Sub-lambda resonators

Permanent members

 Sébastien Bidault
 Valentina Krachmalnicoff
 Yannick De Wilde


From the visible spectum ...

Quantum emitters are non-classical light sources that are intrinsically highly non-linear but interact inefficiently with light at room temperature, while resonant nanostructures interact efficiently with light but in a classical, essentially linear way. This is why it is interesting to couple these types of resonators together in hybrid nanostructures whose interaction with light is optimized. We developed an original method based on DNA strands and gold nanoparticles to achieve a regime of strong coupling between a few fluorescent molecules and a plasmonic nanostructure [Heintz et al., ACS Nano, 2021] (Fig. 8-a) and have proposed how to optimize this coupling using anisotropic nanoparticles [Heintz et al., J. Phys. Chem. Lett., 2022]. We also studied the coupling between resonant nanostructures and emitters that interact with light in the manner of magnetic dipoles to demonstrate the importance of the magnetic component of light waves in light-matter interactions for which we generally only consider the electrical component [Sanz-Paz et al., Nano Lett., 2018] [Bidault et al., J. App. Phys., 2019].

Schematic representation of a dimer of gold nanoparticles, linked by a short DNA strand, which is in strong coupling regime with 5 fluorescent molecules grafted on the DNA strand (left) and experimental verification of the strong coupling regime by measuring the anti-crossing of the resonances of the molecules and of the nanoparticle dimers (right).

To the infrared ...

To study the thermal infrared (mid-IR) emission of individual sub- 𝜆 resonators, we have developed a new method of IR spectroscopy by spatial modulation (IRSMS), which allows far-field measurement of the thermal emission spectrum of individual sub-𝜆 objects by suppressing the largely dominant contribution of background thermal radiation (fig. 8-b). Not only does this ultra-sensitive method enable IR spectroscopy to be carried out without the need for an external source, it also removes a major bottleneck inherent in Fourier transform IR spectroscopy (FTIR), with which it has hitherto been impossible to study objects smaller than a few tens of micrometres. Our studies of the spectrum of individual metal-insulator-metal (MIM) antennas based on silica (SiO2) revealed that their fundamental mode can be excited at two different 𝜆 due to the strong dispersion of SiO2 [Li et al., Phys. Rev. Lett., 2018]. We also observed the spectral signature of hybridization of thermally excited electromagnetic modes, a coherence effect occurring when two MIM antennas couple in the near field [Abou-Hamdan et al., Opt. Lett., 2021]. We then extended the IRSMS method to the study of individual dielectric antennas consisting of SiO2 spheres a few micrometers in diameter. We have shown that it is possible to excite resonances associated with surface polaritons (𝑅𝑒( 𝜖) < 0) or geometric Mie modes (𝑅𝑒( 𝜖) > 0) depending on the size of the spheres [Abou-Hamdan et al., ACS Phot., 2022].

Finally, the IRSMS method has also made it possible to study the spectrum of fibers used in the design of thermal insulators like glass wool [Kallel et al., JQSRT 2019].

This work was carried out within the framework of fruitful collaborations: one with ONERA and the other with Saint-Gobain Research Paris.

Schematic representation of the infrared spatial modulation spectroscopy (IRSMS) setup used to measure the infrared emissivity spectrum of a single nanostructure (left) and spatial dependence of the spectroscopic signal from a single MIM antenna after demodulation by the lock-in amplifier (right).