When a carbon suspension is irradiated with a nanosecond laser, chemical reactions at the carbon surface produce bubbles that come together as they oscillate. The driving force of bubble agglomeration is not clearly understood. We report on the effects of carbon concentration and laser fluence on the bubble radius. Inside a flow cell, a stream of carbon suspension (d = 217 nm) is confined by a cylindrical flow of water. The stream is irradiated with 10 ns pulses of a Q-switched Nd:YAG laser at 1064 nm. A diode laser at 532 nm illuminates the cell at an angle. The intensity of the scattered radiation fluctuates as the bubbles oscillate. The resonant frequency of the bubbles is related to their equilibrium radius by Minnaert . As the carbon concentration is decreased from 1011 particles/cm3 to 105 particles/cm3, the bubble radius decreases as a root function. The bubbles agglomerate even at very low concentrations. As the laser fluence is decreased from 2.5 J/cm2, the bubble radius decreases as a linear function, until the bubbles disappeared at 0.5 J/cm2. The sudden change indicates that the bubbles mainly consist of gases from chemical reactions. Meanwhile, that the bubbles stop growing soon after irradiation suggests that the driving force of bubble agglomeration is transient. Further investigations are needed to account for the observed relations.
Kim, Changhae A.,
"Laser-induced formation and agglomeration of microbubbles in carbon suspensions"
Summer Research Symposium.
Brown Digital Repository. Brown University Library.
Each year, Brown University showcases the research of its undergraduates at the Summer Research Symposium. More than half of the student-researchers are UTRA recipients, while others receive funding from a variety of Brown-administered and national programs and fellowships and go …