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Next-generation all-silica coatings for UV applications
... (g/cm 3 ) [19]. Basing on the relationship between film density and refractive index [28], the value of refractive index in the case of GLAD films is estimated as 1.3, which is close to the published experimental value [29]. ...
... (g/cm 3 ) [19]. Basing on the relationship between film density and refractive index [28], the value of refractive index in the case of GLAD films is estimated as 1.3, which is close to the published experimental value [29]. Table 1. ...
The high-energy glancing angle deposition of silicon dioxide films with alternation of deposition angle is studied using classical atomistic simulation. Both slow and fast alternations are investigated. The growth of vertical tree-like columns and chevron-like regular structures is demonstrated under fast and slow alternations, respectively. Due to high porosity, the density of the deposited silicon dioxide films is reduced to 1.3 ÷ 1.4 g/cm3. This results in reduction of the refractive index to 1.3, which agrees with known experimental data. For slow continuous substrate rotation, formation of a helical structure is demonstrated.
... As can be seen in the plots in Figures 5 and 6, an increase in the deposition angle from α = 60 • to α = 70 • leads to a significant reduction in the film density. This result is consistent with the experiments [33] and results of previous simulations [34]. In the case of α = 70°, an increase in the fraction of O=Si=O molecules leads to multidirectional changes in the density profiles and the dependence of the film's density on its thickness ( Figure 6). ...
An atomistic simulation of silicon dioxide thin films deposited using oxide targets is performed. The influence of the oxide target on the deposition process is taken into account by introducing O=Si=O molecules into the flow of particles moving from the target to the substrate. The fraction of these molecules varied from 0 to 50%. It was found that the presence of O=Si=O molecules leads to film densification during a normal deposition. With a low-energy deposition, the increase in density was twice as high as with a high-energy deposition. The absolute value of the compressive stress increased with an increasing fraction of O=Si=O molecules in the flow of deposited particles at a normal, high-energy deposition. The influence of O=Si=O molecules on the structure of the glancing angle deposited films depends on the deposition angle.
... Thus, the porous film can be even more LIDresistant than the dense film. An increase in the laser induced damage threshold with an Nanomaterials 2021, 11, 2986 8 of 9 increase in the deposition angle and film porosity was observed experimentally for SiO 2 films [34,35]. To summarize, an increase in the concentration of point defects due to heating near the nodular defects can be noted. ...
The full-atomistic classical molecular dynamics simulation of the laser heating of silicon dioxide thin films is performed. Both dense isotropic films and porous anisotropic films are investigated. It is assumed that heating occurs due to nodal structural defects, which are currently considered one of the possible causes of laser induced damage. It is revealed that heating to a temperature of 1000 K insignificantly affects the structure of the films and the concentration of point defects responsible for the radiation absorption. An increase in the heating temperature to 2000 K leads to the growth of the concentration of these defects. For “as deposited” films, this growth is greater in the case of a porous film deposited at a high deposition angle. Annealing of film reduces the difference in the concentration of laser induced defects in dense and porous films. The possible influence of optical active defects arising due to heating on the laser induced damage threshold is discussed.
... The obtained values of σ are two to three times higher than the stresses arising during the highenergy deposition of silicon dioxide films [15]. Such high stresses can be the cause of a thermoelastic breakdown of multilayer dielectric structures [16]. ...
... Thus, a decrease in stresses with an increase in the deposition angle can be accompanied by an increase in the laser-induced damage threshold (LIDT). Indeed, in [22] the increase in the LIDT of silicon dioxide films with growth of the deposition angle has been observed experimentally. The results of the stress calculation for high-energy-deposited silicon dioxide films are shown in Figure 3. ...
The laser-induced thermal stresses in silicon dioxide films are calculated using molecular dynamics simulations. The absorption of the laser energy is simulated by the linear temperature growth from room temperature to 1300 K in a time equal to the laser pulse duration. The maximum values of stresses for picosecond pulses are approximately twice as high as for nanosecond pulses. The stresses in highly porous glancing angle deposited films are approximately two times lower than in dense films. Stress waves caused by picosecond pulses are observed in dense films. An increase in the heating temperature to 1700 K leads to an increase in the absolute stress values for picosecond pulses, and a decrease for nanosecond pulses.
... The substrate matter, deposition method, wavelength at which the refractive index is determined, and substrate temperature are given in the notes below the table. ]; indium tin oxide (ITO) coated glass substrate; electron beam evaporation; 532 nm; 330 K.2 [37] fused silica substrate; 532 nm.3 [38] fused silica substrate; electron beam evaporation; room temperature, 532 nm.4 [39] p-AlGaN substrate; electron beam evaporation; room temperature, 365 nm. ...
In this article, a combined approach for studying the optical anisotropy of porous thin films obtained by the glancing angle deposition is presented. This approach combines modeling on the atomistic and continuum levels. First, thin films clusters are obtained using the full-atomistic molecular dynamics simulation of the deposition process. Then, these clusters are represented as a medium with anisotropic pores, the shapes parameters of which are determined using the Monte Carlo based method. The difference in the main components of the refractive index is calculated in the framework of the anisotropic Bruggeman effective medium theory. The presented approach is tested and validated by comparing the analytical and simulation results for the model problems, and then is applied to silicon dioxide thin films. It is found that the maximum difference between the main components of the refractive index is 0.035 in a film deposited at an angle of 80°. The simulation results agree with the experimental data reported in the literature.
... The films with low refractive index, n = 1.32 (α =70°), were characterized by low values of both stress tensor components. Values of the refractive index for large deposition angles were in the interval of the experimental results for SiO2 GLAD films [31]. ...
Dependence of stress values in silicon dioxide films on its thickness in the initial stage of film growth was investigated using atomistic molecular dynamics simulation. It was shown that the stress in normally deposited films was compressive and varied slightly with growth of film thickness. The stress in the glancing angle deposited films was several times lower than the stress in the normally deposited films, and varied from compressive stress to tensile stress with increasing film thickness. An essential anisotropy of stress tensor components was revealed for the case of glancing angle deposition. The calculated stress values were in the interval of experimental data.
The classical molecular dynamics simulation of the glancing angle deposition of silicon dioxide films with practically meaningful dimensions is performed. The formation of separated slanted columnar structures is investigated for different deposition angles and different energies of sputtered silicon atoms. It is shown that a decrease in the angle between the flux of deposited atoms and the normal to the substrate leads to the decrease of column thicknesses and distances between the columns. The high-energy deposition with small deposition angles results in the formation of dense films without separate columnar structures. The increase of substrate temperature leads to partial merging of nearby columns. The glancing angle deposition with low energies of sputtered silicon atoms results in the growth of disordered columns with different dimensions, shapes, and tilt angles. Annealing of high-energy glancing angle deposited films results in partial merging of slanted columns. The obtained simulation results are in a good agreement with existing experimental data.
A principal possibility to overcome fundamental (intrinsic) limit of pure optical materials laser light
resistance is investigated by designing artificial materials with desired optical properties. We explore
the suitability of high band-gap ultra-low refractive index material (n less than 1.38 at 550 nm) in
the context of highly reflective coatings with enhanced optical resistance. The new generation allsilica
(porous/nonporous) SiO2 thin film mirror with 99% reflectivity was prepared by glancing angle
deposition (GLAD). Its damage performance was directly compared with state of the art hafnia/silica
coating produced by Ion-Beam-Sputtering. Laser-Induced Damage Thresholds (LIDT) of both coatings
were measured in nanosecond regime at 355 nm wavelength. Novel approach indicates the potential
for coating to withstand laser fluence of at least 65 J/cm2 without reaching intrinsic threshold value.
Reported concept can be expanded to virtually any design thus opening a new way of next generation
thin film production well suited for high power laser applications.
Achieving higher optical power in UV laser systems is a challenging task due to the limited performance of their built-in optical elements. As a rule of thumb, interference coatings of such elements are found to be the weakest links by the means of laser-induced damage threshold (LIDT). The optical resistance is directly attributed to the fundamental absorption properties of deposited layers. Unfortunately, there are only a limited set of available materials with discrete refractive indices that are also compatible with UV applications. In this study, an attempt is made to employ sculptured layers in order to produce durable anti-reflective (AR) coatings by using the so-called glancing angle deposition (GLAD) method. Spectral, structural, mechanical and stress properties of GLAD coatings were investigated in detail. AR coatings produced by GLAD were found to be three times more laser damage resistant at 355 nm wavelength as compared to those prepared by ion beam sputtering (IBS).
In this work, the influence of using ion beam sputtered mixtures instead of pure materials and the impact of applied post deposition annealing to residual stress is investigated. Single layer pure films and mixtures of Nb2O5/SiO2 as well as multilayer coatings are examined by the means of residual stress. High residual compressive stress was measured for all as-deposited samples. Pure and mixed monolayer samples were annealed at various temperatures and residual stress was determined after each annealing routine. Residual changes in optical constants, layer thickness and surface roughness upon annealing are examined to explain stress behavior. Obtained data was used to make optimization of high reflectivity structures with completely eliminated residual stress. The proposed method can be used to coat very thin substrates where flatness requirements are essential. (C) 2016 Optical Society of America
In the present state of the art, ion beam sputtering is used to produce low-loss dielectric optics. During the manufacturing of a dielectric layer stack, the deposition material must be changed, which requires rapid mechanical movement of vacuum components. These mechanical components can be regarded as a risk factor for contamination during the coating process, which limits the quality of high-end laser components. To minimize the particle contamination, we present a novel deposition concept that does not require movable components to change the coating material during the coating process. A magnetic field guiding technique has been developed, which enables the tuning of the refractive index in the layer structure by sputtering mixtures with varying compositions of two materials using a single-ion source. The versatility of this new concept is demonstrated for a high-reflection mirror.
This study compares surface roughness of SiO2 thin layers which are deposited by three different processes (plasma-enhanced chemical vapor deposition, physical vapor deposition and ion beam deposition) on three different substrates (glass, Si and polyethylene naphthalate). Plasma-enhanced chemical vapor deposition (PECVD) processes using a wide range of deposition temperatures from 80 to 300 °C have been applied and compared. It was observed that the nature of the substrate does not influence the surface roughness of the grown layers very much. It is also perceived that the value of the surface roughness keeps on increasing as the deposition temperature of the PECVD process increases. This is due to the increase in the surface diffusion length with the rise in substrate temperature. The layers which have been deposited on Si wafer by ion beam deposition (IBD) process are found to be smoother as compared to the other two techniques. The layers which have been deposited on the glass substrates using PECVD reveal the highest surface roughness values in comparison with the other substrate materials and techniques. Different existing models describing the dynamics of clusters on surfaces are compared and discussed.
Substrate defect planarization has been shown to increase the laser resistance of 1053 nm mirror coatings to greater than 100 J / cm 2 , an increase of 20-fold, when tested with 10 ns laser pulses. Substrate surface particles that are overcoated with optical interference mirror coatings become nodular defects, which behave as microlenses intensifying light into the defect structure. By a discrete process of angle-dependent ion etching and unidirectional ion-beam deposition, substrate defects can be reduced in cross-sectional area by over 90%.
A system for measurement of surface roughness based on total integrated scattering at 532 and 355 nm is built and demonstrated. Surfaces up to 25 mm x 25 mm are scanned in 6 min with a spatial resolution of 0.4 mm. Careful attention to reducing stray light and purging the measurement chamber with filtered air allow scattering resolution better than 10(-5). Surface roughness measurements better than 1 nm RMS are demonstrated and confirmed by comparison measurements with an atomic-force microscope.
ZrO2-SiO2 and Nb2O5-SiO2 mixture coatings as well as those of pure zirconia (ZrO2), niobia (Nb2O5), and silica (SiO2) deposited by ion-beam sputtering were investigated. Refractive-index dispersions, bandgaps, and volumetric fractions of materials in mixed coatings were analyzed from spectrophotometric data. Optical scattering, surface roughness, nanostructure, and optical resistance were also studied. Zirconia-silica mixtures experience the transition from crystalline to amorphous phase by increasing the content of SiO2. This also results in reduced surface roughness. All niobia and silica coatings and their mixtures were amorphous. The obtained laser-induced damage thresholds in the subpicosecond range also correlates with respect to the silica content in both zirconia- and niobia-silica mixtures.
Thin films of hafnium oxide have been grown by high pressure reactive sputtering on transparent quartz substrates UV grade silica and silicon wafers. Deposition conditions were adjusted to obtain polycrystalline as well as amorphous films. Optical properties of the films deposited on the silica substrates were investigated by transmittance and reflectance spectroscopy in the ultraviolet, visible and near infrared range UV VIS NIR . A numerical analysis method that takes into account the different surface roughness of the polycrystalline and amorphous films was applied to calculate the optical constants refractive index and absorption coefficient . Amorphous films were found to have a higher refractive index and a lower transparency than polycrystalline films. This is attributed to a higher density of the amorphous samples, which was confirmed by atomic density measurements performed by heavy ion elastic recoil detection analysis ERDA . The absorption coefficient gave an excellent fit to the Tauc law indirect gap , which allowed to obtain a band gap value of 5.54 eV. The structure of the films amorphous or polycrystalline was found to have no significant influence on the nature of the band gap. The Tauc plots also give information about the structure of the films, because the slope of the plot the Tauc parameter is related to the degree of order in the bond network. The amorphous samples had a larger value of the Tauc parameter, i.e., more order than the polycrystalline samples. This is indicative of a uniform bond network with percolation of the bond chains, in contrast to the randomly oriented polycrystalline grains separated by grain boundaries
The initiation of laser damage within optical coatings can be better understood by electric-field modeling of coating defects. The result of this modeling shows that light intensification as large as 24x can occur owing to these coating defects. Light intensification tends to increase with inclusion diameter. Defects irradiated over a range of incident angles from 0 to 60 deg tend to have a higher light intensification at a 45 deg incidence. Irradiation wavelength has a significant effect on light intensification within the defect and the multilayer. Finally, shallow, or in the case of 45 deg irradiation, deeply embedded inclusions tend to have the highest light intensification.
The technology of finishing for optics, ceramics, and semiconductors is one of the most promising uses of the magnetorheological effect. It perfectly coupled with computer control, allowing in quantity production the unique accuracy and quality of a polished surface to be achieved. The polishing process may appear as follows. A part rotating on the spindle is brought into contact with an magnetorheological polishing (MRP) fluid which is set in motion by the moving wall. In the region where the part and the MRP fluid are brought into contact, the applied magnetic field creates the conditions necessary for the material removal from the part surface. The material removal takes place in a certain region contacting the surface of the part which can be called the polishing spot or zone. The polishing process comes to the program-simulated movement of the polishing spot over the part surface. The mechanism of the material removal in the contact zone is considered as a process governed by the particularities of the Bingham flow in the contact zone. The problem like the hydrodynamic theory of lubrication is treated for plastic film. As this takes place the shear stresses distribution in the film is obtained from the experimental measurements of the pressure distribution in the contact spot. Reasonable correlation between calculated and experimental magnitudes of the material removal rate for glass polishing lends support to the validity of the approach.
An experimental and numerical study of the laser-induced damage of the surface of optical material in the femtosecond regime is presented. The objective of this work is to investigate the different processes involved as a function of the ratio of photon to bandgap
energies and compare the results to models based on nonlinear ionization processes. Experimentally, the laser-induced damage threshold of optical materials has been studied in a range of wavelengths from 1030 nm (1.2 eV) to 310 nm (4 eV) with pulse durations of 100 fs with the use of an optical parametric amplifier system. Semi-conductors and dielectrics materials, in bulk or thin film forms, in a range of bandgap from 1 to 10 eV have been tested in order to investigate the scaling of the femtosecond laser damage threshold with the bandgap and photon
energy. A model based on the Keldysh photo-ionization theory and the description of impact ionization by a multiple-rate-equation system is used to explain the dependence of laser-breakdown with the photon
energy. The calculated damage fluence threshold is found to be consistent with experimental results. From these results, the relative importance of the ionization processes can be derived depending on material properties and irradiation conditions. Moreover, the observed damage morphologies can be described within the framework of the model by taking into account the dynamics of energy deposition with one dimensional propagation simulations in the excited material and thermodynamical considerations.
The technology of finishing for optics, ceramics, and semiconductors is one of the most promising uses of the magnetorheological effect. It perfectly coupled with computer control, allowing in quantity production the unique accuracy and quality of a polished surface to be achieved. The polishing process may appear as follows. A part rotating on the spindle is brought into contact with an magnetorheological polishing (MRP) fluid which is set in motion by the moving wall. In the region where the part and the MRP fluid are brought into contact, the applied magnetic field creates the conditions necessary for the material removal from the part surface. The material removal takes place in a certain region contacting the surface of the part which can be called the polishing spot or zone. The polishing process comes to the program-simulated movement of the polishing spot over the part surface. The mechanism of the material removal in the contact zone is considered as a process governed by the particularities of the Bingham flow in the contact zone. The problem like the hydrodynamic theory of lubrication is treated for plastic film. As this takes place the shear stresses distribution in the film is obtained from the experimental measurements of the pressure distribution in the contact spot. Reasonable correlation between calculated and experimental magnitudes of the material removal rate for glass polishing lends support to the validity of the approach.
Starting from the absorption of laser energy at a subsurface
nanoparticle in fused silica, we simulate the consequent buildup of
stresses and resulting mechanical material damage. The simulation
indicates the formation of micropits with size comparable to a
wavelength, similar to experimental observation. Possible mechanism for
enhanced local light absorption are discussed.
Various investigations show that damage threshold of optical coatings by intense ultrashort laser pulses is closely related to the intensity of electric field at layer interfaces. LIDT measurements of high reflectance optical coatings using femtosecond pulses at 800 nm wavelength are presented. ZrO2, HfO2 and Ta2O5 as high refractive index materials for two sets of experiments were chosen. Two different coating designs were investigated: standard quarter-wavelength design with SiO2 overcoat and modified "E-field" non quarter-wavelength design with suppressed electric field. Damage sites were studied using optical and AFM microscopes. Relation between electric field distribution and damage morphology was observed. The results demonstrate, that suppressing electric field at layer interfaces enables to increase LIDT for high reflectance coatings almost twice if compared to standard quarter-wavelength design when using ultrashort laser pulses. However electric field distribution is sensitive to variations in thicknesses of outer layers, so deposition process should be precisely controlled to get improvement in LIDT of coatings.
THE problem of surface reflexion from lenses has led1 to the development of multilayer interference structures which can suppress the reflexion from glass surfaces by a factor of 10 or more throughout the visible spectrum. But observations on the corneas of nocturnal insects indicate that nature may have anticipated the problems2. Electron microscope studies of the corneal lenses of moths reveal that the outer surface is covered in a regular array of conical protuberances, typically of about 200 nm height and spacing. Bernhard2 proposed that the function of this structure might be to suppress reflexions by effectively proving a graded transition of refractive index between the air and the cornea. The proposal was substantiated by measurements with microwave radiation reflected from a model of the array, scaled up appropriately for the longer wavelengths.
Starting from the absorption of laser energy at a subsurface nanoparticle in fused silica, we simulate the consequent buildup of stresses and resulting mechanical material damage . The simulation indicates the formation of micropits with size comparable to a wavelength, similar to experimental observation. Possible mechanisms for enhanced local light absorbtion are discussed.
In this study, the applicability of commonly used Damage Frequency Method (DFM) is addressed in the context of Laser-Induced Damage Threshold (LIDT) testing with pulsed lasers. A simplified computer model representing the statistical interaction between laser irradiation and randomly distributed damage precursors is applied for Monte Carlo experiments. The reproducibility of LIDT predicted from DFM is examined under both idealized and realistic laser irradiation conditions by performing numerical 1-on-1 tests. A widely accepted linear fitting resulted in systematic errors when estimating LIDT and its error bars. For the same purpose, a Bayesian approach was proposed. A novel concept of parametric regression based on varying kernel and maximum likelihood fitting technique is introduced and studied. Such approach exhibited clear advantages over conventional linear fitting and led to more reproducible LIDT evaluation. Furthermore, LIDT error bars are obtained as a natural outcome of parametric fitting which exhibit realistic values. The proposed technique has been validated on two conventionally polished fused silica samples (355 nm, 5.7 ns).
In the past decades, efforts have been concentrated on reaching more
laser resistant multilayers optical components in the Infrared (IR)
range. New designs and materials have been investigated and among them
binary or ternary oxide mixtures have revealed to be very profitable to
improve the laser damage resistance of the coatings in the IR. The
physical characteristics of such mixed materials are indeed tunable and
the deposition process associated allows to obtain multilayers with
smoother interfaces, which reduces considerably the damage threshold of
the component. The present work is focused on the study of pure
materials and their binary oxide mixtures in the UV range, using S-on-1
testing, for two different laser beam sizes. Samples resistance to
multipulse irradiation is then compared for both beam sizes, extracting
the data with a thermal model assuming nanometric inclusions. The
fatigue effects of the set of sample have also been investigated,
showing no clear trend of fatigue for all tested components.
Accurate laser damage measurements are more difficult to perform in nonlinear optical crystals than in glasses due to several effects proper to these materials or greatly enhanced in these materials. Before discussing these effects, we address the topic of error bar determination for probability measurements. Error bars for the measured damage probabilities are especially important when testing small and expensive samples like nonlinear crystals, where only few sites are used for each measurement. The mathematical basics for the numerical calculation of probability error bars corresponding to a chosen confidence level are presented. Effects that possibly modify the maximum light intensity obtained by focusing into a biaxial nonlinear crystal are mainly the focusing aberrations and self-focusing. Depending on focusing conditions, position of the focal point in the crystal, beam propagation direction, and polarization, strong aberrations may change the beam profile and drastically decrease the maximum intensity in the crystal. A correction factor based on former theoretical work is proposed for this effect. The characteristics of self-focusing are quickly reviewed for the sake of completeness, and a note on parasitic second harmonic generation is added at the end. (C) 2008 Society of Photo-Optical Instrumentation Engineers.
This paper reports that SiO2 is selected to fabricate broadband antireflection (AR) coatings on fused silica substrate by using glancing angle deposition and physical vapour deposition. Through accurate control of the graded index of the SiO2 layer, transmittance of the graded broadband AR coating can achieve an average value of 98% across a spectral range of 300–1850 nm. Moreover, a laser-induced damage threshold measurement of the fabricated AR coating is performed by using a one-on-one protocol according to ISOH254–1, resulting in an average damage threshold of 17.2 J/cm2.
The characterization of roughness at the nanoscale by the means of atomic force microscopy (AFM) was performed on high aspect ratio glancing angle deposited titanium thin films. With the use of scanning electron microscopy as well as x-ray photoelectron spectroscopy, it was shown that the AFM measurements gave rise to incorrect roughness values for the films consisting of the highest aspect ratio structures. By correcting for this experimental artefact, the difference between the saturated roughness value of a film grown with conventional physical vapour deposition and films grown with a glancing angle of deposition was shown to behave as a power law function of the deposition angle, with a saturated roughness exponent of κ = 7.1 ± 0.2. This power law scaling was confirmed by three-dimensional molecular dynamics simulations of glancing angle deposition, where the saturated roughness exponent was calculated to κ = 6.7 ± 0.4.
The effect of various HF-based etching processes on the laser damage resistance of scratched fused silica surfaces has been investigated. Conventionally polished and subsequently scratched fused silica plates were treated by submerging in various HF-based etchants (HF or NH4F:HF at various ratios and concentrations) under different process conditions (e.g., agitation frequencies, etch times, rinse conditions, and environmental cleanliness). Subsequently, the laser damage resistance (at 351 or 355 nm) of the treated surface was measured. The laser damage resistance was found to be strongly process dependent and scaled inversely with scratch width. The etching process was optimized to remove or prevent the presence of identified precursors (chemical impurities, fracture surfaces, and silica-based redeposit) known to lead to laser damage initiation. The redeposit precursor was reduced (and hence the damage threshold was increased) by: (1) increasing the SiF62− solubility through reduction in the NH4F concentration and impurity cation impurities, and (2) improving the mass transport of reaction product (SiF62−) (using high-frequency ultrasonic agitation and excessive spray rinsing) away from the etched surface. A 2D finite element crack-etching and rinsing mass transport model (incorporating diffusion and advection) was used to predict reaction product concentration. The predictions are consistent with the experimentally observed process trends. The laser damage thresholds also increased with etched amount (up to ∼30 μm), which has been attributed to: (1) etching through lateral cracks where there is poor acid penetration, and (2) increasing the crack opening resulting in increased mass transport rates. With the optimized etch process, laser damage resistance increased dramatically; the average threshold fluence for damage initiation for 30 μm wide scratches increased from 7 to 41 J/cm2, and the statistical probability of damage initiation at 12 J/cm2 of an ensemble of scratches decreased from ∼100 mm−1 of scratch length to ∼0.001 mm−1.
The investigation of nodular defects in both thick dielectric single layers and multilayer systems by scanning electron microscopy (SEM) reveals the nodules to be of essentially the same shape no matter how many layers were deposited and what materials were used. The SEM micrographs of a thick LaF(3) layer used in IR coatings and of TiO(2)/SiO(2) multilayer systems are presented. Whereas the nodules in the thick fluoride layer are clearly caused by small spherical particles in an underlying layer of Ge, the cause is less obvious with the multilayer nodules. However, micrographs of uncoated glass substrate surfaces obtained by replicating films used for transmission electron microscopy as well as investigations by SEM and electron micro-probe techniques indicated that particular surface defects or contaminations of submicroscopic size act as the nuclei necessary for the formation of nodules. A growth model and possible measures to prevent nodular defects are discussed from a general point of view.
The characteristic matrix method is used to compute the electric field distribution in a multilayer. The use of optically inhomogeneous films is suggested to lessen discontinuity in the material properties and in the absorption distribution at interfaces between the high-index and the low-index layers, thereby enhancing the laser damage threshold.
Previously published vector equations describing angle-resolved scattering from single-layer- and multi-layer-coated optics have been integrated numerically and analytically over all angles in the reflecting hemisphere to obtain numerical results and analytical expressions for total integrated scattering (TIS). The effects of correlation length, polarization, angle of incidence, roughness height distribution, scattered light missed by the collecting hemisphere, and roughness cross-correlation properties of the multilayer stack on the TIS expression are considered. Background material on TIS from optics coated with single opaque reflecting layers is given for completeness and comparison to corresponding multilayer TIS results. It is shown that errors can occur in calculating the true rms surface roughness from actual TIS measurements; ways to correct these errors are discussed.
Effect of Overcoats on 355-nm Reflectors,” in [Laser Induced Damage in Optical Materials
- C Carniglia
- T Hart
- M Staggs
- H Bennett
- A Guenther
- D Milam
- B Newnam
Carniglia, C., Hart, T., and Staggs, M., "Effect of Overcoats on 355-nm Reflectors," in [Laser Induced
Damage in Optical Materials: 1984], Bennett, H., Guenther, A., Milam, D., and Newnam, B., eds., 285-285-6, ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959
(Jan. 1986). DOI: 10.1520/STP23129S.
Characterization of zirconia-and niobia-silica mixture coatings produced by ion-beam sputtering
- A Melninkaitis
- T Tolenis
- L Mažulė
- J Mirauskas
- V Sirutkaitis
- B Mangote
- X Fu
- M Zerrad
- L Gallais
- M Commandré
- S Kičas
- R Drazdys
Melninkaitis, A., Tolenis, T., Mažulė, L., Mirauskas, J., Sirutkaitis, V., Mangote, B., Fu, X., Zerrad, M.,
Gallais, L., Commandré, M., Kičas, S., and Drazdys, R., "Characterization of zirconia-and niobia-silica
mixture coatings produced by ion-beam sputtering," Appl. Opt. 50(9), C188-C196 (2011).