The transient Pauli blocking effect offers a promising route for achieving ultrafast optical switching in semiconductors, enabling a rapid switching from an initially opaque state to a relatively transparent state upon photoexcitation. Herein, we demonstrate broadband ultrafast optical switching in degenerate InN thin films, spanning the visible to near-infrared spectral range, using pump-probe transient transmittance measurements. To elucidate the underlying physical mechanism, we perform probe-energy-resolved analysis for ultrafast dynamics, and we develop a theoretical model based on a quasiequilibrium Fermi-Dirac distribution. The model successfully captures the experimental transients and yields an electron-phonon coupling constant of $1.0\times {10}^{17}{\mathrm{W}/\mathrm{m}}^3\mathrm{K}$, along with an electronic specific-heat coefficient ranging from 1.52 to $2.02\mathrm{mJ}/\mathrm{mol}{\mathrm{K}}^2$, which allows direct prediction of the spectral switching window. Notably, we demonstrate that the Pauli blocking effect can be induced solely by a laser-excitation-driven rise in electronic temperature, without requiring significant carrier injection into the conduction band in degenerate semiconductors. These findings offer new insights for designing ultrafast optical modulators, shutters, and photonic devices for next-generation communication and computing technologies.

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• Electronic structure
• First-principles calculations
• Nonlinear optical materials
• Optical transient phenomena
• Semiconductors
• Thin films
• Transient absorption spectroscopy
• Ultrafast femtosecond pump probe