Ultra-short laser applications require high quality dielectric optics. The natural dispersion of light needs to be matched by dielectric components. However such dispersive components are very challenging for the deposition process and are characterized by high field intensities inside the layer stack. Such layers are expected to diminish the possible laser induced damage thresholds (LIDTs) because of their low optical gap value for suitable high refractive index materials. This paper reports about the manufacturing of amorphous nanolaminates to tune the optical gap. Such sequences are substituted into a conventional high reflective mirror to decrease the electric field of binary Tantala layers by 30 % which correlates to an improvement in LIDT of almost 16%.
The present contribution is addressed to an improved method to fabricate dielectric dispersive compensating mirrors (CMs) with an increased laser induced damage threshold (LIDT) by the use of ternary composite layers. Taking advantage of a novel in-situ phase monitor system, it is possible to control the sensitive deposition process more precisely. The study is initiated by a design synthesis, to achieve optimum reflection and GDD values for a conventional high low stack (HL)n. Afterwards the field intensity is analyzed, and layers affected by highest electric field intensities are exchanged by ternary composites of TaxSiyOz. Both designs have similar target specifications whereby one design is using ternary composites and the other one is distinguished by a (HL)n. The first layers of the stack are switched applying in-situ optical broad band monitoring in conjunction with a forward re-optimization algorithm, which also manipulates the layers remaining for deposition at each switching event. To accomplish the demanded GDD-spectra, the last layers are controlled by a novel in-situ white light interferometer operating in the infrared spectral range. Finally the CMs are measured in a 10.000 on 1 procedure according to ISO 21254 applying pulses with a duration of 130 fs at a central wavelength of 775 nm to determine the laser induced damage threshold.
In the presented work a fast frequency domain measurement system to determine group delay (GD) and group delay dispersion (GDD) of optical coatings is proposed. The measurements are performed in situ directly on moving substrates during the thin film coating process. The method is based on a Michelson interferometer, which is equipped with a high power broad band light source and a fast spectrometer. Especially for the production of chirped mirrors it is advantageous to obtain group delay and group delay dispersion data of the last layers. This additional information allows for online corrections of coating errors to enhance the precision of complex interference filters for short pulse applications.
The present contribution is concentrated on an improved method to manufacture dielectric dispersion compensating mirrors in the ultra violet (UV) range by applying a novel online phase monitoring device. This newly developed measurement tool monitors the group delay (GD) and group delay dispersion (GDD) of the electromagnetic field in situ during the deposition of the layer system. Broad band monitoring of the phase enhances the accuracy in the near infrared spectral range (NIR), significantly. In this study, the correlation of the GDD in the NIR and in the UV spectral range is investigated. A design synthesis is introduced to achieve optimum reflection and GDD target values in the UV and NIR. This requires a similar behavior of both bands according to deposition errors, to guarantee switching off the UV GDD target band proper, while monitoring the GDD in the NIR spectral range. The synthesis results in a design, characterized by a GDD of -100fs2±20fs2 between 330nm and 360nm in the UV and by -450fs2±10fs2 within 820nm to 870nm in the NIR. The fabricated sample, applying an ion beam sputtering process, consists of a 9μm layer stack of Hafnium oxide and Silicon dioxide. The first layers of the stack are switched and controlled by a conventional in situ spectrometric broad band monitoring in conjunction with a forward re-optimization algorithm, which also manipulates the layers remaining for deposition at each switching event. To accomplish the demanded GDD-spectra, the last layers are controlled by the novel in situ GDD monitor.
Enhanced strategies in optical broadband monitoring allow for thin film deposition under rapid production conditions
with very high process stability. Recent developments in the field include simulation techniques with virtual deposition
systems, to enable a pre-selection of different multilayer designs, and hybrid process control strategies which combine
optical monitoring with quartz crystal monitoring. In particular, automated online error re-calculation and design re-optimization
are presently in the focus of research to improve the efficiency of deposition plants. In this contribution a
developed re-optimization module is presented, and the resulting increase in production yield of complicated multilayer
designs is demonstrated by deposition examples. Besides automated design changes directly initiated by the re-calculation
software, the presented approach also considers supervising functions that stop the deposition run when
critical errors are detected.
Ever increasing demands in the field of optical coating systems with highest complexity impose new challenges on the
development of advanced deposition techniques with increased stability, and especially on the corresponding precise
thickness monitoring strategies. Most of the classical thickness monitoring concepts employed in industrial production,
which are based on quartz crystal or optical monitoring, are presently operated near to their precision limits. However,
resulting from extensive research activities, monitoring concepts could be significantly extended during the last years.
On the one hand, newly developed hybrid process control algorithms combine the information of the optical and non-optical
sensors to achieve a higher precision and fault-tolerance. On the other hand, independent thickness monitors are
integrated in flexible manufacturing concepts which include adapted computational manufacturing tools as well as
specific re-calculation and design re-optimization modules. Computational manufacturing allows for a design pre-selection
prior to deposition with essentially improved certainty which could not be achieved with classical error analysis
until now. In contrast, the re-calculation and re-optimization modules are on-line tools that monitor the running
deposition process. In case of critical deviations, a fully automated modification of the residual design assures a
successful achievement of specifications under the chosen monitoring technique.
The term photocatalysis is used to describe a photon-driven catalytic process. Titanium dioxide is a well-known
photocatalyst in such fields as self-cleaning material and anti-microbial effects. Besides these photocatalytic applications,
TiO2 is a widely-used high index material for optical thin films.
In the present investigation, the photocatalytic activity of transparent TiO2 thin films was optimized to achieve
multifunctional high precision optical coatings. The films have been deposited by ion assisted deposition (IAD), applying
a Leybold APS plasma source as well as a Denton CC-105 ion source. The cause-and-effect chain between the use of
different parameters in the IAD process and optical properties of the TiO2 layers as well as their photocatalytic activities
are described.
As test reaction for the determination of the photocatalytic properties, the degradation of methylene blue (MB) was
chosen. The used setup based on a high precision two-path laser measurement system was developed by the LZH in
order to determine the kinetic performance of TiO2 catalysts under well-defined UV illumination conditions. Photonic
efficiencies of the TiO2 thin films were calculated from the obtained data. Additionally, crystal structure analysis has
been investigated for the identification of anatase and rutile modifications.
The comparison of the results shows that ion assisted deposition is an appropriate technology for the preparation of
photocatalytic active thin films for optical applications.
The production of advanced optical coatings with complex spectral characteristics and high performance is directly
dependent on the stability of the deposition process and on the accuracy of the monitoring system employed for
controlling the thickness of the constituent single layers. The present contribution is concentrated on the current state in
deposition control and manufacturing of coatings with improved precision. As major topics the simulation of deposition
processes, modern monitoring concepts, and the handling of errors occurring during the deposition process will be discussed. For illustration of some recent developments, results on the deposition of rugate filters on the basis of an ion beam sputtering process will be presented.
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