Novel Aerogel-Filled Diffractive Optical Elements

该小型企业创新研究第一阶段项目描述了如何通过填充气凝胶（一种非常细的石英泡沫）来保护光学衍射元件中微观表面浮雕图案的凹槽，从而保护凹槽免受灰尘和油脂的影响，从而提高各种类型光学衍射元件的实用性，使其免受光学性能严重下降的影响。在相干光学的应用中，光学衍射元件的应用正在迅速扩展，甚至在某些非激光器件中也很重要。该项目结合了两种最新的材料技术，并将其应用于两个重要的国家需求，其中一个是通过创新的窗户设计来节省建筑物的能源，另一个是开发用于激光设备的新型光学设备。用于窗户的衍射结构（当最终工业上制造成大片时）将被放置成与窗户的上部接触。从东南、南或西南方向入射到建筑物上的阳光被高效地衍射到天花板上，并从那里向下照射到黑暗的角落，这就是所谓的“采光”。气凝胶的作用是填充精细的衍射槽，从而保护它们免受处理和灰尘积聚的损害。平坦的气凝胶膜将进一步改善热绝缘，并且还可以用作热（红外）反射层的沉积的基底。在这种情况下，该结构将联合收割机结合采光功能（入射光的重定向）与阻挡热射线（低辐射玻璃），并隔热。气凝胶是与衍射塑料联合收割机组合的最佳材料，原因有很多：1）其折射率非常接近空气的折射率，这对于在宽入射角范围内保持高效率至关重要，这将在后面详细说明。2)气凝胶在光学上是相当透明的，特别是在薄层中。3)气凝胶是轻质的，并且最近已经沉积成微米厚的膜。4)气凝胶中的空气使其具有非常优异的隔热性能。

This Small Business Innovation Research Phase I project describes how one can protect the grooves of the microscopic surface relief pattern in optical diffractive elements by filling them with aerogel, a very fine quartz foam, which protects the grooves against dust and grease and thereby improves the usefulness of various types of these optical diffractive elements by saving them from severely degraded optical performance. In applications of coherent optics, the use of optical diffractive elements is spreading rapidly and they are even important in certain non laser devices. This project combines two recent material technologies and applies them to two important national needs, one of which is energy savings in buildings through innovative window designs, the other is to develop novel optical devices to be used in laser devices. The diffractive structures for windows (when eventually manufactured industrially in large sheets) would be placed in contact with the upper part of a window. Sunlight incident from the southeast, south, or southwest on the structure is diffracted with high efficiency towards the ceiling and from there shines downwards into dark corners, so called `daylighting.` The role of the aerogel is to fill the delicate diffractive grooves and thus protect them against damage from handling and against dust accumulation. The flat aerogel film would further improve thermal insulation and could also serve as a substrate for deposition of heat (infrared) reflecting layers. In that case, the structure would combine the function of daylighting (redirecting of incident light) with keeping out heat rays (low-E glazing) and be thermally insulating. Aerogel is the optimal material to combine with the diffractive plastic for various reasons: 1) Its refractive index is very close to that of air, which is essential in maintaining large efficiency over a wide range of incident angles as will be elaborated on later. 2) Aerogel is optically quite transparent, particularly in a thin layer. 3) Aerogel is lightweight and has recently been deposited in micron thick films. 4) The trapped air gives aerogel very excellent thermal insulating properties.