Measurement of specular surfaces using electrically tunable lens in digital holography

Abstract

In the field of industrial metrology, the three-dimensional non-destructive imaging of reflecting metallic surfaces is a delicate task. In this work, we propose a novel application of Electrically Tunable Lens (ETL) in Digital Holography for imaging of specularly reflecting objects. The precise surface profile of microscopic step height at different axial depths is obtained by tuning the liquid lens at different currents. Initially, the ETL's focal length is set by tuning its control current to image the specular reflection observed from the surface of the reflecting sample. The current of ETL is tuned accordingly as the sample is moved to different z-positions. In order to demonstrate efficacy of the proposed setup, the object is kept at multiple axial distances within the depth of field (DOF) of the ETL. The step height measurements are done and measurement uncertainty of 0.083µm is calculated for step height measurements at different axial positions ranging from 2cm-21cm. The axial range of the setup is validated by keeping two specularly reflecting samples in the field of view of the ETL. The experimental results demonstrate ETL’s efficiency in a digital holographic system for accurately imaging specularly reflecting objects present at multiple axial depths. The setup is useful for precise step height measurements and for obtaining surface profiles of microstructures.

Soft Contact Lens Engraving Characterization by Wavefront Holoscopy

“…Classically, this technique is based on the self-interference of an illumination beam passing through the sample over a photographic plate [ 34 ] which is substituted, in modern implementations, by a digital sensor [ 35 , 36 , 37 ]. Additionally, novel experiments have introduced several improvements in image capture and processing stages with approaches based on the introduction of tunable optical devices enhancing the hologram capture, focus distance, and magnifications [ 38 , 39 , 40 , 41 ]. More specifically, in this interferometric arrangement based on a classical Gabor in-line configuration, the reference beam directly comes as the non-diffracted light emanating from a partially coherent illumination source, and the object beam is created from the diffracted light coming from the illuminated sample, which is thus considered small in comparison with the reference beam (weak diffraction assumption).…”

Automated surface profile measurement with digital holographic microscopy and large mask inpainting networks

“…Current phase compensation methods in off-axis DHM can be categorized as physical and numerical methods. Physical methods rely on optical path configurations during holographic recording, including methods such as double exposure, introducing microscopic objectives, employing electrically tunable lenses, or integrating common-path interferometers [12][13][14][15][16][17][18][19]. However, these methods demand high system stability and intricate optical alignments, making them less practical for holographic recording experiments.…”