Whispering Gallery Modes in Optical Microcavities

Nanocrystal Superparticles with Whispering-Gallery Modes Tunable through Chemical and Optical Triggers

“…Finite-difference time-domain (FDTD) simulations in Figure c show the confinement of the electric field intensity near the surface of the superparticle. We conclude that the finer features observed in PL and scattering spectra indicate the presence of photonic resonances within the superparticle that lead to an increase in intensity at resonant wavelengths. , In particular, these resonances are consistent with WGMs of the spherical superparticle …”

“…WGMs are a family of photonic modes that describe the trapping of light near the surface of a dielectric structure with at least one axis of symmetry. , Such a structure behaves as a resonant cavity and can be characterized in terms of optical parameters like the effective refractive index of the cavity, n eff , the quality factor, Q , describing the efficiency of light trapping, and the free spectral range, FSR, the distance between two consecutive resonances. For these superparticles of oleate-capped CdSe NCs, we measure Q = λ/Δλ = 109 and FSR = 15.7 nm at λ = 841.2 nm, where λ is the resonant wavelength, and Δλ is the full-width at half-maximum of the resonance.…”

“…After ligand-exchange, we measure the quality factor and the free spectral range of the cavity to be Q = 100 and FSR = 17.7 nm at λ = 838.4 nm. As the value of the free spectral range is inversely proportional to the cavity length, , πD , an increase in FSR suggests a decrease in the diameter of the microresonator. A direct comparison of the optical micrographs of the superparticle before and after ligand-exchange confirms this decrease in size, as shown in Figure b,e.…”

“…We combine the results of SEM imaging and single-superparticle spectroscopy to extract the value of n eff for single NC superparticles. When considering a spherical optical resonator characterized by a diameter D and refractive index n eff , the expected spectral positions of the WGM resonances with mode numbers n and l are well-approximated by ,, where ν = l + 1/2, α n is the n -th root of the Airy function, N = n eff / n env is the ratio between the refractive indices of the resonator and the environment, and P = 1/ N for transverse magnetic (TM) mode polarization or P = N for transverse electric (TE) mode polarization. By using SEM images to obtain values for D and analyzing the results of single-superparticle PL studies to obtain the observed values for , we estimate the value of n eff for a single superparticle by minimizing the sum of the squares of the residuals, , as shown in Figure S1.…”

“…53 WGMs are a family of photonic modes that describe the trapping of light near the surface of a dielectric structure with at least one axis of symmetry. 53,54 Such a structure behaves as a resonant cavity and can be characterized in terms of optical parameters like the effective refractive index of the cavity, n eff , the quality factor, Q, describing the efficiency of light trapping, and the free spectral range, FSR, the distance between two Since the density of optical modes depends on the square of the effective refractive index of the cavity, increasing n eff should prove beneficial to light trapping. 55 For a superparticle, the value of n eff can be approximated as the volumetric average of organic and inorganic components, respectively identified by the ligands and core of the NCs…”