R. Saathof, G. Schutten, J. Spronck, R. Munnig Schmidt:
"Actuation profiles to form Zernike shapes with a thermal active mirror";
Optics Letters, 40 (2015), 2; S. 205 - 209.

Kurzfassung englisch:
In EUV lithography, the absorption of EUV light causes wavefront distortion that deteriorates the imaging process.
An adaptive optics system has been developed ["Adaptive optics to counteract thermal aberrations," Ph.D. thesis
(TU Delft, 2013)] to correct for this distortion using an active mirror (AM). This AM is thermally actuated by absorbing
an irradiance profile exposed by a projector onto the AM. Due to thermal conductivity and bimorph-like deformation
of the AM, the relation between actuation profile and actuated shape is not trivial. Therefore, this Letter
describes how actuation profiles are obtained to generate Zernike shapes. These actuation profiles have been
obtained by a finite-element-based optimization procedure. Furthermore, these actuation profiles are exposed to
the AM, and the resulting deformations are measured. This Letter shows actuated Zernike shapes with purities
higher than 0.9 for most actuation profiles. In addition, superimposed actuation profiles resulted in superimposed
Zernike shapes, showing linearity needed to apply modal wavefront correction. Therefore, this approach can be
used to obtain actuation profiles for this AM concept, which can be used for highly precise wavefront

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