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Applying aspherical and freeform optics in high-end optical systems can improve system performance while decreasing the system mass, size and number of required components. The NANOMEFOS measurement machine is capable of universal non-contact and fast measurement of aspherical and freeform optics up to Ø500 mm, with an uncertainty of 30 nm (2σ). In this machine, the surface is placed on a continuously rotating air bearing spindle, while a specially developed optical probe is positioned over it by a motion system. A separate metrology system measures the probe and product position relative to a metrology frame. The prototype realization, including custom electronics and software, has been completed. The noise level at standstill is 0.88 nm rms. A reference flat was measured with 13 μm and 0.73 mm tilt. Both measurements show an rms flatness of about 8 nm rms, which correspond to the NMi measurement. A hemisphere has also been measured up to 50° slope, and placed 0.2 mm eccentric on the spindle. These measurements reproduce to about 5 nm rms. Calibration and software are currently being improved and the machine is applied in TNO aspherical and freeform optics production. © 2009 SPIE.

A freeform optical surface is typically defined as any surface that does not have an axis of rotational symmetry. These surfaces provide additional degrees of freedom that can lead to improved performance compared to systems that make use solely of conventional optics. The benefits of using freeforms are: • Less optics can be used in the opto-mechanical system and therefore a decrease in the amount of optical surfaces occurs. Since every surface is a reduction of light intensity (e.g. by scattering), a higher throughput of the optical system is the result. • Less optics also means a reduction in mass and size • An improvement in optical quality (e.g. spherical aberration, coma, distortion) • A more favourable position of the optical components is possible. Generally, these freeform surfaces are more difficult to manufacture, and therefore more expensive both in cost and in development time. Furthermore, there is a danger with the application of exotic freeforms that have a large number of parameters, and consequently, degrees of freedom. For the latter reason they may naively seem attractive from the point of view of an optical designer, providing many knobs to optimize the performance; however, the overwhelming number of parameters may also cause a hotchpotch of local optima in merit function landscape. Many of those will not lead to an improved design because e.g. the particular freeform representation does not provide the correct handles, or the location in the optical train is unsuitably chosen. Another difficulty in the application of freeforms is the complexity of describing and evaluating the surface form tolerances of non-symmetric surfaces. Yet another difficulty is the following. An appropriate conventional design can often be obtained as an optimization from a paraxial system that can be defined analytically. For instance, both the telecentric beam expander and the push broom telescope that will be described in more detail below, can be derived from standard optical rules. Then, the paraxial design is a good starting point for an optimization algorithm as is used in optical design software in the hunt for an optimum design. In contrast, for a design that includes nonsymmetric optics, the parameters that provide the departure from symmetry are not so easily obtained with an analytically determined first guess. This makes it difficult to coax the optimizer into the right direction. Thus, with the benefits of using freeforms come disadvantages: • Difficult to determine the optimal freeform representation and location in the optical train • Optical tolerance analyses are not yet common practice in optical design packages • Difficult to manufacture with classical production technologies • Difficult to validate the surface shape • More difficult to align, because of the increased degrees of freedom • For all of the reasons above: more expensive Consequently, optical designers sometimes are hesitant to apply free form surfaces in an optical design difficult as they are to handle both from design and manufacturability of point of view.

The NANOMEFOS machine is capable of fast, non-contact and universal measurement of aspheres and freeforms, up to ø500 mm with a measurement uncertainty below 30 nm (2σ). It is now being applied in asphere and freeform production at TNO.

This paper shows the machine concept, the realization and the test results of the completed NANOMEFOS non-contact measurement machine for freeform optics. The separate short metrology loop results in a stability at standstill of 0.9 nm rms over 0.1 s. Measurements of a tilted flat show a repeatability of 2-4 nm rms, depending on the applied tilt, and a flatness that agrees well with the NMi measurement.

We present a novel optical design tool that makes use of an evolutionary global optimization algorithm. The algorithm has several characteristics that make it well-suited for freeform optics design. With the design tool it is no longer necessary to make the distinction between paraxial degrees of freedom and degrees of freedom related to freeform surface description. The design process, which typically involves a multi-stage scheme consisting of finding an optimal paraxial starting layout, optimization, gradually including freeform degrees of freedom to yield an optimal nominal design, and finally a step in which the as-built design is optimized, is shortened because optimal paraxial starting point and optimal freeform shapes are combined to a single optimization step. Optionally, as-built performance can be included in this step as well. The design tool is applied to the design of a compact spectrometer.

The breakthrough of freeform optics is limited by manufacturing and metrology technology. However, today's manufacturing machines like polishing robots and diamond turning machines are accurate enough to produce good surface quality, so the question is how accurate can a freeform be produced. To investigate how accurate freeform optics can be diamond turned, measurable freeforms (e.g. an "off-axis" sphere) were diamond turned and they were compared to there on-axis equivalents. The results of this study are described in this paper. Furthermore, an overview of the accuracies of freeform optics that TNO diamond turned are presented. An indication of freeform accuracy for diamond turned optics is derived from this, which can be used for optical designers as a guideline in their design work. © 2009 SPIE.

Aspherical and freeform optics are applied to reduce geometrical aberrations as well as to reduce the required number of components, the size and the weight of the system. To measure these optical components with nanometre level uncertainty is a challenge. The NANOMEFOS machine was developed to provide suitable metrology (high accuracy, universal, non-contact, large measurement volume and short measurement time) for use during manufacturing of these surfaces. This paper describes the design, realization and testing of this machine. In particular it describes the design and testing of the air-bearing motion system with parallel stage configuration, and the separate metrology system with Silicon Carbide metrology frame and an interferometry system for direct displacement measurement of the optical probe. Preliminary validation measurements demonstrate the nanometer level repeatability for freeform surface measurement. © 2011 Elsevier Inc.

Aspherical and freeform optical elements have a large potential in reducing optical aberrations and to reduce the number of elements in complex high performance optical systems. However, manufacturing a single piece or a small series of aspherical and freeform optics has for long been limited by the lack of flexible metrology tools. With the cooperative development of the NANOMEFOS metrology tool by TNO, TU/e and VSL, we are able to measure the form of aspheres and freeforms up to 500 mm in diameter with an accuracy better than 10 nm rms. This development opened the possibility to exploit a number of iterative, corrective manufacturing chains in which manufacturing technologies such as Single Point Diamond Turning, freeform grinding, deterministic polishing and classical polishing are combined in an iterative loop with metrology tools to measure form deviation (like CMM, LVDT contact measurement, interferometry and NANOMEFOS). This paper discusses the potentials, limitations and differences of iterative manufacturing chains used by TNO in the manufacturing of high performance optics for astronomical purposes such as the manufacturing of the L2 of the Optical Tube Assembly of the four laser-guide star facility of the ESO VLT, Manufacturing of Aluminum freeform mirrors for the SCUBA-2 instrument. Based on these results we will give an outlook into the new challenges and solutions in manufacturing high-precision optics. © 2012 SPIE.

Aspherical and freeform optical elements have a large potential in reducing optical aberrations and to reduce the number of elements in complex high performance optical systems. However, manufacturing a single piece or a small series of aspherical and freeform optics has for long been limited by the lack of flexible metrology tools. With the cooperative development of the NANOMEFOS metrology tool by TNO, TU/e and VSL, we are able to measure the form of aspheres and freeforms up to 500 mm in diameter with an accuracy better than 10 nm rms. This development opened the possibility to exploit a number of iterative, corrective manufacturing chains in which manufacturing technologies such as Single Point Diamond Turning, freeform grinding, deterministic polishing and classical polishing are combined in an iterative loop with metrology tools to measure form deviation (like CMM, LVDT contact measurement, interferometry and NANOMEFOS). This paper discusses the potentials, limitations and differences of iterative manufacturing chains used by TNO in the manufacturing of high performance optics for astronomical purposes such as the manufacturing of the L2 of the Optical Tube Assembly of the four laser-guide star facility of the ESO VLT, Manufacturing of Aluminum freeform mirrors for the SCUBA-2 instrument. Based on these results we will give an outlook into the new challenges and solutions in manufacturing high-precision optics. © 2012 SPIE.

The development of additive manufacturing is progressing rapidly. One of the main advances in the progression of this technology is 3D printing of metals. To enhance this trend, TNO's additive manufacturing department in Eindhoven, The Netherlands, is devel-oping "Hyproline", a "High Performance Production Line for Smalt Series Metal Parts" which consists of an integrated production line that incorporates printers and modules for finishing small metal products in various designs.

De ontwikkelingen op het gebied van additive manufacturing gaan hard. Een van de belangrijkste stappen van dit moment is het 3d-printen van metalen. Om deze ontwikkeling dichterbij te halen, bouwt TNO nu aan de Hyproline, een productieprinter waarmee kleine metalen producten in honderd varianten tegelijk kunnen worden nabewerkt. Om een vrije en flexibele keuze van software en communicatieprotocollen te kunnen maken, is de Hyproline uitgerust met meerdere besturingen van Beckhoff.

The need for personalised and smart products drives the development of structural electronics with mass-customisation capability. A number of challenges need to be overcome in order to address the potential of complete free form manufacturing of electronic devices. One key challenge is the integration of conductive structures and components into 3D printed devices by combining different materials and printing techniques that have nearly incompatible printing conditions. In this paper, several methods to integrate electronic circuits and components into a 3D printed structure are discussed. The functional performance of the resulting structures is described. Structural parts were manufactured with a stereolithography-based 3D printing technique, which was interrupted to pick and place electronic components, followed by either direct writing or squeegee filling of conductive material. A thermal curing step was applied to enhance the bonding and improve the electrical performance. Optical micrography, 4-point resistance measurement and cross-sectional analysis were performed to evaluate functionality.

TNO is developing the Basic Angle Monitoring Opto-Mechanical Assembly for the GAIA mission of ESA, a space telescope that will create a map of the universe including distant stars and planets. GAIA is being built by EADS Astrium and scheduled for launch in 2011. Due to its stability and hardness properties, Silicon Carbide has been chosen for the structure, payload mirrors and most components of GAIA. The Basic Angle Monitoring subsystem was developed by TNO and is a metrology system for monitoring the angle between the two GAIA telescopes. With the Basic Angle Monitoring an Optical Path Difference as small as 1.5 picometers RMS can be measured. During the design phase of the Basic Angle Monitoring subsystem, TNO also developed solutions for ultra stable mounting of non-Silicon Carbide optical components. These components have to withstand launch with preservation of the alignment and retain optical properties from ambient to 100 K in vacuum. The manufacturing of off-axis Silicon Carbide mirrors of the Basic Angle Monitoring down to nm-level represented another challenge. A comprehensive program was conducted on SiC manufacturing of freeform optics. Status: the Basic Angle Monitoring has past the Critical Design Review.

This article presents developments of freeform mechatronics concepts, enabled by industrial Additive Manufacturing (AM), aiming at breakthroughs for precision engineering challenges such as lightweight, advanced thermal control, and integrated design. To assess potential impact in future applications, representative cases have been considered. First results are briefly described, which are already convincing and encouraging.

The impact of NO2 and other atmospheric trace gases on health and the environment is now acknowledged by governments around the world. The sources, both natural and anthropogenic, have been shown to affect the quality of life due to low air quality in densely populated areas. Consequently, the need for accurate global NO2 measurements with high spatial- A nd temporal resolution to monitor NO2 is becoming ever more important. Through an ESA study, TNO and KNMI have been evaluating measurement requirements and an instrument design for a Compact NO2 Spectrometer', based on a hyperspectral imaging instrument operating in the VIS (405-490nm] spectral range and aimed at combining the performance of state-of-the-art instruments with fine spatial sampling (0.5x0.5 km2). By use of a novel free-form optics a very compact low volume and low mass design has been achieved. Combining this with other small satellite design approaches for components the aim is to create a low cost instrument capable of being flown on a wide variety of space platforms. Global daily coverage can then be achieved with a relatively small constellation of instruments. The key design features are described for a 'Compact NO2 Spectrometer', such as the optical design approach, the use of free-form optics, an thermal' all aluminium approach. An overview of the development and airborne results from a breadboard of a small prototype system (Spectrolite) developed by TNO which uses many of the design features envisaged for this new instrument is given.

Driven by technology developments triggering end user’s attention, the market for nano-and micro satellites is developing rapidly. At present there is a strong focus on 2D imaging of the Earth’s surface, with limited possibilities to obtain high resolution spectral information. More demanding applications, such as monitoring trace gases, aerosols or water quality still require advanced imaging instruments, which tend to be large, heavy and expensive. In recent years TNO has investigated and developed several innovative concepts to realize advanced spectrometers for space applications in a more compact and cost-effective manner. This offers multiple advantages: a compact instrument can be flown on a much smaller platform (nano-or microsatellite); a low-cost instrument opens up the possibility to fly multiple instruments in a satellite constellation, improving both global coverage and temporal sampling; a constellation of low-cost instruments can provide added value to the larger scientific and operational satellite missions. Application of new technologies allowed us to reduce the instrument size significantly, while keeping the performance at a sufficient level. Low-cost instruments may allow to break through the ‘cost spiral’: lower cost will allow to take more development risk and thus progress more quickly. This may lead to a much faster development cycle than customary for current Earth Observation instruments. This new development approach is demonstrated using the most advanced design of a hyperspectral imaging spectrometer (named ‘Spectrolite’) as an example. Several different novel design and manufacturing techniques were used to realize this compact and low-cost design. Laboratory tests as well as the first preliminary results of airborne measurements with the Spectrolite bread board will be presented. The design of Spectrolite offers the flexibility to tune its performance(spectralrange, spectral resolution) to a specific application. Thus, based on the same basic system design, Spectrolite offers a range of applications to different clients. To illustrate this, we present a mission concept to monitor NO2 concentrations over urban areas at high spatial resolution, based on a constellation of small satellites.