Fraunhofer-Institut für Optronik, Systemtechnik und Bildauswertung IOSB

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  • Publication
    Sensitivity enhanced roll-angle sensor by means of a quarter-waveplate
    ( 2021)
    Chen, Chia-Wei
    ;
    Hartrumpf, Matthias
    ;
    Längle, Thomas
    ;
    Beyerer, Jürgen
    Attitude metrology (roll, pitch, and yaw) playsan important role in many different fields. Roll angle is con-sidered the most difficult measurement quantity in angulardisplacements compared to pitch and yaw angles becausethe rotation axis of the roll angle is parallel to the probebeam. In this work, a sensitivity enhanced roll-angle sensor is presented. The principle is based on the polarizationchange of a sensing unit (quarter-waveplate). The polarization model is analyzed by Mueller matrix formalism. TheStokes parameters are detected by a Stokes polarimeter.The novel coaxial design improves the sensitivity and reduce the complexity of optical system alignment by meansof a fixed quarter-waveplate. The proposed sensor providesa simple setup to measure roll angles with a high sensitivity of 0.006∘ and a long unambiguous measurement range of 180∘.
  • Publication
    Ellipsometric inline inspection of dielectric substrates with nonplanar surfaces
    ( 2020)
    Hartrumpf, Matthias
    ;
    Chen, Chia-Wei
    ;
    Längle, Thomas
    ;
    Beyerer, Jürgen
    An analytical solution for the determination of either angle of incidence (AOI) and the refractive index from combined ellipsometric and reflectometric measurements at dielectric substrates is presented. The solution is of special importance for retroreflex ellipsometry (but not limited to this application). Overcoming the geometric restrictions of conventional ellipsometers, the patented retroreflex ellipsometry can detect changes of intensity and the state of polarization in or at test objects even with curved surfaces. In contrast to conventional ellipsometers where the AOI is set by the adjustment procedure, the AOI is usually unknown in retroreflex ellipsometry. For quantitative analysis, the knowledge of the AOI is nevertheless essential. The proposed combination of retroreflex-reflectometry and retroreflex-ellipsometry opens the path to precise measurements of either surface geometry and index of refraction of nonplanar dielectric substrates (e. g. surfaces of freeform optics).
  • Publication
    Measurement of ellipsometric data and surface orientations by modulated circular polarized light
    ( 2019)
    Chen, Chia-Wei
    ;
    Hartrumpf, Matthias
    ;
    Längle, Thomas
    ;
    Beyerer, Jürgen
    Ellipsometry is a widely used optical method for the characterization of materials and thin films. However, only flat or nearly flat surfaces can be measured since small deviations of the angle of incidence might lead to significant experimental errors. In order to overcome the geometrical limitations of ellipsometry, the retroreflex ellipsometry developed at Fraunhofer IOSB is used. Based on this configuration, a new illumination method is proposed. When the sample is illuminated by modulated circular polarized light (LCP and RCP), the ellipsometric parameters (PS, D) and the tilted angle (F) can be determined directly. Combined with reflectance measurement or prior knowledge of optical properties of samples, the surface orientation can be obtained.