Sub-wavelength Uniform Periodic Surface Structures Induced by Low Femtosecond Laser Fluence on Silicon with Optical Glass Covering

摘要

Thus far, femtosecond laser-induced periodic surface structures (LIPSS) on the surfaces of solid materials have been studied in air and liquids. However, few studies have investigated LIPSS for-mation on a solid surface through a solid transparent medium material. In the present study, LIPSS are formed on a silicon wafer surface covered with optical glass (glass environment) and compared with those formed in air. The periodicities of low and high spatial frequency LIPSS (LSFL and HSFL, respectively) formed in the two environments are 650 and 200 nm, respectively. In glass en-vironment, LSFL can be induced by laser fluence of 410 mJ/cm2, which is much lower than that of 570 J/cm2 used in air. Moreover, LIPSS formed in glass environment are rough, contradicting a pre-vious report on LIPSS formation in liquid environments. The possible mechanisms forming the dif-ferent structures in the two environments are discussed.