Min-Cheng Zhong, Zi-Qiang Wang, and Yin-Mei Li
We present an experimental study on oscillation of absorbing particles at the water-air interface. The oscillation is induced by laser tweezers, which are generated with a high numerical aperture objective. When the laser beam is tightly focused at the water-air interface, the optical gradient force attracts the particles to the spot center, and the laser heating of particles results in a strong thermal gradient that drives the particles to leave the spot center. Under the action of thermal and optical gradient force together, the absorbing particles oscillate at the water-air interface.