Research Interests

| Nanoprobing of Semiconductor Surface Dynamics |

We develop a new type of terahertz (THz) nanoprobing system to investigate the surface dynamics of bulk semiconductors, using metallic nanogap accompanying strong THz field confinement. We observed that carrier lifetimes of InP and GaAs dramatically decrease close to the limit of THz time resolution (∼1 ps) as the gap size decreases down to nanoscale and that they return to their original values once the nanogap patterns are removed. Our THz nanoprobing system will open up pathways toward direct and nondestructive measurements of surface dynamics of bulk semiconductors.

| Biochemical Sensing Platforms |

Most existing optical techniques inevitably require labeling to the target material, which sometimes denature the measuring biomaterials. For highly efficient real-time monitoring without complicated pretreatment or labeling, many successes in development of label-free or non-destructive detection techniques via increased sensitivity were accomplished by the additional structures. Metasurface-based two-dimensional photonic/electric devices have recently represented extraordinary performances in both manipulation and sensing for various small particles and biochemical species, repeatedly overcoming the limit of detection achieved right before.

| Terahertz Imaging Techniques |

Many successes in obtaining increased sensitivity with additional nanostructures and improving spatial resolution with geometric beam shaping opened up a way for highly efficient real-time THz imaging. From this Perspective, recent trends in innovative THz sensing and imaging research deserve an introduction regarding the level of reliability and sensitivity that can evolve into an actual medical device and other applications. It can also be expected to enable progress in analysis algorithms (compressive phase retrieval, reconstruction, or machine/deep learning), enabling better data sampling, denoising, deblurring, and efficient computing cost, thus finally providing a leap forward in the THz imaging area beyond the absorption cross-section and diffraction limits.

| Electric-photonic Tweezers |

We introduce various molecular detection schemes employed by metasurfaces and resonant nanostructures at the broadly defined wavelength regime, as they conserve the inherent molecular characteristics with improved sensitivity. Such sensing techniques can be combined with targeted particle manipulation techniques that have been actively studied recently. Various optical sensor technologies based on the metasurfaces that analyze the optical characteristics of trace molecules are introduced. Finally, next-generation sensing technology allows us to precisely control the dynamic movement of particles and measure them at the same time, by overlapping the signal hotspot, even controlling the behavior of small particles under the water environment are reviewed as well.