Stimulated Emission Cross-section Research Articles

Boosting Stimulated Emission via a Hydrogen-Bonded Co-Crystallization Approach in Molecular Crystals.

Stimulated emission of organic π-conjugated molecule in solid state remains a significant challenge, mainly involving the mode of molecular stacking that invariably alters the photo-physical processes. Herein, we successfully realized the stimulated emission in molecular crystals using a hydrogen-bonded co-crystallization strategy. Two hydrogen-bonded co-crystals, obtained from 1,4-bis-p-cyanostyrylbenzene (CNDSB) and two types of co-formers, can boost stimulated emission and show decent amplified spontaneous emission (ASE), whereas the parent CNDSB crystal is not SE-active. Crystal structural analysis demonstrated that the co-crystallization eliminated excimerformation. The resulting higher kr and shorter excited-lifetime led to a larger stimulated-emission cross section, which benefited to the occurrence of ASE. Simultaneously, the uniaxial arrangements along long axis of co-crystal together contributed to highly polarized emission. This system presentsvery rare evidence of boosting stimulated emission by binary co-crystallization, whichenriches our insights into organic solid-state lasers.

Spectator Exciton Effects in Nanocrystals III: Unveiling the Stimulated Emission Cross Section in Quantum Confined CsPbBr3 Nanocrystals.

Quantifying stimulated emission in semiconductor nanocrystals (NCs) remains challenging due to masking of its effects on pump-probe spectra by excited state absorption and ground state bleaching signals. The absence of this defining photophysical parameter in turn impedes assignment of band edge electronic structure in many of these important fluorophores. Here we employ a generally applicable 3-pulse ultrafast spectroscopic method coined the "Spectator Exciton" (SX) approach to measure stimulated-emission efficiency in quantum confined inorganic perovskite CsPbBr3 NCs, the band edge electronic structure of which is the subject of lively ongoing debate. Our results show that in 5-6 nm CsPbBr3 NCs, a single exciton bleaches more than half of the intense band edge absorption band, while the cross section for stimulated emission from the same state is nearly 6 times weaker. Discussion of these findings in light of several recent electronic structure models for this material proves them unable to simultaneously explain both measures, proving the importance of this new input to resolving this debate. Along with femtosecond time-resolved photoluminescence measurements on the same sample, SX results also verify that biexciton interaction energy is intensely attractive with a magnitude of ∼80 meV. In light of this observation, our previous suggestion that biexciton interaction is repulsive is reassigned to hot phonon induced slowdown of carrier relaxation leading to direct Auger recombination from an excited state. The mechanism behind the extreme slowing of carrier cooling after several stages of exciton recombination remains to be determined.

Polarizabilities and emission cross-sections of lanthanide laser crystals

Abstract The dependence between stimulated-emission cross-sections and polarizability volumes has been studied for laser transitions of Nd3+, Ho3+, Er3+, and Tm3+ ions doped in dielectric crystals: complex oxides, simple and complex fluorides. The overall polarizability of each crystal containing Ln3+ ions has been calculated by inclusion of the dopant polarizability in respective concentration. The applied method has revealed distinctly different positions of Nd3+ ions in the mentioned dependence in a series of crystals, e.g. Y3Al5O12, YAlO3, LiYF4, compared to the other Ln3+ ions doped in the same lattices.

Spectroscopic properties of Pr3+-doped Titania-Silicate glass ceramic for photonic applications

Silicate-Titania (SiTi) glass-ceramics doped with Pr3+ (0.6, 1.6, 2.4 and 3.6 mol%) ions were prepared by sol-gel technique. The materials were characterized by powder XRD, FTIR, TEM, EDX, Optical absorption and Photoluminescence spectroscopy. The identification of non-bridging oxygen (NBO) formation and the removal of OH groups are validated through analysis of the FTIR spectra. Additionally, measurements using XRD and TEM showed that the samples contain nano-sized crystallites. The three phenomenological Judd–Ofelt (J–O) intensity parameters Ω2, Ω4, and Ω6 were obtained and used to analyze different radiative characteristics for the fluorescence levels of Pr3+ in the glass ceramic, including radiative lifetime, branching ratio, radiative transition probability and stimulated emission cross-section. Several emissions were observed in the visible region, among which the 1D2→3H4 in the orange-red region is the most intense. All of these reported branching ratios, stimulated emission cross-sections, and visible emission spectra point to the possibility of employing them as red region lasers. The CIE chromaticity coordinates from all of the emission spectra were also assessed to determine if these materials are suitable for orange-red phosphors. According to CIE chromaticity investigations, 1.6 mol% of Pr3+ ion concentration is ideal for SiTiPr glass-ceramic for use as red phosphors and possibly red lasers.

Computational screening of multi-resonance thermally activated delayed fluorescence (MR-TADF) molecules for lasing application

Multi-resonance thermally activated delayed fluorescence (MR-TADF) molecules charactering large emission oscillator strengths, effective reverse intersystem crossing (RISC), and narrow emission spectral width, have great potential as laser materials. We propose a molecular descriptor for quick screening MR-TADF molecules as laser candidate materials, A =ΔESTσeffnet,opt, namely, the product of singlet-triplet energy gap and the optical pumping net stimulated emission cross section. These quantities can be calculated by combining quantum chemistry package Gaussian and our own MOMAP program. Through extensive computations benchmarked with existing experiments, we suggest that A value should be larger than 0.311 ⨉ 10−17 cm2 eV for promising lasing molecules. We virtually designed 119 molecules with MR-TADF property, and based on our theoretical protocol by considering descriptor A, we are able to select 10 molecules as lasing molecules. We then further screen out 2 molecules through analyzing the spectral overlap, indicating that only eight molecules are prospective candidates for laser materials. Particularly, we find that ADBNA-Me-BPy molecule possesses large radiative decay rate and large reverse intersystem crossing rate, 1.90 × 106 s−1 and 1.01 × 108 s−1, respectively, implying a low lasing threshold, promising for electrically pumped lasing.

Polarization switching in a mid-infrared Er:YAlO3 laser.

We report on a polarization-resolved study of mid-infrared emission properties of Er3+-doped orthorhombic yttrium aluminum perovskite YAlO3 single crystal. For the 4I11/2 → 4I13/2 Er3+ transition, the stimulated emission cross section is 0.20 × 10-20 cm2 at 2919 nm for light polarization E ‖ c. Pumped by an Yb-fiber laser at 976 nm, the 10 at.% Er:YAlO3 laser delivered 1.36 W at 2919 nm with a slope efficiency of 31.4%, very close to the Stokes limit, a laser threshold as low as 33 mW and a linear polarization. Pump-induced polarization switching between E || b and E || c eigen states was observed and explained by excited-state absorption from the terminal laser level.

Crystal growth, polarized spectral properties, and 2.3 µm laser performance of Tm:LuVO4 crystal

We report on the Czochralski crystal growth, polarized optical spectroscopy, and the first continuous-wave laser operation of 1.5 at.% Tm:LuVO4 crystal on the 3H4 → 3H5 transition. The polarized absorption and stimulated-emission properties of Tm3+ ions in LuVO4 were revised and the crystal-field splitting of the Tm3+ multiplets was determined by low-temperature (12 K) spectroscopy. The maximum stimulated-emission cross-section for the 3H4 → 3H5 transition is 2.48 × 10−20 cm2 at 2363 nm for π-polarization corresponding to an emission bandwidth of 28 nm. Evidence of phonon-assisted emissions of Tm3+ ions above 2 µm is presented. The broadband emission properties of the Tm:LuVO4 crystal make it promising for ultrashort pulse generation. Additionally, pumped by a 796 nm fiber-coupled laser diode, the Tm:LuVO4 laser generated a Watt-level output power at 2279-2295 nm with a slope efficiency of 9.2% and linearly polarized emission (π-polarization).

Polarized spectral properties and 2.3 µm laser performance of the Tm:YVO4 crystal

The polarized spectral properties and ∼2.3 µm high-power continuous-wave laser operation of Tm3+-doped yttrium orthovanadate crystal (Tm:YVO4) are reported. For the 3H4 → 3H5 transition, the stimulated-emission cross-section σSE is 1.01 × 10−20 cm2 at 2276 nm corresponding to a large emission bandwidth of 52 nm (for π-polarization). Pumped by a 794 nm laser diode, the 1.5 at.% Tm:YVO4 laser delivered 5.52 W at 2.29 µm with a slope efficiency of 19.9%, a laser threshold of 8.70 W, and a linear laser polarization (π). The Tm laser operated on the cascade scheme (on the 3H4 → 3H5 and 3F4 → 3H6 transitions) which was mainly responsible for the observed high laser slope efficiency. We also report on the first passively Q-switched Tm:YVO4 laser at 2.3 µm by employing porous nano-grained cuprous selenide (PNG-Cu2Se) as a saturable absorber. The shortest pulse duration and the highest single pulse energy amounted to 706 ns and 3.65 µJ, respectively, corresponding to a pulse repetition rate of 62.8 kHz.

Spectroscopy and Kerr-lens mode-locked operation of Yb:GdScO3 crystal

A Kerr-lens mode-locked laser based on a Yb3+-doped disordered gadolinium scandate (Yb:GdScO3) crystal is reported for the first time, to the best of our knowledge. The crystal with the perovskite structure was grown using the Czochralski method, and its room temperature (RT) and low temperature (LT) spectra were also investigated. Due to the crystal's multisite structure (Gd3+/Sc3+ site), Yb:GdScO3 offers broad and intense polarized emission spectra in the near-infrared range (975–1075 nm). The stimulated emission cross section σSE is 0.46 × 10−20 cm2 at 1000 nm with an emission band width of 75.7 nm for E // b polarization. The continuous wave (CW) laser was operated pumped by a 976 nm fiber-coupled LD laser, resulting in a maximum output power of 8.74 W with a slope efficiency of 76.1% was obtained. Additionally, a pulses as short as 74 fs are generated at ∼1061.7 nm via Kerr-lens mode-locking. The average output power amounts to 32 mW at a pulse repetition rate of 101.4 MHz. All results indicate Yb:GdScO3 a promising candidate for 1 µm ultrashort laser.

Spectroscopic and electrical properties of europium doped bismuth antimony fluoroborate glasses

Strong luminescence in the red spectral region is a well-known characteristic of the trivalent europium ion (Eu3+). We investigate a novel europium doped glassy substance for their use in optical devices, optoelectronics and radiation shielding. By using the traditional melt quenching technique, Bismuth antimony fluoroborate glasses are synthesized. XRD investigations support the amorphous nature of the material. Spectral measurements of absorption, photoluminescence (PL) excitation, PL emission, and PL decay curve are made in order to study the lasing properties. Judd-Ofelt (J-O) intensity parameters, from emission spectra, exhibit the trend Ω2> Ω4 furthermore used to find the radiative parameters-transition probability (AR), branching ratio (βR), radiative lifetime (τR), and stimulated emission cross-section (σse) for all the glasses. Decay curves show single exponential behavior and is used to find the quantum efficiency of the prepared glasses. The dielectric properties (dielectric constant (ɛ′), dielectric loss (ɛ″)), impedance and electrical conductivity (σac) of these glasses with variation in frequency have also been studied at the ambient temperature. The radiation shielding properties are evaluated for the photon energy range (1 keV–15 MeV). Based on the trends noticed in the radiative parameters, electrical conductivities and radiation shielding parameters, the present glasses could be found useful as optoelectronic devices, non-linear optical materials, battery anode materials and radiation shielding purposes.

Instigating the Asymmetry of Dy3+ Ions Doped in Borate Glasses for Photonic Device w-LED Applications

For usage in solid state white light emitting device applications, dysprosium-activated calcium aluminum barium sodium borate glass was synthesized. The detailed understanding of physical, optical, structural, and photo-luminescence characteristics was examined and compared. To comprehend the oscillator strength of the ligands in the prepared glasses, the Judd-Ofelt intensity characteristics were assessed. The Ω2 greater relative oscillator strength value shows highest for the prepared glasses suggesting their cause due to hypersensitive transitions. In comparison to other glasses in the research, the potential radiative transition probabilities, branching ratios, and stimulated emission cross-section for 575 nm emission all exhibited higher values. The stimulated emission cross-section shows highest for 0.3 mol% Dy2O3 content in the present glasses. The asymmetry of synthesizedglass sample ratio has been evaluated and compared using Yellow to Blue (Y/B) emission ratio. Study of the emission spectra and assessment of CCT and DUV values for the glasses reveal emission in the CIE diagram's white light zone.

Structural, thermal and spectroscopic properties of Er2O3-doped oxyfluoro tellurophosphate glasses

Employing the melt quench method, the oxyfluoro tellurophosphate glasses (PTBMEr), doped with varying erbium concentrations, were prepared. Their physical, structural, optical, and luminescent characteristics were investigated using XRD, EDX, FTIR, absorption and Photoluminescence studies. The amorphous nature and elemental composition were identified using the XRD and EDX spectra. The J-O parameters and radiative parameters, including energy gap (ΔE), branching ratio (βR), radiative lifetime (τrad), and radiative transition probability (AR), were established for different excited levels of erbium in PTBMEr glass matrices. The visible emission spectra were acquired through excitation at a wavelength of 377 nm, resulting in a highly pronounced emission band at 544 nm, corresponding to the transition 4S3/2→ 4I15/2. The NIR emission spectra obtained through excitation at 980 nm showed a prominent broad emission band at 1534 nm pertaining to the transition 4I13/2→4I15/2. Within the set of prepared samples, the PTBMEr05 sample exhibits highest stimulated emission cross section of 0.75 × 10-20 cm2 for the transition 4S3/2→4I15/2. It also exbited superior parameters for the transition 4S3/2→4I15/2 including a stimulated emission crosssection of 1.19 × 10-20 cm2, gain bandwidth of 64.87 × 10-25 cm3, and optical gain of 53.41 × 10-24 cm2s. Experimental lifetime values for the excited level 4I13/2 of erbium in PTBMEr glasses were calculated and found to decrease with concentration due to non-radiative mechanisms and concentration quenching. These results reflect that PTBMEr05 glass is best suited for green laser emission devices and optical fiber communication windows.

Effect of mixed TeO2–B2O3 glass former in Ho3+/Yb3+-doped glass system: Raman spectroscopy, Judd-Ofelt and luminescence investigations

In this work, glass with composition (75-x)B2O3-xTeO2-11Bi2O3–10Li2O-1Ho2O3-3Yb2O3 (x = 10–60 mol%) were synthesized using the melt quenching technique to investigate the effect of mixed glass former between TeO2 and B2O3 on the spectroscopic properties of glass. The Raman Spectroscopy has revealed a structural depolymerization undergone by the glasses with a sudden increment at x = 30 mol% that might arise from structural competition between TeO2 and B2O3. Optical absorption spectra have revealed 9 absorption peaks corresponding to Ho3+ ion transitions while one peak belongs to Yb3+ ion transition. The bonding parameter signifies the glasses are ionic in nature. The oscillator strength and Judd-Ofelt parameter Ω2,4,6 have reduced against increment of TeO2 concentration indicated a low asymmetry and low rigidity except for x = 30 mol% that may be due to strong interaction between TeO2 and B2O3. The radiative properties such as spontaneous emission probability, branching ratio, radiative lifetime and stimulated emission cross-section have showcased the glass potential for laser application. The luminescence spectra of studied glasses upon 450 nm excitation have disclosed two main emission bands which are 530 nm and 642 nm that corresponding to 5F4–5I8 and 5F5–5I8, of Ho3+ respectively whilst an extra emission recorded at 738 nm was ascribed to 5F4–5I7 of Ho3+ due to energy transfer process from Yb3+ to Ho3+. The emission intensity of the samples has enhanced with the TeO2 addition due to reduction of phonon energy. CIE 1931 diagram has shown a greener emission colour of glass samples over TeO2 addition.

Spectral and FTIR Analysis of Ho3+ ions doped ZincLithium Potassium Calcium Alumino Borophosphate Glasses

Abstract: Glasses samples containing Ho3+ in zinc lithium potassium calcium alumino borophosphate glasses (30-x)P2O5: 10ZnO: 10Li2O: 10K2O: 10CaO: 10Al2O3:20B2O3:xHo2O3. (where x=1, 1.5,2 mol %) have been prepared by melt-quenching method. The amorphous nature of the prepared glass samples was confirmed by X-ray diffraction. Optical absorption, Excitation, fluorescence and FTIR spectra were recorded at room temperature for all glass samples. Judd-Ofelt intensity parameters Ωλ (λ=2, 4 and 6) are evaluated from the intensities of various absorption bands of optical absorption spectra. Using these intensity parameters various radiative properties like spontaneous emission probability (A), branching ratio (β), radiative life time (τR) and stimulated emission cross–section ( σp) of various emission lines have been evaluated.

Impact of ZnO on spectroscopic and luminescence characteristics of Sm2O3–SrO–B2O3 glasses for warm reddish orange light emitting applications

Sm2O3–SrO–B2O3 glasses containing ascending ratios of ZnO were created via the standard melt quenching approach. The optical and luminescent properties were assessed by analysing absorption, reflectance, excitation, and emission spectra obtained from measurements. The density, molar volume, metallization criterion, optical basicity, optical bandgap, Urbach energy, and dispersion parameters were evaluated and discussed. The spectral radiative transitions of the Sm3+ ion in different excited states were investigated using the Judd–Ofelt (J–O) theorem. The least square fit method was used to evaluate the J–O intensity parameters, which were subsequently utilized to determine radiative characteristics including transition probability, branching ratio, and lifetime. For all glasses, the reddish orange transition 4G5/2 → 6H7/2 demonstrated the highest strength and had the maximum values for stimulated emission cross section, radiative transition probability, and gain bandwidth. The chromaticity coordinates fell within the reddish orange region and the colour correlated temperatures ranged from 1840 to 1935 K, suggesting the suitability of the glasses for warm reddish orange emission-based laser and photonic applications.

Growth, spectroscopy and SESAM mode-locking of a "mixed" Yb:Ca(Gd,Y)AlO4 disordered crystal.

We present the growth, spectroscopy, continuous-wave (CW) and passively mode-locked (ML) operation of a novel "mixed" tetragonal calcium rare-earth aluminate crystal, Yb3+:Ca(Gd,Y)AlO4. The absorption, stimulated-emission, and gain cross-sections are derived for π and σ polarizations. The laser performance of a c-cut Yb:Ca(Gd,Y)AlO4 crystal is studied using a spatially single-mode, 976-nm fiber-coupled laser diode as a pump source. A maximum output power of 347 mW is obtained in the CW regime with a slope efficiency of 48.9%. The emission wavelength is continuously tunable across 90 nm (1010 - 1100 nm) using a quartz-based Lyot filter. With a commercial SEmiconductor Saturable Absorber Mirror to initiate and maintain ML operation, soliton pulses as short as 35 fs are generated at 1059.8 nm with an average output power of 51 mW at ∼65.95 MHz. The average output power can be scaled to 105 mW for slightly longer pulses of 42 fs at 1063.5 nm.

Cool white light generation of Dy3+ activated aluminum sodium calcium borate glass for W-LED application

The Dy3+-activated aluminum sodium calcium borate glass with white light emission might have been created through the melt-quenching process. This research explores the optical and luminescence characteristics of borate glasses. Dy3+-activated glasses exhibit absorption in the visible (VIS) and near-infrared spectrums. The absorption starts from the 6H15/2 ground state to the higher state concerning optical characteristics. The emission spectra of dysprosium-doped glasses' photoluminescence show greater intensity at 483 nm (blue light) and 575 nm (yellow light), which are critical wavelengths for white light-generating materials. The luminescence intensity of Dy3+ ions increased up to a 0.50 mol% concentration, while the decay time decreased with an increasing dysprosium ion concentration. The emission spectra were used to estimate the CIE 1931 chromaticity and corresponding color temperature, revealing a shift towards the cold white light location at that temperature. The stimulated emission cross-section is calculated via the Judd-Ofelt theory. All characteristic outcomes suggest that the existing dysprosium-enabled glasses are excellent materials for generating cool white light in W-LED applications.

Spectroscopy of thulium ions in solid-solution sesquioxide laser ceramics: Inhomogeneous spectral line broadening, crystal-field engineering and C3i sites

We present a detailed spectroscopic study of Tm3+ ions in stoichiometric and “mixed” (solid-solution) cubic (C-type, sp. gr. Ia3‾) sesquioxides R2O3 (RY, Lu, Sc or their mixture), with the goal of developing broadband-emitting gain media for ultrafast lasers at ∼2 μm. Evidence of a linear variation (increase) of the crystal-field strength when decreasing the ionic radius of the host-forming cation R3+ in the isostructrural R2O3 series is presented. The crystal-field splitting of Tm3+ multiplets is determined for C2 sites and justified using a barycenter plot, and the first evidence of C3i Tm3+ species is presented. A remarkable inhomogeneous spectral broadening for compositionally “mixed” sesquioxides (in particular with Sc3+) with respect to the parent compounds is revealed at low temperatures. It is proven that binary and ternary “mixed” R2O3 compounds form substitutional solid-solutions with a mixing of the host-forming cations at the atomic level. The stimulated-emission and gain cross-sections for the 3F4 → 3H6 Tm3+ transition are determined. Guidelines for material engineering of Tm3+-doped gain media for mode-locked 2-μm lasers are also provided.

Nd, Gd:SrF<sub>2</sub> crystal spectrum gain characteristic study on the broadband laser amplification

Spectral gain narrowing is one of the key factors affecting broadband amplification of ultrashort pulses. In this paper, the spectral gain characteristics in broadband amplification are studied theoretically and experimentally by using the characteristic of Nd,Gd:SrF<sub>2</sub> crystal, i.e. the emission spectrum has a certain width at the higher stimulated emission cross section. Through the numerical simulation, the evolution law of output spectrum of the laser gain medium under different spectral gain lineshapes and different gain values is studied in detail. Theoretical calculation shows that the spectral gain narrows obviously with the increase of gain values of the traditional Gaussian emission spectrum and increasing the spectral bandwidth at the maximum stimulated emission cross section can obviously suppress the spectral gain narrowing. Furthermore, the spectral gain narrowing characteristics of the Nd,Gd:SrF<sub>2</sub> crystal were studied experimentally. The Ф13mm×150mm Nd,Gd:SrF<sub>2</sub> crystal was used as the gain medium which was pumped by flash lamps in the experimental study. The experimental results show that the output spectra of Nd,Gd:SrF<sub>2</sub> crystals are not obviously narrowed when the input laser spectral width is 5nm (FWHM) and the gain is 140 times. The experimental results are consistent with the theoretical calculation and analysis. The crystal can work normally at the repetition rate of 0.2Hz and 1Hz in the experiment, but due to the influence of thermal effect, the gain will decrease to a certain extent with the increase of pump energy and repetition rate. The research results lay the foundation for the application of fluoride crystal in broadband chirped pulse amplification.

Achieving narrow bandwidth and high stimulated cross-section in Nd3+-doped LiCaB glasses for near infra-red laser amplifiers

The aim of this research is to examine the effects of Nd3+ ions on the spectroscopic characteristics of different concentrations of lithium-calcium-borate glasses and improve the emission cross section alongside bandwidth. The prepared glasses were produced with the melt-quenching technique and were thoroughly analyzed to determine their usefulness as laser amplifiers. Various studies were conducted, including X-ray diffraction (XRD), solid-state nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA), absorption and emission measurements, and time decay curve measurements. The structural analysis using XRD and NMR techniques revealed that the glasses were amorphous and that non-bridging oxygen was present. Moreover, it was discovered that the glass-forming tendency and glass stability of these glasses improved with the concentration of Nd3+ ions. The glasses' absorption spectra display 10 transition states in UV and visible regions. Among all the prepared glasses, the lithium-calcium-borate glass doped with 0.5 mol % Nd3+ ions stand out with a stimulated emission cross-section value of 3.40 × 10−20 cm2 and a narrow bandwidth of 33 nm, making it an ideal lasing amplifier medium due to the 4F3/2 → 4I11/2 (1060 nm) transition. Theoretical Judd-Ofelt calculations were conducted to evaluate various parameters, including oscillatory strength, radiative parameters, radiative lifetime, gain bandwidth, figure-of-merit, and saturation current, for all transitions in the near-infrared region, to support the experimental investigations and offer a detailed discussion of these parameters.