We introduce a new experimental method to investigate the photoluminescence and scattering signals of single levitating metallic and dielectric nanoparticles. Our experimental arrangement combines a quadrupole ion trap, a multi-wavelength laser-based dark-field microscope and a spectroscopy system. We illustrate how our measurements of the light scattering intensity or photo-luminescence can be used to either characterize the size or the light-matter excitation pathways of single trapped nanoparticles.

The nanoparticle trap scheme is based on a linear Paul trap and consists of four gold-coated rods embedded in a vacuum chamber. The rods of the trap are diagonally connected to either an oscillating high-voltage or to a direct-current voltage, which generate an electric field capable of trapping single nanoparticles.

The trap is combined with a dark-field microscope allowing us to image the scattered light intensity as a function of the polarization angle of incident laser beams at three wavelengths. We combine these measurements with Mie theory in order to extract the precise size of single trapped particles. A secondary arm of the dark-field arrangement directs the light towards a port with a fiber that guides the scattered or emitted light signals towards a spectrometer equipped with a sensitive EMCCD camera. The method presented here has potential for studying the scattering properties and photoluminescence signature of single trapped nano-objects, such as quantum dots, nanoparticles with different geometries, atomically thin materials or metamaterials.