arXiv subjects

Mihail Petrov

Publications and source records attributed to Mihail Petrov.

At least 37 records · Page 2Linked to original sources

arXiv2024

Nonradiant multiphoton states in quantum ring oligomers

Arrays of coupled dipole emitters support collective single- and multiphoton states that can preserve quantum excitations. One of the crucial characteristics of these states is the lifetime, which is fundamentally limited due to spontaneous emission. Here, we present a mechanism of the external coupling of two states via the radiation continuum, which allows for an increase in the lifetime of both single and double excitations. As an illustrative example, we consider a ringlike ensemble of quantum emitters, demonstrating that upon slight optimization of the structure geometry, one can increase the lifetime of singly and doubly excited states with nonzero orbital momentum by several orders of magnitude. The proposed mechanism of multiphoton excitation lifetime control has a universal nature and might be applied to a wide class of open quantum systems and quantum ensembles besides the particular geometry considered in this paper.

quant-ph↗

arXiv2024

Inverse design of Mie resonators with minimal backscattering

Manipulation and engineering of light scattering by resonant nanostructures is one of the central problems in optics and photonics. In this work, we theoretically study the effect of suppressed back-scattering of dielectric nanoantenna. We employed covariance matrix adaptation evolution strategy to identify the geometries of circular dielectric structures with minimized backward scattering cross section. Zero back-scattering is achieved due to generalized Kerker effect and multipole cancellation condition. We found a set of geometries and shapes of the nanoantenna having back-scattering intensity close to zero. With help of clustering algorithms, all the found geometries fall separated into several groups according to their multipolar content. While the optical properties of scatterers in each group were similar due to similar multipolar content, their shapes can be significantly different which stresses the ambiguity of free-form optimization problem. We believe that the obtained results and found possible classes on generalized Kerker nanoantenna can help in designing nanophotonic structures such as antireflective metasurfaces.

physics.optics↗

arXiv2024

Second-Order Nonlinear Circular Dichroism in Square Lattice Array of Germanium Nanohelices

Second harmonic generation (SHG) is prohibited in centrosymmetric crystals such as silicon or germanium due to the presence of inversion symmetry. However, the structuring of such materials makes it possible to break the inversion symmetry, thus achieving generation of second-harmonic. Moreover, various symmetry properties of the resulting structure, such as chirality, also influence the SHG. In this work we investigate second harmonic generation from an array of nanohelices made of germanium. The intensity of the second harmonic displayed a remarkable enhancement of over 100 times compared to a non-structured Ge thin film, revealing the influence of interaction between nanohelices. In particular, nonlinear circular dichroism, characterized through the SHG anisotropy factor g, changed its sign not only with the helix handedness, but with its density as well. We believe that our discoveries will open up new paths for the development of nonlinear photonics based on metamaterials and metasurfaces made of centrosymmetric materials.

physics.optics↗

arXiv2023

Engineering of high-$Q$ states via collective mode coupling in chains of Mie resonators

Efficient trapping of light in nanostructures is essential for the development of optical devices that are based on the interaction between light and matter. In this work, we show theoretically and experimentally that one-dimensional arrays of subwavelength dielectric Mie-resonant particles can support collective resonances with increased $Q$-factors. We demonstrate that the increase of the $Q$-factor can be explained by interaction between the collective electric and magnetic dipole modes of the chain resulting in appearance of the inflection point at the band edge. The considered effect is studied experimentally in the chain of high-index ceramic cylinders in the microwave spectral range.

physics.optics↗

arXiv2023

Non-radiative configurations of a few quantum emitters ensembles: evolutionary optimization approach

In this work, we employ differential evolution algorithm to identify the optimal configurations of small atomic ensembles supporting quantum states with maximal radiative lifetime. We demonstrate that atoms mostly tend to assemble in quasi-regular structures with specific geometry strongly depending on the minimal interatomic distance $r_{min}$. We identified the clear underlying physics that governs the suppression of the radiative losses in particular geometries. However, we reveal that the specific configurations in small ensembles are not easily predictable based on the knowledge established for the arrays of large size. In particular, the states that inherit their properties from bound states in continuum in infinite lattices turn out to be the most subradiant in a wide range of $r_{min}$ values. We also show that for small interatomic distance the chains with modulated interatomic distances exhibit fast exponential decrease of the radiative losses with the size of the ensemble.

quant-ph↗

arXiv2023

Strongly subradiant states in planar atomic arrays

The optically trapped ensembles of atoms provide a versatile platform for storing and coherent manipulation of quantum information. However, efficient realization of quantum information processing requires long-lived quantum states protected from the decoherence e.g. via spontaneous emission. Here, we theoretically study collective dipolar oscillations in finite planar arrays of quantum emitters in free space and analyze mechanisms that govern the emergence of strongly subradiant collective states. We demonstrate that the external coupling between the collective states associated with the symmetry of the array and with the quasi-flat dispersion of the corresponding infinite lattice plays a crucial role in the boost of their radiative lifetime. We show that among different regular arrangements of the atoms the square atomic arrays support eigenstates with minimal radiative losses that scale with the total number of atoms $N_{tot}$ as $\propto N_{tot}^{-5}$.

quant-ph↗

arXiv2023

Thermo-optical bistability enabled by bound states in the continuum in silicon metasurfaces

The control of light through all-optical means is a fundamental challenge in nanophotonics and a key effect in optical switching and logic. The optical bistability effect enables this control and can be observed in various planar photonic systems such as microdisk and photonic crystal cavities and waveguides. However, the recent advancements in flat optics with wavelength-thin optical elements require nonlinear elements based on metastructures and metasurfaces. The performance of these systems can be enhanced with high-Q bound states in the continuum (BIC), which leads to intense harmonic generation, improved light-matter coupling, and pushes forward sensing limits. In this study, we report on the enhanced thermo-optical nonlinearity and the observation of optical bistability in an all-dielectric metasurface membrane with BICs. Unlike many other nanophotonic platforms, metasurfaces allow for fine control of the quality factor of the BIC resonance by managing the radiative losses. This provides an opportunity to control the parameters of the observed hysteresis loop and even switch from bistability to optical discrimination by varying the angle of incidence. Additionally, we propose a mechanism of nonlinear critical coupling that establishes the conditions for maximal hysteresis width and minimal switching power, which has not been reported before. Our work suggests that all-dielectric metasurfaces supporting BICs can serve as a flat-optics platform for optical switching and modulation based on strong thermo-optical nonlinearity.

physics.optics↗

arXiv2023

Fast simulation of light scattering and harmonic generation in axially symmetric structures in COMSOL

In the field of optics and nanophotonics, simulation of electromagnetic scattering plays a major role in the study of complex nanostructures and optical devices. The numerical analysis of scattering spectra, even for nanocavities with simple geometry, is associated with significant computational difficulties. However, when the system exhibits certain symmetries, it becomes possible to simplify the problem through the process of separation of variables, which leads to a decrease in its dimension. In this paper, we aim to provide a practical guide to a fast simulation of linear and non-linear scattering problems in COMSOL Multiphysics for axisymmetric objects including computation of scattering cross-section as well as its multipolar decomposition, optical forces, and second harmonic generation. We also accompany the provided guide with the ready-to-run COMSOL models.

physics.optics↗

arXiv2023

Bistable scattering of nano-silicon for super-linear super-resolution imaging

Optical bistability is fundamental for all-optical switches, but typically requires high-Q cavities with micrometer sizes. Through boosting nonlinearity with photo-thermo-optical effects, we achieve bistability in a silicon Mie resonator with a volume size of 10-3 um3 and Q-factor < 10, both are record-low. Furthermore, bistable scattering naturally leads to large super-linear emission-excitation power dependence, which we applied to enhance optical resolution by more than 3 times. Our work paves the way toward nanoscale photonics computation and label-free semiconductor nano-inspection.

physics.optics↗

arXiv2023

Exceptional points in single open acoustic resonator due to the symmetry breaking

Exceptional points (EPs) have been widely studied in quantum mechanics, condensed matter physics, optics and photonics. However, their potential in acoustics has only recently been recognized due to the rapid development of acoustic metamaterials. This paper proposes a method for achieving EP conditions in acoustic resonators by lowering their symmetry and enabling resonant mode interaction. The formation of EPs is predicted through direct numerical simulation supported by coupled mode theory and resonant state expansion. These findings have significant implications for the design and optimization of acoustic metamaterials for applications such as acoustic sensing and noise reduction.

physics.class-ph↗

arXiv2022

Nonlinearity-induced optical torque

Optically-induced mechanical torque leading to the rotation of small objects requires the presence of absorption or breaking cylindrical symmetry of a scatterer. A spherical non-absorbing particle cannot rotate due to the conservation of the angular momentum of light upon scattering. Here, we suggest a novel physical mechanism for the angular momentum transfer to non-absorbing particles via nonlinear light scattering. The breaking of symmetry occurs at the microscopic level manifested in nonlinear negative optical torque due to the excitation of resonant states at the harmonic frequency with higher projection of angular momentum. The proposed physical mechanism can be verified with resonant dielectric nanostructures, and we suggest some specific realizations.

physics.optics↗

arXiv2022

Nonlinear optical heating of all-dielectric super-cavity: efficient light-to-heat conversion through giant thermorefractive bistability

Optical heating of resonant nanostructures is one of the key issues in modern nanophotonics, being either harmful or desirable effect depending on the applications. Despite a linear regime of light-to-heat conversion is well-studied both for metal and semiconductor resonant systems generalized as critical coupling condition, the clear strategy to optimize optical heating upon high-intensity light irradiation is still missing. In this work, we propose a simple analytical model for such problem taking into account material properties changes caused by the heating. It allows us to derive a new general critical coupling condition for the nonlinear case, requiring counterintuitive initial spectral mismatch between the pumping light frequency and resonant one. Basing on the suggested strategy, we develop an optimized design for efficient nonlinear optical heating, which employs a cylindrical nanoparticle supporting quasi bound state in the continuum mode (quasi-BIC or so-called `super-cavity mode') excited by the incident azimuthal vector beam. Our approach provides a background for various nonlinear experiments related to optical heating and bistability, where self-action of the intense laser beam can change resonant properties of the irradiated nanostructure.

physics.optics↗

arXiv2022

Multipolar theory of bianisotropic response

Bianisotropy of metaatoms is usually associated with their nonlocal response and the mutual coupling between electric and magnetic dipole moments induced by the incident field. In this work, we generalize the theory of bianisotropy beyond the dipole response to the cases of arbitrary high-order multipole resonances. We demonstrate that bianisotropy is exclusively caused by the absence of the inversion symmetry of metaatoms. The strength of the bianisotropy response is normally increased with the size of a meta-atom but its origin is fully connected to the symmetry of the structure. As an important example of bianisotropic particle, we consider a triangular prism and show how accounting for the higher-order multipoles prevents the violation of the Onsager-Casimir conditions for kinetic coefficients appearing in the dipole approximation. The developed theory is an important step towards a deeper insight into the scattering properties of nanoantennas and meta-atoms.

physics.optics↗

arXiv2022

Thermo-optical reshaping of SHG emission from dimerall-dielectric nanoresonators

In recent years resonant semiconductor and all-dielectric nanophotonics offered a lot of possibilities for thermally-induced light manipulation at the nanoscale. Owing to high-quality resonant states, such nanostructures allow for efficient light-to-heat conversion supported by various temperature detection approaches based on thermally sensitive intrinsic optical responses (photoluminescence, Raman scattering, thermorefraction etc.). In this work, we study theoretically a phenomenon of the photothermal reshaping of the radiation pattern of second-harmonic generation (SHG) that occurs in resonant all-dielectric systems. In the suggested geometry near-IR pulsed laser is utilized for excitation of SHG while simultaneous continuous wave visible laser heats the structure. The thermooptical switching of the resonant optical states in the nanostructures governs the reconfiguration of the emission pattern, without significant loss in the magnitude of the SHG. We believe, that our findings will pave the way for subwavelength-size near-IR thermally switchable nonlinear optical devices.

physics.optics↗

arXiv2022

Second-harmonic generation tuning by stretching arrays of GaAs nanowires

We present a wearable device with III-V nanowires in a flexible polymer, which is used for active mechanical tuning of the second-harmonic generation intensity. An array of vertical GaAs nanowires was grown with metalorganic vapour-phase epitaxy, then embedded in polydimethylsiloxane and detached from the rigid substrate with mechanical peel off. Experimental results show a tunability of the second-harmonic generation intensity by a factor of two for 30% stretching which matches the simulations including the distribution of sizes. We studied the impact of different parameters on the band dispersion and tunability of the second-harmonic generation, such as the pitch, the length, and the diameter. We predict at least three orders of magnitude active mechanical tuning of the nonlinear signal intensity for nanowire arrays. The flexibility of the array together with the resonant wavelength engineering make such structures perspective platforms for future bendable or stretchable nanophotonic devices as light sources or sensors.

physics.optics↗

arXiv2021

Acoustic resonators: symmetry classification and multipolar content of the eigenmodes

Acoustics recently became a versatile platform for discovering novel physical effects and concepts at a relatively simple technological level. On this way, single resonators and the structure of their resonant modes play a central role and define the properties of complex acoustic systems such as acoustic metamaterials, phononic crystals, and topological structures. In this paper, we present a powerful method allowing a qualitative analysis of eigenmodes of resonators in the linear monochromatic acoustic domain based on multipole classification of eigenmodes. Using the apparatus of group theory, we explain and predict the structure of the scattered field knowing only the symmetry group of the resonator by connecting the multipolar content of incident and scattered fields. Such an approach can be utilized for developing resonators with predesigned properties avoiding time-consuming simulations. We have performed full multipole symmetry classification for a number of resonators geometries, and tightened it with scattering spectra profiles.

physics.class-ph↗

arXiv2021

Optical Pulling and Pushing Forces via Bloch Surface Waves

Versatile manipulation of nano- and microobjects underlies the optomechanics and a variety of its applications in biology, medicine, and lab-on-a-chip platforms. For flexible tailoring optical forces, as well as for extraordinary optomechanical effects, additional degrees of freedom should be introduced into the system. Here, we demonstrate that photonic crystals provide a flexible platform for nanoparticles optical manipulation due to both Bloch surface waves (BSWs) and the complex character of the reflection coefficient paving a way for complex optomechanical interactions control. We demonstrate that appearance of enhanced pulling and pushing transversal optical forces acting on a single bead placed above a one-dimensional photonic crystal due to directional excitation of Bloch surface wave at the photonic crystal interface. Our theoretical results, which are supported with numerical simulations, demonstrate angle or wavelength assisted switching between BSW-induced optical pulling and pushing forces. Easy-to-fabricate for any desired spectral range photonic crystals are shown to be prospective for precise optical sorting of nanoparticles, especially for core-shell nanoparticles, which are difficult to sort with conventional optomechanical methods. Our approach opens opportunities for novel optical manipulation schemes and platforms and enhanced light-matter interaction in optical trapping setups.

physics.optics↗

arXiv2021

Bound States in the Continuum in Compact Acoustic Resonators

We reveal that finite-size solid acoustic resonators can support genuine bound states in the continuum (BICs) completely localized inside the resonator. The developed theory provides the multipole classification of such BICs in the resonators of various shapes. It is shown how breaking of the resonator's symmetry turns BICs into quasi-BICs manifesting themselves in the scattering spectra as high-Q Fano resonances. We believe that the revealed novel states will push the performance limits of acoustic devices and will serve as high-Q building blocks for acoustic sensors, antennas, and topological acoustic structures.

physics.class-ph↗