Yu Group People

This research is to develop novel dynamic holography techniques using multi-wave mixing in photorefractive materials for depth-resolved and high-speed functional tissue imaging. The holographic imaging technique will overcome limitations of conventional coherence domain imaging in sensitivity and speed for biological tissue imaging. The enhanced temporal and spatial resolution will allow dynamic imaging of site-specific drug delivery to cancerous tissues. The feasibility of imaging drug tracers in tumor tissues has been demonstrated within the framework of imaging optical dye-peptide conjugates in cancer cells and tumor bearing mice.

2. Fluorescence Mediated Tomography

A novel miniature three-dimensional optical imaging approach for small animal multimodality tumor fusion imaging will be developed. The proposed fluorescence mediated tomography (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. Simultaneous dual-modality imaging of FMT-PET, FMT-SPECT or FMT-MRI can greatly improve the fusion imaging strategies and therefore can eliminate complication and inaccuracy of interpretation of multimodality fusion imaging.

3. Nonlinear Optics

Polar alignment in organic crystals is a potential nonlinear optical (NLO) material that can create high second harmonic generation (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. We have successfully observed huge NLO from the polar aligned organic crystals. Our results showed that the NLO response of the organic crystal (DecO,Cl)-azine (DCA) is 34 times larger than that of urea. The results provide initial evidence of large NLO response due to dipole-parallel alignment. The molecule DCA has been used as an example and the methods developed can be used to test other polar organic crystals as well.

4. ZnO UV Detectors

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 due to quality of the films. In this work a new metal-semiconductor-metal detector based on high quality ZnO films has been realized. The mechanism of carrier generation and recombination has been studied to explain the observed photoresponse.