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One of ESA’s future missions is the Darwin Space Interferometer, which aims to detect planets around nearby stars using optical aperture synthesis with free-flying telescopes. Since this involves interfering white (infra-red) light over large distances, the mission is not possible without a complex metrology system that monitors various speeds, distances and angles between the satellites. One of its sub-systems should measure absolute distances with an accuracy of around 70 micrometer over distances up to 250 meter. To enable such measurements, we are investigating a technique called frequency sweeping interferometry, in which a single laser is swept over a large known frequency range. Central to our approach is the use of a very stable, high finesse Fabry-P´erot cavity, to which the laser is stabilized at the endpoints of the frequency sweep. We will discuss the optical set-up, the control system that controls the fast sweeping, the calibration and the data analysis. We tested the system using long fibers and achieved a repeatability of 50 micrometers at a distance of 55 meters. We conclude with some recommendations for further improvements and the adaption for use in space.

We perform a calculation of the vectorial field distribution in the focal plane of a multi-axial beam combiner and show the fundamental limitations with respect to the longitudinal component of the polarization of such a combiner for nulling interferometry.

In any field theory the interaction of a wave packet with a multilayered potential is of high theoretical and practical relevance. In the present work we show an extension to any number of layers of the classical Fabry–Perot formula that works for any level of absorption, any thickness of the composing layers, any number of layers, any angle of incidence and for evanescent waves as well. More specifically, the ability of dealing with input evanescent waves and complex metal-based structures is of special interest for superlenses analysis and design. Some explicit examples in electromagnetism are also discussed.

The three-dimensional frequency transfer function for optical imaging systems was introduced by Frieden in the 1960s. The analysis of this function and its partly back-transformed functions (two-dimensional and onedimensional optical transfer functions) in the case of an ideal or aberrated imaging system has received relatively little attention in the literature. Regarding ideal imaging systems with an incoherently illuminated object volume, we present analytic expressions for the classical two-dimensional x-y-transfer function in a defocused plane, for the axial z-transfer function in the presence of defocusing and for the x-z-transfer function in the presence of a lateral shift δy with respect to the imaged pattern in the x-z-plane. For an aberrated imaging system we use the common expansion of the aberrated pupil function with the aid of Zernike polynomials. It is shown that the line integral appearing in Frieden's three-dimensional transfer function can be evaluated for aberrated systems using a relationship established first by Cormack between the line integral of a Zernike polynomial over a full chord of the unit disk and a Chebyshev polynomial of the second kind. Some new developments in the theory of Zernike polynomials from the last decade allow us to present explicit expressions for the line integral in the case of a weakly aberrated imaging system. We outline a similar, but more complicated, analytic scheme for the case of severely aberrated systems.

In digital holographic particle image velocimetry, the particle image depth-of-focus and the inaccuracy of the measured particle position along the optical axis are relatively large in comparison to the characteristic transverse dimension of the reconstructed particle images. This is the result of a low optical numerical aperture (NA), which is limited by the relatively large pixel size of the CCD camera. Additionally, the anisotropic light scattering behaviour of the seeding particles further reduces the effective numerical aperture of the optical system and substantially increases the particle image depth-of-focus. Introducing an appropriate Fourier filter can significantly suppress this additional reduction of the NA. Experimental results illustrate that an improved Fourier filter reduces the particle image depth-of-focus. For the system described in this paper, this improvement is nearly a factor of 5. Using the improved Fourier filter comes with an acceptable reduction of the hologram intensity, so an extended exposure time is needed to maintain the exposure level.

This study presents an experimental method to determine the resist parameters at the origin of a general blurring of a projected aerial image. The resist model includes the effects of diffusion in the horizontal plane and image blur that originates from a stochastic variation of the focus parameter. We restrict ourselves to the important case of linear models, where the effects of resist processing and focus noise are de- scribed by a convolution operation. These types of models are also known as diffused aerial image models. The used mathematical frame- work is the so-called extended Nijboer-Zernike ENZ theory, which al- lows us to obtain analytical results. The experimental procedure to ex- tract the model parameters is demonstrated for several 193-nm resists under various conditions of postexposure baking temperatures and bak- ing times. The advantage of our approach is a clear separation between the optical parameters, such as feature size, projection lens aberrations, and the illuminator setting on one hand, and process parameters intro- ducing blur on the other. © 2006 Society of Photo-Optical Instrumentation Engineers.

Birefringence induced by spatial dispersion (BISD), also called intrinsic birefringence, can cause a serious deterioration of the optical imaging quality of deep UV lithographic objectives at wavelengths below 193 nm. Recently the mathematical formalism for analyzing those aspects of the BISD effect that are relevant for optical design has been published. In this paper we give an equivalent but simplified derivation of these results. This mathematical formalism is then applied to optical system design and a compensation strategy is discussed. An example of an optical system is given where the phase retardation caused by the BISD effect has been corrected.

The judgment of the imaging quality of an optical system can be carried out by examining its through-focus intensity distribution. It has been shown in a previous paper that a scalar-wave analysis of the imaging process according to the extended Nijboer-Zernike theory allows the retrieval of the complex pupil function of the imaging system, including aberrations as well as transmission variations. However, the applicability of the scalar analysis is limited to systems with a numerical aperture (NA) value of the order of 0.60 or less; beyond these values polarization effects become significant. In this scalar retrieval method, the complex pupil function is represented by means of the coefficients of its expansion in a series involving the Zernike polynomials. This representation is highly efficient, in terms of number and magnitude of the required coefficients, and lends itself quite well to matching procedures in the focal region. This distinguishes the method from the retrieval schemes in the literature, which are normally not based on Zernike-type expansions, and rather rely on point-by-point matching procedures. In a previous paper [J. Opt. Soc. Am. A 20, 2281 (2003)] we have incorporated the extended Nijboer-Zernike approach into the Ignatowsky-Richards/Wolf formalism for the vectorial treatment of optical systems with high NA. In the present paper we further develop this approach by defining an appropriate set of functions that describe the energy density distribution in the focal region. Using this more refined analysis, we establish the set of equations that allow the retrieval of aberrations and birefringence from the intensity point-spread function in the focal volume for high-NA systems. It is shown that one needs four analyses of the intensity distribution in the image volume with different states of polarization in the entrance pupil. Only in this way will it be possible to retrieve the "vectorial" pupil function that includes the effects of birefringence induced by the imaging system. A first numerical test example is presented that illustrates the importance of using the vectorial approach and the correct NA value in the aberration retrieval scheme.

This paper demonstrates the use of bacteriorhodopsin (bR) as the holographic recording medium for a holographic particle image velocimetry (HPIV) system. Using an off-axis hologram in bR, double-exposed images of particles in a turbulent flow are recorded. A high numerical aperture configuration (NA = 0.75) ensures a maximal signal intensity of the holographic recordings. Using a CCD the real particle images, that were reconstructed in the original object space, were digitized. The reconstructed image has a theoretical depth of focus of 4.73 µm and a diffraction-limited resolution of 0.43 µm. Using a priori knowledge about the flow, the flow pattern is extracted from the double-exposed particle images. A liquid crystal shutter was employed during the reconstruction in order to minimize photo-induced erasure. Details of the experimental set-up, as well as the difficulties which were encountered during this investigation, are discussed in this paper. The paper also discusses various multiplexing methods and their suitability for use with bR to remove directional ambiguity in HPIV.

We present a joint approach to the imaging of object and pupil in an optical system by using the aberration data of specially selected rays in the diaphragm space that are common to both imaging processes. Using the concept of eikonal functions, the wave aberrations of the selected rays are derived when they are applied to either the imaging of the object or the imaging of the pupil. The limitation of an optical system regarding its capability to yield 'perfect' imaging between more than one pair of conjugated planes follows in a straightforward way from our analysis.

In this paper we show various results of aberration retrieval using the pinhole method in conjunction with the extended Nijboer-Zernike theory. The experiments are performed on modern wafer scanners. Keyboard commanded offsets of the movable lens elements of the imaging tool have been used to introduce astigmatism, coma and spherical aberration in a controlled way. The method is designed to estimate these induced aberrations and we show the experimental results regarding the various types of aberrations created this way.

In this paper we give the proof of principle of a new experimental method to determine the aberrations of an optical system in the field. The measurement is based on the observation of the intensity point spread function of the lens. To analyse and interpret the measurement, use is made of an analytical method, the so-called extended Nijboer-Zernike approach. The new method is applicable to lithographic projection lenses, but also to EUV mirror systems or microscopes such as the objective lens of an optical mask inspection tool. Phase retrieval is demonstrated both analytically and experimentally. Theory and experimental results are given.

Item does not contain fulltext Various authors have presented the aberration function of an optical system as a power series expansion with respect to the ray coordinates in the exit pupil and the coordinates of the intersection point with the image field of the optical system. In practical applications, for reasons of efficiency and accuracy, an expansion with the aid of orthogonal polynomials is preferred for which, since the 1980s, orthogonal Zernike polynomials have become the reference. In the literature, some conversion schemes of power series coefficients to coefficients for the corresponding Zernike polynomial expansion have been given. In this paper we present an analytic solution for the conversion problem from a power series expansion in three or four dimensions to a double Zernike polynomial expansion. The solution pertains to a general optical system with four independent pupil and field coordinates and to a system with rotational symmetry in which case three independent coordinate combinations have to be considered. The conversion of the coefficients is analytically in closed form and the result is independent of a specific sampling scheme or sampling density as this is the case for the commonly used least squares fitting techniques. Computation schemes are given that allow the evaluation of coefficients of arbitrarily high order in pupil and field coordinates.

The optical aberration function of an imaging system generally is a function of four independent variables, in particular two pupil coordinates and two field coordinates. We describe an expansion of the aberration function with the aid of Zernike polynomials of both the pupil and the field coordinates. Expressions for the field averaged wavefront aberration OPDRMS and the field averaged RMS blur are given.

We propose a measurement approach that allows the determination of aberrations of a microlens by analyzing the through-focus intensity image it produces when the object is a point source. To simulate image formation by a microlens we apply the extended version of the Nijboer-Zernike diffraction theory (ENZ) that uses the Debye diffraction integral to compute the image point-spread function. Due to the aperture size of the microlens and the finite dimensions of the pixels of the electronic detector the Debye diffraction integral should be adapted according to the Li-Wolf scaling rules to yield correct results. In addition to this we also discuss the experimental requirements posed by this characterization approach and derive from this a suitable experimental setup.

A model is presented with which the effect of lens distortion on the optical transfer function is calculated for a step-and-scan lithographic system. The spatially varying lateral image shift and the relative loss in modulation depth are derived from the exposure pattern that is built up during the image scanning. Other important phenomena such as lens aberrations, the effect of finite image aperture, and polarization are deliberately left out of the model; from the simplified model, analytic expressions can be obtained that relate the distortion coefficients of the projection system to the local shift and the relative loss in modulation depth of the exposed pattern that is built up during scanning. As a scanning aperture, we have taken either part of an annulus or a rectangular section in the image field.

Several options for beam-shaping optics are presented, among them a novel single-element solution with toroidal surfaces in which the far-field angular spread of the outgoing beam is the average of the incoming divergences. The beam-shaping elements are judged with respect to their positioning and fabrication tolerances.

The application of gradient-index (GRIN) lenses in an optical scanning system (e.g., a Compact Disc player) is investigated. The type of lens considered varies from simple rod lenses to plano–convex and convex–convex lenses. The field performance of the lenses and the relations between their thickness, surface curvature, base index, and index profile are given.

The optics of a video disk player are described. The bandwidth and the playing time of a disk had been specified at 12 MHz and 30 min, respectively. A readout photodetector signal of high quality can be obtained with a well-corrected objective having a numerical aperture of at least 0.4. Some alternative readout modes and track formats are indicated. Methods for the generation of error signals for the radial and the vertical tracking are briefly discussed.

In video disk systems based on contactless optical readout, the position of the readout light spot is dynamically controlled with the aid of servo systems. The input of the radial or vertical servo systems in the readout unit is fed with a bipolar function of the position error that has to be corrected. This paper describes a method that generates a radial and a vertical error signal by making use of the phase relations between diffracted orders in the far field of the video disk. These phase relations are derived from the rf signals that appear at the different outputs of a composite photodetector. It is shown that in this way auxiliary beams or supplementary optical elements can be avoided in the readout system.

We study the image formation by a high-numerical-aperture optical imaging system in the presence of a multilayer structure in the region around the image plane. Earlier references to this subject in the literature use numerical solutions of the diffraction integrals. In this paper, we use a numerical approach based on the semi-analytic Extended Nijboer-Zernike (ENZ) theory to solve the diffraction integrals in the presence of a multilayer structure. The specific ENZ calculation scheme uses the complex Zernike expansion of the complex amplitudes of forward and backward propagating plane wave components in a certain layer of the multilayer stack. By its nature, the ENZ approach enables an accurate and fast calculation of the vector field in the stratified image region. Examples of multilayer imaging that are encountered in high-numerical-aperture optical systems and in optical lithography for semiconductor manufacturing are presented and the accuracy of the ENZ approach is examined.

We experimentally demonstrate that a femtosecond frequency comb laser can be applied as a tool for long-distance measurement in air. Our method is based on the measurement of cross correlation between individual pulses in a Michelson interferometer. From the position of the correlation functions, distances of up to 50 m have been measured. We have compared this measurement to a counting laser interferometer, showing an agreement with the measured distance within 2 microm (4x10(-8) at 50 m).

We show numerically that the reflectivity of multilayer extreme-UV (EUV) mirrors tuned for the 11–14-nm spectral region, for which the two-component, Mo/Be and Mo/Si multilayer systems with constant layer thickness are commonly used, can be enhanced significantly when we incorporate additional materials within the stack. The reflectivity performance of the quarter-wavelength multilayers can be enhanced further by global optimization procedures with which the layer thicknesses are varied for optimum performance. By incorporating additional materials of differing complex refractive indices—e.g., Rh, Ru, Sr, Pd, and RbCl—in various regions of the stack, we observed peak reflectivity enhancements of as much as ∼5% for a single reflector compared with standard unoptimized stacks. We show that, in an EUV optical system with nine near-normal-incidence mirror surfaces, the optical throughput may be increased by a factor as great as 2. We also show that protective capping layers, in addition to protecting the mirrors from environmental attack, may serve to improve the reflectivity characteristics.

Results are presented of mask imaging using the Extended Nijboer-Zernike (ENZ) theory of diffraction. We show that the efficiency of a mask imaging algorithm, derived from this theory, can be increased. By adjusting the basic Finite Difference Time Domain (FDTD) algorithm, we can calculate the near field of isolated mask structures efficiently, without resorting to periodic domains. In addition, the calculations for the points on the entrance sphere of the imaging system can be done separately with a Fourier transformed Stratton-Chu near-to-far-field transformation. By clever sampling in the radial direction of the entrance pupil, the computational effort is already reduced by at least a factor of 4.

We present a holographic particle image velocimetry system that uses a reusable holographic material as the recording medium. The measurement system records double-exposure holograms in a film containing the photochromic protein bacteriorhodopsin (BR). The two constituent particle holograms are recorded in a single film using polarization multiplexing. We describe the system in detail and present three-dimensional measurements that determine the system’s accuracy and demonstrate its capabilities.

We present concise formulae for the Zernike coefficients of numerical aperture reduced pupils and show how they can be exploited within the framework of the ENZ-formalism to characterize optical systems with scaled and annular pupils.

In this paper we introduce a new mask imaging algorithm that is based on the source point integration method (or Abbe method). The method presented here distinguishes itself from existing methods by exploiting the through-focus imaging feature of the Extended Nijboer-Zernike (ENZ) theory of diffraction. An introduction to ENZ-theory and its application in general imaging is provided after which we describe the mask imaging scheme that can be derived from it. The remainder of the paper is devoted to illustrating the advantages of the new method over existing methods (Hopkins-based). To this extent several simulation results are included that illustrate advantages arising from: the accurate incorporation of isolated structures, the rigorous treatment of the object (mask topography) and the fully vectorial through-focus image formation of the ENZ-based algorithm.

We present the design of a new testbed experiment to demonstrate nulling interferometry using polarization properties. This three-beam set-up is perfectly symmetric with respect to the number of reflections and transmissions and should therefore allow a high rejection ratio in a wide spectral band.

We show the theoretical limitations of a multi-axial nulling interferometer with respect to longitudinal polarization. We furthermore analyze the filtering capabilities of a single-mode fiber in this case.

Recently, a new type of liquid based deformable mirror has been proposed and demonstrated. The device consists of an array of vertically oriented open capillary channels immersed in a pool of two immiscible liquids and a freefloating reflective membrane, which serves as the reflecting surface. Liquid surface and membrane deformations are facilitated by means of electrocapillary actuation that induces upward or downward flow of liquid inside the capillary. This electrocapillary movement of liquid can be individually controlled. The advantages of this proposed device include high stroke dynamic range, low power dissipation, high number of actuators, fast response time, and reduced fabrication cost. The device is mainly suitable for dynamic wavefront correction. We present some aspects of the modeling of the device.

We present a new type of nulling interferometer that makes use of polarization properties to have on-axis destructive interference. The proposed design, which only involves commercial components and no achromatic device, is also suitable for internal modulation. This type of interferometer should enable a high rejection ratio in a theoretically unlimited spectral band. We implemented that concept on a two-beam white-light interferometer and we present here the first experimental results.

We discuss the previously-reported measurements of a three-beam nulling interferometer without achromatic phase-shifters, using delay lines only. The theoretical rejection ratio of a few thousand has not been achieved experimentally. In order to explain the obtained results, some direct spectral and polarization measurements have been performed. We present here the latest results and discuss some asymmetries in the interference patterns.

The reconstruction of the exit pupil function of an optical system can basically be carried out by collecting intensity data in the focal region from a certain number of defocused image planes. In this paper we present the first results of such a reconstruction operation for optical systems with a high numerical aperture using a point source in the object plane. The main feature of our approach is the use of the extended Nijboer-Zernike diffraction analysis that has been modified to incorporate vector diffraction effects. The quality of the optical system is expressed by means of a set of complex Zernike coefficients that describe the phase and transmission variation in the exit pupil of the imaging system. The ’vector’ method will be compared to the more common scalar diffraction analysis. We also analyse the practical limits of the vector retrieval process regarding the maximum allowed aberration and the noise of the intensity data. The sensitivity of the method with respect to parameter settings (state of polarisation and value of numerical aperture) is also examined.

In 2005, the Board of the European Optical Society (EOS) decided to launch a fully electronic international online journal because it felt that the scientific community in general and the EOS-membership in particular would greatly profit from such a new service. After more than a half year of preparatory work, the journal JEOS Rapid Publications (JEOS:RP) is now online (http://www.jeos.org) and ready to accept submissions from a broad field in optics and photonics. The Editor in Chief of the journal, Mario Bertolotti, his deputy Peter Torok and the Editorial Board are determined to maintain a high scientific level from the very beginning. At the same time, the turn-around time of a submitted paper will be kept as short as possible to justify the epitheton ‘Rapid Publications’. With a well-organized reviewing system, this time between submission and final publication should not exceed three weeks maximum. I would like to bring some particularities of JEOS:RP to your attention. First of all, in contrast to most other journals, the copyright of the published paper remains with the author. This is in line with European law that favours the rights of authors. The only requirement of JEOS:RP is the consent of the author not to publish the paper in another journal, book or other publication means within the first twelve months after publication in JEOS:RP. This is also the only step in the submission and publication process that is not fully electronic. European law requires a written document in which the author signs for this temporary limitation of his full copyright; in practice, a downloadable fax form signed by the author and sent to the EOS office is sufficient. A second point I would like to bring to your attention is the author fee system. For an open-access journal like JEOS:RP, a fee from the author is indispensable to cover the cost of editing the journal. The European Optical Society has been able to fix this fee at a very low level. The basic fee is 400 €; full members and branch members of EOS receive a discount of 50 €. The length of a submitted paper does not play a role. We are convinced that this author fee level is very interesting and we will do our utmost to stick to this competitive level in coming years. A third point of interest, especially for the authors from academia, is the presence of JEOS:RP in the ISI Master Journal List established by Thomson Scientific. All necessary steps have been taken by the Editors to introduce JEOS:RP on this list. Like for all new journals, this insertion will be official after two years of existence of the journal with effectiveness in retrospect from the starting date of the journal (June 2006) The brilliant future of the online journal is now in the hands of you, the authors, via the quality of your submissions to JEOS:RP. The Editorial Board will do its utmost to establish a very high standard by a thorough and efficient reviewing system carried out by an international network of peers. The aspect of publication speed will be primordial but it should be clear that in certain circumstances quality can not be sacrificed to the shortest possible turn-around time of the paper. Having said this, the Editors, Editorial Board and the other officials of EOS committed to JEOS:RP welcome your future submissions to the online journal!

We propose and demonstrate a novel liquid deformable mirror, based on electrocapillary actuation, for high-order wavefront correction. The device consists of a two-dimensional array of vertically oriented microchannels filled with two immiscible liquids, an aqueous electrolyte, and a viscous dielectric liquid, where the dielectric liquid overfills the top end of the channel and forms a thin layer on top. To remedy the poor reflectivity of pure liquids, a free-floating reflective membrane or a dye-coated liquid can be used. The proposed device offers several advantages for adaptive optics applications. These advantages include a high number of actuators, high stroke dynamic range, low power dissipation, fast response time, an initially flat surface, and low cost. However, the device is mainly suitable for dynamic wavefront correction and is limited by its orientation.

We introduce the concept of chromatism compensation in nulling interferometry that enables a high rejection ratio in a wide spectral band. Therefore the achromaticity condition considered in most nulling interferometers can be relaxed. We show that this chromatism compensation cannot be applied to a two-beam nulling interferometer, and we make an analysis of the particular case of a three-telescope configuration.

1 Optics Research Group, Department of Imaging Science and Technology, Faculty of Applied Sciences, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands (j.j.m.braat@tnw.tudelft.nl) 2 Philips Research Laboratories, Kapeldreef 75, B-3001 Leuven, Belgium (peter.dirksen@philips.com) 3 Philips Research Laboratories, Professor Holstlaan 4, 5656 AA Eindhoven, The Netherlands (a.j.e.m.janssen@philips.com)

Phase Measurement Interferometers (PMI) are widely used during the manufacturing process of high quality lenses. Although they have an excellent reproducibility and sensitivity, the set-up is expensive and the accuracy of the measurement needs to be checked frequently. This paper discusses an alternative lens metrology method that is based on an aerial image measurement. We discuss the Extended Nijboer-Zernike (ENZ) method and its application to aberration measurement of a high-NA optical system of a wafer stepper. ENZ is based on the observation of the through-focus intensity point-spread function of the projection lens. The advantage of ENZ is a simple set-up that is easy to run and maintain and provides good accuracy. Therefore the method is useful during lens assembly in the factory. The mathematical framework of ENZ is shown and the experimental procedure to extract aberrations for a high-NA lens is demonstrated on a high-NA DUV lithographic lens. PMI data is given as reference data. It is shown that ENZ provides an attractive alternative to the interferometer.

A strategy to escape from poor local minima by switching merit functions during local optimization is discussed. As a switching partner, we define a new auxiliary merit function, which also tends to zero for ideal systems, but differs significantly from traditional merit functions. The examples include high-dimensional optimization problems. © 2005 Society of Photo-Optical Instrumentation Engineers.

Absolute distance measurements can be performed with an interferometric method that uses only a single tunable laser. This method has one major drawback, because a small target movement of the order of one wavelength during a measurement will be interpreted as a movement of one synthetic wavelength. This effect is usually mitigated by adding a second (nonscanning) laser. We show that absolute distance measurements can be performed with only one laser if the movements encountered are smooth, on the time scale of one measurement. In this case the movement errors can be compensated with a simple algorithm that combines several subsequent measurements. First experimental results show good agreement with theory.

This paper compares two well-known types of interferometer arrays for optical aperture synthesis. An analytical model for both types describes the expected output, in terms of photon counts. The goal is to characterize the performance of both types of array for blind imaging of a wide-field or extended object that would be partially resolved by a single elementary aperture. The spectrum of the source is assumed to be constant over the source and in time, but broad-banded. The light levels are such that only a few photons per pixel or bin are received. The simulated interferometer responses are discussed. The process of reconstructing the source from the 'recorded' responses is presented, but not discussed in this paper. It turns out that both types of interferometer are capable of imaging a partially resolved source with high spatial frequencies present all over the source.

We propose and demonstrate a novel liquid based deformable mirror (LDM). The proposed LDM consists of an array of vertically oriented open capillary channels immersed in a pool of two immiscible liquids. A free-floating thin reflective membrane serves as the reflecting surface. By means of jet action, membrane deformation is induced. The control of jet flow through each channel is achieved by electrostatic means. This individual control enables the generation of complex surface profiles useful for adaptive optics applications. The advantages of this device include high stroke dynamic range, low power dissipation, high number of actuators, fast response time, and reduced fabrication cost. The device, however, can only be operated in a vertical orientation and is suitable for dynamic wavefront correction. A proof of principle of the device using an array of linearly addressed capillary channels is presented. Preliminary measurements showed that the response time is several milliseconds with a stroke of more than 10 microns. The design and fabrication of a prototype with around 100 actuators is in progress.

A previously reported interferometer without intermediate optics is used to perform measurements on an aspherical extreme ultraviolet lithography mirror substrate. Acousto-optic modulation based phase shifting is used together with a novel phase retrieval algorithm to retrieve the phase distribution from our interferograms. The phase distribution is then processed by a previously reported inverse propagation algorithm to give the shape of the mirror under test. Our results are compared with measurements performed with conventional Fizeau interferometry and the discrepancies are discussed with reference to systematic error sources inherent in the classical and novel interferometers.

In the year 2001 it was reported that the birefringence induced by spatial dispersion (BISD), sometimes also called intrinsic birefringence, had been measured and calculated for fluorides CaF 2 and BaF2 in the deep UV range. It was also shown that the magnitude of the BISD in these cubic crystals is sufficiently large to cause serious problems when using CaF2 for lithographic objectives at 157 nm and possibly also in the case of high numerical aperture immersion objectives at 193 nm. Nevertheless the single-crystal fluorides such as CaF 2 are the only materials found with sufficient transmissivity at 157 nm and they are widely used at 193 nm for chromatic correction. The BISD-caused effects lead to the loss of the image contrast. In this work we discuss issues related to the design of optical systems considering the BISD effect. We focus on several approaches to the compensation of the BISD-related phase retardation and give examples of lithographic objectives with the compensated phase retardation.

Previously, we have given a detailed description of the so-called Extended Nijboer-Zernike approach and its application to aberration measurements of the optical projection system in a wafer scanner in the case of a low or medium high-NA system. The Extended Nijboer-Zernike theory provides an analytical description of the through-focus intensity point-spread function in the presence of lens aberrations and defocus. Taking the Extended Nijboer-Zernike description for the electric field components in the case of a high-NA optical system as a starting point, we present an approach to aberration retrieval when the NA is very high. The experimental procedure involves the analysis of a focus-exposure matrix. The differences between aberration retrieval using the low-NA scalar model and the high-NA full vectorial model are discussed. The mathematical framework is shown and the experimental procedure to extract aberrations for a high-NA lens is demonstrated on modern 193 nm wafer scanners.