Coaxial hole array fabricated by ultrafast femtosecond-laser processing with spatially multiplexed vortex beams for surface enhanced infrared absorption

Here, we combined shaping and multiplexing of the laser beam to achieve ultrafast femtosecond-laser patterning of Au films with coaxial and circular hole arrays at a printing rate of 10⁶ elements per second. Fabrication quality of the developed parallel laser-printing approach was found to be enough to replicate coaxial hole arrays with a resonant transmission over 90% in the mid-IR spectral range resulted from coupling between localized electromagnetic mode supported by coaxial unit cell and the lattice-type SPPs. Coupling of the surface plasmons localized within the coaxial holes to the vibration modes of the deposited analyte, widely used antihistamine drag Diphendramine, was found to provide around 800-fold enhancement of the amplitude of characteristic IR bands allowing reliable SEIRA-based fingerprint identification at trace concentrations. Our findings are consistent with the calculated amplitude of the electromagnetic hot spots suggesting their predominant contribution to the observed SEIRA effect. The ability to tune in a facile way the hole geometry and arrangement in the process of fabrication allows to tailor the spectral position of the resonance spanning practically relevant spectral range from 4 to 10 μm. This makes the coaxial microhole arrays produced with ultrafast direct laser printing promising for IR filtering and sensing.