Superparamagnetic Magnetite Nanoparticles for Optical Modulation/Chopping

We demonstrate proof of concept operation of superparamagnetic magnetite nanoparticles and magnetite-TiO$_{2}$ peapod-superstructures for laser intensity optical modulation and chopping. The frequency of the modulation is shown to be twice that of the driving signal and a function of the size of the particles. Specifically, optical modulation with round nanoparticles of sizes 80, 130, 200 nm is compared with optical modulation with magnetite-TiO$_{2}$ peapod-superstructures of sizes of around 1 $\mu$m. The former gave rise to modulations of up to 2 kHz of frequency--a number comparable to that of the commercial optical choppers--, the latter up to 100 Hz. We also show that particle shape asymmetry and anisotropy enhance optical modulation.