Effects of optical forces on the transmission of magnetic fluids investigated by Z-scan technique

Abstract

The dependence of the transmission behavior of magnetic fluids on the incident power density of a laser beam is investigated and the conventional Z-scan technique is employed to continuously vary the optical forces induced by the laser beam. We calculate the optical forces exerted on magnetic nanoparticles and compare them with those for gold and silica nanoparticles. It is found that the optical forces for magnetic nanoparticles are comparable to those for gold nanoparticles. In addition, the calculation results show that the absorption force is dominant at low incident power densities while the gradient and scattering forces become significant at high incident power densities when the clustering of magnetic nanoparticles occurs. In Z-scan experiments, it is observed that the evolution of the Z-scan trace of a magnetic fluid with increasing incident power density cannot be explained only by the nonlinear absorption of the magnetic fluid induced by the thermal diffusion of magnetic nanoparticles. Instead, it indicates that the optical forces exerted on magnetic particles play an important role in determining the transmission of the magnetic fluid. This point is verified by comparing the Z-scan traces for magnetic fluids with different particle concentrations and carrier liquids. The effects of optical forces on the transmission of the magnetic fluids are also manifested in the morphology change of the magnetic fluids.