Mode manipulation in system of coupled microcavities with whispering gallery modes

In recent years the studies of electromagnetic modes in solid spherical microcavities have been of great interest both for their potential applications and fundamental optical properties. A system of coherently coupled microcavities may be called a “photonic molecule” and can be employed in the tight-binding device in order to manipulate photons in micrometer length scale. In this work we demonstrate the possibility of mode manipulation in systems of symmetric photonic molecules formed by placing several high-Q micro-spheres in contact. We observe photonic nanojets that reflect the symmetry of the photonic molecule, with 3 jets located at 120 degrees with respect to each other for the triangular photonic molecule. A benzene molecule-like structure consisting of a 7-microspheres cyclic photonic molecule shows a field emission pattern similar to the spatial distribution of the orbitals of the benzene molecule. We also present some results showing the coexistence of whispering gallery modes and photonic nanojets in the same structure.     

Tunable photon lifetime in photonic molecules: a concept for delaying an optical signal

We experimentally and theoretically studied the photon lifetime spectral distribution in two coherently coupled spherical microcavities of 3-16 microm diameter forming a photonic molecule, which shows a multipeak narrowband modal structure resulting from lifting of the mode degeneracy with respect to the azimuthal quantum number. The results demonstrate the feasibility of photonic molecules as a basis for a multichannel, wavelength-tunable optical delay-line device, which can be used for delay times in the range 10 ps to 1 ns.     

Exciton reflection of ZnSe single crystals with account for the effect of the surface electric field

The mechanism of formation of an exciton reflection band is analyzed using a multilayer model of the near-surface region of ZnSe single crystals. It is shown that the appearance of a fine structure (a spike) in the reflection spectra at large damping parameters of the exciton is due to the surface electric field and the Stark exciton effect. The exciton-resonance energies and the damping parameters of free excitons for temperatures ranging from 12 to 100 K are determined by comparing experimental and predicted contours of the reflection spectrum. The surface concentration of charged centers and the characteristics of the space-charge region are evaluated within the framework of the model employed. Brest Polytechnic Institute, 267, Moskovskaya Str., Brest, 224017, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 3, pp. 401–407, May–June, 1999.     

Polariton-assisted manipulation of energy relaxation pathways: donor–acceptor role reversal in a tuneable microcavity

Resonant interaction between excitonic transitions of molecules and localized electromagnetic field allows the formation of hybrid light–matter polaritonic states. This hybridization of the light and the matter states has been shown to significantly alter the intrinsic properties of molecular ensembles placed inside the optical cavity. Here, we have observed strong coupling of excitonic transition in a pair of closely located organic dye molecules demonstrating an efficient donor-to-acceptor resonance energy transfer with the mode of a tuneable open-access cavity. Analysing the dependence of the relaxation pathways between energy states in this system on the cavity detuning, we have demonstrated that predominant strong coupling of the cavity photon to the exciton transition in the donor dye molecule can lead not only to an increase in the donor–acceptor energy transfer, but also to an energy shift large enough to cause inversion between the energy states of the acceptor and the mainly donor lower polariton energy state. Furthermore, we have shown that the polariton-assisted donor–acceptor chromophores'' role reversal or “carnival effect” not only changes the relative energy levels of the donor–acceptor pair, but also makes it possible to manipulate the energy flow in the systems with resonant dipole–dipole interaction and direct energy transfer from the acceptor to the mainly donor lower polariton state. Our experimental data are the first confirmation of the theoretically predicted possibility of polariton-assisted energy transfer reversal in FRET systems, thus paving the way to new avenues in FRET-imaging, remote-controlled chemistry, and all-optical switching.

Polariton-assisted donor–acceptor role reversal in resonant energy transfer between organic dyes tagged with the terminus of the closed oligonucleotide-based molecular beacon strongly coupled to electromagnetic modes of a tuneable microcavity.     

Photoluminescence Properties of Thin-Film Nanohybrid Material Based on Quantum Dots and Gold Nanorods

The dynamics of coherent propagation of a unipolar subcycle pulse of a large electric-field area (the integral of the electric-field strength with respect to time) in a nonlinear two-level resonant medium is studied theoretically. The propagating pulse is shown to be capable of splitting into a pair of individual components, each of which behaves like a pulse of self-induced transparency. This phenomenon is similar to the well-known phenomenon of splitting of a 4π or 6π pulse into a pair of 2π pulses of self-induced transparency, which occurs in the case of propagation of long pulses, when the notion of the pulse area is applicable and the area theorem holds.     

Anti‐Stokes Luminescence of Cadmium Telluride Nanocrystals

For the first time, the antiStokes luminescence in colloidal solutions of CdTe nanocrystals on excitation below the absorption edge has been discovered. The maximum spectral shift to the shortwave region relative to the excitation energy E _con ^max = 319 meV is obtained for meansized nanocrystals (2.5 nm). The conversion efficiency of the absorbed radiant energy is 1.3·10^–2%. The rise in the antiStokes photoluminescence intensity with increasing temperature and the linear dependence on the exciting radiation intensity have been established. It is shown that the effect observed cannot be caused by twophoton excitation or by Auger recombination. It is assumed that the basic mechanism of the luminescence observed is the radiative recombination through the energy levels of the states attributable to the disturbance of the crystal structure in the nanocrystals.     

Modification of photon states in photonic molecules with semiconductor nanocrystals

We report on the coherent coupling of whispering gallery modes (WGMs) in a photonic molecule formed from two melamine formaldehyde spherical microcavities coated with a thin shell of CdTe nanocrystals. Utilizing different excitation conditions, the splitting of the WGM resonances originating from bonding and antibonding branches of the photonic states is observed and a fine structure consisting of very sharp peaks resulting from lifting of the WGM degeneracy has been detected. Observation of optical wavelength switching with controllable spectral position and separation is reported.