Laser irradiation modulating the acoustic radiation force acting on a liquid ball in a plane progressive wave

We present a theoretical study of the modulation using laser irradiation of an acoustic radiation force (ARF) acting on a liquid ball. The ARFs acting on a laser-irradiated oleic acid (OA) sphere were investigated using a mathematical model and were verified using the finite element method (FEM). It was found that, when the influence of the photoacoustic (PA) effect on the ARF is stronger than that from the acoustic scattering, a negative ARF can be realized. The ARF on a laser-irradiated OA sphere can be greatly modulated by the laser intensity and the phase difference between the plane acoustic wave and the laser beam. There is a region of the phase difference in which a negative ARF can be achieved by changing the laser intensity. In addition, we found that increasing the radius of the OA sphere enhanced the ARF and that a surrounding medium with a higher acoustic impedance enabled a larger negative ARF. Our results may be beneficial to the acoustic manipulation of liquid particles such as biological cells and protein drugs.