Quantum vortex formation in the "rotating bucket" experiment with polariton condensates.

The appearance of quantized vortices in the classical "rotating bucket" experiments of liquid helium and ultracold dilute gases provides the means for fundamental and comparative studies of different superfluids. Here, we realize the rotating bucket experiment for optically trapped quantum fluid of light based on exciton-polariton Bose-Einstein condensate in semiconductor microcavity. We use the beating note of two frequency-stabilized single-mode lasers to generate an asymmetric time-periodic rotating, nonresonant excitation profile that both injects and stirs the condensate through its interaction with a background exciton reservoir. The pump-induced external rotation of the condensate results in the appearance of a corotating quantized vortex. We investigate the rotation frequency dependence and reveal the range of stirring frequencies (from 1 to 4 GHz) that favors quantized vortex formation. We describe the phenomenology using the generalized Gross-Pitaevskii equation. Our results enable the study of polariton superfluidity on a par with other superfluids, as well as deterministic, all-optical control over structured nonlinear light.

Spontaneous Formation of Time-Periodic Vortex Cluster in Nonlinear Fluids of Light.

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.

Noncontact characterization of microstructured optical fibers coating in real time.

Functional nanocoatings have allowed hollow-core microstructured optical fibers (HC-MOFs) to be introduced into biosensing and photochemistry applications. However, common film characterization tools cannot evaluate the coating performance in situ. Here we report the all-optical noncontact characterization of the HC-MOF coating in real time. Self-assembled multilayers consisting of inversely charged polyelectrolytes (PEs) are deposited on the HC-MOF core capillary, and a linear spectral shift in the position of the fiber transmission minima with increasing the film thickness is observed as small as ∼1.5-6nm per single PE bilayer. We exemplify the practical performance of our approach by registering an increase in the coating thickness from 6±1 to 11±1nm per PE bilayer with increasing ionic strength in the PE solutions from 0.15 to 0.5 M NaCl. Additionally, we show real-time monitoring of pH-induced coating dissolving. Simplicity and high sensitivity make our approach a promising tool allowing noncontact analysis of the HC-MOF coating which is still challenging for other methods.

Multispectral sensing of biological liquids with hollow-core microstructured optical fibres.

The state of the art in optical biosensing is focused on reaching high sensitivity at a single wavelength by using any type of optical resonance. This common strategy, however, disregards the promising possibility of simultaneous measurements of a bioanalyte's refractive index over a broadband spectral domain. Here, we address this issue by introducing the approach of in-fibre multispectral optical sensing (IMOS). The operating principle relies on detecting changes in the transmission of a hollow-core microstructured optical fibre when a bioanalyte is streamed through it via liquid cells. IMOS offers a unique opportunity to measure the refractive index at 42 wavelengths, with a sensitivity up to ~3000 nm per refractive index unit (RIU) and a figure of merit reaching 99 RIU-1 in the visible and near-infra-red spectral ranges. We apply this technique to determine the concentration and refractive index dispersion for bovine serum albumin and show that the accuracy meets clinical needs.