High-resolution digital holography for shape measurement of microscopic object

Abstract

Digital holography is particularly well suited for characterization of microstructure such as surface shape, surface nanostructures and surface roughness. The direct availability of both amplitude and phase information offers a range of versatile processing techniques that can be applied to complex field data, including phase imaging, which is particularly straightforward in digital holography. Based on digital off-axis lensless Fourier transform holographic configuration, the principle of topography by digital holography is analyzed. The wavefront deformation created by numerical Fresnel reconstruction is then studied. Thus the model of phase mask which is a parabolic function and related to the recording parameters is built. The phase mask can be obtained automatically by using digital hologram itself to evaluate automatically and accurately the values of the parameters involved by a curve-fitting procedures applied to the phase data extracted along two profiles, which are defined in the region where sample contributions are constant. The reconstructed wave field can be simply obtained by multiplying the phase mask with Fourier transform of the hologram. Both theoretical analysis and the simulation results show that the procedure proposed by Colomb is more suitable for phase reconstruction of digital off-axis lensless Fourier transform holography. Moreover, the correcting procedure can be applied to compensate high-order aberrations.