Axial compression-assisted arc discharge fabrication of SNAP microcavities

We report an arc-discharge technique for fabricating surface nanoscale axial photonics (SNAP) microcavities in hollow-core fibers (HCF). Axial compression applied during the discharge counters capillary collapse, allowing sub-nanometer control of the microcavity profile. A coupled physical model couples viscous capillary-flow dynamics with post-cooling refractive-index changes from densification and photoelasticity, mapping both onto the SNAP cutoff wavelength via perturbation theory. With coupling parameters calibrated within their physically plausible ranges, the model reproduces the slope and intercept of the measured apparent-radius response across the full push-velocity range, with quantitative predictions in the collapse regime confirmed by additional low-velocity measurements. These results extend arc-discharge SNAP fabrication into a high-energy regime previously limited by collapse, and provide quantitative predictive control of the microcavity profile for HCF-SNAP devices in microfluidics and photonics.