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The MicroCarb mission was initiated in Dec 2015 during the COP21 climate conference. Its objective is a better understanding of the carbon cycle within our atmosphere and thus enabling the prediction of its evolution. The French space agency CNES selected Airbus Defense & Space for the development of the satellite and its disruptive instrument with an original concept based on multi freeform mirror design. Safran Reosc was selected by Airbus for the optical manufacturing of all the key optical components of this innovative compact spectrometer, the first in EU of its class entirely based on precision freeform optics. We will first recall the benefits of using freeform optics in an imaging or spectral instrument. Then we will present the MicroCarb satellite and its instrument optical design. Joint design analysis was spent with Airbus towards ‘feasible’ optics despite the fact that this project constituted a unique opportunity for Safran Reosc to make a quantum leap in optical manufacturing and testing technology for precision freeform optics in Silicon Carbide (SiC).

The introduction of freefrom optical surfaces in a space instrument offers the possibility to improve its performance, its volume and weight or a combination of both. This is shown to be valid for either imaging systems or spectroscopic systems. At Safran Reosc we master freeform robotic polishing technology since more than 25 years and we will show how we continue to improve it in term of quality, productivity and adequacy to ceramic materials like Silicon Carbide. Surprisingly, the conservative space industry evolved slowly from spherical to rotationnally symmetric aspherical and off-axis optics during the last decades. This is no more valid today and we are proud to contribute to MicroCarb and IASI NG, two recent innovative projects taking benefit of such freeform optics designs enabling more cost-effective advanced missions. These projects will be briefly presented with their status of progess of work at the company. We will also take this opportunity to present our work on the extreme off-axis optics used within the MERLIN lidar project, produced with the same freeform technology.

The presentation slides for “Small Optics for Earth Science: Roundtable” are available at http://doi.org/10.1117/12.2536006 , under the Supplemental Content tab.

Green light for the construction of the 39-m aperture Extremely Large Telescope (ELT) was given by the Council of the European Southern Observatory (ESO) on Dec 4th, 2014. Procurement of the key elements, especially the optics, the dome and structure and the glass substrates, was soon after initiated by ESO team. Safran-Reosc is proud to have been awarded all the key optical polishing and testing contracts with M4 in 2015, M2 in 2016, M3 and M1 in 2017. This paper reports Safran-Reosc’s work progresses of the last 12 months along these four contracts with their challenges, specifically those related to the mass production of the M1 segments. Keywords: ELT, segmented optics, large optics, optical manufacturing, optical testing, thin glass shell, bonding

Green light for the construction of the 39-m aperture giant Extremely Large Telescope (ELT) was given by the European Southern Observatory (ESO) council on Dec 4th, 2014. Procurement of the key elements, especially the optics, was immediately initiated by ESO team. Up today, Safran Reosc was awarded all the key optical polishing and testing contracts with: 2015-07: contract for the Adaptive Optics M4 mirror thin glass petals, 2016-07: contract for the 4-m M2 convex mirror, 2017-02: contract for the 4-m M3 mirror. 2017-05: contract for polishing and intergation of the 931 1.45-m hexagonal segments for the giant 39-m M1 mirror assembly This paper is dedicated to highlighting the various challenges linked to these various optical fabrication projects and reporting about the progress of our work so far.

In dec 2015, during COP21, France has initiated the development of the MicroCarb satellite dedicated to better understand the carbon cycle within our atmosphere and to predict its evolution. CNES selected Airbus Defense and Space for the development of the instrument and Safran Reosc has been selected for the optical polishing of the key optical components of this innovative compact spectrometer, the first in EU of its class entirely based on precision freeform optics. The benefits of freeform optics will be highlighted before introducing to the MicroCarb satellite and instrument optical design. Our joint design efforts with Airbus Defense and Space towards ‘feasible’ optics will be presented with the latest technology development at Safran Reosc on freeform optics polishing technology.

In this paper Safran-Reosc wants to share with the space community its recent work performed in the domain of space optics. Our main topic is a study about the advantages that freeform optical surfaces can offer to advanced space optics in term of compactness or performances. We have separated smart and extreme freeform in our design exploration work. Our second topic is to answer about the immediate question following: can we manufacture and test these freeform optics? We will therefore present our freeform optics capability, report recent achievement in extreme aspheric optics polishing and introduce to the industrialisation process of large off axis optics polishing for the ESO Extremely Large Telescope primary mirror segments. Thirdly we present our R-SiC polishing layer technology for SiC material. This technique has been developed to reduce costs, risks and schedule in the manufacturing of advanced SiC optics for Vis and IR applications.

Our presentation will focus on the advantages that freeform optical surfaces can offer to advanced space optics in term of compactness and performances. Some experimental results in extreme freeform optics will be presented

Recently Safran Reosc worked and progressed on various thin film technology for: Large mirrors with low stress and stable coatings. Large lens elements with strong curvature and precise layer specifications. Large filters with high spectral response uniformity specifications. IR coatings with low stress and excellent resistance to cryogenic environment for NIR to LWIR domains. Pixelated coatings. Results will be presented and discussed on the basis of several examples.

In this paper we share some recent work performed at REOSC in the domain of advanced optics for space and that is also directly applicable to astronomical instrumentation, e.g. for the Extremely Large Telescopes (ELT), the construction of which has already started. We present firstly the results of some design investigations performed on Three Mirror Anastigmat (TMA) imaging optics when using freeform optical surfaces clearly showing gain in performance (WFE, distortion, … ) or compactness of the optics. We separate smart freeform from more aggressive freeform offering increased level of gain in design performances. Secondly we present our development in freeform and direct off-axis high performance optical manufacturing capabilities and the industrialization efforts conducted in the frame of the European Extremely Large Telescope (E-ELT) primary mirror segments. A third subject is the demonstration of an extreme freeform surface manufacturing with the prototyping of a huge 500 mm aperture, 90° deviation angle, F/2.5 high output NA Off Axis Parabola (OAP), a unique achievement aimed to confirm the viability of potential new design opportunities involving such type of extreme optics. Finally we present in this paper our technology development on polishing layer for SiC material, named R-SiC, a polishing layer that reduces costs, risks and schedule for advanced SiC optics manufacturing for Vis and IR applications.

Reosc has been working on thin glass shells for many years and was recently selected by ESO for the production of the E-ELT M4 mirror thin glass shells. Previously Reosc also produced the aspheric thin shell for the VLT-M2 AO Facility. Based on this experience we will discuss how off axis thin glass shells can be made for the next generation AO systems like the GMT one.

In the frame of the French EUV program PREUVE, different studies are made on different key aspects of EUV lithography. Aspheric optics are fabricated for the exposure test bench as well as mask blanks. All these objects require Mo/Si multilayer coatings with optimized EUV characteristics. As project partner, SOPRA is developing a commercial table-top soft-X-ray/EUV reflectometer to measure, at wavelength, the reflectivity versus wavelength, angle of incidence and position on the sample. These MoSi multilayers are deposited by magnetron sputtering or ion beam sputtering for the optics and the masks, respectively. Hereafter, some structural characterizations of these two kinds of multilayers are measured and compared. The EUV reflectometer is described in detail and first results are presented in relation with the Mo/Si structural characterizations.

The goal of the VIRGO program is to build a giant Michelson type interferometer (3 kilometer long arms) to detect gravitational waves. Large optical components (350 mm in diameter), having extremely low loss at 1064 nm, are needed. Today, the Ion beam Sputtering is the only deposition technique able to produce optical components with such performances. Consequently, a large ion beam sputtering deposition system was built to coat large optics up to 700 mm in diameter. The performances of this coater are described in term of layer uniformity on large scale and optical losses (absorption and scattering characterization). The VIRGO interferometer needs six main mirrors. The first set was ready in June 2002 and its installation is in progress on the VIRGO site (Italy). The optical performances of this first set are discussed. The requirements at 1064 nm are all satisfied. Indeed, the absorption level is close to 1 ppm (part per million), the scattering is lower than 5 ppm and the R.M.S. wavefront of these optics is lower than 8 nm on 150 mm in diameter. Finally, some solutions are proposed to further improve these performances, especially the absorption level (lower than 0.1 ppm) and the mechanical quality factor Q of the mirrors (thermal noise reduction).

Over the past few years, Sagem REOSC has designed, manufactured and tested a 2.5m ALT/AZ telescope and its complete observatory. The next stage - integration - should occur in 2012. The aim of this paper is to develop the different stages of the project from technical and management's point of view. The telescope is a 2.5m-class telescope with an aperture of F/8. It is composed of a 2.5m primary mirror made of Zerodur©, a silica secondary mirror and a rotating tertiary mirror that allows pointing at Nasmyth foci. In addition, a wide field corrector can be adapted either at Cassegrain focus or at Nasmyth focus. Results achieved on the realization of such optics will be presented. An emphasis on the concurrent engineering and the problem solving approach will also be presented.

Glassy thin shells are key components for the development of adaptive optics and are part of future and innovative projects such as ELT. However, manufacturing thin shells is a real challenge. Even though optical requirements for the front face - or optical face - are relaxed compared to conventional passive mirrors, requirements concerning thickness uniformity are difficult to achieve. In addition, process has to be completely re-defined as thin mirror generates new manufacturing issues. In particular, scratches and digs requirement is more difficult as this could weaken the shell, handling is also an important issue due to the fragility of the mirror. Sagem, through REOSC program, has recently manufactured different types of thin shells in the frame of European projects - E-ELT M4 prototypes and VLT Deformable Secondary Mirror (VLT DSM). © (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Sagem is presently working on a new project for the Japanese HISUI instrument made from a Hyper Spectral Sensor and a Multi Spectral Sensor, both including a Three Mirror Anastigmat (TMA) main optics. Mirrors are made from Zerodur from Schott but also from NTSIC, the New Technology Silicon Carbide developed in Japan. This report is also the opportunity to show to the community Sagem recent progress in precision TMA optics polishing and alignment.

In 2010, Sagem-REOSC delivered to Astrium GmbH the last model of the optics for Near Infra-Red Spectrograph (NIRSpec) instrument to be installed on-board the James Webb Space Telescope (JWST) and constituting a key European contribution to this challenging project. We will report the various steps of polishing, coating, integration and cryo test of this rather unusual all-SiC optics for such a high performance space spectrographic instrument.

For several years Sagem has invested in technologies and engineering to develop innovative solutions for collecting optics for LPP and DPP EUV sources. Among the technological challenges for collecting mirrors, thermal control plays a very important role in avoiding degradation of in band EUV reflectivity and maintaining far field optical performance during scanner operation. Sagem proposes solutions based on a metallic mirror with embedded cooling circuits to stabilize the temperature of the mirror during source operation. Results of simulation as well as first technology validations obtained on prototypes will be shown to demonstrate the performance of the cooled mirror design. Another critical performance about the collector is the HSFR (micro roughness) requirements of the optical surface for limiting scattering and optimizing the in band EUV reflectivity. Thanks to the specific polishing process, HSFR values of below 2 Angstroms have been achieved on demonstrator metallic mirrors with high departure aspheres. Reflectivity measurements performed after coating of these parts with MoSi multilayers confirm that the obtained polishing quality is compliant with polishing specifications for high performance EUV optics. Finally, upcoming developments at Sagem in the field of EUV collecting optics will be presented.

Through its participation to European programs, SAGEM has worked on the design and manufacturing of normal incidence collectors for EUV sources. By opposition to grazing incidence, normal incidence collectors are expected to collect more light with a simpler and cheaper design. Designs are presented for the two current types of existing sources: Discharge Produced Plasma (DPP) and Laser Produced Plasma (LPP). Collection efficiency is calculated in both cases. It is shown that these collectors can achieve about 10 % efficiency for DPP sources and 40 % for LPP sources. SAGEM works on the collectors manufacturability are also presented, including polishing, coating and cooling. The feasibility of polishing has been demonstrated with a roughness better than 2 angstroms obtained on several materials (glass, silicon, Silicon Carbide, metals...). SAGEM is currently working with the Institut d'Optique and the Laboratoire des Materiaux Avances on the design and the process of EUV coatings for large mirrors. Lastly, SAGEM has studied the design and feasibility of an efficient thermal control, based on a liquid cooling through slim channels machined close to the optical surface.

The development of new high power EUV sources and EUV space imaging requires optics having specific properties which depend on applications and operating conditions. These both applications are very different in the working multilayers environment. For the high power sources, multilayers are submitted to short pulses with high energy peak whereas, for the space imaging, multilayers are submitted to continuous flux with low level. Moreover photon energy and environment for both applications may be different. The environment may affect structure and top layer contamination when optics are stored, handled, mounted on the final device and finally operating. Main environmental parameters investigated are temperature and humidity variation. One objective is the optimisation of multilayer coatings to offer the highest resistance under photonic, ionic fluxes and temperature cycle. This means that interfacial diffusion between thin layers and degradation of the capping layers have to be avoided or reduced. The present study relies with designing, depositing and testing different structures of multilayer coatings in order to minimise the influence of the environment. Multilayer coatings based on molybdenum, silicon and silicon carbide materials have been deposited by magnetron sputtering on silicon and zerodur substrates. Samples were submitted to radiations emitted by an EUV source at wavelength closed to 13.5 nm. Furthermore they were also submitted to thermal cycles and annealing under warm humidity in the aim to simulate extremes storage or handling conditions as space mission's conditions. The damages and the performance of the multilayers were evaluated by using grazing incidence reflectometry at 0.154 nm and EUV reflectometry at the operating wavelength. After a presentation of the multilayer design, deposition and metrology tools, we will describe the different environmental effects on the coatings to take in care during EUV source exposure, handling and storage conditions. First results on multilayers performances to EUV source exposure and space specification tests are presented. Main damages studies were on annealing, thermal cycling and warm humidity.

This paper is intended to establish, after delivery of the last batch of segments, the final progress report of the manufacturing and testing of the Gran Telescopio Canarias optics.

At Sagem-REOSC we are in the last phase of figuring of the Gran Telescopio Canarias Primary Mirror Segments and Secondary Mirror. This paper's intent is to show, from the optical manufacturer point of view, how astronomy is presently evolving from large monolithic Active Mirrors to segmented optics thus raising new manufacturing challenges. For this we will recall the work done during VLT & Gemini, gaive latest status on Gran Telescopio Canarias and make a rapid overview of the on-going Extremely Large Telescope projects with primary mirror diameter above 20-m.

This paper is intended to give a report after the successful lightweighting of a mirror substrate dedicated to become a third spare secondary mirror for the Gemini 8-m telescopes installed one in Chili and one Hawaii.

This paper is intended to establish, after delivery of the first batch of segments, the third progress report of the manufacturing and testing of the Gran Telescopio Canarias optics.

This manuscript is intended to report some recent astronomical optics achievement in term of large lenses, large area filters, off-axis aspheric mirrors and the SALT Spherical Aberration Corrector (SAC).

This paper is intended to establish the second progress report of the manufacturing and testing of the Gran Telescopio Canarias optics, i.e. the segmented primary mirror and the lightweighted secondary mirror.

PREUVE is the French federative program aimed at developing knowledge concerning the critical issues of EUV Lithography. The project supported by the French ministry of industry is one of the most important project in the field of nano-technologies in France. PREUVE is focused on different relevant aspects of the EUV lithography. Different kinds of EUV sources at 13.5nm for the purposes of lithography and metrology have been studied. Also reflective optics and multilayer coatings for the illuminating and the projection cameras have been realized. A complete development of EUV masks including substrates, multilayer coatings and reticules has been realized. Relevant metrologies for reflectivity measurements and defects detection have been developed. Finally the construction of an experimental exposure bench with high magnification (x10) and very high numerical aperture (0.32) has been pursued for process development. A summary of the results obtained in the frame of the project is presented hereafter.

Within the recently initiated EXTATIC project a complete full-field lithography exposure tool for he 50-nm technology node is being developed. The goal is to demonstrate the feasibility of extreme UV lithography (EUVL) for 50-nm imaging and to reduce technological risks in the development of EUVL production tools. We describe the EUV MEDEA+) framework in which EXTATIC is executed, and give an update on the status of the (alpha) -tool development. A brief summary of our in-house source-collector module development is given, as well as the general vacuum architecture of the (alpha) -tool is discussed. We discuss defect-free reticle handling, and investigated the uses of V-grooved brackets glued to the side of the reticle to reduce particle generation during takeovers. These takeovers do not only occur in the exposure tool, but also in multilayer deposition equipment, e-beam pattern writers, inspection tools, etc., where similar requirements on particle contamination are present. Finally, we present an update of mirror fabrication technology and show improved mirror figuring and finishing results.

The Stratospheric Observatory for Infrared Astronomy (SOFIA) is a joint American-German project dedicated to performing IR astronomy on board a Boeing Aircraft, in near space condition. First flight of the Observatory is planned for 2003. The REOSC Products Unit of SAGEM SA (France) has been contracted by Kayser Threde (Germany) for the design and fabrication of the 2.7-meter diameter, F/1.19 parabolic lightweight SOFIA primary mirror as well as the M3 dichroic and folding mirror assembly. This paper will report the design, fabrication and test of the lightweight primary mirror. The mirror structure has been obtained by machining it out from a solid Zerodur blank. It is the world's largest of this type today. Axial and lateral mirror support system has been conceptually designed and engineered by SAGEM-REOSC engineers in relation with Kayser Threde team. The optical surface is an F/1.19 parabola polished to a high level of quality.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

SAGEM, within its REOSC high performance optics product line, has developed through the years a specific knowledge in large plano, spherical and aspherical optics for high energy or high power laser. This paper is aimed to illustrate the application of aspheric optics for such laser application with several examples of increasing optical surface complexity.

SAGEM, through its REOSC product line, is participating since November 1999 to PREUVE, the French EUV initiative, and work within this program especially in the field of EUV illumination and projection optics. After a short description of the PREUVE main lines of activity, we will detail our contributions to this program and work progress. This is mainly focused on basic EUV optics fabrication technology in order to ensure the fabrication of the entire optics assembly of an EUV micro exposure tool.

On the basis of its experience gained on the VLT and GEMINI primary mirrors polishing REOSC will present his first comments on the preliminary technical specifications of some concepts (OWL, MAXAT) discussed with their instigators (ESO, AURA). Similarities with other projects presently running (CEA LIL) at REOSC that lead to consider such type of giant telescope with some unsuspected serenity. In addition the discussion will be illustrated with the REOSC experience in medium and large size off axis aspheric optics fabrication, the most recent being the Gran Telescopio Canaries project for which REOSC has just been awarded by GRANTECAN S.A. for polishing the 36 segments of this 11-m instrument.

This paper reports the beginning of laser amplifier discs and spatial filtering lens polishing activities performed at REOSC for the Laser Megajoule project Ligne d'Intergation Laser prototype facility.

In 1994, REOSC took the decision to set up a large optics Ion figuring facility to be operational within 18 months. The equipment was designed to be able to accept components up to the maximum dimensions of 1.3 X 1.3 X 1.3 meters mounted in a high-vacuum chamber. After a period of design, fabrication, installation and validation, the Ion Beam Facility came is now, since more than two years, fully integrated in our production line as an efficient complementary technique to the mechanical polishing. We present in this paper some experimental results showing the maturity of the technology as well as some recent improvements and future applications.

Large aspherical focusing and beam deviating square lenses will be used in the framework of the Laser Megajoules project developed by the French Atomic Energy Commission. In order to validate the associated manufacturing processes a half scale prototype lens has been manufactured and tested by REOSC (SFIM subsidiary). Specific aspherical generating process and computer controlled micro-polishing technology have been used in order to demonstrate the faisability of a mass production on an industrial basis (approximately 1300 lenses in 6 years). A 250 mm square lens in Fused Silica with a convex hyperboloid profile (250 microns difference with respect to the best sphere) has been manufactured and REOSC reached a transmitted wavefront better than 130 nm Peak-peak, 11 nm rms. Moreover residual micro-oscillations amplitudes (spatial frequency 0.5 to 30 mm) have been limited to 60 nm PTV and 8 nm rms. The total work duration for this exploratory lens remained below 60 hours.

The primary mirrors of the ESO 8-m class very large telescopes are actively supported, thin Zerodur menisci, 8 - .2-m diameter. The mirror blanks are produced by SCHOTT; the optical figuring, manufacturing and assembling of interfaces and auxiliary equipment are done by REOSC. Three mirror blanks have already been delivered by SCHOTT to REOSC. In November 1995 the project met a critical and very successful milestone, with the completion and testing of the first finished VLT primary mirror at REOSC. Specifications, manufacturing and above all testing methodology are addressed, and the final results are detailed. Optical performance at telescope level is assessed as well.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The primary mirrors for the ESO very large telescope project consist of four f/1.8 8.2-m diameter actively supported Zerodur menisci, 175 mm thick. Their optical figuring is under way at REOSC (France) plant. Two mirror blanks have been delivered to the optical manufacturer and the two remaining at the blanks' manufacturer (SCHOOT Mainz, Germany) are due for delivery by the second hald of 1995. Th polishing of the first Zerodur mirror blank is due for completion in the third quarter of 1995. The REOSC optical fabrication and testing methodology will be presented, and the current results will be compared to the specified performance.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

REOSC has been awarded by the European Southern Observatory (E.S.O.), in July 1989, a contract to transport, grind, polish, figure and test the four 8.2m primary mirrors of the European Very Large Telescope (VLT). The following tasks are included in this contract: - the design and manufacture ofthe mirror handling tool and shipping container, the mirror blank transportation from SCHOTT plant in Mainz to REOSC optical shop, - the design, manufacture and bonding onto the mirror of the axial and lateral interfaces between the mirror and the actuators of the mirror cell lateral and axial supports, - the grinding, polishing, figuring and testing of the four mirrors, -the packing ofthe achieved mirror in the container. Furthermore, in the framework of this contract, a new optical shop specially adapted to mill, grind, polish and test 8m class mirrors has been designed and built. The first 8.2m mirror blank has been successfiuly transported last July from Mainz to REOSC's optical shop and the subject of this paper is to give a short description of this new plant and its equipment and the first results obtained by spherornetry after the first rough mirror grinding.

The purpose of this paper is to present REOSC experience in the field of high energy or high power optics. We review some challenging recent achievements which are: a 1.8 meter mirror assembly for the U.S. Navy, the 1 meter LATEX high energy beam expander telescope, large high energy optics for the CEA laser fusion laboratory, optics for the E.S.R.F. synchrotron prototype adaptive mirror and other beamlines, and the LASCO chronograph off-axis parabola.

The new properties of third-generation synchrotron radiation beams call for corresponding progress in instrumentation technology. This is particularly true for hard x-ray mirrors, for which new technologies have been implemented to meet outstanding requirements. The transfer of experience from other fields such as high-energy lasers and astronomy has been of major importance in the realization of new designs. The European Synchrotron Radiation Facility, the first third-generation hard x-ray source in Europe, has stimulated R&D programs of four European companies in the field of hard x-ray mirrors. This paper presents the major achievements of these companies.

The HIPPARCOS satellite, a project of the European Space Agency (ESA.), is devoted to very high accuracy astrometry for establishing a stellar catalog of 100 000 stars to an accuracy of about two milliarc-seconds. Optically the satellite consists in an all reflective SCHMIDT telescope of 29 cm aperture having the capability to image simultaneously two sky areas separated by a constant angle of 58 degrees called the Basic Angle. (A detailed desciption of this satellite and its requirements can be found in ref 1,2 and 3). The funtion of beam splitting is performed in the entrance pupil of the telescope by the BEAM COMLINER. This paper deals with the design of this mirror, the different steps of its fabrication and the procedure we used for the determination of its optical parameters.

A new ultra precision large optics grinding machine, BoX (R) , has been developed at Cranfield University. This machine is located at the UK's Ultra Precision Surfaces laboratory at the OpTIC Technium, North Wales. This machine offers a rapid and economic solution for grinding large off-axis aspherical and free-form optical components. This paper presents an analysis of surface and subsurface damage assessments of Zerodur(R) ground using diamond resin bonded grinding wheels. Zerodur(R) was tested as it is one of the materials currently under study for making extremely large telescope (ELT) segmented mirrors such as in the E-ELT project. The grinding experiments have been conducted on the BoX(R) grinding machine using wheels with grit sizes of 76 μm, 46 µm and 25 μm. The highest material removal rate (187.5 mm3/s) used ensures that a 1 metre diameter optic can be ground in less than 10 hours. The surface roughness and surface profile were measured using a Form Talysurf. The subsurface damage was revealed using a sub aperture polishing process in combination with an etching technique on small parts. These results are compared with the targeted form accuracy of 1 μm p-v over a 1 metre part, surface roughness of 50-150 nm RMS and subsurface damage in the range of 2-5 μm. This process stage was validated on a 1 metre hexagonal Zerodur(R) part.