Stimulated Emission Cross-section Research Articles

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.

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.

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.

Effect of mixed alkali ions on the structural and spectroscopic properties of Nd3+ doped silicate glasses

In the present work the effect of alkali ions (Li, Na, K) and the combination of them on structural and spectroscopic properties of Nd3+ doped silicate glasses were systematically investigated. Results from infrared and Raman spectroscopy, as well as density and refractive index, were used to investigate the effect on the structural properties of the silicate glasses. Absorption and emission spectra of the glass samples were measured in the UV-VIS and NIR ranges. Relatively large, stimulated emission cross-section at 1.06 μm was obtained for samples containing a combination of alkali ions, especially with potassium. Moreover, the splitting induced by the Stark effect on the hypersensitive transition of Nd3+,4I9/2 → 4G5/2, 2G7/2 was larger for the samples containing potassium, probably due to its larger ionic size. Judd-Ofelt theory was applied to evaluate the phenomenological intensity parameters Ω2, Ω4, Ω6, transition probabilities, radiative lifetimes and branching ratios related to Nd3+ ions, calculated from optical absorption and luminescence spectra and the results were compared to the values obtained for different Nd-doped glasses reported in the literature.

EFFECT OF PRASEODYMIUM ION CONCENTRATION ON OPTICAL AND LUMINESCENCE PROPERTIES OF TELLURITE GLASSES PRODUCED BY MELT-QUENCHING TECHNIQUE

Tellurite glasses with different concentration of praseodymium (Pr3+) ion was produced by melt-quenching technique. The effect of Pr3+ concentration on optical and luminescence properties was presented. The optical absorption spectra of Pr3+ ions in glasses were recorded in the UV-VIS-NIR region. By using the integrated absorption spectrum, the Judd-ofelt parameters for Pr3+ ions were derived. The Judd-Ofelt theory was used to calculate the radiative transition probability, stimulated emission cross-section, and branching ratio of the glasses. These findings support the use of these glasses in laser and other optical device applications.

Six-watt diode-pumped Tm:GdVO4 laser at 2.29 µm

A compact Tm:GdVO4 laser pumped by a 794 nm laser diode generated 6.09 W at 2.29 µm (3H4 → 3H5 Tm3+ transition) with a high slope efficiency of 30.8% and linear laser polarization (π). The polarized spectroscopic properties of Tm3+ in GdVO4 were also revised. The peak stimulated-emission cross section of Tm3+ is 2.97 × 10−20 cm2 at 2280 nm, corresponding to an emission bandwidth of 42 nm for π-polarized light.

Impact of modifiers on structural and optical properties of Dy3+doped different lithium tetraborate glasses for W-LED applications

The melt quenching technique achieved the synthesis of multiple samples of glasses were prepared, each containing Dy3+ ions as dopants and containing alkali and alkaline earth metals. Subsequently, several physical properties of these samples were assessed. The current investigation covers the characterization of Dy3+ doped lithium tetraborate glasses with varying compositions using powder X-Ray Diffraction (PXRD), FTIR, FT-Raman spectroscopy, optical absorption, and photoluminescence spectroscopy. The X-ray powder diffraction (PXRD) analysis indicates that the glass specimens exhibit an amorphous structure. The elemental composition of these materials has been determined using EDS. The utilization of FTIR and FT-RAMAN spectra is employed for the purpose of identifying distinct structural groups. J-O theory is employed to obtain J-O Intensity parameters and radiative parameters based on the absorption spectra. The photoluminescence spectra were utilized to determine the experimental branching ratios (βexp), effective bandwidths (Δʋeff), and stimulated emission cross-sections (σP) for all of the glass matrices that were prepared. The bi-exponential decay profiles of the 4F9/2 state were obtained and analyzed for all glass specimens containing Dy3+ ions. The lifetimes (τ) and quantum efficiencies (η) were determined by measuring decay profiles. Emission spectra are used to calculate correlated color temperatures (CCTs), CIE chromaticity coordinates and yellow-to-blue intensity ratios (Y/B).

Spectroscopic and Judd-Ofelt Analysis of Nd3+ Ion Doped Lithium Antimony-Borate Glasses for Visible and Near Infrared Laser Application Compared to Standard Emission at 1.06 μm

The present work focuses on the spectroscopic luminescence analysis of trivalent neodymium-doped lithium antimony-borate glasses, with the glass composition 70 Sb2O3—(25-x) B2O3–5 Li2O—x Nd2O3 where x = 0.3; 0.5; 0.7 mol% (SBLN). Around 475 nm excitation used by the transition 4I9/2 → 2G9/2 + 2D3/2 + 2K15/2 and that induced emission lines of wavelengths λ emis = 584;673;767;826 nm (red is low intensity). The specific emission follows the transitions 2G7/2 + 4G5/2 → 4IJ (J = 9/2; 11/2; 13/2; 15/2). Previous work on Nd3+ doped glasses studied near-infrared emission in 4F3/2 → 4IJ mode (J = 9/2; 11/2; 13/2) via near-infrared excitation 4I9/2 → 4F5/ 2+2H9/2. The Judd-Ofelt analysis applied to SBLN glasses showed that the ΩK parameters are consistent with the values in the literature. SBLN7 glass has the best spectroscopic factor Ω4/Ω6 = 0.974; while the best luminescence branching ratio is that of the green emission and it stands at an average β = 70%. Similarly, green emission has the best values of stimulated emission cross section and gain bandwidth. Calculated and measured lifetimes are ranged between 15 and 40 microseconds; however, quantum efficiency varies between 50 and 91%. In another side calculated and measured refractive index values are very close. The chromatic coordinates of observed green color showed accurately that lies in the yellowish-green region of the chromaticity diagram edited by CIE 1931. The calculation of its temperature was made by Mc Macy’s equation, and it is in the limits of 5100 K; which corresponds to a cool color similar to midday sunlight.

Studies of luminescence traits and Judd-Ofelt analysis of Sm3+ activated oxyfluoride glasses

Novel Sm3+ activated oxyfluoride glass was synthesized via the melt-quenching approach with subsequent heat treatment. The X-ray diffraction measurement discloses the amorphous nature of prepared glasses. And, FTIR illustrates the molar surplus of Bi2O3 raises the network connectivity by creating bridging oxygen sites in the structure. The Judd-Ofelt (J-O) intensity parameters exhibit Ω4>Ω2>Ω6 trend, witnessing the rigidity of the glass structure and ionic bonding between Sm3+ ions and surrounding ligands. The 4G5/2 → 6H7/2 transition of Sm3+ is the most applicable for reddish-orange lasers due to their higher values of radiative transition probability, branching ratio, and stimulated emission cross-section. The optimum emission intensity is obtained with 30 mol% Bi2O3 and the corresponding decay time is 1.40 ms. Additionally, the F30 glass sample was lit in a reddish-orange region having a CCT value of 1689 K. The thermal luminescence quenching of the prepared glass was studied and the thermal stability parameters activation energy was estimated. Further, the contactless optical thermometry capability of the glass sample was explored within the range of 303 K–603 K using the luminescence intensity ratio (LIR) technique. Thus, the above studies on the glass sample suggest that it can be used as an active medium in lasers, contactless optical temperature sensing, and high-energy scintillator applications.

Optical spectroscopy of the Er3+ ions in heavily doped BaY1.8Lu0.2F8:Er mixed crystals

Here we present the study of spectral and kinetic characteristics of Er3+ ions in the heavily doped BaY1.8Lu0.2F8 mixed crystals, which are homologous to well-known fluoride host BaY2F8 with high value of crystal field splitting.Absorption and luminescence spectra were registered, and the luminescence decay was studied in the IR spectral range for BaY1.8Lu0.2F8 crystals doped with Er3+ ions at concentrations of 20.0 at. % and 30.0 at. %. Based on the Judd-Ofelt theory, the intensity parameters were determined from the absorption spectra with the use of two approaches, the standard theory (J-O), and the intermediate configuration interaction (ICI). It is shown that investigated BaY1.8Lu0.2F8:Er3+ crystals propose the value of stimulated emission cross-section at the wavelength around 2.7 μm higher than that for Er-doped YAG and at the level of Er-doped LiYF4 crystals. In addition, it was shown that for BaY1.8Lu0.2F8 crystals with a high doping level of Er3+ (more than 20.0 at. %), the radiative lifetime of the 4I13/2 state becomes shorter than the lifetime of the 4I11/2 state, which speaks for success on efficient laser oscillation at a wavelength of about 2.7 μm (the 4I11/2 → 4I13/2 transition).