Glassy cholesteric broadband reflectors with a pitch gradient: Material design, optical properties and microstructure

The cholesteric liquid crystal (CLC) phase may selectively reflect light. T he reflection wavelength is correlated with the CLC helical pitch and the w avelength bandwidth Delta lambda with the birefringence. Recent studies hav e aimed to broaden Delta lambda from several tens - an order of magnitude u sually encountered in literature - to several hundreds of nanometers. The l atter case would especially be relevant for specific applications such as f ull-colors displays. Our pur pose is to present a novel experimental proces s to design a CLC with a pitch gradient reflecting light on more than 300 n m. As a novelty, this broadband reflector is a glassy solid. The spectral b ehaviour is analyzed in parallel to the reflector microstructure which is i nvestigated by transmission electron microscopy for the first time.