Optical fiber-based nanoindenter featuring automated measurement

Nanoindentation is a widely used technique for localized mechanical characterization at the micro- and nanoscale, where measurement accuracy critically depends on high-resolution sensing and signal readout mechanisms. In this work, we present an improved fiber-optic nanomechanical probe (FONP) fabricated by femtosecond laser two-photon polymerization and develop a dedicated fiber-optic nanoindentation system specifically designed for automated measurements. The enhanced FONP employs Fabry-Pérot interferometric optical readout and incorporates an optical shielding layer that ensures spectral stability during surface approach without requiring a gold coating, maintaining a cross-correlation coefficient of 1 with the reference spectrum. Using the developed system, we investigate the time-dependent mechanical evolution of onion outer epidermal cells during natural dehydration, revealing a clear increase in Young's modulus. In addition, automated array-based Young's modulus mapping of polydimethylsiloxane (PDMS) samples shows strong agreement with a commercial nanoindenter, with deviations within 10%. These results demonstrate the accuracy, stability, and automation capability of the proposed fiber-optic interferometric nanoindentation system, highlighting its potential for compact and robust nanomechanical characterization.