We observe and analyze formation, decay, and subsequent regeneration of ring-shaped clusters of (2+1)dimensional spatial solitons (filaments) in a medium with cubic-quintic (focusing-defocusing) self-interaction and strong dissipative nonlinearity. The cluster of filaments, which remains stable over ≈17.5 Rayleigh lengths, is produced by the azimuthal modulational instability from a parent ring-shaped beam with embedded vorticity l = 1. In the course of still longer propagation, the stability of the soliton cluster is lost under the action of nonlinear losses. The annular cluster is then spontaneously regenerated due to power transfer from the reservoir provided by the unsplit part of the parent vortex ring. Thus, a secondary interval of the robust propagation of the regenerated cluster is identified. The experiments use a laser beam (at wavelength 800 nm), built of pulses with temporal duration 150 fs, at the repetition rate of 1 kHz, propagating in a cell filled by liquid carbon disulfide. Numerical calculations, based on a modified nonlinear Schrödinger equation which includes the cubic-quintic refractive terms and nonlinear losses, provide results in close agreement with the experimental findings.

We report a study of the nonlinear birefringence induced in a metal-dielectric nanocomposite due to the contributions of third- and fifth-order optical nonlinearities. A theoretical model describing the evolution of the light polarization state of a confined laser beam propagating through the nonlinear medium is developed with basis on a pair of coupled dissipative cubic-quintic nonlinear differential equations related to the two orthogonal polarizations of the optical field. As a proof-of-principle experiment we demonstrate the control of the light beam polarization in a silver-nanocolloid by changing the silver nanoparticles volume fraction, f, and the light intensity. A large nonlinear phase-shift (~20π) was observed using a 9 cm long capillary filled with silver nanoparticles suspended in carbon disulfide. Experiments using colloids with 1.0×10≤f≤4.5×10 and maximum light intensities of tens of MW/cm are performed. In addition, we demonstrate that the modulation instability is highly sensitive to the quintic nonlinearity contribution performed showing good agreement with the experimental results.

Spontaneous Raman scattering is a reliable technique for fast identification of single bacterial cells, when spectra are acquired in laboratory conditions where bacteria growth and state are controlled. We have developped a multi-modal system combining Raman spectroscopy and darkfield imaging, aiming at analysing environmental samples, typically in the field context of biological pathogens detection. Such samples are heterogeneous, both in terms of phenotype content and environmental matrix, even after a preliminary purification step. In this paper, we report a study on the identification of Bacillus Thuriengensis (BT) mimicing pathogen bacteria, embedded in a real-world matrix: a sample of surface water enriched with environmental bacterial species. The purpose is to evaluate both the detection limit of aging BT over time and the false alarm rate, in the conditions of our experiment.

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