Nai-Chia Cheng

Miniaturized video-rate epi-third-harmonic-generation fiber-microscope

With a micro-electro-mechanical system (MEMS) mirror, we successfully developed a miniaturized epi-third-harmonic-generation (epi-THG) fiber-microscope with a video frame rate (31 Hz), which was designed for in vivo optical biopsy of human skin. With a large-mode-area (LMA) photonic crystal fiber (PCF) and a regular microscopic objective, the nonlinear distortion of the ultrafast pulses delivery could be much reduced while still achieving a 0.4 microm lateral resolution for epi-THG signals. In vivo real time virtual biopsy of the Asian skin with a video rate (31 Hz) and a sub-micron resolution was obtained. The result indicates that this miniaturized system was compact enough for the least invasive hand-held clinical use.

Cell death detection by quantitative three-dimensional single-cell tomography.

Ultrahigh-resolution optical coherence tomography (UR-OCT) has been used for the first time to our knowledge to study single-cell basal cell carcinoma (BCC) in vitro. This noninvasive, in situ, label-free technique with deep imaging depth enables three-dimensional analysis of scattering properties of single cells with cellular spatial resolution. From three-dimensional UR-OCT imaging, live and dead BCC cells can be easily identified based on morphological observation. We developed a novel method to automatically extract characteristic parameters of a single cell from data volume, and quantitative comparison and parametric analysis were performed. The results demonstrate the capability of UR-OCT to detect cell death at the cellular level.

Microstructural and microspectral characterization of a vertically aligned liquid crystal display panel

The microstructural and microspectral characteristics of a vertically aligned liquid crystal display (VA-LCD) panel were obtained noninvasively for the first time. With 1 μm axial and 2 μm transversal resolutions, the cell gap profile beneath the patterned thin-film transistor of the VA-LCD panel can clearly be resolved. The thicknesses of the multiple thin-film layers and the embedded defects can also be unveiled. As far as spectral response is concerned, the light transmittance at the layer boundaries can be estimated from the measured reflectance, which is crucial information for the design of a highly transmissive panel. The color shift of the VA-LCD panel due to fabrication error was evaluated.

Toward Single-Mode Active Crystal Fibers for Next-Generation High-Power Fiber Devices

We report what we believe to be the first demonstration of a facile approach with controlled geometry for the production of crystal-core ceramic-clad hybrid fibers for scaling fiber devices to high average powers. The process consists of dip coating a solution of polycrystalline alumina onto a high-crystallinity 40-μm-diameter Ti:sapphire single-crystalline core followed by thermal treatments. Comparison of the measured refractive index with high-resolution transmission electron microscopy reveals that a Ca/Si-rich intragranular layer is precipitated at grain boundaries by impurity segregation and liquid-phase formation due to the relief of misfit strain energy in the Al2O3 matrix, slightly perturbing the refractive index and hence the optical properties. Additionally, electron backscatter diffractions supply further evidence that the Ti:sapphire single-crystalline core provides the template for growth into a sacrificial polycrystalline cladding, bringing the core and cladding into a direct bond. The thus-prepared doped crystal core with the undoped crystal cladding was achieved through the abnormal grain-growth process. The presented results provide a general guideline both for controlling crystal growth and for the performance of hybrid materials and provides insights into how one might design single-mode high-power crystal fiber devices.

Defect-driven fiber-based UV-VIS broadband white light generation

This study reports a facile approach for the emission of ultraviolet-visible broadband from a Ti:sapphire crystalline-core fiber, using a laser-heated pedestal growth technique. White light with CIE (0.287, 0.333) is obtained via the F-Ti centers.

Discrimination of Keratinocytes and Fibroblasts by Parametric Single-cell Tomography

We report using ultrahigh-resolution optical coherence tomography for distinguishing keratinocytes and fibroblasts at the single-cell level. Linear discriminant analysis based on characteristic parameters extracted from volume data was applied for the prediction of cell types.

Non-invasive single cell tomography on skin cells

Non-invasive single cell tomography on keratinocyte and fiberblast were demonstrated in-vitro using a crystalline fiber based broadband light source at visible wavelength. Nuclear-cytoplasmic ratio and other characteristic parameters of single cell were extracted and analyzed.

Glass-clad crystal fibers based functional optical coherence tomography

Broadband emissions centered at 560 nm, 770 nm, and 1380 nm from glass-clad crystal fibers with 3-dB bandwidths of 98, 180, and 240 nm were used for various biomedical and in-vivo optical tomography applications with cellular resolution. The adjacent image pixel cross talks are less than −20 dB due to the near Gaussian spectral shapes of the broadband emissions.

Miniaturized epi-third harmonic generation microscope with a sub-micron spatial resolution and a video rate

With a 2D scanning MEMS mirror, we demonstrate a miniaturized epi-third-harmonic-generation microscope with a video rate and a 0.7µm transverse resolution. In vivo THG imaging of human skin is demonstrated.