arXiv subjects

M. S. Lozhkin

Publications and source records attributed to M. S. Lozhkin.

3 recordsLinked to original sources

arXiv2025

Digital-Alloy Bragg Mirrors in High-Q Microcavities for Polariton Lasing

We present an approach to the molecular-beam epitaxy of high-Q planar GaAs-based microcavities in which the AlGaAs high-index layers of the distributed Bragg reflectors (DBRs) are replaced by short-period GaAs/AlAs superlattices (digital alloys) with similar optical properties. This design enables a significant reduction of interface roughness, precise control of the quarter-wavelength optical thickness and the effective Al content, suppression of the propagation of structural defects, and efficient tuning of intrinsic absorption at the polariton emission wavelength via optimization of the superlattice parameters. Using this approach, we fabricate a microcavity with a low polariton-lasing threshold of approximately 570 W/cm$^2$ and a high experimental quality factor of about 5.4 x $10^4$. This value exceeds by almost a factor of two the theoretical estimate obtained within an equivalent ternary-alloy model. We demonstrate that accurate modeling of the stop-band characteristics and the Q factor requires incorporating the modified electronic density of states in the superlattice, including quantum-confinement and excitonic effects.

cond-mat.mtrl-sci↗

arXiv2020

Amplified Spontaneous Emission and Random Lasing in MAPbBr$_3$ Halide Perovskite Single Crystals

Halide perovskites are a promising optical gain media with high tunability and simple solution synthesis. In this study, two gain regimes, namely amplified spontaneous emission and random lasing, are demonstrated in same MAPbBr$_3$ halide perovskite single crystal. For this, photoluminescence is measured at a temperature of 4 K with pulsed femtosecond pumping by UV light with a 80 MHz repetition rate. Random lasing is observed in areas of the sample where a random resonator was formed due to cracks and crystal imperfections. In more homogeneous regions of the sample, the dominant regime is amplified spontaneous emission. These two regimes are reliably distinguished by the line width, the mode structure, the growth of the intensity after the threshold, and the degree of polarization of the radiation. The spectral localization of the stimulated emission well below the bound exciton resonance raises a question concerning the origin of the emission in halide perovskite lasers.

physics.app-ph↗

arXiv2019

Nonlinear polaritons in monolayer semiconductor coupled to optical bound states in the continuum

Optical bound states in the continuum (BICs) provide a way to engineer very narrow resonances in photonic crystals. The extended interaction time in such systems is particularly promising for enhancement of nonlinear optical processes and development of the next generation of active optical devices. However, the achievable interaction strength is limited by the purely photonic character of optical BICs. Here, we mix optical BIC in a photonic crystal slab with excitons in atomically thin semiconductor MoSe$_2$ to form nonlinear exciton-polaritons with a Rabi splitting of 27~meV, exhibiting large interaction-induced spectral blueshifts. The asymptotic BIC-like suppression of polariton radiation into far-field towards the BIC wavevector, in combination with effective reduction of excitonic disorder through motional narrowing, results in small polariton linewidths below 3~meV. Together with strongly wavevector-dependent Q-factor, this provides for enhancement and control of polariton--polariton interactions and resulting nonlinear optical effects, paving the way towards tunable BIC-based polaritonic devices for sensing, lasing, and nonlinear optics.

cond-mat.mes-hall↗