André L. Moura

Multi-wavelength emission through self-induced second-order wave-mixing processes from a Nd3+ doped crystalline powder random laser.

Random lasers (RLs) based on neodymium ions (Nd3+) doped crystalline powders rely on multiple light scattering to sustain laser oscillation. Although Stokes and anti-Stokes Nd3+ RLs have been demonstrated, the optical gain obtained up to now was possibly not large enough to produce self-frequency conversion. Here we demonstrate self-frequency upconversion from Nd3+ doped YAl3(BO3)4 monocrystals excited at 806 nm, in resonance with the Nd3+ transition 4I9/2 → 4F5/2. Besides the observation of the RL emission at 1062 nm, self-converted second-harmonic at 531 nm, and self-sum-frequency generated emission at 459 nm due to the RL and the excitation laser at 806 nm, are reported. Additionally, second-harmonic of the excitation laser at 403 nm was generated. These results exemplify the first multi-wavelength source of radiation owing to nonlinear optical effect in a Nd3+ doped crystalline powder RL. Contrary to the RLs based on dyes, this multi-wavelength light source can be used in photonic devices due to the large durability of the gain medium.

Observation of Lévy distribution and replica symmetry breaking in random lasers from a single set of measurements

Random lasers have been recently exploited as a photonic platform for studies of complex systems. This cross-disciplinary approach opened up new important avenues for the understanding of random-laser behavior, including Lévy-type distributions of strong intensity fluctuations and phase transitions to a photonic spin-glass phase. In this work, we employ the Nd:YBO random laser system to unveil, from a single set of measurements, the physical origin of the complex correspondence between the Lévy fluctuation regime and the replica-symmetry-breaking transition to the spin-glass phase. A novel unexpected finding is also reported: the trend to suppress the spin-glass behavior for high excitation pulse energies. The present description from first principles of this correspondence unfolds new possibilities to characterize other random lasers, such as random fiber lasers, nanolasers and small lasers, which include plasmonic-based, photonic-crystal and bio-derived nanodevices. The statistical nature of the emission provided by random lasers can also impact on their prominent use as sources for speckle-free laser imaging, which nowadays represents one of the most promising applications of random lasers, with expected progress even in cancer research.

Observation of photonic paramagnetic to spin-glass transition in a specially designed TiO 2 particle-based dye-colloidal random laser

Colloidal-based random lasers (RLs) are highly efficient and have been exploited in a wide range of geometries. However, in the particular case of ethanol solutions of rhodamines and TiO2 particles, the RL behavior is quite unstable due to the fast precipitation of the particles. In this Letter, specially designed amorphous TiO2 particles were synthesized by a sol-gel method, preventing the degradation of the RL for long operating lifetimes of over 105 shots. As a consequence, this modified colloidal RL allowed the observation of a clear replica-symmetry-breaking phase transition from the paramagnetic fluorescent to spin-glass RL behavior, which has not been observed in the system with nonfunctionalized TiO2 particles.By using specially designed nanoparticles scatterers which prevents photodegradation of the dye, we present clear demonstration of replica symmetry break and a photonic paramagnetic to spin-glass phase transition in a random laser operating in the incoherent feedback regime based on ethanol solution of Rhodamine 6G and amorphous TiO2 nanoparticles.

Tunable ultraviolet and blue light generation from Nd:YAB random laser bolstered by second-order nonlinear processes.

Ultraviolet and blue light were obtained by nonlinear frequency conversion in a random laser (RL) based on Nd0.10Y0.90Al3(BO3)4 nanocrystalline powder. RL operation at 1062 nm, due to the 4F3/2 → 4I11/2 transition of neodymium ions (Nd3+), was achieved by exciting the Nd3+ with a tunable beam from 680 to 920 nm covering the ground state absorption transitions to the 4F9/2, (4F7/2,4S3/2), (4F5/2,2H9/2), and 4F3/2 states. Light from 340 to 460 nm was obtained via the second-harmonic generation of the excitation beam while tunable blue light, from 417 to 486 nm, was generated by self-sum-frequency mixing between the excitation beam and the RL emission.

Glassy behavior in a one-dimensional continuous-wave erbium-doped random fiber laser

Anderson S. L. Gomes, ∗ Bismarck C. Lima, Pablo I. R. Pincheira, André L. Moura, 2 Mathieu Gagné, Raman Kashyap, Ernesto P. Raposo, and Cid B. de Araújo Departamento de F́ısica, Universidade Federal de Pernambuco, 50670-901, Recife-PE, Brazil Grupo de F́ısica da Matéria Condensada, Núcleo de Ciências Exatas NCEx, Campus Arapiraca, Universidade Federal de Alagoas, 57309-005, Arapiraca-AL, Brazil Fabulas Laboratory, Department of Engineering Physics, Department of Electrical Engineering, Polytechnique Montreal, Montreal, H3C 3A7, Canada Laboratório de F́ısica Teórica e Computacional, Departamento de F́ısica, Universidade Federal de Pernambuco, 50670-901, Recife-PE, Brazil (Dated: January 8, 2016)

Observation of Lévy statistics in one-dimensional erbium-based random fiber laser

We report on measurements of the statistical fluctuations of the output intensity in a continuous-wave-pumped erbium-doped one-dimensional random fiber laser (RFL), with specially designed Bragg grating scatterers. Transitions from Gaussian to Levy-like and back to the Gaussian regime, similar to those observed in three-dimensional random lasers, are described as the input excitation power increases from below to above the RFL threshold. Our results are consistent with theoretical predictions for the sequence of statistical regimes of output intensity in random laser systems. We also discuss experimental and theoretical connections with the photonic spin-glass behavior of the erbium-doped RFL, which displays a replica-symmetry-breaking phase above the threshold.

Structural and luminescence properties of Nd3+/Yb3+ codoped Al4B2O9 nanocrystalline powders

Morphological, structural and optical properties of Nd3+/Yb3+ codoped Al4B2O9 nanopowders prepared by the polymeric precursor method were investigated. The compounds previously heat-treated at 900 °C were characterized by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) techniques. The Al4B2O9 nanocrystals obtained possess an orthorhombic structure with grain dimensions between 10 and 20 nm. Photoluminescence (PL) spectra under excitation at 804 nm were collected and analyzed. The results indicate that the energy absorbed by Nd3+ (transition: 4I9/2 → 4F5/2 + 2H9/2) is efficiently transferred to Yb3+ in samples having 2 mol% of Nd3+ and 1 mol% of Yb3+, increasing the emission from 930 nm to 1130 nm by 12.2 times in comparison with the samples doped with 1 mol% of Nd3+ and 1 mol% of Yb3+. The dynamics of the PL process was also investigated. The PL decay at 975 nm from Yb3+ (2F5/2 → 2F7/2) and at 1080 nm from Nd3+ (4F3/2 → 4I11/2) was studied. The Yb3+ 2F5/2 level lifetime varies from 201 to 48 μs while the lifetime of the Nd3+ 4F3/2 level varies from 121 to 69 μs when the Nd3+ concentration is changed from 1 to 8 mol%. On the other hand, the Yb3+ 2F5/2 lifetime varies from 176 to 15 μs and the Nd3+ 4F3/2 lifetime varies from 97 to 44 μs when the Yb3+ concentration is changed from 1 to 8 mol%, due to interactions between the rare-earth ions. The present results show that Nd3+/Yb3+ codoped Al4B2O9 nanocrystalline powders have large potential to be tested in solar energy concentrators and IR laser devices.

Random lasing in Nd3+ doped potassium gadolinium tungstate crystal powder

Random laser (RL) emission in Nd3+ doped potassium gadolinium tungstate—KGd(WO4)2:Nd3+—crystal powder is demonstrated. The powder was excited at 813 nm in resonance with the Nd3+ transition 4I9/2→4F5/2. RL emission at 1067 nm due to the 4F3/2→4I11/2 transition was observed and characterized. An intensity threshold dependent on the laser spot area and bandwidth narrowing from ≈2.20 nm to ≈0.40 nm were observed and measured. For a beam spot area of 0.4 mm2, a RL threshold of 6.5 mJ/mm2 (90 MW/cm2) was determined. For excitation intensity smaller than the RL threshold, only spontaneous emission from level 4F3/2 with decay time in the tens microsecond range was observed, but for excitation above the RL threshold, significant shortening of excited level lifetime, characteristic of a stimulated process was found. The overall characteristics measured show that KGd(WO4)2:Nd3+ is an efficient material for operation of solid state RLs in the near-infrared.

Replica Symmetry Breaking in the Photonic Ferromagneticlike Spontaneous Mode-Locking Phase of a Multimode Nd:YAG Laser

We demonstrate the replica symmetry breaking (RSB) phenomenon in the spontaneous mode-locking regime of a multimode Q-switched Nd:YAG laser. The underlying mechanism is quite distinct from that of the RSB recently observed in random lasers. Here, there is no random medium and the phase is not glassy with incoherently oscillating modes as in random lasers. Instead, in each pulse a specific subset of longitudinal modes are activated in a nondeterministic way, whose coherent oscillation dominates and frustrates the others. The emergence of RSB coincides with the onset of ultrashort pulse generation typical of the spontaneous mode-locking regime, both occurring at the laser threshold. On the other hand, when high losses are introduced, RSB is inhibited and only the amplified stimulated emission with replica symmetry is observed. Our results disclose the only theoretically predicted photonic phase with RSB that remained unobserved so far.The recent reports of the replica symmetry breaking (RSB) phenomenon in photonic experiments [1-5] boosted the understanding of the role of disorder in multimode lasers, as well as helped to settle enlightening connections [6-13] with the statistical physics of complex systems. RSB manifests when identically-prepared system replicas reach distinct states, yielding different measures of observable quantities [14]. Here we demonstrate the RSB in the spontaneous mode-locking regime of a conventional multimode Nd:YAG laser in a closed cavity. The underlying mechanism is quite distinct from that of the RSB spinglass phase in cavityless random lasers with incoherently-oscillating modes. Here, a specific nonuniform distribution of the gain takes place in each pulse, and frustration is induced since the coherent oscillation of a given subset of longitudinal modes dominates and simultaneously inhibits the others. Nevertheless, when high losses are introduced only the replica-symmetric amplified stimulation emission is observed. We therefore suggest that the RSB transition can be used as an identifier of the threshold in standard multimode lasers, as recently proposed and demonstrated for random lasers [1,2].