Coupled thermal–optical–structural dynamics enable nonlinear limiting in mid-infrared VO₂/SiO₂ films

Here, we report a VO₂/SiO₂ heterostructure that exhibits self-regulated optical limiting under continuous-wave (CW) excitation at 3.8 μm. In this system, the optical transmission, thermal evolution, and structural phase transition are strongly coupled.

Through real-time dual-band measurements, we uncover a characteristic four-stage dynamical pathway, comprising a thermal-inertia response, a threshold-activated insulator–metal transition (IMT), a saturated optical-limiting regime, and a spontaneous cooling recovery. Importantly, we identify that at the limiting threshold, the thermal diffusion pathway shifts from predominantly lateral heat accumulation to vertically focused conduction.