Fast topographic optical imaging using encoded search focal scan

• Published in: Nature communications Vol. 15; no. 1; p. 2065
• Main Authors: Vilar, Narcís, Artigas, Roger, Duocastella, Martí, Carles, Guillem
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 07.03.2024; Nature Publishing Group; Nature Portfolio
• Subjects: 639/624/1107/510; 639/766/930/328; Coding; Dimensional measurement; Humanities and Social Sciences; Image processing; Image reconstruction; Information processing; multidisciplinary; Optics; Quality control; Science; Science (multidisciplinary); Topography
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-024-46267-y

A central quest in optics is to rapidly extract quantitative information from a sample. Existing topographical imaging tools allow non-contact and three-dimensional measurements at the micro and nanoscales and are essential in applications including precision engineering and optical quality control. However, these techniques involve acquiring a focal stack of images, a time-consuming process that prevents measurement of moving samples. Here, we propose a method for increasing the speed of topographic imaging by orders of magnitude. Our approach involves collecting a reduced set of images, each integrated during the full focal scan, whilst the illumination is synchronously modulated during exposure. By properly designing the modulation sequence for each image, unambiguous reconstruction of the object height map is achieved using far fewer images than conventional methods. We describe the theoretical foundations of our technique, characterise its performance, and demonstrate sub-micrometric topographic imaging over 100 µm range of static and dynamic systems at rates as high as 67 topographies per second, limited by the camera frame rate. The high speed of the technique and its ease of implementation could enable a paradigm shift in optical metrology, allowing the real-time characterisation of large or rapidly moving samples. Quickly acquiring topographical information from a sample remains a challenge in optics. Here, the authors introduce encoded search focal scan, a technique for sub-micrometric imaging of tens of topographies per second based on collecting a reduced set of images.