Speckle Decorrelation in Fundamental and SecondHarmonic Light Scattered from Nonlinear Disorder Samanta, R., R. Pierrat, R. Carminati, and S. Mujumdar Physical Review Applied 18, no. 5 (2022)
Résumé: Speckle patterns generated in a disordered medium carry a lot of information despite the apparent complete randomness in the intensity pattern. When the medium possesses ?(2) nonlinearity, the speckle is sensitive to the phase of the incident fundamental light, as well as the light generated within. Here, we examine the speckle decorrelation in the fundamental and secondharmonic transmitted light as a function of the varying power in the fundamental beam. At low incident powers, the speckle patterns produced by successive pulses exhibit strong correlations, which decrease with increasing power. The average correlation in the secondharmonic speckle decays faster than in the fundamental speckle. Next, we construct a theoretical model, backed up by numerical computations, to obtain deeper physical insights into the faster decorrelations in the secondharmonic light. While providing excellent qualitative agreement with the experiments, the model sheds light on the contribution of two effects in the correlations, namely, the generation of secondharmonic light and the propagation thereof.


Transition from Phononic to Geometrical Mie Modes Measured in Single Subwavelength Polar Dielectric Spheres AbouHamdan, L., L. Coudrat, S. Bidault, V. Krachmalnicoff, R. Haïdar, P. Bouchon, and Y. De Wilde ACS Photonics 9, no. 7, 22952303 (2022)
Résumé: Spherical dielectric resonators are highly attractive for light manipulation, thanks to their intrinsic electric and magnetic resonances. Here, we present measurements of the midinfrared farfield thermal radiation of single subwavelength dielectric spheres deposited on a gold substrate, of radii ranging from 1 to 2.5 μm, which agree quantitatively with simulated absorption cross sections. For SiO2microspheres, we evidence the excitation of both surface phononpolariton (SPhP) modes and geometrical electric and magnetic Mie modes. The transition from a phononmodedominated to a Miemodedominated emission spectrum is observed, with a threshold radius of ∼1.5 μm. We also show that the presence of the metallic substrate augments the computed spheres absorption crosssection due to increased local field enhancement, arising from the nearfield interaction of the spheres oscillating charges with their image in the metallic mirror. In contrast, measurements of single subwavelength SPhPinactive PTFE spheres reveal that the midinfrared response of such lossy spheres is dominated by their bulk absorption. Our results demonstrate how engineering the geometrical and dielectric properties of subwavelength scatterers can enable the control of thermal emission near room temperature, with exciting perspectives for applications such as radiative cooling.


Extended Hybridization and Energy Transfer in Periodic MultiMaterial Organic Structures in Strong Coupling with Surface Plasmon Bard, A., S. Minot, C. Symonds, J. M. Benoit, A. Gassenq, F. Bessueille, B. Andrioletti, C. Perez, K. Chevrier, Y. De Wilde, V. Krachmalnicoff, and J. Bellessa Advanced Optical Materials (2022)
Résumé: The strong light−matter coupling, occurring when the light−matter interaction prevails on the damping, has found applications beyond the domain of optics in chemistry or transport. These advances make the development of various structures in strong coupling crucial. In this paper, a new way to hybridize two materials and transfer energy through a surface plasmon over micrometric distances is proposed. For this purpose, two patterned interlocked dye arrays, one donor and one acceptor, are deposited on a silver surface by successive microcontact printing, leading to a pattern of 5 microns period. The dispersion relation of the structure is measured with reflectometry experiments, showing the hybridization with the plasmon, and the formation of states that mix both excitons and the plasmon with similar weights. The mixing in these polaritonic metasurfaces enables an energy transfer mechanism in the strong coupling, which is observed with luminescence experiments. As the donor and acceptor are spatially separated by a distance larger than the diffraction limit the excitation transfer is directly measured and evaluated by comparison with dye arrays without silver.


Method to measure the refractive index for photoluminescence modelling Bailly, E., K. Chevrier, C. P. De La Vega, J. P. Hugonin, Y. De Wilde, V. Krachmalnicoff, B. Vest, and J. J. Greffet Optical Materials Express 12, no. 7, 27722781 (2022)
Résumé: Light emission by fluorophores can be computed from the knowledge of the absorption spectrum. However, at long wavelengths, the calculated emission may diverge if the decay of the imaginary part of the permittivity is not modelled with precision. We report a technique to obtain the permittivity of fluorophores such as dye molecules from fluorescence measurements. We find that the BrendelBormann model enables to fit the emission spectra accurately.


Purcell effect with extended sources: the role of the cross density of states Carminati, R., and M. Gurioli Optics Express 30, no. 10, 1617416183 (2022)
Résumé: We analyze the change in the spontaneous decay rate, or Purcell effect, of an extended quantum emitter in a structured photonic environment. Based on a simple theory, we show that the cross density of states is the central quantity driving interferences in the emission process. Using numerical simulations in realistic photonic cavity geometries, we demonstrate that a structured cross density of states can induce subradiance or superradiance, and change substantially the emission spectrum. Interestingly, the spectral lineshape of the Purcell effect of an extended source cannot be predicted from the sole knowledge of the spectral dependence of the local density of states.


Singlemolecule imaging of LDOS modification by an array of plasmonic nanochimneys Margoth CordovaCastro, R., D. Jonker, B. Van Dam, G. Blanquer, Y. De Wilde, I. Izeddin, A. SusarreyArce, and V. Krachmalnicoff 2021 Conference on Lasers and ElectroOptics Europe and European Quantum Electronics Conference, CLEO/EuropeEQEC 2021 (2021)
Résumé: The direct measurement of a single emitter decay rate and the simultaneous knowledge of their position is a powerful tool for the study of lightmatter interaction at the nanometer scale. In particular, the decay rate is directly related to the local density of states (LDOS) which measures the number of modes of the electromagnetic environment available for the decay of an emitter.


Nearfield and farfield studies of single and double subλ sized infrared plasmonic nanoantennas Abou Hamdan, L., V. Krachmalnicoff, R. Haidar, P. Bouchon, and Y. De Wilde 2021 Conference on Lasers and ElectroOptics Europe and European Quantum Electronics Conference, CLEO/EuropeEQEC 2021 (2021)
Résumé: The electromagnetic modes of a subwavelength sized antenna can be excited by thermal fluctuations. This thermal radiation is extremely weak, requiring in general the fabrication of a huge number of identical antennas to be detectable. Here, we will first demonstrate experimentally emission spectrum measurement and superresolved mapping of a single nanoantenna, subλ in the infrared spectral domain, based on the detection of its thermal radiation despite an overwhelming background thermal radiation [1]. To achieve a background free detection of the thermal radiation from single or a few subλ sized resonators, we have developed an infrared spatial modulation spectroscopy (IRSMS) technique using a lateral modulation of the sample heated at ~150 °C combined with lockin detection of the infrared signal detected through a Fourier transform infrared spectrometer. We have applied it in combination with thermal radiation scanning tunnelling microscopy [2] to study the thermal radiation from single plasmonic metalinsulatormetal (MIM) antennas both in the near field and in the far field. Our studies performed on single MIMs have revealed the surprising result that when silica is used as insulating material, its strong dispersion in the midinfrared domain is such that the fundamental spatial mode of the antenna can be thermally excited at various wavelengths. This causes multiple resonances in the thermal radiation spectrum to which correspond the same spatial distribution of nearfield thermal radiation [1].


Universal Statistics of Waves in a Random TimeVarying Medium Carminati, R., H. Chen, R. Pierrat, and B. Shapiro Physical Review Letters 127, no. 9 (2021)
Résumé: We study the propagation of waves in a medium in which the wave velocity fluctuates randomly in time. We prove that at long times, the statistical distribution of the wave energy is lognormal, with the average energy growing exponentially. For weak disorder, another regime preexists at shorter times, in which the energy follows a negative exponential distribution, with an average value growing linearly with time. The theory is in perfect agreement with numerical simulations, and applies to different kinds of waves. The existence of such universal statistics bridges the fields of wave propagation in timedisordered and spacedisordered media.

