Synchronous Phase-Shifting Interference for High Precision Phase Imaging of Objects Using Common Optics

Abstract

Quantitative phase imaging and measurement of surface topography and fluid dynamics for objects, especially for moving objects, is critical in various fields. Although effective, existing synchronous phase-shifting methods may introduce additional phase changes in the light field due to differences in optical paths or need specific optics to implement synchronous phase-shifting, such as the beamsplitter with additional anti-reflective coating and a micro-polarizer array. Therefore, we propose a synchronous phase-shifting method based on the Mach-Zehnder interferometer to tackle these issues in existing methods. The proposed method uses common optics to simultaneously acquire four phase-shifted digital holograms with equal optical paths for object and reference waves. Therefore, it can be used to reconstruct the phase distribution of static and dynamic objects with high precision and high resolution. In the experiment, the theoretical resolution of the proposed system was 1.064 µm while the actual resolution could achieve 1.381 µm, which was confirmed by measuring a phase-only resolution chart. Besides, the dynamic phase imaging of a moving standard object was completed to verify the proposed system's effectiveness. The experimental results show that our proposed method is suitable and promising in dynamic phase imaging and measurement of moving objects using phase-shifting digital holography.

Keywords: Mach–Zehnder interferometer; digital holography; quantitative phase imaging; synchronous phase-shifting.

Figure 1

The designed PSDH system. (a) The schematic of the designed PSDH system; (b) The physical diagram of the designed system. P: linear polarization; BS: non-polarizing beamsplitter cube; QWP: quarter-wave plate; PBS: polarizing beamsplitter cube; MO: microscope objective.

Figure 2

The workflow of reconstructing phase using the proposed system. The first column displays four phase-shifted images (including the holograms of the sample and the calibration holograms). The second column are the reconstructed phases. The last column illustrates compensated phase distribution of the resolution chart.

Figure 3

Evaluation of the resolution. (a) The reconstructed phase of the resolution chart; (b) The enlargement of the red square; (c) The phase heights across the designated lines in (b).

Figure 4

Phase reconstruction of a static phase object. (a) Reconstructed phase of 200 nm; (b) Reconstructed phase of 300 nm; (c) Reconstructed phase of 350 nm; (d) The 3D map of (a); (e) The 3D map of (b); (f) The 3D map of (c).

Figure 5

Thickness of the resolution chart reconstructed by the proposed system.

Figure 6

Dynamic phase measurement of the PMMA pellets. (a–f) are the phase maps reconstructed at 0.5 s intervals over a 3-s period. (g) The phase heights across the red line in (a) and blue line in (f).

Figure 7

Dynamic phase image of the new PMMA pellets. (a–f) are the phase maps reconstructed of the new PMMA pellets.