Random Gain Medium Research Articles

Study the Impact of Silica Nanoparticles on the Properties of Several Dyes for the Fabrication of a Random Laser Gain Medium

Random laser gain media is synthesized with different types of dye at the same concentration (1×10-3 M) as an active material and silicon dioxide NPs (silica SiO2) as scatter centers through the Sol-Gel technique. The prepared samples are tested with UV–Vis spectroscopy, Fluorescence Spectroscopy, Field Emission Scanning Electron Microscopy (FESEM), and Energy Dispersive X-ray Diffraction (EDX). The end result demonstrates that doped dyes with silica nanoparticles at a concentration of 0.0016 mol/ml have lower absorbance and higher fluorescence spectra than pure dyes. FESEM scans revealed that the morphology of nanocrystalline silica is clusters of nano-sized spherical particles in the range (25-67) nm. It is concluded that the various dyes with SiO2 as a scattering center can be proposed to build laser media.

Fabrication of a random laser gain medium using Rhodamine 101 dye doped with SiO2 nanoparticles by Sol-Gel technique

Random laser gain media are demonstrated by different concentrations of Rhodamine 101 dye solution mixed with SiO2 nanoparticles. For this purpose, these mediums are fabricated using the sol–gel technique and supplied with a pulsed blue laser to produce random lasing, while the light that reflects is collected using a spectrometer. Fluorescence and lasing activity were amplified as a consequence of nanoparticle scattering due to this optical pumping process. The results demonstrate coherent random lasing at 532–536 nm with the best FWHM equal to 2.1 nm at the optimal concentration (1 × 10−4 M).

Enhancing the Spectral Characteristics of Rhodamine 610 Laser Dye Doped with Chemically Prepared Gold Nanoparticles

In this study, gold nanoparticle samples were prepared by the chemical reduction method (seed-growth) with 4 ratios (10, 12, 15 and 18) ml of seed, and the growth was stationary at 40 ml. The optical and structural properties of these samples were studied. The 18 ml seed sample showed the highest absorbance. The X- ray diffraction (XRD) patterns of these samples showed clear peaks at (38.25o, 44.5o, 64.4o, and 77.95o). The UV-visible showed that the absorbance of all the samples was in the same range as the standard AuNPs. The field emission-scanning electron microscope (FE-SEM) showed the shape of AuNPs as nanorods and the particle size between 30-50 nm. Rhodamine-610 (RhB) was prepared at 10-5 M concentration, the optical measurements were studied, AuNPs and RhB were mixed at ratios (1:1, 1:2, 1:3), and the fluorescence measurements were done. Full width at half maximum (FHWM) and the intensity of RhB after mixing were changed, and this result showed significant efficacy for many applications. The study shows that this mixing could be used after doping with polymer as a random gain medium or saturation absorber for pulse laser generation.

High-purity narrow emission line display of titanium dioxide nanoparticles in laser dyes as random gains

In this work, the dyes Rhodamine B and Coumarin 102 containing titanium dioxide nanoparticles were used as scattering centers to fabricate a random gain medium. The laser dye was dissolved in hexanol and methanol solvent respectively. The titanium dioxide nanoparticles were synthesized by DC reaction magnetron spraying technique. The random-gain medium was made by adding 2.5 mg of titanium dioxide nanoparticles to Rhodamine and coumarin 102 dyes by coating the glass cell with two-sided titanium dioxide with high spectral efficiency and low production cost. A narrow line optical emission was detected at 565 nm for Rhodamine B and 534 nm for coumarin 102, where it was found that rhodamine B dye has FWHM 8 nm and coumarin dye 102 has FWHM 9 nm. Through this, it was concluded that by adding titanium dioxide, we increase the random gain of the pigments added to it. This is a very good start toward making high-efficiency and low-cost laser random transfer fabrication in the visible range.

Preparation and Photoluminescence Spectra of Organometallic Complexes Containing Nanoparticles as Random Gain Media

This work prepared organometallic complexes from the 8-hydroxyquinoline ligand linked to metal ions such as Ba2+, Ca2+, and Zn2+. The effects of metal ion type and adding nanoparticles to the complex solution on the absorption and photoluminescence characteristics of the prepared complexes were introduced. These nanoparticles were added to the prepared complex solutions to act as scattering centers to form random gain media with emission in the visible region of the electromagnetic spectrum. The random gain media made from the Znq2 complex with nanoparticles showed the best characteristics with good chemical and spectroscopic stabilities, high reliability, and reproducibility in addition to the low production cost and reasonably simple requirements.

Organic random laser generation by stimulated cascaded four-wave mixing

Our study investigated the nonlinear lasing properties of a solid-state dye laser. Laser emission was provided by light amplification in static disordered nanostructures with the gain based on a xanthene dye-functionalized epoxy resin polymer. The emission spectrum was found to be reproducible at each near-threshold excitation pulse. We consider that this spectrum results from a non-degenerate cascaded four-wave mixing in the investigated gain medium. The pump beams were generated simultaneously in the bulk isotropic active medium by single-shot excitation on the nanosecond time scale. The downshift and upshift modes were generated via their coherent pump beams. To our knowledge, this type of stimulated highly nondegenerate cascaded four-wave mixing in the visible spectral range (486 nm – 680 nm) has not been experimentally demonstrated before in a random gain medium.

Distributed static and dynamic detection of an acoustic wave in a Brillouin random fiber laser

The interaction of random laser and gain medium is important to understand the noise origin in random fiber lasers. Here, using the optical time domain reflectometry method, the time-resolved distributed acoustic wave generated by a Brillouin random fiber laser (BRFL) is characterized. The dynamic property of the acoustic wave reflects the gain dynamics of the BRFL. The principle is based on the polarization-decoupled stimulated Brillouin scattering (SBS)-enhanced four-wave mixing process, where the probe light experiences maximum reflection when the phase match condition is satisfied. Static measurements present exponentially depleted Brillouin gain along the gain medium in the BRFL, indicating the localized random SBS frequency change in the maximum local gain region, which varies with time to contribute random laser noise as revealed in the dynamic measurement. The SBS-induced birefringence change in the Brillouin gain fiber is approximately 10 − 7 to 10 − 6 . The phase noise of the BRFL is observed directly inside the random laser gain medium for the first time via time and spatially varied acoustic wave intensity. By counting the temporal intensity statistical distribution, optical rogue waves are detected near the lasing threshold of the BRFL. Different temporal intensity statistical distribution at high and low gain positions is found, which is caused by the SBS nonlinear transfer function and localized gain. The distributed characterization methods in the paper provide a new platform to study the interaction of random lasers and gain medium, giving us a new perspective to understand the fundamental physics of the random lasing process and its noise property.

Short-cavity random distributed feedback fiber laser with ultra-low threshold

We experimentally demonstrated a random distributed feedback fiber laser (RDFB-FL) with an ultra-low threshold, utilizing a highly nonlinear optical fiber (HNLF). A piece of HNLF was used as the random laser gain medium to resolve the contradiction between the lasing threshold and cavity length. Consisting of a half-open cavity structure, the proposed RDFB-FL had a lasing threshold as low as 0.408 W (record low) with a relatively short cavity length of 850 m. In a ring cavity, the lasing threshold could be further reduced to 0.284 W with a cavity length of 950 m by the combined action of distributed feedback and cavity feedback.

Flexible ultrahigh Q-factor bottle-like microcavity laser

A comprehensive study on the whispering gallery mode (WGM) lasing characteristics of a rhodamine 6G (R6G)-based flexible bottle-like microcavity has been performed. The closed-loop WGMs excited inside the microcavity were found strongly confined along the radial direction. Thus, the spacing of ultralow loss lasing modes can be realized by controlling the diameter of the bottle-like microcavity. By studying the WGM lasing action, the dependence of lasing threshold and Q-factor on the radius of the microcavity was analyzed. The lasing threshold for the random gain medium was reduced under the influence of radial optical confinement by increasing diameter. In addition, the WGM lasing characteristics of the bottle-like microcavity were also explored by the three-dimensional finite-difference time-domain method. Our approach provides a solution scheme towards the research for lasing characteristic of novel nanocrystal fluorescence or quantum dot materials based on the flexible ultrahigh Q factor bottle-like microcavity.

Detection of gain enhancement in laser-induced fluorescence of rhodamine B lasing dye by silicon dioxide nanostructures-coated cavity

In this work, nanostructured silicon dioxide films are deposited by closed-field unbalanced direct-current (DC) reactive magnetron sputtering technique on two sides of quartz cells containing rhodamine B dye dissolved in ethanol with 10‒5 M concentration as a random gain medium. The preparation conditions are optimized to prepare highly pure SiO2 nanostructures with a minimum particle size of about 20 nm. The effect of SiO2 films as external cavity for the random gain medium is determined by the laser-induced fluorescence of this medium, and an increase of about 200% in intensity is observed after the deposition of nanostructured SiO2 thin films on two sides of the dye cell.

Random lasing actions in self-assembled perovskite nanoparticles

Solution-based perovskite nanoparticles have been intensively studied in past few years due to their applications in both photovoltaic and optoelectronic devices. Here, based on the common ground between the solution-based perovskite and random lasers, we have studied the mirrorless lasing actions in self-assembled perovskite nanoparticles. After the synthesis from solution, discrete lasing peaks have been observed from the optically pumped perovskites without any well-defined cavity boundaries. The obtained quality (Q) factors and thresholds of random lasers are around 500 and 60 uJ/cm2, respectively. Both values are comparable to the conventional perovskite microdisk lasers with polygon shaped cavity boundaries. From the corresponding studies on laser spectra and fluorescence microscope images, the lasing actions are considered as random lasers that are generated by strong multiple scattering in random gain media. In additional to conventional single-photon excitation, due to the strong nonlinear effects of perovskites, two-photon pumped random lasers have also been demonstrated for the first time. We believe this research will find its potential applications in low-cost coherent light sources and biomedical detection.

Raman mode random lasing in ZnS-β-carotene random gain media

Raman mode random lasing is demonstrated in ZnS-β-carotene random gain media at room temperature. A self assembled random medium is prepared with ZnS sub micron spheres synthesized by homogeneous precipitation method. β-Carotene extracted from pale green leaves is embedded in this random medium. The emission band of ZnS random medium (on excitation at 488 nm) overlaps considerably with that of β-carotene, which functions as a gain medium. Here, random medium works as a cavity, leading to Raman mode lasing at 517 nm and 527 nm triggered by stimulated resonance Raman scattering.

Determination of threshold random gain medium in dye: Polymer films containing TiO<sub>2</sub> nanoparticles

Random gain medium based on organic Rhodamine 590 (R590) laser-dye and Titanium dioxide (TiO2) suspended nanoparticles have been prepared with polymethylmethacrylate (PMMA) as a host. Spray-coated homogeneous film samples of 22.4 μm thickness. Optimum concentrations have been determined depending on the normal fluorescence spectra which give evidence that the laser dye provides amplification and TiO2 nanoparticles act as scatter center. At the optimum concentrations, results of the random gain medium under second harmonic Nd: YAG laser excitation shows that the values of bandwidth at full width half-maximum (FWHM) and the threshold energy are about 11 nm and 10 mJ respectively.

Lasing characteristics of random cylindrical microcavity lasers

Room-temperature lasing characteristics of random cylindrical microcavity lasers, which can be realized by coating a layer of random gain medium onto the surface of an optical fiber with various diameters, was studied experimentally. It is shown that closed-loop random modes excited inside the random gain medium are strongly confined along the radial direction so that the spacing of lasing modes is controlled by the diameter of cylindrical microcavity. In addition, lasing threshold of the random gain medium can be reduced by an order of magnitude under the influence of radial optical confinement.

Albedo and gain threshold of a diffusive Raman random laser

The diffuse reflectance (albedo) and transmittance of a Raman random gain medium are derived from a diffusion equation with power dependent gain. The results show good agreement with the experimental data for barium nitrate powder. Both the Raman albedo A R and Raman transmittance T R diverge at a critical gain γ c, interpreted as the threshold for diffusive Raman laser generation. The parametric dependence of the albedo and threshold gain on the scattering characteristics of the random medium is analysed and the feedback effect of Fresnel reflection at the gain boundaries evaluated. The addition of external mirrors, particularly at the pumped surface, significantly reduces the generation threshold.

The dependence of radiation characteristics of random laser on the size and arrangement of crystal grains in PCs

The modulation on radiation characteristics of random laser caused by photonic crystals(PCs) was studied, and its dependence on the size and arrangement of the crystal grains was analyzed. For a random medium, if it is covered by different photonic crystals on its upper and lower surfaces respectively, its output characteristics should be different. The results showed that the grain size of the PCs has a great effect on the radiation characteristics of the system. The PC with a suitable grain size plays a better role in trapping the energy in the system and it can modulate the laser modes effectively. It leads the light to oscillate back and forth, enhancing the interaction between the random gain medium and the light to achieve a greater amplification, and conseguently reducins the lasing threshold. It also controls the spontaneous emission and leads it to the target frequency in the emission spectra. However, if crystal grain size daeznot match the structure of random gain medium, the laser modes could not be modulated as we wish and the energy of the light field could not be localized effectively in the system, thus the laser system has a higher lasing threshold. The arrangement of crystal grains should affect the output characteristics also. In short, there exists an optimum PC/ random medium combination for lasing, for which the lasing threshold reaches a minimum.

Approximate orthogonality relation for the modes of an open cavity

A simple orthogonality relation for the modes of an open cavity is obtained in the scalar field approximation. The relation directly follows from the wave equation and boundary condition at the cavity mirrors and can be applied for a broad class of systems with a cavity that can contain a random gain medium with a weak dispersion.

Two-stream analysis of a random gain medium

A two-stream analysis is applied to determine the generation threshold of a random gain medium in three cases of practical interest, namely a plane layer of finite width, a plane layer backed by a passive scattering layer and a plane layer with reflecting boundaries. Asymmetric and imperfect scattering are included in the analysis, while the non-uniform-gain case is treated by means of the transformed albedo equation du/dτ = a(τ)-b(τ)sin 2u where u = arctan R and a(τ), b(τ) are functions of optical depth. The two-stream model is validated by comparison with transport theory and provides simple analytical solutions to practical problems with an error generally less than 10%.

Coherent, directional, laserlike emission from random gain media

We present experimental evidence for coherent, directional emission from a random gain medium above the threshold for laserlike emission. In particular, we report the first observation (to our knowledge) of a coherent angular backscattering peak above this threshold. A plausible explanation of our findings follows from the assumption that superfluorescent emission occurs in the gain medium above threshold.

Random gain medium with reflecting boundary

The effect of a reflecting boundary on the generation threshold of a random gain medium is analysed for both specular and diffuse reflection, the latter corresponding to feedback scattering from a passive boundary layer. The feedback effect is significant for non-diffusive transfer (optically thin layer) but small in the diffusion regime unless 1−R≪ 3 γ , where γ is the gain parameter, with a maximum reduction by a factor of two for a perfectly reflecting boundary. A second reflecting boundary further reduces the threshold, the reduction depending on the optical parameters of the medium.