Spectrally resolved femtosecond photon echo spectroscopy of astaxanthin

Kumar, Ajitesh; Kumar, Satyendra; Gupta, Aditya; Goswami, Debabrata

doi:10.1117/12.899781

Cited by 1 publication

(1 citation statement)

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“…This is especially true in solid-state dye-doped polymer random lasers, where a relatively small homogeneous linewidth of 0.8 nm can be found 37 . In our system of Rhodamine-6G dye molecules in liquid methanol, the homogeneous linewidth is an order of magnitude larger, estimated at 8 nm with photon-echo spectroscopy 38 . This means that lasing modes spectrally separated by less than 8 nm can couple.…”

Section: Fluctuations and Correlationsmentioning

confidence: 68%

Replica Symmetry Breaking in a Weakly Scattering Optofluidic Random Laser

Sarkar

Bhaktha

Andreasen

2020

Sci Rep

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We report the observation of replica symmetry breaking (RSB) in a weakly scattering optofluidic random laser (ORL). Coherent random lasing is indicated by the presence of narrow peaks rising out of the spectral background. This coherence helps to identify a random laser threshold, which is expected to be gradual with weak scattering. We find that lasing action initiated using optical pulsed pumping coincides with the onset of both RSB and Lévy flight statistics. However, the transition from the photonic paramagnetic to photonic glass phase is more subtle in that the Parisi overlap function broadens instead of completely changing shape. This subtlety is balanced by an accompanying result of identical experimental conditions giving rise to lasing or no lasing depending on the shot. Additional statistical calculations and investigations into the fundamental physical mechanisms present in the ORL support this conclusion. Using simple numerical models, we study the critical spectral properties required for RSB to occur, as indicated by the Parisi overlap function. The simplicity of the models helps demonstrate the sensitive nature of this tool and the necessity of additional verification of the physical mechanisms present in the experiment. Random lasers are a special class of active disordered materials where laser oscillations survive due to the optical feedback provided by multiple scattering 1,2. Random lasers are spectrally distinguished from conventional lasing systems by randomly distributed sharp spikes over the emission. These sharp spikes can be directly attributed to resonances known as quasi bound (QB) states (e.g. 3,4) of the passive cavity when the strength of scattering is strong 5. On the contrary, weakly scattering systems exhibit spatially extended QB states. One-to-one correspondence exists between QB states and lasing modes only at the lasing threshold, only if that threshold is small enough 5 , and only if the pumped region includes the entire spatial area over which the QB states extend 6. When such correspondence breaks down, lasing modes can be described as a mixture of QB states; for example, as scattering becomes very weak. Despite the absence of correspondence with a single QB state, these lasing modes retain the spatial properties of the QB states from which they are composed. Such states exhibit strong spatial overlap, short lifetimes, and strong leakage at the boundary due to their extended nature. This gives rise to mode competition and strong intermodal coupling via spatial hole burning 7,8 , which can result in chaotic behavior with different emission spectra observed pump shot to pump shot 9. Insight into shot-to-shot fluctuations has been provided by spin glass theory 10,11. The replica symmetry breaking (RSB) phase transition was observed experimentally 12 and the theoretical connection between intensity and complex amplitude fluctuations established 13. According to spin glass theory, the statistical distribution of an overlap parameter q, namely the Parisi overlap function P(q), c...

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Section: Fluctuations and Correlationsmentioning

confidence: 68%