Analysis of spatially resolved Z-pinch spectra to investigate the nature of "bright spots" Phys. Plasmas 20, 022707 (2013) Two-dimensional space-resolved emission spectroscopy of laser ablation plasma in water J. Appl. Phys. 113, 053302 (2013) Direct evidence of mismatching effect on H emission in laser-induced atmospheric helium gas plasma J. Appl. Phys. 113, 053301 (2013) "Water window" sources: Selection based on the interplay of spectral properties and multilayer reflection bandwidth Appl. Phys. Lett. 102, 041117 (2013) Additional information on Appl. Phys. Lett.

Use of plasma in water for water treatment and medical treatment is growing and raises expectations of finding advanced functions such as an increase of biological compatibility. In the present study with a focus on the variation of oxidation-reduction potential (ORP), relationships between the electrode polarities of plasma in water and the change of water quality such as conductivity, H2O2 concentration, dissolved hydrogen concentration, pH and ORP were revealed. Similar line spectra of radiation at the electrode tip were observed for each case of positive and negative electrode polarity. The emission intensities of OH (309 nm), Hα (656 nm), and OI (777 nm) for the positive discharge were significantly higher than those for the negative one, though the energy consumption during the discharge period of both cases was nearly the same. Positive electrode polarity was found to be more suitable than negative electrode polarity for increasing dissolved hydrogen gas and hydrogen peroxide. The ORP for the positive polarity decreased from 460 to 45 mV and that for the negative polarity decreased from 460 to 183 mV, although the pH and conductivity were not significantly changed.

Abstract. Nanobubbles of less than 400 nm in diameter were formed by plasma in pure water. Pre-breakdown plasma termed streamer discharges, generated gas channels shaped like fine dendritic coral leading to the formation of small bubbles. Nanobubbles were visualized by an optical microscope and measured by dynamic laser scattering. However, it is necessary to verify that these nanobubbles are gas bubbles, not solid, because contamination such as platinum particles and organic compounds from electrode and residue in ultrapure water were also observed. IntroductionMicro-and nano-bubbles have potential applications in many fields such as medical treatment, medicine, food, cosmetic, health care and machines. For example, they have been applied as contrast media for ultrasound diagnosis, media of targeted drug delivery, bubble washing for beauty treatment, homogeneous cream for improvement of taste, micro pore material for creation of new materials, a power source for micro machines and reduction of drag force around submerged objects in water. For these applications, size control and stability of bubbles are required [1].Generally, bubbles grow in supersaturated liquid and shrink in unsaturated liquid due to diffusion through the bubble interface. It is known that nanobubbles of 100 nm in radius disappear within micro second, the disappearance time becoming shorter with smaller bubbles. However, it has been reported that nanobubbles in water exist for several hours, the plausible mechanism of the reduction of the surface tension being due to the existence of nano particles, OH ions and surface-active agents. This reduction of surface tension causes reduction of internal pressure of nanobubbles, leading to long lifetime. In the field of a lot of researches on interfacial water, the existence and lifetime of nanobubbles are still under discussion [2].