We investigate the effects of two-dimensional confinement on the lasing properties of a classical random laser system operating in the incoherent feedback (diffusive) regime. A suspension of 250 nm rutile (${\mathrm{TiO}}_2$) particles in a rhodamine 6G solution was inserted into the hollow core of a photonic crystal fiber generating the first random fiber laser and a novel quasi-one-dimensional random laser geometry. A comparison with similar systems in bulk format shows that the random fiber laser presents an efficiency that is at least 2 orders of magnitude higher.

We report second-and third-harmonic generation in monolayer MoS 2 as a tool for imaging and accurately characterizing the material's nonlinear optical properties under 1560nm excitation. Using a surface nonlinear optics treatment, we derive expressions relating experimental measurements to second-and third-order nonlinear sheet susceptibility magnitudes, obtaining values of c = | | () s 2 ´-2.0 10 20 m 2 V-1 and, for the first time for monolayer MoS 2 , c = ´-| | () 1.7 10 s 3 28 m 3 V-2. These sheet susceptibilities correspond to effective bulk nonlinear susceptibility values of c = | | () 2.9 b 2-10 11 mV-1 and c = ´-| | () 2.4 10 b 3 19 m 2 V-2 , accounting for the sheet thickness. Experimental comparisons between MoS 2 and graphene are also performed, demonstrating ∼3.4 times stronger thirdorder sheet nonlinearity in monolayer MoS 2 , highlighting the material's potential for nonlinear photonics in the telecommunications C band.

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Black phosphorus has recently emerged as a new layered crystal that, due to its peculiar and anisotropic crystalline and electronic band structures, may have important applications in electronics, optoelectronics and photonics. Despite the fact that the edges of layered crystals host a range of singular properties whose characterization and exploitation are of utmost importance for device development, the edges of black phosphorus remain poorly characterized. In this work, the atomic structure and behaviour of phonons near different black phosphorus edges are experimentally and theoretically studied using Raman spectroscopy and density functional theory calculations. Polarized Raman results show the appearance of new modes at the edges of the sample, and their spectra depend on the atomic structure of the edges (zigzag or armchair). Theoretical simulations confirm that the new modes are due to edge phonon states that are forbidden in the bulk, and originated from the lattice termination rearrangements.