Femtosecond laser micromachining of TiO2 crystal surface for robust optical catalyst

Abstract

The two-photon laser ablation of TiO2 photocatalyst using intense ultrashort titanium sapphire laser was investigated experimentally and theoretically aiming at the enhancement of photocatalytic reaction. The black surfacing of the TiO2 photocatalyst crystal was successfully achieved by drilling a large number of conical microholes with two-photon laser ablation. The ablated surface has a roughness of submicrometer order, and no heat-affected zone was observed. The simple equation is developed to explain two-photon ablation process of the TiO2 photocatalyst and the dependence of the ablation characteristic on the pulse duration. A maximization procedure of the ablated surface area is achieved and the optimization of laser parameters is shown for dense integration of ablated conical holes to increase the surface area.

Fundamentals of energy cascade during ultrashort laser-material interactions (Invited Paper)

“…On the other hand, from 4.4 J/cm 2 to 18.7 J/cm 2 , the ablation depth increases relatively slowly. The flat slope in ablation depth after a steep slope was also observed in other materials before [41,42]. Figure 6.…”

Energy transport and material removal in wide bandgap materials by a femtosecond laser pulse

“…Hence, in applications it may need to choose an ''optimum'' fluence in order to achieve ablation quality and high material removal rate for a specific material. The phenomenon of a steep-increase followed by a slow-increase in ablation depth as a function of fluence was also observed in other materials [39,40]. Another important parameter for laser ablation is the pulse duration.…”

Maskless fabrication of concave microlens arrays on silica glasses by a femtosecond-laser-enhanced local wet etching method

“…Initially, ablation-induced craters with diameters of a few micrometers are induced on polished silica glass chips (10 × 10 × 1 mm 3 , China Daheng Group Inc., GCL-1202) using a 30-fs and 800-nm laser pulses at a repetition of 1 kHz (the laser source is a Ti: sapphire pulsed laser oscillator-amplifier system). The femtosecond laser, owing to its advantages of negligible thermal and shockwave-induced damages [19], when focused by an objective lens (NA = 0.5), can easily induce craters on transparent materials such as silica glasses without melting-ejections and cracks which will impact on the morphology of the fabricated microlenses. The diameter of the focal spot is about 1.4 µm (1/e).…”