Optical refractometry using lensless holography and autofocusing

Conventional optical refractometry methods are often limited by a narrow measurement range, complex hardware, or relatively high cost. Here, we present a novel refractometry method to measure the bulk refractive index (RI) of materials (including solids and liquids) using lensless holographic on-chip imaging and autofocusing, which is simple, cost-effective, and has a large RI measurement range. As a proof of concept, two compact prototypes were built to measure the RIs of solid materials and liquids, respectively, and they were tested by measuring the RIs of a ZnSe plate and a microscopy immersion oil. Experimental results show that our devices have an average accuracy of similar to 3 x 10(-4) RI unit (RIU) with an estimated precision of similar to 3 x 10(-3) RIU for solids; and an average accuracy of similar to 1 x 10(-4) RIU with an estimated precision of similar to 3 x 10(-4) RIU for liquids. We believe that this cost-effective and portable RI measurement platform holds promise to be used in laboratory and industrial settings. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement