Superparamagnetic Magnetite Nanoparticle Superstructures for Optical Modulation/Chopping

We experimentally demonstrate proof of concept operation of superparamagnetic magnetite nanoparticles and magnetite−TiO2 peapod superstructures for laser intensity 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 86, 140, and 190 nm is compared with optical modulation with magnetite−TiO2 peapod superstructures of lengths of around 1 μm. The former gave rise to modulations of up to 2 kHz in frequency, a number comparable to that of commercial optical choppers, the latter up to 100 Hz. We also show that particle shape asymmetry and anisotropy enhance optical modulation and that modulation frequency is inversely proportional to the inertia of the particles used.