This PDF file contains the front matter associated with SPIE Proceedings Volume 9628, including the Title Page, Copyright information, Table of Contents, Invited Panel Discussion, and Conference Committee listing.

The throughput of extreme ultraviolet (EUV) lithography systems is presently strongly limited by the available radiant power at the wafer level. Besides increasing the power of EUV sources, also the quality of the optical elements plays a key role. With state of the art multilayer mirrors the main cause of diminished reflectance is surface and interface roughness as well as interface diffusion. Both properties lead to reduced specular reflectance while only the interface roughness causes diffuse scattering. EUV diffuse scatter thus allows to selectively assess the contribution of the interface roughness.

The intensity distribution of diffusely scattered EUV radiation provides information on vertical and lateral correlations of the surface and interface roughness through the appearance of resonant diffuse scattering (RDS) sheets. The study of off-specular scattering thus serves as a natural tool for the investigation of the roughness of the interfaces. However, upon near-normal incidence impinging EUV radiation, dynamical scattering contributions from thickness oscillations (Kiessig fringes) lead to Bragg lines which intersect the RDS sheets. This causes strong resonant enhancement in the scatter cross section which we called “Kiessig-like peak" in analogy to the well known phenomenon of Bragg-like peaks appearing in hard X-ray grazing incidence measurement geometries. Thus for power spectral density studies of multilayer interface roughness, resonant dynamical scattering cannot be neglected. Theoretical simulations based on the distorted-wave Born approximation enable to separate dynamic features of the multilayer from roughness induced scattering. This allows to consistently determine an interface power spectral density (PSD). We have analyzed magnetron sputtered high-reflectance Mo/Si multilayer mirrors with different nominal molybdenum layer thicknesses from 1.7 nm to 3.05 nm crossing the Mo crystallization threshold.

Our off-specular scattering measurements at multilayer samples were conducted at the PTB-EUV radiometry beamline at the Metrology Light Source (MLS) in Berlin. The samples were produced by magnetron sputtering and pre-characterized by K_α X-ray reflectivity at Fraunhofer IWS, Dresden.

In the framework of an European Space Agency contract, Media Lario Technologies is developing an optical payload for Earth Observation targeted to small satellites. In this paper we present a detailed description of the imager which, by leveraging on aspheric surfaces, bonnet polishing, lightweight materials, an off-the-shelf large format CMOS detector and multispectral filters integrated in the FPA, achieves remarkable image quality with compact volume claim and mass of only 15 kg. The instrument is based on a three mirror anastigmat (TMA) design with an aperture of 200 mm and an F/number of 6. The payload is designed to provide a ground sampling distance (GSD) of 2.75 m for the panchromatic channel at a reference altitude of 600 km, a field of view of 1° and a nominal MTF greater than 60% at Nyquist frequency with a Signal to Noise Ratio (SNR) greater than 100.

Predictable and stable fabrication processes are essential for reliable cost and quality management in optical fabrication technology. This paper reports on strategies to generate and control optimum sets of process parameters for e.g. sub-aperture polishing of small optics (featuring clear apertures smaller than 2 mm). Emphasis is placed to distinguish between machine and process optimization demonstrating, that e.g. it is possible setting up ductile mode grinding process by other means than controlling critical depth of cut. Finally, a recently developed in situ testing technique is applied to monitor surface quality on-machine while abrasively working the surface under test enabling an on-line optimization of polishing processes eventually minimizing polishing time and fabrication cost.

Previously used mirror technologies are not able to fulfil the requirements of future X-ray telescopes due to challenging requests from the scientific community. Consequently new technical approaches for X-ray mirror production are under development. In Europe the technical baseline for the planned X-ray observatory ATHENA is the radical new approach of silicon pore optics. NASA´s recently launched NuSTAR mission uses segmented mirrors shells made from thin bended glasses, successfully demonstrating the feasibility of the glass forming technology for X-ray mirrors. For risk mitigation also in Europe the hot slumping of thin glasses is being developed as an alternative technology for lightweight X-ray telescopes. The high precision mirror manufacturing requires challenging technical developments; several design trades and trend-setting decisions need to be made and are discussed within this paper. Some new technical and economic aspects of the intended glass mirror serial production are also studied within the recently started interdisciplinary project INTRAAST, an acronym for "industry transfer of astronomical mirror technologies". The goal of the project, embedded in a cooperation of the Max-Planck-Institute for extraterrestrial Physics and the University of Applied Sciences Aschaffenburg, is to master the challenge of producing thin mirror shells for future X-ray telescopes. As a first project task the development of low stress coatings for thin glass mirror substrates have been started, the corresponding technical approach and first results are presented.

A new optical characterization method based on imaging spectroscopic reflectometry (ISR) is presented and illustrated on the characterization of rough non-uniform epitaxial ZnSe films prepared on GaAs substrates. The method allows the determination of all parameters describing the thin films exhibiting boundary roughness and non-uniformity in thickness, i.e. determination of the spectral dependencies of the optical constants, map of local thickness and map of local rms values of heights of the irregularities for the rough boundaries. The local normal reflectance spectra in ISR correspond to small areas (37×37 μm²) on the thin films measured within the spectral range 270{900 nm by pixels of a CCD camera serving as the detector of imaging spectrophotometer constructed in our laboratory. To our experience the small areas corresponding to the pixels are sufficiently small so that the majority of the films can be considered uniform in all parameters within these areas. Boundary roughness is included into the reflectance formulas by means of the scalar diffraction theory (SDT) and the optical constant spectra of the ZnSe films were expressed by the dispersion model based on the parametrization of the joint density of electronic states (PJDOS). In general, there is a correlation between the searched parameters if the individual local reflectance spectra are fitted separately and, therefore, the local reflectance spectra measured for all the pixels are treated simultaneously using so called multi-pixel method in order to remove or reduce this correlation and determine the values of all the parameters with a sufficient accuracy. The results of the optical characterization of the same selected sample of the epitaxial ZnSe thin film obtained using the method presented here and combined method of variable-angle spectroscopic ellipsometry, spectroscopic reflectometry and single-pixel immersion spectroscopic reflectometry are introduced in the contribution as well.

Development of antireflective coatings realized by thin film systems requires their characterization and optimization of their properties. Functional properties of such interference devices are determined by optical constants and thicknesses of the individual films and various defects taking place in these systems. In optics industry the characterization of the films is mostly performed in a relatively narrow spectral range using simple dispersion models and, moreover, the defects are not taken into account at all. This manner of characterization fails if applied to real-world non-ideal thin film systems because the measured data do not contain sufficient information about all the parameters describing the system including imperfections. Reliable characterization requires the following changes: extension of spectral range of measurements, combination of spectrophotometry and ellipsometry, utilization of physically correct dispersion models (Kramers-Kronig consistency, sum rules), inclusion of structural defects instrument imperfection into the models and simultaneous processing of all experimental data. This enables us to remove or reduce a correlation among the parameters searched so that correct and sufficiently precise determination of parameter values is achieved. Since the presence and properties of the defects are difficult to control independently by tuning of the deposition conditions, the optimization does not in general involve the elimination of defects. Instead they are taken into account in the design of the film systems. The outlined approach is demonstrated on the characterization and optimization of ultraviolet antireflective coating formed by double layer of Al₂O₃ and MgF₂ deposited on fused silica.

Optical surface quality plays a significant role when considering laser applications. Specifically, short pulses, high pulse energies and shorter wavelength impose high requirements on surface characteristics. Amongst others, scatter losses, absorption, or the damage threshold place high demands on the specification of an optical part, and each application will define the order in priority of these properties. We have conducted several experiments to investigate in the impact of surface characteristics of polished substrates on the performance of coated optics. In this contribution we report on the techniques used to qualify dielectric coatings for excellent power handling capabilities based on the substrate surface finish.

When using the BRDF to learn about surface statistics or to estimate hemispherical scatter from in-plane measurements the assumption is usually made that the surface is isotropic. Unfortunately, this is often not the case; for example a diamond turned mirror is not isotropic. Other common examples are rolled surfaces and situations where scatter is mostly caused by small discrete surface features such as scratches, pits or particles. Another example is scatter from an extended edge that is much longer than the illuminated spot. In these situations the measurements may be made differently and quantified in different units (such as area/sr or 1/deg instead of the common 1/sr associated with BRDF) in order to have a result that can reliably characterize the scatter source. The situation is further complicated by the fact that the popular stray radiation codes accept scatter data only in the standardized BRDF format with units of 1/sr. This paper reviews these situations for both measurement and analysis issues.

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.

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.

Optical components with scattering properties, so-called diffusers, are core elements of calibration units in earth observation instruments. Their performance influences significantly the achievable accuracy of scientific observations. It is of high importance however to characterize the scattering properties of such a diffuser with minimum uncertainty on-ground before launched into orbit and before being utilized in its calibration purpose. Over the past decades TNO has operated an “Absolute Radiometric Calibration Facility (ARCF)” to ensure such accurate characterization of space components. In the recent past TNO has put increased efforts in upgrading and modernizing its facility into a modern high class facility (ARCF 2.0) to measure scattering properties of a variety of materials and components to meet the growing demands for accurate measurements for space applications. This paper describes the above mentioned facility ARCF 2.0 with its unique measurement capabilities and outlies several examples.

Scattermeter II is the second generation device designed and built at The Institute of Physical Engineering, Faculty of Mechanical Engineering, Brno University of Technology. This device has been designed for measuring the angular distribution of the intensity of electromagnetic radiation scattered from a surface of a solid. In this paper, the basic scheme of Scattermeter II and measuring principles with it are described. The results achieved in electromagnetic radiation scattering from surfaces of selected samples of single crystalline silicon wafers used in solar cells are also presented.

Light scattering is an important and classical method for optical surface testing. Typical scheme of light scattering measurement often uses a single laser beam incidence, and then evaluates the surface quality via detecting and analyzing the scattering signal. In this work, a developed method for optical surface testing is proposed and demonstrated, and whose measuring principle is based on the scattering interference effect. In this approach, a single longitudinal mode laser beam is divided into two beams, when these beams irradiate the optical surface, their respective scattering fields would interfere with each other. If the phase between these incidence lights is scanned periodically, their scattering light interference signal would fluctuate simultaneously. Through analyzing this kind of scattering signal, our method can not only determine the scattering loss of optical surface, but also scale its inhomogeneity performance. A simply set of experimental apparatus is built up and used to demonstrated this method, which uses a single mode laser as the light source. Furthermore, to modulate the phase difference between two incidence beams, a piezoelectric ceramic is used. Some typical cases are then experimented and discussed, the results show that this method can be used to calibrate the quality of optical surface.

It is possible to encounter thin films exhibiting various defects in practice. One of these defects is area non-uniformity in optical parameters (e.g. in thickness). Therefore it is necessary to have methods for an optical characterization of nonuniform thin films. Imaging spectroscopic reflectometry provides methods enabling us to perform an efficient optical characterization of such films. It gives a possibility to determine spectral dependencies of a local reflectance at normal incidence of light belonging to small areas (37 μm × 37 μm in our case) on these non-uniform films. The local reflectance is measured by individual pixels of a CCD camera serving as a detector of an imaging spectroscopic reflectometer. It is mostly possible to express the local reflectance using formulas corresponding to a uniform thin film. It allows a relatively simple treatment of the experimental data obtained by imaging spectroscopic reflectometry. There are three methods for treating these experimental data in the special case of thickness non-uniformity, i.e. in the case of the same optical constants within a certain area of the film - single pixel imaging spectroscopic reflectometry method, combination of single-pixel imaging spectroscopic reflectometry method and conventional methods (conventional single spot spectroscopic ellipsometry and spectrophotometry), and multi-pixel imaging spectroscopic reflectometry method. These methods are discussed and examples of the optical characterization of thin films non-uniform in thickness corresponding to these methods are presented in this contribution.

SiC mirrors are of excellent mechanical and thermal properties compared to their glass opponents. Efficient fabrication and testing of SiC mirrors, particularly the large freeform surfaces are very challenging. In this paper, direct CNC generation, deterministic polishing techniques including CCOS, MRF, and IBF were addressed in detail. Since testing is critical to make high accuracy freeform surfaces, the paper focused on Computer Generated Hologram (CGH) design and implement to measure large mirrors. In particular, detector to mirror mapping distortion was discussed in detail. Finally, some results for SiC mirrors were presented.

Extremely low dispersion glasses (e.g. SCHOTT XLD glasses) play an essential role in the color correction of optical systems. Together with short flint glasses (KZFS Types) they can be used for apochromatic color correction in the visible spectrum or even for broadband color correction in combination with lanthanum crown glasses (LAK Types).

Unfortunately the chemical composition of those glasses leads to a high coefficient of thermal expansion, low hardness and low resistance against chemical attacks. As a consequence these glasses tend to be difficult in processing. Therefore the glass engineer’s task is to improve processing characteristics while keeping their special optical properties. N-FK58 XLD is an example of a new generation of XLD glasses from SCHOTT with improved workability. In 2014 a processing study has been conducted to optimize the polishing of XLD glasses. This presentation will show the results of this study for N-FK58 XLD and the application to other fluorophosphates glasses.

For optical systems consisting of metal (in general freeform) mirrors there exist several diamond turning fabrication approaches. These are distuingished by the effort in manufacturing and integration of the later system. The more work one puts into the manufacturing stage the less complicated is the alignment and integration afterwards. For example the most degrees of freedom have to be aligned in integration phase if every mirror of the system is fabricated as a single optical component. For a three mirror anastigmat with three freeform mirrors the degrees of freedom sum up to 18. Therefore the mirror fabrication itself is more or less easy, but the integration is very difficult. There are three major parts in the design and manufacturing process chain to be considered for tackling this integration problem. At the first position in the process chain there is the optical design occuring. At this stage a negotiation between manufacturing and design could improve manufacturability because of more possible integration approaches. The second stage is the mechanical design. Here the appropriate manufacturing approach is already chosen, but may be revisited due to incompatiblities with, e.g., stress specifications. The third level is the manufacturing stage. Here are different clamping approaches and fabrication methods possible. The current article will focus on an approach ("snap-together") where two mirrors are fabricated on one substrate and therefore a reduction of the number of degrees of freedom to be aligned are reduced to six. This improves the amount of time needed for the system integration significantly in contrast to a single mirror fabrication.

The use of autocollimator-based profilometers of the Nanometer Optical measuring Machine (NOM) design has been reported for the evaluation of X-ray optics for some time. We report a related development in the use of a non-contact NOM profilometer for the in situ measurement of base radius of curvature and conic constant for E-ELT primary mirror segments during fabrication. The instrument is unusual in NOM design in that it is deployable onto a CNC polishing machine in an industrial fabrication environment. Whilst the measurement of radius of curvature of spherical surfaces over a single scan has been reported previously, here we report on the use of this instrument to measure optical surfaces with an aspheric departure of 180 micrometers using a grid of multiple scans and bespoke surface fitting software. The repeatability of the measurement has been found to be approximately 1 mm in a measured radius of curvature of approximately 90 m. The absolute accuracy is limited by the accuracy of the calibration of the autocollimator and the in situ calibration of the instrument during operation.

For the manufacturing of high performance optical systems, centered alignment of the optical surfaces within the assembly is becoming increasingly important.

In this contribution, we will present a system for the automated alignment of optical surfaces for the high-throughput manufacturing of cemented doublets (and triplets) with optimized imaging performance. First of all, different concepts for the alignment of doublets etc. are discussed. Standard methods for cementing evaluate mechanical features, such as the outer barrel of one element as reference axis. Using this procedure the optical performance of the assembly that can be achieved is limited by imperfections in the collinearity of the element’s barrel axis and its optical axis. Instead, using the optical axis of the bottom element as target axis opens up perspectives for the production of multiplets with perfect symmetric imaging performance. For this concept, all three center of curvature positions of the optical surfaces are measured. Then, the top surface is aligned to the bottom element's optical axis using high-precision actuators.

In order to increase the throughput of this procedure, the system is equipped with a novel measurement head that acquires autocollimation images of all three surfaces of a doublet at the same time. Thus, the positions of all surfaces are measured simultaneously during just a single rotation, avoiding both additional rotations and focus movements.

Using this approach, cycle times can significantly be reduced from an average of 1 min to less than 10 seconds (w/o curing time). The system is reconfigurable in order to support a wide range of sample designs and enables cementing of high quality optics with centering errors below 2 μm.

CaF₂ is one of the foremost optical materials used in ArF excimer laser optics. Surface quality of optically finished CaF₂ plays an important role in the component’s lifetime. Several techniques were employed to assess surface quality of optically finished CaF₂ in terms of top surface and subsurface damage, resulting in subsurface-damagefree CaF₂. UV light and plasma interaction with CaF₂ surfaces were investigated. The results were discussed in terms of surface roughness and cleanness associated with surface finishing and optical coatings.

Highly chromatic corrected optical systems rely on optical glasses with precise optical positions represented by refractive index and Abbe number. A modern production of optical glasses requires an economical, fast and accurate way of monitoring its fabrication. We demonstrate that an automated Hilger-Chance type refractometer fulfills all these needs. Therefore the uncertainty of a set of optical glasses is analyzed on the basis of a high number and long time reproducibility measurements. It turns out that the standard deviations after several hundreds of measurements taken over almost an decade in refraction is better than 10^-5 in refraction and 0.02% in dispersion.

Two techniques for the measurement of aspheres as well as freeforms are presented. The first method, the tilted wave interferometer, is a full aperture interferometric measurement method without any moving parts during the measurement. The second method applies an optical single point sensor in conjunction with two translational and one rotational axes. Both techniques are compared by measuring a selected asphere and a special freeform surface. Differences between both measurement principles are discussed.

Manufacturing optical components relies on good measurements and specifications. One of the most precise measurements routinely required is the form accuracy. In practice, form deviation from the ideal surface is effectively low frequency errors, where the form error most often accounts for no more than a few undulations across a surface. These types of errors are measured in a variety of ways including interferometry and tactile methods like profilometry, with the latter often being employed for aspheres and general surface shapes such as freeforms. This paper provides a basis for a correct description of power and radius of curvature tolerances, including best practices and calculating the power value with respect to the radius deviation (and vice versa) of the surface form. A consistent definition of the sagitta is presented, along with different cases in manufacturing that are of interest to fabricators and designers. The results make clear how the definitions and results should be documented, for all measurement setups. Relationships between power and radius of curvature are shown that allow specifying the preferred metric based on final accuracy and measurement method. Results shown include all necessary equations for conversion to give optical designers and manufacturers a consistent and robust basis for decision-making. The paper also gives guidance on preferred methods for different scenarios for surface types, accuracy required, and metrology methods employed.

Aspherical optical elements with high accuracy are important in several fields such as third-generation synchrotron radiation and extreme-ultraviolet lithography. Then the demand of measurement method for aspherical or free-form surface with nanometer resolution is rising. Our purpose is to develop a non-contact profiler to measure free-form surfaces directly with repeatability of figure error of less than 1 nm PV. To achieve this purpose we have developed three-dimensional Nanoprofiler which traces normal vectors of sample surface. The measurement principle is based on the straightness of LASER light and the accuracy of a rotational goniometer. This machine consists of four rotational stages, one translational stage and optical head which has the quadrant photodiode (QPD) and LASER head at optically equal position. In this measurement method, we conform the incident light beam to reflect the beam by controlling five stages and determine the normal vectors and the coordinates of the surface from signal of goniometers, translational stage and QPD. We can obtain three-dimensional figure from the normal vectors and the coordinates by a reconstruction algorithm. To evaluate performance of this machine we measure a concave aspherical mirror ten times. From ten results we calculate measurement repeatability, and we evaluate measurement uncertainty to compare the result with that measured by an interferometer. In consequence, the repeatability of measurement was 2.90 nm (σ) and the difference between the two profiles was ±20 nm. We conclude that the two profiles was correspondent considering systematic errors of each machine.

In this paper, we propose an effective method for extracting the important parameters like radius of curvature, conic constant, and deformation coefficients indwelling unknown aspheric surfaces. These parameters can be inversely found from measured data by using the method that is based on aspheric equations and conic surfaces. To demonstrate the precision of the method, it is compared with a higher-order polynomial curve fit, employing two different examples. In a theoretical case, each largest fitting error (or shape error) resulted from the two methods appears a significant difference in precision. Lastly, we apply the proposed method to a real example and show the results.

There are a variety of techniques to determine the quality of optical surfaces, which provide quantitative information of the deformation of the shape of the surface under test. This work proposes to use the deflectometry technique using a Hartmann screen to test a spherical surface with a local deformation. In order to perform the theoretical analysis, a model of experimental setup in which the input parameters: the position of the Hartmann type screen and the location for each of its holes, the distance of the observation plane and the positions of the reflected rays, are known. With this model, based on the diameter of the deformation and deviation of the incident and reflected rays in the observation plane, we determine the theoretical sensitivity of the technique proposed.

Lateral shearing interferometry is an attractive technique to measure the wavefront aberration of high numerical aperture optical systems, of which using two-dimensional grating can divide and shear the wavefront in two-dimension simultaneously. A two-dimension lateral shearing interferometer based on chessboard grating was designed, which can work in dual-mode: the phase shifting mode and the Fourier transform mode. In the phase shifting mode, the phase shifting was realized by moving chessboard grating along the shearing direction in the image plane. In the Fourier transform mode, the spatial carrier frequency was realized by positioning the grating at the Talbot distance of the objective image plane. An experimental setup was designed to measure a 10×, NA0.25 microscope objective at 632.8nm wavelength. The objective was measured by the experimental setup in dual-mode, the results showed that the wavefront of the objective was 0.172λ RMS; in the phase shifting mode, the repeatability (3σ) of RMS was 1.1mλ; in the Fourier transform mode, the repeatability (3σ) of RMS was 2.7mλ; after correcting the coordinates of the wavefront, the differences of Z5 to Z36 between phase shifting mode and the Fourier transform mode were better than 8mλ.

Digital holography is capable of providing surface profiles of samples with axial resolution in the nanometer range. Lensless digital holography is a well-established microscopic method providing diffraction limited resolution of the order of the wavelength of the used light source. It is based on inline holography and usually allows imaging only in transmission geometry.

In this contribution we propose a compact low cost lensless digital holographic microscope capable of performing measurements on reflective microstructures. The novelty of the system consists on a direct use of a laser diode without any need of coupling optics as light source. This simplifies the setup and provides sufficient magnification to measure microstructures. We evaluate our setup by imaging reflective microstructures. We have achieved ̴ 6 mm² field of view amplitude images with ̴ 2.5μm lateral resolution and phase images with axial resolution in nanometer range. The phase image provides a full-field profile measurement of the sample in nanometer range.

Most of the commercial available sub-aperture stitching interferometers measure the surface with a standard lens that produces a reference wavefront, and the precision of the interferometer is generally limited by the standard lens. The test accuracy can be achieved by removing the error of reference surface by the absolute testing method. When the testing accuracy (repeatability and reproducibility) is close to 1nm, in addition to the reference surface, other factors will also affect the measuring accuracy such as environment, zoom magnification, stitching precision, tooling and fixture, the characteristics of optical materials and so on. We establish a stitching system in the thousand level cleanroom. The stitching system is including the Zygo interferometer, the motion system with Bilz active isolation system at level VC-F. We review the traditional absolute flat testing methods and emphasize the method of rotation-shift functions. According to the rotation-shift method we get the profile of the reference lens and the testing lens. The problem of the rotation-shift method is the tilt error. In the motion system, we control the tilt error no more than 4 second to reduce the error. In order to obtain higher testing accuracy, we analyze the influence surface shape measurement accuracy by recording the environment error with the fluke testing equipment.

An improved system for measuring the specific modes’ total loss in high quality ring cavity is presented. The experimental apparatus measuring cavity ring-down signals are described in detail. The specific modes in the passive ring cavity can be obtained by controlling the manually piezoelectric transducer which mounted on the laser cavity mirror. The image of the specific mode was shown on the CCD and its corresponding cavity ring-down signal is obtained when incident laser light was shut off by optical switch. The losses of three specific transverse modes, such as TEM00, TEM01 and TEM10, are measured. The improved system realizes the specific mode real-time monitoring and high precision loss measurement simultaneously when the ring cavity assembling and alignment.

In this work we report the design of a null-screen for corneal topography. To avoid the difficulties in the alignment of the test system due to the face contour (eyebrows, nose, or eyelids), we design a conical null-screen with a novel radial points distribution drawn on it in such a way that its image, which is formed by reflection on the test surface, becomes an exact array of circular spots if the surface is perfect. Additionally, an algorithm to compute the sagittal and meridional radii of curvature for the corneal surface is presented. The sagittal radius is obtained from the surface normal, and the meridional radius is calculated from a function fitted to the derivative of the sagittal curvature by using the surfacenormals raw data. Experimental results for the testing a calibration spherical surface are shown. Also, we perform some corneal topography measurements.

In this paper, we propose the sinusoidal frequency modulation on a laser diode (LD) to achieve both frequency stabilization of the LD and displacement measurement with a homodyne interferometer. The central frequency of the LD is stabilized to a Doppler broadened absorption line of an iodine (I2) molecule near the wavelength of 633 nm. The frequency of the LD is modulated across the absorption line and synchronous detection is utilized to detect the absorption signal. A simple and low-cost homodyne displacement-measuring interferometer can be constructed that can attain high measurement resolution.

The null-screen method has been used to test aspheric surfaces, among them the surface of a parabolic trough solar collector (PTSC). This geometrical method measures the slope of the test surface and by a numerical integration procedure the shape of the test surface can be obtained. In this work, through some numerical simulations sinusoidal deformations with different amplitudes and spatial periods are introduced on PTSC surfaces. Then, an analysis of the deformations of the reflected images of a null-screen by the PTSC surface due to defects on the surface is performed. This procedure allows to validate the kind and magnitude of the surface deformations that can be measured with the proposed method. Also, an analysis of the advantages and limitations of the null-screen testing method will be discussed.

An optical non-contact and full-field system that allows large displacement measurements in x-, y- and z-direction is presented. The system combines 2-dimentional digital image correlation (for in-plane measurements) and fringe projection (for out-of-plane displacements) and uses only one camera. The in- and out-of-plane displacements are obtained at the same instant allowing real-time measurements thanks to a color encoding filtering procedure. The out-of-plane measurement allows the correction of the in-plane measurements and the system has to be precisely aligned by following an established alignment procedure. Furthermore, a calibration has to be done to obtain a fringe parameter k for each pixel of the specimen surface image necessary to relate the shifted phase with the out-of-plane displacements. The presented system obtains different values of k for each pixel because of the divergent and non-normal incidence of the fringe beam onto the sample surface (non zero incidence angle). The calibration is performed automatically and only has to be done once for each configuration of the system. The system is portable and can be easily adapted to measure large displacements and wide areas (using small incidence angle) or smaller distances but with higher resolutions (when increasing the incidence angle).

Three-dimensional image acquisition is still a growing field in optical metrology. Various methods are available to reconstruct an object’s three-dimensional surface. The five main types of 3D cameras are stereo cameras, triangulation (pattern or laser scanning), interferometry, light-field cameras and ToF (time-of-flight) cameras. PMD (photonic mixing device) cameras measure the time of light, and thus belong to the field of ToF cameras. Each camera type has fields of application for which it is particularly well suited. Even within PMD cameras, there is a distinction made between applications for indoor and outdoor use. Until today, there is no method to measure and characterize 3D cameras uniformly. Desirable would be a method, which is able to measure all types of cameras equally. With this work, we want to contribute to the standardization of 3D cameras. In this case, we use a PMD camera for outdoor applications with relatively large pixels. It is shown how to determine the spatial resolution of a PMD camera from both, the amplitude and the distance image. Further, a novel method is presented how to determine the resolution enhancement in an image via gradient image evaluation. Finally, a method is proposed which evaluates the quality of resolution enhancement, when no ground truth data is available. Both are particularly interesting for the use of super-resolution (SR) applications.

With the advent of techniques devised for the mass production of optical components made with surfaces of arbitrary form (also known as free form surfaces) in the last years, a parallel development of measuring systems adapted for these new kind of surfaces constitutes a real necessity for the industry. Profilometry is one of the preferred methods for the assessment of the quality of a surface, and is widely employed in the optical fabrication industry for the quality control of its products. In this work, we present the design, development and assembly of a new profilometer with five axis of movement, specifically suited to the measurement of medium size (up to 150 mm of diameter) "free-form" optical surfaces with sub-micrometer accuracy and low measuring times. The apparatus is formed by three X, Y, Z linear motorized positioners plus and additional angular and a tilt positioner employed to locate accurately the surface to be measured and the probe which can be a mechanical or an optical one, being optical one a confocal sensor based on chromatic aberration. Both optical and mechanical probes guarantee an accuracy lower than the micrometer in the determination of the surface height, thus ensuring an accuracy in the surface curvatures of the order of 0.01 D or better. An original calibration procedure based on the measurement of a precision sphere has been developed in order to correct the perpendicularity error between the axes of the linear positioners. To reduce the measuring time of the profilometer, a custom electronics, based on an Arduino™ controller, have been designed and produced in order to synchronize the five motorized positioners and the optical and mechanical probes so that a medium size surface (around 10 cm of diameter) with a dynamic range in curvatures of around 10 D, can be measured in less than 300 seconds (using three axes) keeping the resolution in height and curvature in the figures mentioned above.

3D printed freeform optical sensors are a different and new approach for optical metrology. Thereby the optical design is adapted to the fabrication characteristics of additive manufacturing. All needed optical elements like mirrors and lenses are reduced to one simple printed sample, which is capable to illuminate a complex shaped industrial part for shaped measurement based on light section technique. Additionally the laser line can be formed on the part in a way, so that no shadow appears–even in the case of kinks etc.. Due to the physical limitations of the printing process and different printing techniques each optical design would present some drawbacks that has to be considered prior a printing process in order to obtain the best results possible.

We propose a swept source optical coherence tomography that uses an original external-cavity laser diode and demonstrate measurements of thickness distribution in two dimensions using this equipment. We first conducted high-speed, wide-range wavelength scanning with an external-cavity laser diode that was equipped with a special antireflection-coated laser diode working at 770 nm. Using an acousto-optic deflector enabled a tuning range and rate of 22 nm and 20 kHz, respectively, with no mechanical elements. Next, we applied this source to an optical coherence tomography and measured the two-dimensional distribution of thickness of a thin glass plate.

Replication techniques for diffractive optical elements (DOEs) in soft materials such as plastic injection molding are state of the art. For precision glass molding in glasses with high transition temperatures, molds with extreme thermal resistivity, low chemical reactivity and high mechanical strength are needed. Glassy Carbon can be operated up to 2000°C making it possible to mold almost all glasses including Fused Silica with a transition temperatures above 1060°C. For the structuring of Glassy Carbon wafers photolithography and a RIE process is used. We have developed a process using Si as a hard mask material. If the flow rates of the etching gases O₂ and SF₆ are chosen properly, high selectivity of GC to Si 19:1 can be achieved, which provides excellent conditions to realize high resolution elements with feature size down to 1 micron and fulfills requirements for optical applications. We fabricated several multilevel GC molds with 8 levels of structuring. Two different optical functionalities were implemented: 6x6 array beamsplitter and 1x4 linear beamsplitter. The molds were applied for precision glass molding of a low T_g glass L-BAL 42 (from Ohara) with a transition temperature of 565°C. Their optical performance was measured. A more detailed analysis of the impact of mold fabrication defects on optical performance is done. Rigorous coupled wave analysis simulations are performed, where we included fabrication constrains such as duty cycle, edge depth errors, wall verticality and misalignment errors. We will compare the results with the design specifications and discuss the influence of fabrication errors introduced during the different process steps.

In lighting applications key drivers for optical design of surface textures are integration of optical elements, the disentanglement of optical functionality and appearance and late stage configuration.

We investigated excimer laser ablation as a mastering technology for micro textured surfaces, where we targeted an increase in correspondence between surface design and ablated surface for high aspect ratio structures. To achieve this we have improved the photo mask design using a heuristic algorithm that corrects for the angular dependence of the ablation process and the loss of image resolution at ablation depths that exceed the depth of field. Using this approach we have been able to demonstrate close correspondence between designed and ablated facet structures up to 75° inclination at 75 μm depth.

These facet design parameters allow for total internal reflection (TIR) as a means of beam deflection which is demonstrated in a range of mono shaped cone arrays in hexagonal tessellation. BSDF analysis was used to characterize the narrow TIR deflection beams that matched the peak positions of the design down to 28° apex. In addition, a single surface TIR-Fresnel lens design with focal distance 5 mm has been manufactured using this photo mask design algorithm and beam collimation up to 12° beam angle and 32° field angle is shown.

These outcomes demonstrate that the laser ablation process intrinsically yields sufficient small dispersion in structure and fillet radii for lighting applications.

Atom lithography is a novel technique for nanofabrication which can be used to grow periodic arrays of highly uniform nanometer-scale structures. The pitch standard of Cr nano-grating is 212.8±0.1 nm, which coincides with λ/2 of the standing wave, in correspondence with the ⁵²Cr atomic resonance transition: ⁷S₃ → ⁷P₄⁰, λ= 425.55 nm. With the utilization of the material removal ability by AFM scratching, the Cr nanostructures have been transferred to an InP substrate for replication and subdivision. The uncertainty analysed based on gravity centre (GC) method is better than 0.5% for both replicated and subdivided nano-gratings. AFM lithography method expands the application of atom lithography in metrology to a smaller scale with high precision.

Shaping of laser light intensities by using Diffractive Optical Elements allows the adaption of the incident light to its application. Fused silica is used where for example UV-light or high temperatures are mandatory. For high diffraction efficiency the quality of the etched surface areas is important. The investigation of different process parameters for Ion Beam and Reactive Ion Etching reveals that only Ion Beam Etching provides surfaces with optical quality. Measurements of the influence of the surface quality on the diffraction efficiencies prove that the surfaces generated by Reactive Ion Etching are not suitable.

Due to the high selectivity of the process Reactive Ion Etching is nevertheless a reasonable choice for the fabrication of Diffractive Optical Elements. To improve the quality of the etched surfaces a post processing with Ion Beam Etching is developed. Simulations in MATLAB display that the angle dependent removal of the surface during the Ion Beam Etching causes a smoothing of the surface roughness. The positive influence of a post processing on the diffraction efficiency is outlined by measurements.

The ion beam post processing leads to an increase of the etching depth. For the fabrication of high efficient Diffractive Optical Elements this has to be taken into account. The relation is investigated and transferred to the fabrication of four-level gratings. Diffraction efficiencies up to 78 % instead of the ideal 81 % underline the practicability of the developed post processing.

The analysis of diffracted light from periodic structures is shown to be a versatile metrology technique applicable to inline metrology for periodic nanostructures. We show that 10 nm changes in periodic structures can be traced optically by means of sub-wavelength diffraction. Polymer gratings were fabricated by electron beam lithography. The gratings have a common periodicity of 6 μm, but different line width, ranging from 370 to 550 nm in 10 nm steps. A comparison between the resulting diffraction patterns shows marked differences in intensity which are used to sense nanometre scale deviations in periodic structures.

We report on the fabrication of all-polymer inverted rib waveguides by hot-embossing and inkjet printing. Inkjet printing as an additive fabrication technique is well suited for a fast, selective and automated patterning of large areas. In general, the lines that can be printed with polymer inks can serve as waveguides themselves but the dimensions are too big to form single-mode waveguides. To overcome this limitation we apply hot-embossed grooves as assist structures to ensure the lateral confinement of the guided wave. We show the waveguide design, spin-coated single-mode waveguides as an intermediate result and finally inkjet printed all-polymer waveguides and their optical performance.

In the optics industry thin film systems are used to construct various interference devices such as antireflective coatings, high-reflectance mirrors, beam splitters and filters. The optical characterization of complex optical systems can not be performed by measurements only in the short spectral range in which the interference devices will be employed because the measured data do not contain sufficient information about all relevant parameters of these systems. The characterization of film materials requires the extension of the spectral range of the measurements to the IR region containing phonon absorption and to the UV region containing the electronic excitations. However, this leads to necessity of a dispersion model suitable for the description of the dielectric response in the wide spectral range. Such model must respect the physical conditions following from theory of dispersion, particularly Kramers-Kronig relations and integrability imposed by sum rules. This work presents the construction of a universal dispersion model composed from individual contributions representing both electronic and phonon excitations. The efficiency of presented model is given by the fact that all the contributions are described by analytical expressions. It is shown that the model is suitable for precise modeling of spectral dependencies of optical constants of a broad class of materials used in the optical industry for thin film systems such as MgF₂, SiO₂, Al₂O₃, HfO₂, Ta₂O₅ and TiO₂ in the spectral range from far IR to vacuum UV.

Spectral interferometric methods utilizing the interference of two beams in a Michelson interferometer to measure the displacement are analyzed theoretically and experimentally. First we consider an experimental setup comprising a white-light source, a dispersion balanced Michelson interferometer and a spectrometer. The position of one of the interferometer mirrors is controlled via a piezo positioning system and the displacement measurement is based on the wavelength interrogation, i.e., the position of a selected interference fringe in the resultant channeled spectrum is measured as a function of the mirror displacement. Second we consider a setup with another interferometer, included in the Michelson interferometer, to increase the sensitivity of the displacement measurement. In this setup, the resultant channeled spectrum is with envelope which shifts with the displacement of the interferometer mirror. We analyze the new measurement method theoretically and show that the displacement measurement is once again possible by using the wavelength interrogation and the sensitivity is substantially increased. We also realized the new measurement setup in which the position of the interferometer mirror is controlled via a closed-loop piezo positioning system and confirmed the theoretical results.

This method of optical scanning presented in this paper is used for precision measurement deformation in shape or absolute forms in comparison with a reference component form, of optical or mechanical components, on reduced surfaces area that are of the order of some mm² and more. The principle of the method is to project the image of the source grating to palpate optically surface to be inspected, after reflection; the image of the source grating is printed by the object topography and is then projected onto the plane of reference grating for generate moiré fringe for defects detection. The optical device used allows a significant dimensional surface magnification of up to 1000 times the area inspected for micro-surfaces, which allows easy processing and reaches an exceptional nanometric imprecision of measurements. According to the measurement principle, the sensitivity for displacement measurement using moiré technique depends on the frequency grating, for increase the detection resolution. This measurement technique can be used advantageously to measure the deformations generated by the production process or constraints on functional parts and the influence of these variations on the function. The optical device and optical principle, on which it is based, can be used for automated inspection of industrially produced goods. It can also be used for dimensional control when, for example, to quantify the error as to whether a piece is good or rubbish. It then suffices to compare a figure of moiré fringes with another previously recorded from a piece considered standard; which saves time, money and accuracy. The technique has found various applications in diverse fields, from biomedical to industrial and scientific applications.

A focal length is a basic optical characteristic of an optical system. Thus, it is important to be able to measure this value for a given optical system very accurately in practice. At present there exist various physical principles of the focal length measurement which can achieve a different measurement accuracy. In our work we analyse several methods of measurement of the focal length with respect to factors, which are important for a measurement accuracy. The analysis is performed on examples.

We show a proof-of-concept demonstration of a multi-parameter analysis low-cost optical detection system for the flowcytometric identification of vinegars. This multi-parameter analysis system can simultaneously measure laser induced fluorescence, absorption and scattering excited by two time-multiplexed lasers of different wavelengths. To our knowledge no other polymer optofluidic chip based system offers more simultaneous measurements. The design of the optofluidic channels is aimed at countering the effects that viscous fingering, air bubbles, and emulsion samples can have on the correct operation of such a detection system. Unpredictable variations in viscosity and refractive index of the channel content can be turned into a source of information. The sample is excited by two laser diodes that are driven by custom made low-cost laser drivers. The optofluidic chip is built to be robust and easy to handle and is reproducible using hot embossing. We show a custom optomechanical holder for the optofluidic chip that ensures correct alignment and automatic connection to the external fluidic system. We show an experiment in which 92 samples of vinegar are measured. We are able to identify 9 different kinds of vinegar with an accuracy of 94%. Thus we show an alternative approach to the classic optical spectroscopy solution at a lowered. Furthermore, we have shown the possibility of predicting the viscosity and turbidity of vinegars with a goodness-of-fit R² over 0.947.