Electrodynamic single-particle trap integrated into double-cavity ring-down spectroscopy for light extinction

The study of the interaction of light with matter upon changing environmental conditions requires new platforms that provide accurate and reliable measurements. One suitable technique for studying such interaction uses electrodynamic traps to levitate micro or nanoparticles in combination with an optical interrogation technique, but improvements and new developments that complement spectroscopic information are necessary. Here, we use a Paul Electrodynamic Trap (PET) coupled to a Double-Cavity Ring Down Spectroscopy (D-CRDS) to measure the extinction cross section of single levitated particles at two different wavelengths (405 and 532 nm). The level of control achieved over the motion and stability is such that the particle can be consecutively placed at the central maximum of two independent TEM00 Gaussian modes of the ring-down cavities. Therefore, we can directly measure the dynamic change of the extinction cross section of a single particle at two different wavelengths. The combination of simulations using Mie theory and experiments demonstrates the potential of this robust and versatile setup applied to 1,2,6-hexanetriol particles. Unlike standard methods, our system provides crucial information of drastic and reversible change in the extinction cross-section of a sodium chloride particle in efflorescence and deliquescence points, indicating changes in solute mass, charge, refractive index, sphericity and size during the dehydration and hydration processes.