Polariton Lasing Research Articles

Low Threshold Room Temperature Polariton Lasing from Fluorene‐Based Oligomers

AbstractOrganic semiconductors possessing tightly bound Frenkel excitons are known to be attractive candidates for demonstrating polariton lasing at room temperature. As polariton lasing can occur without inversion, it is a potential route to very low threshold coherent light sources. However, so far, the thresholds of organic polariton lasers have generally been much higher than those of organic photon lasers. Here this problem has been addressed by investigating two new organic molecules with a structure combining fluorene and carbazole groups. The materials are readily deposited from solution and exhibit high photoluminescence quantum yields, high absorption coefficients, and large radiative decay rates in neat films. Room temperature polariton lasing is realized in both materials with incident thresholds of 13.5 and 9.7 µJ cm−2, corresponding to absorbed thresholds of 3.3 and 2.2 µJ cm−2, respectively. These are the lowest values reported to date for polariton lasing in organic semiconductor materials, and approach typical values for organic photon lasers. The step‐like power dependent blue‐shift of polariton modes indicates an interplay between different depletion channels of the exciton reservoir. This work brings practical room temperature polaritonic devices and future realization of electrically driven polariton lasers a step closer.

Polariton lasing and energy-degenerate parametric scattering in non-resonantly driven coupled planar microcavities

Abstract Multi-level exciton-polariton systems offer an attractive platform for studies of non-linear optical phenomena. However, studies of such consequential non-linear phenomena as polariton condensation and lasing in planar microcavities have so far been limited to two-level systems, where the condensation takes place in the lowest attainable state. Here, we report non-equilibrium Bose–Einstein condensation of exciton-polaritons and low threshold, dual-wavelength polariton lasing in vertically coupled, double planar microcavities. Moreover, we find that the presence of the non-resonantly driven condensate triggers interbranch exciton-polariton transfer in the form of energy-degenerate parametric scattering. Such an effect has so far been observed only under excitation that is strictly resonant in terms of the energy and incidence angle. We describe theoretically our time-integrated and time-resolved photoluminescence investigations by an open-dissipative Gross–Pitaevskii equation-based model. Our platform’s inherent tunability is promising for construction of planar lattices, enabling three-dimensional polariton hopping and realization of photonic devices, such as all-optical polariton-based logic gates.

Polariton Modes in a Cylindrical Microcavity in the Polariton Lasing Regime

Polariton Modes in a Cylindrical Microcavity in the Polariton Lasing Regime

Size dependent polaritonic effects in GaN microrod studied through optical property investigation

We have investigated the optical properties of gallium nitride microrods systematically by spatially resolved cathodoluminescence, Raman and photoluminescence measurements. Blueshifting in near band gap energy with the decrease in diameter of studied microrods has been observed from cathodoluminescence and is attributed to the formation of whispering gallery mode polaritons in microrod cavity. Raman spectra along the length of the tapered microrod shows no noticable shifting in Raman mode positions confirm that the band gap energy changes with the decrease in diameter is not due to the stress/strain or different doping concentration. PL was carried out to look at the probable possibilities of polariton formation in microrod cavity. Exciton photon coupling strength depends on the diameter of the microrods and the coupling strength decreases with the decrease in diameter as studied from spatial-resolved photoluminescence spectra. Rabi splitting energy of nearly 300 ± 40 meV and so polariton lasing was observed from the wide end but that gradually decreases with the decrease in diameter.

Coherent Topological Polariton Laser

Topological concepts have been applied to a wide range of fields in order to successfully describe the emergence of robust edge modes that are unaffected by scattering or disorder. In photonics, indications of lasing from topologically protected modes with improved overall laser characteristics were observed. Here, we study exciton-polariton microcavity traps that are arranged in a one-dimensional Su-Schrieffer-Heeger lattice and form a topological defect mode from which we unequivocally observe highly coherent polariton lasing. Additionally, we confirm the excitonic contribution to the polariton lasing by applying an external magnetic field. These systematic experimental findings of robust lasing and high temporal coherence are meticulously reproduced by a combination of a generalized Gross-Pitaevskii model and a Lindblad master equation model. Thus, by using the comparatively simple SSH geometry, we are able to describe and control the exciton-polariton topological lasing, allowing for a deeper understanding of topological effects on microlasers.

Ultralow Threshold Polariton Condensate in a Monolayer Semiconductor Microcavity at Room Temperature.

Exciton-polaritons, hybrid light-matter bosonic quasiparticles, can condense into a single quantum state, i.e., forming a polariton Bose-Einstein condensate (BEC), which represents a crucial step for the development of nanophotonic technology. Recently, atomically thin transition-metal dichalcogenides (TMDs) emerged as promising candidates for novel polaritonic devices. Although the formation of robust valley-polaritons has been realized up to room temperature, the demonstration of polariton lasing remains elusive. Herein, we report for the first time the realization of this important milestone in a TMD microcavity at room temperature. Continuous wave pumped polariton lasing is evidenced by the macroscopic occupation of the ground state, which undergoes a nonlinear increase of the emission along with the emergence of temporal coherence, the presence of an exciton fraction-controlled threshold and the buildup of linear polarization. Our work presents a critically important step toward exploiting nonlinear polariton-polariton interactions, as well as offering a new platform for thresholdless lasing.

Strongly Coupled Systems for Nonlinear Optics

AbstractStrong coupling is a distinct light–matter interaction regime, in which the interaction is manifested in coherent oscillations of energy between matter and a photonic subsystem. The consequence of such a strong coupling is the adjustment of the energy states of molecules and materials, which can bring about fascinating chemical and physical properties, and therefore result in advanced applications in many fields such as Bose–Einstein condensation and coherent emission, polariton lasing, superfluidity, quantum information processing, Raman scattering, chemical landscape, etc. Recently, strong coupling has also demonstrated profound impacts on the nonlinear optical (NLO) properties of molecular materials. In this review, the recent research progress in the field of strongly coupled systems for NLO applications is summarized. The underlying concepts and the detailed features of strongly coupled molecular systems are introduced, and the NLO characteristics of strongly coupled systems are reviewed. Finally, an outlook of future directions for this emerging field is given.

Metamorphosis of Goldstone and soft fluctuation modes in polariton lasers

For a driven-dissipative quantum many-body system prepared in a spontaneous broken-symmetry steady state, in addition to the Goldstone mode, the soft fluctuation modes provide important insight into the system's dynamics. Using a microscopic polariton laser theory, we find a rich transformation behavior of discrete and continuum soft modes in a two parameter (pump density and cavity dissipation rate) space. Our theory yields a unified picture of a variety of seemingly disconnected physical concepts including Mott transition, Mollow spectra or relaxation oscillations, polaritonic Bardeen-Cooper-Schrieffer gaps, and Goldstone companion modes. In particular, transformation paths connect the Goldstone companion modes with the Mollow analog modes across a line of exceptional points.

Continuous-wave operation of an electrically pumped single microribbon based Fabry-Perot microlaser.

Fabry-Perot (FP) mode microlasers have been popularized and applied widely in on-chip coherent light sources because of the unique advantages of directional output emission. In this work, a heterojunction light-emitting diode (LED) made of a Ga-doped ZnO (ZnO:Ga) microribbon and p-GaAs template is fabricated. And its electroluminescence characteristics of strong coupling of exciton-photon and polariton lasing, in the blue-violet spectrum, were demonstrated under continuous-wave operation of an electrical injection. In the device structure, a single microribbon with a rectangular-shaped cross section can achieve the FP-mode lasing action by the optical oscillation between the two lateral sides of the microcrystals in the ultraviolet spectrum. As the reverse-current is below the threshold value, the device can have radiative polaritonic lighting directly from bilateral sides of the microribbon, yielding strong coupling between excitons and FP-mode microresonator. And the exciton-polariton coupling strengths characterized by a Rabi splitting energy were extracted to be 500 meV. Further, when the input current increased more than a certain value, strong laser illuminating developed as two sharp peaks at the lower energy shoulder of the spontaneous emission peak, and these oscillating modes can dominate the waveguide EL spectra. The experimental results can provide us with further unambiguous evidence that the lasing is originated from the polariton resonances for the microribbon with strong exciton-polariton coupling. Since single microribbon based optical FP-mode microresonators do not require additional feedback mirrors, their compact size and resulting low thresholds make them a powerful candidate to construct on-chip coherent light sources for future integrated nanophotonic and optoelectronic circuitry.

Lead halide perovskites Fabry-Pérot resonant cavity laser

With the advent of the post-Moore era, the demand for large-capacity and high-speed information processing has caused the application of semiconductor devices to shift from electronic integration to photonic integration. High-performance micro-nano lasers are an important part of achieving photonic integration. Varieties of semiconductor materials have promoted the rapid development of semiconductor micro-nano lasers. In recent years, with the advent of a large number of new semiconductor materials (such as two-dimensional semiconductors, lead halide perovskites, etc.), it is expected that the performances of semiconductor micro-nano lasers will be further improved. Perovskite materials have excellent optical properties such as high light absorptions, high defect tolerances, and large exciton binding energy, which <u>make</u> them excellent candidate materials for high-gain, low-threshold semiconductor micro-nano lasers. The Fabry-Perot (F-P) resonator laser is a type of perovskite laser with extensive research, simple structure and high application value. In this paper, we take lead halide perovskite F-P resonator laser for example, and summarize its working mechanism and recent research results, by starting from two aspects of photon laser with exciton and photon weak coupling and strong coupling polariton laser. And we introduce the lasing principle and influencing factors of F-P structure lasers with perovskite materials as both gain medium and resonant cavity and F-P cavity lasers with perovskite as only gain medium in detail. Finally, the current challenges of perovskite F-P resonant lasers are summarized, and the possible prospects of its further development are also presented.

Поляритонные моды в цилиндрическом микрорезонаторе в режим поляритонного лазера

The spectra of exciton-polariton photoluminescence from cylindrical microcavities under optical excitation below and above the threshold of transition to the polariton laser regime under conditions of strong exciton-photon coupling were studied. At relatively weak optical excitation, lateral quantization modes of polaritons and whispering gallery modes appeared. Both the spectral distribution of these modes and the spatial dependence of their wave functions in the resonator plane were observed. With an increase in the excitation intensity and a transition to the polariton laser regime, only one, the longest-wavelength lasing line remained in the spectrum. It has been suggested that under strong optical excitation, the spectrum contains not only exciton-polariton radiation, but also trion-polariton radiation.

Multimode Organic Polariton Lasing.

We present a beyond-mean-field approach to predict the nature of organic polariton lasing, accounting for all relevant photon modes in a planar microcavity. Starting from a microscopic picture, we show how lasing can switch between polaritonic states resonant with the maximal gain, and those at the bottom of the polariton dispersion. We show how the population of nonlasing modes can be found, and by using two-time correlations, we show how the photoluminescence spectrum (of both lasing and nonlasing modes) evolves with pumping and coupling strength, confirming recent experimental work on the origin of blueshift for polariton lasing.

Room Temperature Polariton Lasing in Ladder‐Type Oligo(p‐Phenylene)s with Different π‐Conjugation Lengths

Polariton lasing is coherent emission that originates from macroscopic accumulation of polariton population in the ground state and is a promising route toward efficient coherent light sources as population inversion is not necessary. Unlike most Wannier–Mott excitons in inorganic semiconductors, Frenkel excitons created in organic semiconductors have high oscillator strength and high exciton binding energy, which sustain stable exciton–polaritons at room temperature. Herein, room temperature polariton lasing from a novel class of ladder‐type oligo(p‐phenylene)s is demonstrated. The polariton lasers exhibit a nonlinear increase of their spectrally integrated emission, a reduction in spectral linewidth, blueshift of emission peaks, and long‐range spatial coherence when the pump fluence is increased above threshold. By tuning the π‐conjugation length of the molecular structure, the polariton lasing wavelength can be changed from 430 to 457 nm. Optically pumped thresholds of 12 and 17 μJ cm−2 are observed, which are among the lowest values reported for polariton lasing in organic semiconductors.

Managing the flow of liquid light

Strongly coupled light-matter systems can carry information over long distances and realize low threshold polariton lasing, condensation and superfluidity. These systems are highly non-equilibrium in nature, so constant nonzero fluxes manifest themselves even at the steady-state and are set by a complicated interplay between nonlinearity, dispersion, pumping, dissipation and interactions between the various constituents of the system. Based on the mean-field governing equations of lasers or polariton condensates, we develop a method for engineering and controlling the velocity profiles by manipulating the system's spatial pumping and dissipation. We present analytically exact pumping and dissipation profiles that lead to a large variety of spatially periodic density and velocity profiles. Besides these, any physically relevant velocity profiles can be engineered by finding the stationary state of the conservative nonlinear Schrodinger equation in an external potential related to the velocity. Our approach opens the way to the controllable implementation of laser or polariton flows for ultra-fast information processing, integrated circuits, and analogue simulators.

Electrically controlled waveguide polariton laser

Exciton–polaritons are mixed light–matter particles offering a versatile solid state platform to study many-body physical effects. In this work, we demonstrate an electrically controlled polariton laser, in a compact, easy-to-fabricate and integrable configuration, based on a semiconductor waveguide. Interestingly, we show that polariton lasing can be achieved in a system without a global minimum in the polariton energy-momentum dispersion. The cavity modes for the laser emission are obtained by adding couples of specifically designed diffraction gratings on top of the planar waveguide, forming an in-plane Fabry–Perot cavity. It is due to the waveguide geometry that we can apply a transverse electric field to finely tune the laser energy and quality factor of the cavity modes. Remarkably, we exploit the system sensitivity to the applied electric field to achieve an electrically controlled population of coherent polaritons. The precise control that can be reached with the manipulation of the grating properties and of the electric field provides strong advantages to this device in terms of miniaturization and integrability, two main features for the future development of coherent sources for polaritonic technologies.

Polariton relaxation and polariton nonlinearities in nonresonantly cw-pumped III-nitride slab waveguides

Polariton lasers are mostly based on planar cavities. Here we focus on an alternative configuration with slab waveguide modes strongly coupled to excitons confined in GaN/AlGaN quantum wells. We study experimentally and theoretically polariton relaxation at temperatures ranging from 4 to 200 K. We observe a good robustness of the lower polariton population peak energy position against temperature changes due to a balance between the shift of the exciton energy and the change in the normal mode splitting, a promising feature for future applications such as lasers and amplifiers where a small temperature drift in the emission wavelength is a desired asset. Finally, at $T=4\phantom{\rule{4pt}{0ex}}\mathrm{K}$ we observe the signature of polariton nonlinearities occurring in the continuous wave regime that are assigned to an optical parametric oscillation process.

Direct Generation of Radially Polarized Vector Vortex Beam with an Exciton-Polariton Laser

Vector vortex beams are a class of optical beams with singularities in their space-variant polarization. Vector vortex beam lasers have applications in many areas including imaging and communication, where vertical-cavity lasers emitting Gaussian beams have been most widely used so far. Generation of vector vortex beams from vertical-cavity lasers has required external control or modulation. Here, by utilizing a polarization-selective subwavelength grating as one of the reflectors in a vertical semiconductor microcavity, we design the spin textures of the polariton mode and demonstrate polariton lasing in a single-mode, radially polarized vector vortex beam. Polarization and phase distributions of the emission are characterized by polarization-resolved imaging and interferometry. This method of vector vortex laser beam generation allows low threshold power, stable single-mode operation, scalability, and on-chip integration, all of which are important for applications in imaging and communication.

Efficient Bosonic Condensation of Exciton Polaritons in an H-Aggregate Organic Single-Crystal Microcavity

Although organic polariton condensation has been recently demonstrated, they only utilize the photon part of polaritons and ignore the excitonic contribution because the polariton-polariton and polariton-reservoir interactions are weak in organic microcavities owing to the absence of Coulomb exchange-interactions between Frenkel excitons. We demonstrate highly efficient and strongly polarization-dependent polariton condensates in a microcavity consisting of an H-aggregate organic single-crystalline microbelt sandwiched between two silver reflectors. Benefitting from the advantages of vibronic coupling in H-aggregates and heavy exciton-like polaritons, both macroscopic coherent polariton ground-state population and high-energy quantized-modes are observed. The measurements are qualitatively reproduced based on simulations of the spatiotemporal polariton dynamics. The observation of low threshold polariton lasing, the ease of fabrication, and the potential for efficient electronic charge injection make microcrystals of organic semiconductors attractive candidates for continuous wave and electrically pumped functional photonic polariton circuits and organic polariton lasers, operating at room temperature.

Nano-second exciton-polariton lasing in organic microcavities

Organic semiconductors are a promising platform for ambient polaritonics. Several applications, such as polariton routers, and many-body condensed matter phenomena are currently hindered due to the ultra-short polariton lifetimes in organics. Here, we employ a single-shot dispersion imaging technique, using 4 ns long non-resonant excitation pulses, to study polariton lasing in a λ/2 planar organic microcavity filled with BODIPY-Br dye molecules. At a power threshold density of 1.5 MW/cm2, we observe the transition to a quasi-steady state, 1.2 ns long-lived, single-mode polariton lasing and the concomitant superlinear increase in photoluminescence, spectral line-narrowing, and energy blueshift.

Retracted: Emerging 2D MXene/Organic Heterostructures for Future Nanodevices

AbstractMXenes are a rapidly growing family of 2D materials. Their unique combination of metallic conductivity, hydrophilicity, and highly charged surfaces endow them with excellent electrochemical performance. Appropriate surface functional groups determine their semiconducting properties. The wide selection of various MXene structures and surface functional groups enable tunable work functions and bandgaps, making them prime candidates for many optoelectronic applications. In addition, the discovery of 2D organic semiconductors having single molecular thickness has also greatly attracted research attention due to their optical, electronic, optoelectronic, and mechatronic properties. Moreover, the formation of MXenes/organic 2D heterostructures enables many interesting phenomena in the 2D quantum limit to be observed. This review aims to increase motivation toward the investigation of newly emerging MXenes, 2D organic materials, and their combinational heterostructures. It overviews recent progress in the fundamental investigations of the optical, electronic, and optoelectronic properties in isolated 2D MXenes and organic materials; then, highlights the major importance of 2D MXene/organic heterostructures for applications in exciton–polariton lasers, light emitting devices, wearable electronics, and spintronic devices. The review aims outlines a future roadmap for 2D MXenes, organic materials, and their heterostructures for advanced nanotechnology applications.