Magneto-Optical Spectroscopy of Short Spin Waves by All-Dielectric Metasurface.

The optical method of spin dynamics measurements via the detection of various magneto-optical effects is widely used nowadays. Besides it being a convenient method to achieve time-resolved measurements, its spatial resolution in the lateral direction is limited by a diffraction limit for the probe light. We propose a novel approach utilizing a Mie-resonance-based all-dielectric metasurface that allows for the extraction of a signal of a single submicron-wavelength spin wave from the wide spin precession spectra. This approach is based on the possibility of designing a metasurface that possesses nonuniform magneto-optical sensitivity to the different nanoscale regions of the smooth magnetic film due to the excitation of the Mie modes. The metasurface is tuned to be unsensitive to the long-wavelength spin precession, which is achieved by the optical resonance-caused zeroing of the magneto-optical effect for uniform magnetization in the vicinity of the resonance. At the same time, such a Mie-supporting metasurface exhibits selective sensitivity to a narrow range of short wavelengths equal to its period.

Design of an Artificial Opal/Photonic Crystal Interface for Alcohol Intoxication Assessment: Capillary Condensation in Pores and Photonic Materials Work Together.

Alcohol intoxication has a dangerous effect on human health and is often associated with a risk of catastrophic injuries and alcohol-related crimes. A demand to address this problem adheres to the design of new sensor systems for the real-time monitoring of exhaled breath. We introduce a new sensor system based on a porous hydrophilic layer of submicron silica particles (SiO2 SMPs) placed on a one-dimensional photonic crystal made of Ta2O5/SiO2 dielectric layers whose operation relies on detecting changes in the position of surface wave resonance during capillary condensation in pores. To make the active layer of SiO2 SMPs, we examine the influence of electrostatic interactions of media, particles, and the surface of the crystal influenced by buoyancy, gravity force, and Stokes drag force in the frame of the dip-coating preparation method. We evaluate the sensing performance toward biomarkers such as acetone, ammonia, ethanol, and isopropanol and test sensor system capabilities for alcohol intoxication assessment. We have found this sensor to respond to all tested analytes in a broad range of concentrations. By processing the sensor signals by principal component analysis, we selectively determined the analytes. We demonstrated the excellent performance of our device for alcohol intoxication assessment in real-time.

Effect of l-carnitine and mildronate on the mitochondrial metabolism of heart and bacterial composition of the gut microbiome in ageing mice.

Ageing is the most significant risk factor for cardiovascular diseases. l-Carnitine has a potent cardioprotective effect and its synthesis decreases during ageing. At the same time, there are pharmaceuticals, such as mildronate which, on the contrary, are aimed at reducing the concentration of l-carnitine in the heart and lead to slows down the oxidation of fatty acids in mitochondria. Despite this, both l-carnitine and mildronate are positioned as cardio protectors. We showed that l-carnitine supplementation to the diet of 15-month-old mice increased expression of the PGC-1α gene, which is responsible for the regulation of fatty acid oxidation, and the Nrf2 gene, which is responsible for protecting mitochondria by regulating the expression of antioxidants and mitophagy, in the heart. Mildronate activated the expression of genes that regulate glucose metabolism. Probably, this metabolic shift may protect the mitochondria of the heart from the accumulation of acyl-carnitine, which occurs during the oxidation of fatty acids under oxygen deficiency. Both pharmaceuticals impacted the gut microbiome bacterial composition. l-Carnitine increased the level of Lachnoanaerobaculum and [Eubacterium] hallii group, mildronate increased the level of Bifidobacterium, Rikinella, Christensenellaceae. Considered, that these bacteria for protection the organism from various pathogens and chronic inflammation. Thus, we suggested that the positive effects of both drugs on the mitochondria metabolism and gut microbiome bacterial composition may contribute to the protection of the heart during ageing.

Plasmonic dichroism and all-optical magnetization switching in nanophotonic structures with GdFeCo.

We report on a phenomenon of plasmonic dichroism observed in magnetic materials with transverse magnetization under excitation of surface plasmon polariton waves. The effect originates from the interplay of the two magnetization-dependent contributions to the material absorption, both of which are enhanced under plasmon excitation. Plasmonic dichroism is similar to circular magnetic dichroism, which is at the base of all-optical helicity-dependent switching (AO-HDS) but observed for linearly polarized light, and the dichroism acts upon in-plane magnetized films, where AO-HDS does not take place. We show by electromagnetic modeling that laser pulses exciting counter-propagating plasmons can be used to write +M or -M states in a deterministic way independent of the initial magnetization state. The presented approach applies to various ferrimagnetic materials with in-plane magnetization, exhibiting the phenomenon of all-optical switching of a thermal nature and broadens the horizons of their applications in data storage devices.

Magnetization Switching in the GdFeCo Films with In-Plane Anisotropy via Femtosecond Laser Pulses.

Ferrimagnetic rare-earth substituted metal alloys GdFeCo were shown to exhibit the phenomenon of all-optical magnetization switching via femtosecond laser pulses. All-optical magnetization switching has been comprehensively investigated in out-of-plane magnetized GdFeCo films; however, the films with the in-plane magnetic anisotropy have not yet been studied in detail. We report experimental observations of the magnetization switching of in-plane magnetized GdFeCo films by means of the femtosecond laser pulses in the presence of a small magnetic field of about 40 µT. The switching effect has a threshold both in the applied magnetic field and in the light intensity.

Silicon-Based All-Dielectric Metasurface on an Iron Garnet Film for Efficient Magneto-Optical Light Modulation in Near IR Range.

All-dielectric nanostructures provide a unique low-loss platform for efficiently increasing light-matter interaction via excitation of the localized or propagating optical modes. Here, we report on the transverse magneto-optical Kerr effect enhancement in an all-dielectric metasurface based on a two-dimensional array of Si nanodisks on a cerium substituted dysprosium iron garnet thin film. We observed up to 15% light intensity modulation under TM modes excitation. The observed magneto-optical effect is nearly independent of the rotation of the light incidence plane with respect to the metasurface. Being compatible with conventional semiconductor technology, our structure holds promise for device applications, such as light modulators, magnetic and chemical sensors.

Nrf2/ARE Activators Improve Memory in Aged Mice via Maintaining of Mitochondrial Quality Control of Brain and the Modulation of Gut Microbiome.

Aging is one of the most serious factors for central nervous dysfunctions, which lead to cognitive impairment. New highly effective drugs are required to slow the development of cognitive dysfunction. This research studied the effect of dimethyl fumarate (DMF), methylene blue (MB), and resveratrol (RSV) on the cognitive functions of 15-month-old mice and their relationship to the maintenance of mitochondrial quality control in the brain and the bacterial composition of the gut microbiome. We have shown that studied compounds enhance mitochondrial biogenesis, mitophagy, and antioxidant defense in the hippocampus of 15-month-old mice via Nrf2/ARE pathway activation, which reduces the degree of oxidative damage to mtDNA. It is manifested in the improvement of short-term and long-term memory. We have also shown that memory improvement correlates with levels of Roseburia, Oscillibacter, ChristensenellaceaeR-7, Negativibacillus, and Faecalibaculum genera of bacteria. At the same time, long-term treatment by MB induced a decrease in gut microbiome diversity, but the other markers of dysbiosis were not observed. Thus, Nrf2/ARE activators have an impact on mitochondrial quality control and are associated with a positive change in the composition of the gut microbiome, which together lead to an improvement in memory in aged mice.

Sensing of Surface and Bulk Refractive Index Using Magnetophotonic Crystal with Hybrid Magneto-Optical Response.

We propose an all-dielectric magneto-photonic crystal with a hybrid magneto-optical response that allows for the simultaneous measurements of the surface and bulk refractive index of the analyzed substance. The approach is based on two different spectral features of the magneto-optical response corresponding to the resonances in p- and s-polarizations of the incident light. Angular spectra of p-polarized light have a step-like behavior near the total internal reflection angle which position is sensitive to the bulk refractive index. S-polarized light excites the TE-polarized optical Tamm surface mode localized in a submicron region near the photonic crystal surface and is sensitive to the refractive index of the near-surface analyte. We propose to measure a hybrid magneto-optical intensity modulation of p-polarized light obtained by switching the magnetic field between the transverse and polar configurations. The transversal component of the external magnetic field is responsible for the magneto-optical resonance near total internal reflection conditions, and the polar component reveals the resonance of the Tamm surface mode. Therefore, both surface- and bulk-associated features are present in the magneto-optical spectra of the p-polarized light.

Effect of long-term methylene blue treatment on the composition of mouse gut microbiome and its relationship with the cognitive abilities of mice.

In recent years, methylene blue (MB) has attracted considerable interest as a potential drug for the treatment of methemoglobinemia and neurodegenerative diseases. MB is active against microorganisms from various taxonomic groups. However, no studies have yet been conducted on the effect of MB on the intestinal microbiome of model animals. The aim of this work was to study the effect of different concentrations of MB on the mouse gut microbiome and its relationship with the cognitive abilities of mice. We showed that a low MB concentration (15 mg/kg/day) did not cause significant changes in the microbiome composition. The Bacteroidetes/Firmicutes ratio decreased relative to the control on the 2nd and 3rd weeks. A slight decrease in the levels Actinobacteria was detected on the 3rd week of the experiment. Changes in the content of Delta, Gamma, and Epsilonproteobacteria have been also observed. We did not find significant alterations in the composition of intestinal microbiome, which could be an indication of the development of dysbiosis or other gut dysfunction. At the same time, a high concentration of MB (50 mg/kg/day) led to pronounced changes, primarily an increase in the levels of Delta, Gamma and Epsilonproteobacteria. Over 4 weeks of therapy, the treatment with high MB concentration has led to an increase in the median content of Proteobacteria to 7.49% vs. 1.61% in the control group. Finally, we found that MB at a concentration of 15 mg/kg/day improved the cognitive abilities of mice, while negative correlation between the content of Deferribacteres and cognitive parameters was revealed. Our data expand the understanding of the relationship between MB, cognitive abilities, and gut microbiome in respect to the antibacterial properties of MB.

All-dielectric magnetic metasurface for advanced light control in dual polarizations combined with high-Q resonances.

Nanostructured magnetic materials provide an efficient tool for light manipulation on sub-nanosecond and sub-micron scales, and allow for the observation of the novel effects which are fundamentally impossible in smooth films. For many cases of practical importance, it is vital to observe the magneto-optical intensity modulation in a dual-polarization regime. However, the nanostructures reported on up to date usually utilize a transverse Kerr effect and thus provide light modulation only for p-polarized light. We present a concept of a transparent magnetic metasurface to solve this problem, and demonstrate a novel mechanism for magneto-optical modulation. A 2D array of bismuth-substituted iron-garnet nanopillars on an ultrathin iron-garnet slab forms a metasurface supporting quasi-waveguide mode excitation. In contrast to plasmonic structures, the all-dielectric magnetic metasurface is shown to exhibit much higher transparency and superior quality-factor resonances, followed by a multifold increase in light intensity modulation. The existence of a wide variety of excited mode types allows for advanced light control: transmittance of both p- and s-polarized illumination becomes sensitive to the medium magnetization, something that is fundamentally impossible in smooth magnetic films. The proposed metasurface is very promising for sensing, magnetometry and light modulation applications.

Magneto-optics of subwavelength all-dielectric gratings.

We provide the experimental research on a novel type of all-dielectric magnetic structure designed to achieve an enhanced magneto-optical response. 1D grating fabricated via etching of bismuth substituted iron garnet film supports the excitation of optical guided modes, which are highly sensitive to the external magnetic field. A unique feature of proposed structure is the synergetic combination of high transparency, tunability, high Q-factor of the resonances and superior magneto-optical response that is two orders higher in magnitude than in the non-structured smooth iron-garnet film. The considered all-dielectric magnetic garnet structures have great potential in various fields including the magneto-optical modulation of light, biosensing and magnetometry.

All-Dielectric Nanophotonics Enables Tunable Excitation of the Exchange Spin Waves.

Launching and controlling magnons with laser pulses opens up new routes for applications including optomagnetic switching and all-optical spin wave emission and enables new approaches for information processing with ultralow energy dissipation. However, subwavelength light localization within the magnetic structures leading to efficient magnon excitation that does not inherently absorb light has still been missing. Here, we propose to marriage the laser-induced ultrafast magnetism and nanophotonics to efficiently excite and control spin dynamics in magnetic dielectric structures. We demonstrate that nanopatterning by a 1D grating of trenches allows localization of light in spots with sizes of tens of nanometers and thus launch the exchange standing spin waves of different orders. The relative amplitude of the exchange and magnetostatic spin waves can be adjusted on demand by modifying laser pulse polarization, incidence angle, and wavelength. Nanostructuring of the magnetic media provides a unique possibility for the selective spin manipulation, a key issue for further progress of magnonics, spintronics, and quantum technologies.

Resonances of the magneto-optical intensity effect mediated by interaction of different modes in a hybrid magnetoplasmonic heterostructure with gold nanoparticles.

Here we demonstrate a novel magnetoplasmonic heterostructure for efficient control of light. It consists of gold nanoparticles embedded in a thin magnetic film covered with a gold layer pierced with periodic nanoslit array. Unique feature of the proposed structure is that it supports four different types of optical modes in the same frequency range including localized and propagating surface plasmons along with waveguide modes. A peculiar magneto-optical response appears at the frequencies of the mode hybridization. The most important result comes from hybridization of the localized and propagating plasmons leading to a significant increase of the magneto-optical effect intensity.

Magneto-optical plasmonic heterostructure with ultranarrow resonance for sensing applications.

Currently, sensors invade into our everyday life to bring higher life standards, excellent medical diagnostic and efficient security. Plasmonic biosensors demonstrate an outstanding performance ranking themselves among best candidates for different applications. However, their sensitivity is still limited that prevents further expansion. Here we present a novel concept of magnetoplasmonic sensor with ultranarrow resonances and high sensitivity. Our approach is based on the combination of a specially designed one-dimensional photonic crystal and a ferromagnetic layer to realize ultralong-range propagating magnetoplasmons and to detect alteration of the environment refractive index via observation of the modifications in the Transversal Magnetooptical Kerr Effect spectrum. The fabrication of such a structure is relatively easy in comparison with e.g. nanopatterned samples. The fabricated heterostructure shows extremely sharp (angular width of 0.06°) surface plasmon resonance and even sharper magnetoplasmonic resonance (angular width is 0.02°). It corresponds to the propagation length as large as 106 µm which is record for magnetoplasmons and promising for magneto-optical interferometry and plasmonic circuitry as well as magnetic field sensing. The magnitude of the Kerr effect of 11% is achieved which allows for detection limit of 1∙10(-6). The prospects of further increase of the sensitivity of this approach are discussed.

Plasmonic pulse shaping and velocity control via photoexcitation of electrons in a gold film.

We study the possibility of surface plasmon polariton (SPP) pulse shape, delay and duration manipulation on sub-picosecond timescales via a high intensity pump SPP pulse photoexciting electrons in a gold film. We present a theoretical model describing this process and show that the pump induces the phase modulation of the probe pulse leading to its compression by about 20% and the variation of the delay between two SPP pulses up to 15 fs for the incident fluence of the pump of 1.5 mJ∙cm⁻².