E. K. Panina

Microaxicon-generated photonic nanojets

We report on the calculations of optical radiation scattering at micrometer-sized conical-shape dielectric particles (microaxicons) with special attention given to the specific spatially localized near-field area constituting a photonic nanojet (PNJ). By virtue of finite-difference time-domain simulations we show for the first time, to the best our knowledge, that the PNJ produced by a microaxicon of specific spatial orientation can exhibit extreme axial elongation up to ∼25λ (at defined intensity level) while retaining high peak intensity and subwavelength transverse width.

Comparative analysis of spatial shapes of photonic jets from spherical dielectric microparticles

A photonic jet is a specific spatially-localized region in the near field of optical radiation scattering by a micron-size particle. The spatial shape and basic characteristics of photonic jets depend to a large extent on the internal structure and size of microparticles. A qualitative classification of morphological types of photonic jets from spherical dielectric microparticles formed in vicinity of the shadow surface is presented. The classification is based on the analysis of their spatial shapes by taking into consideration the dimensional and power characteristics of the jets. Particles with homogeneous and radially inhomogeneous changes in the refractive index are studied.

Controlling the parameters of photon nanojets of composite microspheres

We consider the spatial and amplitude characteristics of PNJ forming in the neighborhood of the shadow surface of micron-sized composite particles consisting of a nucleus and a shell with various refraction indices when laser radiation scatters on them. We study the longitudinal and transverse dimensions of a photon flux and its peak intensity depending on the microparticle shell thickness. We show that a certain choice of the refraction index of the shell relative to the nucleus in two-layer composite spherical microparticles can significantly lengthen the forming PNJ or increase their peak intensity. The width of the photon flux during this changes insignificantly.

Simulation of spatial distribution of absorbed laser energy in spherical microcapsules

Specific features of optical field distribution in composite spherical particles consisting of a liquid core and nanocomposite absorbing shell are theoretically studied at different wavelengths of incident radiation. Using the numerical simulation it is shown that the thickness of the shell of the spherical microcapsule particle and its intrinsic absorption coefficient determine the character of the spatial distribution and the absorbed power. The variation of these parameters allows one to change the spatial position of efficient volume absorption regions and peak absorption values. This provides favourable conditions for opening the shells in appropriate spatial zones to release the contents of the microcapsules.

Characteristics of photonic nanojets from ordered microassemblies of dielectric spheres

Spatially localised light structures (photonic nanojets) formed in the near field of light scattering from an ordered ensemble of single-layer clusters of transparent glass microspheres have been theoretically studied. The main parameters of photonic nanojets (length, width, focal distance and intensity) are calculated based on numerical solution of Maxwell equations, and their behaviour under conditions of interference between neighbouring microparticles is analysed. The degree of manifestation of collective effects during the formation of a nanojet array is found to depend on the spatial structure of the ensemble of microspheres, their size and repetition period. It is found that in some cases, having chosen an appropriate configuration of a microsphere ensemble, one can improve significantly the characteristics of the photonic nanojets formed by this ensemble.

The influence of spherical microcapsules on the spatial distribution of absorbed laser radiation power

Particular properties of formation of optical fields in composite spherical microcapsules of different size consisting of a polymer absorbing shell and a nonabsorbing liquid core are considered. The numerical simulation shows that changes in the thickness of the shell grown on the fixed-radius core and in the coefficient of proper radiation of the shell determine the nature of spatial distribution and amplitude characteristics of the absorbed power. Variations in these parameters allow changing the position and peak values of the regions of the effective spatial absorption of the particles and, consequently, create conditions favorable for opening the shells in the appropriate spatial zones. This is important for the solution of practical tasks associated with the problem of release of the encapsulated material.

Localized light jets from radially symmetric nonspherical dielectric microparticles

The results of numerical modeling of the near field of light wave scattering (“photonic (nano)jet”—PNJ region) by radially symmetric nonabsorbing dielectric microparticles are presented. It is shown that the homogeneous silica microparticles of different spatial shape and orientation form PNJ of different sizes and amplitudes. Photonic nanojets from hemispheres are of high extent but moderate intensity. Use of microaxicons provides for a record increase in the PNJ length of the order of twenty wavelengths of the incident radiation.

Spatial and energy characteristics of nanofields in the vicinity of isolated spherical particles

Theoretical aspects of the extreme focusing of the optical field to a spatial zone of the subwavelength size are considered in the case of using isolated nanometer- and micrometer-sized spherical particles for this purpose. The intensity of the optical field near the surface of nanospheres of some metals in environments with different values of the refractive index under the exposure to laser radiation in a wide spectral range is calculated numerically. It is shown that as the particle radius decreases, the relative intensity of the optical field of surface plasmons increases and the zone of field nanofocusing shortens. The obtained data are compared with the calculations for gold and aluminum nanoparticles in water. Numerical results illustrating the influence of the shell thickness of composite nanoparticles (dielectric nucleus and metal shell) on the intensity of the optical field of plasmon modes are obtained. The problem of local optical focuses of a transparent microparticle or the so-called photonic nanojets is considered. It is found that varying a micron particle size, its optical properties, and laser radiation parameters allows us to efficiently control the amplitude and spatial characteristics of the photonic nanojet zone.

Modeling of multiphoton-excited fluorescence from a spherical droplet irradiated by an ultrashort laser radiation using the method of computation electrodynamics

The numerical modeling of two-dimensional spatial field distribution of multiphoton excited fluorescence in the vicinity of a micron spherical ethanol droplet upon illumination by a laser beam was carried out based on the FDTD-technique for the solving of Maxwell equations. Fluorescence sources are considered to be located in “hot” spots inside a spherical particle and can have various power and volume. It is established that the field of fluorescence radiated from backward and forward hemispheres of a particle (in relation to the direction of the excited radiation) is characterized by various angular orientation. With the increase of the multiphoton order of the excitation of fluorescence from the ethanol droplet and corresponding increase in imbalance between the source’s power, “forward” directivity of the radiation reduces and effective angular divergence of the fluorescence in the “backward” direction changes insignificantly.

Characteristics of photonic jets from microcones

The near field of light wave scattering by dielectric conical particles of micron dimensions (microcones) is numerically simulated. The main attention is paid to studying dimensional and amplitude parameters of a specifically spatially localized “photonic jet” region. It is shown for the first time that using a microaxicon with a definite shape yields a record-breaking increase in the extension of the appearing photonic jet to magnitudes of about two tens wavelengths of the incident radiation (by the fixed intensity level) with the preservation of the subwave transverse size of the localized light flux.