Angular Goos-Hänchen Shift Sensor Using a Gold Film Enhanced by Surface Plasmon Resonance

Area of Science:

• Optics
• Nanotechnology
• Sensing

Background:

• The Goos-Hänchen (GH) shift describes the spatial or angular displacement of a reflected light beam at an interface.
• Surface plasmon resonance (SPR) is a phenomenon sensitive to changes at a metal-dielectric interface, often used for sensing.

Purpose of the Study:

• To demonstrate and enhance the angular GH shift using SPR.
• To investigate the effect of a focused incident beam on SPR-enhanced GH shift.
• To explore the potential of this enhanced angular GH shift for sensing applications.

Main Methods:

• Utilized a Kretschmann configuration with a gold (Au) film on a substrate to excite surface plasmons.
• Employed a focused incident beam to induce an enhanced angular GH shift (Θ).
• Simultaneously measured reflectivity for SPR and beam shift for GH shift.

Main Results:

• Achieved a significantly large enhancement in the angular GH shift (Θ) using a focused beam, despite a decrease in spatial GH shift (Δ).
• Demonstrated that focused geometry, while reducing SPR excitation efficiency, still induces a substantial Θ.
• Showcased the potential for sensing applications by measuring enhanced Θ in response to local environmental changes.

Conclusions:

• Focused beam SPR configuration effectively enhances the angular GH shift.
• The enhanced angular GH shift is a promising parameter for developing sensitive optical sensors.
• This method offers a viable approach for detecting local environmental changes using simple thin-film structures.