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In the area of high performance optics aspherical surfaces have become the solution of choice over the past years [1] [2]. The advantage of aspherical, compared to spherical elements, is the highly increased degree of freedom for the optics design. This allows better correction of aberrations, by simultaneously reducing the number of elements needed to fulfill a given design target, enabling the construction of more compact optical systems, with higher optical performance at the same time. As a result of these convincing advantages aspherical optics are widely used in state of the art optical systems, starting from mass products like imaging systems for micro cameras in smartphones, reaching to high end optical systems used in lithography or space applications. Even more degrees of freedom in the design can be reached, if the rotational symmetry of the aspheric surface is broken. Such free-form surfaces that do not have to show any symmetry at all can be used to further improve the performance of an optical system. One possibility is the construction of systems where the elements are no longer arranged along a straight line, but where the optical axis is folded. By taking advantage of this design option it is possible to develop very compact systems, which also are less sensitive to mechanical and thermal influences. Another advantage of off-axis systems that can be realized with free-form elements is the avoidance of reflexes that often occur at the center of the lens in a classical system. This is especially important for applications with coherent sources. Further, certain wavelengths demand the usage of mirror optics instead of lenses, if there aren’t any optical refractive materials with tolerable absorption available. To avoid central obscurations, here again the easiest way is to use free-from mirrors. One example for this kind of optical systems is the EUV lithography that will be used in the next generation of semiconductor fabrication.

In interferometric testing of surfaces a major task is to avoid the introduction of aberrations due to misalignment of the surface under test (SUT). An automated method for the positioning of aspheric and free-form surfaces in a non-null test interferometer, as well as a method for the distinction between alignment introduced aberrations and surface errors is presented. A combination of both methods allows for a fully automated alignment with low accuracy requirements concerning the positioning stage. In this work the method for the alignment as well as the alignment error correction is presented and the misalignment introduced measurement uncertainties are estimated. Simulation results as well as experimental results showing the feasibility of the method are presented.

Microoptical components play an increasing role in different technology fields such as medical engineering, materials and information processing, imaging and metrology. But their realization needs the combination of modern design concepts with sophisticated processing technologies, new materials and design tools. Furthermore, the introduction of ambitious processing technologies must be accompanied by effective metrology and inspection tools. Therefore, this paper reports about the technologies for making microoptics at ITO. Because sophisticated measurement tools are an indispensable part of the fabrication process, the paper describes our multi-scale inspection approach for the testing of microstructures on wafer-scale level. Finally, some representative applications of microoptical components for advanced measurement and imaging are explained.

The tilted-wave interferometer (TWI) was recently developed by the University of Stuttgart for the high-accuracy measurement of aspheres and freeform surfaces. The system works in a non-null measurement fashion and si­ multaneously uses several test beams with different tilts. Reconstruction of the specimen under test from TWI measurements is challenging and in order to correctly separate the real surface topography from systematic aberrations, the employed interferometer needs to be characterized. This characterization, as well as the recon­ struction of the specimen from TWI measurements, requires sophisticated data analysis procedures including ray tracing and the solution of an inverse problem. A simulation environment was developed at the Physikalisch-Technische Bundesanstalt (PTB) in order to inves­ tigate the accuracy and stability of TWI systems, and to explore possibilities and limitations of this promising measurement technique. Virtual experiments were carried out to quantify the sensitivity of the results with respect to the assumed linearity in the reconstruction procedure, positioning errors, and measurement noise. Our first results suggest that the mathematical TWI reconstruction technique basically allows highly accurate measurements with uncertainties down to a few nanometers, provided that calibration errors of the optical sys­ tems are kept small. The stability of the results and their accuracy can, however, depend significantly on the particular surface of the specimen and on the choice of experimental settings.

The tilted wave interferometer is a non-null test interferometer for the measurement of aspheres and freeform surfaces without dedicated null-optics that uses an array of tilted waves to locally compensate the deviation of the surface from the spherical form. The concept allows for short measurement times of only a few minutes and high lateral resolutions at the same time. The calculation of the surface error is performed by perturbation of a polynomial representation of the surface. Since we are also interested in higher frequency errors of the surface which cannot be described by a polynomial of finite order these errors are evaluated in an additional step. Since every wavefront only covers a small area of the surface the challenge here is to reconstruct the surface from the information that is distributed over the different patches. We will present the method that was developed for the reconstruction of these high frequency errors as well as measurement results of aspheres and freeform surfaces without rotational symmetry that were obtained by this method.

An absolute testing method for cylindrical surfaces is presented in a null test setup with a computer-generated hologram. The absolute test exploits the symmetry of cylinders, which allows us to introduce a certain shift of the test surface both parallel to and rotated about the centerline while the null test condition is still maintained. With two shifts of the cylindrical surface, four measurements belonging to two groups in conjugate positions can be accomplished to obtain the absolute differential map with the interferometer and null optics errors removed. The absolute surface can be obtained by wavefront reconstruction from local differential data. A simulation of the method is presented to estimate the error propagation. Experimental absolute test results of a concave cylindrical surface with 100-mm radius are given. The measured profiles are compared with those obtained from a commercial profiler, showing a difference of less than 15 nm (root-mean-square).

We report on the first demonstration of a radially polarized passively mode-locked thin-disk oscillator. Radial polarization was achieved by the use of a novel circular grating waveguide output coupler. We showed mode-locked operation up to a maximum average output power of 13.3 W with an optical efficiency of 21.8%. The degree of radial polarization of the emitted beam was measured to be 97±1%. The laser system generated pulses with a duration of 907 fs and an energy of 316 nJ corresponding to a peak power of 0.35 MW. To the best of our knowledge, these values exceed the performance of previously reported radially polarized mode-locked oscillator systems.

We investigate the possibility to produce photochromic CGHs with maskless lithography methods. For this purpose, optical properties and requirements of photochromic materials will be shown. A diarylethene-based polyurethane is developed and characterized. The resolution limit and the in uence of the writing parameters on the produced patterns, namely speed rate and light power, have been determined. After the optimization of the writing process, gratings and Fresnel Zone Plates are produced on the photochromic layer and diraction eciencies are measured. Improvements and perspectives will be discussed.

A hybrid imaging system was developed to enable the application of laser-based measurement techniques like UV laser-induced fluorescence in near-production engines with small access ports. For this task, wide-angle characteristics and high lens speed are required in combination with small engine-bound optics able to survive in harsh environmental conditions. Our approach combines a simple and robust access lens with refractive/diffractive (hybrid) imaging stages away from the engine that are customized for individual wavelength bands. We give a detailed insight into the design strategy, including the integration of diffractive optics and the performance of the system with analysis of the modulation transfer function (MTF), lens speed, and stray light. Finally, results from applications in an actual engine are shown.

We present a laser direct writing system for the efficient fabrication of high-resolution axicon structures. The setup makes use of scanning beam interference lithography incorporated with a fringe locking scheme for tight fringe phase control and allows us to fabricate large area structures with a period down to 450 nm.

Rotary sensors are an essential component in numerous applications where a rotation movement has to be detected. With optical encoders, a high angular resolution can be achieved. As a disadvantage, the resolution enhancement is associated with increasing cost. To overcome this issue, a coding principle is presented that uses a diffractive solid measure on a microstructured plastic disc. Like a DVD, this encoder disc can be manufactured in a cost effective injection molding process. For this approach, a differential incremental code, as well as an absolute code, has been developed.

Recent lithographic technologies allow for the fabrication of high period diffractive structures on planar and curved optical surfaces with high precision. Such diffractive surfaces offer the optical designer extra degrees of freedom, which are of special importance for optical systems, where light collection efficiency is important. We illustrate the usage and benefit of diffractive elements within fast optical systems in various applications. For these hybrid design classes it is mandatory to include the realistic as-built performance of the employed diffractive elements into the design phase. Correspondingly we present simulation techniques to include fabrication specific diffraction efficiencies and stray light into the optimization and evaluation process.

Rotary and linear position sensors are used in numerous manufacturing and automotive applications, where cost effectiveness and the ability of integration are major goals. To meet the increasing demand for competitive optical rotary encoders, in recent years a novel type of optical encoders have been proposed and demonstrated using a micro grating based encoding scheme. This proceeding will give details on the operation principle of this novel kind of position encoder and will show its performance on two exemplary implementations: A compact absolute rotary encoder with a micro-structured plastic disc, which can be manufactured in a conventional and cost effective DVD-molding process and a linear encoder which is based on a pseudo-random coding scheme. The implementation as well as results from their experimental characterization are presented.

Axicon surfaces are widely used in nowadays optical engineering, requiring accurate metrology for these highly aspheric surfaces. In this contribution, we present a complete approach to determine the shape deviation of axicons in an absolute manner. The setup is an interferometric null configuration using a computer generated hologram (CGH) as null optics. We demonstrate an absolute shifting method and the calibration issues connected with measuring the absolute cone angle. Experimental results are shown for the metrology of a 90° cone angle sample.

An automatic method for the positioning of a test surface in a non-null interferometer is presented. If the test surface is positioned incorrectly with respect to the test beam this leads to aberrations, which distort the measurement of the surface. A central issue in the interferometric characterization of surfaces is to avoid aberrations due to an incorrect placement of the test surface. In case of spherical and plane surfaces these errors can usually be distinguished from the surface figure errors and are eliminated in post processing. For aspheric and free-form surfaces this task is no longer trivial. Therefore it is important to minimize the alignment error of the surface. In this work the effect on the measured phase due to lateral and axial displacements of the aspheric surface is calculated and an adjustment method for the positioning of the surface at a predefined measurement location is presented. Experimental results showing the feasibility of the proposed procedure are presented.

Optical metrology has shown to be a versatile tool for the solution of many inspection problems. The main advantages of optical methods are the noncontact nature, the non-destructive and fieldwise working principle, the fast response, high sensitivity, resolution and accuracy. Consequently, optical principles are increasingly being considered in all steps of the evolution of modern products. However, the step out of the laboratory into the harsh environment of the factory floor was and is a big challenge for optical metrology. The advantages mentioned above must be paid often with strict requirements concerning the measurement conditions and the object under test. For instance, the request for interferometric precision in general needs an environment where high stability is guaranteed. If this cannot be satisfied to a great extent special measures have to be taken or compromises have to be accepted. But the rapid technological development of the components that are used for creating modern optical measurement systems, the unrestrained growth of the computing power and the implementation of new measurement and inspection strategies give cause for optimism and show that the high potential of optical metrology is far from being fully utilized. In this article current challenges to optical metrology are discussed and new technical improvements that help to overcome existing restrictions are treated. On example of selected applications the progress in bringing optical metrology to the real world is shown.

The established method to measure aspherical surfaces is interferometric testing with null optics, but due to economical reasons the applications are limited. A special null optic has to be calculated, fabricated and qualified for each individual type of asphere. This time- and money consuming method is only cost-efficient for large quantities or when tests require high accuracy. We propose a new and flexible technique for measuring an ensemble of different aspheres with only one measurement setup. The main idea is to use the wavelength as a tunable parameter. Because it is possible to change the wavelength without introducing new errors by mechanical movements, the wavelength variation results in a higher measurement flexibility without reducing the measurement accuracy. We present the chromatic Fizeau Interferometer with a diffractive element as null-optic for the measurement of a set of four aspheres. We will show the influence of unwanted diffraction orders and the expected measurement accuracy. As in the monochromatic setup, especially the area around the optical axis is problematic and can not be measured with the desired accuracy. The use of a small aperture stop on the optical axis is recommended because errors in other radial domains are filtered as well. The results show, that the chromatic Fizeau interferometer makes the established monochromatic method far more flexible and that different aspheres can be measured in the same setup.

One of the most challenging 3D metrology tasks in terms of required accuracy is the metrology of aspheric surfaces. Due to the required accuracies in the nanometer range, interferometry is one of the preferred methods. The reconstruction of the actual asphere shape from the measured phase data is presented for computer generated hologram approaches as well as for a new, flexible approach that was developed to avoid the use of null test configurations.

The efficient fabrication of diffractive optics is of growing interest for many applications. Laser direct writing of such structures has proven to be a flexible, fast and cost-effective approach. In this contribution we present a direct laser writing system, that, in the final stage, will allow the fabrication of diffractive optics with sub-micrometer resolution on aspheric surfaces. High throughput for grating-like nano scale structures is obtained by means of an intrinsically parallel writing approach based on scanning beam interference lithography (SBIL) [1]. The combination of diffractive and refractive functions in one single optical element provides additional degrees of freedom enhancing the possibilities in the design process of specialised optical systems, e.g. imaging systems for time of flight (TOF) cameras [2], optics for laser beam shaping, or reference structures for asphere metrology. High resolution rotational symmetric periodic structures are of high interest e.g. for intra cavity polarisation control [3], interferometry [4] or novel optical micro system based approaches for rotary encoders.

A novel non-null interferometer for the precise measurement of aspheric surfaces is presented. In contrast to a classical interferometer, where only one test wavefront is used, the proposed system makes use of multiple test beams propagating under different angles through the interferometer. This allows the measurement of aspheric surfaces in a very short time, even for strong aspheres with deviations from the best-fit sphere of up to 900 microm. The non-null test configuration implies that any additional aberrations introduced by the interferometer have to be well characterized to precisely measure the asphere. Experimental measurements of a calibrated non-null interferometer on an aspheric element with 900 microm SAG deviation are presented.

Laser-based diagnostics are well established in engine research. The requirement of large-scale optical accesses makes the application expensive. Miniaturized specific endoscopes combining refractive and diffractive optics show a huge potential to overcome these restrictions.

A new interferometric technique for the measurement of aspheric elements based on multiple test beams is presented. By means of an array of sources (Point Source Array) an aspheric surface is illuminated under different angles which allow the measurement of the zones where the local gradient of the test piece is compensated. One of the main advantages of the system is that the measurement process is performed in parallel (many sources are used at the same time) thus requiring extremely short measurement time in comparison with other available subaperture testing techniques. Another important aspect is that the asphere stays in the same position during the whole process; there are no mechanical movements of the test part involved. The technique allows the measurement of strong aspheric elements with departures from the best fit sphere up to ±10°. The method was developed to obtain accuracies of up to λ/30 and better. Simulations and first experimental results are presented.

Absolute interferometric testing methods for aspheric surfaces based on computer-generated holograms (CGHs) are reviewed. Limiting factors and critical issues such as parasitic diffraction orders and the setup alignment are discussed and measurement results are given.

Time-resolved observation of the fuel/air mixing process prior to ignition is crucial for the development of modern internal combustion engine concepts. The presented fiber optic sensor is designed for the acquisition of in-cylinder data in the area close to the ignition spark, based on UV-laser-induced fluorescence of organic fuel compounds. Excitation and fluorescence light are separately guided through silica fibers. The detection volume is defined by the optical design of the sensor head. Since the related components are completely integrated into a modified spark plug, the sensor can be applied to unmodified production line engines. We present the fundamental spectroscopic concept, the solution for the minimal invasive access through the spark plug and tracer spectra measured with a prototype.

In this paper, the realization and characterization of a microoptical sensor using the chromatic confocal principle is presented. The sensor head is designed for distance gauging applications in high aspect ratio cavities with a diameter of about 2 mm. The first part of this paper focuses on the design and fabrication process of the hybrid optical benches, which combines refractive and diffractive micro optical components. Very tight tolerances of the optical path are required for the functionality of the sensor. Therefore the alignment structures and mounts between the different optical elements are produced from PMMA using deep X-ray lithography, the first step of the LIGA process. In the second part of this paper the characterization of first prototypes using different light sources are described and results presented.

Increasing demands for the monitoring of tolerances of small mechanical and optical precision components require improved measurement techniques. In this paper the basic concept and different optical designs of a confocal microoptical distance-sensor are presented. The sensors use the chromatic-confocal measurement principle which does not require a mechanical depth scan. Therefore, a chromatic-confocal point sensor can be designed without any moving parts. This fact is used to design a miniaturized sensor head with an outer diameter smaller than two millimetres. A special feature of the sensor head is its capability to measure sideways. This enables e.g. to measure surfaces in small drilling holes.

Active and adaptive optics are becoming more important in the field of beam shaping and wave front analysis. One of the main reasons for the progress and recent activities in active optics is the availability of new active elements like deformable mirrors, micro mirrors and liquid crystals. The application of spatial light modulators for wave front adaption, shaping and sensing will be discussed. An important application is a flexible testing procedure for testing aspheric surfaces using adaptive optics such as deformable mirrors liquid crystals and micro mirrors.

A complete absolute interferometric test of aspheres is presented. The method is based on a specially designed computer-generated hologram (CGH), which reconstructs an aspherical wave as well as auxiliary waves. The auxiliary waves are used for calibration. The aberrations of the auxiliary waves are measured absolutely by means of established absolute testing methods. The errors of the auxiliary waves can be transferred to those of the aspheric wave. Methods for absolute testing of aspheric surfaces using multiplex CGHs are described. Test procedures are explained and equations are derived. For axially symmetric aspheres, experimental results are presented and a comparison with the established N-position rotation test is given.

A complete absolute interferometric test of axially symmetric aspheres is presented. The method is based on a specially designed computer-generated hologram (CGH) that reconstructs an aspherical wave as well as a spherical auxiliary wave. Since both phase functions have the same symmetry and their pattern is simultaneously encoded, we call this type of multiplex hologram a Twin-CGH. The spherical wave is used for calibration. The aberrations of the spherical auxiliary wave are measured absolutely with either a spherical mirror or an absolute test for Fresnel zone plates. Thus the two types of aberration inherent in the CGH can be identified and separated from each other. The errors of the spherical wave can be transferred to those of the aspherical wave. Two different methods that use Twin-CGHs for absolute testing of aspheric surfaces are described. Test procedures are explained, equations are derived, and experimental results are presented. A mutual comparison of the two results and a comparison with the established N-position rotation test are given.

The expansion of the field of diffractive optics applications is accompanied by toughening performance requirements for CGHs. Optical testing sets especially high requirements, concerning wavefront accuracy and diffraction efficiency. The key point in fabrication technology is the writing system creating the photomask or the profiled pattern. The diffractive optics fabrication facility at ITO (University of Stuttgart) is based on the circular laser writing system CLWS-300. This flexible and high-accurate tool was originally designed for binary diffractive optics fabrication. This paper presents novel enhancements of this system allowing direct laser writing of a wide range of binary and continuous-relief CGHs on photoresist layers, chromium films and LDW-glass. Main topics of the enhancements were the scanning accuracy and exposure control. Many types of CGHs (binary precision holograms for optical testing, Shack-Hartmann arrays, microlens discs for confocal microscopy, diffractive interferometer objectives, doughnut generators etc.) have been manufactured using the developed algorithms and hardware.

It has been shown that high precision diffractive objectives are an alternative to their refractive counterparts for application in interferometers. A design for an all-diffractive, double-sided objective that fulfills the Abbe sine condition has been proposed. It allows eliminating aberrations due to a finite field angle. Ray tracing simulations show that field angles up to 0.1 ° cause aberrations less than ?/20 PV in single pass. A single-sided prototype (diameter - 80 mm; NA. - 0.158; designed wavelength - 632.8 nm) has been fabricated by direct laser writing on photoresist. It was written on a polar coordinate laser system CLWS-300 that is capable of writing high precision DOEs up to a diameter of 300 mm. The blazed diffractive structures were written directly into a photoresist layer that was spinned on a high-precision substrate. Recalibration of the radial coordinate by reading marker positions on the substrate was used to eliminate machine drifts. The writing parameters were optimized by modelling the writing process in order to maximize the diffraction efficiency. The fabricated objective has a rms wavefront error of less than ?/2O in single pass. The residual errors are predictable using manufacturing data that is recorded during the writing process for each element. This permits to supply calibration data for each element. Measurements of the fabricated DOE show excellent agreement between the predicted and measured wavefront quality.

The entire process of designing the test setup with a computer-generated hologram (CGH) and performing the CGH-null test of an asphere will be described in detail. Critical aspects in testing aspherics with CGH-nulls e.g. caustic of the asphere, influence of alignment errors, lateral distortion and lateral resolution of the measurement are discussed. Detection, specification and calibration methods of fabrication errors of the CGH-null are analyzed with respect to the fabrication technology of the CGH. For a high accuracy CGH-null test of an asphere, the errors of the CGH must be negligible or well calibrated. Techniques to calibrate the systematic error of the test setup are presented with examples. Experimental results of interferometric CGH-null tests of an asphere are presented.

Computer-generated holograms (CGHs) are increasingly used in optical shop testing, especially for testing aspheric surfaces. For precise interferometrical measurements the error influence of the CGHs must be known and needs to be characterized. Different error types of two-level binary CGHs are identified and their contribution to the reconstructed wavefront are discussed: pattern errors of the CGH structure, duty cycle errors, surface figure errors of the CGH-substrate, etching depth variations in phase holograms and thickness variations of the chromium layer of amplitude chrome-type holograms. Methods to determine all these different errors are explained and an error budget of the total CGH error is given. Since the pattern error of a CGH is the most critical error it will be discussed in detail. This error depends on the writing technology (e-beam, laser beam) and on the type of the CGH (inline, off-axis). As examples of the two CGH-types a test method for measuring the pattern errors of Fresnel zone plates and linear gratings is presented. Experimental results of the tests are discussed.

The measurement of aspheric and free-form surfaces in a non-null test configuration has the advantage that no compensation optics is required. However, if a surface is measured in a non-null test configuration, retrace errors are introduced to the measurement. We describe a method to calibrate the test space of an interferometer, enabling to compensate retrace errors. The method is effective even for strong deviations from null test configuration up to several 100 waves, enabling the fast and flexible measurement of aspheres and free-form surfaces. In this paper we present the application of the method to the calibration of the Tilted Wave Interferometer. Furthermore, the method can be generalized to the calibration of other setups.

In the last years the application of gray-scale masks (GSM) for diffractive optics manufacturing attracts attention because of cost-effective possibility to produce a lot of diffractive elements on hard and heat-resistant thermally stable substrates. Direct laser writing of GSMs and fabrication of diffractive optical elements are effectively realized with application of LDW-glass (material for Laser Direct Write from CANYON MATERIALS, Inc). An important advantage of this material is the real-time change of transmittance in a single-step process without liquid development. It is shown that optimal transmittance range in which track width is not more than 1 micrometers is from 5-10% (transmittance of unexposed area) to 60-65% for LDW-glass type I having thinner colored layer. Power modulation and surroundings dependent peculiarities of direct laser writing on LDW-glass are discussed. Results of fabrication of diffractive optical elements using LDW-glass masks are presented. Among several types of LDW glasses studied the advantages of new GS-11 glass are elaborated. Application of GS-11 glass for GSMs allowed to fabricate blazed diffractive structures with backward slope width of 0.8 micrometers .

Aspheric surfaces are becoming interesting for the reduction of elements in optical systems as well as for improving the quality of the image forming system. The fabrication process of aspheric surfaces has been improved. For optical testing of aspheric surfaces computer generated holograms (CGHs) are interesting and already used. To perform aspheric testing in the same accuracy as spherical surface testing, further improvements of the CGH-null test method are required. A new concept for testing aspheric surfaces with CGH-nulls, including a calibration of the system, will be described. To specify and verify CGH quality, systematic errors due to fabrication inaccuracies of the CGHs will be analysed. On the other hand, alternative methods that provide more flexibility but possibly less accuracy than the CGH-null technique are required. Potential alternative testing methods of aspherics will be discussed.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We report on the generation of beams with azimuthal polarization using resonant grating waveguide structures (GWSs) inside an Yb:YAG thin-disk laser (TDL) oscillator. Two different GWS concepts were used to select the polarization of the emitted beam. The first uses the resonant reflection principle, and the second is based on the leaky-mode approach already reported in our previous work. Up to 93 W and 103 W of output power were extracted from a TDL with an optical efficiency, η(oo), of 36.2% and 40.1% using the first and the second approaches, respectively. In both cases, a pure azimuthal polarization and a beam quality factor, M2, of about 2.2 were measured. The design, fabrication, and different experimental results, as well as the laser performances for both GWSs, are discussed in the present Letter.

A single-layer resonant-waveguide grating consisting of a sub-wavelength grating coupler etched into a waveguide is proposed in order to achieve high polarization and high spectral selectivity inside an Yb:YAG thin-disk laser resonator. The designed structure was fabricated with the help of a Lloyd's-mirror interference lithography setup followed by reactive ion beam etching down to the desired grating groove depth. The wavelength and polarization dependent reflectivity is measured and compared to the design results. The behaviour of the device at higher temperatures is also investigated in the present work. The device is introduced as the end mirror of an Yb:YAG thin-disk laser cavity. Output powers of up to 123 W with a spectral bandwidth of about 0.5 nm (FWHM) is demonstrated in a multimode configuration (M2~6). In fundamental-mode operation (TEM00 with M2~1.1) 70 W of power with a spectral bandwidth of about 20 pm have been obtained. Moreover, the degree of linear polarization was measured to be higher than 99% for both multimode and fundamental mode operation.

We present a method for absolute testing of axicon surfaces in a null test setup. The absolute test exploits the symmetry of axicons, which allows us to introduce a shift of the surface under test in both the axial and rotational directions while still maintaining the null test condition. With two shifts of the surface under test and four measurements, the interferometer and null optics error can be removed. The absolute surface local deviation can be obtained by wavefront reconstruction with a double-side spiral-path direct integration method. A simulation of the method, including typical systematic as well as statistical errors as input, is presented to estimate the error propagation. Experimental absolute test results of a 90° axicon surface are given.

Computer-generated holograms (CGHs) allow to transfer the high 2D-positioning accuracy of modern lithography equipment into high precision 3D-shape measurements, e.g. in CGH asphere metrology. In this contribution, we give a detailed look into the characterization of steep topologies with CGHs on the example of a 90 deg axicon surface, requiring rather high line densities in the hologram. Several aspects gain importance with increasing CGH line densities when measuring dimensional quantities such as the cone angle of the surface: misalignment of the setup, fabrication effects of the CGH rigorous effects of the high density grating, and effects due to wavelength variations of the interferometer. This paper presents the experimental approach for the cone angle measurement and a systematic analysis of its measurement uncertainty, focusing on the specifics of this null test CGH measurement.

Radially polarized beams with an output power of 275 W, M2 = 2.3 and an efficiency of about 52.5% were generated from an Yb:YAG thin-disk laser. An intra-cavity circular resonant waveguide grating was used as a polarization selective mirror inside the laser cavity. We report on the design and the fabrication using a scanning beam interference lithography system and discuss the calculated and measured performances of the presented polarizing grating mirrors.

We present a simple and novel algorithm for the phase extraction from a single interferogram based on the spatial processing of interference patterns. This new evaluation procedure is suitable for application in environments where the presence of vibrations impedes the use of a classical phase-shifting interferometry scheme with multiple exposures. The algorithm does not require the introduction of a linear carrier as required in Fourier transform techniques. The addition of a carrier can be a significant drawback, e.g. in the case of wavefronts with strong aberrations where the minimum required linear carrier is not even resolved by the detector. The basic idea relies on the spatial application of a temporal phase-shifting algorithm and an iterative correction process to obtain an accurate reconstruction of the wavefront. The validity and performance of the proposed method is shown with numerical and experimental results.

With surface-relief structures, optical functions that are required for radiation power management such as antireflection, light trapping, or light distribution and redirection can be obtained for new applications in solar energy systems and in displays. There, structures with submicrometer features must be distributed over large areas homogeneously. We address the design and the whole experimental process chain from the microstructure origination on large areas to the replication and the system integration in the specific application. Topics are antireflective surfaces for solar systems and displays, light trapping in polymer solar cells, sun protection systems for facades, and diffusers for projection displays and in glazing. For the microstructure origination we investigate the suitability of holographic recording in photoresist using a large-scale interferometer. We use an argon ion laser as a coherent light source at a wavelength of 364 nm. Periodic and stochastic interference patterns are recorded in positive photoresist with the interferometer setup. In the case of periodic structures, grating periods between 200 nm and 20 µm are realized. By carefully modeling the resulting resist profiles it is possible to originate even prismatic surface-relief profiles. Structures with good homogeneity are originated on areas of up to 4800 cm2 by optimizing the interferometer setup and the photoresist processing.

We present the intracavity generation of beams with radial polarization at an average output power of 750 W and an optical efficiency of 43% from a continuous wave thin-disk laser. Circular grating waveguide output couplers (GWOC) were used to select the radial polarization. The sensitivity of the polarizing function of the GWOC with regards to the fabrication tolerances is also analysed in details with a particular emphasis on the effect of the duty cycle and the geometrical profile of the gratings. Furthermore, we present the conversion of femtosecond laser pulses from linear to azimuthal polarization using a nanograting-based polarization converter. Azimuthally polarized beams with an average power of up to 850 W, a pulse duration of 400 fs and a pulse repetition rate of 1 MHz were generated in this way with a conversion efficiency of >90%.

Emergence of products that feature functional surfaces with complex geometries, such as freeform optics in consumer electronics and augmented reality and virtual reality, requires high-accuracy non-contact surface measurement. However, large discrepancies are often observed between the measurement results of optical methods and contact stylus methods, especially for complex surfaces. For interference microscopy, such as coherence scanning interferometry, the three-dimensional surface transfer function provides information about the instrument spatial frequency passband and about lens aberrations that can result in measurement errors. Characterisation and phase inversion of the instrument's three-dimensional surface transfer function yields an inverse filter that can be applied directly to the three-dimensional fringe data. The inverse filtering is shown to reduce measurement errors without using any data processing or requiring any a priori knowledge of the surface. We present an experimental verification of the characterisation and correction process for measurements of several freeform surfaces and an additive manufactured surface. Corrected coherence scanning interferometry measurements agree with traceable contact stylus measurements to the order of 10 nm.