3D diffractive elements through fs-laser direct writing

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Diffractive optical elements (DOEs) are powerful tools for shaping light into almost arbitrary patterns. They find increasing use in advanced laser material processing and imaging applications, for instance to parallelize and thus accelerate fabrication steps.DOEs are commonly made by etching micro-meter structures into the surface of a glass blank. However, it is known that they could be even more powerful and versatile if they were three-dimensional, i.e., if the structures were directly written into the bulk of a small glass slab. Such 3D DOEs could exhibit exquisite sensitivity to color and beam incidence angle, thus enabling a new class of optical elements. For instance, they could be made small enough to fit onto a microscopy glass slide and at the same time sufficiently sensitive to differentiate closely resembling cell types, solely from the light they reflect.Current limitations of realizing 3D DOEs of higher complexity are given by the required large computational costs as well as the lack of fabrication strategies that are sufficiently fast and capable of writing sub-micron sized voxels in millimetre depths. Our research aims to take significant steps towards the realization of 3D DOEs. We plan to develop new algorithms for their design as well as a novel fabrication approach which is apt to fulfil the high demands imposed by the fabrication task. Our approach will be based on parallel femtosecond-laser direct writing (FLDW), where many voxels are simultaneously produced by irradiating the material with short-pulsed laser foci. In the course of our project, we will address the design and production of DOEs with increasing difficulty and complexity. In three subsequent stages we will design and produce 2D, multilayer and finally 3D DOEs.