Diffusive dynamics of Brownian nanoparticles in a flashing optical field

We experimentally studied the diffusive dynamics of polystyrene nanoparticles in a flashing optical field using coaxial differential dynamic microscopy. When using a chopper to generate a periodic optical field from a semiconductor laser, we observed the oscillatory motion, which reduced the effective diffusion coefficient of the nanoparticles, making it smaller than that in a continuous optical field (reaching a minimum at a fixed frequency of 2400 Hz). Moreover, the diffusion of the nanoparticles slowed as the laser power increased in the flashing optical field. Our experimental results not only facilitated our understanding of the diffusion of nanoparticles in complex optical fields but also paved the way for potential applications in optical micromanipulation and atom cooling.