Abstract
We present an effective method for the topography characterization of large gradient micro-structure based on digital holographic microscope (DHM). Due to the limitation of numerical aperture of DHM system, high frequency information corresponding to large gradient regions of specimen is prohibited from entering the imaging system and the complete collection of specimen features cannot be implemented. To solve this problem, we use a common configuration of off-axis DHM system to capture the holograms from multiple angles of the sample, and the various object waves coming from the sample of different tilt angle is corrected and spliced into a fully topography by multi-angle stitching process. In this way, the measurement of large gradient topography of specimen can be realized. Experimental results of large gradient microlens demonstrate the practicability and precision of the presented method.
Highlights
Nowadays, micro-structures have acted as an element in various systems play an important role in measurement [1,2], optical fiber communication [3,4], display [5,6] and other fields [7,8].In order to ensure the performance of the micro-structure, the characterization of surface topography of micro-structure is crucial
When the largest slope angle of the object wave exceeds the range of angles that the microscopic objective (MO)
Of Digital holography microscopy (DHM) system can receive, the corresponding large gradient regions cannot be measured effectively since the object wave is limited by the small numerical aperture (NA) of MO of the DHM system
Summary
Micro-structures have acted as an element in various systems play an important role in measurement [1,2], optical fiber communication [3,4], display [5,6] and other fields [7,8]. Sci. 2020, 10, 6110 of grating is fixed so that the grating provided only stationary direction and angle of illumination, so the measurement of multiple objects can only be implemented by replacing the corresponding grating, which is inefficient This method, based on the super-resolution concept, was developed by Józwik et al [12]. We only need to replace the ordinary sample carrier platform with a four degrees of freedom stage in the conventional DHM system The purpose of this modification is to provide rotation angle for the sample and decrease the relative gradient of partial region, and the system can image the sample from multiple angles and obtain large gradient topography information in all directions. This method is suitable for measurement of various micro-structures with large gradients surface shape and extends the measurable gradient range of the DHM system without reducing the field of view
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