Abstract
Creation of patterns and structures on surfaces at the micro- and nano-scale is a field of growing interest. Direct femtosecond laser surface structuring with a Gaussian-like beam intensity profile has already distinguished itself as a versatile method to fabricate surface structures on metals and semiconductors. Here we present an approach for direct femtosecond laser surface structuring based on optical vortex beams with different spatial distributions of the state of polarization, which are easily generated by means of a q-plate. The different states of an optical vortex beam carrying an orbital angular momentum ℓ = ±1 are used to demonstrate the fabrication of various regular surface patterns on silicon. The spatial features of the regular rippled and grooved surface structures are correlated with the state of polarization of the optical vortex beam. Moreover, scattered surface wave theory approach is used to rationalize the dependence of the surface structures on the local state of the laser beam characteristics (polarization and fluence). The present approach can be further extended to fabricate even more complex and unconventional surface structures by exploiting the possibilities offered by femtosecond optical vector fields.
Highlights
The crucial role of surface morphology in regulating the properties of a surface accounts for the growing interest in laser surface machining of metals, semiconductors and insulators in view of diverse applications based on the properties of the processed solid surfaces
The q-plate (QP) is an optical device based on liquid crystal technology that is capable of generating and manipulating light beams carrying orbital angular momentum (OAM)[18,19]
The state of polarization (SoP) of the optical vortex (OV) beam can be manipulated by means of wave plates whose optical axis is appropriately aligned with respect to the QP optical axis
Summary
The crucial role of surface morphology in regulating the properties of a surface accounts for the growing interest in laser surface machining of metals, semiconductors and insulators in view of diverse applications based on the properties of the processed solid surfaces (e.g., optical, mechanical, chemical, biological, wetting, etc.). Complex polarization patterns in a single laser beam can offer the possibility of generating complex surface structures. The possibility to use vector optical fields to directly fabricate surface microstructures is emerging as a fascinating possibility and is proposed as an effective method for vector beams characterization[10,11,12] as well as for unconventional surface structuring[13,14,15,16]. We report on direct fs laser surface structuring using an optical vortex (OV) beam, generated by a q-plate and carrying an orbital angular momentum l = ± 1 (per photon, in units of ħ), with different spatial distributions of its SoP. Numerical simulations based on a scattered surface wave theory are exploited to rationalize the relationship between the local state of the laser beam polarization and fluence and the surface structures
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