Natalia Noginova

Stimulated emission of surface plasmon polaritons

We have observed stimulated emission of surface plasmon polaritons (SPPs) propagating at the interface between a silver film and a film of optically pumped polymethyl methacrylate (PMMA) doped with rhodamine 6G (R6G) dye.

Effect of metallic surface on electric dipole and magnetic dipole emission transitions in Eu 3+ doped polymeric film

Spontaneous emission of Eu(3+) ions is studied in thin organic films deposited onto several different substrates. It has been demonstrated that the presence of a metallic surface in close vicinity to emitting Eu(3+) ions causes modifications of their spontaneous emission spectra, in particular, the change in the relative strengths of magnetic-dipole and electric-dipole transitions. The character and the magnitude of the effect depend on the polarization and the observation angle. The experimental data are discussed in terms of modification of transition probabilities and account for the interference between directly emitted and reflected light waves.

Spin and valence states of manganese ions in manganese-doped yttrium orthoaluminate

Abstract Two paramagnetic charge states of manganese with total electron spin of S=5/2 (Mn2+) and S=3/2 (Mn4+) were identified by electron paramagnetic resonance (EPR) method in Mn doped YAlO3. In addition to the allowed ΔMS=1 spin transitions, low field forbidden ΔMS=2 transitions were observed for both Mn4+ and Mn2+ and ΔMS=3 transitions for Mn2+. Relative intensities of forbidden transitions increase with a decrease of temperature and decrease with an increase of Mn concentration. The effect is due to the increase of spin–lattice and/or spin–spin relaxation times at low temperature and the decrease of spin–spin relaxation time at higher dopant concentration. Optically induced disproportionation reaction 2Mn4+→Mn3++Mn5+ in YAlO3 was studied by EPR.

Magnetic dipole based systems for probing optical magnetism

Recent advances in plasmonic-based metamaterials show that the magnetic component of an optical field can be strongly affected by the material’s properties and geometry of metallic nanostructures, leading to such interesting effects as negative magnetic permeability and magnetic resonance in the optical range. To probe such effects experimentally, systems containing Eu3+ ions can be used as spectroscopic tools. The study of the magnetic dipole-related transition at ∼590nm in comparison with the electric dipole-related transition at ∼615nm can reveal information on the relative distribution of magnetic and electric fields as well as effective permeability and permittivity. We report the development of such systems, demonstrating very high emission efficiency, and the first experimental results.

Interferometric studies of coherence in a powder laser

Abstract Longitudinal and transversal coherence in powder laser emission was studied using two different interferometric techniques. It has been shown that longitudinal coherence length in Nd0.5La0.5Al3(BO3)4 powder (ceramics) laser emission corresponds to 0.7 A linewidth. This value is in agreement with the results of direct spectroscopic linewidth measurements published in the literature. The transversal coherence has not been shown to be noticeable when the distance between two points on the emitting surface is equal to ≈85 μm. The possible explanation of the result obtained is discussed.

Study of the pumping regimes in Ti-sapphire and Nd0.5La0.5Al3(BO3)4 powders

Abstract Stimulated emission without a cavity was obtained (at λ=800 nm) in powders of Ti-sapphire laser crystal and compared to that in Nd0.5La0.5Al3(BO3)4. The formation of a narrow channel in a powder sample by a pumping laser beam was found to be advantageous for stimulated emission in Ti-sapphire and disadvantageous in Nd0.5La0.5Al3(BO3)4. The effect of the material volume density on stimulated emission in scattering Nd0.5La0.5Al3(BO3)4 was experimentally studied. The experimental results are explained in terms of absorption of pumping light in scattering materials, penetration depth for pumping, and residence time for emission photon in the pumped volume.

Modification of electric and magnetic dipole emission in anisotropic plasmonic systems

In order to investigate the effects of plasmonic environments on spontaneous emission of magnetic and electric dipoles, we have studied luminescence of Eu³⁺ ions in close vicinity to gold nanostrip arrays. Significant changes in the emission kinetics, emission polarization, and radiation patterns have been observed in the wavelength range corresponding to the plasmonic resonance. The effect of the plasmonic resonance on the magnetic dipole transition ⁵D₀-->⁷F₁ is found to be very different from its effect on the electric dipole transitions. This makes Eu³⁺₋ containing complexes promising for mapping local distributions of magnetic and electric fields in metamaterials and plasmonic systems.

Enhancing Eu 3+ magnetic dipole emission by resonant plasmonic nanostructures

We demonstrate the enhancement of magnetic dipole spontaneous emission from Eu3+ ions by an engineered plasmonic nanostructure that controls the electromagnetic environment of the emitter. Using an optical microscope setup, an enhancement in the intensity of the Eu3+ magnetic dipole emission was observed for emitters located in close vicinity to a gold nanohole array designed to support plasmonic resonances overlapping with the emission spectrum of the ions.

Effect of diamagnetic dilution and non-stoichiometry on ESR spectra in manganites

ESR spectra are studied in a series of diamagnetically diluted manganites, single crystals of LaGa1?xMnxO3, in a broad range of the Mn ion concentration, . With increase in Mn concentration, a complex multi-line spectrum, typical for low Mn concentrations, evolves to an exchange-narrowed several-?or single-line spectrum at x>0.05. The temperature behaviour of the ESR line-width in the range of 80?300?K is found to be very different in the materials with high and intermediate concentration of Mn ions: a slight growth of the line-width is observed in the former case, while a steep line narrowing occurs at x = 0.05 and?0.1 with increase in temperature. Similar temperature dependence of the line-width is also observed for an additional ESR line arising in the non-stoichiometric oxygen-deficient LaMnO3?? manganite. We explain the experimental data by taking into account the effect of the thermo-activated Jahn?Teller reorientation process on spin dynamics in Mn clusters, and estimate its activation energy as 50?100?meV.

Photorefractive effects in Mn-doped YAlO 3

Mn-doped YAlO3 crystals were investigated for photorefractive properties under 488-nm and 632.8-nm illumination. Dependences of the kinetics and efficiency of holographic recording on the light grating period were obtained.