Spatiotemporal measurement of non-equilibrium density in switching arcs using two-color quadri-wave lateral shearing interferometric wavefront sensor

Addressing the challenge of precise plasma density diagnostics in switching arcs, this study proposes a novel measurement approach based on two-color quadri-wave lateral shearing interferometry wavefront sensing. The developed 532/1064 nm dual-pulse laser system enables simultaneous high spatiotemporal resolution measurements of both electron and neutral particle densities in air arcs within a model circuit breaker. Experimental results show that during the arcing phase, the measured electron density in the arc core agrees well with local thermodynamic equilibrium (LTE) assumptions. In the post-arc free recovery phase without gas flow cooling, thermal inertia causes slow thermal recovery, with a 1 ms delayed rupture phenomenon observed in residual electron density channels. The measured density distribution during the decay process deviates from LTE predictions, demonstrating the need for non-equilibrium modeling. Compared with conventional interferometry, this method maintains high spatial resolution while offering superior advantages including strong anti-interference capability and simplified optical configuration through its common-path design. The method can be extended to arc density diagnostics in SF₆ and its eco-friendly alternative gases, providing crucial experimental evidence for understanding non-equilibrium arc-quenching mechanisms and supporting the development of next-generation high-voltage switching devices.