Capillary Nylon 6 polymer material produced by femtosecond laser processing.

A wicking Nylon 6 polymer material was produced through surface structuring by a direct femtosecond laser nano/microstructuring approach. The produced wicking structure is an array of parallel microgrooves, the surface of which is textured with irregular nanostructures and fine microstructures. High-speed imaging of water spreading vertically uphill against the gravity discloses a series of capillary flow regimes with h ∝ t, h ∝ t1/2, and h ∝ t1/3 scaling laws, where h is the height of capillary rise and t is the time. In the initial stage, the capillary flow occurs with a single front, from which at a certain time a precursor front forms and advances ahead of the main one. Our study shows that the onset of the precursor front occurs in h ∝ t flow regime. The created material exhibits excellent wicking properties and may find applications in various technologically important areas.

Antireflection effect of femtosecond laser-induced periodic surface structures on silicon.

Following direct femtosecond laser pulse irradiation, we produce a unique grating structure over a large area superimposed by finer nanostructures on a silicon wafer. We study, for the first time, the antireflection effect of this femtosecond laser-induced periodic surface structures (FLIPSSs) in the wavelength range of 250 - 2500 nm. Our study shows that the FLIPSSs suppress both the total hemispherical and specular polarized reflectance of silicon surface significantly over the entire studied wavelength range. The total polarized reflectance of the processed surface is reduced by a factor of about 3.5 in the visible and 7 in the UV compared to an untreated sample. The antireflection effect of the FLIPSS surface is broadband and the suppression stays to the longest wavelength (2500 nm) studied here although the antireflection effect in the infrared is weaker than in the visible. Our FLIPSS structures are free of chemical contamination, highly durable, and easily controllable in size.

Enhanced efficiency of solar-driven thermoelectric generator with femtosecond laser-textured 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.

Laser turns silicon superwicking.

Using high-intensity femtosecond laser pulses, we create a novel surface pattern that transforms regular silicon to superwicking. Due to the created surface structure, water sprints vertically uphill in a gravity defying way. Our study of the liquid motion shows that the fast self-propelling motion of water is due to a supercapillary effect from the surface structures we created. The wicking dynamics in the produced surface structure is found to follow the classical square root of time dependence.

Brighter light sources from black metal: significant increase in emission efficiency of incandescent light sources.

By applying the femtosecond laser blackening technique directly to a tungsten incandescent lamp filament, we dramatically brighten the tungsten lamp and enhance its emission efficiency to approach 100%. A comparison study of emission and absorption for the structured metal surfaces shows that Kirchhoff's law is applicable for the black metal. Furthermore, we demonstrate that we can even obtain partially polarized light as well as control the spectral range of the optimal light emission from the laser-blackened tungsten lamp.

Femtosecond laser nanostructuring of metals.

In this paper, we report on various nanostructures produced through direct surface modification on metals using femtosecond laser pulses. We show, for the first time, that these nanosctructures are natural consequence following femtosecond laser ablation. The optimal conditions for producing various nanostructures are determined.

Enhanced energy coupling in femtosecond laser-metal interactions at high intensities.

It is commonly believed that thermal energy remaining in a target is negligible following femtosecond laser ablation. In contrast to this belief, however, we observe a significant enhancement in thermal energy retained in a target following single-pulse ablation. Ambient gas plasmas produced near the sample surface are shown to play a key role in the enhanced residual energy coupling. Our study reveals, for the first time, an enhanced energy coupling in single-shot high-intensity femtosecond laser-metal interactions and provides new guidelines for a broad range of technological applications.