam BE , Foltyn SR , Jolin LJ , Carniglia CK
Published: March 2009

The damage resistance of multilayer dielectric reflectors designed for 248 nm has been substantially increased by use of nonquarterwave (QW) thicknesses for the top few layers. These designs minimize the peak standing-wave electric field in the high-index layers, which have proven to be weaker than the low-index components.

Previous damage tests of infrared- and visible-wavelength reflectors based on these designs have produced variable results. However, at the ultraviolet wavelength of 248 nm, 99% reflectors of Sc2O3, MgF2, and SiO2 strongly demonstrated the merit of non-QW designs. Four sets of reflectors of each of four designs (all QW thickness; one modified-pair substitution; two modified-pair substitution; one modified pair plus an extra half-wave layer of Sc2O3) were tested for damage resistance with a KrF laser operating at 35 pps with a pulsewidth of 8 ns and spot-size diameter of 0.6 mm. Each of 50 sites were irradiated for 1000 shots or until damage occurred.

On the average, the reflectors with one-modified-thickness pair had a 50% higher threshold (10 of 10 sites survived) than the all-quarterwave design. Addition of a second modified-layer pair resulted in no further increase in threshold but the saturation fluence (10 of 10 sites damage) was 110% higher. Reflectors with an additional half-wave of Sc2O3 had lower thresholds of the order of 10% as expected. The thresholds correlated best with the peak-field model, whereas the best model correlating the saturation fluences involved the sum of the upper two scandia layer thicknesses.