Here, we apply a novel technique involving Joule-assisted active plasmonics to enhance the sensitivity of the well-established surface plasmon resonance (SPR) method. Typically, SPR curves are generated from an angularly resolved scan of the reflected light beam from a metal thin film – dielectric interface. Due to the sensitivity of Surface Plasmon Polaritons (SPPs), and confinement to the vicinity of the interface, they are an important utility in a variety of applications. In this work, a modified setup involving a heated active plasmonic bridge allows insight into the metal surface characteristics not seen through classical Attenuated Total Reflection (ATR) measurements. Here, a constriction in the metal acts as a microscale bridge which is heated, via the Joule effect, and whose temperature follows the cycle of an alternating current. Employing a lock-in amplifier, referenced to the applied sine wave, enables detection of the reflected light now modulated by the alternating current resulting in a change in the optical constants. This dynamic technique is more sensitive than the conventional ATR technique and hence is capable of detecting metal composition, surface chemistry, and morphology above the active plasmonic element. This has opened the door to enhance already highly sensitive SPR devices currently on the market. In this study, we focus on the phase relationship between the Joule heating of an active plasmonic device and demonstrate that the laser spot alignment is of crucial importance to reach optimal sensitivity.
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