Study on wavelength- and intensity-dependent ultrafast electron response of 3C-SiC to femtosecond laser irradiation using first-principles calculations

Understanding wavelength-dependent electron excitation and energy deposition is essential for clarifying the early stage surface electronic response of 3C-SiC during femtosecond laser processing, but remains poorly understood. In this work, time-dependent density functional theory (TDDFT) is used to study 3C-SiC with femtosecond laser pulses at 13.5, 400, and 1030 nm over a wide intensity range, clarifying how ultrafast electronic excitation may influence the early stage surface electronic response of 3C-SiC. Under 13.5 nm irradiation, the response is dominated by direct high energy interband excitation, causing smooth current evolution and harmonic spectra dominated by the fundamental component. Under 400 and 1030 nm irradiation, increasing intensity induces strong current modulation and spectral broadening, indicating a transition from weak to strong field nonlinear response. Excited electrons and absorbed energies increase with intensity, with weak field scaling reflecting distinct excitation pathways. At 1 × 10¹³ W/cm², 400 and 1030 nm pulses induce pronounced charge redistribution and drive the excited electron density to ∼10²¹ cm⁻³, whereas 13.5 nm requires 1 × 10¹⁴ W/cm². These findings show that medium- and long-wavelength femtosecond lasers more readily drive 3C-SiC toward a high density nonequilibrium electronic regime, suggesting favorable electronic precursor conditions for subsequent transient surface destabilization and electron-lattice energy transfer.