Refractive index measurement of IP-S and IP-Dip photoresists at THz frequencies and validation via 3D photonic metamaterials made by direct laser writing

Abstract

Direct laser writing (DLW) is widely used to fabricate complex metamaterials (MMs) and photonic devices for nanoscale applications across the electromagnetic frequency spectrum. While the optical properties of conventional photoresists used in DLW are well studied in the visible and infrared range, it is still unclear how they behave at lower frequencies. Here, we measure the refractive index and absorption of IP-S and IP-Dip photoresists within the THz range of the electromagnetic spectrum. Further, we utilize THz time-domain spectroscopy (THz-TDS) to experimentally measure the laser-processed three-dimensional (3D) MM structures. We conduct full-wave electromagnetic simulations using the measured refractive index values to validate our experiments. The THz-TDS measurements are in excellent agreement with the theoretical predictions verifying the validity of our refractive index measurements. This study aims to support and lead future investigations utilizing standard DLW photoresists for photonic applications in the THz range.