Reduction of parasitic diffraction effects in reflective microscope objectives
Examensarbete för masterexamen
Wireless, photonics and space engineering (MPWPS), MSc
Imaging systems employing reflective elements for focusing light can be superior to traditional lens-based systems for use in broadband applications, or at wavelengths where lenses are unavailable. They are, however, hampered by stray intensity spikes caused by diffraction against the secondary mirror support structure. The use of curved vanes for reducing the intensity spikes present for conventional straight supports has previously been investigated[1, 2] but their implementation in short focal length systems, such as microscope objective lenses, has until now remained fairly unexplored. This thesis investigates the reduction of intensity spikes in 15X and 40X reflective Schwarzschild microscope objective lenses, where, among different support geometries, the use of curved vanes is further analysed. By simulating diffraction of various support designs it was found that a constant curvature structure, comprising three arms, each with a subtended arc angle of 70° minimised the intensity spikes whilst still performing well with regard to other image quality criteria. In addition, the use of non-constant curvature structures for compensation of Gaussian beams was shown beneficial using numerical methods. Practical implementation was carried out in the design of a 15X curved support structure Schwarzschild objective lens and was further experimentally tested and compared to a 15X Schwarzschild objective lens employing straight vanes. Results show a clear improvement in reduction of intensity spikes in favour of the curved vane structure. The measured data furthermore indicate a minor degradation with respect to other image quality criteria, in accordance with simulations.
Informations- och kommunikationsteknik , Materialvetenskap , Nanovetenskap och nanoteknik , Övrig elektroteknik, elektronik och fotonik , Information & Communication Technology , Materials Science , Nanoscience & Nanotechnology , Other electrical engineering, electronics and photonics