Peak Emission Cross Section Research Articles

Tm3+-doped tellurium germanate glass and its double-cladding fiber for 2 μm laser

The thermal and spectroscopic performance of 40GeO2–35TeO2–15PbO–5Al2O3–5(CaO+SrO)–1Tm2O3 (in mol%) tellurium germanate glass suitable for fiber drawing is investigated. The glass developed has a low phonon energy of ~780cm−1 and excellent thermal stability against devitrification. The peak emission cross-section of Tm3+ at 1.8μm is calculated to be 5.18×10–21cm2 and the measured lifetime is 0.83ms. Tm3+-doped tellurium germanate double-cladding fiber with a hexagonal-shaped inner cladding is fabricated by a stacking-and-drawing method, and a laser output of 1.938μm is realized in a 250-mm-long fiber.

Continuous-wave broadly tunable high-power Cr:CdS laser.

We report spectroscopic characteristics and laser properties of the mid-infrared active laser medium Cr2+:CdS. Temperature-dependent absorption, luminescence and lifetime measurements of the 5E exited state allow determination of peak emission cross section value of 1.35 × 10−18 cm2 in σ-polarization at room temperature. Lifetime values vary from 7.6 µs at 8 K to 0.48 µs at 320 K, corresponding to 22 % quantum yield at 285 K. Under Tm-fiber laser pumping, the continuous-wave output reached 1.8 W at 2.5 μm with 35.5 % slope efficiency. With a single CaF2 prism, the CW Cr2+:CdS laser could be tuned from 2.240 to 3.285 µm.

Spectroscopic properties and continuous-wave laser operation of Yb:Bi₄ Si₃ O₁₂ crystal.

Yb3+:Bi4Si3O12 single crystal with Yb3+ concentration of 5.7 at.% has been grown successfully by the Czochralski method. The energy level positions of Yb3+ in Bi4Si3O12 crystal were determined based on the absorption and fluorescence spectra. The peak absorption cross-section is 0.98 × 10−20 cm2 at 976 nm and the peak emission cross-section is 0.57 × 10−20 cm2 at 1035 nm. The fluorescence lifetime of the excited multiplet is 1.26 ms. Diode-pumped continuous-wave laser operation around 1038 nm has been demonstrated in the Yb3+:Bi4Si3O12 crystal with a slope efficiency of 27% and maximum output power of 240 mW.

Spectroscopic Foundations of Lasers: Spontaneous Emission Into a Resonator Mode

We review the physics underlying the process of spontaneous emission, with a special focus on spontaneous emission into a resonator mode. We define the mode volume, verify the fundamental modal dimensions, present the spectral mode profile, the coherence time, the Q-factor, the Füchtbauer-Ladenburg equation, and the Purcell factor, and discuss their influence on different types of lasers. We obtain the relation between peak emission cross section, radiative lifetime, and emission linewidth. By interpreting spontaneous emission as stimulated emission driven by vacuum fluctuations, we derive the spontaneous-emission rate into a resonator mode and establish physical expressions for the fractions of spontaneous emission and total decay from the upper laser level into this mode. Furthermore, we discuss coupling of the atomic system with the coherent field inside a lasing resonator mode, resulting in the formation of a Mollow triplet, and demonstrate that it leads to a reduction of the spontaneous-emission rate by a factor of 2.

Spectroscopic properties of ～2 μm emissions of Tm3+-doped germanate-tellurite glasses

Tm2O3-doped 40GeO2-35TeO2-15PbO-5Al2O3-2.5CaO-2.5SrO glasses with different Tm3+ ion concentrations are fabricated by conventional melt-quenching method. From the measurements of thermal properties it follows that the glass transition temperature is 446 ℃ and crystallization peak does not exist. The maxmium phonon energy of the host is ~ 750 cm-1. The Judd-Ofelt strength parameter Ωt (t = 2, 4, 6), the radiative transition probalities, the branching ratios and the radiative lifetime are calculated according to Judd-Ofelt theory. The emission spectra of Tm3+ doped glasses with different Tm2O3 concentrations are measured under the excitation by an 808 nm diode laser. The result shows that the emission intensity at ~ 1.8 μm reaches a maximal value when the Tm2O3-doping concentration is 1 mol% and then it decreases with the further increase of Tm2O3-doping concentration. The emission cross section of 3F4 → 3H6 is calculated based on the McCumber theory. The peak emission cross-section is 6.5 × 10-21 cm2. The non-radiative transition rate of 3F4 caused by OH is calculated quantitatively by rate equation. The results indicate that the germanate-tellurite glass is a new candidate for mid-infrared laser application.

Effect of alkali metal oxides R2O (R=Na, K) on 1.53 μm luminescence of Er3+-doped Ga2O3-GeO2 glasses for optical amplification

This paper reported the thermal stability and spectroscopic properties of Ga2O3-GeO2-Na2O-K2O (GGNK) glasses doped with Er3+. The GGNK glasses were characterized by differential scanning calorimetry (DSC), Raman spectra, absorption and infrared-visible fluorescence spectra. Measured DSC result showed that these glasses possessed an excellent stability (ΔT=188.6 °C). The relationship between glass composition and Judd-Ofelt intensity parameters and other optical properties of Er3+, such as the absorption and stimulated emission cross-sections, were clarified. Meanwhile an intense broadband 1.53-μm emission with a full width at half- maximum of 51 nm and peak emission cross-section of 9.32×10−21 cm2 of Er3+-doped GGNK glass was obtained upon 980 nm diode-laser excitation. Effects of K2O replacing Na2O on the thermal stability and spectroscopic properties were investigated. It was found that the incorporation of K2O into Er3+-doped Ga2O3-GeO2-Na2O glass could effectively improve the 1.53 μm emission luminescence. The results showed that GGNK glass might be more attractive host material for their application in C-band optical fiber amplifiers.

Suppression of second-order cooperative up-conversion in Er/Yb silicate glass

This paper reports the efforts of suppressing Er ion’s second-order cooperative up-conversion (CUC). Er/Yb and Er/Y silicate glass waveguides were fabricated, which have same structure, similar Er concentration and peak emission cross-section. Under same 1480nm pump power, Er/Yb silicate glass shows 4.7 times weaker visible up-conversion luminescence and four times stronger infrared luminescence than Er/Y silicate glass. Through analyzing the physical mechanism, we found that the energy back transfer from Er to Yb plays a significant role on the luminescence difference, which affects and further suppresses the second-order CUC process in Er/Yb co-doped materials.

Crystal growth and optical properties of Sm:CaNb2O6 single crystal

Sm:CaNb2O6 single crystal has been grown by the Czochralski method. Its high-temperature X-ray powder diffraction, optical absorption, emission spectroscopic as well as lifetime have been studied. Thermal expansion coefficients (α), J–O parameters (Ωi), radiative lifetime (τrad), branching ratios (β) and stimulated emission cross-sections (σe) were calculated. The quantum efficiency (η) was calculated to be 97%. The intense peak emission cross section at 610, 658nm were calculated to be 2.40×10−21, 2.42×10−21cm2. These results indicate that Sm:CaNb2O6 crystal has potential use in visible laser and photonic devices area.

Spectroscopic characterization and diode-pumped 910 nm laser of Nd:LiLuF4 crystal

Polarized absorption and fluorescence spectra Nd3+-doped LiLuF4 single crystal were investigated. The peak emission cross section at 905 and 910 nm are 0.97 × 10−20 and 0.82 × 10−20 cm2, respectively. Two samples with different dimensions were tested in the laser experiments. With a laser-diode as the pump source, a maximum 1.17 W laser output at 910 nm has been obtained with a slope efficiency of 16.3% with respect to the pump power.

Luminescence Properties of Er<sup>3+</sup>-Doped Ga<sub>2</sub>O<sub>3</sub>-GeO<sub>2</sub>-Bi<sub>2</sub>O<sub>3</sub>-R<sub>2</sub>O (R=Na and K) for 1.53 μm Fiber Amplifier

An intense broadband 1.53-μm emission with a full width at half-maximum of 51.2 nm and peak emission cross-section of 8.58×10-21 cm2 of Er3+-doped Ga2O3-GeO2-Bi2O3-R2O (R= Na+, K+) glass have been obtained upon 980 nm diode-laser excitation. Effects of alkali metal ions on the thermal stability and spectroscopic properties of Er3+-doped Ga2O3-GeO2-Bi2O3 glass have been investigated. It is found that the incorporation of Na+ replacing K+ into Er3+-doped Ga2O3-GeO2-Bi2O3 glass can effectively improve the 1.53-μm emission and deduce upconversion luminescence .The results show that Ga2O3-GeO2-Bi2O3-Na2O glass might be an attractive host material for their application in C-band optical fiber amplifiers.

Experimental Study on Temperature Dependence of Absorption and Emission Properties of Yb:YAG Crystal as a Disk Laser Medium

In this paper, the absorption and fluorescence emission spectra of Yb:Y3Al5O12 (YAG)(25 at%) crystal as a disk laser medium are measured at high temperature (300-450K). The absorption and emission cross sections of Yb:YAG crystal are determined using Reciprocity method. Temperature dependence of 941nm absorption cross section and 1031nm emission cross section is extracted in the range of 300-450K. According to our experimental results, an exponential temperature dependence between 300K and 450K is acquired for the 1031nm peak emission cross section and also for 941nm peak absorption cross section of Yb:YAG crystal. These results could be used for simulation and design of high power highly doped Yb:YAG thin disk lasers. Keywords—Yb:YAG crystal, Emission cross section, Absorption coefficient, Temperature dependence, Reciprocity method .

Broad near‐infrared fluorescence properties of Nd‐doped PbClF crystals

AbstractNd‐doped PbClF crystals were grown with modified Bridgman method. Broad and flat emission band at 1.0 μm was observed. The FWHM value of 0.0091 wt.% Nd3+‐doped PbClF crystal at 1064 nm reached up to 30 nm with the peak emission cross‐section of 1.05×10‐19 cm2. All the results indicated that Nd‐doped PbClF crystal should be a promising tunable and ultrafast laser material. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Spectroscopic study of neodymium doped potassium lead bromide for mid-infrared solid state lasers

We present spectroscopic results of the mid-infrared (MIR) emission (4I11/2→4I9/2) properties of neodymium (Nd) doped potassium lead bromide (KPb2Br5). Following optical excitation at either 0.808 or 0.89μm, Nd:KPb2Br5 showed a broad MIR emission band centered at 5.25μm with a bandwidth of 0.76μm at full width half maximum. For low concentration samples (5×1018cm−3), the emission lifetime was determined to be 43ms at room temperature and increased to 57ms at low temperature (15K). Based on the energy-gap law, non-radiative decay through multi-phonon relaxation is predicted to be negligibly small in this low phonon energy host material with ℏωmax=138cm−1. Therefore, the modest temperature dependence of the MIR lifetime is most likely due to the existence of non-radiative decay related to residual defects in the sample. The peak emission cross-section for the 4I11/2→4I9/2 transition was determined to be 0.65×10−20cm2. Some comparative results on Nd:KPb2Cl5 were also included in this study.

Spectroscopic Properties of Er<sup>3+</sup>-Doped Ga<sub>2</sub>O<sub>3</sub>-GeO<sub>2</sub>-Bi<sub>2</sub>O<sub>3</sub>-PbO Glass

Spectroscopic properties in Er3+-doped Ga2O3-GeO2-Bi2O3-PbO（BP）glass have been investigated and their promising application as Er3+-doped fiber amplifiers (EDFA) has also been evaluated under the excitation of 980 nm. The important roles of Bi2O3 substitution for PbO on spectroscopic properties, such as Judd-Ofelt intensity parameters (t=2, 4, 6) and emission spectra of Er3+, have been studied. The calculated peak emission cross-section of the 4I13/2→4I15/2 transition of Er3+ ions are 16.03×10-21 cm2 when the substituted PbO content by Bi2O3 is about 25 mol. The product of the peak emission cross-section ( ) and the full width at half-maximum (FWHM) of the sample is~689.29×10-28 cm3, which is higher than that of Er3+-doped silicate, phosphate and ZBLAN glasses. It was found that the substitution of Bi2O3 for PbO provides two potentials: broadening the full width at half-maximum of 1.53 μm fluorescence and improving the values of FWHM× of Er3+. The results strongly support that the Er3+-doped BP2 glass could be identified as a promising material for achieving 1.53 μm fiber amplifier.

Optical spectra and excited state relaxation dynamics of Sm3+ in Gd2SiO5 single crystal

Single crystals of gadolinium orthosilicate Gd2SiO5 containing 0.5 at% and 5 at% of Sm3+ were grown by the Czochralski method. Optical absorption spectra, luminescence spectra and luminescence decay curves were recorded for these systems at 10 K and at room temperature. Comparison of optical spectra recorded in polarized light revealed that the anisotropy of this optically biaxial host affects the intensity distribution within absorption and emission bands related to transitions between multiplets rather than the overall band intensity. It has been found that among four bands of luminescence related to the 4G5/2→6HJ (J=5/2–11/2) transitions of Sm3+ in the visible and near infrared region the 4G5/2 →6H7/2 one has the highest intensity with a peak emission cross section of 3.54×10−21 cm2 at 601 nm for light polarized parallel to the crystallographic axis c of the crystal. The luminescence decay curve recorded for Gd2SiO5:0.5 at% Sm3+ follows a single exponential time dependence with a lifetime 1.74 ms, in good agreement with the 4G5/2 radiative lifetime τ rad=1.78 ms calculated in the framework of Judd-Ofelt theory. Considerably faster and non-exponential luminescence decay recorded for Gd2SiO5:5 at% Sm3+ sample was fitted to that predicted by the Inokuti-Hirayama theory yielding the microparameter of Sm3+–Sm3+ energy transfer C da=1.264×10−52 cm6×s−1. It is concluded that the system under study may be of interest as a VUV-UV excited visible phosphor or laser material operating in the yellow region of the spectrum.

Polarized spectral properties of Tm 3+:K 5Bi(MoO 4) 4 crystal

Trivalent thulium-doped K 5Bi(MoO 4) 4 single crystals were grown by the Czochralski method. Its polarized absorption and fluorescence spectra and fluorescence decay curves were recorded at room temperature. On the basis of the Judd–Ofelt theory, the spectral parameters of the Tm 3+:K 5Bi(MoO 4) 4 crystal were calculated. The cross relaxations between Tm 3+ ions were analyzed. The emission cross sections of the 3F 4 → 3H 6 transition were obtained by the Fuchtbauer–Ladenburg formula and then the gain cross sections around 1.9 μm were calculated. The peak emission cross section and width of emission band around 1.9 μm are comparable to those for Tm 3+:YAG and the tunable range is about 280 nm for the potential ∼1.9 μm laser operation via the 3F 4 → 3H 6 transition.

Tm<sup>3+</sup>-doped Bismuth Tellurite Glasses for S- and U-band Optical Amplifiers

Effective ~1.47mm and powerful ~1.8mm infrared emissions have been observed in Tm3+-doped bismuth tellurite glasses with low phonon energy under the excitation of 793nm diode laser. Judd-Ofelt parameters W2 (4.65´10-20cm2), W4 (1.15´10-20cm2), and W6 (1.16´10-20cm2) indicate a higher asymmetric and stronger covalent environment in the optical glasses. In 0.5wt% Tm3+-doped sample, the peak emission cross-sections of 3H4®3F4 and 3F4®3H6 transitions are derived to be 2.83´10-21 and 6.13´10-21cm2, respectively, and the maximum gain coefficients of 0.38 and 2.21dB/cm at 1.675 (U-band edge) and 1.856mm wavelengths were anticipated in an ideal status. These results indicate the Tm3+-doped bismuth tellurite glasses are a promising candidate in developing S- and U-band amplifiers.

Enhanced 1.53-μm and lowered upconversion luminescence in Er3+-doped Ga2O3–GeO2–Bi2O3–Na2O glass by codoping rare earths

Spectroscopic properties and energy transfer (ET) in Ga2O3–GeO2–Bi2O3–Na2O (GGBN, glass doped with Er3+ and rare earths (RE3+; RE3+=Ce3+, Tb3+) have been investigated. Intense 1.53-μm emission with the peak emission cross-section achieved to 7.58×10−21cm2 from Er3+-doped GGBN glass has been obtained upon excitation at 980nm. Effects of RE3+ (RE3+=Ce3+, Tb3+) codoping on the optical properties of Er3+-doped GGBN glass have been investigated and the possible ET mechanisms involved have also been discussed. Significant enhancement of the 1.53μm emission intensity and decrease of upconversion (UC) fluorescence with increasing Ce3+ concentration have been observed. The incorporation of Tb3+ into Er3+-doped GGBN glass could significantly decrease the UC emission intensity, but meanwhile decrease the 1.53μm emission intensity due to the ET from Er3+:4I13/2 to Tb3+:7F2. The results indicate that the incorporation of Ce3+ into Er3+-doped GGBN glass can effectively improve 1.53-μm and lower UC luminescence, which makes GGBN glass more attractive for use in C-band optical fiber amplifiers.

Temperature dependence of the emission cross section of Nd:YVO_4 around 1064 nm and consequences on laser operation

We propose an accurate measurement of the evolution of the emission cross section of Nd:YVO4 versus temperature around 1064 nm. This was done by using two complementary methods involving spectrum acquisition and laser oscillator small signal gain measurement. We observed a 44% decrease of the peak emission cross section for a 64 °C temperature increase but also a shift of the peak emission cross section wavelength at a rate of 3 pm/°C. The influence of the crystal temperature on the performance of a laser oscillator in continuous wave was also investigated.

Spectroscopic properties of ytterbium doped KLu(WO 4) 2

Monoclinic Yb 3+-doped KLu(WO 4) 2 (Yb:KLuW) crystal with large sizes was grown by top-seeded solution growth (TSSG) method. Room-temperature absorption and fluorescence spectra were measured. The ground-state energy-level splitting was 562 cm −1. The absorption cross section, peak emission cross section as well as the minimum inversion fraction β min and the minimum absorbed pump intensity I min were calculated. The measured emission lifetime was 0.676 ms and the emission spectral bandwidth (FWHM) was up to 55 nm. In comparison with established laser crystals the results suggested that this crystal has potential application in efficient tunable and femtosecond laser operation.