bluuebunny/crossref_metadata_2025 huggingface dataset:
Dependence of Damage Threshold of Anti-Reflection Coatings on Substrate Surface Roughness
Authors: Nose Y , Kato Y , Yoshida K , Yamanaka C
Published: February 2009

Geometrical shapes of the damage sites in the 5-layer SiO2/ZrO2 anti-reflection (AR) coatings generated by lμm laser irradiation have been accurately determined. The damages can be classified into two types; deep damage and shallow damage, the former having the lower threshold. Dependence of the damage threshold of the deep damages on substrate surface roughness is given. It is suggested that presence of absorption centers embedded in the substrate is responsible for determining the damage threshold. Possible approaches that will lead to stronger AR coatings are proposed.
Quantification of the Magnitude and Duration of the Preconditioning Effect in AR Coated BK-7 Glass
Authors: Frink ME , Arenberg JW , Mordaunt DW , Seitel SC , Teppo EA
Published: February 2009

This paper presents the difference observed in laser damage thresholds between a ramped preconditioned type test and an unconditioned test method. The enhancement of the laser induced damage threshold observed by the preconditioned test was found to be on the order of 40%. We investigated the amount of preconditioning required to induce the threshold enhancement as well as the duration of the preconditioning effect. Our studies demonstrate that the test procedure used to induce catastrophic coating damage on AR coated BK-7 glass is critical in defining the absolute laser induced damage threshold level. Furthermore, preliminary measurements indicate that the observed preconditioning enhancement is not a permanent effect.
A Study of Thin Film Growth in the ZrO2 - SiO2 System
Authors: Farabaugh EN , Sun YN , Sun J , Feldman A , Chen H-H
Published: February 2009

X-ray diffraction and transmission electron microscopy have been used to examine the microstructures of thin films of pure ZrO2 - SiO2 films formed by e-beam coevaporation. The results suggest that films composed of 100% ZrO2 grow by the formation of tapered polycrystalline columns. Near the substrate the columns are small in diameter and consist of a single crystalline phase, but at increasing distances from the substrate the column diameters increase and material with two polycrystalline phases appears. At a given distance from the substrate, small additions of SiO2 to the film composition result in a smaller column diameter. Films with 25 mole% SiO2 show an amorphous electron diffraction pattern, a result consistent with previously observed x-ray diffraction patterns. The surfaces of the amorphous films appear nearly featureless and are significantly smoother than the surfaces of the pure ZrO2 films.
Long-Range Pulselength Scaling of 351 nm Laser Damage Thresholds
Authors: Foltyn SR , Jolin LJ
Published: February 2009

In a series of experiments incorporating 351-nm pulselengths of 9, 26, 54, and 625 ns, it was found that laser damage thresholds increased as (pulselength)X, and that the exponent averaged 0.36 and ranged, for different samples, from 0.23 to 0.48. Similar results were obtained when only catastrophic damage was considered. Samples included Al2O3/SiO2 in both AR and HR multilayers, HR's of Sc2O3/SiO2 and HfO2/SiO2, and an Al-on-pyrex mirror; 9-ns thresholds were between 0.2-5.6 J/cm2.

When these data were compared with a wide range of other results — for wavelengths from 0.25 to 10.6 μm and pulselengths down to 4 ps — a remarkably consistent picture emerged. Damage thresholds, on average, increase approximately as the cube-root of pulselength from picoseconds to nearly a microsecond, and do so regardless of wavelength or material under test.
Time to Failure in Single Pulse Laser Induced Damage in Thin Film Optical Coatings
Authors: Boyer J
Published: February 2009

Measurement of the time between the start of the laser pulse and the disruption of the irradiated surface provides information not available in traditional damage measurements. The importance of the rate of energy input versus the total energy deposited may be studied by varying the pulse energy and measuring the time at which damage is initiated. If the diagnostics are of adequate sensitivity, a damage threshold fluence can be assigned to each damage event and the fluence distribution of the defect population can be measured.

I will discuss the test configuration and diagnostics for both transmitting and reflecting coatings. Preliminary data at 248 nm with a 23 ns pulse length will be presented.
Thermal Conductivity of Dielectric Films and Correlation to Damage Threshold at 1064nm
Authors: Akhtar SMJ , Ristau D , Ebert J
Published: February 2009

An infrared line scanning technique has been used to measure thermal conductivities of TiO2, Ta2O5, ZrO2, HfO2, A12O3 and SiO2 layers. Damage thresholds are determined using a two stage Nd:Yag laser with pulse length of 14ns and spot size of 300μ. A correlation between thermal conductivity, absorption coefficient, melting point and damage threshold is established. To explain the relation, theoretical models based on absorption and inclusion breakdown are analysed.
1064 nm and 350 nm Laser Damage Thresholds of High Index Oxide Films Deposited from Organic Solutions and Sols
Authors: Thomas I , Wilder J , Gonzales R , George D
Published: February 2009

High index optical coatings of the oxides TiO2, Ta2O5, ZrO2 and HfO2 have been prepared from solutions of metal organic precursors and from colloidal oxide suspensions. Room temperature processing gives porous coatings of comparatively low refractive index (1.8-1.9). Heat treatments can, in some cases, increase the index. Laser damage threshold levels at 1064 nm with a single 1 ns pulse are in the range 6–10 J/cm2, which is comparable with coatings of the same materials produced by electron beam evaporation. Lower figures are obtained at 350 nm with a 25 ns pulse under multishot (25 Hz) conditions.
Effect of Diamond Machining on Laser Damage Threshold of Germanium
Authors: Lewis KL , Charlwood L , Chew NG , Cullis AG , Dosser OD , Mannion A
Published: February 2009

A study has been carried out of the various factors influencing the laser damage thresholds of diamond machined Ge components. Planar surfaces were generated using both Pneumo Precision and Bryant Symons machines in both centre turned and fly-cut configurations. Laser damage thresholds were correlated not so much with the surface relief produced by the machining process but with the degree of pitting of the surface caused by excessive cutting rates and the extent of subsurface damage induced by the DM technique. Although limited to germanium optics, the study raises important fundamental issues relevant to other materials.
Scattering Distribution from Multilayer Mirrors -Theoretical Research of a Design for Minimum Losses
Authors: Amra C
Published: February 2009

The vector theory of light scattering from slightly rough surfaces allows a prediction in the whole space of the scattering distribution from a high-reflecting multilayer coating. A comparison with experimental results concerning classical quarterwave multidielectric coatings enables us to point out the influence of the initial substrate roughness and that of the fine microstructure of the materials used for the coating. Some results are presented for two materials (TiO2, SiO2), and we specify the consequences of the microstructure “grain size” for each one.

In order to reduce scattering losses, it is interesting to know if it is possible to use non-quarterwave multilayer stacks. A theoretical search for solutions leads us to study the consequences of a protective layer deposited on a classical mirror. The influence of the optical thickness of this layer is first studied. Then we examine the case where the top layers of the stack are non-quarterwave layers, so that the electric field associated with the stationary wave is reduced. We can show that, in some particular cases, the total integrated scattering is perceptibly reduced. Nevertheless, this result is only obtained when the roughnesses of the successive interfaces are not correlated. From an experimental point of view, it is not obvious that we can meet this condition whatever the spatial frequency of the defects, and this leads us to study the effect of the cross-correlation coefficient between interfaces.
A Model for Probing Small Absorption Changes During Multiple Pulse Laser-Induced Damage
Authors: Kitriotis D
Published: February 2009

A sensitive technique for the detection of temperature changes in the bulk of a transparent material due to absorption of any laser beam is the thermal-lensing technique. So far to our knowledge the thermal-lensing models will yield zero signal, if one probes the temperature changes in the space where the laser beam focuses. We developed a model that uses a low power c.w. laser to detect the absorption changes in the focal volume of a Q-switched laser beam. The change in the absorption from pulse to pulse will be detected as a change in the far field intensity profile of the c.w. beam; taking in account the aberrant nature of the induced thermal-lens, an expression for the above profile is given; the far field fractional axial intensity is derived without any high order terms elimination, which allows for an accurate and sensitive measurement of the absorption coefficient for one and n-photon absorption processes.
An Investigation of the Possibility that Laser-Induced Color Centers are Responsible for Multiple Pulse Damage
Authors: Kitriotis D , Merkle LD
Published: February 2009

The mechanisms responsible for multiple pulse laser damage in transparent solids are still not understood. Recent reports related to laser generation of point defects in fused silica and BK-7 glass raise the possibility that such defect generation is the cause of multiple pulse damage. The difference in defect generation between high-OH and low-OH fused silica offers a means to test this possibility.

We have compared multiple pulse damage properties of “wet” and “dry” fused silica at 1064 nm and 532 nm. Nearly identical behaviors are observed for the two materials. In addition we have studied laser damage in BK-7 X-irradiated to produce color centers. The presence of these centers lowers the damage threshold only modestly. We conclude that optical generation of color centers is not the primary mechanism in multiple pulse damage in these materials.
A Versatile Laser Glass Inspection and Damage Testing Facility
Authors: Marion JE , Greiner GJ , Campbell JH , Chaffee PH , Hildum JS , Grens JZ , Weinzapfel CL , Winfree SM , Milam D
Published: February 2009

Most glass optical components for high power lasers are melted and homogenized in platinum-lined crucibles leading to the potential presence of microscopic platinum inclusions. In situations where large optics are exposed to high laser fluences, a significant problem can be created by an extremely low density of inclusions, as low as one per component. Previously, direct visual examination or optical microscopy was used to inspect for these particles, limiting reliable detection to inclusions greater than 10μm diameter. Unfortunately, much smaller inclusions can initiate damage in modern lasers operated at high fluences.

A test facility is described which detects small opaque inclusions in large transparent components by using a commercial laser which delivers high energy pulses to the test sample at moderate frequency in a small diameter beam. The sample is automatically scanned such that each point in the volume is irradiated with ten pulses at twice the inclusion damage threshold--an amount sufficient to cause visible damage at inclusion sites. This approach permits detection of opaque inclusions in the parts per trillion and lower concentration range. The specifics of the device design, and its performance are discussed in the context of automatic inclusion inspection and mapping in large laser optics.
Computer-Controlled Facility for Laser Switching and Damage Testing
Authors: Chivian JS , Cotten WD , Fuller DF , Hemphill RB , Scott MW
Published: February 2009

Apparatus has been assembled for mostly-automatic laser switching and damage measurements in which dynamic events are followed in real time. Lasers, optical elements, and detectors are available for operation at 2.8 μm and at 10.6 μm. Sample exposure time is variable from 50 μs to cw. Sample positioning in X:Y:Z is controllable to 0.2 μm. Testing can be done with static beam position or with a scanning beam. Samples can be tested at ambient temperature, or from near 77°K to 370°K.

Software provides for test control, data processing, and graphic, hard copy output. Beam profiling can be done automatically at the sample position, and the profile fit to a Gaussian of the same 1/e2 width. Sample data acquisition is sequenced by the computer after an enable pulse is given at the discretion of the experimenter. The computer records and processes the incoming data, presents intermediate data display, completes data manipulation, and compares processed measurement data with internally available prediction models in graphic form. Representative output for a thin film nonlinear optical material is shown.
Damage Testing in Optics Production and Procurement
Authors: Seitel SC , Teppo EA
Published: February 2009

Laser-induced damage studies reported at these symposia have emphasized basic understanding of the light-matter interaction physics, and development of new, more durable materials and coatings. This paper reports a parallel trend toward routine use of damage testing in the procurement and production of reliable optics for low energy, high peak power military and commercial laser systems. Materials and coating designs are conventional, and in practice, in-service failures are as often due to system design effects and contamination as to improper finishing or coating design errors.

The emerging roles of damage testing as a production process-control tool, in acceptance testing, and in failure diagnostics, are discussed and illustrated with specific examples and color photomicrographs. Particular attention is paid to the problems of (1) meeting widely varying test requirements, often on deliverable part of complex geometry, in timely and cost-effective fashion; and (2) relating calibrated single-mode damage test results to optics durability in highly multimode military systems. A brief review of a new repetitively pulsed dual-wavelength damage test station with exceptional configurational flexibility and advanced digital fluence profiling features is included.
A Computer Automated Laser Damage Laboratory
Authors: Sweet MR , Jolin LJ , Foltyn SR
Published: February 2009

The UV Laser Damage Program has been in existence at Los Alamos for over five years. Recently, the damage laboratories have been upgraded by using a computer system to control and monitor testing parameters, and to display and store the damage data.

The system was designed around already existing testing equipment merged with an IBM-XT for cost effectiveness. The damage fluence is set by a programmable beam attenuator configured in a closed-loop control system with the computer and an energy meter. A matrix of damage sites is set up at the test plane such that the operator can move the sample sequentially between sites or pick sites at random. To aid the operator in choosing test fluence values, a damage plot may be generated on the monitor or on a high resolution plotter.

By automating the Laser Damage Laboratory with a computer, consistent results can be achieved over a short testing time.
U.V. Laser Beam Diagnostics using a Computer Controlled Video Frame Store System
Authors: Clark SE , Laidler I , Emmony DC , Omar BA , Shaw MJ
Published: February 2009

In the past the spatial intensity profile of a laser beam has been measured using such techniques as scanning pinholes, detector arrays and photography.

This new system converts the Excimer beam into visible light using a glass fluorescer with a very small penetration depth giving a good 2D image of the beam. The fluorescence has been found to be linear over a wide range of input energy and is imaged by a CCD camera linked to the computer controlled video frame store.

The digitised information is then computer processed to yield such results as the intensity profile along an arbitary line, peak fluence, the difference between two images and various statistical values.

This new technique has been applied to beams with widely varying diameters including analysis in the focal region and in the early detection of damage in materials.
Beam Profiling Characteristics of a Sensitivity-Enhanced Silicon Vidicon System at 1.06 Microns
Authors: O'Connell RM , Vogel RA , Stewart AF , Smith DA
Published: February 2009

A beam profiling system consisting of a silicon vidicon detector and an image processing computer is described, and results of measurements to characterize the system are presented. For the transmission and display of geometrically accurate images, a unique relationship was found to exist between pixel clock frequency, channel time and channel length. The vidicon target's dark current and 1.06 μm detection sensitivity were found to have peak-to-peak variations of 5.6% and 3.75%, respectively, throughout the target's central 3.75 × 3.13 mm region. Signal-to-noise levels were optimum at a target temperature near 0° C. Without being optimized, cathode voltage switching improved the pulsed-mode dynamic range of the system to approximately 4.
Directo n2Measurement in Yttria Stabilized Cubic Zirconia
Authors: Guha S , Mansour N , Soileau MJ
Published: February 2009

We present here the results of direct measurement of the nonlinear refractive index, n2, of yttria doped cubic zirconia at 1.06 μm using external self-focusing. The value of n2 was found to be independent of the yttria concentration. The measured value (6 × 10-13 esu) compares well with that calculated from the breakdown measurements [1].
Measurement of Optical Damage Threshold of Wire Grid Polarizers at 10.6 μm
Authors: Mohebi M , Said A , Soileau MJ
Published: February 2009

We report the results of measurement of laser induced surface damage threshold of wire grid polarizers at 10.6 μm as a function of orientation of the wires and polarization of light. We also measured the absorption of wire grids at 10.6 μm, 1.06, and 0.53 μm. The results of surface damage thresholds are consistent with the results of absorption measurements and theory.
Laser Damage Studies of Several Acrylic Polymers
Authors: Romberger AB , Mullins BW , Shaffer AA , Hilbing JF , Siegenthaler KE , Deaton TF , Chang Y
Published: February 2009

The bulk laser damage resistance of several acrylic copolymers and of pure poly (ethyl)methacrylate (PEMA) were investigated with a 1.06μm wavelength pulsed Hd:YAG laser having a pulse length of 8 ± 2 ns and an e-2 radius spot size of 30 ± 0.7 ¼m. These materials were synthesized in the bulk after extensive filtration or distillation to remove absorbing dust particles. A correlation is made between the damage thresholds and the number of scattering centers per volume observed in a HeNe beam. The HeNe laser beam scattering in the sample was used as an indicator of the impurity content of the sample. In the course of this experiment a spatial filter was installed in order to make the focused YAG laser beam more nearly Gaussian. Comparison of results obtained from the filtered beam and the unfiltered beam (which is mathematically described as a sombrero function) indicated that previous characterization of the non-Gaussian beam provided an incorrectly low damage threshold value.
Platinum Particles in the Nd:doped Disks of Phosphate Glass in the Nova Laser
Authors: Milam D , Hatcher CW , Campbell JH
Published: February 2009

The disks of Nd:doped phosphate glass in the amplifiers of the Nova laser contain platinum particles with sizes ranging from <5μm (detection limit) to about lOOμm. The particle density varies from about 0.01 to 1.0 cm-3. These particles cause fractures when irradiated at fluences >2.5 J/cm2 delivered in 1-ns, 1064-nm pulses. Under repeated irradiation at 5–7 J/cm2, damage from small (< 5μm) particles asymptotically approaches a limiting size, but damage surrounding the larger particles grows steadily. The damage threshold fluence, 2.5 J/cm2, corresponds to operation of Nova at one-half the desired output for pulse durations longer than 1 nsec. Operation at higher fluences causes accumulation of damage in the output amplifiers and requires replacement of the disks in those amplifiers on an accelerated schedule.

Large-area damage tests have been used to characterize samples from recent melts made to reduce the number of platinum particles. The 500-J, 1-ns pulses available at the midpoint of an arm were used to produce fluences of 7–10 J/cm2 over test areas 6–9 cm in diameter. Similar irradiations of areas 25–30 cm in diameter were accomplished using 5-kJ, 1-ns pulses available at the output of an arm. Preliminary results from these experiments indicate that a significant reduction of the inclusion density can be obtained through changes in the vendor's glass melting conditions.
Evolution During Multiple-Shot Irradiation of Damage Surrounding Isolated Platinum Inclusions in Phosphate Laser Glasses
Authors: Gonzales RP , Milam D
Published: February 2009

Platinum inclusions in samples of laser glass were placed in the center of a 2-mm-diameter beam and repeatedly irradiated with 1064-nm laser pulses having durations of 1.3, 9 or 50 ns. The initial major dimensions of the particles ranged from 4–75 μm. The thresholds for initiation of damage were 2.5 ± 0.3, 4 ± 0.4 and 8 ± 0.8 J/cm2, respectively, for the three pulse durations used in the tests. Thresholds were independent of particle size. Three particles with initial dimensions of 4, 5 and 8 μm caused damage smaller than 250 μm. One 6 μm particle and all particles larger than 10 μm caused larger damage.
Picosecond Nonlinear Investigation of Accumulated Damage in Molecular Crystals
Authors: Kosic TJ , Hill JR , Dlott DD
Published: February 2009

Accumulated damage in aromatic molecular crystals at low temperature is studied by a variety of novel picosecond laser techniques. Damage in these materials is qualitatively different than in fused quartz, where dielectric breakdown is the predominant mechanism. In the aromatic crystals, multiphoton ionization creates reactive chemical fragments which are stabilized by the low temperature crystal matrix. These species accumulate until a high concentration is reached. At that point, phonon and photon assisted interactions release enough energy to damage the crystal. In a sense the process can be viewed as a chemical explosion.

The picosecond YAG--dual dye laser system used for these experiments is described. With this system we have demonstrated new methods to study damage. Subnanosecond damage is time-resolved with a sampling technique. The mechanism of defect production and crystal destruction is probed using damage detected spectroscopy. Scattering of the optical phonons by the accumulating defects is detected via picosecond time-delayed coherent Raman scattering.
Ion Exchange Strengthening of Nd Doped Phosphate Laser Glass
Authors: Cerqua KA , Jacobs S , McIntyre BL , Zhong W
Published: February 2009

Recent advancements in high repetition rate and high average power laser systems have put increasing demands on the development of solid state laser materials with high thermal loading capabilities.

We have investigated strengthening of commercially available Nd doped phosphate glass via an ion-exchange process. Introduction of a compressive layer to the glass' exterior surfaces through this exchange, results in dramatically improved (approximately 4–5x) thermal shock resistance for specific sample geometries. This resulting increase in strength was directly measured through thermal shock resistance tests.

Our thermal shock test data showed extremely small (approximately ± 5%) standard deviations compared with data acquired through conventional mechanical fracture techniques. Additional topics investigated were strengthened layer thickness and effectiveness as a function of treatment time and the relationship of strengthening to the overall optical quality of the strengthened sample's surface.
Laser Induced Damage and Ion Emission of GaAs at 1.06 μm
Authors: Huang AL , Becker MF , Walser RM
Published: February 2009

The experiments in this study were focused on the N-on-1 laser damage and sub-damage threshold ion emission of gallium arsenide. The initial goals were (1) to determine the N dependent damage threshold due to N-on-1 laser irradiance and (2) to correlate ion emission with surface damage events. A Q-switched Nd:YAG laser (1.064 μm, 45 nsec pulse, 580 μm spot diameter) was used to irradiate the ⟨100⟩ single crystal gallium arsenide samples.

Using values of N from 1 to 100, we obtained accumulation curves based on 50% damage probability. Corresponding damage threshold fluences were 0.4 – 0.8 J/cm2 for N>1 and approximately 1.5 J/cm2 for N=1. We observed large site-to-site fluctuations in ion emission, and emission occurred before surface damage was initiated. We found the onset of ion emission at a fluence of 0.2 J/cm2 for all cases, whereas the damage threshold fluence was two to five times larger and dependent on N. Experimental measurements of linear and nonlinear absorption coefficients were made to check for anomalous absorption. The measured values were in agreement with those previously reported. Once surface damage occurred, ion emission was greatly increased. This type of behavior seems to support a surface cleaning model for ion emission which precedes surface damage.
N-on-1 Damage Testing of Single Crystal Metal Surfaces at 1.06 μm
Authors: Jee Y , Becker MF , Walser RM
Published: February 2009

We examined the accumulation dependence of laser damage on single crystal metal surfaces under Q-switched Nd:YAG laser irradiation (1.064μm, 20 nsec pulses with a 200μm spot diameter). The samples were chemically polished, electropolished, and single point diamond machined Al, Cu and Ni single crystal surfaces of several crystallographic orientations. The single point diamond machined samples did not have single crystal surfaces as detected by electron channeling patterns, whereas the other samples had good single crystal surfaces.

Damage probability curves and accumulation curves were plotted to investigate N-on-1 damage behavior. The slope of the damage probability curve increased with the number of pulses required for damage. Accumulation curves, derived from 50% damage fluences, often had two regions showing different slopes. We interpret these measurements to indicate two different damage mechanisms, a defect related local melting at low pulse numbers and plastic deformation damage at high pulse numbers. These observations correlate with typical damage morphologies obtained by a Nomarski optical microscope and by SEM.
Yttrium Oxide Coatings for High Power Lasers at 351 nm
Authors: Smith DJ , Hayden CJ , Krakauer BU , Schmid AW , Guardalben MJ
Published: February 2009

Yttrium oxide has proven to be a useful coating material for high power UV lasers. In combination with silicon dioxide it produces an effective dual wavelength antireflection coating at 351 and 1054 nanometers which has good resistance to damage at both wavelengths. While a durable coating material, yttrium oxide may be removed safely from a lightly damaged optic and reapplied. Index inhomogeniety of the material is investigated as well as modification of the film structure with ion-assisted deposition.
Self-Consistent Dependence of Porosity and Refractive Index on Composition in Co-Evaporated Films
Authors: Feldman A , Farabaugh EN , Stempniak RA
Published: February 2009

Zirconia:silica films grown by e-beam coevaporation show a decreased porosity compared to pure zirconia films. This decreased porosity causes an anomalous dependence of refractive index on composition. A maximum in refractive index occurs at about 20 percent by volume of silica, the concentration at which the films appear to become amorphous. A simple model which derives the porosity as a function of composition from the deposition parameters predicts the general compositional behavior of the refractive index. The results agree best with the Drude model of refractive index for mixed component systems.
The Formation and Development of Nodular Defects in Optical Coatings
Authors: Liao B , Smith DJ , McIntyre B
Published: February 2009

We have investigated the nodular defect using computer simulations and experimental techniques. A modified version of the hard-disk model, in which the migration and attraction of atoms are introduced in simplified ways, is used to simulate the formation and development of nodules. This simulation reveals the self-extending nature of nodule growth and the dependence of the nodule shape and size upon the conditions of the coating's formation, including deposition geometry, migration, and capture length of atoms. By planting artificial seeds on substrate surfaces and overcoating with single and multilayer stacks, we have encourged nodular formation under controlled and variable deposition conditions. Fractured cross-sections of these coatings have been examined by scanning microscopy (SEM). A comparison between our experimental observations and the modeling results help explain the mechanisms for nodule growth.
Interfacial Structure of Ion-Beam Sputter Deposited SiO2/TiO2 Coatings
Authors: Sites JR , Demiryont H
Published: February 2009

X-ray photoelectron spectroscopy (XPS) was used to evaluate the interfaces between ion-beam sputter deposited SiO2 and TiO2 layers, their free surface, and their interface with a silicon substrate. XPS depth profiles of nominally abrupt SiO2/TiO interfaces showed mixing over an 7 nm range, but no valence states other than Si+4 and Ti+4. Thus the interfacial region consists of Si1-x Tix 02 where x varies from 0 to 1. The free surface of either SiO2 or TiO2 extends over 1.5 nm and shows evidence of OH bonds, presumably due to absorbed water. Interfaces between SiO2, or TiO2, and an optically smooth silicon substrate are about 3 nm wide and exhibit +2 and 0 bonding states for Si, and +2 for Ti, states characteristic of oxygen deficient films. The TiO2/Si interface also contains Ti-Si bonds, or partial silicide formation.
Ion Beam Deposited Oxide Coatings
Authors: Raj T , Price JS , Carniglia CK
Published: February 2009

Single-layer coatings of SiO2, Al2O3 and ZrO2 were deposited by ion beam deposition (IBD). IBD is carried out by directing an ion source at a target made of the desired coating material. The material sputtered from the target is directed toward the substrate being coated. The targets chosen for this work were commercially available hot-pressed oxides. To further modify the coating properties, a secondary ion gun was directed toward the substrate to assist the deposition. Thus, ion assisted deposition (IAD) can be combined with IBD. The following coating deposition parameters were varied: composition of the sputter deposition gas mixture, composition of the ion assist gas mixture, and beam voltage and beam current for the ion assist beam. No external heat was applied to the substrates.

Single-layer ZrO2 coatings were also deposited from a Zr metal target by bombarding this target with an O2:Ar ion beam (Reactive Ion Beam Deposition [RIBD]). These depositions were performed with ion assistance (RIBD/IAD) and without. However, filament life of the ion guns was found to be a problem with these coatings because of the presence of oxygen in the ion beam.

The refractive indices for all the coatings were determined by ellipsometry at 633 nm. Representative coatings were analyzed by Auger Electron Spectroscopy (AES) to determine stoichiometry and to provide information on the nature and level of impurities. The RMS surface roughness was determined by TIS (Total Integrated Scatter) measurements. In addition, absorption was determined for a few selected coatings from spectral transmission measurements. The influences of ion beam deposition parameters and ion assist-beam parameters on thin film properties of SiO2, Al2O3 and ZrO2 coatings are discussed.

High reflector coatings at 351 nm were deposited on super-polished substrates utilizing the optimum deposition parameters obtained from the single-layer studies. The reflectors were made from ZrO2 and SiO2 targets. A peak reflectance greater than 99% was achieved.
Detection of Laser Damage by Raman Microscopy
Authors: Fauchet PM , Campbell IH , Adar F
Published: February 2009

We demonstrate that Raman microscopy is a sensitive and quantitative tool to detect and characterize laser-induced damage in solids. After damage is induced with single or multiple high power laser pulses, a Raman microprobe maps the surface of the sample with one micron spatial resolution. By performing accurate measurements of the Stokes line, we have been able to measure stress, strain and crystallinity in various samples which had been exposed to high intensity pulses. These results are compared to those obtained using conventional tools such as Nomarski microscopy. Major advantages of Raman microscopy include sensitivity to subtle structural modifications and the fact that it gives quantitative measurements.
Thresholds Measured With 350-nm Pulses at 25–100 Hz for Bare Polished Crystals of CaF2 and for Silica Sol-gel AR Coatings on Silica Substrates
Authors: Staggs MC , Milam D , Thomas IM , Wilder JG
Published: February 2009

An XeF laser-damage experiment was used to measure damage thresholds for bare polished crystals of CaF2 and porous silica antireflection coatings on fused silica substrates. Damage was induced by applying 1000 350-nm, 25-ns pulses at repetition rates of 25–100 Hz to small (typically 0.12 × .03 cm) sites on the surfaces of the sample. Eight samples of fluorescence-free CaF2 exhibited both surface and bulk damage at fluences as low as 10 J/cm2. Three samples of UV-grade CaF2 also had surface damage thresholds of 10 J/cm2, and bulk damage was not observed in this material. Thresholds for the porous silica coatings were 17–23 J/cm2.
Study of Temporal and Spatial Intensity Variations and Intracavity Damage Thresholds of Alexandrite Lasers
Authors: Harter DJ , Rainnee H , Heiney AJ
Published: February 2009

The energy densities which can be obtained in a laser resonator before optical damage occurs are usually much lower than the optical damage thresholds measured in extracavity laser experiments. We have measured intracavity optical damage thresholds in an alexandrite laser operating in both single- and multitransverse mode and found the multitransverse mode laser has a much lower damage threshold. We studied the temporal and spatial variations of a multitransverse mode laser and found intensity hot spots which may be an important factor in the difference in the intracavity damage thresholds.
Investigation of Metal Coatings for the Free Electron Laser
Authors: Scott ML , Arendt PN , Springer RW , Cordi RC , McCreary WJ
Published: February 2009

We are investigating the deposition and characteristics of metal coatings for use in environments such as the Free Electron Laser where the radiation resistance of metal coatings could prove to be of great benefit. We have concentrated our initial efforts on silver laminate coatings due to the high reflectance of silver at 1 micron wavelength. Our initial laminate coatings have utilized thin layers of titanium oxide to break up the columnar structure of the silver during electron-beam deposition on fused silica substrates. Our initial results on equal coating thickness samples indicate an improvement in damage threshold that ranges from 1.07 to 1.71 at 351 nm.
Dependence of Damage Threshold of Anti-Reflection Coatings on Substrate Surface Roughness
Authors: Nose Y , Kato Y , Yoshida K , Yamanaka C
Published: February 2009

Geometrical shapes of the damage sites in the 5-layer SiO2/ZrO2 anti-reflection (AR) coatings generated by l μm laser irradiation have been accurately determined. The damages can be classified into two types; deep damage and shallow damage, the former having the lower threshold. Dependence of the damage threshold of the deep damages on substrate surface roughness is given. It is suggested that presence of absorption centers embedded in the substrate is responsible for determining the damage threshold. Possible approaches that will lead to stronger AR coatings are proposed.
CO2 Laser Induced Damage in a Model Thin Film System: ZnS on Ge
Authors: Gibson DR , Wilson AD
Published: February 2009

The CO2 laser absorption and damage characteristics of thermal and electron beam evaporated ZnS films on Ge substrates have been investigated. The substrate temperature during deposition is shown to be an important parameter controlling film porosity and hence water ingress. The role of water is probed by a variety of techniques including laser induced desorption (mass) spectroscopy. Water is shown to lead to high film-substrate and bulk-film absorptances and to low laser damage thresholds (LDTs) with damage originating in the film. Physically dense films, which do not allow water ingress, have high LDTs limited by damage to the Ge substrates. Examination of ZnS films on Si and ZnS substrates indicates that the film absorptances and LDTs are dependent on the substrate material.
Laser Induced Damage in Dense Optical Thin Films
Authors: Lewis KL , Pitt AM , Cullis AG , Chew NG , Charlwcod L
Published: February 2009

Molecular beam deposition techniques have been used to generate dense optical thin films and film structures for studies which allow the assessment of the onset of laser damage effects, and which explore the control of microstructure. In the first study, ZnS films have been examined on germanium substrates by electron microscopy and the evidence available suggests that damage is initiated by laser beam interactions at dislocation loop clusters in the Ge surface. In the second study the feasibility of using stratified films to control microstructure has been assessed. Damage thresholds in (ZnS/ZnSe)n are equivalent to those of uncoated substrates despite the incorporation of 100 or so separate interfaces. A wide range of coatings can be synthesized utilising such structures, which offer the potential of enhanced damage thresholds and broadband optical properties.
Transient Absorption of Light Induced by Radiation
Authors: Godwin R , Harrison FB , Larson A
Published: February 2009

We have measured two components in the radiation-induced absorption of 250-nm light in fused silica. For the first, the time constant is 48.3 ± 1.3 ns and the absorption coefficent is 6.68 ± 0.37 cm-1 per Mrad. For the second, the time constant is long compared to 3 μs, and the absorption coefficient is 1.65 ± 0.36 cm-1 per Mrad. The errors quoted are purely statistical.
Effects of Radiation Induced Defects on Laser-Induced Breakdown in SiO2
Authors: Soileau MJ , Mansour N , Canto E , Griscom DL
Published: February 2009

The effects of radiation damage on bulk laser-induced breakdown in SiO2 were investigated. Samples studied included Spectrasil A, B, and WF (water free). Measurements of laser-induced breakdown were conducted with 532 and 1064 nm laser pulses of approximately 20 nsec duration. Reductions of up to 40% in the laser-induced breakdown threshold were observed at 532 nm for samples exposed to 108 rads of γ-radiation. The decrease in breakdown threshold for irradiated SiO2 samples at 532 nm was found to be proportional to the linear absorption of the specimen at 266 nm. These results are in good agreement with a proposed model which suggests that two-photon absorption initiated avalanche process is responsible for laser-induced breakdown for these materials.
Time of Damage and the Effect of the Pulse Repetition Frequency on the Laser Induced Damage Threshold
Authors: Wood RM , Sharma SK , Waite P , Gorton EK , Lewis K
Published: February 2009

The time of damage has been measured as a function of pulse input energy for a range of i-r windows and mirrors.

More data and understanding of the mechanisms involved has been gained of the effect of laser pulse repetition frequency on the laser induced damage thresholds of infra-red transmitting window materials. Results on Ge, Si, GaAs, ZnS, ZnSe, NaCl and KCl are presented together with comments on the mechanisms which lower the damage threshold from the single shot damage level.
Excitation and Determination of Protein-Fluorophore Complexes Using Aqueous Peroxyoxalate Chemiluminescence
Authors: Woolf EJ , Grayeski ML
Published: February 2009

This paper demonstrates a chemiluminescence-based method for the determination of proteins with hydrophobic sites. The measurement is based on the chemical excitation of a complex formed by the binding of a fluorescent molecule to the hydrophobic portion of the protein. The fluorophore is excited with an aqueous peroxyoxalate chemiluminescence reaction and the resulting chemiluminescence signal is enhanced by the hydrophobic environment of the protein. The major advantage is that chemical modification of the analyte is not required. Low nanogram per millilitre concentrations of human albumin have been detected using the method.
Chromatographic Determination of Thiols through Selective Fluorescence Derivatization: A Review
Authors: Baeyens WRG , Imai K , Lin Ling B
Published: February 2009

For the sensitive detection of solutes in the picomole to nanogram range, fluorimetric analyses are often adopted. As there are growing needs for quantifying specifically and sensitively naturally occurring thiols and for measuring therapeutic concentrations of thiol-containing drugs, several fluorigenic reagents for thiols have been developed and some of them now are being used as pre- and post-column derivatization reagents in HPLC. HPLC combined with fluorescence detection is one of the most suitable techniques for the specific and sensitive determination of thiols because of its effective separation and selective detection. A few types of relevant reagents (dansylaziridine, maleimides, bimanes, and halogenobenzofurazans) were used for this purpose. All of them show promise for the analysis of various samples; likewise they each have their limitations. Dansylaziridine is fluorescent itself and gives an interfering peak in the chromatograms. The various substituted maleimides form multiple fluorescent products because of hydrolysis of the fluorophors. Bimanes produce several reagent peaks in the chromatograms and may react with non-thiolic functional groups, while several halogenobenzofurazans require drastic derivatizing conditions. The present work summarizes the current state of the art of thiol determinations using HPLC and fluorescence derivatization, with emphasis on the measurement of drugs in biological samples.
The Role of Cross-Slip of Screw Dislocations in Fatigue Behavior of Copper Single Crystals
Authors: Jin NY , Winter AT
Published: February 2009

Differently oriented copper single crystals were fatigued, where the Schmid factor for primary screw dislocations moving on the cross-slip plane differed markedly while that for primary slip remained more or less constant. The experimental results show that the cyclic hardening rate depends on crystal orientation. The saturation properties, the saturation stress, and the plastic strain in the persistent slipbands, are orientation independent. It seems likely that cross-slip is important only in the early stage of cyclic deformation, but not in the saturation.
Crack Nucleation in Persistent Slipbands
Authors: Hunsche A , Neumann P
Published: February 2009

The development of persistent slipband topography, crack nucleation, and crack growth in fatigued copper single crystals was studied by an new section technique, which reveals surface topographies with a resolution of 20 nm. Experiments were performed in air, oxygen, hydrogen, water vapor, high vacuum, and ultrahigh vacuum in order to study the influence of the environment on these processes. The development of persistent slipband topography, including intrusions, extrusions, and the protrusion of the whole persistent slipband, does not depend on environment. Crack nucleation and early propagation, however, do strongly depend on the environment. Intrusions can also be distinguished from crack nuclei by their finite vertex angle of approximately 30 deg. Quantitative data of the average protrusion growth as well as crack growth are presented. Chains of large voids were found in high vacuum and ultrahigh vacuum along the trace of the primary slip plane and are interpreted as remnants of rewelded Stage I cracks.
What Are the Kinetics of Slipband Extrusion?
Authors: Baxter WJ
Published: February 2009

It is well known that the development of persistent slipbands plays an important role in the initiation of fatigue cracks. This paper describes the application of photoelectron microscopy to measure the kinetics of the early stages of growth of persistent slipbands in 6061-T6 aluminum. The persistent slipbands (PSBs) are shown to consist of a periodic array of approximately semicircular extrusions 1 to 2 μm in diameter. Initially a single extrusion appears. The PSB elongates by the addition of further extrusions. The lengths of individual PSBs increase as the square root of the number of fatigue cycles. A model is proposed based upon an array of cells similar to the dislocation structure which has been observed in the PSBs of other materials. The cyclic strain within these cells is shown to be 10 to 100 times greater than the applied macroscopic strain.
Unified Treatment of Deep and Shallow Notches in Rotating Bending Fatigue
Authors: Nisitani H , Endo M
Published: February 2009

As a concept useful for evaluating the strength of notched members, “linear notch mechanics” is proposed. It is explained by this concept that the elastic-plastic behavior near the root of a notch under the condition of small-scale yielding is controlled by the maximum elastic stress σmax and the notch root radius ρ alone, independently of the other notch geometries. In order to confirm the effectiveness of “linear notch mechanics” in fatigue problems, rotating bending fatigue tests are carried out on notched steel specimens having widely varying notch geometries. Moreover, the fatigue notch effects of extremely shallow notches, whose depths are of the order of the grain size, are also discussed.

Summarizing the present studies, a unifying treatment of fatigue notch effects is presented.
Critical Behavior of Nonpropagating Crack in Steel
Authors: Kunio T , Yamada K , Kim MG
Published: February 2009

A study has been made on the critical condition for the nonpropagation of a crack in Stage II growth at the endurance limit of pearlitic steel with special emphasis on the closure behavior of the crack.

It is found from fatigue experiments and measurements of crack opening displacement that a tip of the nonpropagating crack (NPC) is closed at the stress level of the endurance limit. It is also found that the tip of the NPC opens again under the original endurance limit when the NPC is vacuum-annealed. Therefore, it turns out that the crack which has propagated in Stage II growth stops its propagation by the closure effect resulting mainly from the local residual compressive stress at the crack tip.

Further experimental evidence implies that not only the crack closure due to residual compressive stress (plasticity induced), but also the closure associated with the oxidation during the reduced crack propagation, is responsible for the existence of NPC at the endurance limit.