(Feb 11th) 2D materials based metasurfaces & THz near-field spectroscopy

Manipulation of light is of paramount importance in optics. Recently, progress has been made over a  class  of new  artificial media, metamaterials, which  consist of the  arrangement of periodic subwavelength  optical  elements  that  exhibit  unusual  optical  properties  beyond  what  natural materials  can  offer.  Since  their  effective  electromagnetic  properties  can  be  engineered  by designing  subwavelength  scale  metallic  structures,  called  ‘meta-atoms’,  these  artificially constructed materials have promised a vast variety of otherwise unexpected physical phenomena such  as  a  negative  index  of  refraction,  gigantic  chirality,  and  invisible  cloak.  Even  though fascinating  effects  can  be  obtained  by  passive  metamaterials  described  above,  for  practical applications, it is highly desirable to enable dynamic tunability to their operations.

In this talk, I will introduce electrically controllable unique optical properties such as optical activity [1],  anomalous  refraction  and  focusing  [2],  and  analogue  of electromagnetically induced transparency  (EIT)  [3] by  integrating  2D  graphene  layer  onto  metamaterials  with  different functional unit cells. The switching and linear modulation of unique optical properties are realized by changing coupling among meta-atoms or electrical conductivity of metallic structures caused by increased sheet conductivity of the single layer graphene. Besides, I will introduce a single annular aperture  as  a  practical  platform  for  THz  absorption  spectroscopy.  THz  tip-probe  near-field measurement system is used  to  investigate  the electric field  distribution  in  a  single  annular aperture and near-field image clearly shows that the electric field is strongly confined at the gap. After inserting lactose in the gap, we can couple the intense optical fields of the single annular gap into the vibrational modes of lactose molecules. We observed high contrast THz absorbance signals drastically suppressing of the transmitted light. This result indicates that the single annular aperture can be used as a platform that is promising avenues toward future drastic miniaturization of THz devices and sensors.