Advanced Laser Science Research Section

概要

Laser is a versatile technique to probe various
dynamics and also fabricate various devices. This
year we have developed a few different techniques to
probe the electrochemical processes during hydrogen
evolution, fabricate the functional metal surfaces, and
modify the size and shape of nanoparticles for the
utilization toward green energy.
2. Influence of liquid viscosity and temperature on
the morphologies of laser-induced microstructures
Laser materials processing is a useful technique
to fabricate micro/nanostructures on the material
surface, and performed not only in air but also in liquids in some cases to fabricate desired surface morphologies. How and how much the property of the
liquid influences the surface morphology of the laser-irradiated target is not yet completely understood.
This is particularly true in terms of liquid viscosity.
To clarify the role of liquid viscosity in laser materials processing we undertake the study to ablate the
metal target in different liquids at different temperatures and compare the morphology of the ablation
crater. The liquids we employ in this study are water
(H2O), ethanol (ET), ethylene glycol (EG), and glycerol (GOL) at room temperature (RT), and additionally EG and GOL at 100 °C, since their viscosities
significantly change at different temperatures. Representative results with Ni targets are shown in Fig. 1.
In Fig. 1(a) we clearly see the confinement effects.
From Fig. 1(b), we notice that the diameter of the
crater in each liquid linearly increases with laser fluence, and at a given laser fluence, the crater diameters are air < ET < water < EG at 100 °C < EG at RT
< GOL at 100 °C < GOL at RT. Similar is true for
the volume (Fig. 1(c)). To explain the different ablation efficiencies in different liquids at different temperatures we consider the pressure exerted to the target under the confined geometry by laser-induced
plasma, and estimate the plasma-induced recoil
pressure. ...