High quality nanogratings far beyond diffraction limits on silicon efficiently fabricated using femtosecond laser dual-beam interference direct writing

This study demonstrated a femtosecond laser dual-beam interference direct writing (DBIDW) method for fabricating high-quality nanogratings on silicon. The nanogratings had Λ/2, Λ/3, and Λ/4 periods, with Λ slightly smaller than the laser wavelength. The grating stripes exhibited extremely smooth and straight edges, with an average line edge roughness (LER) of 2.23 nm and a difference in structural orientation angle (DSOA) of 2.3°. The formation mechanism involves interference enhancement inducing nanoplasma formation in periodic stripes, while local asymmetric enhancement by surface plasmons significantly increases light intensity inside the nanogrooves. This method greatly reduces thermal effects and debris deposition, offering significant advantages for high-efficiency, low-cost, large-area nanolithography.