Microbubble resonators as scattering-free thermometric micro-spectrometers.

Frigenti G., Cavigli L., Ratto F., Centi S., Farnesi D., Pelli S., Soria S., Nunzi Conti G.
  Giovedì 15/09   09:00 - 13:00   Aula L - Christa Mc Auliffe   VI - Fisica applicata, acceleratori e beni culturali   Presentazione
We report on a proof-of-concept experiment where the absorption spectrum of a nanoparticles (GoldNano Rods, GNRs) suspension is reconstructed through the temperature shifts that the optical absorption induces in a MicroBubble Resonator (MBR). In the presented configuration, the nanoparticles suspension is placed inside of the MBR through a microfluidic circuit, producing maximal thermal contact between the two parts and an extremely compact system ({\approx 40 ${nL}$). High temperature sensitivity ({\approx 10 ${mK}$) is achieved by monitoring the position of the narrow optical resonances of the MBR while using a low optical power to excite the GNRs ({\approx 20 $\mu W).$ Since the detection of the absorption is thermometric, the measurement process is intrinsically scattering-free and we experimentally verified this point by reconstructing the GNRs spectrum in a clear host (water) as well as in an opaque host (water and milk). The scattering-free element is promising for the identification of absorbers in highly opaque materials ($e.g.$, nanoparticles/molecules in a biological sample), since in these cases the scattering spectrum could hide the absorption spectrum.