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The role of defects in laser damage of multilayer coatings

Description: Laser induced damage to optical coatings is generally a localized phenomenon associated with coating defects. The most common of the defect types are the well-known nodule defect. This paper reviews the use of experiments and modeling to understand the formation of these defects and their interaction with laser light. Of particular interest are efforts to identify which defects are most susceptible to laser damage. Also discussed are possible methods for stabilizing these defects (laser conditioning) or preventing their initiation (source stabilization, spatter particle trapping).
Date: December 21, 1993
Creator: Kozlowski, M. R. & Chow, R.
Partner: UNT Libraries Government Documents Department

2-1/2-D electromagnetic modeling of nodular defects in high-power multilayer optical coatings

Description: Advances in the design and production of high damage threshold optical coatings for use in mirrors and polarizers have been driven by the design requirements of high-power laser systems such as the proposed 1.8-MJ National Ignition Facility (NIF) and the prototype 12- kJ Beamlet laser system. The present design of the NIF will include 192 polarizers and more than 1100 mirrors. Currently, the material system of choice for high-power multilayer optical coatings with high damage threshold applications near 1.06 {mu}m are e-beam deposited HfO{sub 2}/Si0{sub 2} coatings. However, the optical performance and laser damage thresholds of these coatings are limited by micron-scale defects and insufficient control over layer thickness. In this report, we will discuss the results of our 2-1/2-D finite-element time- domain (FDTD) EM modeling effort for rotationally-symmetric nodular defects in multilayer dielectric HR coatings. We have added a new diagnostic to the 2-1/2-D FDTD EM code, AMOS, that enables us to calculate the peak steady-state electric fields throughout a 2-D planar region containing a 2-D r-z cross-section of the axisymmetric nodular defect and surrounding multilayer dielectric stack. We have also generated a series of design curves to identify the range of loss tangents for Si0{sub 2} and HfO{sub 2} consistent with the experimentally determined power loss of the HR coatings. In addition, we have developed several methods to provide coupling between the EM results and the thermal-mechanical simulation effort.
Date: July 1996
Creator: Molau, N. E.; Brand, H. R.; Kozlowski, M. R. & Shang, C. C.
Partner: UNT Libraries Government Documents Department

A comparison of nodular defect seed geometeries from different deposition techniques

Description: A focused ion-beam milling instrument commonly utilized in the semiconductor industry for failure analysis and IC repair, is capable of cross-sectioning nodular defects. Utilizing the instrument`s scanning on beam, high-resolution imaging of the seeds that initiate nodular defect growth is possible. In an attempt to understand the origins of these seeds, HfO{sub 2}/SiO{sub 2} and Ta{sub 2}O{sub 5}/SiO{sub 2} coatings were prepared by a variety of coating vendors and different deposition processes including e-beam, magnetron sputtering, and ion beam sputtering. By studying the shape, depth, and composition of the seed, inferences of its origin can be drawn. The boundaries between the nodule and thin film provide insight into the mechanical stability of the nodule. Significant differences in the seed composition, geometry of nodular growth and mechanical stability of the defects for sputtered versus e-beam coatings are reported. Differences in seed shape were also observed from different coating vendors using e-beam deposition of HfO{sub 2}/SiO{sub 2} coatings.
Date: December 29, 1995
Creator: Stolz, C.J.; Tench, R.J.; Kozlowski, M.R. & Fornier, A.
Partner: UNT Libraries Government Documents Department

Laser-induced damage of fused silica at 355 and 1065 nm initiated at aluminum contamination particles on the surface

Description: 1-{mu}m thick circular dots, 10-250 {mu}m dia, were deposited onto 1.14 cm thick fused silica windows by sputtering Al through a mask. Al shavings were also deposited on the windows to investigate effects of particle-substrate adhesion. The silica windows were then illuminated repetitively using a 3-ns, 355 nm and an 8.6-ns, 1064 nm laser. The tests were conducted at near normal incidence with particles on input and output surfaces of the windows. During the first shot, a plasma ignited at the metal particle and damage initiated on the fused silica surface. The morphology of the damage at the metal dots were reproducible but different for input and output surface contamination. For input surface contamination, minor damage occurred where the particle was located; such damage ceased to grow with the removal of contaminant material. More serious damage (pits and cracks) was initiated on the output surface (especially at 355 nm) and grew to catastrophic proportions after few shots. Output surface contaminants were usually ejected on the initial shot, leaving a wave pattern on the surface. No further damage occurred with subsequent shots unless a shot (usually the first shot) cracked the surface; such behavior was mostly observed at 355 nm and occasionally for large shavings at 1064 nm. The size of the damaged area scaled with the size of the particle (except when catastrophic damage occurred). Onset of catastrophic damage on output surface occurred only when particles exceeded a critical size. Damage behavior of the sputtered dots was found to be qualitatively similar to that of the shavings. The artificial contamination technique accelerated the study by allowing better control of the test conditions.
Date: January 1, 1997
Creator: Genin, F.Y.; Michlitsch, K.; Furr, J.; Kozlowski, M.R. & Krulevitch, P.
Partner: UNT Libraries Government Documents Department

Towards predicting the laser damage threshold of large-area optics

Description: As the size of optics increases, such as in the optical coatings being developed for the National Ignition Facility in US and the Laser MegaJoules in France, the difficulty also increases in measuring and defining their laser damage threshold. Measuring the threshold on small witness samples ({le}cm) rather than full aperture optic (=m) is advantageous, and in this article, the threshold of large-area components is addressed in two ways. First, a model based on the R-on-l threshold distribution is shown to predict the threshold of a large optic with a high degree of confidence. The average R-on-l threshold provides a reliable, accurate value to evaluate coatings. An automated damage test bench has been developed at CEA. Secondly, the damage threshold has to be defined according to final use of the component. LLNL has defined a functional damage threshold to set limits on maximum damage size. An empirical power law dependence of average damage size on peak fluence was found; this can be used to predict the damage behavior of large-aperture optics exhibiting the same damage morphology.
Date: October 1, 1996
Creator: Hue, J.; Genin, F.Y.; Maricle, S.M. & Kozlowski, M.R.
Partner: UNT Libraries Government Documents Department

Contamination effects on optical damage

Description: The development and construction of high fluence lasers for inertial confinement fusion such as the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL) or the Laser Megajoule in France continues to generate strong interest in the behavior of optical components under intense laser irradiation. the design of such lasers has created significant technological challenges in the area of laser glass, KDP crystal growth, surface finishing, and fused silica damage in the ultraviolet (UV). The damage of fused silica lenses at 355 nm is of particular concern since the optical design requires peak fluences that are very close to the damage threshold of the most resistant fused silica lenses available today.
Date: March 2, 1998
Creator: Genin, F.Y.; Kozlowski, M.R. & Feit, M.D.
Partner: UNT Libraries Government Documents Department

Characterization of defect geometries in multilayer optical coatings

Description: Laser-induced damage in optical coatings is generally associated with micrometer-scale defects. A simple geometric model for nodule-shaped defects is commonly used to describe defects in optical coatings. No systematic study has been done, however, to prove the applicability of that model to standard optical coating deposition. Some defects are known not to have a classic nodule geometry. The present study uses atomic force microscopy (AFM) and scanning electron microscopy to characterize the topography of coating defects in a HfO{sub 2}/SiO{sub 2} multilayer mirror system. Focused ion-beam cross-sectioning is then used to study the underlying defect structure. This work develops a model for defect shape such that the overall geometry of a coating defect, particularly seed size and depth, can be inferred from non-destructive evaluation measurements such as AFM. The relative mechanical stabilities of nodular defects can be deduced based on the nodule`s geometry. Auger analysis showed that the seed material that causes nodular defects in HfO{sub 2}/SiO{sub 2} multilayers is a hafnia oxide. Such characterization capabilities are needed for understanding the enhanced susceptibility of particular defects to laser damage and for developing improved techniques for depositing low-defect density coatings.
Date: December 1, 1993
Creator: Tench, R. J.; Chow, R. & Kozlowski, M. R.
Partner: UNT Libraries Government Documents Department

Large-area conditioning of optics for high-power laser systems

Description: In order to reach the high fluence goals of the Beamlet laser at Lawrence Livermore National Laboratory (LLNL), the polarizers in the system must be laser conditioned to increase their damage thresholds. Research has shown that by using a six-step raster-conditioning program, the damage thresholds of the HfO{sub 2}/SiO{sub 2} multilayer polarizer coatings can be increased to meet the Beamlet 3-ns design goal of 8 J/cm{sub 2}. Because of the large size of the polarizers (73 cm {times} 37 cm {times} 9 cm), a large-area conditioning facility was constructed capable of rastering a one-meter optic, weighing as much as 400 pounds, at any specified use angle. A large translational stage moves the optic in a raster pattern through a stationary, 10-Hz rep-rated, 1064-nm beam with 10-ns pulses. A scatter measurement diagnostic allows on-the-fly evaluation of laser-induced damage and logs the coordinates of the damage. Laser energy is measured pulse-to-pulse in order to ensure stability during a scan. A small amount of minor coating damage does occur during the process, but the damage does not grow upon further irradiation. This damage causes only a small increase in total scatter compared to that due to the preexisting defects, and would not influence the system performance.
Date: December 21, 1993
Creator: Sheehan, L. M.; Kozlowski, M. R.; Rainer, F. & Staggs, M. C.
Partner: UNT Libraries Government Documents Department

Current 3 {omega} large optic test procedures and data analysis for the quality assurance of National Ignition Facility

Description: A reliable metric is required to describe the damage resistance of large aperture 3{omega} transmissive optics for the National Ignition Facility (NIF) laser. The trend from single site testing to the more statistically valid Gaussian scanning test requires a well modeled experimental procedure, accurate monitoring of the test parameters, and careful interpretation of the resulting volumes of data. The methods described here provide reliable quality assurance data, as well as intrinsic damage concentration information used to predict the performance expected under use conditions. This paper describes the equipment, test procedure, and data analysis used to evaluate large aperture 3{omega} optics for the NIF laser.
Date: December 22, 1998
Creator: Schwartz, S; Feit, M D; Kozlowski, M R & Mouser, R P
Partner: UNT Libraries Government Documents Department

Depth profiling of polishing-induced contamination on fused silica surfaces

Description: Laser-induced damage on optical surfaces is often associated with absorbing contaminants introduced by the polishing process. This is particularly the case for UV optics. Here secondary ion mass spectroscopy (SIMS) was used to measure depth profiles of finished process contamination on fused silica surfaces. Contaminants detected include the major polishing compound components (Ce or Zr from CeO2 or ZrO2), Al presently largely because of the use of Al2O3 in the final cleaning process (Fe, Cu,Cr) incorporated during the polishing step or earlier grinding steps. Depth profile data typically showed an exponential decay of contaminant concentration to a depth of 100-200 nm. This depth is consistent with a polishing redeposition layers formed during the chemo-mechanical polishing of fused silica. Peak contaminant levels are typically in the 10-100 ppm range, except for Al with exceeds 1000 ppm. A strong correlation has been shown between the presence of a gray haze damage morphology and the use of CeO2 polishing compound. No strong correlation was found however between high levels of Ce, or any other contaminant and the low damage threshold was observed. In fact one of the strongest indications of a correlation is between increased damage thresholds and increased Zr contamination. This suggests that the correlation between redeposition layer and laser damage threshold is not simple an absorbing contaminant issue.
Date: December 20, 1997
Creator: Kozlowski, M.R.; Carr, J.; Hutcheon, I,; Torres, R.; Sheehan, L. Camp, D. & Yan, M.
Partner: UNT Libraries Government Documents Department

Effect of Silica overlayers on laser damage of HfO{sub 2}-SiO{sub 2}56{sup degree} incidence high reflectors

Description: A series of hafnia/silica, oblique incidence (56{degrees}), 1064 nm high reflectors (HRs) were prepared and coated with silica overlayers of varying optical thickness from {lambda}/2 to 4{lambda} in order to determine the effect of an overlayer on the laser-damage resistance of the HRs. The stress and laser damage thresholds for S and P polarization of the HRs were measured, and the damage sites for P polarization examined by Atomic Force Microscopy (AFM). All the multilayers were found to be in compression, with an intrinsic stress increasing with overlayer thickness. The presence of an overlayer and its thickness did not affect the damage threshold significantly. However, the presence of an overlayer greatly influenced the size and morphology of the damage. First, the overlayer prevented catastrophic ``burns`` of the hafnia top layer. Second, as the overlayer thickness increased, two distinct damage morphologies were found: agged pits and round craters. The diameter of these pits and craters then increased somewhat with thicker overlayers. The depths of the pits and craters also increased with overlayer thickness, and the depths showed failure occurring at the interfaces below the hafnia layers. The side-wall angles of the craters were shallower with thicker overlayers, but there was no angle dependence for the pits. The craters showed fracture-like features and a small hillock or pit on their bottom surfaces. No correlation of damage morphology to conditioning or fluence was found.
Date: January 5, 1995
Creator: Walton, C.C.; Genin, F.Y.; Chow, R.; Kozlowski, M.R.; Loomis, G.E. & Pierce, E.
Partner: UNT Libraries Government Documents Department

Laser damage performance of fused silica optical componets measured on the beamlet laser at 35nm

Description: A statistics-based model is being developed to predict the laser-damage-limited lifetime of UV optical components on the NIF laser. In order to provide data for the model, laser damage experiments were performed on the Beamlet laser system at LLNL (aperture: 34 cm x 34 cm). Three prototype NIF focus lenses were exposed to 351 nm pulses (1.5 ns or 3 ns) during four experimental campaigns, each consisting of 23 to 38 pulses at NIF relevant fluences. Each lens was sol-gel AR coated and all laser exposures were performed in a vacuum environment. Through inspections of the lens before, during and after the campaigns, pulse-to-pulse damage growth rates were measured for damage initiating both on the surfaces and at bulk inclusions. Radial growth rates measured for rear surface damage was typically 10x higher than that measured in the bulk or at the front surface. No significant correlation of growth rate to precursor type was indicated. For 5 J/cm², 3 ns pulses the typical radial growth rate was nominally 20 µm/pulse. Average growth rates measured on three lenses made by two manufacturers were in good agreement. While the growth rate clearly increased with fluence, the data obtained was insufficient to quantify the dependence. The growth rates reported here were 20x-50x higher than values predicted from off-line studies of bare surfaces in air.
Date: December 22, 1998
Creator: Kozlowski, M R; Maricle, S; Mouser, R; Parham, T; Schwartz, S; Wegner, P et al.
Partner: UNT Libraries Government Documents Department

Effects of wet etch processing on laser-induced damage of fused silica surfaces

Description: Laser-induced damage of transparent fused silica optical components by 355 nm illumination occurs primarily at surface defects produced during the grinding and polishing processes. These defects can either be surface defects or sub-surface damage.Wet etch processing in a buffered hydrogen fluoride (HF) solution has been examined as a tool for characterizing such defects. A study was conducted to understand the effects of etch depth on the damage threshold of fused silica substrates. The study used a 355 nm, 7.5 ns, 10 Hz Nd:YAG laser to damage test fused silica optics through various wet etch processing steps. Inspection of the surface quality was performed with Nomarski microscopy and Total Internal Reflection Microscopy. The damage test data and inspection results were correlated with polishing process specifics. The results show that a wet etch exposes subsurface damage while maintaining or improving the laser damage performance. The benefits of a wet etch must be evaluated for each polishing process.
Date: December 22, 1998
Creator: Battersby, C.L.; Kozlowski, M.R. & Sheehan, L.M.
Partner: UNT Libraries Government Documents Department

Growth of laser-induced damage during repetitive illumination of HfO2-SiO2 multilayer mirror and polarizer coatings

Description: As peak fluence of high power lasers is increased, it becomes necessary to tolerate damage on mirrors, polarizers. To study how different types of damage morphologies initiate and grow during repetitive illumination, hafnia-silica multilayer mirror and polarizer coatings were laser damage tested. The coatings were prepared by e-beam evaporation and irradiated with a 3-ns pulse at 1064 nm. The damage morphology was recorded after each shot to determine the types of damage that cause massive unstable failure and lower the optic`s functional damage threshold. Results were summarized on damage stability maps plotting the average damage size vs number of shots for fluences ranging from 10 to 40 J/cm{sup 2}. The maps indicate that the commonly observed damage morphologies (pits, flat bottom pits, scalds, outer layer delamination) have distinct growth behaviors and influence the value of the functional damage threshold differently. While pits are stable up to fluences as high as 40 J/cm{sup 2}, flat bottom pits can grow during repetitive illumination above a critical fluence of about 35 J/cm{sup 2}. Scalds are formed in the first shot and never grow at fluences below 40 J/cm{sup 2}. Finally, delaminates are highly unstable and have the potential for damaging the coating catastrophically above 15 J/cm{sup 2}. Results show that delaminate damage should be prevented; this knowledge has allowed coatings development efforts to focus on eliminating the origin of such damage morphology.
Date: January 1, 1997
Creator: Genin, F.Y.; Stolz, C.J. & Kozlowski, M.R.
Partner: UNT Libraries Government Documents Department

Laser conditioning methods fo hafnia silica multiplayer mirrors

Description: Large aperture multilayer hafnia silica high reflector coatings at 1064 nm, deposited by reactive electron-beam deposition, were prepared to examine different laser conditioning methods for manufacturing high fluence optics in the National Ignition Facility. Laser conditioning is a process where the damage threshold of the coating is increased or the damage that is created is minimized so that it does not grow upon further irradiation. Two laser conditioning methods were examined for coatings deposited from only oxide starting materials. Off-line laser conditioning consists of raster scanning a mirror past a 1 mm diameter Gaussian beam over the entire clear aperture; a process that takes approximately 24 hours per scan. On-line laser conditioning consisted of a large aperture 300 mm x 300 mm beam from the Beamlet laser that irradiated the entire full clear aperture of a series of mirrors; a process that was limited by a 2-4 hour shot rate. In both cases a six-step process was used with the mirror first irradiated at a low fluence, then successively higher fluences increased in equal increments up to the peak laser operating fluence. Mirrors that were only partially laser conditioned damaged catastrophically while fully conditioned mirrors survived fluences exceeding the safe operating Beamlet fluence. An alternative off-line laser conditioning method was examined for coatings deposited from hafnia or metallic hafnium sources. Single-step laser conditioning consists of off-line raster scanning an optic at the peak operating fluence, thus decreasing the laser conditioning cost by reducing the number of scans and required laser conditioning stations to process all the mirrors for the National Ignition Facility. Between pulses the optic is stepped approximately one fourth of the l/e* Gaussian beam diameter so each area of the coating is irradiated by different segments of the beam starting at a low fluence at the outer edge ...
Date: January 6, 1998
Creator: Stolz, C.J.; Sheehan, L.M.; Maricle, S.M. Schwartz, S.; Kozlowski, M.R.; Jennings, R.T. & Hue, J.
Partner: UNT Libraries Government Documents Department

Study of the effects of polishing, etching, cleaving, and water leaching on the UV laser damage of fused silica

Description: A damage morphology study was performed with a 355 nm Nd:YAG laser on synthetic UV-grade fused silica to determine the effects of post- polish chemical etching on laser-induced damage, compare damage morphologies of cleaved and polished surfaces, and understand the effects of the hydrolyzed surface layer and waste-crack interactions. The samples were polished , then chemically etched in buffered HF solution to remove 45,90,135, and 180 nm of surface material. Another set of samples was cleaved and soaked in boiling distilled water for 1 second and 1 hour. All the samples were irradiated at damaging fluencies and characterized by Normarski optical microscopy and scanning electron microscopy. Damage was initiated as micro-pits on both input and output surfaces of the polished fused silica sample. At higher fluencies, the micro-pits generated cracks on the surface. Laser damage of the polished surface showed significant trace contamination levels within a 50 nm surface layer. Micro-pit formation also appeared after irradiating cleaved fused silica surfaces at damaging fluences. Linear damage tracks corresponding cleaving tracks were often observed on cleaved surfaces. Soaking cleaved samples in water produced wide laser damage tracks.
Date: December 23, 1997
Creator: Yoshiyama, J.; Genin, F.Y.; Salleo, A.; Thomas, I.; Kozlowski, M.R.; Sheehan, L.M. et al.
Partner: UNT Libraries Government Documents Department

Influence of microstructure on laser damage threshold of IBS coatings

Description: Ion-beam sputtering (IBS) coatings were developed for the laser gyro industry to meet significantly different requirements than those of fusion lasers. Laser gyro mirrors are small (< 25 mm) and require low losses (< 30 ppm typical) and high stability with long exposures to low power laser energy. In contrast, fusion laser optics are large (< 1 meter), have significantly reduced loss requirements (< 5,000 ppm) and high damage thresholds (> 26 J/cm{sup 2} at 1,064 nm with 3-ns pulses). As part of the National Ignition Facility (NIF) coating development effort, IBS coatings are being studied to explore the possible benefits of this technology to NIF optics. As an initial step to achieving the NIF size and damage threshold requirements, the coating process is being scaled to uniformly coat a 20 x 40 cm{sup 2} area with reduced spectral, reflected wavefront, and laser damage threshold requirements. Here, multilayer coatings deposited by ion-beam sputtering with amorphous layers were found to have lower damage thresholds at 1,064 nm than similar coatings with crystalline layers. Interestingly, at higher fluences the damage was less severe for the amorphous coatings. The magnitude of the difference in damage thresholds between the two different microstructures was strongly influenced by the size of the tested area. To better understand the microstructure effects, single layers of HfO{sub 2} with different microstructures were studied using transmission electron microscopy, ellipsometry, and a photothermal deflection technique. Since the laser damage initiated at defects, the influence of thermal diffusivity on thermal gradients in nodular defects is also presented.
Date: January 5, 1996
Creator: Stolz, C.J.; Genin, F.Y.; Kozlowski, M.R.; Long, D.; Lalazari, R.; Wu, Z.L. et al.
Partner: UNT Libraries Government Documents Department

Laser modulated scattering as a nondestructive evaluation tool for optical surfaces and thin film coatings

Description: Laser modulated scattering (LMS) is introduced as a non-destructive evaluation tool for defect inspection and characterization of optical surfaces and thin film coatings. This technique is a scatter sensitive version of the well-known photothermal microscopy (PTM) technique. It allows simultaneous measurement of the DC and AC scattering signals of a probe laser beam from an optical surface. By comparison between the DC and AC scattering signals, one can differentiate absorptive defects from non-absorptive ones. This paper describes the principle of the LMS technique and the experimental setup, and illustrates examples on using LMS as a tool for nondestructive evaluation of high quality optics.
Date: December 22, 1999
Creator: Feit, M D; Kozlowski, M R; Rubenchik, A M; Sheehan, L & Wu, Z L
Partner: UNT Libraries Government Documents Department

Large-aperture, high-damage-threshold optics for beamlet

Description: Beamlet serves as a test bed for the proposed NIF laser design and components. Therefore, its optics are similar in size and quality to those proposed for the NIF. In general, the optics in the main laser cavity and transport section of Beamlet are larger and have higher damage thresholds than the optics manufactured for any of our previous laser systems. In addition, the quality of the Beamlet optical materials is higher, leading to better wavefront quality, higher optical transmission, and lower-intensity modulation of the output laser beam than, for example, that typically achieved on Nova. In this article, we discuss the properties and characteristics of the large-aperture optics used on Beamlet.
Date: February 23, 1995
Creator: Campbell, J.H.; Atherton, L.J.; DeYoreo, J.J.; Kozlowski, M.R.; Maney, R.T.; Montesanti, R.C. et al.
Partner: UNT Libraries Government Documents Department

Extrapolation of damage test data to predict performance of large-area NIF optics at 355 nm

Description: For the aggressive fluence requirements of the NIF laser, some level of laser-induced damage to the large (40 x 40 cm) 351 nm final optics is inevitable. Planning and utilization of NIF therefore requires reliable prediction of the functional degradation of the final optics. Laser damage tests are typically carried out with Gaussian beams on relatively small test areas. The tests yield a damage probability vs energy fluence relation. These damage probabilities are shown to depend on both the beam fluence distribution and the size of area tested. Thus, some analysis is necessary in order to use these test results to determine expected damage levels for large aperture optics. The authors present a statistical approach which interprets the damage probability in terms of an underlying intrinsic surface density of damaging defects. This allows extrapolation of test results to different sized areas and different beam shapes (NIF has a flattop beam). The defect density is found to vary as a power of the fluence (Weibull distribution).
Date: December 22, 1998
Creator: Schwartz, S; Feit, M D; Genin, F Y; Kozlowski, M R; Rubenchik, A M & Sheehan, L M
Partner: UNT Libraries Government Documents Department

High damage threshold anti-reflectors by physical vapor deposited amorphous fluoropolymer

Description: High laser-resistant anti-reflective coatings were made from an amorphous fluoropolymer (Teflon AF2400) material by physical vapor deposition. Single layers of Teflon AF2400 were thermally deposited in a vacuum chamber. Refractive index and adhesion of the coatings were determined as a function of deposition rate (2 to 20 {Angstrom}/s), substrate temperature (20 to 200C), and glow-discharge bias potential ({minus}1500 to 1500 V). An anti-reflective coating of an amorphous fluoropolymer (Teflon AF2400) had a laser resistance of > 47 J/cm{sup 2} (1.06 {mu}m, 3-ns pulselength) and is transparent from 200 nm to 1600 nm. The majority of the coatings had a 1.30 refractive index, similar to that of the bulk material. Scanning electron microscopy and preliminary nuclear magnetic resonance observations indicated that morphological changes caused the variations in the refractive index rather than compositional changes. The coatings adhered to fused silica and silicon wafers under normal laboratory handling conditions. Scotch tape with 12.6 gr/mm tension was sufficient to pull off every coating from fused silica substrates.
Date: November 1, 1993
Creator: Chow, R.; Spragge, M. K.; Loomis, G. E.; Thomas, I. M.; Rainer, F.; Ward, R. L. et al.
Partner: UNT Libraries Government Documents Department

A historical perspective on fifteen years of laser damage thresholds at LLNL

Description: We have completed a fifteen year, referenced and documented compilation of more than 15,000 measurements of laser-induced damage thresholds (LIDT) conducted at the Lawrence Livermore National Laboratory (LLNL). These measurements cover the spectrum from 248 to 1064 nm with pulse durations ranging from < 1 ns to 65 ns and at pulse-repetition frequencies (PRF) from single shots to 6.3 kHz. We emphasize the changes in LIDTs during the past two years since we last summarized our database. We relate these results to earlier data concentrating on improvements in processing methods, materials, and conditioning techniques. In particular, we highlight the current status of anti-reflective (AR) coatings, high reflectors (HR), polarizers, and frequency-conversion crystals used primarily at 355 nm and 1064 nm.
Date: December 21, 1993
Creator: Rainer, F.; De Marco, F. P.; Staggs, M. C.; Kozlowski, M. R.; Atherton, L. J. & Sheehan, L. M.
Partner: UNT Libraries Government Documents Department

Characterization of physically vapor deposited AF2400 thin films

Description: Anti-reflective coatings made with Teflon AF2400 had the highest damage thresholds recorded for physical vapor deposited coatings at the Lawrence Livermore National Laboratory damage facility. Physical vapor deposited layers of Teflon AF2400, a perfluorinated amorphous polymer, maintained the bulk optical properties of a high transmittance from 200 nm to 1600 nm, and a low refractive index. In addition, the refractive index can be intentionally reduced by control of two common deposition parameters, deposition rate and substrate temperature. Scanning electron microscopy and nuclear magnetic resonance observations indicated that morphological changes caused the variations in the refractive index rather than compositional changes. The coatings adhered to fused silica and silicon wafers under normal laboratory handling conditions.
Date: November 1, 1993
Creator: Chow, R.; Spragge, M. K.; Loomis, G. E.; Rainer, F.; Ward, R.; Thomas, I. M. et al.
Partner: UNT Libraries Government Documents Department

An amorphous fluoropolymer: Next generation optical coating candidate

Description: Anti-reflective (AR) and high reflector (HR) optical coatings were made by physical vapor deposition (PVD) of Teflon AF2400, a perfluorinated amorphous polymer. The AR had the highest laser damage thresholds recorded for PVD coatings at the Lawrence Livermore National Laboratory damage facility. The HR was a multilayer of ZnS and AF2400. The bandwidth was 550 mn, centered at 1064 mn. Single layers of Teflon AF2400 deposited by PVD were characterized optically. The refractive index could be intentionally reduced below the bulk value by varying either deposition rate or substrate temperature. Scanning electron microscopy and nuclear magnetic resonance observations indicated that morphological changes caused the variations in the refractive index rather than compositional changes.
Date: May 1, 1994
Creator: Chow, R.; Loomis, G. E.; Spragge, M. K.; Lindsey, E. L.; Rainer, F.; Ward, R. L. et al.
Partner: UNT Libraries Government Documents Department