Direct three-photon excitation of upconversion random laser emission in a weakly scattering organic colloidal system

Room-temperature up-conversion random lasing from CsPbBr3 quantum dots with TiO2 nanotubes

We report successful room-temperature up-conversion random lasing by distributing CsPbBr₃ quantum dots (QDs) uniformly into TiO₂ nanotubes (NTs). In order to overcome the difficulty in purifying the QDs, TiO₂ NTs were designed to collect QDs and enhance the optical multiple scattering effect. A threshold of 9.54  mJ/cm² and narrow full width at half-maximum of 0.49 nm with a relatively high quality factor of 1089 were successfully observed. These results indicate that CsPbBr₃QDs/TiO₂ NTs can be high-performance up-conversion lasers for practical applications, especially when the phase matching required by conventional approaches cannot be fulfilled.

Two-photon excited lasing of Coumarin 307 for lysozyme amyloid fibrils detection

Amyloid fibrils are a well-recognized hallmark of neurodegeneration. A common approach to detect amyloid fibrils is staining with organic molecules and monitoring optical properties using fluorescence spectroscopy. However, the structural diversity of amyloids necessitates new sensitive methods and probes that can be reliably used to characterize them. Here, Coumarin 307 is applied for lysozyme fibrils detection by observation of laser action in the process of two-photon excited stimulated emission. It is shown that the lasing threshold and spectrum significantly depend on the adopted structure (α-helix or β-sheet) of the lysozyme protein, whereas fluorescence spectrum is insensitive to the protein structure. The applications of coherent stimulated emission light that can be emitted deep inside a scattering medium can be particularly promising for imaging and therapeutic purposes in the neurodegeneration field. Two-photon excitation with the near-infrared light, which allows the deepest penetration of tissues, is an important advantage of the method.

Self-structuring of stable dissipative breathing vortex solitons in a colloidal nanosuspension

The self-structuring of laser light in an artificial optical medium composed of a colloidal suspension of nanoparticles is demonstrated using variational and numerical methods extended to dissipative systems. In such engineered materials, competing nonlinear susceptibilities are enhanced by the light induced migration of nanoparticles. The compensation of diffraction by competing focusing and defocusing nonlinearities, together with a balance between loss and gain, allow for self-organization of light and the formation of stable dissipative breathing vortex solitons. Due to their robustness, the breathers may be used for selective dynamic photonic tweezing of nanoparticles in colloidal nanosuspensions.

Observation of photonic paramagnetic to spin-glass transition in a specially designed TiO2 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.

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 (4)F3/2 → (4)I11/2 transition of neodymium ions (Nd(3+)), was achieved by exciting the Nd(3+) with a tunable beam from 680 to 920 nm covering the ground state absorption transitions to the (4)F9/2, ((4)F7/2,(4)S3/2), ((4)F5/2,(2)H9/2), and (4)F3/2 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.

Polarized three-photon-pumped laser in a single MOF microcrystal

Higher order multiphoton-pumped polarized lasers have fundamental technological importance. Although they can be used to in vivo imaging, their application has yet to be realized. Here we show the first polarized three-photon-pumped (3PP) microcavity laser in a single host-guest composite metal-organic framework (MOF) crystal, via a controllable in situ self-assembly strategy. The highly oriented assembly of dye molecules within the MOF provides an opportunity to achieve 3PP lasing with a low lasing threshold and a very high-quality factor on excitation. Furthermore, the 3PP lasing generated from composite MOF is perfectly polarized. These findings may eventually open up a new route to the exploitation of multiphoton-pumped solid-state laser in single MOF microcrystal (or nanocrystal) for future optoelectronic and biomedical applications.

Random lasing in Eu³⁺ doped borate glass-ceramic embedded with Ag nanoparticles under direct three-photon excitation

We report the observation of random lasing from Eu(3+) doped borate glass ceramic films embedded with Ag nanoparticles through three-photon absorption at room temperature. Under 1179 nm ultrashort femtosecond pulse excitation, discrete sharp peaks with linewidth ∼0.4 nm emerge randomly from a broad emission band with peak wavelength at ∼612 nm. In addition, the number of sharp peaks increases with the increase of excitation power. We also show that the emission spectrum varies with different observation angles and the corresponding lasing threshold is dependent on the excitation area. Hence, we verify unambiguously that the Eu(3+) doped borate glass ceramic film supports random lasing action via three-photon absorption excitation. In addition, Ag nanoparticles, which act as light scatterers, allow the formation of random microcavities inside the bulk film.

Multi-photon excited coherent random laser emission in ZnO powders

We report the observation and analysis of anti-Stokes coherent random laser (RL) emission from zinc oxide (ZnO) powders excited by one-, two- or three-photon femtosecond laser radiation. The ZnO powders were produced via a novel proteic sol-gel, low-cost and environmentally friendly route using coconut water in the polymerization step of the metal precursor. One- and two-photon excitation at 354 nm and 710 nm, respectively, generated single-band emissions centred at about 387 nm. For three-photon excitation, the emission spectra showed a strong ultraviolet (UV) band (380-396 nm) attributed to direct three-photon absorption from the valence band to the conduction band. The presence of an intensity threshold and a bandwidth narrowing of the UV band from about 20 to 4 nm are clear evidence of RL action. The observation of multiple sub-nanometre narrow peaks in the emission spectra for excitation above the RL threshold is consistent with random lasing by coherent feedback.