Common-mode plasmon sensing scheme as a high-sensitivity compact SPR sensor.

Area of Science:

• Optics and Photonics
• Nanotechnology
• Chemical Sensing

Background:

• Surface Plasmon Resonance (SPR) is a label-free optical sensing technique.
• Conventional SPR often relies on single-order plasmon coupling, leading to strong absorption and limited sensitivity.
• Developing advanced SPR schemes is crucial for high-performance chemical sensing applications.

Purpose of the Study:

• To demonstrate a novel SPR sensing scheme utilizing quasi-phase-matched simultaneous excitation of two counterpropagating surface plasmon modes.
• To investigate the angular reflection spectra and identify unique features for enhanced detection.
• To establish a high-sensitivity gas sensing platform based on the proposed SPR method.

Main Methods:

• Fabrication of a deep metal grating for controlled diffraction orders.
• Simultaneous excitation of counterpropagating surface plasmon modes using +1st and -2nd diffraction orders.
• Analysis of angular reflection spectra for the -1st and zeroth orders, focusing on interleaved zeros and maxima.
• Experimental validation using a pressure-controlled chamber for gas monitoring.

Main Results:

• The deep metal grating enabled quasi-phase-matched excitation of two surface plasmon modes.
• Angular reflection spectra showed unique interleaved zeros and maxima, differing from typical absorption dips.
• Two crossing angles in the zeroth and -1st orders were identified for common-mode detection.
• A limit of detection (LOD) of 2 × 10⁻⁷ refractive index unit (RIU) was achieved for gas sensing.

Conclusions:

• The developed SPR sensing scheme offers a significant improvement over conventional methods.
• The unique spectral features and common-mode detection capability enable high-sensitivity and robust sensing.
• This approach holds promise for advanced applications in chemical sensing and environmental monitoring.