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Optics (physics.optics)

Mon, 22 May 2023

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1.Probing and control of guided exciton-polaritons in a 2D semiconductor-integrated slab waveguide

Authors:Valeriy I. Kondratyev, Dmitry V. Permyakov, Tatyana V. Ivanova, Ivan V. Iorsh, Dmitry N. Krizhanovskii, Maurice S. Skolnick, Vasily Kravtsov, Anton K. Samusev

Abstract: Guided 2D exciton-polaritons, resulting from the strong coupling of excitons in semiconductors with non-radiating waveguide modes, provide an attractive approach towards developing novel on-chip optical devices. These quasiparticles are characterized by long propagation distances and efficient nonlinear interaction. However, as guided exciton-polaritons are uncoupled from the free space, it is challenging to investigate them using conventional far-field spectroscopy techniques. Here we demonstrate a powerful approach for probing and manipulating guided polaritons in a Ta$_2$O$_5$ slab integrated with a WS$_2$ monolayer using evanescent coupling through a high-index solid immersion lens. Tuning the nanoscale gap between the lens and the sample, we demonstrate in-situ control over radiative losses and Rabi splitting of guided polaritons at ambient conditions. This extra degree of freedom allows for extracting all the intrinsic parameters of the strongly coupled system under study. Our results enable the future development of integrated optics employing room-temperature exciton-polaritons in 2D semiconductor-based structures.

2.Polariton lasing in Mie-resonant perovskite nanocavity

Authors:M. A. Masharin, D. Khmelevskaia, V. I. Kondratiev, D. I. Markina, A. D. Utyushev, D. M. Dolgintsev, A. D. Dmitriev, V. A. Shahnazaryan, A. P. Pushkarev, F. Isik, I. V. Iorsh, I. A. Shelykh, H. V. Demir, A. K. Samusev, S. V. Makarov

Abstract: Deeply subwavelength lasers (or nanolasers) are highly demanded for compact on-chip bioimaging and sensing at the nanoscale. One of the main obstacles for the development of single-particle nanolasers with all three dimensions shorter than the emitting wavelength in the visible range is the high lasing thresholds and the resulting overheating. Here we exploit exciton-polariton condensation and mirror-image Mie modes in a cuboid CsPbBr$_3$ nanoparticle to achieve coherent emission at the visible wavelength of around 0.53~$\mu $m from its ultra-small ($\approx$0.007$\mu$m$^3$ or $\approx\lambda^3$/20) semiconductor nanocavity. The polaritonic nature of the emission from the nanocavity localized in all three dimensions is proven by direct comparison with corresponding one-dimensional and two-dimensional waveguiding systems with similar material parameters. Such a deeply subwavelength nanolaser is enabled not only by the high values for exciton binding energy ($\approx$35 meV), refractive index ($>$2.5 at low temperature), and luminescence quantum yield of CsPbBr$_3$, but also by the optimization of polaritons condensation on the Mie resonances. Moreover, the key parameters for optimal lasing conditions are intermode free spectral range and phonons spectrum in CsPbBr$_3$, which govern polaritons condensation path. Such chemically synthesized colloidal CsPbBr$_3$ nanolasers can be easily deposited on arbitrary surfaces, which makes them a versatile tool for integration with various on-chip systems.

3.Linear Optical Random Projections Without Holography

Authors:Ruben Ohana, Daniel Hesslow, Daniel Brunner, Sylvain Gigan, Kilian Müller

Abstract: We introduce a novel method to perform linear optical random projections without the need for holography. Our method consists of a computationally trivial combination of multiple intensity measurements to mitigate the information loss usually associated with the absolute-square non-linearity imposed by optical intensity measurements. Both experimental and numerical findings demonstrate that the resulting matrix consists of real-valued, independent, and identically distributed (i.i.d.) Gaussian random entries. Our optical setup is simple and robust, as it does not require interference between two beams. We demonstrate the practical applicability of our method by performing dimensionality reduction on high-dimensional data, a common task in randomized numerical linear algebra with relevant applications in machine learning.

4.Single-shot spatial coherence of a plasma based soft X-ray laser

Authors:Martin Albrecht, Ondřej Hort, Michaela Kozlová, Miroslav Krůs, Jaroslav Nejdl

Abstract: Many applications of short-wavelength radiation impose strong requirements on the coherence properties of the source. However, the measurement of such properties poses a challenge, mainly due to the lack of high-quality optics and source fluctuations that often violate assumptions necessary for multi-shot or cumulative techniques. In this article, we present a new method of single-shot spatial coherence measurement adapted to the soft X-ray spectral range. Our method is based on a far-field diffraction pattern from a binary transmission mask consisting of a non-redundant array of simple apertures. Unlike all currently available methods, our technique allows measuring radiation field with an arbitrary spatial coherence function without any prior assumption on intensity distribution or the model of the degree of spatial coherence. We experimentally verified the technique by retrieving the spatial coherence functions of individual shots of laser-driven Zn plasma soft X-ray laser with one- and two-dimensional masks. The experimental results revealed nontrivial illumination pattern and strong asymmetry of the spatial coherence function, which clearly calls for abandoning the often used models that assume rotational invariance of the coherence function, such as the popular Gaussian-Schell beam model.

5.Observation of Quantum metric and non-Hermitian Berry curvature in a plasmonic lattice

Authors:Javier Cuerda, Jani M. Taskinen, Nicki Källman, Leo Grabitz, Päivi Törmä

Abstract: We experimentally observe the quantum geometric tensor, namely the quantum metric and the Berry curvature, for a square lattice of radiatively coupled plasmonic nanoparticles. We observe a non-zero Berry curvature and show that it arises solely from non-Hermitian effects. The quantum metric is found to originate from a pseudospin-orbit coupling. The long-range nature of the radiative interaction renders the behavior distinct from tight-binding systems: Berry curvature and quantum metric are centered around high-symmetry lines of the Brillouin zone instead of high-symmetry points. Our results inspire new pathways in the design of topological systems by tailoring losses or gain.

6.Pseudospin-orbit coupling and non-Hermitian effects in the Quantum Geometric Tensor of a plasmonic lattice

Authors:Javier Cuerda, Jani M. Taskinen, Nicki Källman, Leo Grabitz, Päivi Törmä

Abstract: We theoretically predict the full quantum geometric tensor, comprising the quantum metric and the Berry curvature, for a square lattice of plasmonic nanoparticles. The gold nanoparticles act as dipole or multipole antenna radiatively coupled over long distances. The photonic-plasmonic eigenfunctions and energies of the system depend on momentum and polarization (pseudospin), and their topological properties are encoded in the quantum geometric tensor. By T-matrix numerical simulations, we identify a TE-TM band splitting at the diagonals of the first Brillouin zone, that is not predicted by the empty lattice band structure nor by the highly symmetric nature of the system. Further, we find quantum metric around these regions of the reciprocal space, and even a non-zero Berry curvature despite the trivial lattice geometry and absence of magnetic field. We show that this non-zero Berry curvature arises exclusively from non-Hermitian effects which break the time-reversal symmetry. The quantum metric, in contrast, originates from a pseudospin-orbit coupling given by the polarization and directional dependence of the radiation.

7.Effective Electromagnetic Wave Properties of Disordered Stealthy Hyperuniform Layered Media Beyond the Quasistatic Regime

Authors:Jaeuk Kim, Salvatore Torquato

Abstract: Disordered stealthy hyperuniform dielectric composites exhibit novel electromagnetic wave transport properties in two and three dimensions. Here, we carry out the first study of the electromagnetic properties of one-dimensional (1D) disordered stealthy hyperuniform layered media. From an exact nonlocal theory, we derive an approximation formula for the effective dynamic dielectric constant tensor ${\boldsymbol \varepsilon}_e({\bf k}_q,\omega)$ of general 1D media that is valid well beyond the quasistatic regime and apply it to 1D stealthy hyperuniform systems. We consider incident waves of transverse polarization, frequency $\omega$, and wavenumber $k_q$. Our formula for ${\boldsymbol \varepsilon}_e({k}_q,\omega)$, which is given in terms of the spectral density, leads to a closed-form relation for the transmittance $T$. Our theoretical predictions are in excellent agreement with finite-difference time-domain (FDTD) simulations. Stealthy hyperuniform layered media have perfect transparency intervals up to a finite wavenumber, implying no Anderson localization, but non-stealthy hyperuniform media are not perfectly transparent. Our predictive theory provides a new path for the inverse design of the wave characteristics of disordered layered media, which are readily fabricated, by engineering their spectral densities.