Tunable light absorbance by exciting the plasmonic gap mode for refractive index sensing

Area of Science:

• Plasmonics
• Nanophotonics
• Optical Sensing

Background:

• Tunable narrowband optical response typically requires complex periodic metal nanostructures.
• Fabricating large-scale, defect-free nanostructures is often expensive and challenging.

Purpose of the Study:

• To develop a cost-effective method for achieving tunable and sharp optical responses.
• To investigate the potential of plasmonic gap modes for refractive index sensing.

Main Methods:

• Excitation of plasmonic gap mode in large-area samples.
• Design of hexagonal arrangement gold microholes atop a gold continuous film with a spacer.
• Numerical calculations to analyze resonant wavelength shifts with environmental refractive index changes.

Main Results:

• Achieved characteristic and sharp absorbance via plasmonic gap mode excitation.
• Demonstrated tunability of resonant wavelength by altering metal structure dimensions or spacer thickness.
• Observed a sharp reflectance dip due to intense plasmonic gap mode.
• Reported a linear relationship between resonant wavelength and environmental refractive index.
• Achieved high sensitivity (∼1287 nm/RI unit) and figure of merit (>300) for refractive index sensing.

Conclusions:

• The developed method provides a low-cost and scalable approach for tunable optical responses.
• The plasmonic gap mode is effective for creating sensitive refractive index sensors.
• The hexagonal gold microhole array design exhibits excellent sensing performance.