3D diffractive elements through fs-laser direct writing

衍射光学元件（DOEs）是将光塑造成几乎任意图案的强大工具。它们在先进的激光材料加工和成像应用中越来越多地使用，例如并行化，从而加快制造步骤。do通常是通过在玻璃毛坯表面蚀刻微米结构制成的。然而，众所周知，如果它们是三维的，也就是说，如果这些结构直接写在一块小玻璃板上，它们可能会更加强大和通用。这种3D do可以对颜色和光束入射角表现出极高的灵敏度，从而成为一类新的光学元件。例如，它们可以做得足够小，可以放在显微镜玻片上，同时又足够灵敏，仅凭它们反射的光就能区分相似的细胞类型。目前实现更高复杂性的3D do的限制是由于所需的大量计算成本以及缺乏足够快的制造策略，并且能够在毫米深度中写入亚微米尺寸的体素。我们的研究旨在朝着实现3D do迈出重要的一步。我们计划为它们的设计开发新的算法以及一种新的制造方法，这种方法易于满足制造任务所施加的高要求。我们的方法将基于平行飞秒激光直接写入（FLDW），其中通过短脉冲激光聚焦照射材料同时产生许多体素。在我们的项目过程中，我们将解决越来越困难和复杂的do的设计和生产。在随后的三个阶段，我们将设计和生产2D，多层和最后的3D do。

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.