CAREER: Breaking the Freeform Optics Metrology Barrier with Synthetic Wavelength Interferometry

职业：利用合成波长干涉测量打破自由曲面计量障碍

• 批准号: 1851739
• 负责人: Jonathan Ellis
• 金额: $ 46.58万
• 依托单位: University of Arizona
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-09-30 至 2021-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1851739&HistoricalAwards=false
• 关键词: CAREER; Breaking; Freeform; Optics; Metrology

Freeform optics use complex surfaces that are not necessarily axisymmetric, potentially very complex, and have many applications. A continuing problem is the measurement (metrology) of such surfaces. Existing metrology solutions use interferometry, but suffer from fringe visibility issues and other errors, while touch systems such as coordinate measuring machines and profilometry have insufficient accuracy (i.e., micrometer scale as opposed to nanometer scale) and may damage the optical surface, especially for softer materials. The PI will execute a multi-faceted research program aimed at improving the metrology of freeform optics. Central to his approach is the combination of two light sources, each with a different wavelength, in order to evaluate the surface profile of the lens. This approach will lead to the measurement of high aspect ratio surfaces, where interference fringes would normally be spaced too close together to discern from each other. This is enhanced by the consideration of trace and retrace (going over the same path in opposite directions with the light source), and the differences between the two measurements. The approach uses mathematical models that will be used to extract the desired geometry. The result is a methodology that can be used in measuring free-form optics to a higher resolution than currently possible. One Broad Impact of this Faculty Early Career Development (CAREER) program research project is to empower optical designers and manufacturers with metrology methodologies that can measure advanced freeform optics. Freeform optics are the foundation for future vision-based technologies and lightweight, portable, unobtrusive mobile devices. Potential devices range from compact satellites for monitoring environmental changes to better optical sensors for autonomous vehicles. This research will have educational impact at the university level through mentoring research assistants, incorporating research in undergraduate student experiential learning, and outreach with high school students. The PI performs outreach via high school outreach, through workshops, and through extensive podcasting and blogging activities. This research will address this fundamental research question: Can synthetic wavelength interferometry (SWI) be used to produce new enabling capabilities in measuring freeform optics? The PI will examine (theoretically and experimentally) the impact of transmission sphere f-number and local slope departure on vignetting, in order to measure optics that normally have fringe ambiguity and retrace errors. This will be also investigated through the application of synthetic wavelength interferometry (SWI), where two light wavelengths are combined so that the phase difference can be examined and the limits to conventional interferometry can be identified and improved upon. The critical aspect of this technique is that the synthetic wavelength can be generated to resolve fringe ambiguities for lengths potentially much larger than the constitutive wavelengths. This is especially important for optics where the local slope departure is high. Fringe ambiguities arise from insufficient sampling of dense fringe patterns in interferometers, which create aliasing in the measurement. These ambiguities manifest from exceeding Nyquist sampling limits from high slope departure optical surfaces like steep aspheric and freeform optics. The investigations in this research will focus on two main aspects: dispersion effects from using synthetic wavelengths and retrace errors from steep slopes causing the returning light to pass through a different spatial location in the optical system. Both Fizeau and Twyman-Green interferometer configurations will be considered, as each system has a different placement of the reference surface and may cause different effects for both dispersion and retrace errors. The wavelength selection for the synthetic wavelength influences in both the non-ambiguity range and extending the Nyquist sampling limit. This, and the coupling with signal processing present potential contrasting criteria for utilizing synthetic wavelength interferometry for measuring freeform optics.

自由曲面光学使用复杂的表面，不一定是轴对称的，可能非常复杂，并且有许多应用。一个持续存在的问题是这些表面的测量（计量学）。现有的计量解决方案使用干涉测量法，但存在条纹可见性问题和其他误差，而触摸系统，如坐标测量机和轮廓测量法精度不足（即微米尺度与纳米尺度相反），并且可能损坏光学表面，特别是对于较软的材料。PI将执行一项多方面的研究计划，旨在改进自由曲面光学的计量学。他的方法的核心是结合两个光源，每个光源都有不同的波长，以评估透镜的表面轮廓。这种方法将导致测量高纵横比的表面，其中干涉条纹通常间距太近而无法相互辨别。考虑到跟踪和重跟踪（与光源在相反方向上走过相同的路径）以及两次测量之间的差异，这一点得到了增强。该方法使用数学模型来提取所需的几何形状。其结果是一种方法，可用于测量自由形式光学比目前可能的更高的分辨率。这个教师早期职业发展（Career）项目研究项目的一个广泛影响是为光学设计师和制造商提供可以测量先进自由曲面光学的计量方法。自由曲面光学是未来基于视觉的技术和轻便、便携、不显眼的移动设备的基础。潜在的设备包括用于监测环境变化的小型卫星，以及用于自动驾驶汽车的更好的光学传感器。本研究将透过指导研究助理、整合本科生体验式学习的研究，以及与高中生的外展，在大学层面产生教育影响。PI通过高中外展、研讨会以及广泛的播客和博客活动开展外展活动。这项研究将解决这个基本的研究问题：合成波长干涉测量（SWI）是否可以用于产生新的测量自由曲面光学的能力？PI将检查（理论和实验）透射球f数和局部斜率偏离对渐晕的影响，以测量通常有条纹模糊和回溯误差的光学器件。这也将通过合成波长干涉法（SWI）的应用进行研究，其中两个光波长相结合，以便可以检查相位差，并可以确定和改进传统干涉法的限制。该技术的关键方面是，合成波长可以产生，以解决长度可能比本质波长大得多的条纹模糊。这对于局部斜率偏差较大的光学器件尤其重要。条纹模糊产生于干涉仪中密集条纹图案采样不足，从而在测量中产生混叠。这些模糊性表现在高斜度离场光学表面（如陡坡非球面和自由曲面光学）超过奈奎斯特采样限制。本研究的研究将集中在两个主要方面：使用合成波长产生的色散效应和陡坡导致返回光通过光学系统中不同空间位置的回溯误差。菲索和特怀曼-格林干涉仪的配置都将被考虑，因为每个系统有不同的参考面位置，可能会对色散和回溯误差产生不同的影响。合成波长的波长选择既影响非模糊范围，又影响奈奎斯特采样极限的扩展。这一点，以及与信号处理的耦合，为利用合成波长干涉测量自由光学提供了潜在的对比标准。