Research

We are developing medical imaging techniques using special light beams such as Airy beams. The techniques can be used for optical coherence tomography and holographic optical coherence imaging. Another biomedical imaging project we are working with is fluorescence mediated tomography (FMT) based on the heterodyne method and the development of site-specific fluorescent peptides. The proposed FMT technique is an in vivo biomedical imaging technique that can provide quantitative and molecular imaging of fluorescent probes in small animals. The system is to be used for simultaneous imaging of fusion probes of tumor-targeting radiolabeled and fluorescent peptides by optical and other modalities.

We are working on several material systems using second harmonic generation (SHG). Polar alignment in organic crystals is a potential nonlinear optical (NLO) material that can create high SHG. Since the dipole cancellation is avoided, the nonlinear coefficients can be enhanced at certain configuration according to the symmetry of the crystal and the polarization of light waves. The huge SHG is achieved with defined orientation of the crystal to allow the phase matching.

Wide-bandgap semiconductors have shown great potential for ultraviolet (UV) detection. During the past decade, wide-bandgap III-V GaN and AlGaN photodetectors have been extensively studied and show high photoresponsivity. However, these devices suffer from the problem of persistent photoconductivity due to deep level defects, grain boundaries and surface states in the material. As a wide-bandgap II-VI semiconductor, ZnO is a potential candidate material for UV detectors. Previous UV detectors based on ZnO showed either relatively low photoresponsivity or lacked the capability of visible rejection. In our current work new metal-semiconductor-metal and s-I-n ZnO UV detectors have been realized. The mechanism of carrier generation and recombination has been studied to explain the observed photoresponse.

The development of nanoporous carbon is significant for energy storage and transport based on reversible hydrogen storage. To increase the hydrogen storage capacity, metalloid atoms such as boron are proposed to dope into activated carbon. Boron atoms serve as strong sites to increase the capability of hydrogen adsorption. It is very important that boron and carbon form a chemical bond, so that the boron doped nanoporous carbon matrix is a stable structure. We study chemical bonds by using microscopic FTIR for nanoporous materials. Boron doped nanoporous carbon is an excellent example for the studies.