Fabrication of homogenous subwavelength grating structures on metallic glass using double-pulsed femtosecond lasers. (November 2020)

• Record Type: Journal Article
• Authors: Lei, Yuhao; Yang, Jianjun; Cong, Cong; Guo, Chunlei
• Is Part Of: Optics and lasers in engineering. Volume 134(2020)
• Publication Date: 2020-11
• Subjects: Femtosecond laser -- Laser-induced periodic surface structures -- Metallic glass; Lasers in engineering -- Periodicals; Optical measurements -- Periodicals; Optics -- Periodicals; Lasers en ingénierie -- Périodiques; Mesures optiques -- Périodiques; Optique -- Périodiques; 621.36605
• DOI: 10.1016/j.optlaseng.2020.106273
• Languages: English
• ISSNs: 0143-8166

Abstract

Highlights: In this work, we demonstrated high-quality uniform periodic microstructures on Fe-based metallic glass using a collinear propagation of two time-delayed femtosecond laser beams that are linearly polarized in different directions. Laser-induced surface structures have been studied extensively for decades, however, most of the structures appear to be regular in a short range but irregular in a long range. In this manuscript, we found that the subwavelength grating structures are highly ordered throughout the entire laser beam spot/ablation area, and they can be robustly extended along the laser scanning direction, which are in sharp contrast to the observations with single-beam femtosecond laser irradiation. Moreover, our experimental results also revealed that the temporal delay between two femtosecond pulses plays an important role in the generation of such long-range regular structures. In theory, we have newly introduced two parameters for quantitative evaluating the structure uniformity through Fourier transform, and the physical mechanisms for the ultra-uniform structure formation were discussed as well. Moreover, the chemical elements shows various removal percentage after laser ablation due to their different diffusion coefficients. Abstract: We report a formation of highly homogenous subwavelength grating structures on the bulk Fe-based metallic glass, using two nondegenerate linear polarization of femtosecond laser pulse sequences at certain temporal delays. In contrast to the previous observations, the well-defined surface structures can take place across the entire laser ablation regions, with the spatial period and the modulation depth of 722 nm and 115 nm, respectively. Through the Fourier transformation analysis, we introduce two parameters to quantitatively evaluate the structure uniformity. The underlying mechanisms are attributed to the surface scattered wave of the second femtosecond laser pulse onto the transient material surface tailored by the first laser pulse. Moreover, different diffusion coefficients of the chemical elements are found responsible for their various removal percentages after laser irradiation.