A Simulation Study of Plasmonic Substrate for In-Process Measurement of Refractive Index in Nano-Stereolithography

Abstract

Functional surfaces are in demand for recent value-added products. Stereolithography based on evanescent light has been proposed as a technique to fabricate surface nanostructures, but some fabrication error sources must be addressed. In-process measurement is an essential solution to improve the fabrication performance. For in-process measurement in stereolithography, the refractive index of resin is an inherent parameter for product and condition monitoring. This study proposes the in-process measurement of the refractive index of resin based on surface plasmon resonance (SPR). The optical phase response at SPR is highly sensitive to changes in the refractive index of resin but has a narrow sensing range. Therefore, we propose a substrate with a tunable sensing range using lanthanum-modified lead zirconate titanate (PLZT). The structural design was considered using numerical simulation. The SPR conditions were calculated with regard to thickness combinations of PLZT and metal (Ag) films. Depending on these combinations, a sensing range can be tuned on the order of 10^-3 to 10^-4 RIU with a sensitivity of 10⁶ rad/RIU. However, to realize these performances, the manufacturing accuracy of Ag thin films must be better than 0.1 nm.