Controlled periodicities of ladder-like structures via femtosecond laser of wavelength from 400 nm to 2200 nm

Abstract

A special type of femtosecond laser-induced periodic surface structures (LIPSS) combined of low spatial frequency LIPSS (LSFL) and high spatial frequency LIPSS (HSFL) are fabricated simultaneously on a stainless-steel surface. These LSFL and embedded HSFL are oriented orthogonal to each other and appear like a ladder-like structure. The periodicity of these structures is systematically controlled by varying the wavelength covering a broad range from 400 nm to 2200 nm. This work demonstrates that the LSFL periodicities can be varied from λ/1.7 to λ/4.7 with the increase in wavelength. We demonstrated the control of HSFL periodicities is possible anywhere from 44 nm to 95 nm (λ/8 to λ/30). Our results show that the LSFL periodicities vary linearly with wavelengths up to 1500 nm. However, at higher wavelengths, the LSFL periodicities cannot increase beyond a maximum limit, suggesting some possible constraints in forming surface plasmon mode frequencies. Similar behavior is observed in the formation of HSFL periodicities with wavelength variation, suggesting that the embedded HSFL periodicities depend on the primary LSFL formations. These new experimental insights will help to understand several existing theories or develop new theoretical models that describe the formation of the LIPSS. We demonstrated the fabrication of controlled ladder-like structures with LSFL spatial periodicity from 240 nm to 780 nm on stainless steel surfaces. The desired periodic structures can be printed on any large area, with a plethora of applications in science and industry.