Surface plasmon resonant splitting and merging due to infrared incidence through thermal imaging lens

In previous work, the present authors discovered the resonant splitting phenomenon of a plasmonic perforated gold film (PGF), as the incident light comes in the polar angle. However, in reality, the light through the imaging lens could be incident on the PGF not only in the polar angle but also in the azimuth angle. The transmission of a PGF against the incident light is analysed in both polar and azimuth angles in spherical coordinates. To mimic the incidence through the lens, a PGF sample is rotated by simultaneously varying both types of angles as normal incidence arrives. For the measurement, the sample has been fabricated with a PGF on a semi-insulating gallium arsenide (GaAs) substrate. The measured transmission spectra show both resonant splitting and merging under TM and TE polarisations as the azimuth angle is increased. Results drawn from this work will pave the way to fully understanding the interaction between the imaging lens and the plasmonic structure (PGF).