Sub-wavelength ripples in fused silica after irradiation of the solid/liquid interface withultrashort laser pulses

Abstract

Laser-induced backside wet etching (LIBWE) is performed using ultrashort 248 nm laserpulses with a pulse duration of 600 fs to obtain sub-wavelength laser-induced periodicsurface structures (LIPSS) on the back surface of fused silica which is in contact with a0.5 mol l−1 solution of pyrene in toluene. The LIPSS are strictly one-dimensionalpatterns, oriented parallel to the polarization of the laser radiation, andhave a constant period of about 140 nm at all applied laser fluences(0.33–0.84 J cm−2) and pulse numbers (50–1000 pulses). The LIPSS amplitude varies due tothe inhomogeneous fluence in the laser spot. The LIPSS are examined withscanning electron microscopy (SEM) and atomic force microscopy (AFM). Theirpower spectral density (PSD) distribution is analysed at a measured area of10 µm × 10 µm. The good agreement of the measured and calculated LIPSS periods stronglysupports a mechanism based on the interference of surface-scattered and incidentwaves.