bluuebunny/crossref_metadata_2025_split huggingface dataset:
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 (&lt;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 (&lt;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.
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.
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.
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.
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.
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.
Studies of Diamond-Like Carbon Coatings for Protection of Optical Components
Authors: Stein ML , Aisenberg S , Bendow B 
Published: March 2009

Ion-deposited diamond-like carbon is a promising candidate for thin protective coatings for optical components. Our recent studies have been directed to ascertaining several key properties of the coating, and verifying its protective nature.
Tests performed on coated discs of CaF2 indicated improved resistance to environmental attack by acids, bases, and solvents. Hermeticity was corroberated by comparing the effects of HF-acid on coated and uncoated surfaces. The tenacity to substrates such as glass and CaF2 was demonstrated by the difficulty to remove the coating with standard techniques, such as exposure to HF and water. Also, a marked decrease in abrasion was found (by measuring forward optical scatter) for the coated portion of a disc.
Optical measurements performed on these coated discs indicated that the coating neither significantly decreased transmission as measured from 2 to 6 microns, nor induced visible scatter. High resolution scanning and transmission electron micrograph studies indicate that the films are partly amorphous with a partial ordering of carbon atoms; while Raman studies indicated both graphite as well as microcrystalline diamond-type behavior. ESCA studies indicated a C to CaF2 gradient throughout the coating indicative of ion implantation. Thickness determinations were made by substrate dissolution and surface profile measurements.
Preliminary Experimental Results of Spot Size Scaling in Laser Induced Damage to Optical Coatings
Authors: Stewart AF , Guenther AH 
Published: March 2009

The laser damage threshold of various thin film coatings has been assessed using 1.06 μm radiation at a pulse length of 6ns FWHM. Samples of conventional coatings of several materials have been tested as a function of film thickness and spot size. Beam diameters employed range from approximately 9μm and larger.
From these preliminary data, previously observed scaling has been verified, i.e., thinner films are more damage resistant, while smaller spot sizes yield higher damage thresholds, as expected. The samples employed in these tests were conventional coatings of ThF4, ZrO2 and HfO2 as well as specially prepared “Low defect” coatings of Cerac and RAP grown ThF4. These “low defect” coatings are initial efforts and unfortunately showed no advantage over conventional coatings in terms of damage threshold.
Nonlinear Absorption and Self-Defocusing of Intense IR-Laser Radiation in Semiconductors Due to Generation of Free Carriers
Authors: Danileiko YK , Lebedeva TP , Manenkov AA , Sidorin AV 
Published: March 2009

Results of experimental studies of the interaction of high power CO2 (λ = 10.6 μm), CaF Er3+ (λ = 2.76 μm) and YAG Er3+ (λ = 2.96 μm) lasers with undoped Ge and Si are presented. The experiments included photoconductivity, microwave absorption and laser beam transmission measurements at various intensities up to the level of laser damage. For both the Ge and Si samples, nonequilibrium carrier generation has been observed with both CO2 and Er-laser excitation.
It is shown that the carrier generation in Ge is due to two-photon ionization at the Er-laser wavelength, whereas none of the considered mechanisms (impact, multiphoton and thermal ionizations), explain the anomalous dependence of carrier density upon CO2-laser excitation intensity.
Nonequilibrium carrier generation results in nonlinear absorption and self-defocusing, which in turn lead to the intensity saturation of high power laser beams. Analysis of these effects for prefocused beams is presented. It is shown, in particular, that the absence of bulk damage in Ge under CO2 and Er-laser radiation is attributed to these effects even at very high incident intensities. It is pointed out that these effects play an important role in the application of Ge as a material for use in high power IR lasers.
Evaluation of Plate Specimens Containing Surface Flaws Using J-Integral Methods
Authors: Reuter WG , Chung DT , Eiholzer CR 
Published: March 2009

Using annealed Type 304 stainless steel plate specimens containing ellipsoidal, rectangular, or triangular-shaped surface flaws, critical values of J are calculated for three separate situations: (1) the assumption that the specimen consists of a single-edge notch (SEN) and two unflawed specimens, (2) the prediction of an equivalent-length through-thickness defect for the surface flaw, and (3) the use of an equation developed by Paris. It was concluded that Jinit (Charpy specimen) and JIc cannot be used to successfully predict structural integrity using any of the three approaches for the 6.4-mm-thick (0.25-in.) annealed Type 304 stainless steel.
Since it was not possible to develop a comparison between the absolute values of Jinit (from the surface-flawed specimen) and JIc, an attempt was made to evaluate a possible relative agreement. Values of Jinit and Jpen from only those specimens containing rectangular-shaped defects were used to calculate ΔJ/Δα. The average values agree reasonably well with those obtained in the open literature.
Obtaining More Precise Descriptions of Peats by Use of Oriented Microtome Sections
Authors: Cohen AD 
Published: March 2009

A procedure is described for making relatively undistorted, oriented microtome sections of peat for microscopic analysis. This simple procedure results in a permanent sample from which data can be produced that are precise, statistically reproducible, and easily transmitted and compared with data from other sources.
Highly accurate fiber-to-matrix ratios, porosities, and mineral contents can be quickly and easily determined from area point-counts of these peat sections. The terms fibric, hemic, and sapric, which have been widely used in the United States for describing peats, can be very precisely applied to peat samples in which fiber contents are determined in this way.
Color and translucency of peatified tissues can be measured from unstained microtome sections; or microtome sections may be differentially stained to bring out chemical or physical difference between tissues at different levels. Optical birefringence and fluorescence are two characteristics of peat tissues which can also be accurately measured. Both can be related to source substances and degree of decomposition.
This microtome sectioning technique has been used to describe and classify peats from the Everglades-Mangrove Region of Florida, the Okefenokee Swamp of Georgia, the Snuggedy Swamp of South Carolina, and the Albemarle-Pamlico Peninsular Swamps of North Carolina. The technique worked equally well on peats ranging in physical characteristics from coarsely-fibrous or woody (fibric) to finely-granular (sapric).
A Multistage Sampling Technique for Peat Deposits Utilizing Soil Survey Maps
Authors: Smith MR , LeMasters GS , Bartelli LJ 
Published: March 2009

One purpose of this paper is to report on a multistage sampling scheme used in a Michigan peat resources study. A second purpose is to show how variations of this method can be applied in a sequential manner to adjust for incoming data or changing budgetary parameters.
The sampling plan for this study is a multistage sampling scheme utilizing clustering and multiple stratification. The State of Michigan has been stratified into soil-geomorphic provinces in order to group together organic soils formed on similar associated land surfaces. Within each province the unit of interest is the county or portion of the county. Each county or portion is then sampled. Each township within a county is stratified into four levels of organic soil deposit size, based on dot counts of soil survey maps. The townships form stratified clusters, and within each township a stratified sample of sections is chosen. Within each section systematic transect samples of the organic soils are obtained. The sampling plan should result in good point and interval estimates of organic soil characteristics by section, township, county, province, and total state evaluation.
The advantages and disadvantages of this sampling method are discussed in detail. Its advantages include: simplicity to implement in the field; ability to change with different geographic, personnel, or budgetary restrictions; and ability to be modified in a sequential manner as data are collected. The major disadvantage is the resulting relatively complex estimating equations. An attempt is made to simplify the explanation of these equations.
The utilization of this sampling scheme in conjunction with soil survey maps gives a very efficient method of estimating the total amount and characteristics of peat over a large geographic area.
Effect of Peat Type and Decomposition on the Calorific Value of Some New Brunswick Peats
Authors: D Keys 
Published: March 2009

A detailed inventory of the peatlands in the Province of New Brunswick has been used to select representative sites on major peatlands for determination of several physical and chemical characteristics. At the selected sites a core was recovered for the entire thickness of the deposit using either a 4-cm piston sampler or a 10-cm Macaulay sampler. The core was subdivided into sample intervals on the basis of changes in peat type and humification (decomposition). The samples were oven-dried and calorific value was determined. Ash content was also determined to facilitate comparison of results on an ash-free basis.
The values obtained were grouped by degree of humification for comparison. The values were then subdivided into Sphagnum-dominated and Carex-dominated (sedge) peats for further comparison. Sedge peats were found to have higher calorific values than Sphagnum peats at all observed degrees of humification. For both peat-type groups the calorific value increased with increased decomposition, with the rate of increase being greater for Sphagnum peats.
Characterization of Organic Soils as Energy Sources
Authors: LeMasters GS , Bartelli LJ , Smith MR 
Published: March 2009

Organic soil materials are characterized by the National Cooperative Soil Survey as fibric, hemic, or sapric, using the rubbed fiber volume and the sodium pyrophosphate extract color (SPEC) as differentiae. The U.S. Department of Energy (DOE) defines fuel-grade peat as having a minimum gross calorific value of 8000 Btu/oven-dry lb (18.6 J/kg), and a maximum ash content of 25% by weight. The object of this study was to determine the nature of the correlations between the unrubbed and rubbed fiber volume, SPEC, calorific value, and percent ash parameters for selected organic soil materials.
Thirty-four samples of the most common kinds of materials collected as part of the Peat Resource Estimation in Michigan research project were selected for characterization. Fiber volumes and pyrophosphate solubility were determined in duplicate after procedures of the National Soil Survey Laboratory of the Soil Conservation Service. Calorific value and ash content were determined in accordance with ASTM Test for Gross Calorific Value of Solid Fuel by the Isothermal-Jacket Bomb Calorimeter (D 3286-77) and ASTM Test for Ash in the Analysis Sample of Coal and Coke (D 3174-73). Correlation analyses were performed between these five data sets.
The correlation between rubbed fiber and calorific value was not significant (α = 0.05). Unrubbed fiber and SPEC were significantly correlated with calorific value (r = 0.363, r = 0.530), while a much stronger correlation existed between the ash content and calorific value (r = −0.869). The results suggest that the ash content of the materials is a very useful indicator of the calorific value, much more so than the other parameters studied.
Other systems of characterizing organic soil materials for fuel used by other peat resource estimation projects are compared with the system used in Michigan. Ash content and calorific value data reported by these projects are compared with the aforementioned findings.