Enhanced light–matter interactions in plasmonic–molecular gas hybrid system

Fascinating phenomena have been demonstrated in plasmonic materials due to their enhanced light–matter interaction and high sensitivity. Surface plasmon resonance (SPR), where resonance is obtained for a specific combination of angle and wavelength of the incident light, is of particular interest for sensing applications, but is somewhat limited due to its relatively broad resonance line and the lack of referencing to a known source of absolute resonance. We mitigate these deficiencies by exploiting the coupling between plasmonic and molecular resonance in a hybrid device consisting of SPR and acetylene. The coupled system inherits the angular sensitivity, enhanced light–matter interactions, and miniaturization of the SPR, while the acetylene provides a narrow and accurate resonance in the telecom band. These qualities make our hybrid system very sensitive to minute variations in the incident angle. SPR is very sensitive to refractive index variations that originate from the highly dispersive nature of acetylene. Combined with the narrow transition line of acetylene in the telecom band, this allows for the generation of a feedback signal for laser stabilization in a miniaturized volume. Taking advantage of these properties, we have stabilized a telecom laser to our hybrid system with a precision better than 300 kHz at 100 s. Furthermore, we have used the high sensitivity and accuracy to demonstrate an angular sensor with angular resolution on the order of microradians. The ability to demonstrate a hybrid plasmonic–molecular coupled system in the telecom regime may enable a variety of other applications, such as chip-scale advanced spectroscopy, metrology, and chip-scale light sources.