Xin Ji Lai

Resolution enhancement of spectrum normalization in synthetic aperture digital holographic microscopy

This study describes the overlapping of spatial frequency bands for synthetic aperture in digital holography using spectrum normalization to effectively enhance the spatial resolutions of image reconstruction. Synthesized spectrum swelling induced by excessive frequency overlaps can be normalized through the inverse apodization of an adjustable window function, which is similar to the effects of suppressing low-frequency expansion and strengthening high-frequency components of the reconstructed images. The results indicated that using the normalized spectrum synthesis that requires only a few frequency bands effectively enhances the spatial resolution and phase sensitivity of reconstructed images in digital holographic microscopy.

Efficient FPGA-Based Fresnel Transform Architecture for Digital Holography

This paper presents a novel FPGA-based hardware architecture for realtime diffraction computation of digital holography. The hardware circuit is based on Fresnel transform in basic form for diffraction computation. A novel pipeline is adopted in the circuit so that all the components are operated concurrently. The computation time of the circuit is comparable to a single fast Fourier transform (FFT). Experimental results reveal that the proposed architecture has the advantages of high throughput, high accuracy and low power consumption for the 3D reconstruction of holograms.

In situ mapping of light-induced refractive index gratings by digital holographic microscopy

This work presents a technique for in situ measurement of light-induced refractive index gratings in epoxy resin using digital holographic microscopy (DHM). The reconstructed phase image derived from a digital hologram can exhibit the grating structure and refractive index profile of an epoxy resin hologram. Reconstruction properties of finite aperture effect in the DHM system are considered and analyzed theoretically. Due to the high spatial frequency components collected by the objective lens, the DHM system can measure fine grating structures and numerically determine the reconstructed images in increased detail. Grating formation and dynamic behavior during the light-induced holographic process can be demonstrated experimentally and characterized using the proposed scheme. Compared with an optical holographic readout, the proposed technique facilitates direct observation and substantial understanding of the holographic recording mechanism in a microscopic view.

Applications of digital holographic microscopy in therapeutic evaluation of Chinese herbal medicines

Therapeutic use of Chinese herbal medicines (CHMs) is a new approach to treat neurodegenerative diseases, such as Alzheimers disease and Parkinsons disease. The detection of soma volume and neurite outgrowth of living neurons is a highly relevant biomarker related to various application fields, including therapy efficacy and drug safety evaluation. Through the use of digital holographic microscopy (DHM), we may evaluate the therapeutic effect of CHMs in curing neurodegeneration. Panax ginseng has been used in traditional Chinese herbal medicine for centuries. In this study, DHM is applied to monitor the three-dimensional morphology change of retinoic acid-induced human neuroblastoma SH-SY5Y cells during Panax ginseng treatment. We demonstrate the capability of DHM to detect noninvasively SH-SY5Y cell apoptosis and rescue through the measurement of neuronal volume and neurite outgrowth regulation without any labeling reagent. Through DHM, we observed the phase images of the rapidly shrinking cells with decreasing soma volume and shortening neurite outgrowth during glutamate treatments. Then shrinkage in glutamate-induced cells is significantly alleviated during Panax ginseng treatment. The results through DHM are consistent with the result from MTT assay for assessing cell viability during Panax ginseng treatment. Thus, we suggest that application of DHM for measuring soma volume and neurite outgrowth of living neurons may be one appropriate therapeutic evaluation for CHMs.

Coded aperture structured illumination digital holographic microscopy for superresolution imaging

This paper proposes a coded aperture structured illumination (CASI) technique in digital holographic microscopy (DHM). A CASI wave is generated using two binary phase codes (0° and 120°) for spatial phase shifting. The generated CASI wave then interferes with a reference wave to form a coded Fresnel hologram at a single exposure with compressive sensing (CS) to avoid the temporal phase-shifting process of the structured illumination (SI). The CS algorithm is applied to retrieve the missing data of decoded phase-shifted SI-modulated waves, which are used to separate overlapped spatial frequencies for obtaining a larger spatial frequency coverage to provide superresolution imaging. Two phase-only spatial light modulators are applied to generate a directional SI pattern for obtaining a coded aperture with a suitable size to perform one-shot acquisition in the DHM system.

Superresolution imaging in synthetic aperture digital holographic microscopy

This study presents a superresolution imaging technique based on synthetic aperture digital holographic microscopy (SA-DHM). The synthetic aperture for superresolution imaging in digital holographic microscopy is theoretically derived and analyzed, which indicates that the frequency coverage and spatial resolution increase as the effective aperture size. We experimentally performed the scanning synthetic aperture for superresolution and tomographic imaging in the DHM system. The experimental results show that the spatial resolution of the DHM system can increase up to two times than that in using conventional numerical-aperture microscopy.

Structured illumination induced moiré fringes for resolution enhancement in digital holographic microscopy

This work describes resolution enhancement of digital holographic microscopy based on structured illumination, in which low-frequency moire fringes are induced and recorded for hologram reconstruction. Higher resolution can be performed with the known structured patterns.

Ultrashort Pulse-induced Phase Change by Dual-wavelength Pump-probe Digital Holographic Microscopy

A novel technique of dual-wavelength pump-probe digital holographic microscopy is proposed to observe the ultrafast phenomenon of single pulse-induced phase change in low dispersion materials. The induced phase of each pulse are determined and analyzed.

Low-frequency moiré fringes synthesize by mutual correlation for resolution enhancement in structured illumination digital holographic microscopy

This study employed the mutual correlation to perform low-frequency moire fringes synthesize for resolution enhancement in structured illumination digital holographic microscopy. The correlation peak with different angular displacements is capable of determining phase matching performance.

Angular- and polarization-multiplexing with spatial light modulators for resolution enhancement in digital holographic microscopy

This work demonstrates angular- and polarization-multiplexing based on spatial light modulators for resolution enhancement in synthetic aperture digital holographic microscopy. Frequency bands can be dynamically selected in single-shot for the hologram synthesis and frequency coverage.