Three-dimensional imaging of microstructure by dual-wavelength digital holography

Abstract

In this paper, dual-wavelength digital holography is demonstrated by both numerical simulation and experiment. Simulations were done for two wavelengths of 500 nm and 550 nm. The objects are a wedge prism with a height of 2.5 μm and four abrupt steps. Three-dimensional (3D) reconstruction profiles of the original objects are obtained in the simulations. We find that dual-wavelength phase unwrapping is a fast and robust method for removing 2π discontinuities compared to software algorithm-based methods. In the experiment, two lasers of the different wavelengths 632.8 nm and 671 nm are used to obtain a larger beat wavelength. The object is a phase grating. In dual-wavelength phase unwrapping, two individual phase images are obtained by using each wavelength, respectively, and the phase image for beat wavelength is obtained by subtracting one single wavelength phase image from the other and then adding 2π whenever the resultant value is less than zero. In the final synthetic image, 3D profile of the phase grating is obtained after removing, the discontinuities by reducing the noise of the beat wavelength phase image. The experiment results demonstrate the effectiveness of the dual-wavelength phase unwrapping in digital holography.