NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenIPH Teisnach
R. Schachtschneider, I. Fortmeier, M. Stavridis, J. Asfour, G. Berger, R. Bergmann, A. Beutler, T. Blümel, H. Klawitter, K. Kubo, Johannes Liebl, F. Löffler, R. Meeß, C. Pruss, D. Ramm, M. Sandner, G. Schneider, M. Wendel, I. Widdershoven, M. Schulz, C. Elster
Interlaboratory comparison measurements of aspheres
Measurement Science and Technology, vol. 29, no. 5
The need for high-quality aspheres is rapidly growing, necessitating increased accuracy in their measurement. A reliable uncertainty assessment of asphere form measurement techniques is difficult due to their complexity. In order to explore the accuracy of current asphere form measurement techniques, an interlaboratory comparison was carried out in which four aspheres were measured by eight laboratories using tactile measurements, optical point measurements, and optical areal measurements. Altogether, 12 different devices were employed. The measurement results were analysed after subtracting the design topography and subsequently a best-fit sphere from the measurements. The surface reduced in this way was compared to a reference topography that was obtained by taking the pointwise median across the ensemble of reduced topographies on a $1000 \times 1000$ Cartesian grid. The deviations of the reduced topographies from the reference topography were analysed in terms of several characteristics including peak-to-valley and root-mean-square deviations. Root-mean-square deviations of the reduced topographies from the reference topographies were found to be on the order of some tens of nanometres up to 89 nm, with most of the deviations being smaller than 20 nm. Our results give an indication of the accuracy that can currently be expected in form measurements of aspheres.
Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen
G. Bergmann, P. Jackson, J.H.C. Hogg, Thomas Stirner, M. O’Neill, W. Duffy, S. Kelly, G. Clark
Photoinduced changes of surface order in coumarin side-chain polymer films used for liquid crystal photoalignment
Applied Physics Letters, vol. 87
Specular x-rayreflectivity probes morphological changes in a crosslinkable coumarin photoalignment polymer film resulting from ultraviolet irradiation. An ordered surface layer with density oscillations compatible with planar side-chain alignment is obtained before irradiation. The ordering is enhanced in the early stages of crosslinking. This is attributed to the photoinduced increase of mobility of the side-chains resulting from the creation of free volume by the crosslinking process. The expansion of the thin film confirms that free volume is created. The surface ordering decreases with prolonged ultraviolet irradiation because of increased material viscosity resulting from a high crosslinked density. The implications of surface ordering on liquid crystal photoalignment are discussed.