Digital Holography Interferometry for Refractive Index Characterization and Temperature Mapping of Aqueous Solutions at Supercooled Temperatures

Abstract

Cryopreservation of biological matter nigh-universally requires cooling organic aqueous solutions through the metastable supercooled temperature regime. However, for many solutions of interest, very little thermophysical data exists at these temperatures, hampering the meaningful design of cryopreservation protocols or interrogation of cryopreservation processes. Digital holography interferometry (DHI) has recently emerged as a promising technique for measuring and characterizing the physical properties of liquids. Herein, DHI is proposed as a thermal imaging and characterization tool capable of measuring optical properties, such as temperature-dependent refractive index, and providing high-resolution two-dimensional (2D) visualization of temperature distribution in the supercooling regime. This approach overcomes the limitations of traditional techniques such as thermocouples and thermal cameras. This work describes a DHI platform instrumented with a custom thermoelectric supercooling apparatus, demonstrates 2D temperature mapping in the supercooled regime, and measures the refractive index of water, 10% dimethyl sulfoxide (DMSO), and 49% DMSO solutions at sub-273 K temperatures. Overall, DHI is demonstrated as a noninvasive optical tool with high resolution for studying supercooled liquids, potentially enhancing cryopreservation protocols and providing new thermo-optical information on cryoprotective agents at sub-273 K temperatures.