The IBS2000-project aims to develop a coating machine to coat optics with up to 2m in diameter. IBS is chosen as coating process due to the high optical quality and precision, low losses, and high mechanical and environmental stability.
Common limitations regarding the size of the coated optics are overcome due to a novel approach, where both, the substrate and the target material source are movable. The sputter assembly located below the substrate will move linearly, while the substrate rotates on a stationary axis around its center.
Simulations are done to validate the mechanical concept with a virtual coater concept. First, the material distribution in the substrate plane is calculated and afterwards combined with the movement of the target carrier and the substrate rotation, which gives a first indication of the 2D distribution. The results will be applied to homogenize the projected coating distribution on the final 2m optics.
Information technology advancements are revolutionizing optical components, necessitating a solid theoretical foundation for optically active components. Optical thin films are traditionally designed using the transfer matrix method to calculate linear spectral responses. However, recent developments also address nonlinear optical responses by integrating nonlinearities into the matrix formalism or by applying a maxwell solver, which offers spatially and temporally resolved pulse propagation simulations in thin films.
The transfer matrix method has been extended to include third harmonic generation and ultrafast switching via the Kerr effect. We compare the results from the nonlinear transfer matrix method to results obtained by a maxwell solver. Furthermore optimization routines for nonlinear response design like Monte Carlo algorithms and machine learning with neural networks are shown.
The talk presents concepts for integrating essential active optical functions into thin film coatings, which allows a high degree of miniaturization compared to classical alternatives. Due to the amorphous structure of thin film coating materials, only uneven orders of nonlinear effects will be considered. The chosen applications comprise a concept for frequency tripling mirrors, where the third harmonic generation is performed in the thin film stack, and an all-optical switch, the so-called Kerr-band-switch based on the optical Kerr-effect. The chosen materials, design considerations, and measurements validating the function of the concepts will be presented.
Quantizing nanolaminates (QNLs) are a promising alternative as high-index material in thin film coatings providing high flexibility with respect to their refractive index and bandgap energy. However, the fabrication of QNLs requires high precision in the deposition of the layers. Common monitoring strategies are not applicable due to the nanometer to subnanometer layer thicknesses needed to achieve a significantly increased bandgap energy.
This contribution investigates the impact of thickness errors on the bandgap energy of QNLs. Calculations show a diminishing of the bandgap energy increase due to thickness errors in a single layer. This effect will be investigated experimentally. Moreover, the QNLs linear and nonlinear absorption will be tested as function of layer numbers determining the impact of the increased interfaces of QNL structures.
Applying the new insights, the final goal is the fabrication of functional QNL-coatings with optimized electrical field intensity and increased LIDT for the ultra-short pulse regime.
Contaminations can lead to a reduction of the laser-induced damage threshold (LIDT) leading to an unexpected damage of the components coating inducing damaged areas significantly larger than the beam size. In this study, we developed a process to contaminate the surface of anti-reflective and high-reflective coated optics with Polyether ether ketone particles of the size 10-100 µm. Contaminated samples were then irradiated with a ns-pulsed high repetition 1 µm laser system regarding the determination of the LIDT. We especially illustrate detection as well as the irradiation and monitoring of a single particles during laser irradiation. In conclusion, we have not observed any damages on clean samples up to an energy density of 1 J/cm². However, the particles got already damaged one to two magnitudes below this leading to a significant decrease in the surface damage threshold.
Quantizing nanolaminates are an interesting alternative to classical coating materials with greater independence of refractive index and the optical bandgap energy. This leads to more flexibility and considerable potential to increase the laser-induced damage threshold in the ultra-short pulse regime. The following study presents and compares the design choices, characterization, and LIDT testing of different quantizing nanolaminates for the ultraviolet spectral range to classical coating materials.
Atomic layer deposition offers unique advantages compared to more classical PVD coating processes. These advantages include an inherently high coating thickness homogeneity and conformal coating of both micro-optical structures, such as gratings, and large free-form optics, such as aspheric lenses. The talk will introduce the coating process, compare its properties to those of more classical PVD processes and give an overview of recent developments of ALD coatings in optical applications.
All-silica mirrors manufactured using GLancing Angle Deposition (GLAD) are a promising approach for optics with improved LIDT. However, water content may increase over time due to the porosity of the low index silica layers, potentially changing the LIDT. Additionally, consecutive irradiation during LIDT testing may remove stored water and influence the LIDT.
Laser calorimetry, spectrophotometry and LIDT measurements, applying S-on-1 and R-on-1 methods, were used in order to determine the impact of laser-induced removal of stored water on the absorption, spectral behavior and laser damage resistance of all-silica mirrors. Influence of water reabsorption was investigated under different environmental atmospheric conditions.
We demonstrate a novel concept for an all-optical switch based on the optical Kerr-effect in thin film interference coatings. The switching between transmittance and reflectance relies on highly Kerr-active coating materials in combination with large internal intensity enhancement in thin film interference coatings. The paper investigates the switching performance as well as its relation to the laser induced damage threshold of these novel components. A modulation depth of 30 % was achieved without damage to the component, which very promising for later applications as power limiters or mode locking components.
We present a novel concept for optical switches, which is based on the optical Kerr-effect. In contrast to previous approaches, the switching is achieved by a combination of strongly Kerr-active materials with specially designed and produced optical interference filters. Intense laser irradiation causes refractive index changes in the sensitive Kerr-active layers of the components and the interference filter changes its spectral characteristics, i.e. becomes reflective, depending on design factors. The concept offers several advantages when compared to currently applied switching methods, such as the easier integration into photonic systems because of their compact nature and wide spectral application range.
We propose a figure of merit that characterizes the femtosecond laser damage behavior of optical coatings. This figure of merit, based on the complete spatiotemporal evolution of the field in a multilayer system, can be included in optics design. The monochromatic intensity enhancement widely used in “electric field-engineering” is sufficient only in certain structures such as high-reflectivity quarter-wave mirrors. In more complex systems, for example, in group delay dispersion mirrors and frequency tripling mirrors, one should consider the actual (typically smaller) intensity enhancement produced by short pulses and the change (typically increase) of pulse duration within the stack.
When designing femtosecond laser mirrors, one tries to minimize the peak intensity within the high-index layers to increase the laser-induced damage threshold. Typically, the optimization procedure utilizes the electric field distribution in the layer stack generated by monochromatic irradiation. This approach is sufficient for certain structures like high-reflectors based on quarter-wave films. More complex structures require to take into account the exact evolution of the pulse parameters such as peak intensity and duration within the multi-layer system. We exemplify this by discussing a merit function that can be included in femtosecond optics design.
Epsilon-near-zero-materials and their unique properties are key to successful integration and miniaturization of optical components. Novel concepts, which promise significant progress in this field of research, such as optical switches and thin film electro-optical modulators, are possible, when the electrical and optical properties of ENZ-materials are carefully exploited. To achieve a greater understanding of these properties, this contribution investigates the electrical conductivity, optical transmittance as well as losses of thin indium tin oxide films and links them to their LIDT at various ultrashort pulse durations.
Third harmonic generation (THG) in dielectric films with femtosecond laser pulses is used to study properties of dielectric thin films and stacks thereof below and above the 1-on-1 laser damage threshold. Deviations from the ideal cubic relationship between third-harmonic signal and incident fundamental fluence are a result of several fundamental processes. Their relative contributions are assessed by comparing results from LIDT and conversion efficiency measurements as well as beam profile and pump-probe studies.
The exploitation of nonlinear effects in multi-layer thin films allows for optics with novel functions, such as all- optical
switching and frequency conversion. In this contribution, an improved interferometric setup for the measurement of the
nonlinear refractive index in dielectric substrates and deposited single layers is presented. The setup is based on the wave
front deformation caused by the self-focusing in the measured samples. Additionally, measurement results for a highly
nonlinear material, indium-tin-oxide (ITO) are presented with respect to the materials power handling capabilities and
compared to values from other materials.
We have studied laser induced material modification in a frequency tripling mirror (FTM) consisting of alternating hafnia and silica layers. The third-harmonic signal generated by a train of femtosecond laser pulses (791 nm, 55 fs, 110 MHz) drops over time until it reaches about 20% of the initial value. From the observed changes in reflection and transmission of the mirror a refractive index change of 0.07 was estimated, which occurs in the layer with the highest field enhancement. This index change triggers a drop in the field enhancement, which reduces the efficiency of nonlinear optical processes. The estimated value of ▵n allowed us to explain the 80% reduction in conversion efficiency and as well as an observed decrease in two-photon absorption.
Based on the z-scan method, an interferometric set-up for measuring the optical Kerr-effect was engineered and optimized. Utilizing a Mach-Zehnder configuration, the wave front deformation caused by the Kerr induced selffocusing is monitored. Fitting this deformation to a theoretical approach basing on a beam propagation model, the nonlinear refractive index is obtained. The procedure can be applied to measure the nonlinear refractive index of both, the substrate material as well as the deposited dielectric layer on top of the substrate. The nonlinear refractive index of a layer specially deposited for this purpose as well as for several substrate materials was measured and the results presented.
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