Quantum Optics Seminar by Cefe Lopez – Niels Bohr Institute - University of Copenhagen

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Quantum Optics Seminar by Cefe Lopez

A random laser is formed by a haphazard assembly of nondescript optical scatters with optical gain. In these structures multiple light scattering replaces the optical cavity found in traditional lasers and the interplay between gain, scattering and size determines their unique properties. Random lasers studied till recently, consisted of irregularly shaped or polydisperse scatters, with some average scattering strength constant across the gain frequency band that made them lase at frequency where gain reached its maximum.

Photonic glasses can sustain scattering resonances that can be placed in the gain window, since they are formed by monodisperse spheres [1]. The unique resonant scattering of this novel material allows a degree of control over the lasing color via the diameter of the particles and their refractive index. Profiting from this feature a random laser with a priori set lasing peak can be designed [2].

Further control over random lasers is attained if a special pumping scheme that enables to select the number of activated modes is employed. RLs can thus be set to work in two distinct regimes by controlling directionality through the pump [3]. When pumping is essentially unidirectional, few (barely interacting) modes are turned on that show as sharp, uncorrelated peaks in the spectrum. By increasing angular span of the pump beams, many resonances intervene generating a smooth emission spectrum with a high degree of correlation, and shorter lifetime. These are signs of a phase-locking transition, in which phases are clamped together so that modes oscillate synchronously.


[1] R Sapienza, et al. "Observation of Resonant Behavior in the Energy Velocity of Diffused Light" Phys. Rev. Lett. 99, 233902 (2007).
[2] S Gottardo, et al. "Resonance driven random lasing" Nature Photonics 2 (7), 429-432 (2008).
[3] M Leonetti et al.  "The mode-locking transition in random lasers" Nature Photonics 5, 615-617 (2011).