Fanjing Wang

Coherent noise reduction in digital holographic phase contrast microscopy by slightly shifting object

A method to reduce coherent noise in digital holographic phase contrast microscopy is proposed. By slightly shifting the specimen, a series of digital holograms with different coherent noise patterns is recorded. Each hologram is reconstructed individually, while the different phase tilts of the reconstructed complex amplitudes due to the specimen shifts are corrected in the hologram plane by using numerical parametric lens method. Afterward, the lateral displacements of the phase maps from different holograms are compensated in the image plane by using digital image registration method. Thus, all phase images have same distribution, but uncorrelated coherent noise patterns. By a proper averaging procedure, the coherent noise of phase contrast image is reduced significantly. The experimental results are given to confirm the proposed method.

Twin image elimination from two in-line holograms via phase retrieval

The reconstruction quality of in-line holography suffers from the superposition of twin images that have different foci but identical information content. We propose a phase retrieval method using two axially displaced holograms and a finite transmission constraint to eliminate the conjugate image. The simulation and experimental results demonstrate a better elimination effect and a faster rate of convergence compared with those of previously reported methods. Two holograms can be recorded simultaneously using two cameras, thus this technique can be used in real-time imaging.

Improvement of speckle noise suppression in digital holography by rotating linear polarization state

An improved polarization recording approach to reduce speckle noise in digital holography is proposed. Multiple off-axis holograms are obtained by rotating the linear polarization state of both illumination and reference wave simultaneously. By averaging the intensity fields, the speckle noise in the reconstructed images is well suppressed. Statistical evaluation of the experimental results shows the effectiveness and improvement of the proposed method.

Long-term quantitative phase-contrast imaging of living cells by digital holographic microscopy

The dynamic analysis of biological living samples is one of the particular interests in life sciences. An improved digital holographic microscope for long-term quantitative phase-contrast imaging of living cells is presented in this paper. The optical configuration is optimized in the form of a free-space-fiber hybrid system which promotes the flexibility of imaging in complex or semi-enclosed experimental environment. Aberrations compensation is implemented taking into account the additional phase aberration induced by liquid culture medium in long-term observation. The proposed approach is applied to investigate living samples of MC3T3-E1 and MLO-Y4 cells. The experimental results demonstrate its availability in the analysis of cellular changes.

Real-time Micro-vibration Measurement Based on Digital Holographic Interferometry

An experimental system based on digital holographic interferometry is proposed for real-time high-precision micro-vibration measurement. Vibration information can be extracted directly and instantaneously from the holograms by using the fast micro-vibration testing algorithm. As the received light of the proposed system is scattered beam, no assumption is made on the object surface. Unlike other optical detection approaches, the proposed method can detect plane vibration rather than point vibration without any assumptions on object surface feature and receiving angle. The feasibility of the proposed system is demonstrated by using a vibrating object driven by standard sinusoidal signal.