  Recently, we demonstrated that the local heating of degassed water can
generate water vapor microbubbles and induce a rapid flow around the bubble.
Although flow generation involves the self-excited oscillation of bubbles at a
local heating point, the conditions under which the bubbles oscillate are not
fully understood. In this study, the dependence of microbubble size and
oscillation frequency on the concentration of non-condensable gas in water was
investigated. A continuous-wave laser beam was focused on a $\beta$-FeSi$_2$
thin film, and water was locally heated using the photothermal conversion
properties of the film. The results showed that the lower the concentration of
non-condensable gas dissolved in water, the smaller the bubble size and the
higher the oscillation frequency. Furthermore, it was found that the bubbles
oscillate when the amount of non-condensable gas absorbed by the bubbles, i.e.,
the bubble size, falls below a specific level. This study can provide a new
understanding of the bubble oscillation mechanism and lead to the development
of fluid control technology using bubbles.
