Vlokh Institute of Physical Optics

This study explores the nonlinear optical properties of aluminum oxide (Al2O3) matrices embedded in ammonium dihydrogen phosphate (ADP) nanocrystals using third-harmonic generation (THG) techniques. The successful integration of ADP crystallites within the nanopores of the Al2O3 matrix was confirmed using x-ray structural analysis and electron microscopy. The optical absorption characteristics were examined over a wide wavelength range, revealing that the reflection and transmission spectra were notably affected by pore size and surface scattering effects. THG measurements conducted with a high-intensity infrared laser demonstrated a pronounced third-order nonlinear response, whereas second-harmonic generation was not observed. The absence of SHG can be attributed to phase mismatch and inherent material properties, including centrosymmetry and surface roughness. The comparative and Reintjes models were used to calculate the third-order nonlinear optical susceptibilities. Among these, the Reintjes model provided the most accurate fit for the experimental data. This research underscores the considerable influence of nanopore size on THG efficiency, highlighting the importance of light scattering and phase-matching conditions. These findings contribute to a growing body of knowledge regarding nonlinear optical phenomena in nanocomposite materials and offer valuable insights for future applications in photonic devices. This comprehensive analysis highlights the potential of Al2O3 matrices with embedded ADP nanocrystals to advance the field of nonlinear optics in nanocomposite materials and offers insights for prospective applications in photonic devices.

Multifunctional nanocomposites from an equimolar As4S4/Fe3O4 cut section have been successfully fabricated from coarse-grained bulky counterparts, employing two-step mechanochemical processing in a high-energy mill operational in dry- and wet-milling modes (in an aqueous solution of Poloxamer 407 acting as a surfactant). As was inferred from the X-ray diffraction analysis, these surfactant-free and surfactant-capped nanocomposites are β-As4S4-bearing nanocrystalline-amorphous substances supplemented by an iso-compositional amorphous phase (a-AsS), both principal constituents (monoclinic β-As4S4 and cubic Fe3O4) being core-shell structured and enriched after wet milling by contamination products (such as nanocrystalline-amorphous zirconia), suppressing their nanocrystalline behavior. The fluorescence and magnetic properties of these nanocomposites are intricate, being tuned by the sizes of the nanoparticles and their interfaces, dependent on storage after nanocomposite fabrication. A specific core-shell arrangement consisted of inner and outer shell interfaces around quantum-confined nm-sized β-As4S4 crystallites hosting a-AsS, and the capping agent is responsible for the blue-cyan fluorescence in as-fabricated Poloxamer capped nanocomposites peaking at ~417 nm and ~442 nm, while fluorescence quenching in one-year-aged nanocomposites is explained in terms of their destroyed core-shell architectures. The magnetic co-functionalization of these nanocomposites is defined by size-extended heterogeneous shells around homogeneous nanocrystalline Fe3O4 cores, composed by an admixture of amorphous phase (a-AsS), nanocrystalline-amorphous zirconia as products of contamination in the wet-milling mode, and surfactant.

Based on the analysis of influence of a natural optical activity on the efficiency of isotropic acousto-optic (AO) diffraction, it has been found that accounting for the optical activity and a nonzero ellipticity of optical eigenwaves in quartz crystals leads to a peak-like increase in the effective elasto-optic coefficients and the acousto-optic figure of merit.We have shown that the AO figure of merit for the type I of AO interactions increases by 54%, reaching the value 1.5810 -15 s 3 /kg.In case of AO interactions of the type II, it increases by more than three times and achieves nearly the same value.A similar situation also occurs for the types III and IV of AO interactions with the acoustic wave QT 1 .In particular, the peak value of the AO figure of merit for the type III of AO interactions increases by 19% and reaches 1.2210 -15 s 3 /kg, while the AO figure of merit for the type IV of AO interactions increases more than order of magnitude (from 9.610 -17 to 1.2210 -15 s 3 /kg).The results of our study can be useful for developing the AO devices based on crystalline quartz and minimizing their energy consumption.

The laser beam shaping is a practical problem in both information transmission, detection and material processing. Many applications focus on beam intensity and phase control in the so-called near-field, but far-field phenomena in microsystems should be no less interesting. One new way to control far-field distributions is by applying what is called “supercollimation”. It can be observed in systems consisting of periodically arranged phase gratings made from concentric features that repeat along the optical axis. Supercollimation is defined as the transformation of a broad-angular-intensity profile beam into a very thin well-defined high-peak-intensity and low-divergence beam. Such a beam can be compared to a Bessel Beam, however, a sharp central peak does not appear in the near field, but on the contrary: in the far field. There is no simple way to understand how a supercollimated beams are formed because it does not occur with 1D or 2D periodic systems. What is clear is that it is a cascading process that requires multiple diffraction. In sufficiently, long structures, plane waves diffracted from 0-order to higher diffraction orders are diffracted back resonantly with a broadened angular distribution that can overlap with the zero-angle component in the spatial spectrum. Thus, the aim of this paper is to reveal how such a phenomenon can occur in periodic systems with rotational (axial) symmetry, such as photonic crystals and resonators with concentric gratings. Finally, I will discuss how to use the “broken” symmetry of asymmetric photonic crystals in interpreting this phenomenon in practical contexts.