By applying aspherical and freeform optics in optical systems, the optical quality can be improved, while reducing dimensions, mass and number of required components. The NANOMEFOS measurement machine, developed by TNO, TU/e and VSL, is a unique measurement instrument for measuring the absolute form of aspherical and freeform optical surfaces (mirrors as well as lenses).
Applying aspherical and freeform optics has many advantages for high-end optical systems in for instance space, astronomy and lithography applications. TNO is working on technology development for designing, fabricating and measuring of these surfaces. In combination with diamond turning and corrective polishing, this machine enables TNO to fabricate complex and large optical surfaces with nanometer level accuracy. These surfaces are produced for internal projects as well as for external customers. Measurements of customers' surfaces are also performed.
Properties of this machine are:
The surface to be measured is placed on a continuously rotating air bearing spindle, while a specially developed optical probe is scanned over it. The optical probe allows for high scanning speeds (up to 1.5 m/s) and the departure from rotation symmetry of the surface is within the large measurement range of 5 mm of the probe. The height profile is measured using circular tracks or a continuous spiral. The position of the probe is measured with an interferometry system relative to a Silicon Carbide metrology frame. Capacitive probes measure the error motion of the spindle, also relative to the metrology frame. With this short metrology loop, the dataprocessing can compensate for static as well as dynamic positioning errors, which allows for a measurement repeatability of single nanometers rms.
NANOMEFOS is fully calibrated and operational. Aspherical and freeform surfaces are measured using custom software, where all measurement parameters can be optimized for the surface to be measured. Results are presented grafically (3D), in line-scans and in Zerniky polynomials. Data can be exported in various formats and an extensive measurement report can be made. Due to the universal nature of the machine, this requires little preparation and measurements can be done very quickly.