Fabrication of thermally stable mid-infrared optical filters using tantalum microdisc array

To fabricate a thermally stable optical filter in the mid-infrared (MIR) region, a plasmonic metal disk array (PMDA) using tantalum (Ta) was proposed, and the filter performance was compared with that of conventional silver (Ag)-based PMDAs. A finite-difference time-domain method was utilized to systematically analyze the effects of geometric configuration and constituent materials on the optical properties of PMDA filters with a periodic hexagonal lattice. Unlike the Ag PMDA filters, whose transmission dip at resonance wavelengths gradually decreased with increasing temperature, the Ta PMDA filters revealed almost the same transmission spectra even after annealing at 700 °C for 30 min. The Ta-based MIR PMDA filter exhibited similar optical properties to those of the Ag PMDA. The PMDAs with a duty cycle (d.c.) of 60% exhibited stop band spectra with sufficiently deep dip and wide linewidth. MIR filters fabricated with the Ta disks were demonstrated to quantify different types of alcohols through the monitoring of transmission spectra.