Efficient ultrafast control of the intensity and wavefront of light is essential for many modern optical devices, from LiDAR scanning systems to advanced laser beam shapers. A CMOS-compatible approach to spatial light control is based on tailoring the directional scattering from metasurfaces made of arrays of Mie-resonant semiconductor nanoparticles-meta-atoms. All-optical ultrafast tuning is possible by generating photoinduced carriers in semiconductor meta-atoms and is usually traced by overall transient reflection or transmission. However, the high intensities of light pulses required for effective modulation impose a limit for applications. Here, we introduce a diffractive metasurface based on gallium arsenide and demonstrate that ultrafast tuning of intensity is an order of magnitude stronger for the diffracted beam than for the transmitted one. Experimentally, the intensity modulation of the first diffraction order reaches 16% at a pump fluence level of only a few mu J/cm(2), with a switching time of 200 fs and a relaxation time of 1.2 ps. The results constitute an important milestone in ultrafast optical switching device development for efficient low-power spatial light control.

We present a straightforward approach for measuring the thickness of highly porous and rough single-walled carbon nanotube (SWCNT) pristine thin films. Using the developed approach, the linear dependence of the film thickness on its absorbance at 550 nm was obtained with a slope coefficient of 404 nm, which can be used as a calibration curve for an optical determination of SWCNT pristine film thickness on the basis of spectrophotometry measurements. Transmittance and reflectance of free-standing SWCNT pristine films with thicknesses in the range of 20-120 nm are studied, and ultra-low specular reflectance below 0.05 % is obtained for the thinnest membrane. Perspectives of SWCNT-based antireflective coatings are explored using Si wafer as a reference. Finally, femtosecond laser 3D lithography is performed using free-standing SWCNT film as a substrate, which opens up new directions for the application of SWCNTs, for instance, in X-ray optics.

Silicon nanoparticles with Mie resonances are among the most prospective building blocks for state-of-the-art all-dielectric metasurfaces. Here we focus on linear and nonlinear optical responses of silicon nanoparticles printed by laser-induced transfer from silicon-on-insulator wafer. Second-harmonic generation and broadband multiphoton-absorption-induced luminescence are studied as a function of pump wavelength. The key role of magnetic quadrupole Mie resonances in the nonlinear optical response from silicon nanoparticles is revealed. We also show the influence of Si nanoparticle shape and structure modification, realized by additional femtosecond laser irradiation, on their linear and nonlinear optical properties.

Nanofabrication technologies significantly influence the development of modern optical science. One of such technologies is laser-induced transfer, which allows the creation of single Mie-resonant spherical particles on a wide range of substrates. This study shows that this method can provide asymmetric dimers at the output: a single femtosecond pulse being focused on a silicon-on-insulator wafer results in appearing two nearly spherical particles of different sizes. The resulting dimers are characterized by scanning electron microscopy, elastic light scattering and Raman spectroscopy to gain insight into their structural properties. Back focal plane imaging and variable-color evanescent-wave illumination are then employed to measure the light scattering patterns from isolated dimers. Due to the interference of the excited resonances, the observed patterns are strongly asymmetric in a range of visible wavelengths, which is consistent with theoretical predictions. The results demonstrate the potential of asymmetric silicon dimers made by single-shot laser-induced transfer for color routing at visible light. The laser-induced transfer, when applied to silicon-on-insulator wafers, is shown to create pairs of silicon particles of different size. The dimers are characterized, their structural features and light scattering patterns are revealed. The observed scattering pattern asymmetry in visible wavelengths aligns with theoretical expectations, showcasing the potential of these silicon dimers for visible light color routing.image

The method of two-photon lithography is used to fabricate GRIN microstructures. Test rectangular structures with sizes 25 × 25 × 3 micrometers were used with varying laser intensity by linear or gaussian distribution in one dimension. The resulting refractive index has been tuned in the range of 0.03. The suggested method can be applied to produce arbitrarily shaped 3D GRIN micro-optical elements.

Three-dimensional microprinting by two-photon laser lithography is a promising way to manufacture X-ray lenses. However, as the radius of curvature approaches the voxel size, the refractive surface of the lens deviates from the specified shape, that leads to a deterioration in the focusing of X-ray radiation and astigmatism. In this work we suggest a method for correcting a model for 3D printing of a parabolic X-ray lens taking into account the finite voxel size.

The method of two-photon lithography is used to fabricate microstructures with gradient of refractive index. The rectangular structures with sizes 25 × 25 × 3 μm were fabricated with varying laser intensity by linear or Gaussian distribution in one dimension. The resulting refractive index has been tuned in the range of 0.03. The suggested method can be applied to produce arbitrarily shaped 3D GRIN micro-optical elements.

Nanophotonics is an actively developing field of optics that finds application in various areas, from biosensing to quantum computing. The study of ultrafast modulation of the refractive index Delta is an important task in nanophotonics, since it reveals the features of light-matter interaction inside devices. With the development of active photonic devices such as emitters and modulators, there is a growing need for Delta n imaging techniques with both high spatial and high temporal resolutions. Here, we report on an all-optical ultrafast Delta n imaging method based on phase-sensitive optical coherence microscopy with a resolution of 1 ps in time and 0.5 mu m in space and a sensitivity to Delta n down to 10(-3) RIU. The advantages of the method are demonstrated on emerging nanophotonic devices-perovskite microlasers, in which the ultrafast spatiotemporal dynamics of the refractive index during lasing is quantitatively visualized, illustrating the features of relaxation and diffusion of carriers in perovskites. The developed method allows us to estimate the ultrafast carrier diffusion and relaxation constants simultaneously and to show that the CsPbBr3 perovskite carrier diffusion coefficient is low compared to other semiconductors even during lasing at high carrier densities, which leads to high localization of the generated carrier cloud, and, consequently, to high fluorescence and lasing efficiency. The resulting technique is a versatile method for studying ultrafast carrier transport via Delta n imaging, paving an avenue for the applications of optical coherence tomography and microscopy in the research of nanophotonic devices and materials. (c) 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

One-dimensional photonic crystals that support the propagation of Bloch surface electromagnetic waves attract the interest of researchers as an alternative platform for integrated optics with potential applications in nanophotonics, sensing, and optical manipulation of micro- and nanoparticles. In this paper, we numerically study the properties of surface wave modes in curved waveguides on top of a one-dimensional photonic crystal. It is shown that, when the waveguide is bent, an additional channel of radiation losses appears, which is associated with light leakage from the surface wave mode into bulk modes of the photonic crystal, and the waveguide mode profile becomes asymmetric with respect to the middle of the waveguide. We also determine the conditions for minimizing transition losses, which occur at the junctions of waveguides with different curvatures, by transverse displacement of the waveguide facets relative to each other.

Thanks to a high refractive index, giant optical anisotropy, and pronounced excitonic response, bulk transition metal dichalcogenides (TMDCs) have recently been discovered to be an ideal foundation for post‐silicon photonics. The inversion symmetry of bulk TMDCs, on the other hand, prevents their use in nonlinear‐optical processes such as second‐harmonic generation (SHG). To overcome this obstacle and broaden the application scope of TMDCs, MoS 2 nanodisks are engineered to couple Mie resonances with C‐excitons. As a result, their alliance produces 23‐fold enhancement of SHG intensity with respect to the resonant SHG from a high‐quality exfoliated MoS 2 monolayer under C‐exciton excitation. Furthermore, SHG demonstrates a strongly anisotropic response typical of a MoS 2 monolayer due to the single‐crystal structure of the fabricated nanodisks, providing a polarization degree of freedom to manipulate SHG. Hence, these results significantly improve the potential of bulk TMDCs enabling an avenue for next‐generation nonlinear photonics.

The Dzyaloshinskii–Moriya interaction (DMI) is an antisymmetric exchange in magnetic structures with broken inversion symmetry. In magnetic heterostructures, the bulk DMI may coexist with the conventional interfacial DMI contributing to the chiral magnetic behavior of the system. Here, we report the enhancement of DMI in Pt/Co heterostructures wherein Pt-Co alloy intralayers with compositional gradients are sandwiched between Pt and Co. Due to the composition gradient-induced bulk magnetic asymmetry and the face-centered cubic (fcc) (111) multilayer crystal structure, the DMI shows a complex behavior attributed to both the interfacial (i-DMI) and bulk-like (b-DMI) contributions. While the b-DMI is defined by the presence of composition differences and structure symmetry, the i-DMI hosts the interfacial contributions in the multilayer structure. Our approach allows the creation of graded magnetic thin films, where the structural inversion symmetry is broken solely due to the predefined compositional gradient of an intralayer, thereby giving rise to an 'all-interface-bulk' DMI with the controllable spatial distribution.

SnS2 and SnSe2 have recently been shown to have a wide range of applications in photonic and optoelectronic devices. However, because of incomplete knowledge about their optical characteristics, the use of SnS2 and SnSe2 in optical engineering remains challenging. Here, we addressed this problem by establishing SnS2 and SnSe2 linear and nonlinear optical properties in the broad (300–3300 nm) spectral range. Coupled with the first-principle calculations, our experimental study unveiled the full dielectric tensor of SnS2 and SnSe2. Furthermore, we established that SnS2 is a promising material for visible high refractive index nanophotonics. Meanwhile, SnSe2 demonstrates a stronger nonlinear response compared with SnS2. Our results create a solid ground for current and next-generation SnS2- and SnSe2-based devices.

Halide perovskite micro- and nanolasers have become a novel platform for efficient generation of coherent emission in the whole visible range. However, the laser emission outcoupling from the perovskite microcrystals faces a number of problems related to large divergence angle, light-soaking by a substrate, and high losses in the case of coupling with nanowaveguides. Here the perovskite nano- and microlasers are proposed to be integrated with a photonic crystal supporting Bloch surface waves (BSWs), which are coupled directly from the perovskite lasers with the efficiency of over 16%. The BSWs exciting at 535-nm wavelength show high in-plane directivity, down to 9 degrees, and long-propagation length, up to 50 mu m. Moreover, a pronounced beam steering effect for the generated laser emission is demonstrated by varying the pumping laser beam position, which provides an additional degree of freedom for in-plane control of the lasing mode outcoupling.

One of the main issues in integrated photonics is the coupling of free‐space or optical fiber radiation to waveguides on the photonic chip surface. The ideal coupler is miniature, highly efficient, and provides a large number of addressable devices. Here, a new concept of 3D out‐of‐plane coupler is introduced, which is a microscale prism exploiting frustrated total internal reflection in the Otto configuration to excite surface electromagnetic waves or near‐surface waveguide modes. A method for designing the couplers operating at normal incidence is proposed and it is applied to excite Bloch surface waves (BSWs) in 1D photonic crystals. Polymer microprisms are printed using two‐photon laser lithography and allow transferring more than 40% of the incident light energy into BSWs. The couplers enable focusing BSWs simultaneously with their excitation. Advanced design prisms can provide nearly 100% efficiency, making the proposed concept an alternative to actual coupling concepts in integrated photonics.

A new deep machine learning method is proposed for the task of selecting the parameters of a multilayer photonic structure to obtain a target optical spectrum of the reflection coefficient. The proposed training method is based on the connection of an artificial neural network for solving the inverse problem and the analytical transfer matrix method. This approach allows achieving high accuracy of the network. The developed method can be applied to the design of a structure that takes the derivative of the coordinate for an incident optical -signal.

Enhanced second-harmonic generation in a single MoS2 nanodisk due to the overlap of Mie resonances at the fundamental wavelength with the C-exciton resonance at the second-harmonic wavelength is observed.

Molybdenum disulfide (MoS2) is a layered material of transition metal dichalcogenides (TMDCs) with a high refractive index in the visible and infrared spectral range. Therefore, by constructing MoS2 into dielectric nanoresonators, one can generate highly confined electromagnetic Mie-type modes. In this work, we applied lithography and etching techniques to single crystal MoS2 flakes to fabricate nanodisks that support magnetic dipole Mie resonances in near infrared spectral range. The nanodisks were studied by second-harmonic generation (SHG) rotational anisotropy revealing the retention of crystallinity and the orientation of the crystallographic axes of the single disk structure after fabrication. Magnetic dipole resonances manifest as resonant intensity enhancement in SHG spectra. Tuning Mie resonances by selecting the geometrical size of MoS2 nanodisks, we demonstrated strongly enhanced SHG due to the overlap of the optical resonance at the fundamental wavelength with the C-exciton resonance at the second-harmonic wavelength.

Possibility of femtosecond laser pulses to affect the materials properties arises the interest in ultrafast processes based research and technology. In the case of graphene surface modification and functionalization using femtosecond laser, there are several effects appear, such as ablation, covalent bonding of different chemical groups, re-crystallization in three-dimensional shapes. CVD grown graphene was transferred on Si/SiO2. Through several lithography steps, graphene-based field-effect transistors were formed with Cr/Au source-drain electrodes and Si back gate electrode. For graphene modification we used 100 fs 80 MHz laser with 780 nm wavelength with different irradiation doses. Exposure of graphene to a femtosecond laser pulse is determined by the prevalence of physical or chemical effects during exposure to a laser pulse. The range of laser exposure was narrowed down to values causing the formation of atomic defects in the carbon lattice, which makes it possible to form nanopores in graphene and these doses are below the graphene ablation. The main tool for studying the effect of femtosecond laser irradiation was Raman spectroscopy. By evaluating the intensity ratio of certain peaks, namely the G-band (~1600 cm-1) and D-band (~ 1350 cm-1), the degree of functionalization, or amorphization of graphene, was estimated. It was found that the ablation threshold starts from 18 mW at the beam speed in the range of 400-500 μm/s. Just below this range, both graphene functionalization and a change in the graphene surface roughness were observed. Despite the change in the morphology of graphene, the graphene resistance fell by only ~4 times, and the transfer current-voltage curves of the graphene transistor did not change much, showing a shift towards higher voltages. With a decrease in the slope of the transfer current-voltage characteristics, the resistance of the structure also decreases with an increase in the dose of laser exposure, since the number of defects and functional groups in graphene increases. In addition, we found the effect of the laser polarization on the modification of graphene. The difference in parameters between the samples modified with different polarization directions along the direction of the beam motion can be explained as the interference interaction of the electron density in graphene. A beam passing over the graphene region excites hot electrons, which partially cause the graphene modification. After passing by the laser, the electron density does not have time to relax, and the next beam of photons affects the already excited electrons, increasing the total dose of laser radiation.

In this work, we numerically study the luminescence of nanodiamonds with NV centres embedded in a polymer layer on the surface of one-dimensional photonic crystal. The interaction of NV center spontaneous emission with the Bloch surface wave (BSW) is demonstrated. The presence of a photonic crystal leads to a change in the angular distribution of the emitter radiation due to the coupling of luminescence to BSW. We show that the best coupling efficiency of 71% is observed when NV centres are located in the close proximity to the BSW field maximum.