Activity: Talk or presentation › Oral presentation
Multilayer mirrors (MLM) are key components of optics in the soft x-ray and extreme ultraviolet (XUV) wavelength range, and are being used for microscopy, space telescopes, materials analysis, lithography and spectroscopy. Despite the high reflection, the absorbed fraction of the light could lead to surface deformations and aberrations in the reflected wavefronts. Adaptive XUV mirrors are needed to mitigate such aberrations and improve the resolving power. In this work, we show results on the development of adaptive MLMs based on piezoelectric thin films. We demonstrate a piezoelectric actuator stack and show that wavelength-scale, gradual surface profile corrections can be achieved. In all piezoelectric materials, both ceramics and thin films, hysteresis is a key point determining the actuation accuracy. However, the understanding in epitaxial thin films is rather limited. We investigated the hysteresis and nonlinearity of strain and polarization at sub-coercive electric fields for a rhombohedral epitaxial Pb(Zr0.52Ti0.48)O3 thin film. We observe a linear hysteresis behavior for the strain and a nonlinear hysteresis behavior for the polarization. In contrast to ceramics or sol gel thin films, the observed behavior cannot be explained by the commonly referred Rayleigh-model. We present a new model by taking into account the change of the rhombohedral unit cell due to the rotation of the polarization vector to explain the observed scaling of hysteresis and nonlinearity with the applied field.