Formation of 100-nm periodic structures on a titanium surface by exploiting the oxidation and third harmonic generation induced by femtosecond laser pulses

Abstract

Periodic surface structures with periods as small as about one-tenth of the irradiating femtosecond (fs) laser light wavelength were created on the surface of a titanium (Ti) foil by exploiting laser-induced oxidation and third harmonic generation (THG). They were achieved by using 100-fs laser pulses with a repetition rate of 1 kHz and a wavelength ranging from 1.4 to 2.2 μm. It was revealed that an extremely thin TixOy layer was formed on the surface of the Ti foil after irradiating fs laser light with a fluence smaller than the ablation threshold of Ti, leading to a significant enhancement in THG which may exceed the ablation threshold of TixOy. As compared with Ti, the maximum efficacy factor for TixOy appears at a larger normalized wavevector in the direction perpendicular to the polarization of the fs laser light. As a result, the THG-dominated laser ablation of TixOy induces 100-nm periodic structures parallel to the polarization of the fs laser light. The depth of the periodic structures was found to be ~10 nm by atomic force microscopy and the formation of the thin TixOy layer was verified by energy dispersive X-ray spectroscopy.

Laser-induced periodic surface structures on titanium upon single- and two-color femtosecond double-pulse irradiation

“…In that latter reference, an involvement of superficial laser-induced oxidation processes in the formation of HSFL on titanium was proposed. Recently, this hypothesis was further supported in fs-laser third harmonic generation experiments during HSFL formation [34].…”

Liquid Gallium Nanospheres Emitting White Light

“…In Figure b, efficient SHG was observed in a Ga NS placed on a glass substrate where there are no plasmonic hot spots. Since the liquid Ga core is expected to give weak SHG, the efficient SHG might come from the Ga 2 O 3 shell which is a transparent semiconductor in the visible light spectrum, similar to the efficient SHG commonly observed in ZnO and TiO 2 nanoparticles or nanostructures …”

Nanograting formation on metals in air with interfering femtosecond laser pulses

“…7,8,[18][19][20][21][22][23][24][25][26][27][28] For the SUS and Ti concerned, the surfaces are covered mainly with a thin layer of Cr 2 O 3 33 and TiO 2 , 23 respectively. The native oxide layer is a few to several nanometers in thickness, which would be further developed in air with the local-temperature increase due to irradiation of intense fs laser pulses.…”