The mode-locking transition of random lasers


The discovery of the spontaneous mode-locking of lasers1,2, that is, the self-starting synchronous oscillation of electromagnetic modes in a cavity, has been a milestone of photonics allowing the realization of oscillators delivering ultrashort pulses. This process is so far known to occur only in standard ordered lasers and only in the presence of a specific device (the saturable absorber). We engineer a mode-selective pumping of a random laser formed by a self-assembled cluster of nanometric particles. We show that the random laser can be continuously driven from a configuration exhibiting weakly interacting electromagnetic resonances4,5 to a regime of collectively oscillating strongly interacting modes6,7. This phenomenon, which opens the way to the development of a new generation of miniaturized and all-optically controlled light sources, may be explained as the first evidence of spontaneous mode-locking in disordered resonators.

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Figure 1: The two random lasing regimes.
Figure 2: From spiky to smooth RL spectra.
Figure 3: Onset of a correlated random laser.
Figure 4: Results from numerical CMT calculations.


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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 (; MAT2009-07841 (GLUSFA) and Comunidad de Madrid S2009/MAT-1756 (PHAMA).

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All authors contributed equally to the work presented in this Letter.

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Correspondence to Cefe Lopez.

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Leonetti, M., Conti, C. & Lopez, C. The mode-locking transition of random lasers. Nature Photon 5, 615–617 (2011).

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