Ion beam sputtering (IBS) is the state-of-the-art coating technique to produce highest quality optical filters and laser optics. In both fields the requirements regarding surface flatness have increased through the last decade. Since IBS thin films usually show a high compressive intrinsic stress, a suitable compensation approach as well as the precise determination of the material dependent stress values are essential to fulfill challenging specifications. This contribution compares intrinsic stress results for several coating materials realized with different IBS machines in side sputtering and sputter up configuration. Furthermore, a stress compensation approach is discussed on a concrete example including the influence of the substrate material. As a major topic the temporal evolution of the coating stress is investigated. Finally, we present a post coating process step to reduce the surface irregularity around the substrate rim induced by the fixturing.

Metal oxide mixture materials enable the production of dielectric multilayer coatings for highest power laser applications. During thin film deposition, when using sputtering techniques in combination with composite target materials, preferential sputtering occurs on the target surface. The quantitative analysis of the mixture thin film composition, usually performed by ion beam based depth profiling methods, is also affected by preferential sputtering. To gain a deeper understanding, the atomic composition variation of sputtered mixture material surfaces is calculated applying the Monte Carlo simulation program tridyn. The simulation results are compared to the atomic composition gradient measured via depth profiling x-ray photoelectron spectroscopy for mixture thin films composed of HfO2, Sc2O3, Al2O3, and SiO2. The deviations between the experimental and simulated data are discussed with respect to the different mixture material combinations.

This contribution describes an approach to realize dichroic mirrors for fifth-harmonic separation with a diameter of 12”. The optics will be used at the National Ignition Facility to build a diagnostic based on Optical Thomson Scattering, which requires a high energy, pulsed laser operating at 211nm wavelength. Since the ultra-violet absorption edge of the most commonly used high refractive coating materials is above 211nm, only a few oxide materials as for example alumina are suitable for this wavelength. The applied material combination Al2O3/SiO2 provides a small refractive index contrast of about 0.2, which requires a coating process with a very high precision and uniformity to realize complex thin film designs. To achieve a physical layer thickness uniformity better than 0.5%, the linear motion concept of the MAXIMA ion beam sputtering machine [1] is combined with an additional substrate rotation. The layer thickness is controlled precisely by optical broad band monitoring in the wavelength range from 220nm to 1050nm. To realize a surface figure of λ/10 at 633nm for a clear aperture of 250mm diameter, the multi-antireflection coating on the backside is utilized for stress compensation. Experimental results regarding the spectral performance, the mechanical stress, the surface roughness and the laser damage resistance will be presented and discussed.

Optical thin films are essential for many laser applications in industry and science. The increasing demand for highest quality laser optics, requires the enhancement of existing coating technology as for example Ion Beam Sputtering (IBS). By facing new challenges like the large area deposition for line beam optics with up to two-meter edge length, LASEROPTIK is already pushing the limits of coating technology. This contribution describes an approach to combine Glancing Angle Deposition (GLAD) with IBS utilizing the MAXIMA deposition machine. To analyse the dependence of the refractive index, the ultra violet absorption edge, the mechanical stress and the laser damage resistance on the mean deposition angle to the substrate surface, single layers as well as multilayer coatings are realized at five different mean deposition angles between 30 degrees and 90 degrees. By coating one substrate at each of the five different mean deposition angles in the same batch the influence of run to run process variations is minimized. Besides fundamental research regarding this coating technology the results of this experiment will gain further insight into the deposition of thin films on strongly curved surfaces applying curvature dependent velocity profiles.

New ultrashort pulse laser systems exhibit an ever increasing performance which includes shorter pulses and higher pulse energies. Optical components used in these systems are facing increasing requirements regarding their durability, and therefore understanding of the damage mechanism is crucial. In the ultra-short pulse regime electron ionization processes control the damage mechanisms. For the single wavelength, single pulse regime the Keldysh [1] and the Drude model [2] allow a quantitative description of these ionization processes. However, in this model, the electrical field is restricted to a single wavelength, and therefore it cannot be applied in the case of irradiation with two pulses at different wavelengths. As frequency conversion is becoming more common in ultra-short pulse applications, further research is needed in this field to predict the damage resistance of optical components. We investigate the damage behavior of high reflective mirrors made of different metal oxide materials under simultaneous exposure to ultra-short pulses at the wavelengths 387.5 nm and 775 nm, respectively.

Laser material processing plays an important role in the fabrication of the crucial parts for state-of-the-art smartphones and tablets. With industrial line beam systems a line shaped beam with a length above one meter and an average power of several thousand watts can be realized. To ensure excellent long axis beam homogeneity, demanding specifications regarding the substrate surface form tolerances and the coating uniformity have to be achieved for each line beam optic. In addition, a high laser damage threshold and a low defect density are required for the coatings. In order to meet these requirements, the MAXIMA ion beam sputtering machine was developed and built by LASEROPTIK.This contribution describes the functional principle of MAXIMA deposition machine, which adapts the ion beam sputtering technology with its highest coating quality to the field of large area deposition. Furthermore, recent developments regarding the process control by optical broadband monitoring are discussed. Finally experimental results on different thin film characteristics as for example the coating uniformity, the microstructure and the laser damage resistance of multilayers are presented.

Optical coatings are essential for many applications of excimer or solid state lasers in industry and science. An increasing demand for larger optics of highest quality, mainly generated by the display industry processing active matrix organic light emitting diode (AMOLED) backplanes, is posing new challenges for substrate and coating suppliers. For the deposition process development principally the coating uniformity, but also the handling and the cleaning steps of optics with one edge length (L) above 1 meter and several kilograms of weight have to be considered. To provide coatings for optics up to 2 meter edge length, a new ion beam sputtering (IBS) machine was developed and built at LASEROPTIK.This contribution describes an approach to adapt the IBS technology with its advanced coating quality for small optics (L <= 50mm) to the field of large area deposition (L >= 1m). Applying a customized linear drive, the MAXIMA deposition machine is able to coat optics of up to 100kg weight sequentially. Experimental results on the uniformity, the spectral characteristics and the laser damage resistance of dielectric single-and multilayer coatings are presented and compared with the performance of standard IBS thin films. Furthermore, the deposition of thin films on convex curved surfaces applying curvature dependent movement profiles is discussed. Finally the run to run stability is evaluated on the basis of concrete coating examples.

Advanced optical thin film design is the key to increase laser durability significantly: either by optimizing the electric field distribution within the coating, or by multi-index or rugate designs. Both ways may be even combined. The electric field distribution within a thin film stack was optimized to avoid peak intensities in critical layers using refractive index engineering and/or layer thickness grading. Femtosecond laser mirrors and dichroics for 780 nm and 390 nm were designed, realized and characterized. Here we present LIDT measurements of electric field optimized mirrors and dichroics, which are almost a factor of three higher compared to standard coating designs. At 780 nm a LIDT of 1.49 J/cm2 has been achieved and at 390 nm 0.58 J/cm2. With the exception of Al2O3, all investigated coating materials show a proportional dependence of the LIDT with electric field maximum, as expected by theory. For Al2O3 based systems the electrical field penetrates deep into the layer stack, a high number of interfaces are involved and interface effects probably limit the achievable LIDT. A similar effect was observed for rugate designs. To exclude such interface effects from the LIDT measurement, a special AR design was developed, which is practically equal for all high index materials. Here a LIDT above substrate damage threshold of 1.7 J/cm2 was achieved.

The laser-induced damage of mixtures of Sc2O3, HfO2, Al2O3 with SiO2 has been characterized in the infrared for both nanosecond and subpicosecond pulses. Laser-induced damage thresholds (LIDTs) are reported and discussed versus band gap for different compositions. The distributions versus fluence of nanosecond damage precursor densities are extracted fitting damage probability curves. Two models are used: first, a statistical approach, i.e., direct calculation of damage precursor density from damage probability, and second a thermal model based on absorption of initiator. The results show a good agreement. The nature, shape, and size of these precursors are discussed. The critical temperature in the thermal model is dependent on the band gap energy.

Electron beam evaporation (without and with plasma assistance) as well as ion beam sputtering are used to prepare optical mixture coatings for applications in the ultraviolet spectral range. It is demonstrated that intermixing aluminum oxide/ aluminum fluoride materials by these physical vapor deposition techniques results in optical coatings with flexible refractive indices varying between 1.40 and 1.75 in the deep ultraviolet spectral region. At the same time, extinction coefficients vary between less than 1x10(-4) and 2x10(-3). For evaporated layers, at certain mixture ratios, mechanical stress appears to be close to zero. (C) 2014 Optical Society of America

We report on the realization of aluminum oxyfluoride thin films and alumina/silica mixture coatings with different ratios by ion beam sputtering. The atomic compositions quantified by energy dispersive x-ray spectroscopy are correlated with the optical properties calculated from spectrophotometry and laser calorimetry measurements. Furthermore, the femtosecond laser damage resistance (τ=400  fs) of single layers is investigated in the infrared at 1030 nm and in the ultraviolet at 343 nm wavelengths. Experimental results on the wavelength scaling of the laser-induced damage threshold for oxyfluoride and oxide composite coatings are presented.

We report on the correlation between the laser damage resistance, the optical and the physical properties of Sc(2)O(3)/SiO(2) mixture coatings. Several sets of samples with ten different mixture ratios have been prepared by ion-beam sputtering. The atomic compositions of the mixture thin films are quantified employing x-ray photoelectron spectroscopy depth profiles. Laser-induced damage thresholds are determined with single subpicosecond pulses (500 fs) at 1030 nm. Furthermore, Son1 multishot measurements are realized in the ultraviolet wavelength range (355 nm) at pulse durations of 5 ns. In addition, the influence of two different substrate polishing qualities on the radiation resistance of the composite thin films is discussed.

Summary form only given. The development of new, more powerful laser systems in the last decades has been accompanied by an extensive research in the development of more laser-resistant coated components. Abrupt interfaces between deposited layers of such components have been shown to be the main cause of low laser-damage resistance. Indeed, defects and impurities concentrate at interfaces, and efforts have been concentrated on the development of new designs with smother interfaces. To perform those designs, like in "rugate" filters [1], binary oxide mixtures have been employed and the resulting components have shown a higher laser resistance in the infra-red range (IR). Moreover, oxide mixtures show interesting physical effects because in some cases, their properties are not simply a linear combination of both pure deposited materials [2], but the whole structure behaves as a new material with its own physical properties. In the Ultra-Violet (UV) range, where photon energies are particularly high, the lack of laser resistant optical components is critical, and oxide mixtures are seen as good potential candidates to increase the performances of optical components in terms of laser-resistance. In laser induced damage investigations, the beam diameter is known to play an important role in the damage probability [3,4]. In this present work, the impact of three beam waists (15μm, 50 μm and 170 μm) has been tested on a series of six monolayers deposited on superpolished fused silica substrates. The set of components is composed of three pure materials (HfO2, Al2O3 and SiO2) and of their binary mixtures. All components have been tested in the nanosecond regime (pulse duration of 8ns), in multiple pulse mode (S-on-1 testing) at 355nm and with a repetition rate of 50Hz. The installed setup includes a dynamic in-situ damage detection using a fast camera, which allows to study the so-called "fatigue effects" of the tested layers. For data reduction, a thermal model with nanometric inclusions was assumed leading to a precursor density versus fluence relation that follows a two-parameter power-law [5]. Adjustment of these parameters provides a fit of the damage probability (Fig. 1). The resulting precursor density and the damage threshold fluence are drawn from the fit and can be compared from one component to the next.

Oxifluoride and oxide mixture thin films with different ratios are produced by ion beam sputtering. The optical properties and the composition of Al2O3/AlF3 and Al2O3/SiO2 mixture coatings are correlated with the femtosecond laser damage resistance.

We report on the laser damage resistance of thin films prepared by Ion Beam Sputtering. The samples are fused silica substrates coated with single layer films of pure oxides (SiO2, Nb2O5, ZrO2, HfO2, Ta2O5, Al2O3, Sc2O3) and oxide mixtures with various ratios (Nb2O5/SiO2, ZrO2/SiO2, HfO2/SiO2, Ta2O5/SiO2, Al2O3/SiO2 and Sc2O3/SiO2). For this study the LIDT of more than 60 different samples have measured at 1030nm with pulse durations of 500fs with single pulse irradiation. The results are expressed and compared in terms of LIDT as a function of the measured band gap energy and refractive index. For simple oxide materials a linear evolution of the LIDT with bandgap is observed, with the exception of Sc2O3 material where a very high damage threshold is observed, compared to other high index materials. In the case of mixtures, a more complex behavior is evidenced.

We report on the laser damage resistance of ion beam-sputtered oxide materials (Al2O3, Nb2O5, HfO2, SiO2, Ta2O5, ZrO2) and mixtures of Al2O3-SiO2, Nb2O5-SiO2, HfO2-SiO2, Ta2O5-SiO2, and ZrO2-SiO2, irradiated by single 500 fs pulses at 1030 nm. Laser-induced damage threshold (LIDT), refractive index, and bandgaps of the single-layer coatings are measured. For pure oxide materials a linear evolution of the LIDT with bandgap is observed. The results are in accordance with our simulations based on photo-ionization and avalanche-ionization. In the case of mixtures, however, deviations from the previous behaviors are evidenced. The evolution of the LIDT as a function of the refractive index is analyzed, and an empirical description of the relation between refractive index and LIDT is proposed.

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.

The generation of third harmonic radiation (THG) is required for many pulsed solid-state laser applications in industry and science. In this contribution, the coatings for two necessary optical components, dichroic mirrors and nonlinear optical (NLO) crystals are in the focus of investigation. Because of the high bulk damage threshold lithium triborate (LBO) crystals are applied for this study. HfO2/SiO2 mixtures are employed as high refractive index material to improve the power handling capability of the multilayers. All coatings are produced by ion beam sputtering (IBS) using a zone target assembly for the deposition of material mixtures. The atomic composition and the oxidation ratio of different HfO2/SiO2 mixtures are analyzed by X-ray photoelectron spectroscopy (XPS). The influence of different deposition temperatures and post annealing on the optical properties and the amorphous micro structure of the films is investigated by UV/Vis/NIR spectroscopy and X-ray diffraction (XRD). The laser induced damage thresholds at 355 nm wavelength for nanosecond pulse durations are measured in a 10,000on1 experiment according with the standard ISO21254. Furthermore, the optical components are tested under real application conditions.

Laser-induced damage in the nanosecond domain has been connected to the heating and breakdown of local defects within the thin film and the various interfaces. Within the femtosecond regime, the damaging events can be traced back to multiphoton-based excitation into the conduction band. When critical electron density is exceeded, an optical breakdown will occur. In this Letter we report on evidence that two-photon absorption also significantly triggers laser-induced damage in Ta(2)O(5) thin films at 532 nm and 8 ns pulse duration. For experimental verification, single layers of Ta(2)O(5)/SiO(2) mixtures have been analyzed.

The present study deals with the characterization of hafnia, alumina, and zirconia coatings as well as mixtures thereof with respect to applications in the UV. Emphasis is placed on optical properties, particularly on the relation between UV refractive index and absorption edge. The shift of the coatings is investigated as well as the mechanical stress. Finally, we present the results of stress measurements performed for quarterwave stacks deposited on different substrates in a broad range of deposition temperatures. In this study, no systematic dependence of the result of the stress measurement on the substrate material and geometry could be identified.