**Acknowledgements**

White-light emission was observed during the reaction from a binchotan block in water. As shown in **Figure 12a**, a broad spectrum over the visible range is apparent on both sides of the 532 nm excitation wavelength, across the penetration gap of the super notch filter, in water (solid red line), or in 50% ethanol aqueous solution (broken black line). No emission was observed from the water itself. The relatively narrow peaks at 650 and 630 nm are attributed to the Raman scattering lines at 3400 and 2930 cm−1, because the peak positions changed following excitation wavelengths. There was no indication of the plasma emission from neutral/ionized atoms typically observed in LIBS. The Raman scattering lines are assigned to vibration of the O─H stretch mode under a hydrogen bond and Raman-active C─H vibrational

280 Applications of Laser Ablation - Thin Film Deposition, Nanomaterial Synthesis and Surface Modification

The white-light emission appeared only above a threshold excitation energy density. As shown in **Figure 12b**, the emission intensity at 470 nm increased nonlinearly in accordance with variations in the incident laser fluence. The threshold at 50 mJ/cm2 was identical for both specimens in the water (red solid circles) and 50% ethanol aqueous solution (blue open circles). Note that the threshold for the appearance of the white light is coincident with the threshold for hydrogen generation (**Figure 7**). Therefore, it is reasonable to consider that the white-light emission is a simultaneous product of the hydrogen generation reaction. With a carbon electrode (99.9%), one fifth of emission intensity was observed above similar threshold

Spectral shape at shorter than 650 nm is well reproduced by Planck's law at a temperature 3860 K. Furthermore, time-resolved spectrum revealed a repetitive spectral change due to the temperature variation in the duration of laser pulse [36]. From these experimental facts, it was confirmed that the laser pulse supplies heat energy through optical absorption, and the whitelight emission can reasonably be attributed to blackbody radiation from the irradiated site. It implies that hydrogen generation induced by laser irradiation proceeds similarly to classical coal gasification, which features reactions at HPHT. Finally, it was concluded that the hydrogen generation induced by the laser pulse irradiation occurs under high-pressure and high-

The extended abilities of laser ablation in liquid phase were presented through two topics. The first is nanoparticle formation of an organic material, which produced a colloidal solution of a small organic material. In a yellow pigment QQ, a systematic blueshift of the absorption peak corresponding to the decrease of particle size in colloidal solutions was discoverd. This dependence provides an easy estimation method of the averaged diameter of the ensemble that will be applied to organic devices by a wet process. Furthermore, the population of an excited triplet state through optical excitation might be one guideline to select and synthesize

The second is hydrogen gas generation from solid carbon in water by a photochemical reaction. Even under a lower energy irradiation that achieves no plasma state, the irradiated site

excitation energy, and the generated gas volume was also small.

modes of ethanol [48].

temperature conditions.

materials for laser fragmentation.

**5. Conclusion**

This work was supported by the Original Research Support Project of Wakayama University, 2011–2012. All experiments presented here were done with students of master's and bachelor's courses in Wakayama University from 2011 to 2016. TEM observations were performed under the Inter-university Cooperative Research Program of the Institute for Materials Research, Tohoku University. This publishing project was supported by the Kansai Research Foundation for technology promotion (2016P001).
