Interaction of Ultrafast Laser Pulses With Nanostructure Surfaces

Abstract

The interaction of ultrafast laser pulses with surfaces on the nanoscale paves the way for various innovative technologies in spectroscopy, photovoltaics, photocatalysis, or medicine, to mention only a few. The basic mechanisms, however, are still the subject of intense research. We take a closer look at this topic from different viewpoints. The first aspect is the enhancement of the efficiency of physical or chemical processes by producing local field maxima and resonances at top-down or bottom-up structured surfaces. A further aspect is the dynamic change of optical properties by inducing free carriers and plasmons. Last but not least, permanent nanostructures can be obtained as a result of nano-feedback and self-organization. In high-energy laser physics, all three aspects play a role at once. Therefore, particular attention will be paid to this emerging field.

Feedback-Driven Plasmonic-Thermal Route to Femtosecond-Laser-Induced Periodic Surface Structures in Silicon Indicated by Pump-Probe Scattering and Diffraction

“…The relevance of accumulation effects is underlined by the pulse number dependence [74]. The model of LIPSS formation can be described by three regimes [20]: (I) plasmon regime (free electron generation, electron heating), (II) structure regime (nonthermal melting, electron-lattice heating), and (III) stabilization regime (thermal melting, ablation, resolidification), which dominate the dynamics at different time scales (0-250 fs, 250-100 ps, 100 ps-2 ns). In all regimes, the feedback enhances with increasing pulse number, which leads to more distinct diffraction patterns.…”

“…For example, dynamic polarization flip effects near the plasmon resonance [18] or intrinsic frequency conversion [19] can strongly modify the orientation of the ripples. The optical feedback directly modulates the rates and efficiency of absorption and ablation by field enhancement, resonance effects, and light-redistribution [20,21]. Grating-like patterns consisting of alternating melted and solid zones were observed, which are closely related to the length scales of different optical and thermodynamically mechanisms [22].…”

“…Here, we report on complementary femtosecond-laser experiments by (i) exploring the very early process stages by analyzing the microscale structural changes with respect to the spatial frequency evolution and the convergence of the angular characteristics of micro-craters, and (ii) analyzing the structural evolution by pump-probe scattering and diffraction measurements [20,51].The micro-crater evolution is investigated following an alternative strategy targeting self-organized spatial frequency and angular domain parameters simultaneously. Moreover, pump-probe measurements are performed with a femtosecond-range temporal resolution and two-dimensional, highly sensitive detectors.…”