We observe polariton condensation in the yellow part of the visible spectrum from a planar organic semiconductor microcavity containing the molecular dye BODIPY-Br. We provide experimental fingerprint of polariton condensation under non-resonant optical excitation, including the non-linear dependence of the emission intensity and wavelength blueshift with increasing excitation density, single excitation pulse dispersion imaging and real space interferometry. The latter two allow us to visualise the collapse of the energy distribution and the long-range coherence of the polariton condensate.

Artificial lattices of coherently coupled macroscopic states are at the heart of applications ranging from solving hard combinatorial optimization problems to simulating complex many-body physical systems. The size and complexity of the problems scale with the extent of coherence across the lattice. Although the fundamental limit of spatial coherence depends on the nature of the couplings and lattice parameters, it is usually engineering constraints that define the size of the system. Here, we engineer polariton condensate lattices with active control on the spatial arrangement and condensate density that results in near-diffraction limited emission, and spatial coherence that exceeds by nearly two orders of magnitude the size of each individual condensate. We use these advancements to unravel the dependence of spatial correlations between polariton condensates on the lattice geometry.

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 nanosecond 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 1.5MW /cm 2 , we observe the transition to a quasi-steady state, 1.2 ns long-lived, single-mode polariton lasing and the concomitant superlinear increase of photoluminescence, spectral line-narrowing, and energy blueshift.

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Vorticity is a key ingredient to a broad variety of fluid phenomena, and its quantised version is considered to be the hallmark of superfluidity. Circulating flows that correspond to vortices of a large topological charge, termed giant vortices, are notoriously difficult to realise and even when externally imprinted, they are unstable, breaking into many vortices of a single charge. In spite of many theoretical proposals on the formation and stabilisation of giant vortices in ultra-cold atomic Bose-Einstein condensates and other superfluid systems, their experimental realisation remains elusive. Polariton condensates stand out from other superfluid systems due to their particularly strong interparticle interactions combined with their non-equilibrium nature, and as such provide an alternative testbed for the study of vortices. Here, we non-resonantly excite an odd number of polariton condensates at the vertices of a regular polygon and we observe the formation of a stable discrete vortex state with a large topological charge as a consequence of antibonding frustration between nearest neighbouring condensates.

Metasurfaces represent a powerful paradigm of optical engineering that enables one to control the flow of light across material interfaces. We report on a discovery that metallic metasurfaces of a certain type respond differently to spatially coherent and incoherent light, enabling robust speckle-free discrimination between different degrees of coherence. The effect has no direct analogue in conventional optics and may find applications in compact metadevices enhancing imaging, vision, detection, communication and metrology.Over the last decade the concept of artificially engineered media (known as metamaterials) has revolutionized the field of optics, pushed the boundaries of microfabrication and stimulated the development of novel characterization techniques [1,2]. Recent demonstrations of anomalous reflection and refraction of light by metasurfaces opened another exciting chapter in optical engineering [3]. Metasurfaces correspond to a class of low-dimensional (planar) metamaterials and are typically formed by optically thin metal films periodically patterned on a sub-wavelength scale. Despite their vanishing thickness, metasurfaces interact strongly with light, which they can transmit, absorb or reflect without diffraction, effectively acting as optical media of zero dimension in the direction of light propagation. That sets metasurfaces aside from diffractive resonant waveguide gratings (aka photonic crystal slabs) [4,5] and perforated metal films exhibiting extraordinary optical transmission [6]. Metasurfaces are fully compatible with existing fabrication processes adopted by CMOS technology, and offer unmatched flexibility in the design and control of light propagation, replacing conventional bulk optical components and exhibiting exotic electromagnetic phenomena. In particular, metasurfaces have already enabled spectral [7,8,9] and directional [10,11,12] filtering, absorption enhancement and energy harvesting [13,14,15,16,17], polarization control [18,19,20] and analysis [21,22], imaging [23,24,25] and sensing [26,27], as well as have allowed the demonstration of exotic effects of asymmetric transmission [28,29] and specular optical activity [30].In this paper we describe and investigate an intriguing optical phenomenon whereby apparently trivial, non-diffracting metallic metasurfaces exhibit different levels of speckle-free transmission, depending on whether they are illuminated with spatially coherent or incoherent light (as illustrated in Fig. 1). This effect, previously unseen in artificially engineered media, is robust and exceptionally strong, and does not affect the beam quality, which makes it immediately suitable for practical applications, such as optical metrology, imaging and communications.The phenomenon was discovered experimentally with zigzag metasurfaces operating in the near-IR part of the spectrum. The metasurfaces were milled with a focussed ion beam in an 80 nm thick film of amorphous gold that had been sputtered on a 0.5 mm thick fused-quartz substrate beforehand. The fabricated samp...

We demonstrate spontaneous formation of a nonlinear vortex cluster state in a microcavity exciton-polariton condensate with time-periodic sign flipping of its topological charges at the GHz scale. When optically pumped with a ring-shaped nonresonant laser, the trapped condensate experiences intricate high-order mode competition and fractures into two distinct trap levels. The resulting mode interference leads to robust condensate density beatings with periodic appearance of orderly arranged phase singularities. Our work opens new perspectives on creating structured free-evolving light, and singular optics in the strong light-matter coupling regime.

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