Ethanol Solution Of Rhodamine 6G Research Articles

Random laser materials: from ultrahigh efficiency to very low threshold (Anderson localization)

Random lasers hold the premise for cheap coherent light sources that can be miniaturized and molded into any shape and used for speckle-free imaging in biology, remote sensing, display technology, encrypting, cancer detection and distributed amplification. However, they require improvements specifically in terms of efficiency and low emission threshold. This work details for the first time a strategy for increasing the efficiency of a random laser that consists in using smaller particles, trapped between large particles to serve as absorption and gain centers whereas the large particles control mainly the light diffusion into the sample. A record slope efficiency of more than 50% was achieved using yttrium vanadate particles with mean particle size of 54 μm by optimizing the distribution of the polydispersed particles. In addition, random lasing with very low emission threshold (0.24 mJ/cm2) is also reported in a strongly disordered optical medium that is in the transition regime to Anderson localization composed by a colloidal suspension of core–shell TiO2@Silica nanoparticles in ethanol solution of rhodamine 6G. A promising method called fraction of absorbed pump power allowed us to infer the emission threshold for localized modes (peaks mode). The classical super-fluorescence band (ASE) of the random laser was measured separately by collecting the emission at the back of the samples, showing a linear dependence with pumping fluence without gain depletion. The intensity of peaks during Anderson transition is approximately equal within a broad frequency range, indicating suppression of the interaction between the peak modes. The random lasers have been characterized by measurements of backscattering cone, absorption and reflection measurement, transport mean free path, average photon path length and fill fractions.

Random Lasing at Localization Transition in a Colloidal Suspension (TiO2@Silica).

Anderson localization of light and random lasing in this critical regime is an open research frontier, which besides being a basic research topic could also lead to important applications. This article investigates the random laser action at the localization transition in a strongly disordered scattering medium composed of a colloidal suspension of core–shell nanoparticles (TiO2@Silica) in ethanol solution of Rhodamine 6G. The classical superfluorescence band of the random laser was measured separately by collecting the emission at the back of the samples, showing a linear dependence with pumping fluence without gain depletion. However, frontal collection showed saturation of the absorption and emission. Narrow peaks of approximately equal intensity are observed on top of the classical superfluorescence band, indicating suppression of the interaction between the peaks modes. The linewidth of these peaks is lower than that of the passive modes of the scattering medium. A method called fraction of absorbed pumping allowed us to infer that this peak’s mode (localized modes) is confined to a shallow region near the input-pumping border.

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.

Theoretical description of the spectrum of emission of a droplet of ethanol solution of rhodamine 6G under femtosecond laser irradiation

Spectral features of the Stokes emission from an ethanol droplet with dissolved Rhodamine 6G under femtosecond laser irradiation are explained based on numerical solution of the equations for light field spectral density, formulated by the authors. A correlation between the considered spectrum formation model and experimental data is possible only with accounting for the spatial inhomogeneity of excited matter in the droplet focus.

A decrease in the superluminescence threshold of composites of an organic dye with nanoparticles

It is established that admixture of Ag, Al, Cu, Ni, Zn, and Fe 3 O 4 nanoparticles to a rhodamine 6G solution in ethanol with a concentration of 10−2 mol/L that fills a cell with a thickness of 600 µm results in a decrease in the superluminescence thresholds by no less than 50 folds.

Nanosecond Time-Resolved Laser-Induced Fluorescence Spectra of Rhodamine 6G Solution in Ethanol under Shock Loading of up to 3.5 GPa

Nanosecond time-resolved laser-induced fluorescence spectroscopy was performed on rhodamine 6G (R6G) solution in ethanol under laser-driven shock compression under pressures of up to 3.5 GPa. Although under static compression the fluorescence peak shift changed from a redshift to a blueshift at 1.6 GPa, the fluorescence peak underwent a redshift under shock wave loading under pressures of up to 3.5 GPa. The effect of the quadric term on the pressure dependence of the peak shift was observed without the occurrencce of a photoreaction under high pressure. The quadric term was determined using the pressure distribution of laser-induced shock wave profiles.

Fabrication of Microarrays on Fused Silica Plates Using the Laser-Induced Backside Wet Etching Method

A novel approach in the fabrication of microarrays of dye and protein on fused silica plates using the laser-induced backside wet etching (LIBWE) technique is described. The surface of fused silica plates was initially precoated using trimethoxysilane self-assembled monolayers (SAMs) and then etched using the LIBWE method to obtain the desired microstructures on the plate surface. Using this technique, the SAMs on the nonirradiated areas were able to survive the LIBWE process and were used as templates for the subsequent deposition of dye molecules or proteins via chemical bonding or physical adsorption. In the case of fused silica plates precoated with fluorinated SAMs, the LIBWE method is used to remove the SAMs to expose the etched silica surfaces, on which a thin layer of pyranine molecules can be site-selectively deposited using an aqueous solution of pyranine. In another application, an ethanol solution of rhodamine 6G was preferentially deposited onto the nonirradiated areas. In yet another application, bovine serum albumin was preferentially deposited onto the laser-irradiated areas; in this case, the fused silica plates were precoated with poly(ethylene oxide) SAMs. Interestingly, when an aqueous suspension of polystyrene (PS) microbeads was cast onto the fused silica precoated with the fluorinated SAMs, hexagonally close-packed PS microbeads were deposited into the etched cavities. Depositions of the dye, protein, and microbeads were confirmed by visualization using a fluorescence microscope and scanning electron microscope.

Surface-Enhanced Nonresonance Raman Scattering from Size- and Morphology-Controlled Gold Nanoparticle Films

Gold nanoparticle films with different particles sizes (35 ± 5, 15 ± 1 nm) and agglomerated states were prepared on glass substrates, by salting-out the colloidal solutions with NaClO4 or NaOH. An ethanol solution of rhodamine 6G was cast on the gold nanoparticle film and the surface-enhanced Raman scattering (SERS) spectrum was measured. We found that the intensity of the SERS signal was higher for the film with larger particles and that the film prepared from NaClO4 gave higher SERS signals than that prepared from NaOH. Considerable coalescence of larger gold nanoparticles was quite effective for obtaining larger SERS signals. The SERS enhancement factor was estimated to be ∼108 for the film prepared from NaClO4.

Dependence of Lasing Efficiency on Excitation Frequency in the Pumping of a Rhodamine 6G Solution by Laser Pulses of Microsecond Duration

We have revealed an anomalous dependence of the lasing characteristics of an ethanol solution of rhodamine 6G on the spectral composition of the exciting radiation due to the structure of the excited singlet-singlet absorption spectra and the absorption spectra of short-lived photoexcitation products. Elucidation of the influence of the indicated characteristics makes it possible to select optimum pumping spectra and increase the efficiency and stability of the spectral characteristics of dye-laser systems operating in the microsecond and nanosecond wavelength ranges.

Collective spontaneous emission of dye molecules and lasing

The threshold pump power density for lasing in dye solutions is found to depend on the photon energy of pumping radiation. An increase in the pumping photon energy can significantly lower the threshold pump power of dye lasers. For an ethanol solution of rhodamine 6G with a concentration of 4×1018 cm−3, the threshold power density for pumping radiation with a wavelength of 532 nm is 20-fold higher than for pumping radiation with a wavelength of 347 nm. This phenomenon is associated with the competition of collective spontaneous emission, which can lead to the efficient deactivation of excited molecules in femtosecond times, and the dephasing of excited molecules due to the intramolecular nonradiative processes of absorbed-energy conversion. An increase in the dephasing rate with the increasing energy of exciting photons lowers the efficiency of collective spontaneous emission and increases the concentration of dephased excited molecules responsible for lasing.

Dye laser with an output energy of 1 J, a beam divergence of 0.3 mrad, and flashlamp excitation

A study was made of the use of an unstable telescopic resonator in a laser utilizing an ethanol solution of rhodamine 6G excited by a coaxial transverse-discharge flashlamp. When the stored electrical energy was 300 J, the output energy of the laser was 1 J and the angle of divergence of the beam at half the maximum energy was 0.3 mrad. A mode structure of the radiation was observed within the limits of this angle and it was found that, in addition with the lowest symmetric modes, modes with a nonzero azimuthal index were generated. The kinetics of thermooptic distortions of the active medium was also investigated.

Pulsed tunable dye laser with a low level of wide-band background

A bent resonator with radiation extracted through a rotating mirror was developed for suppressing a wide-band superradiance background (amplified spontaneous emission) in pulsed tunable dye lasers. At the exit from the oscillator the superradiance energy was less than 5×10−6 of the narrow-band (0.01 nm) output energy. For a two-stage amplifier utilizing an ethanol solution of rhodamine 6G pumped by a pulsed YAG laser with a peak power of 2.8 MW (λ = 532 nm), the maximum laser efficiency was 20% and the superradiance background over the whole tuning range (560–620 nm) was less than 10−3 of the output energy.

Flashlamp-pumped submicrosecond dye laser

A laser flashlamp pumping system having an input energy of 330 J and a pulse duration of ∼ 230 nsec was developed experimentally and tests were made using a solution of rhodamine 6G under lasing conditions. The maximum lasing energy was 1.1 J, the efficiency was 0.33%, the angle of divergence of the beam at half-energy in a planar resonator was 1.2–1.3 mrad, and the illumination of an ethanol solution of rhodamine 6G halved the output energy when the intensity was 170 kJ/liter.

Influence of thiourea on the emission characteristics of a laser based on an aqueous solution of rhodamine 6G

An investigation was made of the spectral (luminescence and lasing) characteristics of an aqueous solution of rhodamine 6G with an addition of thiourea. When the thiourea concentration in the solvent was ?30%, the absorption and fluorescence spectra changed greatly, the lasing threshold decreased approximately fourfold, and the output power increased by an order of magnitude. The good thermooptical properties of water as a solvent, in combination with the disaggregation properties of thiourea, made it possible to realize (without circulation of the solution) a pulse-periodic lasing regime at a repetition frequency of ?50 Hz and with output radiation parameters typical of a laser with continuous circulation of an ethanol solution of rhodamine 6G.

Output characteristics of a laser utilizing rhodamine 6G in microporous glass

A study was made of the lasing characteristics of new active media in the form of microporous glass containing a dye. The efficiency of conversion of the pump radiation, and the spatial and frequency spectra of the output radiation were determined for lasers with dispersive and nondispersive resonators and with active elements in the form of an ethanol solution of rhodamine 6G or microporous glass containing either rhodamine 6G or its ethanol solution. It was found that the use of active elements made of microporous glass and containing rhodamine 6G improved considerably the spatial characteristics of the output radiation compared with those obtained using liquid active media.

Subpicosecond pulse generation and amplification in a passively mode-locked cw dye laser

An investigation was made of the parameters of a passively mode-locked cw dye laser utilizing a jet of a rhodamine 6G and DODCI solution in ethylene glycol. A continuous train of pulses of 0.4 psec duration was obtained. The tuning range under mode-locking conditions was 590–610 nm. The subpicosecond pulses were amplified by a factor of 100 using an amplifer comprising a rhodamine 6G solution in ethanol pumped by N2 laser radiation.

Waveguide dye laser amplifier

A single-stage flash-lamp-pumped waveguide dye laser amplifier is presented. A Pyrex cylindrical dye cell filled with a rhodamine 6G solution in ethanol acts as an active hollow dielectric waveguide for the light to be amplified. Over-all efficiency and absolute energy gain are about one order of magnitude larger than for a conventional single-pass dye laser amplifier. Such a device can be conveniently used when inserted, with suitable couplers, in an optical waveguide system.

TIME DEPENDENCE OF THE GAIN OF AN OPTICALLY PUMPED SOLUTION OF RHODAMINE 6G

The time dependence of the gain of an ethanol solution of rhodamine 6G was determined during excitation with conventional lamps producing pulses of 80 μsec duration. The gain maximum was reached much earlier than the maximum of the excitation pulse. It was demonstrated experimentally that because of insufficient chemical purity of the solution, the gain was replaced by a reversible absorption due to an increase in the singlet-triplet conversion probability.