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.

Tungstate fluorophosphate glasses of good optical quality were synthesized by fusion of the components and casting under air atmosphere. The absorption spectra from near-infrared to visible were obtained and the Judd-Ofelt parameters determined from the absorption bands. Transition probabilities, excited state lifetimes and transition branching ratios were determined from the measurements. Pumping with a 354.7 nm beam from a pulsed laser resulted in emission at 450 nm due to transition 1 D 2 → 3 F 4 in Tm 3ϩ ions and a broadband emission centered at Ϸ550 nm attributed to the glass matrix. When pumping at 650 nm, two emission bands at 450 nm ( 1 D 2 → 3 F 4 ) and at 790 nm ( 3 H 4 → 3 H 6 ) were observed. Excitation spectra were also obtained in order to understand the origin of both emissions. Theoretical and experimental lifetimes were determined and the results were explained in terms of multiphonon relaxation.

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.

Blue and ultraviolet upconversion (UC) emissions at 455 and 363 nm were observed from Tm 3+ doped fluoroindate glasses pumped at 650 nm. The time behavior of the UC signals was studied for different Tm 3+ concentrations. The measurements revealed the origin of the UC process as well as allowed to quantify the interaction between Tm 3+ ions. The results indicate that a two-step one-photon absorption process is responsible for the UC emissions, and dipole-dipole interaction provides the main contribution for energy transfer (ET) among active ions. The critical distance between Tm 3+ ions at which the ET rate is equal to the decay rate of noninteracting Tm 3+ ions was determined.

Optical spectroscopic properties of Tm 3ϩ -doped 60TeO 2 Ϫ10GeO 2 Ϫ10K 2 OϪ10Li 2 O Ϫ10Nb 2 O 5 glass are reported. The absorption spectra were obtained and radiative parameters were determined using the Judd-Ofelt theory. Characteristics of excited states were studied in two sets of experiments. Excitation at 360 nm originates a relatively narrow band emission at 450 nm attributed to transition 1 D 2 → 3 F 4 of the Tm 3ϩ ion with photon energy larger than the band-gap energy of the glass matrix. Excitation at 655 nm originates a frequency upconverted emission at 450 nm ( 1 D 2 → 3 F 4 ) and emission at 790 nm ( 3 H 4 → 3 H 6 ). The radiative lifetimes of levels 1 D 2 and 3 H 4 were measured and the differences between their experimental values and the theoretical predictions are understood as due to the contribution of energy transfer among Tm 3ϩ ions.

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Bombyx mori silk fibroin offers unlimited opportunities for functionalization, processing, and biological integration.

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