Microfabrication using Laser-Induced Bubble (microFLIB) technique was developed as a microfabrication method of a thermoset polymer polydimethylsiloxane (PDMS). The bubble generated on a metal sample in laser ablation in liquid PDMS retains its shape and position for a while. When the laser was scanned along the sample surface in liquid PDMS, connected bubbles were formed like a tunnel and the bubbles are kept their shape and position for a while. After heat treatment, the connected bubbles transferred to a microgroove in cured PDMS. Additionally, it was found that selective metallization by electroless plating is possible to microgroove region. This result suggests that a plasma plume which includes metal particles was generated by laser ablation and the metal particles remain on the polymer to act as seeds for the plating process.

We have observed the phenomena in shingle shot laser ablation in liquid PDMS by high-speed shadowgraph imaging. The expansion process of laser-induced bubble and the formation of fiber-like bridges/membrane between the bubble and the sample surface were observed. The laser-induced bubble was retained its shape and position over a hundred seconds with increasing radius, then, finally floated upwards leaving the fiber-like bridges on the sample. These fiber-like shadows would be polymerized PDMS formed by rapid local heating due to the laser ablation of metal. However, shadowgraph imaging is not enough to understand nanoparticle formation and distribution.

To elucidate these points, we tried to observe photoluminescence from YAG:Ce particles under blue light excitation in single-shot laser ablation of a sintered YAG:Ce in liquid PDMS. YAG: Ce is a yellow-emitting phosphor under blue excitation. Continuous images at 60 fps were recorded. The 1st image obtained at 16 ms shows that the entire bubble has already appeared as a light-emitting region, and it grows until around 200 s after the laser irradiation. The emitting region gathered toward the lower part of the bubble during 200 s to 500 s with increasing size. After 1000 s or later, the bubble started to float upwards while the shell-like emitting region remained where the bubble was located as shown in the 1600 s image. From the photoluminescence observation, we conclude that the inner surface of the bubble is covered with YAG:Ce particles and these particles are contained inside the bubble during its evolution.