Peak Emission Cross Section Research Articles

3D Laser Writing of Low-Loss Cross-Section-Variable Type-I Optical Waveguide Passive/Active Integrated Devices in Single Crystals.

Optical waveguides fabricated in single crystals offer crucial passive/active optical components for photonic integrated circuits. Single crystals possess inherent advantages over their amorphous counterpart, such as lower optical losses in visible-to-mid-infrared band, larger peak emission cross-section, higher doping concentration. However, the writing of Type-I positive refractive index modified waveguides in single crystals using femtosecond laser technology presents significant challenges. Herein, this work introduces a novel femtosecond laser direct writing technique that combines slit-shaping with an immersion oil objective to fabricate low-loss Type-I waveguides in single crystals. This approach allows for precise control of waveguide shape, size, mode-field, and refractive index distribution, with a spatial resolution as high as 700nm and a high positive refractive index variation on the order of 10-2, introducing new degrees of freedom to design and fabricate passive/active optical waveguide devices. As a proof-of-concept, this work successfully produces a 7mm-long circular-shaped gain waveguide (≈10µm in diameter) in an Er3+-doped YAG single crystal, exhibiting a propagation loss as low as 0.23dBcm-1, a net gain of ≈3dB and a polarization-insensitive character. The newly-developed technique is theoretically applicable to arbitrary single crystals, holding promising potential for various applications in integrated optics, optical communication, and photonic quantum circuits.

Growth, spectroscopy and Dy3+→Tb3+ energy transfer of TbAl3(BO3)4 and Dy3+:TbAl3(BO3)4 crystals

TbAl3(BO3)4 and Dy3+:TbAl3(BO3)4 crystals were grown by the top-seeded solution method and the polarized optical spectra of the crystals were investigated at room temperature. Peak absorption cross-sections for the 6H15/2 → 4I15/2 transition of Dy3+ in the Dy3+:TbAl3(BO3)4 crystal are 1.2 × 10−21 cm2 at 453 nm and 0.6 × 10−21 cm2 at 452.4 nm for σ and π polarizations, respectively. Under excitation at 453 nm, a strong green fluorescence of Tb3+ around 541 nm was observed in the Dy3+:TbAl3(BO3)4 crystal due to the efficient energy transfer from Dy3+ to Tb3+ ions. Peak emission cross-sections for the 5D4→7F5 transition of Tb3+ in the Dy3+:TbAl3(BO3)4 crystal are 2.8 × 10−21 and 1.5 × 10−21 cm2 at 541 nm for σ and π polarizations, respectively. Fluorescence lifetime of the 5D4 level of Tb3+ is 1.4 ms and the efficiency of energy transfer from Dy3+ to Tb3+ ions is about 92% in the Dy3+:TbAl3(BO3)4 crystal. The results show that a commercial high-power 450 nm diode laser may be used as the pumping source for Dy3+/Tb3+ co-doped crystal to realize Tb3+ visible laser.

Polarized spectral characteristics and 1.5–1.6 μm laser operation of Er:Yb:CaSrAl2SiO7 crystal

An Er:Yb:CaSrAl2SiO7 single crystal was grown by the Czochralski method, and its polarized spectral properties were investigated at room temperature. The peak absorption cross-sections of the crystal at 978 nm are 3.30 × 10−20 and 1.42 × 10−20 cm2 for σ and π polarizations, respectively. The peak emission cross-sections at 1536 nm are 0.87 × 10−20 and 0.95 × 10−20 cm2 for σ and π polarizations, respectively. The fluorescence lifetime of the 4I13/2 multiplet of Er3+ is 8.66 ms, and energy transfer efficiency from Yb3+ to Er3+ in the crystal is 70%. Pumped by a 975 nm diode laser, a continuous-wave laser with a slope efficiency of 5.5% and a maximum output power of 70 mW was achieved in the Er:Yb:CaSrAl2SiO7 crystal.

Spectroscopic and 1.5–1.6 μm laser properties of Er:Yb:GdSr3(PO4)3 crystal

An Er:Yb:GdSr3(PO4)3 crystal was grown by the Czochralski method, and its spectroscopic properties were investigated at room temperature. The peak absorption cross section is 1.12 × 10−20 cm2 at 975 nm and the full width at half maximum of the absorption band is 5.8 nm. The peak emission cross section is 0.74 × 10−20 cm2 at 1535 nm and the full width at half maximum of the fluorescence band is 41 nm. Fluorescence lifetime of the 4I13/2 multiplet of Er3+ and Yb3+→Er3+ energy transfer efficiency in the crystal are 7.97 ms and 91.8 %, respectively. End-pumped by a 975 nm diode laser, a 1563 nm continuous-wave laser with a maximum output power of 60 mW and a slope efficiency of 16.1 % was realized in an Er:Yb:GdSr3(PO4)3 crystal at an absorbed pump power of 413 mW. Using a SiO2 birefringent filter as a wavelength tuning element, a continuously tunable 1.5–1.6 μm laser with a range of 45 nm and a maximum output power of 30 mW at 1541 nm was obtained at the same pump power.

Ho3+-activated calcium zinc silico-aluminate glass for 2 µm and 533 nm laser application

This study reports the synthesis and property analysis (thermal, mechanical, physical, and luminescence) of Ho3+ doped Calcium Zinc Silico-Aluminate glasses (CZSAHoy; y = 0.1, 0.4, 0.8, and 1.6 mol% ) which are prepared by melt quenching technique. All the synthesized glass samples show good thermal stability (ΔT=134–158 °C), elastic modulus (E = 110–115 GPa), and hardness (Hv=7.16–7.45 GPa) properties. The intensity of emission peaks at 2 µm and 553 nm is increased up to 0.8 mol% of Ho2O3 and beyond this concentration, quenching effect is dominated due to ion-ion interactions. By analyzing luminescence properties along with thermal and mechanical properties, the CZSAHo0.8 glass displays optimum properties. The broad emission bandwidth of 180 nm with high gain coefficient of 1.55 cm−1 and low pumping laser threshold (population inversion, p ≥ 0.4) for 2 µm emission from CZSAHo0.8 glass can be considered as suitable for fiber laser/amplifier application. Further, the high stimulated peak emission cross-section value of 6.59 × 10−21 cm2 and color purity (98.9%) of CZSAHo0.8 glass for 553 nm emission makes it suitable for green laser application.

Alkali/mixed alkali oxides having Nd3+: B2O3-TeO2-BaO-ZnO-NaF glasses: Perlustration of optical and luminescence traits for O-band amplification and near-infrared lasers

Six 1.0 mol% Nd2O3-doped NaF+ZnO+BaO+TeO2+B2O3 glasses containing single and mixed alkali oxides (K2O, Na2O, Li2O, K2O/Li2O, K2O/Na2O, and Na2O/Li2O) were prepared via melt-quenching approach and optical and NIR (near-infrared) emission traits including fluorescence decay times were explored. In all samples, Na ions comprising glass possesses 53.68 nm ∆λeff (effective bandwidth), 6.16 × 10‒21 cm2σmaxemi(peak emission cross-section), and 3.31 × 10‒26 cm3σmaxemi × ∆λeff (gain bandwidth) for transition 4F3/2→4I13/2 for O-band amplification, and also owns larger σmaxemi, σmaxemi × ∆λeff, and optical gain for 4F3/2→4I11/2 for NIR lasing action at 1.06 μm. Further, K ions constituting glass holds larger full width at half maximum (= 46.23 nm) or better ∆λeff (= 51.62 nm), moderate branching ratios (βR (= 42.37%) and βexp (= 19%)), and higher radiative decay time (= 662 μs) and τmeas (= 76.10 μs) for transition 4F3/2→4I9/2 for ∼0.9 μm laser operation.

Enhancing 2.7 µm emission of Er3+ in bismuth germanium glasses by introducing BaF2 in the composition

Recently, 2.7 µm lasers have attracted much attention because of their wide applications in remote sensing, and medical laser surgery. The effect of Bi2O3 ↔ BaF2 substitution in the Er3+ doped Bi2O3-GeO2-BaF2 glasses on physical and 2.7 µm emission properties have been studied. Under the excitation of 976 nm LD, an intense and broad 2.7 µm emission originating from the 4I11/2 → 4I13/2 transition of Er3+ was observed. BaF2 was found to enter the glass network as Ba2+ and F−, which may contribute to a reduction in the bridge oxygen content. The 1.55 µm emission was attenuated and the 2.7 µm emission was enhanced due to the combined effect of F− reducing the OH− content of the glass and Ba2+ expanding the distance between Er3+ ions. Furthermore, the peak emission cross-section is calculated to be 12.9 × 10−21 cm2. The Er3+ doped Bi2O3-GeO2-BaF2 glasses show potential as broadband mid-infrared emission gain material.

Temperature dependence of the emission cross-section and fluorescence lifetime in Cr:LiCAF, Cr:LiSAF, and Cr:LiSGaF between 78 K and 618 K

Cr:Colquiriites (Cr:LiCAF, Cr:LiSAF, and Cr:LiSGaF) are well-known for their broad emission bands in the near-infrared region. Unfortunately, due to their relatively weak thermomechanical strength, average powers from Cr:Colquiriite lasers have been so far limited to sub-5 W level in continuous-wave operation at room temperature. In this study, the promise of cryogenic operation, which shows significant power scalability in Yb-based systems, is investigated in detail for Cr-doped Colquiriite crystals in terms of the temperature dependence of the fluorescence lifetime and emission cross-section (σ e ) in the 78-618 K range. The lifetime measurements showed that the fluorescence, as well as the radiative lifetimes of Cr:Colquiriites are temperature dependent. The emission cross-section measurements revealed that while cooling the crystals from 300 K to 78 K, the peak σ e in E||c polarization increases moderately for all crystals: from around 1.3 × 10−20 cm2 to 1.6 × 10−20 cm2 in Cr:LiCAF, from around 4.5 × 10−20 cm2 to 6.3 × 10−20 cm2 in Cr:LiSAF and from around 3.1 × 10−20 cm2 to 3.95 × 10−20 cm2 in Cr:LiSGaF. We provide analytical formulas describing the measured temperature dependence of all relevant quantities such as fluorescence/radiative lifetime, peak emission wavelength, peak emission cross-section, and emission full-width at half-maximum. Overall, the reported results constitute a solid basis for the modeling of Cr:Colquiriite-based laser and amplifier systems, especially for the assessment of their potential at cryogenic temperatures.

Spectral studies of Nd3+ doped different fluorophosphate glasses for their aptness in laser applications at 1060 nm

Neodymium doped fluorophosphate (FP:Nd3+) glasses with different chemical compositions (59NH4H2PO4+15ZnO +15BaF2+10X+1·0NdF3 (X=LiF, NaF, CaF2, SrF2, AlF3)) were prepared by melt quenching. Their structures and spectroscopic properties were studied using x-ray diffraction, FTIR, FT-Raman and 31P, 27Al MAS NMR techniques. Various structural groups were identified using FTIR and FT-Raman spectra. The depolymerisation of metaphosphate chains are described by the decrease of Q2 tetrahedral sites allowing the formation of pyrophosphate groups revealed by 31P MAS NMR spectroscopic studies. Optical properties were studied using absorption and photoluminescence spectroscopy. Judd–Ofelt intensity parameters Ωλ (λ=2, 4 and 6) were estimated from absorption spectra. Radiative parameters such as transition probabilities (A), radiative lifetimes (τR), integrated absorption cross-sections (Σ) and branching ratios (βR) were calculated. Two emission lines at 1060 and 1330 nm were observed for Nd3+ in all the fluorophosphate glasses. From the emission spectra, emission characteristics were studied via optical band gains (σe×τR) and gain bandwidths (σe×Δλeff). Fairly large numerical values for peak emission cross-sections (σe) and branching ratios (β) for 4F3/2Æ4I11/2 transition of Nd3+ ion doped calcium fluorophosphate glass were observed. These results are rosy for NIR laser application at 1060 nm.

Deactivation effects of Tb3+ on Ho3+ emission in fluoroindate glasses for 3.9 μm laser applications

A series of Ho3+/Tb3+ co-doped fluoroindate glasses with good thermal stability have been synthesized to study the deactivation effects of Tb3+ on the Ho3+: 3.9 μm emission. Efficient 3.9 μm emission enhancement is obtained under excitation by an 888 nm laser diode (LD). The Judd-Ofelt (J-O) intensity parameters and radiative properties are calculated to evaluate the spectroscopic properties. Possible energy transfer processes resulting in emission reinforcement are discussed. A higher spontaneous transition probability and larger peak emission cross section are achieved with the inclusion of Tb3+. This analysis supports the conclusion that Ho3+/Tb3+ co-doped fluoroindate glass is a potentially useful laser material for highly efficient 3.9 μm fiber lasers.

Crystal growth and spectral properties of Ho:Sc2O3

Edge-defined film-fed growth (EFG) was successfully used to grow a Ho3+ doped Sc2O3 crystal. At room temperature, the spectroscopic characteristics of the Ho:Sc2O3 crystal were measured. At 650 nm, 1144 nm, and 1922nm, respectively, the peak absorption cross sections were 0.430 × 10−20 cm2, 0.159 × 10−20 cm2, and 0.513 × 10−20 cm2, with complete widths at half maximum of 16 nm, 22 nm, and 122 nm. The crystal's 5I7→5I8 and 5I6→5I7 peak emission cross-sections were 5.205 × 10−21 cm2 and 5.059 × 10−21 cm2, respectively. The measured fluorescence lifetimes 5I6 and 5I7 were 0.135 ms and 8.389 ms, respectively. The results demonstrated the great potential of Ho:Sc2O3 crystal for 3 µm laser operation.

Spectroscopic properties of Er:Yb:Bi4Si3O12 crystal for 1.5–1.6 μm laser

An Er3+ and Yb3+ co-doped Bi4Si3O12 single crystal was grown by the Czochralski method and the spectroscopic properties of the crystal were studied at room temperature in detail. The crystal has a peak absorption cross section of 0.98 × 10−20 cm2 at wavelength of 975 nm, and a peak emission cross section of 1.01 × 10−20 cm2 at wavelength of 1544 nm. The fluorescence lifetimes of the 4I11/2 and 4I13/2 multiplets of Er3+ are 14.4 μs and 5.64 ms, respectively. The fluorescence quantum efficiency of the 4I13/2 multiplet of Er3+ and the Yb3+ → Er3+ energy transfer efficiency are 88.4% and 77.5%, respectively. The results indicate that the Er:Yb:Bi4Si3O12 crystal is a promising 1.5–1.6 μm laser gain medium.

Spectral analysis of 1G4 level in the Pr3+:YLF crystal

The spectral measurement and energy level analysis of 1G4 are performed. Based on the absorption characteristics of the 1G4 level with different concentrations of Pr3+:YLF，the modified J-O theory was introduced to calculate the main spectral parameters. The emission cross-section spectra with two polarizations of the 1G4→3H5 transition excited by 1028 nm pumping and the fluorescence lifetime at the target wavelength (1322 nm) were measured. At the doping concentration of 1.0 at.%, the calculated peak emission cross section is close to the order of ∼1 × 10−20 cm2. Furthermore, we also discuss the energy level scheme of 1G4 in detail and proposed a cascade mechanism，which allows to further improve the output performance of the 915 nm (3P0→1G4) laser. For the first time, we propose a new approach to generate the fluorescence of 1322 nm by using 1G4 as an upper level.

Spectroscopic properties of stoichiometric CaTbAlO4 crystal as a visible laser gain medium

A CaTbAlO4 crystal was grown by the Czochralski method and the polarized spectroscopic properties of the crystal were investigated at room temperature. The peak absorption cross sections at 484.6 nm for σ and π polarizations are 2.97 × 10−22 and 0.68 × 10−22 cm2, respectively. Based on the Judd-Ofelt theory, the spontaneous transition probabilities, fluorescence branching ratios, and radiative lifetime of the 5D4 multiplet of Tb3+ in the crystal were obtained. For σ and π polarizations, the peak emission cross sections at 545 nm are 9.55 × 10−22 and 2.48 × 10−22 cm2, as well as the full widths at half maximum of the green fluorescence bands are about 7 and 10 nm, respectively. The fluorescence lifetime and fluorescence quantum efficiency of the 5D4 multiplet of Tb3+ are 1.84 ms and 79%, respectively. Above results indicate that the CaTbAlO4 crystal is a promising gain medium for visible laser.

Polarized spectroscopic properties of Er3+/Yb3+ co-doped Ca9Y(VO4)3(PO4)4 crystal

An Er3+/Yb3+ co-doped Ca9Y(VO4)3(PO4)4 crystal was grown by the Czochralski method and the polarized spectroscopic properties of the crystal were investigated at room temperature. The peak emission cross sections of the 4I13/2→4I15/2 transition of Er3+ are 1.04 ×10−20 and 0.8 × 10−20 cm2 at 1533 nm for σ and π polarizations, respectively. The full width at half the maximum of the emission band around 1.55 µm is about 50 nm for π polarization. The fluorescence lifetimes of the 4I11/2 and 4I13/2 multiplets of Er3+ in the crystal are 14.27 µs and 4.89 ms, respectively. The energy transfer efficiency from Yb3+ to Er3+ in the crystal was estimated to be about 69.3%.

Crystal growth, spectral properties and Judd-Ofelt analysis of Ho:GdScO3 crystal

Ho3+-doped GdScO3 crystal was successfully grown by the edge-defined film-fed growth (EFG) method. The spectroscopic properties of Ho:GdScO3 crystal were investigated at room temperature. The peak absorption cross-sections were 0.33 × 10−20 cm2 and 1.24 × 10−20 cm2 at 1160 nm and 653 nm with full widths at half maximum of 171.7 nm and 11.5 nm. The peak emission cross-sections of 5I7→5I8 and 5I6→5I7 transitions for the crystal were 0.49 × 10−20 cm2 and 1.24 × 10−20 cm2, respectively. The fluorescence lifetimes of the 5I6 and 5I7 multiplets were measured to be 1.12 ms and 6.13 ms, respectively. The results show that Ho:GdScO3 crystal is a very promising material for 3 μm laser operation.

Survey of optical and fluorescence traits of Tm3+-doped alkali/mixed alkali oxides constituting B2O3-BaO-ZnO-LiF glasses for 0.45 μm laser and 1.46 μm fiber amplifier

For six 1 mol% Tm3+-doped B2O3-BaO-ZnO-LiF glasses containing single and mixed alkali oxides (fabricated by melt-cast approach), optical absorption, and visible and near-infrared (NIR) fluorescence features including visible luminescence decay times were explored. Optical band gaps, Urbach energy, and two-photon absorption coefficients were evaluated for all studied glasses. Judd–Ofelt (J–O) analysis from absorption spectra was performed to compute Tm3+: 4f–4f transitions J–O parameters Ωλ (λ = 2, 4, 6), and utilizing Ω2, Ω4 and Ω6 values radiative transition probabilities (AR), branching ratios (βR), and radiative lifetimes (τR) for all Tm3+ ion’s excited levels were assessed. For obtained intense blue emission band (454 nm) upon 358 nm excitation, various parameters considered in developing visible laser systems were calculated. Tm3+: Na ions having sample exhibits high AR, highest peak emission cross-section (σmaxem) (=5.89 × 10–21 cm2) and gain bandwidth(σmaxem × Δλeff) (=9.69 × 10–27 cm3) for 1D2→3F4 luminescence transition in all glasses for a favorable blue lasing process. All emission decay curves of the 1D2 upper level showed nonexponential nature. Commission Internationale de l'éclairage (CIE) coordinates, color purity, and luminous efficiency of radiation were derived from visible fluorescence spectra, and attained CIE (x,y) coordinates values reflect the purplish-blue light region. Under direct optical pumping of 3H6→3H4 transition using 808 nm laser diode, NIR fluorescence spectra exhibit a wideband within 1.3–1.6 μm spectral range peaked at 1.46 μm (3H4→3F4 transition). NIR emissions effective bandwidth (Δλeff) was varied relying on different alkali oxides. Δλeff ~ 121 nm was deduced for Tm3+: Li ions comprising glass with large σmaxem (=1.832 × 10–21 cm2), high(σmaxem × Δλeff) (=2.22 × 10–26 cm3), and optical gain (=12.608 × 10–25 cm2s) for 3H4→3F4 emission transition and its gain profile wraps the entire S-optical communication band range for efficient broadband amplification purpose in wavelength-division multiplexing systems.

Structural evolution, crystallization behaviour and mid-infrared emission properties in Yb/Ho codoped oxyfluoride germanosilicate glass ceramics with varied Si/Ge ratio

Changes in glass structure and crystallization behaviour from oxyfluoride silicate glass to oxyfluoride germanate glass were studied by modifying the ratio of Si/Ge in oxyfluoride germanosilicate glass ceramics, and transparent glass ceramic with low light scattering and efficient mid-infrared emissions were obtained. The NaYF4 nanocrystals crystallization ability of oxyfluoride glass was decreased with the increase in Ge content, which can be attributed to the weakened oxide and fluoride phase separation in GeO2-rich glass. Upconversion and down-conversion emission spectra together with Ho3+: 5I6 energy level fluorescent decay curves have been discussed for SiO2-rich glass ceramics and GeO2-rich glass ceramics, in which the fluoride crystallization induced the decrease of multi-phonon non-radiative decay rates plays the main role in the energy transfer processes. The influence of Si/Ge ratio on 2 μm and 3 μm fluorescent emissions in glasses and glass ceramics, and its link with glass network structural changes were discussed. The optimized Yb/Ho codoped oxyfluoride germanosilicate glass ceramic with low light scattering, high peak emission cross section(11.18 × 10−21cm2) and maximum gain coefficient (1.387 cm−1) at 2888 nm provides a potential application in the development of new 3 μm laser devices based on transparent oxyfluoride glass ceramic materials.

Polarized spectral properties and laser operation of Nd:SrAl12O19 crystal

Nd:SrAl11O19 (Nd:SRA) crystal has been grown by the Czochralski method. Polarized absorption spectra, polarized fluorescence spectra and fluorescence lifetime were investigated. For σ-polarization, the peak absorption cross section at 798 nm is 2.08 × 10−20 cm2 with full width at half maximum (FWHM) of 10.2 nm and the peak emission cross section is 3.36 × 10−20 cm2 at 1048.5 nm with FWHM of 4.80 nm. The Judd-Ofelt parameters Ω2,4,6 were obtained to be 0.51 × 10−20 cm2, 2.08 × 10−20 cm2, and 2.12 × 10−20 cm2, respectively. Continuous-wave laser operation of the a-cut and c-cut Nd:SRA sample has been demonstrated. The maximum output power of 8.33 W was achieved from c-cut sample at an absorbed power of 27.73 W, corresponding to a slope efficiency of 31.3%.

High efficient and broadband ∼3.5 μm emission of Er3+:YAG crystal

The YAG single crystals doped with 10 at.%, 20 at.% and 50 at.% Er3+ were successfully grown by the micro-pulling down method and spectroscopic properties of the crystals were investigated. The main interest was focus on the relation between the Er3+ concentration and ∼3.5 μm emission of Er3+:YAG crystals. Room temperature absorption spectra were analyzed by the Judd-Ofelt theory. The stimulated emission cross-sections were calculated by the Füchtbauer-Ladenburg equation. The fluorescence intensities and peak emission cross-sections of the crystals at ∼3.5 μm are slightly decreasing with the increase of Er3+ concentration. The trend of the emission properties in NIR and visible region with the Er3+ concentration was also discussed and compared. The results indicate that the highly doped Er3+ concentration is beneficial to realize the ∼3.5 µm laser output.