Within the diverse order of beetle species that produce color through structural coloration, some beetles produce light with a strong left-handed circular polarization caused by a chiral structure...Show moreWithin the diverse order of beetle species that produce color through structural coloration, some beetles produce light with a strong left-handed circular polarization caused by a chiral structure in their outer shells. From an evolutionary perspective, there should be no substan- tial benefit to left-handed over rather-handed polarization. This raises the question why no beetles have been found showing right-handed polarization. Large-scale beetle surveys are required to investigate this question further. A systematic beetle classification scheme based on polarization would aid in such a survey and highlight species with interesting optical prop- erties for further investigation. To this end we constructed a setup capable of measuring the Stokes parameters of a beetle specimen for angles of incidence and observation. We tested this setup on the beetle species protaetia speciosa jousselini and verified that the setup produces accurate results. We are however sceptical this method will result in identifying beetle-specific Stokes parameters, as their values vary with respect to both location on the beetle cuticle as well as observational angles. Furthermore we provide quantitative evidence for earlier re- ported inversion of the polarization handedness in beetle species jousselini at large angles of observation. We detect such inversion at angles of observation of at least 70◦.Show less
In this thesis we present two distinct interferometric set-ups for displacement measuring interferometry in cryogenic Low Energy Electron Microscopy (LEEM), specifically for use in ESCHER, the LEEM...Show moreIn this thesis we present two distinct interferometric set-ups for displacement measuring interferometry in cryogenic Low Energy Electron Microscopy (LEEM), specifically for use in ESCHER, the LEEM at Leiden University. The set-ups are based on: 1. circular polarization and 2. 3x3 fiber couplers to obtain a quadrature measurement. Whilst the 3x3 coupler based set-up is limited by thermal drift and other environmental effects, the circular polarization based method displays a 3\sigma resolution of 1.75 nm, and we provide a framework for further increasing this resolution, including a set of alternate set-ups with slight added complexity but a great potential gain in resolution. Keywords: Displacement, Interferometry, Fiber Couplers, Polarization, LEEM, cryogenic, DMI, Quadrature, Fiber.Show less
