We report on the light transport phenomena in linear chains composed of several tens of touching spherical
microcavities. A new optical mode type, namely nanojet-induced modes (NIMs) is observed. These modes result from
the optical coupling of microspheres acting as a series of micro-lenses, which periodically focus propagating wave into
photonic nanojets. Theoretically, formation of periodic nanojets has been predicted in Z. Chen et al., Opt. Lett. 31, 389
(2006). The chains were produced by means of the self-assembly directed by micro-flows of water suspension of
polystyrene microspheres. The mean size of spheres was varied in the 2-10 micron range. To couple light to NIMs we
used built-in emission sources formed by several locally excited dye-doped microcavities from the same chain.
Conversion of modes emitted by the light source into the NIMs results in losses of several dB per sphere in the vicinity
(first few tens of spheres) of such sources. At longer distances we found an attenuation rate as small as 0.5 dB per sphere
that reveals low intrinsic propagation loss for NIMs. The NIMs have potential applications for coupling and guiding of
light in compact arrays of spherical cavities with extremely high quality (Q) whispering gallery modes.
Mesoscopic structures with characteristic size either of the order of an electron de Broglie wavelength in semiconductors (1 - 10 nm) or close to the optical photon wavelength (100 - 1000 nm) exhibit non-trivial properties due to modified electron or photon density of states. 3D spatial confinement of electrons in nanocrystals (quantum dots) results in size- dependent energies and probabilities of optical transitions. The photon density of states can be modified in structures with strong modulation of the refractive index in three dimensions (photonic crystals) and in microcavities. Because of the essentially different electron and photon wavelengths, electron and photon densities of states can be engineered separately within the same mesostructure. We report here on synthesis and properties of semiconductor quantum dots corresponding to the strong confinement limit embedded either in a photonic crystal exhibiting a pseudogap or in a planar microcavity. We show that the interplay of electron and photon confinement within the same structure opens a way towards novel light sources with controllable spontaneous emission. Spontaneous emission which is not an inherent property of quantum systems but a result of their interaction with electromagnetic vacuum can be either promoted or inhibited depending on the modification of the photon density of states in a given mesostructure.
We show that a promising way towards photonic crystals for the visible range is connected with the synthetic opals which consist of close-packed submicron silica spheres. By filling intersphere voids with different liquids and titanium oxide it is possible to enhance refraction index modulation and to optimize the topology of the structure. Impregnation of opal with absorbing material, such as Fe2O3, allows us to investigate the influence of absorption on the optical properties of the photonic crystals.
The effect of permanent hole burning is studied in absorption spectra of quantum sized CdS nanocrystals with the mean diameter of about 30 angstroms and wide size distribution embedded in polymeric film. The selective photoexcitation of appropriate CdS quantum dots followed by their ionization and further irreversible oxidation of CdS phase by holes h+ is considered to be responsible for this effect.
The spectrometer is described designed for studies of the small deviations in inhomogeneously broadened systems under selective laser excitation as well as for time-resolved analysis of irreversible photochemical processes after single-shot excitation. The set-up includes tunable pulse laser and registration system based on CCD-array. Computer control and built-in memory for 256 frames provide sensitivity of about 0.002 optical density units when studying differential absorption spectra and time-resolved single shot spectral measurements in the millisecond range.