Sub-diffraction thin-film sensing with planar terahertz metamaterials.

Area of Science:

• Metamaterials
• Terahertz (THz) spectroscopy
• Nanophotonics

Background:

• Planar metamaterials with subwavelength resonators are used for terahertz (THz) thin dielectric film sensing.
• Conventional methods are limited by the diffraction-limited spot size of THz beam excitation, requiring a larger sample area.
• Reducing the sensed area is crucial for analyzing micro-scale samples and improving sensor sensitivity.

Purpose of the Study:

• To investigate the application of THz near-field sensing to reduce the minimal area required for metamaterial-based thin film sensing.
• To enhance the resonance quality factor (Q factor) of the metamaterial sensor.
• To demonstrate the feasibility of sub-diffraction sensing for ultra-thin dielectric films.

Main Methods:

• Utilizing THz near-field sensing by positioning the metamaterial platform close to a sub-diffraction THz source.
• Analyzing the reduction in the number of excited resonators and its effect on the minimal film area.
• Measuring the resonance Q factor and comparing near-field to far-field measurements.

Main Results:

• THz near-field sensing significantly reduced the minimal sensed film area to as small as 0.2λ × 0.2λ for a film thickness of λ/375.
• The number of excited resonators was reduced, leading to decreased inter-cell coupling.
• The resonance Q factor was increased by more than a factor of two compared to far-field measurements.

Conclusions:

• THz near-field sensing is an effective method for achieving sub-diffraction-limited sensing with planar metamaterials.
• This approach enhances sensor performance, particularly the Q factor, enabling detection of ultra-thin films.
• The developed platform holds promise for future metamaterial-based sensors, including applications in biomolecular detection.