Amplified Spontaneous Emission Spectra Research Articles

Enhanced amplified spontaneous emission performance through effective regulation of phase distribution in Ruddlesden-Popper perovskite films.

Ruddlesden-Popper (RP) perovskites promise next-generation gain media for laser devices. However, most RP perovskite lasers are still suffering from inferior performance characteristics, such as inadequate energy transfer, unstable emission, and short lifetime. To address the above problems, high crystalline quality, compact, and smooth PEA2FA2Pb3Br10 films with uniform phase distribution were successfully prepared by ionic liquid (IL) methylammonium acetate (MAAc) in an air environment. Compared with the PEA2FA2Pb3Br10 film prepared by the traditional solvent dimethyl sulfoxide (DMSO), an enhanced amplified spontaneous emission (ASE) with a lower threshold of 58 µJ·cm-2 from the MAAc-treated film was obtained under nanosecond laser excitation. The transient absorption (TA) spectroscopy revealed that a uniform phase distribution and more efficient energy transfer processes were achieved in the PEA2FA2Pb3Br10-MAAc film, leading to an enhanced band-to-band spontaneous emission process. Furthermore, the films exhibited better stability, showing no signs of degradation under the 120 min pulsed laser pumping in air and stability of ASE spectra at even 95% humidity conditions. This study provides an important foundation for achieving high-performance optically pumped lasers based on the unique RP perovskites.

Extremely Low Threshold Quasi‐CW Amplified Spontaneous Emission Achieving and Its Mechanism Study

AbstractThe development of lasing materials with weak pile‐up effect from triplet excitons, low lasing threshold, and long operational lifetime is much significant for truly continuous wave operation and electrically pumping organic lasers. However, most of organic gain media has been verified to have extreme quenching effect from triplet excitons due to its wide‐band distribution of triplet absorption spectrum. Here, it is found that the phenanthroimidazole derivatives as gain media have congenital advantages on handling triplet's issues. A very low amplified spontaneous emission (ASE) threshold of 0.56 µJ cm−2 and a long operational lifetime of 5.77 × 105 pump pulses in air atmosphere are well obtained. When increasing the pump repetition frequency from 20 Hz to 20 kHz, the operational lifetimes of the thin films have small reduction. Under a high pump repetition frequency of 200 kHz, which is quasi‐continuous wave operational regime, the PI2PhDPO thin film exhibits very low ASE threshold of 0.78 µJ cm−2 due to the tiny overlap between triplet absorption and ASE spectra.

Exploring the photodynamic profile of laser-generated exciplex from a conjugated polymer

In this work, we investigated the impact of the concentration on the spectral and amplified spontaneous emission spectra (ASE) of a conducting polymer of poly(2,5-di(3,7-dimethyloctyloxy) cyanoterephthalylidene) (PDDCP) in tetrahydrofuran (THF). The findings demonstrate that the absorption spectra exhibited two peaks at 330 and 445 nm across the concentration range (1–100 µg/mL). Irrespective of the optical density, altering the concentrations did not affect the absorption spectrum. Also, the analysis indicated that the polymer did not agglomerate in the ground state for any of the concentrations mentioned. However, changes in the polymer had a substantial effect on its photoluminescence spectrum (PL), likely due to the formation of exciplexes and excimers. Also, the energy band gap also varied as a function of concentration. At a certain concentration (25 µg/mL) and pump pulse energy (3 mJ), PDDCP produced a superradiant ASE peak at 565 nm with a remarkably narrow full width at half maximum (FWHM). These findings can provide insight into the optical characteristics of PDDCP, which may have potential applications in the fabrication of tunable solid-state laser rods, Schottky diodes, and solar cell applications.

Effect of Gamma Irradiation on the Optical Properties of the Conjugated Copolymer B-co-MP

The conjugated polymer poly {[2-[2′,5′-bis(2″-ethylhexyloxy)phenyl]-1,4-phenylenevinylene]-co-[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene]} (B-co-MP) has been proven to be an excellent laser medium with a high photochemical stability. Moreover, the impact of γ-irradiation on its optical and chemical properties has been investigated. Herein, the spectral and amplified spontaneous emission (ASE) characteristics of B-co-MP at various concentrations under γ-irradiation doses are studied. Various concentrations of B-co-MP in tetrahydrofuran (THF) were prepared. The samples were irradiated with various γ-doses from 5 to 20 kGy using a Co-60 source at room temperature. The absorption, fluorescence, and ASE spectra were dramatically blue-shifted after the γ-irradiation. This indicates that the increment in the γ-irradiation dose led to a widening in the energy gap and reduction in the number of carbon atoms (N). The change in the spectral profiles could be attributed to chain conformational alterations and/or chain scission induced by the γ-irradiation. We anticipate this study to boost our understanding of optical and structural profiles of B-co-MP under various conditions, including γ-irradiation and the potential utility of this copolymer in a variety of applications.

Phase segregation leading to tunable amplified spontaneous emission in mixed halide perovskites

The amplified spontaneous emission (ASE) of a MAPbI1.5Br1.5 film is studied under continuous wave (CW) and pulsed illumination. The different ASE spectra evolution, especially in the range of 680 nm to 720 nm, indicates the different compositional distribution of bromide in the iodine-rich domains during phase segregation process under different illumination conditions. Furthermore, using light control such as adjusting the repetition rate of pulsed illumination or the duty cycle of Quasi-CW illumination, is of benefit to stabilize the ASE output at any wavelength in the range of ∼ 675 nm to ∼ 775 nm.

Low-Threshold Amplified Spontaneous Emission from Air-Stable CsPbBr3 Perovskite Films Containing Trace Amounts of Polyethylene Oxide.

Organic additives can enhance the amplified spontaneous emission (ASE) performance of inorganic cesium lead halide perovskites (CsPbBr3 ) but volatility, potential hygroscopicity and oxidative degradation of these additives jeopardizes the thermal stability and shelf-life of blended CsPbBr3 films. To address this problem, we have fabricated perovskite films in a two-step solution protocol involving as little added polyethylene oxide (PEO) as possible. These films exhibited enhanced crystallization, improved photoluminescence (PL) intensity and prolonged lifetimes. Their hierarchical morphology and surface passivation lowered the ASE threshold from 278 to 176 μЈ/cm2 under one-photon nanosecond laser excitation. The proportion of added PEO was 0.3 wt% and was subsequently almost fully removed, thereby reducing its adverse influence on the stability of resulting films under continuous pulsed laser excitation. Stable ASE spectra could be stimulated after storage in air for 10 months.

Synthesis of novel pyrrolidinyl chalcone derivatives: Spectral properties, energy band-gap tailoring, and amplified spontaneous emission

This work demonstrates the synthesis, structural features, and spectral properties of novel 3-(4-(pyrrolidinyl) phenyl)-1-(4,3 di-substituted phenyl)-(2E)-propen-1-one chalcone derivatives. Their absorption, fluorescence, NMR spectra, influence of functional groups, energy band gaps, Stokes shift, and amplified spontaneous emission (ASE) are thoroughly studied. The band gaps of these chalcones are significantly lowered by adding electron-donating groups. In contrast, the electron-withdrawing groups lead to decreasing the energy band gap value. When the pyrrolidinyl group is replaced with N, N-dimethylamino group, the energy gap value decreases. The effect of functional groups (altering the pyrrolidinyl by N, N dimethylamino) red-shifts the ASE spectra to longer wavelengths. Under a suitable pump power energy excitation and concentration, these chalcones exhibit a wide range of ASE spectra.

Air-Processed MAPbBr3 Perovskite Thin Film with Ultrastability and Enhanced Amplified Spontaneous Emission.

The poor stability, in particular with respect to temperature, moisture, and light exposure, remains a ubiquitous impediment virtually for metal halide perovskite materials and devices in their future practical application. Herein, from the perspective of precursor solution chemistry, ionic liquid solvent methylammonium acetate (MAAc) is introduced to prepare high-quality MAPbBr3 perovskite thin films in a one-step air-processing process without anti-solvent treatment. Due to formation of pinhole-free, uniform, and compact MAPbBr3 perovskite film, excellent amplified spontaneous emission (ASE) with high emission efficiency and low threshold is obtained under nanosecond laser. Furthermore, the prepared MAPbBr3 perovskite exhibits excellent two-photon induced ASE with a low threshold of 100 µJ cm-2 under 800nm femtosecond laser excitation. More importantly, in comparison with the traditional MAPbBr3 films prepared with N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO), the MAPbBr3 film prepared with MAAc shows excellent optical stability: no signs of degradation under more than 2 h pulsed laser excitation, stable ASE emission spectra under the humidity of 95% and ASE spectra can be stimulated when films are kept in air for more than 6000 h without encapsulation.

Time-resolved excited state dynamics of super-exciplex in the coumarin dye laser

It has been known for a few decades that laser dye, 7-diethylamino 4-methyl coumarin (DAMC) exhibits one absorption and one fluorescence peak but produces dual amplified spontaneous emission (ASE) bands (at 427 and 460 nm) in certain solvents, under high power pulsed laser pumping. The appearance of the new peak manifested only under high pump energy excitation, is attributed to a rare excited state species, called a “superexciplex” (SX). This is a transient excited state bimolecular association in which two excited state molecules get bonded with the help of an unexcited solvent molecule acting as an intermediary. In principle, the formation of excited state species would take a time of the order of a few hundred picoseconds or even nanoseconds. The objective of this paper is to delineate the formation of such super - exciplex employing time resolved ASE spectra where the three-dimensional display gives clearer perspectives. Since the formation of the SX depends on dye concentration, pump energy, and temperature, in the present time-resolved spectroscopy (TRS) paper all the above factors had been studied in some detail.

A series of aromatric-amine-cored fluorescent emitters for amplified spontaneous laser emission and emission turn-on sensing

In this paper, five boron dipyrromethene dyes were designed with aromatric-amine-cored structure. Their molecular structure and photophysical performance were discussed in detail in various solvents. It was found that these five dyes were highly fluorescent ones in toluene with emission quantum yield higher than 95%. Amplified spontaneous emission (ASE) performance of these fluorescent dyes was then analyzed in toluene. Efficient and promising ASE spectra peaking at ~545 nm were observed for four of these fluorescent dyes with full width at half maximum value of ~5 nm and ASE efficiency up to 9%. It was confirmed that aromatric-amine-cored structure was positive to improve ASE performance. The reason for ASE missing in one of these fluorescent dyes was revealed as the vibrational relaxation of its N–H group. In solvent MeCN, however, this dye showed an interesting phenomenon, emission turn on effect towards Hg(II). Its sensing performance and sensing mechanism were discussed in detail as well. Good linear response and high selectivity were found for both colorimetric sensing and emission turn on sensing.

Donor-Acceptor Type Pendant Conjugated Molecules Based on a Triazine Center with Depressed Intramolecular Charge Transfer Characteristics as Gain Media for Organic Semiconductor Lasers.

A set of fluorene-capped pendant conjugated molecules (T-m and T-p), which consist of a triazine center with three carbazole substituents as the donor-acceptor (D-A) type pendant structure, were designed, synthesized, and investigated as gain media for organic semiconductor lasers (OSLs). In particular, varying the capping positions of the fluorene units on the pendant core structures results in significantly different intramolecular charge transfer (ICT) properties, where T-m manifested depressed ICT characteristic and high fluorescence quantum yield. The lowest amplified spontaneous emission (ASE) threshold in neat films was recorded as 1.9 μJ cm-2 for T-m and 83.8 μJ cm-2 for T-p, which indicated that the depressed ICT characteristics in the case of T-m help to enhance the ASE properties. Remarkably, the ASE threshold remained almost unchanged and the ASE spectra showed very small shifts (within 1 nm) for T-m with film samples annealed up to 180 °C in open air. In contrast, its linear counterpart 2FEtCz-m showed a clearly increased ASE threshold upon annealing above 100 °C. The results suggest that the selective construction of conjugated pendant molecules with depressed ICT characteristics is beneficial for finely modulating the optical and electrical properties as well as improving the thermostability and photostability, which manifests the great potential as a robust gain media for OSLs.

Amplified Spontaneous Emission and Optical Gain in Organic Single Crystal Quinquethiophene

In this paper, we report optical characteristics of an organic single crystal oligomer 5,5⁗-diphenyl-2,2′:5′,2″:5″,2‴:5‴,2⁗-quinquethiophene (P5T). P5T crystal is a thiophene/phenylene co-oligomer that possesses better charge mobility as well as photoluminescence quantum efficiency (PLQE) as compared to other organic materials. Stimulated emission in P5T is investigated via amplified spontaneous emission (ASE) measurements within broad pump energies ranging from 35.26 to 163.34 µJ/cm2. An Nd-YAG femtosecond-tunable pulsed laser is used as a pump energy source for the ASE measurements of P5T crystals at an excitation wavelength of 445 nm. The ASE spectra exhibit optical amplification in P5T crystals at a 625 nm peak wavelength with a lower threshold energy density (Eth) ≈ 52.64 μJ/cm2. P5T also demonstrates higher optical gain with a value of 72 cm−1, that is calculated by using the variable stripe-length method. The value of PLQE is measured to be 68.24% for P5T. This study proposes potential applications of P5T single crystals in organic solid state lasers, photodetectors, and optical amplifiers.

Simultaneous retrieval of optical gains, losses, and threshold in active waveguides

The generation of Amplified Spontaneous Emission (ASE) is routinely used to assess the performance of active materials prior to developing thin film lasers. The Variable Stripe Length method has been profusely used for decades to measure the optical gain in these materials and devices, but experimental and theoretical evidences cast doubts upon its reliability. With the advent of an ever increasing number of solution-processed laser compounds that can be implemented as low-cost, flexible, and/or integrated devices, there is now more than ever a need to develop an alternative and trustful method to delineate all their amplifying signatures. Herein, a new formalism to fully characterize the ASE properties, based on the most frequent Variable Pump Intensity method, is reported. An analytical expression taking into account the most relevant spatiotemporal and photophysical effects has been found that can be fitted to ASE spectra. This expression allows retrieving, from a single ASE experiment, the spectrally resolved losses coefficient and net optical gains at all pump values, as well as to calculate, instead of visually finding, the ASE threshold. The reported formalism serves as a tool to categorize the best candidates for a given laser application through a reliable, robust, time-saver, and standardized methodology.

Decrease of amplified spontaneous emission threshold achieved by core–shell Ag nanocube@SiO2 with ultrasmall shell thicknesses

The amplified spontaneous emission (ASE) threshold reduction of R6G/PMMA film with a quasi-waveguide structure was observed by doping core–shell Ag nanocube@SiO2. When the SiO2 shell thickness was only 3 nm, the ASE threshold declined from 0.8 to 0.2 mJ cm−2, presenting a large decreased ratio of 75%. With the enhancement of the emission intensity, the pulse width of the ASE spectra also narrowed from 8 to 6.8 nm after doping. An efficient coupling between the R6G media and Ag nanocube through the proper ultrathin spacer was concluded as the main reason for such phenomena.

Gain and emission spectrum characteristics of 465nm laser diode pumped Tm3+-doped telluride glass fibers

Gain and emission spectrum characteristics of Tm3+-doped telluride glass fibers pumped with 465 nm lasers are analyzed. The rate and power propagation equation groups of the fibers are solved numerically and the effects of the fiber parameters including active ion concentration, length and pump power on the gain spectra and amplified spontaneous emission (ASE) spectra are analyzed. The results show that with a pump parameter of 465 nm/200mW, a doping concentration of 2.5×1025 ion/m3 and a fiber length of 16m, the gain and ASE spectra can cover from 1.100 to 1.900 μm, and the gain and ASE power peaks can reach 52 dB and 8mW, respectively.

Stimulated emission and laser behaviors of Nd3+/Yb3+ Co-doped phosphate glass fiber

The energy transfer phenomenon between Nd3+ and Yb3+ generates the research interest in Nd3+/Yb3+ co-doping, because it provides a straight-forward way to combine the features of Nd3+ and Yb3+ to develop some potential applications,such as solar cells,high energy pulse and tunable lasers.Substantial research work has been conducted to study the spectroscopic properties of Nd3+/Yb3+ in different glasses,crystal and ceramic host materials.However,it is still not very clear about the laser properties of the Nd3+/Yb3+ co-doping system,especially the high rare-earth solubility phosphate glass.This work reports the stimulated emission and laser properties of an Nd3+/Yb3+ co-doped phosphate glass fiber under singly 970 nm and 808 nm LD pumping.The molar doping ratio of Nd3+:Yb3+ is 4:1.Using the free-space coupled method,the laser properties of the co-doped fiber under 970 nm pump are tested first in a laser cavity comprised of a butt-coupled dichroic mirror with high reflectivity (≥ 99.5%) and a cleaved fiber ended with~4.6% Fresnel reflectivity.It is found that with the increase of 970 nm pump power (P970) two discrete laser peaks and one peak located at 1053 nm with a larger threshold can be observed for fiber length equal to and less than 0.7 m.The 1053 nm laser is produced by Yb3+ → Nd3+ energy transfer,and its lasing threshold decreases with increasing fiber length in this length region.Then,the amplified spontaneous emission (ASE) spectra for fiber lengths of 0.35 m,0.9 m and 5.0 m under 970 nm pumping are tested by cutting 6° at the output port.The test results indicate that the Yb3+ → Nd3+ energy transfer has a modulation effect on fiber spectrum,and the modulation becomes more obvious for a longer fiber length.A two-fold promotion mechanism is suggested to explain the modulation effect:1) the reabsorption effect of Yb3+ leading to relatively lifetime prolongation increases the Yb3+ → Nd3+ energy transfer efficiency;2) the red-shifted oscillator laser wavelength leads to a larger emission cross section difference between Nd3+ and Yb3+.Besides,the measurement results in 0.35-m-long fiber also suggest that the 1053 nm laser in fiber laser test may be due to a fiber temperature raising effect during the increase of P970.The laser properties and ASE spectra of the fiber under 808 nm pumping have been studied in the same fiber test setup.However,the tested results are quite different from the 970 nm pumping case. Only one lasing peak at 1053 nm is detected,and it is found that the peak is not dependent on the 808 nm pump power (P808) nor the fiber length.To explain this phenomenon,one energy transfer model with taking into consideration the stimulated emission of Nd3+ is derived.According to this theoretical model,Nd3+ → Yb3+ energy transfer efficiency fast decreases with the increase of simulated emission intensity of Nd3+.This explanation is experimentally supported by a 0.05-m-long Nd3+/Yb3+ co-doped phosphate glass fiber with varying P808.Therefore,the adoption of Nd3+ to sensitize Yb3+ for developing some laser applications needs to consider the suppression effect of Nd3+ stimulated emission on Nd3+ → Yb3+ energy transfer.

Gamma-Irradiation Effects on the Spectral and Amplified Spontaneous Emission (ASE) Properties of Conjugated Polymers in Solution.

In this paper, we investigate the effects of gamma (γ) radiation on the spectral and mplified spontaneous emission (ASE) properties of two conjugated polymers (CPs) viz., poly [2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH–PPV) (CPM) and poly{[2-[2′,5′-bis(2″-ethylhexyloxy)phenyl]-1,4-phenylenevinylene]-co-[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene]} (BEHP-co-MEH–PPV) (BMP) in tetrahydrofuran (THF). Gamma irradiation strongly affected the photophysical properties of these CPs. To explore these changes, gamma radiation, in the range of 2–50 kGy, was used to maintain the temperature at 5 °C constant for all doses at a dose rate of 12.67 kGy/h, using a 60Co gamma ray. The ASE profiles of the CPs in THF were obtained under the high power excitation of a Nd:YAG laser (355 nm), pre- and post-radiation. The result revealed a dramatic blue shift of the fluorescence and the ASE spectra after gamma irradiation. This shift in the luminescence and ASE spectra could be a response to the conformational disorders such as gamma irradiation-induced polymer crosslinking, which was verified using Raman spectra, FTIR, and swelling experiments. This could be the first report on the effect of gamma radiation on the ASE properties of conjugated polymers.

Amplified spontaneous emission from the exciplex state of a conjugated polymer “PFO” in oleic acid

The amplified spontaneous emission (ASE) characteristics of a conjugated polymer poly (9, 9-dioctylfluorenyl-2, 7-diyl) (PFO) in oleic acid have been studied under different concentrations and temperatures. Here, the ASE spectra of PFO in oleic acid have been obtained using a transverse cavity configuration where the conjugated PFO was pumped by laser pulses from the third harmonic of Nd: YAG laser (355nm). The PFO in oleic acid produces ASE from an exciplex state – a new molecular species. The obtained results were compared with the PFO in benzene. Such ASE spectra from the exciplex state have not been observed for the PFO in benzene.

Morphology dependent amplified spontaneous emission in π-conjugated polymer

Abstract The amplified spontaneous emission (ASE) spectra of a π-conjugated polymer Poly [2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) are studied in as-cast film, annealed film, 1 mg/ml solution and 2.5 mg/ml solution, respectively, using a 10 ns pulsed laser as an excitation source. We found that for annealed film (420 K), the ASE is hardly achieved compared to the as-cast film, which is consistent with the formation of the aggregation; whereas the film's temperature had much less effect on its ASE threshold. In solution, the ASE spectra show both 0–0 peak and 0–1 peak in 1 mg/ml solution, but only 0–1 peak in 2.5 mg/ml one. When the temperature of solution increases slightly from 300 K to 330 K, the ASE threshold increases dramatically in 1 mg/ml solution but slightly in 2.5 mg/ml one. Our results show the important role the morphology played in the ASE spectra in both film and solution. Therefore, controlling the interchain interaction in PCPs may be the key factor for performance of the organic lasers.

Dual ASE from the monomeric and excimeric states of a conjugated-polymer (PDHF) in solution

Abstract In this work, the spectral and amplified spontaneous emission (ASE) properties of a conjugated polymer poly [9, 9-di-(2′-ethylhexyl) fluorenyl-2, 7-diyl] (PDHF) in tetrahydrofuran (THF) have been studied. Our results showed that the absorption spectra of PDHF in THF have only one peak under wide range of concentrations (0.012 mol/m3 to 0.39 mol/m3), it could be seen that the shape of the absorption did not change; this indicates no dimer formation in these solutions for all concentrations mentioned above. On the other hand, the fluorescence spectra of PDHF in THF, at low concentration, showed two peaks, the primary at 415 nm and the secondary at 435 nm. The effects of concentration and the temperature on PDHF in THF under same conditions were studied. For example, the intensity of the peak at 435 nm became increasingly stronger for higher concentration and lower temperature. These are analogs to the excimeric behavior of organic molecules. Under high power pulsed laser excitation, we observed ASE at 418 nm and 437 nm. These ASE peaks could arise from the monomer and excimer states of the macromolecule respectively. The ASE spectra of PDHF were compared with the rhodamine 6 G (Rh 6 G). The most important and distinguishing features are that PDHF has a two times better photochemical stability than rhodamine 6 G and high optical gain compared with the conventional laser dyes.