bluuebunny/crossref_metadata_2025 huggingface dataset:
Chapter 25—Consideration of the Medical and Health Care Environment: Standards and Clinicians
Authors: Caceres CA , Hanlin DC , Schick JW
Published: March 2009

Clinical effectiveness is an assessment of how well a therapy, protocol, or device achieves its purposes in the clinical environment. Effectiveness of standards should be measured against similar criteria. Factors included in such criteria include cost-effectiveness, clinical benefits, safety, availability, and efficacy.
Large-Diameter Czochralski Silicon Crystal Growth
Authors: Lin W , Hill DW
Published: March 2009

Some practical aspects of the engineering and science of large-diameter crystal growth are presented. Growth characteristics and problems associated with thermal stress and crystal shape are discussed. Oxygen distribution in the melt and its incorporation into the crytal are investigated. Finally, a double-crucible technique is presented and its application to N+ silicon growth is discussed.
Considerations of Resist Processing
Authors: Bowden MJ , Frackoviak J
Published: March 2009

Resist processing is taken here to refer to the variety of steps performed on the resist pursuant to defect-free pattern delineation. These processing steps include spin coating, pre-baking, exposure, post-exposure curing, development, and post-development treatment (post-baking, plasma de-scumming, etc.). Not all of these processing steps are necessarily performed, since the particular processing steps chosen, together with their operational sequence, are dictated by the chemical and physical properties of the resist. This paper discusses some of the considerations pertinent to process optimization of several electron resists and shows how processing relates to sensitivity, resolution, and defect levels.
Reduced-Pressure Chemical Vapor Deposition of Polycrystalline Silicon
Authors: Hammond ML
Published: March 2009

The practice of depositing polycrystalline silicon by low-pressure chemical vapor deposition (LPCVD) is discussed in terms of effect of deposition parameters on structural property relationships. Electrical and oxidation properties are also discussed.
Plasma-Enhanced Chemical Vapor Deposition of Silicon and Silicon-Containing Films
Authors: Hess DW
Published: March 2009

The use of a radio frequency (rf) glow discharge or plasma has recently come into favor for the deposition of thin films. In plasma-enhanced chemical vapor deposition (PECVD), chemical reactions can be carried out at low (<300°C) temperatures, since the energy needed to break chemical bonds is supplied by the high-energy electrons generated by the applied rf field. Further, due to the complex chemistry occurring within the glow discharge, materials with unique properties can be fabricated. This paper reviews the characteristics of nonequilibrium glow discharges as used for PECVD of silicon and silicon-containing films. The glow-discharge-modified chemistry of film deposition is discussed as it relates to the physical and chemical properties of the resulting films. Examples include amorphous and single-crystal silicon films, as well as silicon dioxide and silicon nitride films, which are widely used as intermetallic and passivation layers in integrated circuit manufacture.
Process Technology Requirements for VLSIC Fabrication
Authors: Kumar R , Nowak MM , Tyler EH , Vinson MA
Published: March 2009

The fabrication of high-density, high-performance integrated circuits to provide a lower cost per function requires N-channel metal-oxide-semiconductor (NMOS) circuits with smaller minimum dimensions, thinner gate oxides, and shallower junction depths. This paper provides an overview of process technology constraints and requirements for the fabrication of scaled NMOS very-large-scale integrated circuits (VLSICs). Devices with shallow junction depths are required to minimize short channel effects in such VLSICs; this places numerous constraints on processing. These constraints require low-temperature processing and cause several deviations from present production processing techniques. We shall review some solutions to these constraints, especially in the junction formation and low pressure chemical vapor deposition areas.
Temperature-Dependent Infrared Characterization of Silicon Wafers
Authors: Mead DG , Gummer RM , Anderson CR
Published: March 2009

The use of infrared measurements to characterize impurities in doped semiconducting silicon wafers at room and low temperatures is reviewed. Examples include the detection of antimony, arsenic, boron, phosphorus, carbon, and oxygen impurities; the spectral features of these elements are qualitatively discussed. In particular, the design and implementation of a cryostat suitable as an accessory to an infrared interferometer for nondestructive characterization of large-diameter silicon wafers at liquid nitrogen and liquid helium temperatures are also given.
Automated Detection of Wafer Surface Defects by Laser Scanning
Authors: Galbraith LK
Published: March 2009

Several systems are presently being marketed that automatically detect and map surface defects on unpatterned wafers by means of light scattering. Applications of these wafer inspection systems in process control and incoming inspection are described. Systems based on scanned laser beams, discussed here in detail, have considerably higher dynamic range and give more reproducible results with non-isotropically-scattering defects than systems using television cameras.
Ductile Fracture of Circumferentially Cracked Pipes Subjected to Bending Loads
Authors: Zahoor A , Kanninen MF
Published: March 2009

A plastic fracture mechanics methodology is presented for part-through cracks in pipes under bending. A previous analysis result on the behavior of part-through cracks in pipes is reviewed. Example quantitative results for the initiation and instability of radial growth of part-through cracks are presented and compared with the experimental data to demonstrate the applicability of the method. The analyses in our previous work are further developed to include the instability of circumferential growth of part-through cracks. Numerical results are then presented for a compliant piping system, under displacement controlled bending, which focus on (1) instability of radial growth (unstable wall breakthrough) and (2) instability of circumferential growth of the resulting through-the-thickness crack. The combined results of the above two types of analyses are presented on a safety assessment diagram. This diagram defines a curve of critical combination of length and depth of part-through cracks which delineates leak from fracture. The effect of piping compliance on the leak-before-break assessment is discussed.
JR-Curve Testing of Large Compact Specimens
Authors: McCabe DE , Landes JD
Published: March 2009

This paper describes experiences and special testing techniques applied to JR-curve development using compact specimens ranging in size by factors up to 20. All specimens were 20 percent side-grooved. The material used was A508 Class 2A and the tests were made at 477 K (400°F). Unloading compliance was used to measure crack growth and a special displacement measuring gage having high sensitivity and linearity was developed to detect minute compliance changes of the order of 0.1 percent. High-temperature creep effects were present but these were readily eliminated from interfering with unloading compliance precision by prior partial unloading to below the creep deformation range. Crack growth was calculated using a differential compliance formula and was usually predicted accurately within ±15 percent of the heat tint indicated growth. This was generally true over a wide range of specimen sizes and initial crack sizes.

An example JR-curve comparison is given, comparing small-specimen versus large-specimen data. Deviation from a common JR-curve develops when Δap ⩾ 0.06 b0, where b0 is the initial specimen ligament size. For the smallest specimen data, a modified J calculation was applied which reestablishes comparability between large- versus small-specimen JR data, and this can be maintained over crack growth that represents a substantial ligament size change.
Evaluation of the Elastic-Plastic Fracture Mechanics Methodology on the Basis of Large-Scale Specimens
Authors: Kussmaul K , Issler L
Published: March 2009

Within the scope of the cooperative project “Integrity of Components” (FKS) which is a part of the German Nuclear Safety Research Programme of the Federal Minister for Research and Technology, the theoretical and experimental investigation on ductile fracture is of decisive importance. The FKS is mainly concentrated on tearing tests on large-scale heavy-section specimens, in both the base material and welded conditions. Universal facilities up to 100 MN are available to test large-scale round and flat bars containing sharp defects in the form of machined notches, fatigue cracks, and natural flaws, such as segregation and heat-affected zone cracking. The dimensions are chosen so that it is possible to realize the significant technological states of material and stress over all conditions in the light-water reactor pressure vessel. The tested materials similar to A508 Class 2 and 3 cover a wide range of ductility (Cv upper-shelf toughness-40 to 200 J, crack initiation Ji = 50 to 200 kN/m, T-modulus = 10 to 300).
Computer-Controlled Single-Specimen J-Test
Authors: Van Der Sluys WA , Futato RJ
Published: March 2009

The development of a computer-controlled single-specimen J-test procedure is described. The results of a sensitivity study to determine the effect of analog-to-digital converter resolution and transducer signal noise on elastic unloading compliance crack length measurements are presented. The results are used to estimate the minimum equipment performance specifications needed for successful J-test automation. The actual test system is described along with the details of the automated procedure.

A comparison is made between results obtained using the automated procedure and the more conventional heat-tinting technique for HY-130 at room temperature (tested as part of the American Society for Testing and Materials J-Integral R-Curve Round Robin Program) and nuclear pressure vessel grade steels at 200 to 290°C. Good agreement in the generation of J-Δa data was found in all cases. However, some difficulty was encountered in predicting absolute crack lengths by compliance in the round-robin tests, apparently due to specimen design.
Specimen Geometry and Extended Crack Growth Effects on JI-R Curve Characteristics for HY-130 and ASTM A533B Steels
Authors: Davis DA , Vassilaros MG , Gudas JP
Published: March 2009

An evaluation of the ductile fracture toughness and JIR curve properties of HY-130 and ASTM A533B-HSST-03 steels in response to systematic variations of thickness and crack length in the side-grooved compact specimen geometry was carried out. A series of 2T compact specimens was produced to varying thicknesses, and with various fatigue crack lengths. Elastic compliance JI-R curve tests were performed, and analyses ofJIc, the slope of the JIR curve, the accuracy of the Ernst-Paris-Landes approximation for JI and an assessment of the ω criterion for J-controlled crack growth were carried out. Results showed that JIc of both steels was geometry independent when validity criteria were met. Both steels displayed a clear dependence of the slope of the JI-R curve as related to thickness/ligament ratio and degree of crack extension. A limiting thickness/ ligament ratio of 1 is necessary to ensure a conservative JIR curve slope over the full range of crack growth. The Ernst-Paris-Landes expression was shown to accurately describe JI to crack extension values of 0.4 b0 for HY-130 steel. Limited evidence suggests that a minimum value of ω to guarantee J-controlled crack growth with compact specimens in HY-130 steel is 2.
Studies of Different Criteria for Crack Growth Instability in Ductile Materials
Authors: Kaiser S , Carlsson AJ
Published: March 2009

A general instability condition of solid mechanics, valid for a nonlinear structural component in an otherwise elastic system, is shown to be inherent in the T-modulus concept of instability. This condition involves the slope of the descending part of the load-displacement curve of the nonlinear component. It is shown that this slope can be used to evaluate T appl at instability; Tappl can then be used to give a simple estimation of Tmat without the need for exact crack length determination.

In this paper such evaluations for large panel specimens and smaller bend and CT specimens are reported for three structural steels. The obtained data are in good agreement with conventionally determined data. However T-evaluations for tension-type specimens give values which are higher by a factor of two than those calculated for bendtype specimens. This indicates that T is not geometry independent, but that T from bend and CT specimens gives a lower bound.

A method is discussed of analyzing the instability of a large structure with a cracked, ductile component using the slope of the load-displacement curve and the general instability criteria of mechanics without recourse to fracture parameters.
An Elastic-Plastic Fracture Mechanics Study of Crack Initiation in 316 Stainless Steel
Authors: Davies PH
Published: March 2009

An experimental study of crack initiation in solution-treated 316 stainless steel was undertaken to test the validity of the elastic-plastic fracture mechanics parameters, J and crack opening displacement (COD), in the presence of extensive yield. Measurements of the J-integral are obtained for 6.4 to 25-mm-thick compact specimens using the proposed ASTM equation. The latter is shown to give results within 2 percent of those obtained using the original calibration method of Begley and Landes. However, deviations from the proposed crack blunting line, J = 2σfΔa are found for this high work-hardening material. Midsection COD is also determined using a rubber infiltration technique. Critical values of the J-integral and COD at crack initiation are shown to be constant independent of plate thickness under plane-strain and non-plane-strain crack-tip conditions as defined by B = 25 to 50 (Ji/σf) and B = 25 CODi. These results are supported by measurements of the surface crack-tip contraction.
Micromechanisms of Ductile Stable Crack Growth in Nuclear Pressure Vessel Steels
Authors: Belcher WPA , Druce SG
Published: March 2009

The objective of this work was to investigate the relationship between the micromechanisms of ductile crack growth, the microstructural constituent phases present in nuclear pressure vessel steel, and the observed fracture behavior as determined by impact and fracture mechanics tests.

Results from a microstructural and mechanical property comparison of an A508 Class 3 pressurized water reactor nozzle forging cutout and a 150-mm-thick A533B Class 1 plate are reported. The variation of upper-shelf toughness between the two steels and its orientation sensitivity are discussed on the basis of inclusion and precipitate distributions. Inclusion clusters in A533B, deformed to elongated disks in the rolling plane, have a profound effect on short transverse fracture properties.

Data derived using the multi-specimen J-integral method to characterize the initiation of ductile crack extension and resistance to stable crack growth are compared with equivalent Charpy results. Results of the JR-curve analyses indicate (1) that the A533B short transverse crack growth resistance is approximately half that observed from transverse and longitudinal specimen orientations, and (2) that the A508 initiation toughness and resistance to stable crack growth are insensitive to position through the forging wall, and are higher than exhibited by A533B at any orientation in the midthickness position.
Ductile Fracture with Serrations in AISI 310S Stainless Steel at Liquid Helium Temperature
Authors: Tobler RL
Published: March 2009

Fracture toughness tests were performed on annealed austenitic stainless steel AISI 310S, immersed in liquid helium at 4 K, using 25-mm-thick compact specimens. The JIc results (360 to 380 kJ/m2) from single- and multiple-specimen test techniques are compared and shown to be in close agreement. Attention is called to the remarkable failure process of this steel at 4 K: Crack extension occurs by ductile tearing, while the test records exhibit serrations due to repeated bursts of unstable plastic flow and arrests. The nature of this behavior is discussed, and the performance of stable austenitic AISI 310S is compared with that of related steels, including those that transform from austenite to martensite during testing at 4 K.
Photoacoustic Measurement of Nonlinear Absorption in Solids
Authors: Van Stryland EW , Woodall MA
Published: March 2009

The photoacoustic technique, using a piezoelectric transducer to detect acoustic signals induced in semiconductors by the absorption of light, has been used to measure two-photon absorption. The transducer signal amplitude is directly proportional to the absorbed energy from all absorption processes, nonlinear as well as linear. This signal was monitored as a function of the intensity of single, picosecond, 1.06 μm, pulses. At high intensities, beam depletion was observed, and a direct comparison was made with the sample transmission. The sensitivity of this technique allows nonlinear absorption to be measured at intensities significantly lower than when using transmission. In addition, the advantage of the nonlinear photoacoustic technique over the recently described calorimetric technique is that powerful signal averaging techniques can be used. This is because the absorption at a given intensity can be determined by a single pulse in a few microseconds while calorimetry requires at the least several seconds.
1.3 μm Laser Rate Calorimetry and Photoacoustic Studies of the Surface and Bulk Optical Absorption in CaF2 Single Crystal Samples
Authors: Fernelius NC , Dempsey DV , O'Quinn DB
Published: March 2009

There are a variety of techniques for measuring the surface-to-bulk optical absorption ratio most of which require specially prepared samples. In most works only one technique was employed on a given sample. In this work we tried three different techniques to measure the surface-to-bulk optical absorption ratio, r, at 1.3 μm on a group of similar CaF2 single crystal samples. Laser rate calorimetry results on a series of samples of varying thickness gave r = βS/βB = 0.14 cm where βS is the surface absorption and βB is the bulk optical absorption in cm−1. A second slope was not seen on the long bar samples which implies that r is less than 0.3 cm. Analysis of photoacoustic chopping frequency variation studies using the Bennett-Forman theory gave r = 0.07 cm about half the multithickness result. Considering the experimental uncertainties all three technique yielded consistent results.
Internal Damage to Optical Glasses with 3 ns-Pulse Laser
Authors: Hack H , Neuroth N
Published: March 2009

The beam of a 3 ns pulse laser (1060 nm) is focussed with a convex lense with 1,1 m focal length. The glass sample to be tested is 20 mm thick: its rear surface has a distance of 100 mm from the focus. The part of the sample which will be shot is illuminated with a Xenon lamp and inspected with a microscope with four fold magnification before and after the shot. In each case a photo is taken.

Two types of internal damage are to be recognized: pointlike damage and threadlike damage. Some glass types show only pointlike damage, even at higher energies (applied energy densities up to 65 J/cm2); other glass types show only threadlike damage caused by self-focussing (dependent to the n2-value). In the most cases both damage types occur but at different levels of energy densities. In BK 1 and BK 7 glass no internal damage is to be seen when applying energy densities up to 65 J/cm2.
Material Property Requirements for Laser Windows
Authors: Glassman AT
Published: March 2009

Systems designers and theoreticians require reliable matrial properties—the designer to make informed selections of window materials, and the theoretician as input to his performance models and figure of merit calculations. The information is not always available, however, because (a) some measurements are difficult to make and exist for only a few selected materials; (b) stable lasers have not been readily available for use in making measurements, etc. at all wavelengths of interest. This paper indicates some gaps in material properties relevant to windows and gives directions for future experimental work, based on a literature search to compile data on candidate materials for infrared windows.

The types of gaps in material properties are illustrated by constructing a three-dimensional matrix of values, pointing out areas for future work. Data availability for many materials of interest is given.

Material properties for materials of interest are tabulated.
A New Photographic Technique for Observing Bulk Laser Damage
Authors: Thomas N , Sonderman J , Stokowski S , Wallerstein P , Walmer D
Published: March 2009

A damage site camera was developed to record the onset of bulk laser damage in materials. The camera images and magnifies the damage track using forward-scattered laser light. Employing this camera we can detect the presence of very small (<10 μm) damage sites with densities as low as 10/cc. The camera is used at oblique incidence.

We have observed discrete damage sites generated within the bulk of some materials, such as silicate glass, fluorophosphate glass, and KDP crystals, by 1-ns, 1064-nm laser pulses. The energy fluxes at which bulk damage is initiated are in the range of 2 to 20 J/cm2, much lower than the fluxes required to cause damage by intrinsic processes. Small foreign inclusions (<1 μm diameter) are the cause of these low bulk damage thresholds. The inclusion density varies from 107/cc to less than 10/cc. At threshold the damaged volumes are small (1–5 μm in diameter) and thus, can be observed most easily by their forward-scattered light.

Several photographs are shown to illustrate the onset of bulk laser damage in fluorophosphate glass and KDP crystals.
Regrowth in Laser Irradiated Elemental Metals and Alloys: Surface Nonuniformities and Coupling Phenomena
Authors: Draper CW
Published: March 2009

The last half dozen years have seen a rapid growth in research on the effects of laser surface melting (LSM) and rapid self quenching on metallic systems. Modification of surface sensitive behavior has been demonstrated in a number of alloys systems. Even more recently there has been a renewed interest in laser surface alloying (LSA)—the melting/rapid quenching of predeposited film plus metal substrate.

The coupling process between metallic surface and focussed beam is sensitive to pre-irradiation surface quality. The resulting LSM or LSA area may be uniform as a result of controlled processing, or very nonuniform due to local variations in the coupling phenomena. Four categories are identified as the major causes for nonuniformities: topographical inhomogeneities, structural/chemical inhomogeneities, impurity effects and interference effects. If LSM or LSA processing is to move out of the laboratory and into the real world the significant of these differences will have to be addressed.
Pulsed Laser Initiation of Surface Plasma on Metal Mirrors
Authors: Musal HM
Published: March 2009

Plasma formation at the surface of a metal mirror under intense pulsed laser irradiation in an ambient atmosphere usually leads to enhanced thermal and mechanical coupling with consequently increased surface damage.

Exo-electron emission associated with plastic micro-yielding of the metal surface under thermomechanical stress induced by a surface temperature rise (ΔT) is proposed here as a plasma initiation mechanism. Emission starts when ΔT exceeds a relatively small critical value. Rapid buildup of the plasma proceeds via nonequilibrium ionization cascade in the ambient atmosphere when the incident laser flux exceeds a threshold value. Formation of a highly absorbing plasma layer requires delivery of a minimum fluence while the incident flux is higher than the above-mentioned flux threshold. At high values of incident flux, the required fluence decreases to an asymptotic minimum.

The critical temperature rise, threshold flux, and asymptotic minimum fluence required for surface plasma formation are defined here in terms of the pertinent radiation, material, and atmosphere parameters.
Evaluation of Bichromatic Coatings Designed for Pulsed Laser Fusion Applications at 0.53 and 1.06 Micrometers
Authors: Wirtenson GR , Willis JB , Enemark EA
Published: March 2009

Various bichromatic coatings designed to operate at both 0.53 and 1.06 micrometers have been evaluated for spectral performance and laser damage threshold to determine the suitability of these coatings for 1 nanosecond pulse laser fusion experiments and to establish baseline data. Anti-reflection, partially transmitting high reflection, and maximum reflection coatings, consisting of titania and silica layers, were deposited onto BK-7 substrates. For each type of coating, two different designs were examined. Spectral measurements indicate the coatings met performance goals. Laser damage threshold values at 1.06 micrometers were similar to those of previous monochromatic production coatings, while damage levels at 0.53 micrometers were about one-half these 1.06 micrometer values.
Ion-Beam Deposited Ge-As-Se Glass For Applications in the 1μ to 16μ Wavelength Region
Authors: Herrmann WC , McNeil JR
Published: March 2009

We have investigated application of Ge-As-Se glass as an optical coating material for use in the 1μ to 16μ wavelength region. Thin films of the material have demonstrated the following desirable characteristics: low absorption over the wavelength region of 1μ to 16μ; low inherent stress; amorphous, homogeneous structure. Laser damage tests have been performed at 1.06μ and 10.6μ. Interpretation and results of the damage tests are discussed. The films are robust and resistant to attack by HF.

The deposition technique employed ion beams to pre-clean the substrate and to deposit the Ge-As-Se material. Deposition was a hybrid process, with coating material initially being sputtered by the ion beam and subsequently being generated thermally due to target heating by the ion beam. Thus the advantages of sputter deposition are realized during initial stages of film growth, and faster deposition rates can then be achieved using thermal generation. Films of Ge-As-Se in excess of 100μ thick have been easily deposited, and a variety of materials has been used as substrates. This same sputter-thermal technique has been applied to other thin film materials.
On Self-Focusing and Spot-Size Dependence of Laser-Induced Breakdown
Authors: Soileau MJ , Franck JB , Veatch TC
Published: March 2009

The laser-induced breakdown power (PB) was measured for various neat liquids and various combinations of miscible liquids. PB for the neat liquids and the mixtures was found to be proportional to 1/n2 (n2 is the nonlinear index of refraction). From this result, we conclude that self-focusing dominates the breakdown process for these liquids (CS2, benzene, nitrobenzene, chlorobenzene, bromobenzene, and toulene). The dependence of PB for the neat liquids and mixtures on the f-number of the focusing optics was then measured and found to be in excellent agreement with the predictions of self-focusing theory for liquids with large n2's. The liquids were then used as a “model system” to compare the results of similar measurements in single-crystal NaCl. This comparison indicates that the observed focal spot-size dependence in NaCl is not due to self-focusing.
The High Frequency Electron Scattering Rate and Drude Zener Theory in Compound Semiconductors
Authors: Jensen B
Published: March 2009

Recent advances in laser and semiconductor device technology have generated a growing concern over the validity of the standard transport theory in the limit of small length scales, high frequencies, and high field intensities. This has necessitated a reexamination of the foundations of transport theory and the necessary quantum extension in these limits. In this paper, the response of free carriers in a polar semiconductor to a high frequency electric field is examined. A frequency dependent relaxation time has been derived for free carriers in polar semiconducting compounds with the band structure of the Kane theory from a quantum extension of the Boltzmann transport equation. The expression obtained reduces to the usual quasiclassical Boltzmann result in the limit of low frequencies, elastic scattering mechanisms, and parabolic bands, and gives the quantum result at high frequencies when used in the Drude Zener formula for the optical conductivity. A high frequency extension of the Drude theory is thus obtained which gives the observed λ3 dependence of the absorption coefficient characteristic of polar scattering in III–V and II–VI compounds in the near infrared, and reduces to the usual λ2 dependence at sufficiently low frequencies. At high intensities, the scattering rate becomes a function of field intensity.

Numerical results for the electron scattering rate are calculated as functions of frequency and carrier concentration and compared with available experimental data for a number of III–V compounds.
Band Structure Calculations of the Two-Photon Absorption Coefficients of GaAs, InP, CdTe, and ZnSe
Authors: Vaidyanathan A , Guenther AH , Mitra SS
Published: March 2009

The two-photon absorption coefficients of crystalline GaAs, InP, CdTe and ZnSe at 1.064 μm and 0.694 μm are calculated by means of a new model which combines the elements of second order perturbation thoery and band structure calculations. A sufficient number of intermediate states are included to assure adequate convergence. This calculational procedure is shown to represent a significant improvement over currently available theoretical models, and the results are in good agreement with available experimental data.
Theory of Nonlinear Beam Propagation in Optical Waveguides
Authors: Bendow B , Gianino PD , Tzoar N
Published: March 2009

We analyze the effect of transverse inhomogeneity on nonlinear beam propagation in a dielectric medium. Specifically, we consider the propagation of both CW beams and pulses in optical waveguides possessing a real nonlinear refractive index of the form n=n1 (¯r,ω) + n2|E|2. The CW problem is treated within the paraxial approximation, for the case of a Gaussian beam incident on-axis. For powers lower than the homogeneous medium critical power, waveguiding dominates, and the beam focal parameter, although altered quantitatively, continues to vary sinusoidally as a function of distance as in the linear waveguide case, with a spectral period independent of the nonlinearity. Above the critical power, however, waveguiding is superceded and nonlinearity dominates. The beam becomes unstable, and displays oscillatory focussing in a fashion which is very similar to self-focussing in homogeneous media. Our pulse propagation studies employ a rather different starting point, based on the slowly varying envelope approximation and involving an averaging over the transverse coordinates. Our principal objective is to determine the conditions for undistorted pulse propagation, i.e., the existence of optical solitons. We obtain the equations governing the existence of solitons and find that they differ significantly from those for the homogeneous medium case. In particular, while “bright” soliton propagation is restricted to the anomolous dispersion regime in homogeneous media, in waveguides it is possible to propagate “bright” solitons in regimes of normal dispersion as well.
Transient Model I and Mixed-Mode Stress-Intensity Factors During Elastic Crack-Wave Interaction
Authors: Rossmanith HP , Shukla A
Published: March 2009

A detailed experimental photoelastic investigation of the history of dynamic Mode I and apparent mixed-mode stress-intensity factor during the passage of elastic stress waves over the crack tip is presented. Experimental recordings of isochromatic fringe pattern about static and moving crack tips permit the determination of the history of the complex stress-intensity factor K = K1 − iK2 which is associated with a mixed-mode crack stress loading.

A first cracking time and a first branching time problem is formulated for stationary and moving cracks. The dependence of the local state of stress at the crack tip on the rate of change of the overall stress field is discussed.
Stress Intensity and Fatigue Crack Growth in a Pressurized, Autofrettaged Thick Cylinder
Authors: Parker AP , Underwood JH , Throop JF , Andrasic CP
Published: March 2009

Stress-intensity factors are determined using the modified mapping collocation (MMC) method for a single, radial, straight-fronted crack in a thick cylindrical tube that has been subjected to full autofrettage treatment (100 percent overstrain). By superposition of these results and existing solutions, stress-intensity factors are determined for the same geometry with internal pressure and any amount of overstrain from 0 to 100 percent.

Correction factors for crack shape and nonideal material yielding are determined from various sources for the pressurized, autofrettaged tubes containing semielliptical cracks. These results are employed in the life prediction of pressurized thick tubes with straight-fronted and semicircular cracks, for various amounts of autofrettage. Experimentally determined lifetimes for tubes having 0 and 30 percent nominal overstrain are significantly greater than the predictions for both straight-fronted and semicircular cracks. This is related to multiple initiation and early growth of cracks from the notch.

Experimentally determined lifetimes for a tube with 60 percent nominal overstrain are somewhat less than predicted. This effect is partially explained by additional experimental work, which shows that the angle of opening of rings cut from autofrettaged tubes is somewhat less than the ideal predictions. The latter effect is attributed to the Bauschinger effect and the associated reduced yield strength in compression during the unloading of tubes during the autofrettage process.
A Review of Generalized Failure Criteria Based on the Plastic Yield Strip Model
Authors: de Wit R
Published: March 2009

A review is given of the failure criteria developed by Hahn and Sarrate for through-cracked pressure vessels, whereby they established three failure categories. This work was based on the Dugdale and Bilby-Cottrell-Swinden (D-BCS) model for the crack-tip opening displacement (CTOD) in an infinite plate. The model was extended in an approximate way by Heald-Spink-Worthington (D-BCS-HSW) to finite geometries and structures by combining the effects of plasticity and geometry as multiplicative factors. In this paper the criteria of Hahn and Sarrate are extended to the D-BCS-HSW model. The three failure categories are relabelled: (1) linear-elastic fracture mechanics (LEFM), (2) elastic-plastic fracture mechanics (EPFM), and (3) plastic collapse (PC). The model is plotted in a variety of dimensionless forms and several related developments also are reviewed: (1) the two-criteria approach and universal failure curve, (2) the CTOD design curve, and (3) the Failure Assessment Diagram. Finally, the residual strength diagram for the D-BCS-HSW model is presented. In all these presentations the three failure categories based on Hahn and Sarrate's criteria are included. Thus, it is shown that the D-BCS-HSW model, though approximate, presents a unified picture that embodies many features of fracture mechanics from LEFM through EPFM to PC.
Influence of Specimen Size and Stress Field on Energy Loss During a Fracture Event
Authors: Shukla A , Fourney WL
Published: March 2009

The influence of specimen size and stress field on energy loss away from the crack tip was studied using dynamic photoelasticity and fracture mechanics. The method of analysis utilized a balance of energy in the system. Experiments were conducted with three different sizes of modified compact tension (MCT) specimens, and it was found that energy loss increased with specimen size. Energy loss increased from 34 percent of total available energy to 48 percent as the specimen size was doubled.

The influence of stress field on energy loss was modelled by using different starter crack lengths in MCT specimens. It was observed that energy loss as well as crack propagation behavior are dependent on the stress field into which the crack propagates.
Theoretical Fracture Resistance of Particle-Hardened Brittle Solids
Authors: Gavigan TH , Queeney RA
Published: March 2009

The addition of dispersions of relatively stiff particulates to brittle materials is recognized to increase their fracture resistance as measured with conventional fracture mechanics parameters. Extant analytical models address the problem of particle hardening indirectly. One class of predictions is essentially a rule-of-mixtures approach and is of limited success in predicting particle strengthening. Another predictive model hypothesizes the existence of a line tension associated with the bowing of the crack front line as the crack front encounters particulates on the plane of crack extension; however, this approach fails to predict the measured effects of particle stiffness and particle size. The present analytical model deals directly with the extensibility of a crack on a plane containing particulates of an average size, spacing and stiffness. The elastic strain energy associated with the particulate field is calculated and compared to the energy of the non-particle-containing matrix. The strain energy release rate then is examined for unstable crack extension in the particle-hardened matrix, and the fracture resistance of the composite is compared to that of the plain matrix. The predictions are used to examine experimental data previously generated, and the model is found to be satisfactorily accurate in predicting changes in fracture resistance as particulate character is manipulated.
Multispectral Chemically Vapor-Deposited ZnS: An Initial Characterization
Authors: Williangham C , Klein C , Pappis J
Published: March 2009

Standard-grade chemically vapor-deposited (CVD) ZnS has a dark orange, yellow milky appearance and exhibits a substantial amount of scatter in the near infrared, which limits its usefulness at the shorter wavelengths. Recently, we have succeeded in developing a “multispectral” CVD-ZnS material configuration, which is colorless and shows evidence of much improved transmittance throughout the spectral range of interest. In this paper, we report on work that has been carried out in the context of assessing the properties of this material, particularly with regard to (a) Infrared absorption. Thermocouple calorimetry measurements conducted at 1.3, 2.7, and 3.8 μm indicate that multispectral CVD Zns has effective absorption coefficients of 1 × 10−3cm−1 or less, thus establishing this material as a credible candidate for chemical-laser window applications. (b) Elastic behavior. Measurements of Young's modulus (87.6 GPa) and Poisson's ratio (0.318) in conjunction with sound-velocity measurements in the longitudinal mode (5.47 km/sec) demonstrate that multispectral CVD ZnS behaves precisely as predicted for a randomly-oriented single-phase polycrystalline aggregate of cubic ZnS. (c) Fracture mechanics. The results of Knoop hardness, flexural strength, and laser-damage experiments will be presented; we will also discuss techniques for improving the fracture toughness.
Surface-to-Bulk Optical Absorption on Uncoated Sapphire and Zinc Selenide Using Photoacoustic Chopping Frequency Studies
Authors: Fernelius NC
Published: March 2009

Experimental photoacoustic (PA) signal amplitude and phase angle data were taken on uncoated CVD ZnSe at 10.6 μm and on (0001) oriented single crystal sapphire (Al2O3) at 1.3 μm. The data were interpreted using the Rosencwaig-Gersho theory, the McDonald-Wetsel composite-piston model and the Bennett-Forman theory. A modified version of the Rosencwaig-Gersho theory was developed which explicitly incorporates surface absorption. It was also applied to these cases. Comparisons are made with some multithickness sample studies on related materials.
Calorimetric Measurement of Temperature Dependent Absorption in Copper
Authors: Quimby RS , Bass M , Liou L
Published: March 2009

This paper reports the temperature dependence of optical absorption in copper as measured by laser rate calorimetry. It is found that the measured values of the temperature dependence agree well with the predictions of the simple Drude theory for wavelengths of 10.6 μm and 1.08 μm. At 0.647 μm the temperature dependence is stronger, due to the effect of interband transitions. Absolute values of the absorptance are measured to be somewhat higher than predicted by the simple Drude theory, indicating the importance of the anomalous skin effect and possibly other absorption mechanisms. After cycling to a temperature of 200°C or greater, a permanent increase in the room temperature absorptance is observed. This increased absorption is pronounced at 1.08 μm and 0.647 μm, whereas it is not observable at 10.6 μm. The permanent change is correlated with a change in the observed microstructure of the surface.
Reversible and Irreversible Changes in NaCl and KCl Absorption During Multiple Pulse 10.6 μm Irradiation
Authors: Wu S-T , Bass M , Stone JP
Published: March 2009

Repetitively pulsed laser calorimetry was used to detect both reversible and irreversible increases in the 10.6 μm absorption of NaCl and KCl. The irreversible changes are first noted at the same intensity that is found to cause damage after multiple irradiations. Just below this intensity damage is not detected even after ∼1800 pulses. As a result of this work, a redefinition of the fatigue threshold is necessary as it must be distinguished from the breakdown damage threshold studied in earlier research.
Polarization Monitor For Thin Film Depositions
Authors: Tirri B
Published: March 2009

An automatic ellipsometer has been designed, fabricated and integrated into a large vacuum chamber to monitor the deposition of multilayer phase retarders. This technique offers several advantages over conventional monitoring techniques. Precise control of the phase retardance properties of multilayer coatings is possible due to the sensitivity of the ellipsometric parameters Δ and ψ to the changes in film thickness. Phase measurements of several multilayer coating designs deposited using this monitoring technique are presented.
Cavity Phase Shift Method For High Reflectance Measurements
Authors: Kwok MA , Herbelin JM , Ueunten RH , Segal GI
Published: March 2009

The cavity phase shift method can measure high reflectances on spherical surfaces with good spatial resolution. Successful demonstration at 2.9 microns wavelength is described. A reflectance of 0.9920 ± .0050 has been measured.
The Effect of the Treatment and Ageing on KC1 Surface Breakdown Threshold
Authors: Bilibin SV , Egorov VN , Katsnelson AA , Kovalev VI , Kolesova NS , Sidorov YS , Tkachenko NL , Faizullov FS
Published: March 2009

The breakdown thresholds of bare surfaces of KC1 windows treated in different ways were measured with a gain-switched-pulse CO2 laser at 10.6 μm. The studies indicated that grinding abrasive grain size and moisten-cooling liquid determine the destructed layer depth and the breakdown threshold for freshly polished KC1 surfaces. The ageing of these samples decreases breakdown thresholds considerably. The high-temperature baking of KC1 samples before final polishing increases the surface break-down threshold up to bulk damage for freshly polished and twice for aged samples as compared with those unbaked.
Surface Finishing Using Soft Abrasives
Authors: Vora H , Anderson RH , Stokes RJ
Published: March 2009

In an effort to produce scratch- and damage-free flat surfaces, two non-conventional polishing techniques, mechano-chemical and float, were recently introduced by Yasunaga et al. and Namba and Tsuwa, respectively. The emphasis in both these techniques is on employing an abrasive whose hardness is less than that of the workpiece. This paper describes the results of our efforts to apply these techniques to tape-cast alumina, hot-pressed Si3N4, sapphire and single crystals of silicon and gallium arsenide. Samples of polished materials were observed to be scratch free, and in the case of single crystals, very smooth with a peak-to-peak roughness of ≤ 40Å. The polished surfaces have been characterized using several techniques, including reflection high-energy electron diffraction (RHEED), interferometry, profilometry, electron spectroscopy for chemical analysis and Auger electron spectroscopy.
Laser Desorption Analysis of H2O and Other Contaminants from Optical Surfaces
Authors: Porteus JO , Faith WN , Allen SD
Published: March 2009

Contamination at surfaces and interfaces is known to cause lowered damage threshold in high power laser optical components; therefore, it is important to be able to identify and measure the amount of adsorbed species. A technique has been developed for detecting water and other adsorbed molecules on optical surfaces at incident intensities below the damage threshold. A pulsed laser is focused onto the optical surface of interest in a UHV chamber. The laser energy absorbed in the surface layer causes desorption of the contaminants. Detection and identification of the desorbed species are via a quadrupole mass analyzer. As water and other contaminants such as hydrocarbons are strong optical absorbers in the 2.8- to 3.8-μm wavelength region, an HF/DF laser was chosen for the initial investigation. H2O, OH, and other species have been observed from both coated and uncoated optical surfaces. Surface mapping of adsorbed H2O with a 121μm focal spot shows considerable variation with spatial position. This effect may be associated with surface microcracks and other defects which may precipitate laser damage. Possible applications are characterization of laser optical components and laser cleaning of optical surfaces prior to film deposition.
Electrostatic Technology for Control of Dust and Hydrocarbon Vapors in High Power Laser Systems
Authors: Hoenig SA
Published: March 2009

The application of electrostatic techniques has been investigated as a repulsion system to keep dust off mirrors that might be used in high power laser systems. A demonstration unit for a 30 cm mirror was built and shipped to Kirtland Air Force Base, New Mexico as part of the program.
Laser Mirror Operation at Cryogenic Temperatures
Authors: Decker DL , Hodgkin VA
Published: March 2009

It has been suggested many times that operation of laser mirrors at low temperatures could result in significant performance improvements. Specifically for metal mirrors, the advantage perceived is in decreased absorption and increased thermal conductivity. For dielectric-enhanced mirrors, presumably a similar advantage would be present in lowering both the absorption of the initial metal film and perhaps lowering absorption in the dielectric films as well. From an engineering point of view, this proposition is not entirely academic, at least for space applications, where entirely passive methods of cooling could be employed.

This paper presents experimental absorptance vs wavelength and temperature data over the range from 1 to 10 μm and from room temperature to 80°K. Included in this study are silver samples prepared by different techniques including diamond single-point machining. Also included are similar data for a multilayer dielectric mirror. Theoretical interpretation of the performance of both mirror types is made with recommendations for actual use.