Agour Mostafa, Fallorf Claas, Bergmann Ralf B
Opt Express. 2021 Jan 4;29(1):385-399. doi: 10.1364/OE.413182.
We present a fast shape measurement of micro-parts based on depth discrimination in imaging with LED illumination. It is based on a 4f-setup with an electrically adjusted tunable lens at the common Fourier plane. Using such a configuration, the opportunity to implement a fast depth scan by means of a tunable lens without the requirement of mechanically moving parts and depth discrimination using the limited spatial coherence of LED illumination is investigated. The technique allows the use of limited spatially partially coherent illumination which can be easily adapted to the test object by selecting the geometrical parameters of the system accordingly. Using this approach, we demonstrate the approach by measuring the 3D form of a tilted optically rough surface and a cold-formed micro-cup. The approach is robust, fast since required images are captured in less than a second, and eye-safe and offers an extended depth of focus in the range of few millimetres. Using a step height standard, we determine a height error of ±1.75 μm (1σ). This value may be further decreased by lowering the spatial coherence length of the illumination or by increasing the numerical aperture of the imaging system.
我们提出了一种基于LED照明成像中的深度辨别来对微零件进行快速形状测量的方法。它基于一种4f设置，在公共傅里叶平面处有一个电调谐的可调透镜。利用这种配置，研究了通过可调透镜实现快速深度扫描而无需机械移动部件的可能性，以及利用LED照明的有限空间相干性进行深度辨别的可能性。该技术允许使用有限的空间部分相干照明，通过相应地选择系统的几何参数，可以很容易地使其适应测试对象。使用这种方法，我们通过测量倾斜的光学粗糙表面和冷成型微杯的三维形状来演示该方法。该方法稳健、快速（因为所需图像在不到一秒的时间内即可捕获）、对眼睛安全，并且在几毫米的范围内提供了扩展的焦深。使用台阶高度标准，我们确定高度误差为±1.75 μm（1σ）。通过降低照明的空间相干长度或增加成像系统的数值孔径，该值可能会进一步降低。
