Optical Studies of Materials for Spectral Design

Optical material properties have been studied in a wide wavelength range. The aim is future use of spectral design for camouflage. The main characterization techniques used in this work are Reflection Spectroscopy, Scatterometry (BRDF) and Mueller Matrix Ellipsometry. Six camouflage evaluation criteria based on reflection, emissivity, polarization, gloss, dynamic coloring and broad band properties, are more or less related to the interaction between light and materia. Almost all are connected to the work of this thesis and are exemplified through different material categories with potential for use in camouflage applications. The included papers presents: a broad band (visible-infrared-microwave) study, two examples of dynamic optical properties of thin films, and polarization and scattering properties of a natural surface. Preface This thesis is a part of my PhD studies at Laboratory of Applied Optics, Department of Physics, Chemistry and Biology (IFM), Linköping University, where I am enrolled as a part-time student within the work as a scientist at FOI (Swedish Defence Research Agency). As a PhD student I have been enrolled in the research schools Forum Securitatis and Agora Materiae at Linköpings University. My topic is on camouflage related materials issues and some results from the years past are collected here. The theme is wide, the electromagnetic range covered is broad, and when you scratch on the surface it may seem shallow. But remember that, as in the rest of the world, it is almost only the surface that matters... The word camouflage has been used since late 19-th century. It is thought to originate from the French word camoufler (to disguise) via a combination of the Italian camuffare and a French wording for the practical joke to "whiff smoke in the face"camouflet. And that is what it is about, to mock with colors to look alike, to confound with structures and reflections to not be looked at, but hide. In the ancient game hide and seek, for children a fun game, but all sincere war fighters know the ability to hide it is often the difference between life and death. Today there is a challenging duel between the development of the camouflage materials (signature management technology) on the hiding side, and sensors of different kinds and combinations, threatening with detection, revealing and identification, on the seekers side. With emerging sensor technology, the hiding becomes trickier while the seekers always seem to be one step ahead. Despite the advances in technical development of sensors there are still limitations giving hope for camouflage management. However, to not be defeated, a vast improvement of camouflage materials and signature technology is needed. Will the real "game" develop to an almost fictive reality where the urge towards invisibility as the ultimate camouflage, only seen its alike in tales and in the recent science fiction and fantasy movies expressed through examples as the invisible car of James Bond and the invisibility cloak of Harry Potter? Future will tell! 1 Die Another Day (2002), directed by Lee Tamahori. 2 Harry Potter and the Philosopher's Stone is the first of the book of seven written by J.K. Rowling.