The development of highly complex microlens arrays via the natural way and with remarkably simple components: Chemists of the University of Konstanz and the Max-Planck-Institute of Colloids and Interfaces have developed a process which highly simplifies the production of microlens arrays. Based on calcium carbonate (chalk), the researchers generate naturally grown surface layers with an ordered position of micrometer sized half spherical chalk lenses. So far, micro lens arrays could only be generated with a sophisticated lithographic process on basis of plastics
For the generation of the optically fully functional microlens arrays, the researchers exclusively need a saturated calcium solution, carbon dioxide from air and a broadly available surfactant (a soap molecule), which regulates the formation of the microlens structure. The process is by far more cost effective and simple than existing production methods. „It is remarkable that structure formation occurs by itself in water at room temperature – completely similar to the archetype Nature. This is an example for the successful application of biological principles for the generation of advanced optical elements completely without use of energy or toxic chemicals“, summarises Konstanz chemist Prof. Dr. Helmut Cölfen the advantages. The new process in which the micro lens arrays equally “grow” in a natural way was developed starting from a natural archetype: The so-called brittlestar, a relative of the starfish, uses a chalk microlens array on its skin to change colour according to the lighting conditions.
A microlens array is an optical field with a large number of micrometer sized miniature lenses placed closely together. Microlens arrays are applied for miniaturisation of optical systems, focussing of light with a precision of a millionth meter and to work with very small wavelengths. Amongst other applications, microlens arrays are applied for cell phone cameras but also in medical technology. The new process is also suitable to generate anti-reflex coatings, which are for example known from eyeglasses. Further advantages of the new method are that the chalk lens systems have shorter focal lengths compared to the so far exisiting plastic lens arrays and that the lens systems can be transferred to other surfaces by a simple dip coating. Furthermore, living cells like the microlens surface which enables future biomedical research combined with optics.
„It is truly remarkable how simple the generation of the microlens arrays is: All applied materials are common and biocompatible chemicals, energy supply is not necessary. The reaction takes place at room temperature in water according to a principle which Nature uses for Biominerals“, explains Helmut Cölfen. „Beside all these technical advantages, the amazing fact that such highly complex structures like a microlens array can be generated using comparatively simple molecules makes this process highly interesting for the scientist“, Cölfen outlines further perspectives for science.
The development of the new synthesis process was achieved in cooperation with the Korea Institute of Geoscience and Mineral Resources and the South Korean university KAIST.