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Compact planar photonic elements serving for efficient control over the polarization of light are of paramount importance in photonics. Here, we propose a design of a chiral periodic metasurface based on plasmonic nanodisks and nanorods arranged asymmetrically in a unit cell. Using the finite-difference time-domain analysis, we show that the collective lattice resonance harnessed by the diffraction coupling of the plasmonic unit cells is the heart of the revealed resonant 38% circular dichroism effect. The circular dichroism enhancement of the considered structure is improved using the deep-learning-assisted optimization of the metasurface design.

Micro- and nanostructuring of optical media is the cornerstone for a wide range of applications in optics. Artificial structures significantly enrich the interaction of light with dielectrics and metals and are harnessed to reveal exciting optical effects. Recently hypercrystals were proposed as intriguing class of periodic structures bringing together hyperbolic dispersion law of hyperbolic metamaterials and the Bragg diffraction. In this work we proposed the finite-difference frequency-domain method for modeling of light diffraction in these highly anisotropic structures. The method is suitable for one- and two-dimensional gratings as well as multilayer gratings made of anisotropic materials. Developed approach gives advantages over the finite-difference time-domain method (FDTD) and rigorous-coupled mode analysis (RCWA) widely used for calculation of light diffraction in gratings. Proposed method eliminates evaluation of time dynamics and discretization of whole volume of a structure as the FDTD does. Instead, Yee’s mesh of the cross section of the unit cell of grating is involved. As well information about the Bloch modes of the field inside the structure inaccessible directly for the FDTD is obtained. We used of values of electromagnetic field in mesh nodes instead Fourier series applied in the RCWA to overcome difficulties of the RCWA for high contrast and highly anisotropic structures as hypercrystals. Using the proposed numerical approach, we demonstrate that interface of one-dimensional hypercrystals formed by ridges of hyperbolic metamaterial can support excitation of the Dyakonov plasmons, which merge the Dyakonov waves supported by the interface of birefringent crystal and surface plasmon polaritons in metals.

Time-resolved photoluminescence decay measurements have been performed on samples with varying-sized self-assembled InAs/GaAs quantum dot ensembles, formed by substrate misorientation. Ground-state radiative recombination lifetimes from 0.8 to 5.3 ns in the incident power density range of 0.05–3400 W cm−2 at a temperature of 77 K have been obtained. It was found that a reduction of the quantum dot size led to a corresponding reduction of the radiative lifetime. The evident biexponential decay was obtained for the ground state emission of the quantum dot array, with the slower second component attributed to a carrier recapturing process.

We have studied photoreflectance (PR) and reflectance spectra of undoped molecular‐beam‐epitaxy GaAs films on semi‐insulating GaAs substrates at low temperature. In the PR spectra a sharp structure near the band‐gap energy was observed which is sensitive to pump and probe light intensity. The origin of this structure was investigated by combining time‐resolved and depth‐resolved measurements. It is shown that the sharp PR structure arises from the superposition of a fast and a slow component of the modulated spectra. The slow PR signal originates from the epilayer–substrate interface. Both components are attributed to the modulation of exitonic transitions centered at slightly different energies.

Below‐gap structures in photoreflectance spectra of semi‐insulating GaAs were observed originating from electroabsorption of light reflected from the back surface. The peak amplitude of these structures was strongly temperature dependent within the range (78–290) K. The different lineshape at low temperature in comparison to that at room temperature suggested different physical mechanisms. This conclusion was proven experimentally using a two phase lock‐in technique by which a fast (X) and slow (Y) component of the spectra could be separated. A fit procedure provides the pure back surface reflection effect for both components. The X mode dominating at low temperatures is attributed to electromodulation of the field‐broadened excitonic absorption tail whereas the Y mode originates from the Franz–Keldysh electroabsorption.

We present the realization of the multiperiodic optical pendulum effect in 1D porous silicon photonic crystals (PhCs) under dynamical Bragg diffraction in the Laue scheme. The diffraction-thick PhC contained 360 spatial periods with a large variation of the refractive index of adjacent layers of 0.4. The experiments reveal switching of the light leaving the PhC between the two spatial directions, which correspond to Laue diffraction maxima, as the fundamental wavelength or polarization of the incident light is varied. A similar effect can be achieved when the temperature of the sample or the intensity of the additional laser beam illuminating the crystal are changed. We show that in our PhC structures, the spectral period of the pendulum effect is down to 5 nm, while the thermal period is about 10 °C.