Marco Leonetti

The mode-locking transition of random lasers

Researchers report the first observation of the synchronous oscillation of electromagnetic modes in a cavity — known as mode-locking — in random lasers.

Condensation in disordered lasers: Theory, 3D+1 simulations, and experiments

The complex processes underlying the generation of a coherent emission from the multiple scattering of photons and wave localization in the presence of structural disorder are still mostly unexplored. Here we show that a single nonlinear Schrödinger equation, playing the role of the Schwalow-Townes law for standard lasers, quantitatively reproduces experimental results and three-dimensional time-domain parallel simulations of a colloidal laser system.

Active subnanometer spectral control of a random laser

We demonstrate an experimental technique that allows to achieve a robust control on the emission spectrum of a micro random laser and to select individual modes with sub-nanometer resolution. The presented approach relies on an optimization protocol of the spatial profile of the pump beam. Here we demonstrate not only the possibility to increase the emission at a wavelength but also that we can “isolate” an individual peak suppressing unwanted contributions form other modes.

Optical gain in DNA-DCM for lasing in photonic materials

We present a detailed study of the gain length in an active medium obtained by doping of DNA strands with 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran dye molecules. The superior thermal stability of the composite and its low quenching permit one to obtain an optical gain coefficient larger than 300 cm(-1). We also demonstrate that such an active material is feasible for the infiltration into photonic nanostructures, allowing one to obtain fluorescent photonic crystals and promising lasing properties.

Random laser tailored by directional stimulated emission

This work was supported by ERC Grant (FP7/2007-2013) No. 201766, CINECA, EU FP7 NoE Nanophotonics4Enery Grant No. 248855, the Spanish MICINN CSD2007-0046 (Nanolight.es), MAT2009-07841 (GLUSFA), and Comunidad de Madrid S2009/MAT-1756 (PHAMA).

Observation of migrating transverse anderson localizations of light in nonlocal media

We report the experimental observation of the interaction and attraction of many localized modes in a two-dimensional system realized by a disordered optical fiber supporting transverse Anderson localization. We show that a nonlocal optically nonlinear response of thermal origin alters the localization length by an amount determined by the optical power and also induces an action at a distance between the localized modes and their spatial migration. Evidence of a collective and strongly interacting regime is given.

Tunable degree of localization in random lasers with controlled interaction

We show that the degree of localization for the modes of a random laser (RL) is affected by the inter mode interaction that is controlled by shaping the spot of the pump laser. By experimentally investigating the spatial properties of the lasing emission we infer that strongly localized modes are activated in the low interacting regime while in the strongly interacting one extended modes are found lasing. Thus we demonstrate that the degree o localization may be finely tuned at the micrometer level.

Switching and amplification in disordered lasing resonators

Controlling the flow of energy in a random medium is a research frontier with a wide range of applications. As recently demonstrated, the effect of disorder on the transmission of optical beams may be partially compensated by wavefront shaping, but losing control over individual light paths. Here we demonstrate a novel physical effect whereby energy is spatially and spectrally transferred inside a disordered active medium by the coupling between individual lasing modes. We show that it is possible to transmit an optical resonance to a remote point by employing specific control over optical excitations, obtaining a random lasing system, which acts both as a switch and as an amplifier.

Light focusing in the Anderson regime

Anderson localization is a regime in which diffusion is inhibited and waves (also electromagnetic waves) get localized. Here we exploit adaptive optics to achieve focusing in disordered optical fibres in the Anderson regime. By wavefront shaping and optimization, we observe the generation of a propagation-invariant beam, where light is trapped transversally by disorder, and show that Anderson localizations can be also excited by extended speckled beams. We demonstrate that disordered fibres allow a more efficient focusing action with respect to standard fibres in a way independent of their length, because of the propagation-invariant features and cooperative action of transverse localizations.

Measurement of transport mean-free path of light in thin systems.

We extensively investigate in-plane light diffusion in systems with thicknesses larger than but comparable with the transport mean free path. By exploiting amplified spontaneous emission from dye molecules placed in the same holder of the sample, we obtain a directional probe beam precisely aligned to the sample plane. By comparing spatial intensity distribution of laterally leaking photons with predictions from random walk simulations, we extract accurate values of transport mean free path, opening the way to the investigation of a previously inaccessible kind of sample.