Measurement of Aspheres and Freeform Surfaces

The use of aspheric and freeform surfaces becomes more and more important in the design of modern optical systems.

The use of aspheric and freeform surfaces becomes more and more important in the design of modern optical systems. These surfaces offer additional degrees of freedom to the optical design, allowing to improve the optical imaging as well as to reduce the number of surfaces needed for an optical design. However the fabrication and testing of such surfaces is still a difficult task. At the ITO we developed and patented the so called Tilted Wave Interferometer [1-7] (TWI) which makes it possible to measure these kinds of surfaces. The TWI is a non-null, full-field interferometric measuring technique for aspheric and free-form surfaces with a new degree of flexibility. The interferometer uses a set of tilted wavefronts to locally compensate the deviation of the surface under test from its spherical form. Since it is a non-null technique, there is no need for costly compensation optics. The measurement data acquisition is highly parallelized, leading to a short measurement time in the region of few seconds, by simultaneously achieving a high lateral resolution. The unique combination of these characteristics makes the TWI a perfect candidate for the integration into the process chain of aspheric and free-form surface manufacturing.

Current Projects: Tilted Wave Interferometer


  1. E. Garbusi, C. Pruss, and W. Osten, “Interferometer for precise and flexible asphere testing”, Optical Letters, Dec. 15, 2008 / Vol. 33, No. 24
  2. J. Liesener, E. Garbusi, C. Pruss, and W. Osten, “Verfahren und Messvorrichtung zur Vermessung einer optisch glatten Oberflaeche,” Deutsches Patent und Markenamt, 10 2006 057 606.3 (2006)
  3. E. Garbusi and W. Osten, “Perturbation methods in optics: application to the interferometric measurement of surfaces,” J. Opt. Soc. Am. A 26, 2538–2549 (2009)
  4. G. Baer, J. Schindler, C. Pruss, J. Siepmann and W. Osten. “Calibration of a non-null test interferometer for the measurement of aspheres and free-form surfaces” Optics Express, Vol. 22, Issue 25, pp. 31200-31211 (2014)
  5. G. Baer, J. Schindler, J. Siepmann, C. Pruss, W. Osten, and M. Schulz, “Measurement of aspheres and free-form surfaces in a non-null test interferometer: reconstruction of high-frequency errors,” Proc. SPIE 8788, 878818 (2013).
  6. G. Baer, G. Garbusi, E. Lyda, W. and Osten, W. 2010 “Automated surface positioning for a non-null test interferometer” OE 49(9), 095602
  7. G. Baer, J. Schindler, C. Pruss, and W. Osten. 2013. “Correction of misalignment introduced aberration in non-null test measurements of free-form surfaces” JEOS Vol 8 130874
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