Manipulation of resonant dielectric nanostructures is of paramount importance for next-generation photonic devices. Traditionally, researchers use two-dimensional or phase-change materials for this purpose. However, the former leads to small efficiency, while the latter lacks continuous changes. Here, we provide an alternative approach through laser-induced modification. Specifically, via a laser ablation process we synthesized molybdenum disulfide (MoS₂) nanoparticles (NPs), the composition of which we then controlled through laser fragmentation. It causes a transformation of MoS₂ into its oxide MoO_3−x, which, in turn, results in pronounced modification of the optical response, owing to a large difference between their optical constants. In addition, laser-fragmented NPs have a several times larger photothermal response, compared to the original MoS₂ and classical silicon NPs. Thus, our MoS₂-based laser-tunable NPs open up a new perspective for resonant nanophotonics, in particular, photothermal therapy.

Resonant optical responses of anisotropic molybdenum disulfide (${\mathrm{MoS}}_2$) nanoparticles (NPs) and their two-dimensional arrays (metasurfaces) are investigated. The nanoparticles in the form of disks with holes and with ${\mathrm{MoS}}_2$ layers oriented perpendicular to the disk's basis (in-plane material anisotropy) are considered. Using numerical calculations with analytical multipole analysis, we show that the material anisotropy of NPs provides an additional degree of freedom for manipulation of their resonant magnetic and electric dipole responses and affect the effective dipole polarizabilities. Based on this possibility and applying a special tuning procedure, we construct the ${\mathrm{MoS}}_2$ metasurfaces supporting the quasitrapped mode (QTM) resonance around the telecom wavelength of 1550 nm with high quality factor and high sensitivity to the environment. It is shown that regardless of extremely weak absorption of the single nanoparticles, the excitation of the QTM leads to effective narrowband absorption in the telecom wavelength range depending on the polarization direction of normally incident waves. It is demonstrated that a metasurface, composed of the ${\mathrm{MoS}}_2$ disks with the in-plane material anisotropy, has the properties of a continuous birefringent medium. Due to these properties, a normally incident linearly polarized wave can be transformed into transmitted and reflected waves with changed polarizations.

The present paper theoretically investigates features of quantum dynamics for localized plasmons in three-particle or four-particle spaser systems consisting of metal nanoparticles and semiconductor quantum dots. In the framework of the mean field approximation, the conditions for the observation of stable stationary regimes for single-particle plasmons in spaser systems are revealed, and realization of these regimes is discussed. The strong dipole-dipole interaction between adjacent nanoparticles for the four-particle spaser system is investigated. We show that this interaction can lead to the decreasing of the autocorrelation function values for plasmons. The generation of entangled plasmons in a three-particle spaser system with nonlinear plasmon-exciton interaction is predicted. The use of an external magnetic field is proposed for control of the cross correlations between plasmons in the three-particle spaser system.

The formation of pulses of surface electromagnetic waves at a metal–dielectric boundary is considered in the process of cooperative decay of excitons of quantum dots distributed near a metal surface in a dielectric layer. It is shown that the efficiency of exciton energy transfer to excited plasmons can, in principle, be increased by selecting the dielectric material with specified values of the complex permittivity. It is found that in the mean field approximation, the semiclassical model of formation of plasmon pulses in the system under study is reduced to the pendulum equation with the additional term of nonlinear losses.

New practical ways to reach the lasing effect in symmetrical metasurfaces have been developed and theoretically demonstrated. Our approach is based on excitation of the resonance of an octupole quasi-trapped mode (OQTM) in heterostructured symmetrical metasurfaces composed of monolithic disk-shaped van der Waals meta-atoms featured by thin photoluminescent layers and placed on a substrate. We revealed that the coincidence of the photoluminescence spectrum maximum of these layers with the wavelength of high-quality OQTM resonance leads to the lasing effect. Based on the solution of laser rate equations and direct full-wave simulation, it was shown that lasing is normally oriented to the metasurface plane and occurs from the entire area of metasurface consisting of MoS₂/hBN/MoTe₂ disks with line width of generated emission of only about 1.4 nm near the wavelength 1140 nm. This opens up new practical possibilities for creating surface emitting laser devices in subwavelength material systems.