Random laser properties of Nd3+ crystal powders

Obtaining the spectroscopic quality factor through the luminescent thermometry in 50Li2O · 45B2O3 · 5Al2O3 glasses doped with Nd3+ and fluorides

Lithium-boron-aluminum (LBA) glasses doped with N d ³⁺ and fluorides were produced. From the absorption spectra, their Judd-Ofelt intensity parameters, Ω _2,4,6, and spectroscopic quality factors were calculated. Exploiting their near infrared temperature dependent luminescence, we investigated their potential for optical thermometry based on the luminescence intensity ratio (LIR) methodology. Three LIR schemes were proposed, and relative sensitivity values up to 3.57±0.06% K ^-1 were obtained. From the temperature dependent luminescence, we alternatively calculated their corresponding spectroscopic quality factors. The results indicated that N d ³⁺-doped LBA glasses are promising systems for optical thermometry and as gain mediums for solid-state lasers.

Random laser emission from neodymium doped alumina lead-germanate glass powder

Random lasing is reported for the first time, to our knowledge, in neodymium doped alumina lead-germanate (GPA) glass powder. The samples were fabricated by a conventional melt-quenching technique at room temperature, and x-ray diffraction was used to confirm the amorphous structure of the glass. Powders with average grain size of about 2 µm were prepared by grinding the glass samples and using sedimentation in isopropyl alcohol to remove the coarsest particles. The sample was excited using an optical parametric oscillator tuned to 808 nm, in resonance with the neodymium ion (N d ³⁺) transition ⁴ I _9/2→{⁴ F _5/2,² H _9/2}. Random laser (RL) emission at 1060 nm (N d ³⁺ transition: ⁴ F _3/2→⁴ I _11/2) was observed for an energy fluence excitation threshold (E F E _{r m t h} ) of about 0.3m J/m m ². Above the E F E _{t h} , a short RL pulse in the nanosecond range is observed, corroborating the lasing process. Contrary to what one might suppose, the use of large quantities of neodymium oxide (10% wt. of N d ₂ O ₃) in the GPA glass, which leads to luminescence concentration quenching (LCQ), is not a disadvantage, once stimulated emissions (RL emission) occur faster than the nonradiative energy-transfer time among N d ³⁺ ions responsible for the LCQ.

Spectro-temporal behavior of dye-based solid-state random lasers under a picosecond pumping regime: Part III

In two recent works, the authors have investigated the spectro-temporal properties of the random laser emission from solid state dye-doped powders in picosecond pumping regime. Each emission pulse consists, both above and below threshold, in a collection of narrow peaks of a spectro-temporal width at the theoretical limit (ΔωΔt≅1). The distribution of path lengths traveled inside the diffusive active medium by photons that can be amplified by stimulated emission explains this behavior, as demonstrated by a simple theoretical model developed by the authors. The aim of the present work is, first, to develop an implemented model that does not depend on fitting parameters, and which is compatible with the energetic and spectro-temporal properties of the material; and second, to get knowledge about the spatial properties of the emission. The transverse coherence size of each emitted photon packet has been measured; and in addition, we have shown the existence of spatial fluctuations of the emission of these materials, as our model predicts.

Random lasing and replica symmetry breaking in GeO2-PbO-MgO glass–ceramics doped with neodymium

We investigated the random lasing process and Replica Symmetry Breaking (RSB) phenomenon in neodymium ions (Nd³⁺) doped lead-germanate glass–ceramics (GCs) containing MgO. Glass samples were fabricated by conventional melt-quenching technique and the GCs were obtained by carefully devitrifying the parent glasses at 830 °C for different time intervals. The partial crystallization of the parent glasses was verified by X-ray diffraction. Photoluminescence (PL) enhancement of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\approx$$\end{document}≈ 500% relative to the parent glasses was observed for samples with a higher crystallinity degree (annealed during 5 h). Powders with grains having average size of 2 µm were prepared by griding the GCs samples. The Random Laser (RL) was excited at 808 nm, in resonance with the Nd³⁺ transition ⁴I_9/2 → {⁴F_5/2, ²H_9/2}, and emitted at 1068 nm (transition ⁴F_3/2 → ⁴I_11/2). The RL performance was clearly enhanced for the sample with the highest crystallinity degree whose energy fluence excitation threshold (EFE_th) was 0.25 mJ/mm². The enhanced performance is attributed to the residence-time growth of photons inside the sample and the higher quantum efficiency of Nd³⁺ incorporated within the microcrystals, where radiative losses are reduced. Moreover, the phenomenon of Replica Symmetry Breaking (RSB), characteristic of a photonic-phase-transition, was detected by measuring the intensity fluctuations of the RL emission. The Parisi overlap parameter was determined for all samples, for excitation below and above the EFE_th. This is the first time, for the best of the authors knowledge, that RL emission and RSB are reported for a glass–ceramic system.

Spectro-temporal behavior of dye-based solid-state random lasers under picosecond pumping regime: part II

In a very recent work the spectral and temporal properties of the random laser emission from solid state dye-doped powders have been investigated by the authors in picosecond pumping regime. The emission shows within each pulse, peaks of more intensity than background, and of a spectro-temporal width at the theoretical limit (ΔωΔt≅1), even in conditions well below the threshold. The relationship between the distribution of paths lengths traveled by photons inside the active medium, and the amplification by stimulated emission explains this behavior. The aim of the present work is to propose a simple model that, in addition to explaining these characteristics of the emission, is compatible with the energetic properties of the material. Particularly interesting is the behavior predicted by the model for the emission decay in sub-threshold conditions, as well as its very good fit with the experimental measurements and its comparison with the one found in low dispersive media, that shows the decisive effect of scattering. The set of results is hardly compatible with a mode structure.

Simultaneous evaluation of intermittency effects, replica symmetry breaking and modes dynamics correlations in a Nd:YAG random laser

Random lasers (RLs) are remarkable experimental platforms to advance the understanding of complex systems phenomena, such as the replica-symmetry-breaking (RSB) spin glass phase, dynamics modes correlations, and turbulence. Here we study these three phenomena jointly in a Nd:YAG based RL synthesized for the first time using a spray pyrolysis method. We propose a couple of modified Pearson correlation coefficients that are simultaneously sensitive to the emergence and fading out of photonic intermittency turbulent-like effects, dynamics evolution of modes correlations, and onset of RSB behavior. Our results show how intertwined these phenomena are in RLs, and suggest that they might share some common underlying mechanisms, possibly approached in future theoretical models under a unified treatment.

Non-resonant power-efficient directional Nd:YAG ceramic laser using a scattering cavity

Non-resonant lasers exhibit the potential for stable and consistent narrowband light sources. Furthermore, non-resonant lasers do not require well-defined optics, and thus has considerably diversified the available types of laser gain materials including powders, films, and turbid ceramics. Despite these intrinsic advantages, the practical applications of non-resonant lasers have been limited so far, mainly because of their low power efficiency and omnidirectional emission. To overcome these limitations, here we propose a light trap design for non-resonant lasers based on a spherical scattering cavity with a small entrance. Using a porous Nd³⁺:YAG ceramic, directional laser emission could be observed with significant enhancements in the slope efficiency and linewidth (down to 32 pm). A theoretical model is also developed to describe and predict the operation characteristics of proposed non-resonant laser.

Nonlinear effects and photonic phase transitions in Nd3+-doped nanocrystal-based random lasers

The interplay between gain and scattering of light propagating in disordered media allows operation of random lasers (RLs)-lasers without conventional optical cavities. In the present paper, we review our recent contributions in this area, which include the demonstration of self-second-harmonic and self-sum-frequency generation, the characterization of Lévy's statistics of the output intensity fluctuations, and replica symmetry breaking (analogue to the spin-glass phase transition) by RLs based on nanocrystals containing trivalent neodymium ions.

Input/output energy in solid state dye random lasers

A new approach to the problem of energy in solid state dye random lasers is presented. The measurements performed in terms of absolute energy show that the slope efficiency depends on the measurement conditions. In particular, in lasers with pumping in the picoseconds range, the result is really different if measured by recording the emission in the same time range or in a longer one (nanoseconds range). In the last case, no energy threshold is observed. A previously developed model has been applied to the solid state dye random laser. It is a rate-equations model, based on a distribution of paths with different lengths, which partially share population inversion. The results of the model are satisfactory and show that the dynamic behavior is pretty similar in solid state dye random lasers and in inorganic powders.

Random lasing emission tailored by femtosecond and picosecond pulsed polymer ablation

We report the realization of random lasers with spatially localized feedback in which the average number of lasing modes is tuned via the fabrication process. The scattering elements required for optical feedback are obtained by short-pulsed laser ablation. By varying the pulse parameters, we control the scattering properties of the induced defects and, thus, the emission spectra. We demonstrate a large variety of spectral signatures typical of resonant random lasing with sub-nanometer linewidths, low thresholds (about 40  pJ/μm²), and single-to-multimode emission. Our simple approach allows us to obtain optical resonators with sharp linewidths at frequencies covering the entire gain window for multiple applications.

Random laser model for Nd3+-doped powders and its application to stimulated emission cross-section calculations

A new theoretical approach for random lasing of Nd³⁺doped powders is presented. The model's singularity lies in the fact that it proposes a probability distribution of the stimulated photon paths lengths in the sample, as well as a population inversion shared by different photon paths. The model's predictions satisfactorily compare with the results of laser threshold and absolute input/output energy slope of a real Random Laser. The main novel issue is that the best fit to the experimental results requires considering a high level of shared population inversion among different paths. The model simulation of local and spatially integrated Random Laser emissions, as well as their time evolution, is in accordance with the experimental behavior. These results also provide a new method of measuring the stimulated emission cross-section in this kind of random laser materials.