| Abstract [eng] |
In recent decades, surface micro- and nanostructuring has emerged as a key technological field for imparting novel functional properties to materials. Among industrially relevant materials, transparent dielectrics are of critical importance; however, their direct processing via conventional lithography is costly and environmentally toxic, while direct laser writing is restricted by the optical diffraction limit. Direct laser interference patterning is highly attractive due to its high throughput and maskless nature. However, spatio-temporal chirp in femtosecond pulses reduces the peak intensity within the processing zone, which, combined with high material damage thresholds, limits the efficiency of this method on transparent media. The aim of this work is to experimentally investigate and evaluate the tendencies and limitations of direct laser interference patterning using ultraviolet femtosecond pulsed beams when forming periodic structures on the surfaces of various dielectrics. During the study, an experimental Talbot interferometer setup was assembled and optimized, utilizing third-harmonic (λ = 343 nm) femtosecond (~300 fs) pulses with an energy of 850 μJ. Experimentally determined material damage thresholds were found to be consistent with theoretical values, proving that spatio-temporal chirp effects were successfully minimized within the optimized configuration. This interferometer setup enabled successful structuring of soda-lime and borosilicate glasses, fused silica, sapphire, and crystalline quartz surfaces, yielding periodic structures with a spatial period of Λ ≈ 750 nm and a depth contrast h ranging from 266–360 nm (corresponding to record-breaking aspect ratios of h/Λ = 0.36–0.48). The results show that the structural depth enhancement of the periodic surface modifications under an increasing number of pulses is limited either by the generation of self-organized nanogratings or by a reduction in the local material damage threshold caused by structural changes from prior pulses. The resulting increase in the absorbed energy density leads to adjacent area melting or a severe Coulomb explosion, which obliterates the pre-recorded periodic structures. Consequently, the selection of optimal processing parameters is non-universal, necessitating the individual identification of processing windows for each material. In this work, such technological processing windows were experimentally demonstrated and characterized for fused silica, crystalline quartz, sapphire, borosilicate glass, and soda-lime glass. The obtained results open up new possibilities for the efficient and stable fabrication of submicrometer optical and microfluidic components, as well as metamaterials, in transparent media. |
