A system for two dimensional mapping of Total Scattering (TS) and Transmission (T) of optical flat surfaces in the spectral range from deep UV to NIR will be introduced. The adaptation of the scatter detector concept for the special requirements of the DUV range will be discussed. Also, the specifications of the set-up such as working ambient, background level, and data calibration procedure demonstrate the performance of the system for the analytical tasks in industrial optics production. <p> </p>On the basis of the presented measurement facility, the essential properties of bare flat optics in respect of their polishing state, roughness level, state of cleaning and defect distribution can be investigated with the TS system in a nondestructive way. The homogeneity of the whole surface of an optical component can be tested with a defined lateral resolution. The knowledge of the inhomogeneity is an important indication for the quality evaluation of optical components. We present the TS result and the calculated defect density distributions of selected components, which are handled by different cleaning procedures. Also, additional effects in TS and T will be outlined and compared with spectral photometric measurement.
In optical coating production the generation of particles and defects is always an undesirable side effect and cannot be
completely avoided in the handling steps of the optical components. Particles and defects on the substrates and in the
functional coatings lead to scattering and absorption, which may cause a lower damage threshold for components of high
power laser application.
In this study, results of a long term investigation in the quality and the state of the cleanliness of multilayer systems
produced by different deposition techniques are presented. Coated samples of different coating processes are investigated
with the help of a Fast Total Scatter scanning system. Adapted data reduction algorithms for the determination of the
particle sizes derived from the scattering measurements are developed and applied to the measurement results. On this
basis, the density distribution of particle contamination on the samples is evaluated for selected coating runs over a long
term period. The calculated statistics of the samples are related to the corresponding production conditions of individual
coating plants to extract specific effects of the process environment.
The inspection of the surface quality of optical components is an essential characterization method for high power laser applications. We report about two different mapping methods based on the measurement of Total Scattering (TS) and phase contrast microscopy. The mappings are used for the determination of the defect density distribution of optical flat surfaces. The mathematical procedure relating data points to a defect area and to the form of objects will be illustrated in details. The involved differential operators and the optimized sub routines adapted to a large number of defects will be underlined. For the decision about the form of the objects, a parameter set including the “fill factor”, “edge ratio” and the “polar distance” will be discussed in respect to their versatility range for the basic forms. The calculated distribution will be expressed in terms of affine probability compared to the basic forms. The extracted size and form distribution function of the defects will be presented for selected high reflective and anti-reflective coating samples.
Optical scatter measurements are the basis for efficient methods in the quality management of
optical components in all production steps. Especially, the Total Scattering (TS) of an optical
surface can be evaluated in respect of the roughness and the state of cleanliness. In many
applications defects on the surface or the imperfections in the bulk of the components are of
major interest and have to be controlled systematically.
In this paper a fast TS measurement procedure is presented for flat components, which can
map a surface completely in the timescale of few ten to hundred seconds. The mapping covers
the entire test area with spatial steps of less than one micron. The set-up can be adapted to
wavelengths from the UV- to the IR- spectral ranges.
The present study is dedicated to the technical specifications, problems during
implementation and the resolution limits of the Fast TS set-up. TS measurements on samples
with defined micro structures are employed to demonstrate the spatial resolution. Results of
TS measurements in forward and backward direction will be presented for selected samples
with defined particle distribution and sizes.
For the determination of the scatter behavior of materials with different aggregate states such as solid components, liquids and particles an Angle Resolved Scatter (ARS) measurement set-up has been developed at LZH. The set-up can be operated in conjunction with different laser sources and arc lamps. Spectral investigations in the range from the DUV to the NIR can be performed by using a monochromator and filters. Mappings are possible by moving of the test specimens in two spatial directions.
In this paper, we present result on efficiency measurements for holographic gratings in the visible spectral range. The spatial transfer functions of transmittive gratings are measured very precisely at 633nm. Also, scatter characteristic of nano and micro particles in liquids as well as the scatter distribution of some functional dielectric coated samples are discussed.
For precise angle resolved scatter (ARS) investigations on optical components, a scatterometer has been developed, which allows three dimensional scanning of the scattered radiation from the test specimen. By combining the set-up with different radiation sources, measurements in the spectral region from the DUV- to the NIR-spectral range can be performed. The optical properties of the components: reflection, transmittance, and the scatter behavior can be
determined in the same run. The measured data are absolutely calibrated to the incident power. In this paper, we report about ARS- measurements on different samples such as holographic gratings, bare and anti reflective coated substrates. Additionally, results of scatter measurements on high reflective mirrors for 633nm with
different numbers of layers will be presented. The comparison of the ARS-data and the results of Total Scattering (according to ISO 13696) on the same samples will be discussed.
The development of characterization tools for the deep-ultraviolet
(DUV)/vacuum-ultraviolet (VUV) spectral range gains of increasing importance considering the applicability of optics in adequate facilities. At the Laser Zentrum Hannover, procedures for the
investigation of optical parameters, i.e. transmittance, reflectance, absorption and scattering, are developed. In the last two years, a spectrophotometric unit was redesigned allowing a comprehensive characterization of optical components in the wavelength range between 115nm and 310nm. The paper describes the developed device in detail and discusses the sources of error with regard to their influence on measured data. Different investigations were performed and are presented in dependence on the wavelength, the adjusted angle of incidence (AOI) and the polarization of the incident beam. Furthermore, numerous measuring methods are explained which are supported by the in-house compiled software package.
In the course of the rapid progress of DUV/VUV lasers and their employment in semiconductor lithography, micro material processing, and medical surgery systems, the characterization of optical components in this spectral region gains of increasing importance. The precise determination of the optical properties, such as reflectance (R) and transmittance (T), is essential for further progresses of the components. Currently, standardized procedures for measurement of R&T are described in the international standard draft ISO/WD 15368, which is optimized for the whole wavelength range above DUV. In the DUV/VUV spectral range, scatter losses caused by the surface and bulk of the components increase with decreasing wavelengths. This effect is not considered in the standardized measurement procedures for T and R. In this study, a spectral photometer device, which has been developed at Laser Zentrum Hannover, will be presented. The set-up allows measurements of total reflectance for a defined acceptance angle range. In the current state, the DUV.VUV-photometer covers a spectral range from 115nm up to 300nm. Investigations on the scatter behavior of optics for this spectral range indicate a need for precise separation between ordinary reflected or transmitted beam and scattered radiation on the test samples. The dependence of the R and T values on the collection angles will be illustrated.
Optical scattering is a fundamental loss mechanism in high power laser applications, especially for optical systems in the DUV/VUV spectral range. For recording of total optical scattering (TS) several standardized measurement procedures which are optimized for the UV/VIS/NIR spectral range, are already existing. In this study, the problems of total scatter measurement techniques in the DUV/VUV will be discussed in respect to their practicability. In addition improvements for the standardized measurement procedures will be presented. TS measurements on selected coated laser components for 157nm and 193nm will be discussed in view of the loss mechanisms in thermally evaporated dielectric multilayer coating systems. The change or rms surface roughness of the components in dependence of the physical thickness of coated thin films will be described with the help of TS measurements. Also, the TS results for bare substrates in VUV and VIS will be compared and considered in relation to applications in short wavelength ranges.
Light scattering is an optical loss mechanism, which reduces the efficiency of imagin systems and beam guiding arrangements in many applications of high power excimer lasers. Therefore, the measurement of total scattering by optical components plays an important role for the development and optimization of thin film components and high power optics for the DUV/VUV-spectral range. In this work, a set-up for the measurement of total scattering (TS) is described and the limitations of the different functional parts are considered. The imaging properties of the Coblentz hemisphere, which is employed for collection of the scattered radiation from the specimen, are investigated in respect to the precision of the scatter measurements in the DUV/VUV spectral range. Also, the technical demands for the beam preparation system, the signal detection and the calibration of the set up are compared to specifications of the current Draft International Standard ISO/DIS 13696 for the measurement of total scattering. The study is concluded by typical TS measurements at 193nm and preliminary result for scatter measurements at 157nm.
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.
Light scattering of optical laser components gains in importance for the short wavelength range. A standard procedure for the measurement of 'total scattering' is described in the Draft International Standard ISO/DIS 13696, which is based on integration or collection of the scattered radiation. Meanwhile the measurement concepts have qualified for the VIS- and NIR-spectral region, investigations are necessary for an application of the standard procedure in the DUV/VUV. In this work the optical properties of selected diffuse reflective materials are studied in the DUV/VUV spectral region. For the determination of the angle resolved scattering and the relative spectral reflectance of the samples, a commercial vacuum spectrophotometer is employed. Some of the samples exhibit a cosine angle distribution for the scattered light at 193 nm and 157 nm and can be used as calibration targets. Total scatter values of different thin film samples were measured at 193 nm by using these qualified calibration targets.