Detecting Resonant Evanescent orders in Terahertz Metagratings

Ms. Shreeya Rane1, Mr. Ajinkya Punjal2, Prof. Shriganesh Prabhu2, Prof. Dibakar Roy Chowdhury1
1Mahindra University, Hyderabad, India. 2Tata Institute of Fundamental Research, Mumbai, India


Resonant evanescent modes being a unique deep sub-wavelength event, is recognized for confining intense electromagnetic energy at the interface between air and suitably designed grating. While evanescent orders present intriguing physical phenomena, the experimental detection of these modes exhibit a formidable challenge due to their inherent non-propagating nature and exponentially decaying characteristics. Additionally, detecting the near-field evanescent orders generated by a metagrating (subwavelength grating) possess challenges due to the simultaneous presence of propagating and non-propagating diffraction orders. In an effort to address these challenges, we employ Fourier transformed terahertz spectroscopy (FTTS) using near-field scanning terahertz microscopy (NSTM) to experimentally detect the non-propagating (evanescent orders) and propagating orders utilzing a one-dimensional dielectric metagrating. We have employed all dielectric grating which is devoid of any plasmonic losses, additional advantage in our demonstrated system.