Today’s high brilliance Laser sources cause huge thermal effects on optical components, affecting process stability.
This paper shows the holistic approach to the improvement of objective lenses to minimum thermal effects as focus shift.
A new approach to the transient simulation of thermal behavior, starting with FEM Analysis, analytical description of
surface deformation and refraction index distribution resulting in transient plot of image quality changes by optics design
simulation. Optics material selection and characterization of bulk material, surface and coating by newly developed
measurement techniques is shown. The optimum setting of opto-mechanical design, material selection, surface finish and
coating allows to produce lenses with focus shift by 0,05times the Rayleigh range @1064nm, 4kW multimode at
High reflective coatings for 193nm wavelength and 45° incidence were developed which combines the advantages of all-oxide
and all-fluorides layer stacks. Using plasma-assisted evaporation very smooth and dense Al2O3/ SiO2 multilayers showing small light scatter were deposited onto fused silica substrates. In the same coating process followed metal
fluoride stacks, which could reduce the resulting coating absorption at 193nm. The non-polarized reflectance of
combined stacks at 193nm is R>98.5% at 45° and R>98.0% for an angle range of 42°-48°. As the number of fluoride
layers could be drastically reduced compared to all-fluoride coatings any formation of micro-cracks could be avoided.
The stress of the oxide/fluoride stacks was less than 40MPa.
Within the EUREKA-project EU 2359 (Instruments and Standard Test Procedures for Laser Beam and Optics Characterization) a "Round-Robin"-experiment on reflectivity measurements at the wavelength λ = 1.06 μm has been carried out. The topic of this "Round-Robin"-experiment was the evaluation of the Working Draft ISO/WD 13697 and Committee Draft ISO/CD 15368 and the comparison to simple transmission and reflectivity measurements.
For the determination of transmittance and reflectance of laser components, commercially available spectrophotometers are used in industry to monitor the quality at a medium accuracy level. If a higher level of precision is required, especially to resolve the reflectivity of high-reflecting dielectric mirrors, the measurement set-up described in ISO/WD 13697 should be preferred. This standard procedure was elaborated in the framework of the CHOCLAB project.
This paper analyzes the results of the "Round-Robin"-experiment; the accuracy and comparability of measurements according to different methods will be given.
Light scattering measurements are important tools for characterizing optical surfaces can basically be divided into two main groups: total scatter measurements (TS) and Angle Resolved Scattering (ARS). Since TS measurements are fairly straight forward and widely used, international standardization has formulated an international draft standard on it, ISO/DIS 13696. ARS is a more complex method and not as common as TS measurements. However ARS data in form of the Bi-directional Reflectance Distribution FUnction (BRDF) can be used to predict stray light in Laser and Industrial Optical Systems. Because of increasing importance of this topic the EC is sponsoring a project regarding 'Standard procedures for stray light specification, measurement and testing - SLIOS'. During the project two of the activities are: performing a round robin experiment of measuring BRDF data at 5 different sites including some complementary techniques; compiling of an open access data base of measured BRDF data, measured according to procedures agreed upon between the SLIOS partners and proposed for 'Standard Procedures'. Results of these two activities will be presented.
The measurement of total scatter losses is a major prerequisite for the development, optimization and commercialization of high quality optical components. Especially in laser technology, optical scattering gained of importance in the source of the development of laser system with ever increasing output power and improved beam parameters. Besides its influence on the efficiency of laser systems and the beam steering arrangement, total scattering is an important safety aspect for application of these laser systems in materials processing, medicine and fundamental research. As a consequence of this global trend, working groups of TC 172/SC 9 initialized the development of an International Standard for the measurement of total scattering in optical components.
We investigated thin MgF2/LaF3- and LaF3/MgF2-layers on opaque glass with angle resolved light scattering to analyze the different scattering contributions. We already showed the possibility of separating the volume scattering from the interface contribution for a single MgF2-layer on BK7. In this work we concentrated on layers with thicknesses common for multilayer mirrors in the UV. The roughness of the interfaces was included in the calculations by the power spectral density measured with the atomic force microscope. This has proven to be better than a Gaussian or exponential correlation function ansatz. In order to obtain as much information as possible we also investigated the uncoated substrates and the corresponding single layer systems. We found again that the investigated layers, which have columnar structure, showed generally non-negligible volume scattering. Additionally crosscorrelation between the different interfaces must be taken into consideration.
A theoretical formalism and experimental methods are presented, which enable statistical fluctuations of the films bulk and interface roughness properties to be estimated from volume scattering and roughness scattering, respectively. The theoretical model is implemented in a numerical algorithm that allows one to optimize experimental strategies and to determine morphological parameters from measured scattering curves. Angle resolved scattering (ARS) measurements are performed on MgF2 films on glass substrates while varying the illumination and observation parameters. Atomic force microscopy (AFM) provides helpful additional information on the surface morphology.
An attempt is presented of a systematic experimental approach to the problem of scattering and roughness modification after deposition of an optical thin film. BK 7 substrates with different surface qualities have been coated with evaporated MgF2, LaF3 and magnetron sputtered SiO2 and Nb2O5 films as representatives of low index/high index columnar structured and structureless films, respectively. Investigations by total integrated scattering (TIS) and angle resolved scattering (ARS) at 633 nm and 325 nm as well as atomic forced microscopy (AFM) demonstrate the possibility of quite different effects of scattering and roughness modification to occur.
The microtopography of a certain surface is a complicated structure varying across the complete surface. Every surface has different elements of microstructure. In this paper, we consider roughness as a fine structure and defects as large structure elements. Roughness measurement on BK7-glass and CaF2 samples is considered using different techniques. The comparison includes the automatic scatterometer STREUIX 2 and a TIS-measurement system, the ZYGO microprofilometer MAXIM (DOT) 3D, and the NANO SCOPE III of Digital Instruments. For the investigation of scattering characteristics of different surface defects, a special measuring device was developed. The scattered light distribution of different defects and contaminations measured with this set-up is discussed.