Emission Cross-section Spectra Research Articles

Growth, characterization, and efficient laser operation of Czochralski- and micro-pulling-down-grown Yb3+:YScO3 mixed sesquioxides

We report on the growth, spectroscopy and laser operation of Yb3+-doped mixed sesquioxide crystals. Various Yb3+-doped crystals with compositions close to (Y0.5Sc0.5)2O3 have been successfully grown by the Czochralski method and by the micro-pulling down (µ-PD) method. Our spectroscopic investigations reveal broadened stimulated emission and absorption cross-section spectra originating from the structural disorder of the mixed crystals. We find the peak wavelengths to shift by ∼1.6 nm between Y:Sc-ratios of 54:46 and 46:54 and confirm a linear relation of the peak position with the lattice constant of the host composition. In the laser experiments, we obtain highly efficient continuous-wave laser operation under pumping with an optically-pumped semiconductor laser (OPSL) at ∼975 nm, reaching slope efficiencies of up to 89% at optical-to-optical efficiencies exceeding 80% at laser wavelengths between 1037 nm and 1086 nm.

LiNbO3:Tm3+ Crystal: Material for Radiation-Balanced Laserin the Wave length Range of 1650 – 2000 nm

The absorption and emission cross-section spectra of LiNbO3:Tm3+ crystals were investigated within the wavelength range of at room temperature. This study delves into the potential for achieving radiation-balanced lasing. Optimal parameters for both the pump and emission wavelengths, denoted as and , respectively, were determined. At these wavelengths, the corresponding optimal values for gain and radiation-balanced generation efficiency were identified. These findings underscore the feasibility of radiation-balanced lasing in LiNbO3:Tm3+ crystals under the specified conditions.

Flat-gain L-band amplifier containing AlPO4 units in aluminophosphosilicate erbium-doped fibers.

We present a flat-gain single-stage L-band erbium-doped fiber amplifier (EDFA) with a gain ripple of ±0.7 dB from 1580 to 1615 nm, by using aluminophosphosilicate erbium-doped fiber (APS-EDF) with an estimated AlPO4 composition of 13.3 mol%. A series of APS-EDFs were fabricated with increasing AlPO4 and Er concentrations, while maintaining a low background loss of 0.031 ± 0.005 dB/m and preventing Er ion clustering. The spectroscopic study shows a slightly narrowing Er cross section and flattened emission cross-section spectrum in the L-band with more AlPO4, thus favoring the L-band amplification with an improved gain flatness. Also, the gain coefficient, gain saturation, and temperature-dependent gain characteristics were reported. A better temperature tolerance was observed with increasing AlPO4.

The role of tungsten oxide in Er3+-doped bismuth-germanate glasses for optical amplification in L-band

A series of novel Er3+-doped bismuth-germanate glasses containing different tungsten concentrations with a molar composition of 97.5[(75 − x)GeO2–25Bi2O3–(x)WO3]–2Sb2O3–0.5Er2O3 (x = 5, 10, 15, 20, and 25 mol%) were fabricated. Their thermal properties are measured by differential scanning calorimetry. A structural investigation by Raman spectroscopy suggested that changes occurred in the glass network by WO3 incorporation. By laser excitation at 980 nm, a strong emission from Er3+ ions at 1532 nm is observed, while the WO3 addition caused changes in the emission spectra. The emission cross-section spectra of Er3+ are calculated by both McCumber and Füchtbauer–Ladenburg theories and their comparison showed these theories yielded slightly different results, but in both cases, the calculations showed that a gain signal in L-band can be achieved when 30% of the Er3+ ions are at the excited state. This study proves that the Er3+-doped bismuth-germanate glasses are suitable for optical fiber amplifier applications operating at C- and L-band.

Crystalline Phase, Cross-Section, and Temporal Characteristics of Erbium-Ion in Lu3Ga5O12 Crystal

An erbium-doped Lu3Ga5O12(LuGG) single crystal was grown by the Czochralski method. The crystalline phase in the grown crystal was analyzed by powder X-ray diffraction. The erbium-ion emission spectra of the crystal were acquired. The erbium-ion emission cross-section (ECS) spectrum was computed from the acquired emission spectrum. The erbium-ion absorption cross-section (ACS) spectrum was computed using the McCumber relationship. The results are discussed in contrast to those computed from the acquired absorption spectrum, and the comparison shows that both methods give consistent results. The temporal characteristics of the emissions were also studied based on 0.98 μm pulse pumping. The study shows that the infrared emissions at 1.0, 1.5, and 2.8 μm show mono-exponentially temporal behavior. Instead, the decays of two visible emissions at 0.56 and 0.67 μm show considerable non-exponential features; each trace can be fitted double-exponentially. The non-exponential behavior is associated with those erbium ions that are present in the form of clusters, which enables non-radiative upconversion depopulation and hence additional contribution to the decay through cross relaxation between the erbium ions in clusters. The study also shows that about half of the erbium ions are present in the cluster state in the studied crystal.

Influence of Er3+ concentration in Er:GGAG crystal on spectroscopic and laser properties

Detail spectroscopy study of erbium-doped active media is crucial for understanding of the behavior of erbium-based lasers. In this paper, for the first time, detailed study of the concentration dependence of Er3+ in garnet-based active media is presented. Wide range of novel samples Er:GGAG (26 in total) with various Er3+ concentration (0.5–38 at%), were investigated for the first time. The complete spectroscopy (absorption and emission cross-section, Raman, mid- and far-infrared transmission spectra, decay times at 4I11∕2 and 4I13∕2) together with Judd-Ofelt analysis and laser characteristics were measured at room temperature. Results shows strong dependence of the first excited state (4I13∕2) on concentration, on the other hand, the 4I11∕2 level is completely independent of the erbium doping level. The Judd-Ofelt analysis show that erbium doping has minimal effect on the structural properties of Er:GGAG. Also it is shown that Er:GGAG laser has a slope efficiency of 15.3 % (almost half of the theoretical limit) and generated maximal output power of 350 mW.

Cross-section spectra and transient characteristics of Er3+ emissions in Gd3(Al, Ga)5O12 garnet single crystal

We measured fluorescence spectra of visible and infrared electronic transitions at 530 (2H11/2 → 4I15/2), 560 (4S3/2 → 4I15/2), 670 (4F9/2 → 4I15/2), 980 (4I11/2 → 4I15/2), 1530 (4I13/2 → 4I15/2) and 2700 nm (4I11/2 → 4I13/2) of Er3+ in Gd3(Al0.4Ga0.6)5O12 garnet single-crystal excited at the wavelength 520 nm (for the 980 nm emission) or 980 nm (for other emissions). From measured fluorescence spectrum, Er3+ emission cross-section spectrum was calibrated for each transition. Absorption cross-section spectra were further derived on the basis of McCumber equation, and compared with those spectra obtained from measured absorption spectrum on the basis of the Beer-Lambert law. The comparison showed that the results given by two methods can be regarded as same within the error. The transient features of visible and infrared emissions were also studied under pulse excitation. The results showed that, while the three IR emissions at 980, 1530 and 2700 nm all follow a mono-exponential function, both green and red 980-nm-upconverted emissions at 560 and 670 nm exhibit non-mono-exponentially decaying feature, and each decaying trace can be fitted by a sum of two exponential functions. The non-mono-exponential feature is related to cross relaxation caused by non-radiative short-distance energy transfer between clustered Er3+ sites.

Spectral analysis and emission properties of 3P0 and 1D2 levels in Pr:ZBLAN fiber

In order to investigate the optical properties of Pr:ZBLAN fibers, the standard and modified Judd-Ofelt theory are introduced to calculate the spectral parameters. The experimental and measured dipole line strength is obtained to derive the intensity parameters. Also, the emission properties are comprehensively estimated. For the 3P0 energy level, the generated transitions are represented in detail, and the quantum efficiency is obtained by measuring the fluorescence lifetime. The emission cross-section spectrum is presented as well. Moreover, we have further explored the emission properties of 1D2 level and analyzed the main transitions in the emission cross-section spectrum, which provides a solid theoretical foundation for the development of new mechanisms lasing in the Pr:ZBLAN fiber.

Diode-pumped continuous-wave laser of a self-frequency-doubling Yb:La2CaB10O19 crystal.

We report the first, to the best of our knowledge, laser operation of acentric Yb3+-doped La2CaB10O19 (Yb:LCB) crystal since its discovery in 1998. The polarized absorption and emission cross-section spectra of Yb:LCB were calculated at room temperature. Using a fiber-coupled 976 nm laser diode (LD) as the pump source, we realized effective dual-wavelength laser generation at around 1030 and 1040 nm. The highest slope efficiency of 50.1% was obtained in the Y-cut Yb:LCB crystal. In addition, via resonant cavity design on a phase-matching crystal, a compact self-frequency-doubling (SFD) green laser at 521 nm was also realized in a single Yb:LCB crystal with an output power of 152 mW. These results promote Yb:LCB as a competitive multifunctional laser crystal, especially for highly integrated microchip laser devices ranging from the visible to the near-infrared regime.

Investigating the structure-sensitive factors relevant to cryogenic laser operation of Yb3+ ions in oxide crystals

Optical absorption and luminescence spectra of Yb3+ ions in Gd3(Al0.5Ga0.5)5O12, (Lu0.3Gd0.7)2SiO5 and YAl3(BO3)4 hosts crystals were examined as a function of temperature between 80 and 300 K. The analysis of obtained data provided detailed information on the thermally induced change of intensities, wavelengths and bandwidths of Yb3+ transitions that governs the temperature dependence of absorption and emission cross section spectra. This information, combined with structural peculiarities of the systems studied made it possible to propose generalizations regarding the importance of the structural disorder in the Yb3+-doped laser crystals operating at cryogenic temperatures.

Synthesis and Laser-Related Spectroscopy of Er:Y2O3 Optical Ceramics as a Gain Medium for In-Band-Pumped 1.6 µm Lasers

In this paper, Er:Y2O3 optical ceramics were fabricated and details of the synthesis were presented. The spectral–luminescent properties of Er3+:Y2O3 optical ceramics were investigated. The absorption and emission cross-section spectra were determined. The luminescence kinetics at near 1.6 µm was single exponential and the lifetime of erbium 4I13/2 energy level was determined. In the frame of the conventional Judd–Ofelt theory, the emission properties of the energy levels of erbium 4I13/2 and 4I11/2 involved in laser operation at near 1.6 µm were calculated. The gain coefficient curves for typical values of the relative population of the upper laser level 4I13/2 were presented. The composition and structure were studied using the SEM, XRD, FTIR spectroscopy, and X-ray computer tomography techniques.

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.

Er<sup>3+</sup>,Yb<sup>3+</sup>:YGdSiO<sub>5</sub> Crystal as Gain Media for Lasers Emitting in the Spectral Range of 1.5–1.6 µm

Solid-state erbium lasers, emitting in the spectral range of 1.5–1.6 µm, are of great interest for several industrial applications. Nowadays the Er:glass is the most widespread laser material for obtaining laser radiation at the wavelength near 1.5 µm. However, the maximal output powers of such lasers are restricted by hundreds of milliwatts because low thermal characteristics of the glass host. By this reason the search for new crystalline hosts doped with erbium ions is the actual task.In this article the investigation results of spectroscopic properties of Er3+,Yb3+:YGdSiO5 (YGSO) crystals are reported. Polarized absorption and luminescence spectra were measured. The lifetimes of energy levels were determined. The excited state absorption spectra were measured. It was shown that excited state absorption band does not overlap with gain band in the range 1.5–1.6 µm. The energy transfer efficiency from ytterbium to erbium ions was estimated. The stimulated emission and gain cross-section spectra for Er3+ ions in YGSO were calculated.

High Power Diode-Pumped Erbium Laser Emitting at Near 1.5 μm

Solid-state lasers emitting in the 1.5–1.6 μm spectral range are very promising for eye-safe laser range finding, ophthalmology, fiber-optic communication systems, and optical location. The aim of this work is the investigation of spectrosposcopic and laser properties of gain medium based on borate crystal for abovementioned lasers.Spectroscopic and laser properties of Er,Yb:YAl3(BO3)4 crystals with different concentrations of dopants were investigated. Polarized absorption and emission cross-section spectra were determined. The ytterbium- erbium energy transfer efficiency was estimated. The maximal energy transfer efficiency up to 97 % was obtained for Er(4 at.%),Yb(11 at.%):YAl3(BO3)4 crystal.The laser operation of heavily doped crystals with erbium concentration up to 4 аt.% (2.2^1020 cm^3) was realized. By using of Er(2 at.%),Yb(11 at.%):YAl3(BO3)4 crystal a maximal continuous- wave (CW) output power of 1.6 W was obtained at 1522 nm with slope efficiency of 32 %. By using of Er(4 at.%),Yb(11 at.%):YAl3(BO3)4 crystal a maximal peak output power up to 2.2 W with slope efficiency of 40 % was realized in quasi-continuous-wave regime of operation. The spatial profile of the output beam was close to TEM00 mode with M2 < 1.2 during all laser experiments.Based on the obtained results, it can be concluded that Er,Yb:YAl3(BO3)4 crystals are promising active media for lasers emitting in the spectral range of 1.5-1.6 pm for the usage in laser rangefinder and laser- induced breakdown spectroscopy systems, and LIDARs.

Er-doped crystalline active media for ~ 3 μm diode-pumped lasers

Lasers based on erbium ions using 4I11/2 ​→ ​4I13/2 transition can generate laser radiation in the spectral range from 2.7 ​μm to 3 ​μm. Since the strong absorption peak of water is located at 3 ​μm, there has been an effort to develop a suitable laser source for various medical applications, e.g. dentistry, dermatology, urology, or surgery. Laser radiation from this wavelength range can also be used in spectroscopy, as a pumping source for optical parametric oscillators, or for further mid-infrared conversion.This paper represents an overview of the erbium-doped active media (e.g. Er:YAG, Er:YAP, Er:GGG, Er:SrF2, Er:YLF, Er:Y2O3, Er:KYW, etc.) for laser radiation generation in the spectral range 2.7–3 ​μm. In the first part of this paper, the particular active media are discussed in detail. On the other hand, the experimental results summarized absorption and emission cross-section spectra together with decay times at upper (4I11/2) and lower (4I13/2) laser levels of all tested Er-doped samples at room temperature. Moreover, laser results in CW and pulsed laser regime with tunability curves, achieved in recent years, are presented, too.

The effects of Er3+ ion concentration on 2.0-μm emission performance in Ho3+/Tm3+ co-doped Na5Y9F32 single crystal under 800-nm excitation* *Project supported by the National Natural Science Foundation of China (Grant No. 51772159), the Natural Science Foundation of Zhejiang Province, China (Grant No. LZ17E020001), the Natural Science Foundation of Ningbo City (Grant No. 202003N4099), and K C Wong Magna Fund in

Na5Y9F32 single crystals doped with ∼ 0.8-mol% Ho3+, ∼ 1-mol% Tm3+, and various Er3+ ion concentrations were prepared by a modified Bridgman method. The effects of Er3+ ion concentration on 2.0-μm emission excited by an 800-nm laser diode were investigated with the help of their spectroscopic properties. The intensity of 2.0-μm emission reached to maximum when the Er3+ ion concentration was ∼ 1 mol%. The energy transfer mechanisms between Er3+, Ho3+, and Tm3+ ions were identified from the change of the absorption spectra, the emission spectra, and the measured decay curves. The maximum 2.0-μm emission cross section of the Er3+/Ho3+/Tm3+ tri-doped Na5Y9F32 single crystal reached 5.26 × 10−21 cm2. The gain cross section spectra were calculated according to the absorption and emission cross section spectra. The cross section for ∼ 2.0-μm emission became a positive gain once the inversion level of population was reached 30%. The energy transfer efficiency was further increased by 11.81% through the incorporation of Er3+ ion into Ho3+/Tm3+ system estimated from the measured lifetimes of Ho3+/Tm3+- and Er3+/Ho3+/Tm3+-doped Na5Y9F32 single crystals. The present results illustrated that the Er3+/Ho3+/Tm3+ tri-doped Na5Y9F32 single crystals can be used as promising candidate for 2.0-μm laser.

Yb: CaYAl3O7 crystal: a promising candidate for an ultrashort pulse laser with a disordered structure

We report on the crystal growth, structure, thermal, spectral properties, and laser performance of a novel disordered crystal, Yb3+-doped CaYAl3O7 (Yb: CYAM). The complete set of anisotropic thermal properties were systematically studied. Due to the random distributions of Y3+ and Ca2+ ions, the internal disordered structure determines a significant broadening of the absorption (FWHM=25 nm) and emission (FWHM=60 nm) bands. Polarized absorption, emission and gain cross-section spectra are determined. A maximum σem at 1011 nm for π polarization was calculated to be 0.57 × 10−20 cm2. CW laser operation at 1.06 µm with the c-cut sample has been demonstrated. A maximum power of 505 mW was achieved at 1026.5 nm, corresponding to the slope efficiency and optical conversion efficiency being 12.5% and 6.7%, respectively. Yb: CYAM crystal reveals its superiority and potentiality in the ultrashort pulse laser field.

Radiative transition properties of Yb3+ in Er3+/Yb3+ co-doped NaYF4 phosphor

Usually, it is difficult to quantitatively express the optical transition properties of Yb 3+ in powdered samples owing to the difficulty in measuring the absolute absorption spectra. In this work, we developed an approach for confirming the absorption and emission cross section spectra and the radiative transition rates for the absorption and emission transitions between 2 F 7/2 and 2 F 5/2 states of Yb 3+ . The proposed approach was examined for Yb 3+ in Er 3+ /Yb 3+ co-doped NaYF 4 powders. The absorption cross section for 2 F 7/2 → 2 F 5/2 transition and emission cross section for 2 F 5/2 → 2 F 7/2 transition of Yb 3+ in NaYF 4 :Er 3+ /Yb 3+ were confirmed. Meanwhile, the transition rates for the absorption and emission transitions were also calculated. A route for calculating the radiative transition rate, absorption and emission cross sections of Yb 3+ in powdered samples is proposed. Furthermore, the radiative transition properties of Yb 3+ in NaYF 4 :Er 3+ /Yb 3+ phosphor derived from an auto-combustion-assisted fluoridation was studied via our proposed route. • NaYF 4 : Er 3+ and NaYF 4 : Er 3+ /Yb 3+ phosphors were prepared via an auto-combustion assisted solid-state reaction. • A new calculation method of radiation transition rates of Yb 3+ was proposed and used for Er 3+ /Yb 3+ co-doped NaYF 4 powders. • The absorption cross section spectra of Er 3+ /Yb 3+ co-doped NaYF 4 and Er 3+ doped NaYF 4 powders were confirmed. • The absorption and emission cross sections of Yb 3+ in NaYF 4 were derived. • The transition rates of Yb 3+ for the absorption ( 2 F 7/2 → 2 F 5/2 ) and emission ( 2 F 5/2 → 2 F 7/2 ) transitions were calculated.

Characterisation and laser performance of a Yb:LuAG double-clad planar waveguide grown by pulsed laser deposition

We report on the fabrication of a crystalline multi-layer lutetium aluminium garnet planar waveguide, with a ytterbium-doped core, via hetero-epitaxial pulsed laser deposition on an undoped yttrium aluminium garnet substrate. Physical and optical characterization of the device revealed good crystallinity of the grown films and mode propagation investigations confirmed waveguiding properties. The measured fluorescence lifetime and calculated absorption and stimulated emission cross section spectra are found to be comparable with those reported for Yb:LuAG crystals grown by traditional methods. When end-pumped by a diode-laser bar, the crystalline double-clad Yb:LuAG planar waveguide lased using a quasi-monolithic cavity configuration. An output power of > 3 W with a 20% slope efficiency was obtained, limited by a waveguide propagation loss of 1.2 dB cm−1. This first demonstration of a multi-layer LuAG double-clad planar waveguide laser shows great potential for realising compact high-power waveguide lasers and amplifiers.

Temperature dependence of Alexandrite effective emission cross section and small signal gain over the 25-450 °C range

We present detailed measurements of effective emission cross section spectra of the Alexandrite gain medium in the 25-450 °C temperature range and provide analytic formulas that can be used to match the measured spectra. The measurement results have been used to investigate the wavelength and temperature dependence of small signal gain, as well as gain bandwidth relevant for ultrafast pulse generation/amplification. We show that the estimated laser performance based on the measured spectroscopic data provides a good fit to the results in the literature. We further discuss the need for a detailed measurement of excited-state absorption cross section in future studies.