WISPFI Experiment: Prototype Development

Axions and axion-like particles (ALPs) are well-motivated dark matter (DM) candidates that couple to photons in external magnetic fields. The parameter space around mₐ ~ 50~μeV remains largely unexplored by haloscope experiments. We present the first prototype of WISP Searches on a Fiber Interferometer (WISPFI), a table-top, model-independent scheme based on resonant photon-axion conversion in a hollow-core photonic crystal fiber (HC-PCF) integrated into a Mach-Zehnder interferometer (MZI). Operating near a dark fringe with active phase-locking, combined with amplitude modulation, the interferometer converts axion-induced photon disappearance into a measurable signal. A 2 W, 1550 nm laser is coupled into a 1 m-long HC-PCF placed inside a 2 T permanent magnet array, probing a fixed axion mass of mₐ 49~μeV with a projected sensitivity of gaγγ 1.3 × 10⁻⁹~GeV⁻¹ for a measurement time of 30 days. Future upgrades, including pressure tuning of the effective refractive index and implementation of a Fabry-Pérot cavity, could extend the accessible mass range and improve sensitivity, establishing WISPFI as a scalable platform to explore previously inaccessible regions of the axion parameter space.