Nature Features Luca Dal Negro’s New Class of Random Lasers
LASER (Light Amplification by Stimulated Emission of Radiation) just turned 60 but is not ready to retire yet. To the contrary, it has become ubiquitous in our daily lives. While a laser pointer is one obvious example, the fact that lasers are used to capture 3D information in time-of-flight sensors (think iPhone X and Kinect 2) is largely unknown. Many do-it-yourselfers have used laser tape measure, but few know that lasers are used to measure the Earth-to-Moon distance by bouncing laser light off reflectors left by the Apollo missions. Beyond that, lasers have enabled unprecedented applications to medicine, sensing, precision manufacturing, communications and information technology as well as specialized military and law enforcement devices.
ECE Prof. Luca Dal Negro and his collaborators Yuyao Chen (ECE) and Alfredo Fiorentino (Catania University, Italy) are developing a new, more efficient class of lasers. In a recent article entitled “A fractional diffusion random laser”, that appeared in the journal Scientific Reports published by Nature, they introduced a new type of random lasers leveraging structural correlations in random media to improve their lasing performance.
So how do lasers work? Lasers rely on the confinement of light inside an active medium which, when properly energized, can amplify radiation resulting in an intense and coherent output. Traditional lasers achieve confinement using carefully-designed optical mirrors arranged in specialized cavity geometries. This increases complexity and cost and also affects laser reliability. As an alternative, the so-called “random lasers” operating without cavity mirrors, were theoretically proposed in the late 60s and experimentally demonstrated only in the 90s. This is possible if the laser medium is sufficiently “disordered” at the microscopic wavelength-scale; such that light is scattered many times along its propagation and eventually confined within very small volumes.
In order to design a new type of random laser, Chen, Fiorentino and Dal Negro applied the advanced mathematics of fractional calculus to photonics, which allows one to accurately describe the complicated effects of long-range correlations in light propagation through a random medium. In the paper, they introduced and studied different “fractional diffusion models” for photons in random media. They were able to rigorously obtain simple closed-form expressions for the critical amplification volumes required to initiate laser action. Their work also establishes the benefits of anomalous sub-diffusive photon transport for the engineering of novel random lasers; reducing footprint and amplification volumes. They anticipate innovative applications of the new device to miniaturized smart lighting systems, on-chip spectroscopy, and optical sensing.
Professor Dal Negro’s research focuses on the study of optical nanostructures and light scattering in complex media. His is a Fellow of the Optical Society of America (OSA) for numerous contributions in the theoretical and experimental aspects of wave interaction with aperiodic nanostructures, nanophotonics and plasmonics leading to novel engineering applications. He is also a recipient of the NSF CAREER Award and Boston University’s Early Career Research Excellence Award. Yuyao Chen is a PhD student in Prof. Dal Negro group working on mathematical modeling of complex photonics and plasmonics media.
To learn more about Prof. Dal Negro and his team’s research, please visit http://www.bu.edu/nano/