arXiv subjects

Omri Meron

Publications and source records attributed to Omri Meron.

5 recordsLinked to original sources

arXiv2026

Polytype-Dependent Upconversion Photoluminescence in 3R-MoS2

Ferroelectric van der Waals materials offer switchable polarization states, yet optical readout of their stacking configurations remains challenging. Here, building on the resonant exciton-exciton annihilation (EEA) mechanism recently identified in 2H-phase TMDs, we report the first observation of upconversion photoluminescence (UPL) in rhombohedral MoS$_2$ and demonstrate that this many-body process is strongly polytype-dependent. Using low-temperature spectroscopy, we observe anti-Stokes emission with superlinear power dependence characteristic of EEA. Beyond serving as an accurate layer-number sensor due to discrete bandgap variations, UPL provides a sensitive probe of stacking order across thicknesses. The two neutral trilayer polytypes, which remain indistinguishable by surface potential measurements and second harmonic generation, exhibit markedly different UPL intensities. This sensitivity persists in thicker samples where multiple configurations coexist. First-principles calculations suggest that the intensity contrast originates primarily from the layer confinement of the annihilating excitons, while energy matching to the $\Gamma$ final-state manifold provides additional intensity selectivity. Power-dependent spectroscopy further disentangles two distinct annihilation channels originating from different dark exciton valleys, identified through their contrasting intensity scaling and opposite density-induced energy shifts. Crucially, the annihilation process doubles the energy separation of nearly degenerate dark excitons while converting their weak emission into bright signal, providing experimental access to valley-specific responses that are obscured in direct dark-exciton spectroscopy. Our findings demonstrate that ferroelectric configurations provide a new degree of freedom for controlling nonlinear optical processes.

cond-mat.mtrl-sci↗

arXiv2026

Single-Shot Multispectral Mid-Infrared Imaging with Incoherent Light via Adiabatic Upconversion

Multispectral mid-infrared (2-5 ${{\mu}m}$) imaging is a critical capability across science and technology, offering a window into the vibrational and thermal landscape of matter that is inaccessible to visible sensors. It bridges the microscopic world of molecular interactions with macroscopic sensing technologies, with applications in environmental sensing, defense and molecular diagnostics. However, current mid-IR cameras require cryogenic cooling and exhibit limited pixel resolution, high cost, and restricted spectral access. Optical up-conversion provides a pathway to overcome these limitations, but existing systems typically rely on narrowband phase matching, mechanical scanning, or angular tuning, limiting imaging speed and practicality. Here, we demonstrate the first single-shot, room-temperature multispectral mid-IR imaging of incoherent thermal light enabled by adiabatic sum-frequency conversion. Our system simultaneously converts the entire (2-5 ${{\mu}m}$) region into the visible domain, capturing the image on a Silicon detector with spatial resolution below 20 ${{\mu}m}$ and high angular tolerance. We validate full-field imaging using a USAF resolution target and demonstrate spectroscopic contrast imaging in dielectric metamaterials by resolving wavelength and polarization dependent scattering resonances, all achieved without scanning, thermal control, or cryogenic operation. This compact and robust approach bridges the gap between laboratory-grade infrared sensors and scalable Silicon-based detection technologies suitable for real-world deployment.

physics.optics↗

arXiv2025

Shaping Ultrafast Pulses for Enhanced Resonant Nonlinear Interactions

Coherent control with shaped ultrafast pulses is a powerful approach for steering nonlinear light-matter interactions. Previous studies in quantum control have shown that, beyond transform-limited pulses, those with antisymmetric spectral phases can drive nonresonant multiphoton transitions with comparable efficiency. However, in resonant multiphoton transitions, the material's spectral-phase response introduces dispersion that degrades nonlinear efficiency. Pre-shaping the pulse to compensate for the material's impulse response can restore and enhance nonlinear interactions beyond the transform-limited case. Yet, is this the only spectral phase that can yield such enhancement? Here, we study sub-10 fs single-pulse four-wave mixing in resonant plasmonic nanostructures using arctangent spectral-phase-shaped pulses. We uncover two distinct enhancement regimes: one compensating for material dispersion, and a counterintuitive regime where the arctangent phase induces an antisymmetric polarization response, driving constructive multiphoton pathway interference. Our theoretical analysis provides clear physical explanation for both phenomena. Notably, it predicts that both enhancement mechanisms scale exponentially with harmonic order, offering a powerful strategy for dramatically enhancing high-order harmonic generation in resonant systems.

physics.optics↗

arXiv2025

Photoluminescence Detection of Polytype Polarization in r-MoS2 Enabled by Asymmetric Dielectric Environments

The rhombohedral (r) polytypes of transition metal dichalcogenides (TMDs) constitute a novel class of two-dimensional ferroelectric materials, where lateral shifts between parallel layers induce reversible out-of-plane polarization. This emerging field, known as SlideTronics, holds significant potential for next-generation electronic and optoelectronic applications. While extensive studies have investigated the effects of electrical and chemical doping on excitonic signatures in 2H-TMDs, as well as the influence of dielectric environments on their optical properties, the impact of intrinsic polarization in asymmetric environments remains largely unexplored. Here, we demonstrate a striking polarization-dependent photoluminescence (PL) contrast of up to 400\% between ferroelectric domains in bilayer and trilayer rhombohedral molybdenum disulfide (r-MoS2). This pronounced contrast arises from an asymmetric dielectric environment, which induces polarization-dependent shifts in the Fermi energy, leading to a modulation of the exciton-trion population balance. A detailed temperature-dependent line shape analysis of the PL, conducted from 4K to room temperature, reveals domain-specific trends that further reinforce the connection between polarization states and excitonic properties. The persistence of these distinct optical signatures at room temperature establishes PL as a robust and non-invasive probe for ferroelectric domain characterization, particularly in fully encapsulated device architectures where conventional techniques, such as Kelvin probe force microscopy, become impractical.

cond-mat.mtrl-sci↗

arXiv2023

Shaping Exciton Polarization Dynamics in 2D Semiconductors by Tailored Ultrafast Pulses

The ultrafast formation of strongly bound excitons in two-dimensional semiconductors provide a rich platform for studying fundamental physics as well as developing novel optoelectronic technologies. While extensive research has explored the excitonic coherence, many-body interactions, and nonlinear optical properties, the potential to study these phenomena by directly controlling their coherent polarization dynamics has not been fully realized. In this work, we use a sub-10fs pulse shaper to study how temporal control of coherent exciton polarization affects the generation of four-wave mixing in monolayer WSe2 under ambient conditions. By tailoring multiphoton pathway interference, we tune the nonlinear response from destructive to constructive interference, resulting in a 2.6-fold enhancement over the four-wave mixing generated by a transform-limited pulse. This demonstrates a general method for nonlinear enhancement by shaping the pulse to counteract the temporal dispersion experienced during resonant light-matter interactions. Our method allows us to excite both 1s and 2s states, showcasing a selective control over the resonant state that produces nonlinearity. By comparing our results with theory, we find that exciton-exciton interactions dominate the nonlinear response, rather than Pauli blocking. This capability to manipulate exciton polarization dynamics in atomically thin crystals lays the groundwork for exploring a wide range of resonant phenomena in condensed matter systems and opens up new possibilities for precise optical control in advanced optoelectronic devices.

physics.optics↗