In this paper, we study nanostructure-covered laser induced periodic surface structures (NC-LIPSSs) on metals produced by femtosecond laser pulses incident at various angles. For the first time, we show that the dependence of NC-LIPSS period on the incident beam angle deviates significantly from that of regular LIPSSs studied previously using longer laser pulses. Our study shows that this deviation is due to the nanostructures on LIPSSs that can be explained by the Maxwell–Garnett theory of effective media.

Significance: Dynamics of positively and negatively charged carriers at surfaces and interfaces plays a fundamental role in a myriad of phenomena, including those involved in the catalysis of chemical reactions and the efficacy of nanoscale devices. However, the visualization of such dynamics in space and time is a nontrivial task. In this contribution we report the methodology for mapping the behavior of such carriers in the semiconductor material GaAs and in two regimes of optical and electron excitation. The technique, which is capable of providing femtosecond temporal resolution and nanometer spatial resolution, has the potential of unraveling phenomena in many other materials and in relating their nature to the electronic structure of matter.

We perform a comparison study on femtosecond laser-induced nanostructures on three noble metals, Cu, Ag, and Au. Under identical experimental conditions, the three metals each gain a different amount of surface area increase resulting from nanostructuring. We show that the different surface area increase from nanostructuring directly relates to the competition of two ultrafast processes, electron-phonon coupling and hot electron diffusion, following femtosecond laser heating of metals.

Through femtosecond laser irradiation, we produce in this work a unique type of surface nanostructure on Al that have enhanced absorption at UV and visible but a relatively small emissivity in infrared. By integrating this laser-treated Al to a solar-driven thermoelectric generator, we show that the thermoelectric generator integrated with the femtosecond laser-treated Al foil generates a significantly higher power than the ones without. Our study shows that our technique can dramatically enhance the efficiency of solar-driven thermoelectric devices that may lead to a leap forward in solar energy harnessing.

In this paper, through femtosecond laser pulse irradiation with various polarizations and incident angles, we create arrays of nanostructure-covered conical microstructures (NC-CMs) on Ni. We show that the shape of CMs depends significantly on the polarization and incident angle of the laser beam, and find that the size of nanostructures is distributed asymmetrically on the CMs at off normal incidence. We suggest that nonuniform energy deposition owing to the polarization and the incident angle of laser beam plays an important role in the asymmetric nanostructure distribution and shape of CMs on Ni.

In this paper, we find that the resonant angle of surface plasmons (SPs) excited on a unique type of nanostructure-covered laser-induced periodic surface structure (NC-LIPSS) on platinum can be significantly different from the calculated value based on regular periodic grooves. We believe that this SP resonant angle shift is caused by an increase in the real part of the effective refractive index at the air-metal interface. We also find that the excitation of SPs can significantly enhance photoelectron emission on NC-LIPSSs.