Plasmonic "pump-probe" method to study semi-transparent nanofluids.

Nanofluids have been increasingly used in a wide range of thermal applications. Although these applications can benefit greatly from investigating the behavior of nanoparticles under different heating scenarios, there is a lack of experiments that can achieve this. To overcome this challenge, an optical "pump-probe"-type experiment is suggested in this paper. In experiments of this type, a set of "pumping" nanoparticles are specifically selected to absorb laser radiation. These particles represent a flexible tool for volumetric heating. A second set of "probing" nanoparticles can be tailored to scatter a separate optical probing signal. This work presents a selection procedure for nanoparticles of both types. The selection procedure is then demonstrated for a specific example where the pump and probe wavelengths are of 980 and 532 nm, respectively. Gold nanorods with diameters of 10 and a length of 58 nm are selected as the "most suitable" absorbing particles, while silver nanospheres with a diameter of 110 nm are selected as the "most suitable" scattering particles. These particles are synthesized and shown to experimentally match the desired optical properties. Overall, this paper proposes and demonstrates an approach by which it is possible to design and fabricate particles for a wide range of optical studies in semi-transparent nanofluids.