Random lasers have fascinating emission properties that lie somewhere between those of a conventional laser and a common light-bulb. We have created a random laser that can be brought above and below its threshold for laser emission by small changes in its temperature, thereby creating a light source with a temperature-tunable colour spectrum. As a single random laser can be made as small as a grain of tens of micrometres in diameter, we expect our device to find application in photonics, temperature-sensitive displays and screens, and in remote temperature sensing. Lasers are now commonplace - for example, they are used in industry and in hospitals, in bar-code scanners and compact-disc players. Conventional lasers are based on an optically active material and some sort of laser cavity that traps light for long enough for laser action to occur. A new type of laser source, known as a random laser, has been discovered that does not require a regular cavity but instead depends on a diffusive material such as a fine powder. In a random laser, light waves are trapped by multiple light scattering (that is, light diffusion), which takes over the role of the cavity in a regular laser (Fig. 1). The emission of a random-laser source has a well defined colour spectrum and can be pulsed, just like a regular laser, although its emission is in several directions because of the intrinsic randomness of the system.

Statistical fluctuations of the light emitted from amplifying random media are studied theoretically and numerically. The characteristic scales of the diffusive motion of light lead to Gaussian or power-law (Lévy) distributed fluctuations depending on external control parameters. In the Lévy regime, the output pulse is highly irregular leading to huge deviations from a mean-field description. Monte Carlo simulations of a simplified model which includes the population of the medium demonstrate the two statistical regimes and provide a comparison with dynamical rate equations. Different statistics of the fluctuations helps to explain recent experimental observations reported in the literature

We report on random lasing in a disordered system in which the multiple scattering feedback mechanism can be switched from a three-dimensional random walk to a quasi-two-dimensional type of transport. The emission from this system is anisotropic, extraordinary polarized, and is controlled via an external electric field. The phenomenon is observed in dye-doped polymer dispersed liquid crystals and makes use of the strong scattering anisotropies in these materials.

We present a theoretical and experimental study aimed at characterizing statistical regimes in a random laser. Both the theoretical simulations and the experimental results show the possibility of three region of fluctuations increasing the pumping energy. An initial Gaussian regime is followed by a Lévy statistics and Gaussian statistic is recovered again for high pump pulse energy. These different statistical regimes are possible in a weakly diffusive active medium, while the region of Lévy statistics disappears when the medium is strongly diffusive presenting always a Gaussian regime with smooth emission spectrum. Experiments and theory agree in identification of the key parameters determining the statistical regimes of the random laser.

Metastatic melanoma was the first malignancy in which immune checkpoint inhibitors demonstrated their successful efficacy. Currently, the knowledge on the interaction between the immune system and malignant disease is steadily increasing and new drugs and therapeutic strategies are overlooking in the clinical scenario. To provide a comprehensive overview of immune modulating drugs currently available in the treatment of melanoma as well as to discuss of possible future strategies in the metastatic melanoma setting, the present review aims at analyzing controversial aspects about the optimal immunomodulating treatment sequences, the search for biomarkers of efficacy of immunocheckpoint inhibitors, and innovative combinations of drugs currently under investigation.