RUI: Spatial light modulator technology for the on-demand fabrication of optical microstructures in polarization-sensitive materials

光学微结构是材料表面的变形，其尺度太小，肉眼无法看到，但可以有效地将光重新定向，从而使表面呈现彩色甚至自发光的外观。这样的结构是自然产生的，例如导致蝴蝶翅膀的鲜艳颜色。光学微结构的合成制造在信息存储和显示等领域已经产生了深远的技术影响，通常是基于将光敏薄膜暴露在灯或激光的规定照明图案下。虽然这项技术已经很成熟了，但它不适合快速成型。另一个限制是，一旦胶片处理完成，所制造的结构在胶片表面上是不能移动的。然而，人们发现一种新兴的材料类别，即高度有色的有机分子与柔性聚合物耦合，对照明方向敏感，而不是对其亮度敏感。这种对光偏振的敏感性可以被利用来制造动态的表面微结构，不仅能够实现永久的光学微结构，而且能够响应于光而重新配置结构。另外，最近出现的可编程空间光调制器使快速可重新配置的偏振光场的产生成为可能。这项拟议的研究将新型偏振敏感聚合物与空间光调制器技术相结合，创建了一种可按需制造静态和动态光学微结构的台式系统。这样的系统将使广泛的光学制造商能够获得光衍射表面的快速原型，同时也使依赖于使用微尺度表面来研究细胞响应的生物工程新技术成为可能。该项目还将使TCNJ的教育和培训受益，TCNJ主要是一所本科院校。该项目为理科本科生提供了一个获得综合经验的绝佳机会。本科生研究人员将成为一个多学科和国际研究项目的合作伙伴，该项目利用光子学和材料科学的新兴研究。光学微结构是通过将感光薄膜曝光到光学强度图案来制造的。传统的光敏薄膜响应光强，需要曝光后的化学处理，而新型的超分子偶氮聚合物薄膜响应光学偏振，表面微结构随着光照的响应而立即增长，不需要后续处理。为了更好地利用这些新的偏振敏感材料，需要一个可编程的光源，可以投射空间定义的线偏振光图案，例如空间光调制器。因此，拟议的研究将致力于开发一种基于超分子偶氮聚合物材料和数字偏振光学的新的微结构制造系统。这一发现的第一步是确定可用空间光调制器获得的光学表面结构的幅度、分辨率和表面形貌。采用多元校正光学元件后，分辨率有望达到500纳米数量级，表面幅度有望达到2微米。第二个目标是利用空间光调制器的光电扫描能力，利用多次曝光与适当确定的曝光时间和相移的叠加来傅里叶合成非正弦表面图案。此外，还将利用空间光调制器数字光学系统的动态可编程性来探索动态表面微结构。这种移动的表面结构只能在表现出可逆光机械响应的材料中诱导，如偶氮聚合物。通过对特征尺寸和结构的探索，将使用纳米压印光刻技术研究偶氮聚合物薄膜上光学表面微结构的复制。原子力和扫描电子显微镜将补充这一努力，并将用于评估复制保真度。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Optical microstructures are deformations of a material surface on a scale too small to be seen with the human eye, but which can efficiently redirect light so as to give the surface a colored or even self-illuminated appearance. Such structures occur naturally, and for example lead to the brilliant colors of a butterfly wing. Synthetic fabrication of optical microstructures has had far-reaching technological impact in fields such as information storage and display, and is typically based on exposing a photosensitive film to a prescribed illumination pattern from a lamp or laser. While this technique is well-established, it is not suited for rapid prototyping. A separate limitation is that the fabricated structures are immobile on the film surface once the film processing is complete. However, an emerging material class of highly colored organic molecule coupled with a flexible polymer have been found to be sensitive to the direction of illumination and not its brightness. This sensitivity to light polarization can be exploited to make dynamic surface microstructures, enabling not only permanent optical microstructures, but also structures which can be reconfigured in response to light. Separately, the recent emergence of programmable spatial light modulators makes possible the generation of rapidly reconfigurable polarized light fields. The proposed research combines new polarization-sensitive polymers with spatial light modulator technology to create a benchtop system for the on-demand fabrication of both static and dynamic optical microstructures. Such a system will make rapid prototyping of light-diffracting surfaces accessible to a wide range of optical manufacturers, while also enabling new techniques in bioengineering that rely on the use of microscale surfaces to study cellular response. The project will also benefit education and training at TCNJ that is a primarily undergraduate institution. The project offers an outstanding opportunity for undergraduate science students to gain integrative experience. Undergraduate researchers will become partners in a multidisciplinary and international research program that leverages emerging research in photonics and material sciences. Optical microstructures are fabricated by exposing photosensitive film to an optical intensity pattern. While conventional photosensitive films respond to optical intensity and require post-exposure chemical processing, new supramolecular azopolymer films respond to optical polarization, with the surface microstructure growing immediately in response to illumination, with no subsequent processing required. To best leverage these new polarization-sensitive materials requires a programmable source that can project spatially-defined patterns of linearly polarized light, such as a spatial light modulator. The proposed research will therefore pursue the development of a new microstructural fabrication system based on supramolecular azopolymer materials and digital polarization optics. The first step towards this discovery is to establish the amplitude, resolution, and surface topographies of optical surface structures obtainable with the spatial light modulator. Resolutions of order 500 nm and surface amplitudes of 2 µm are expected following the incorporation of multielement corrected optics. A second goal is to exploit the optoelectronic scanning capability of the spatial light modulator to Fourier synthesize nonsinusoidal surface patterns using the superposition of multiple exposures with appropriately determined exposure times and phase shifts. In addition, the dynamic programmability of the spatial light modulator-enabled digital optics system will be exploited to explore dynamic surface microstructures. Such moving surface structures can only be induced in materials such as azopolymers which exhibit a reversible photomechanical response. Throughout this exploration of feature sizes and structures, the replication of optical surface microstructures on azopolymer films will be studied using nanoimprint lithography. Atomic force and scanning electron microscopy will complement this effort and will be used to assess replication fidelity.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.