Off-axis Lensless Fourier Research Articles

Digital Holographic Interferometry for Micro-Deformation Analysis of Morpho Butterfly Wing

In this study, we present an analysis of deflections in a Morpho butterfly wing using digital holographic interferometry (DHI). Our methodology revolves around an off-axis lensless Fourier holographic setup, using laser excitation to induce deflections in the object. The implementation of a DHI setup, tailored for rapid monitoring of micro-deformation, is a central aspect of our research. We offer an overview of the theoretical foundations of this technique, complemented by both experimental and numerical results aimed at validating our findings. We designed an optical setup that enhanced both laser illumination and hologram reconstruction for the sample. The experimental findings decisively show that the proposed method is effective for rapid deformation analysis. The deformation of the wing can be measured with micro-meter accuracy thanks to numerical analysis.

Dynamic measurement of 3D displacements using dual-camera lensless Fourier transform digital holography.

Dynamic 3D displacement field measurement is an effective means to characterize the electrical performance stability and structural soundness of microsystems. Combining off-axis lensless Fourier transform multiplexed digital holography and multi-illumination profilometry, a dual-wavelength dual-camera optical setup with a multi-illumination system is developed to simultaneously acquire four phase images with different sensitivity vectors, as well as the object shapes. Meanwhile, the shared reference wave in off-axis lensless Fourier holography gives a convenient way for sensitivity vector modification and phase image registration, which are based on the stereo checkerboard calibration method. The dynamic 3D displacement fields and the strain maps of an energized integrated circuit board reveal that the inhomogeneous thermal expansion may cause some damage to chips, such as pin desoldering and microstructure fracture.

Speckle suppression in off-axis lensless Fourier transform digital holography

Speckle noise suppression in off-axis lensless Fourier transform digital holography by laterally shifting of object is analyzed quantitatively. Speckle decorrelation is directly proportional to the object displacement therefore object is shifted by three different amounts to test its effect on the speckle contrast reduction that is pixel size of camera, averaged speckle size and resolution pixel size of reconstruction plane. Phase-only spatial light modulator (LCOS) is used in object beam path to introduce the lateral shift in its position digitally without mechanical efforts by displaying a grating function. In comparison with the typical methods, the externally input lateral position shifts of object are controlled accurately, which makes the system effective and practicable. Averaged reconstructed results for three quantitative object lateral position shifts are compared and it has been found that the object shift by resolution pixel size of reconstruction plane shows better speckle contrast reduction and is in good agreement with the theoretical prediction.

离轴无透镜傅里叶变换数字全息的分辨率分析

Based on the off-axis lensless Fourier transform digital holography principle,two main determining factors,which effect the imaging resolution of the Fourier transform digital holography are discussed in this paper.One is the recording distance and the size of the object.The other is the size of reference light source.The 1.0×1.0 mm2 and 1.5×1.5 mm2 areas in the center of an USAF 1951 Style Resolution Target serve as the objects.Corresponding experiments are performed employing three reference light sources with the sizes 2 μm,6.5 μm and 15 μm respectively,at different recording distances.Both the theory and the experimental results show that as in meeting three terms (twin images and zero order in reconstructed image) separation from each other and sampling theorem conditions,shortening the recording distance or decreasing scale of the reference light source may improve the system resolution of lensless Fourier transform digital holography of micro object.