Deep-subwavelength (∼λ/160 000) terahertz sensing with an ultrathin flexible metasurface
Abstract
Terahertz (THz) sensing of deep-subwavelength dielectric films remains a formidable challenge due to the stark mismatch between the long wavelengths of terahertz radiation and the nanoscale thicknesses of the analytes. Although high-quality-factor (Q) metallic resonators are widely used to enhance light–matter interaction, their performance is fundamentally constrained by intrinsic radiative and non-radiative losses. Overcoming these limitations is crucial to achieving strong local-field enhancement and detecting ultrathin films. Here, we present a planar metasurface sensor fabricated on an ultra-low-index, flexible cyclic olefin copolymer substrate, engineered to achieve strong electromagnetic field confinement within an effective mode volume of 7.52 μm3 [approximately 10−7(λ/n)3] at 0.94 THz. This design achieves a high Q/Veff ratio of ∼1.463, effectively overcoming the limitations of conventional high-Q resonance approaches. Using conventional THz time-domain spectroscopy, we experimentally detect an ultrathin 2 nm germanium (Ge) overlayer equivalent to λ/160 000, where λ is the resonant wavelength. To the best of our knowledge, this demonstrates the thinnest analyte layer ever detected at terahertz frequencies, achieved through exceptional sensitivity of micrometer-scale resonators that obviate the need for complex nanoscale fabrication. The sensor exhibits a refractive index sensitivity of 15.54 GHz/RIU for a 40 nm analyte layer, establishing a new paradigm for deep-subwavelength THz sensing and paving the way for compact, flexible, and high-performance THz photonic platforms.
Article Details
Journal Info
Applied Physics Letters
American Institute of Physics
Authors (11)
Vanlal Rinfela
Ultrafast Terahertz Photonics Laboratory (UTPL), Department of Physics, Indian Institute of Technology Hyderabad 1 , Kandi, Sangareddy, Telangana 502284,
Bhawana Andola
Ultrafast Terahertz Photonics Laboratory (UTPL), Department of Physics, Indian Institute of Technology Hyderabad 1 , Kandi, Sangareddy, Telangana 502284,
Rajour Tanyi Ako
Functional Materials and Microsystems Research Group and the Micro Nano Research Facility, ARC Centre of Excellence for Transformative Meta-Optical Systems, RMIT University 3 , Melbourne, VIC 3000,
Naveen Periketi
Bhaswati Biswas
Department of Material Science and Metallurgical Engineering (MSME), Indian Institute of Technology Hyderabad 5 , Kandi, Sangareddy, Telangana 502284,
Madhu Bhaskaran
Functional Materials and Microsystems Research Group and the Micro Nano Research Facility, ARC Centre of Excellence for Transformative Meta-Optical Systems, RMIT University 3 , Melbourne, VIC 3000,
Chandrasekhar Murapaka
Department of Material Science and Metallurgical Engineering (MSME), Indian Institute of Technology Hyderabad 5 , Kandi, Sangareddy, Telangana 502284,
Anil Kumar Chaudhary
DIA-CoE (ARCHEM), School of Physics, University of Hyderabad 4 , Prof. CR Rao Road, Hyderabad 500046,
Sharath Sriram
Functional Materials and Microsystems Research Group and the Micro Nano Research Facility, ARC Centre of Excellence for Transformative Meta-Optical Systems, RMIT University 3 , Melbourne, VIC 3000,
Prem Pal
MEMS & Micro/Nano Systems Laboratory, Department of Physics, Indian Institute of Technology Hyderabad 2 , Kandi, Sangareddy, Telangana 502284,
Yogesh Kumar Srivastava
Ultrafast Terahertz Photonics Laboratory (UTPL), Department of Physics, Indian Institute of Technology Hyderabad 1 , Kandi, Sangareddy, Telangana 502284,