Gain Cross Section Research Articles

Thermal Characterization, Crystal Field Analysis and In-Band Pumped Laser Performance of Er Doped NaY(WO4)2 Disordered Laser Crystals

Undoped and Er-doped NaY(WO4)2 disordered single crystals have been grown by the Czochralski technique. The specific heat and thermal conductivity (κ) of these crystals have been characterized from T = 4 K to 700 K and 360 K, respectively. It is shown that κ exhibits anisotropy characteristic of single crystals as well as a κ(T) behavior observed in glasses, with a saturation mean free phonon path of 3.6 Å and 4.5 Å for propagation along a and c crystal axes, respectively. The relative energy positions and irreducible representations of Stark Er3+ levels up to 4G7/2 multiplet have been determined by the combination of experimental low (<10 K) temperature optical absorption and photoluminescence measurements and simulations with a single-electron Hamiltonian including both free-ion and crystal field interactions. Absorption, emission and gain cross sections of the 4I13/2↔4I15/2 laser related transition have been determined at 77 K. The 4I13/2 Er3+ lifetime (τ) was measured in the temperature range of 77–300 K, and was found to change from τ (77K) ≈ 4.5 ms to τ (300K) ≈ 3.5 ms. Laser operation is demonstrated at 77 K and 300 K by resonantly pumping the 4I13/2 multiplet at λ≈1500 nm with a broadband (FWHM≈20 nm) diode laser source perfectly matching the 77 K crystal 4I15/2 → 4I13/2 absorption profile. At 77 K as much as 5.5 W of output power were obtained in π-polarized configuration with a slope efficiency versus absorbed pump power of 57%, the free running laser wavelength in air was λ≈1611 nm with the laser output bandwidth of 3.5 nm. The laser emission was tunable over 30.7 nm, from 1590.7 nm to 1621.4 nm, for the same π-polarized configuration.

Er3+ ions doped tellurite glasses with high thermal stability, elasticity, absorption intensity, emission cross section and their optical application

Three samples of tellurite glasses within system 46TeO2⋅15ZnO⋅9.0P2O5⋅30LiNbO3 doped with xEr2O3 ions (where x=4000, 8000 and 10,000ppm) have been prepared by using the conventional melt-quenching method. These glasses have high thermal stability proved by using differential thermal analysis (DTA) measurements. Elastic properties of the glasses were investigated by measuring both longitudinal and shear velocities using the pulse-echo overlap technique at 5MHz. Elastic moduli such as: longitudinal (λ), shear (μ), Bulk (B) and Young’s (Y) increased with the Er3+ concentration in the prepared glasses matrix. The optical properties of the glasses were estimated by measuring UV–vis-NIR spectroscopy. The Judd–Ofelt parameters, Ωt (t=2, 4, 6) of Er3+ were evaluated from optical absorption spectra. The oscillator strength type transition probabilities, spectroscopic quality factors, branching ratio and radiative lifetimes of several excited states of Er3+ have been predicted using intensity Judd–Ofelt parameters. Gain cross-section for the Er3+ laser transition 4I13/2→4I15/2 was obtained. The results show 46TeO2⋅15ZnO⋅9.0P2O5⋅30LiNbO3⋅10,000ppm Er2O3 glass has the effective emission cross section bandwidth (64nm) and large stimulated emission cross-section (0.89×10−20cm2). The thermal stability, elastic and spectroscopic properties indicate that this glass doped with Er3+ is a promising candidate for optical applications and may be suitable for optical fiber lasers and amplifiers.

Growth and Spectral Assessment of Yb3+-Doped KBaGd(MoO4)3 Crystal: A Candidate for Ultrashort Pulse and Tunable Lasers

In order to explore new more powerful ultrashort pulse laser and tunable laser for diode-pumping, this paper reports the growth and spectral assessment of Yb3+-doped KBaGd(MoO4)3 crystal. An Yb3+:KBaGd(MoO4)3 crystal with dimensions of 50×40×9 mm3 was grown by the TSSG method from the K2Mo2O7 flux. The investigated spectral properties indicated that Yb3+:KBaGd(MoO4)3 crystal exhibits broad absorption and emission bands, except the large emission and gain cross-sections. This feature of the broad absorption and emission bands is not only suitable for the diode pumping, but also for the production of ultrashort pulses and tunability. Therefore, Yb3+:KBaGd(MoO4)3 crystal can be regarded as a candidate for the ultrashort pulse and tunable lasers.

Lasing characteristics of crystal

The spectral dependences of the gain cross section of the , transition of ions in the crystal are calculated at different relative population inversions using the absorption and luminescence spectra of the and transitions of ions at . Lasing of these crystals at the transition is obtained for the first time under pumping by a laser (). The lasing wavelength is .

Fabrication and spectral properties of Yb:(Sc0.9Y0.1)O3 transparent ceramics

Yb3+ doped Sc2O3 and (Y0.9Sc0.1)2O3 transparent ceramics were fabricated by solid-state reaction and sintered in H2 atmosphere. The effects of Y2O3 on Yb:Sc2O3 ceramics were investigated. Y2O3 can inhibit the excessive grain growth in Yb:Sc2O3 ceramics, and increase the transparency effectively. The lattice parameter of Yb:(Sc0.9Y0.1)2O3 ceramics became larger due to the introducing of Y3+ ions. The gain cross-sections (σg) were evaluated with different β values. The energy level diagrams were calculated based on the absorption and emission spectra, Yb:(Y0.9Sc0.1)2O3 ceramics exhibits a large ground-state splitting of 2F7/2. Furthermore, the emission bands of Yb:(Sc0.9Y0.1)2O3 ceramics are inhomogeneously broadened compared to Yb:Sc2O3 ceramics. Broad emission bandwidths of Yb:(Sc0.9Y0.1)2O3 ceramics are favorable for the generation of ultrashort pulse laser in mode-locked operation.

Defect structures and optical characteristics of Er3+ ion in Er:LiNbO3 crystals

Congruent Er:LiNbO3 crystals were grown by Czochraski method. The OH− absorption and UV–vis-near infrared absorption spectra indicated that Er3+ cluster sites were formed in LiNbO3 crystal doped with 3mol% Er3+ ions. Studies on the stokes and anti-stokes spectra showed that the formation of Er3+ cluster sites could increase the rate of cross relaxation processes. Judd–Ofelt theory was carried out to discuss the spectral characteristics of Er3+ ions in Er:LiNbO3 crystals. Based on Füchtbauer–Ladenburg and McCumber theory, the emission cross section of the 4I13/2→4I15/2 transition of Er3+ ion was calculated, and the potential laser performance was evaluated by the gain cross section spectra. Er:LiNbO3 crystal codoped with Zn2+ ions was also grown to discuss the relation between the defect structure and optical characteristics of Er3+ ion.

Fabrication, spectral and laser performance of 5 at.% Yb3+ doped (La0.10Y0.90)2O3 transparent ceramic

A 5at.% Yb3+ doped (La0.10Y0.90)2O3 transparent ceramic was fabricated with nano-powders and sintered in H2 atmosphere. Spectroscopic properties and laser performance of Yb:(La0.10Y0.90)2O3 ceramic were studied. The ceramic exhibits excellent spectroscopic properties, with broad absorption and emission bands, and its refractive index (n) is close to 2. The gain cross-section (σg) was calculated at different population inversion ratio (β) values. In addition, among Yb3+ doped YAG crystal, Y2O3 and (YLa)2O3 ceramic, (YLa)2O3 ceramic has the least pump intensity (Imin) of 1.25KWcm−2. Furthermore, a diode-pumped C–W ceramic laser output has been demonstrated at 1075nm with a slope-efficiency of 60.2%.

Spectral, luminescent, and lasing properties of ZrO2—Y2O3—Tm2O3 crystals

The absorption spectra corresponding to the transitions from the ground 3H6 state to the excited multiplets 1G4, 3F2, 3F3, 3H4, 3H5, 3F4, as well as the luminescence spectrum of the 3F4 → 3H6 laser transition of Tm3+ ions excited to the 3H4 level in ZrO2 — 12 mol % Y2O3 — 2 mol % Tm2O3 crystals are studied at a temperature of 300 K. The cross-relaxation (3H4 → 3F4, 3H6 → 3F4) efficiency of Tm3+ ions estimated by the integral characteristics of decay curves of luminescence from the 3H4 level exceeds 90 %. The spectral dependences of the gain cross section of the 3F4 → 3H6 laser transition of Tm3+ ions are calculated for different relative population inversions. Lasing at the 3F4 → 3H6 transition of Tm3+ ions in diode-pumped ZrO2 — 12 mol % Y2O3 — 2 mol % Tm2O3 crystals is obtained for the first time. The lasing wavelength is 2046 nm.

Classical model of strong-field parametric amplification of soft x rays

We present a detailed theoretical description of laser driven x-ray parametric amplification, which has been experimentally demonstrated by Seres et al. [Nature Phys. 6, 455 (2010)] together with a supporting basic model. The process is based on the parametric interaction of an x-ray photon with a laser accelerated electron in a Coulomb field. With the extended model we are able to estimate the gain cross section also for a finite energy distribution of the interacting electrons as well as to consider dephasing between the electrons and the x-ray field. The improved model is capable of describing the recent experimental findings much more accurately.

Relationship between electron-LO phonon and electron-light interaction in quantum dots

The relationship between the Fr\"olich electron-LO phonon interaction and the electron-light interaction in the conduction band of quantum dots (QDs) based on polar semiconductors is investigated and used to parametrize the intersublevel polaron lifetime. Based on this, the ratio of the optical gain cross section and nonradiative lifetime is described in terms of the QD geometrical and compositional parameters, which is important for possible intraband lasing transitions in QDs.

The spectroscopy investigation of ZnWO4:Tm3+ single crystal

The single crystal ZnWO4:Tm3+ has been grown by Czochralski method. The XRD, refractive index, absorption and fluorescence spectra are measured. The Judd–Ofelt parametersΩ2, Ω4, Ω6 are obtained to be 6.3×10−20, 1.3×10−20, 1.4×10−20cm2, respectively. The fluorescence decay time of the 3H4 level is measured to be 0.113ms and the quantum efficiency is 57%. The gain cross sections corresponding to 3F4→3H6 transition at ∼2μm are estimated by the reciprocity method (RM). The strong gain at ∼2μm indicates that the ZnWO4:Tm3+ crystal is a promising laser host for ∼2μm laser.

The influence of Zn2+ ion on the 1.5 μm laser properties of LiNbO3 crystal heavily doped with Er3+ ion

The spectral characteristics of 1.54μm emission in a series of Zn/Er:LiNbO3 crystals with heavy Er content and variable Zn content were reported. The inductively coupled plasma mass spectrometry (ICP-MS) was used to determine the concentration of Er3+ ion in the crystal. The absorption and emission spectra of Zn/Er:LiNbO3 crystals were measured. Based on Judd–Ofelt theory, the spectral parameters such as intensity parameters Ωt (t=2, 4 and 6), transition strengths, radiative transition probabilities, radiative lifetime and fluorescence branching ratio have been obtained in Zn/Er:LiNbO3 system. The emission cross section corresponding to 4I13/2→4I15/2 transition of Er3+ ion was obtained according to Füchtbauer–Ladenburg theory. The gain cross section of Er:LiNbO3 crystal codoped with 6mol% Zn2+ ions were also discussed in this work.

Optical spectroscopy and laser parameters of Zn2+/Er3+/Yb3+-tridoped LiNbO3 crystal

The Zn/Er/Yb:LiNbO3 and Er/Yb:LiNbO3 crystals were grown by the Czochralski technique. The laser characteristics of 1.54μm emission were predicted based on the Judd–Ofelt theory, and the intensity parameters Ωt (Ω2=7.23×10−20cm2, Ω4=3.15×10−20cm2 and Ω6=1.43×10−20cm2) were obtained. The stimulated emission cross sections (σem) at 1.54μm emission in Zn/Er/Yb:LiNbO3 were calculated based on the McCumber theory and the Füchtbauer–Ladenburg theory. The gain cross section spectrum of Zn/Er/Yb:LiNbO3 crystal was also investigated. Under 980nm excitation, a lenghthening lifetime of 1.54μm emission and an enhancement of green upconversion emission were observed for Zn/Er/Yb:LiNbO3 crystal. The studies on the power pump dependence and the upconversion mechanism suggested that both green and red upconversion emissions were populated via the three-photon process, and Zn2+ ion tridoping increases the probability of cross relaxation process between the two neighboring Er3+ ions.

Spectroscopic characteristics of 1.54 μm emission in Er/Yb:LiNbO3 crystals tridoped with In3+ ions

A series of Er/Yb:LiNbO3 crystals tridoped with x mol% In3+ ions (x=1, 2 and 3mol%) was grown by Czochralski technique. Under 980nm excitation, the strongest intensity of 1.54μm emission was observed for 2mol% In3+-tridoped Er/Yb:LiNbO3 crystal. The UV–vis–infrared absorption spectra of In/Er/Yb:LiNbO3 crystals were measured, and Judd–Ofelt (J–O) theory was carried out to predict the J–O intensity parameters (Ωt), radiative lifetime τrad and fluorescence branching ratio β. The emission cross-section of the 4I13/2→4I15/2 transition of Er3+ ion was calculated by Füchtbauer–Ladenburg (F-L) method. The gain cross-section, estimated as a function of the population inversion ratio, allowed us to evaluate a potential laser performance of In/Er/Yb:LiNbO3 crystal at 1.54μm emission. The fluorescence lifetimes of the 4I13/2→4I15/2 transition in In/Er/Yb:LiNbO3 crystals were measured.

Er3+–Yb3+ codoped phosphate glasses used for an efficient 1.5 μm broadband gain medium

In order to develop efficient optical amplifiers with broad and flat gain profiles in the near-infrared range an active phosphate matrix codoped with Er3+ and Yb3+ rare earth optically active ions has been studied by carrying out steady-state and time-resolved luminescence spectroscopies. Taking advantage of the high absorption transition probability of the Yb3+ ions, these ions are excited with cw 980nm radiation from a commercial laser diode and subsequently de-excited by efficiently transferring energy to the Er3+ ions, producing an intense emission at around 1.5μm at which wavelength-division-multiplexing devices work. From the experimental data, the emission cross-section σem(λ) of the 4I13/2→4I15/2 transition at 1.5μm has been calculated using the Füchtbauer–Landerburg method. The result of this calculation, together with the absorption cross-section σabs(λ), allows the gain cross-section G to be estimated. Other important spectroscopic parameters associated with this transition, such as full width at half maximum FWHM, effective bandwidth Δeff and lifetime of the 4I13/2 level τexp, have been measured and analysed as a function of the Er3+ concentration. As figures of merit, FWHM×σem(λ), Δeff×σem(λ) and σem(λ)×τexp calculations have been carried out. Comparing the obtained values to those reported in other Er3+-doped materials, the phosphate glasses doped with 1mol% of Yb2O3 ions and 1–2mol% of Er2O3 can be considered excellent candidates for developing broadband optical amplifiers, providing a large gain cross-section that covers the C (1530–1565nm) and the L (1565–1625nm) bands in the optical telecommunication window.

Spectroscopic characteristics of Yb3+-doped Li3Ba2Y3(WO4)8 crystal

This paper reports the spectroscopic properties of Yb3+:Li3Ba2Y3(WO4)8 crystal. The polarized spectral properties of Yb3+:Li3Ba2Y3(WO4)8 crystal were investigated. The laser performance parameters βmin, Isat and Imin of Yb3+:Li3Ba2Y3(WO4)8 crystals have been also established. Yb3+:Li3Ba2Y3(WO4)8 crystal has a broad FWHM of the gain cross-section and larger absorption and emission cross-sections. These results may regard the Yb3+:Li3Ba2Y3(WO4)8 crystal as a tunable laser material.

Growth, structure and spectral properties of a novel crystal CaErAlO4 for 2.7 μm lasers

Novel stoichiometric CaErAlO4 crystals were successfully grown by the Czochralski method. The structure was determined to belong to the I4/mmm space group, in which the Ca2+ and Er3+ cations share the same crystallographic site, resulting in the inhomogeneous broadening of the spectra. The spectra were measured at room temperature. The absorption peak at 972 nm with a broad FWHM of 29 nm and a high coefficient up to 23.2 cm−1 is very suitable for commercial InGaAs laser diodes. In the 4I11/2 → 4I13/2 transition, the maximum emission peak was at 2.790 μm with a broad FWHM of 125 nm, and the emission cross section was calculated to be 1.03 × 10−20 cm2, which is on the order of that of Er3+:YAG. The gain cross sections were also estimated. These results imply that this CaErAlO4 crystal may be regarded as a candidate for 2.7 μm lasers.

Characterization of a Surface Wave Driven Plasma Monopole Antenna

—This theoretical study examines the characteristics of a surface wave driven argon plasma monopole antenna with excitation power level up to 100 W and gas pressure of 0.4 mb using finite difference time domain method. Input impedance, radiation pattern, gain, efficiency and radar cross section of plasma antenna at different excitation power are presented here. The results show that variations of the excitation powers can be used for construction of a dynamically reconfigurable antenna. Since the plasma tube is one of the important factors which can affect the performance of the antenna, the input impedance and gain of plasma antenna was studied under different thicknesses and materials. The least thickness can cause a more efficient antenna while minimizing its bandwidth.

Fluorescence and Spectroscopic Properties of Yb3+-Doped Phosphate Glasses

Abstract The concentration dependent Yb 3+ : phosphate (P2O5 + K2O + MgO + Al2O3 + Yb2O3) glasses have been prepared and characterized their fluorescence and laser properties. The stimulated emission cross-section and laser performance parameters were determined from the measured absorption spectra using the method of reciprocity. The refractive index, absorption and emission cross-sections and fluorescence lifetimes varied with Yb3+ ion concentration. The higher emission cross-section was found to be 1.01 × 10-20 cm2 at the extraction wavelength of 1005 nm. The fluorescence lifetime of 2F5/2 level decreases from 1.04 ms to 0.28 ms with increase of Yb2O3 concentration from 0.05 to 6.0 mol %. The gain cross-section spectra can be obtained from the measured absorption and emission cross-sections with different population levels. The values of emission cross-section, fluorescence lifetime, minimum pulse duration, pump power, extraction efficiency and gain coefficients suggest that these glasses can be used as a laser gain media for the generation of ultrashort pulse and high power laser applications.

Optical spectroscopy of Tm 3+ in a locally disordered Li 2Gd 4(MoO 4) 7 crystal: A candidate for tunable and ultrafast pulse lasers

The optical properties of a locally disordered Tm 3+:Li 2Gd 4(MoO 4) 7 crystal have been investigated extensively to assess its feasibility of efficient ultrafast laser operation in the 2 μm spectral region. The main spectroscopic parameters relevant to laser applications have been evaluated by analyzing the polarized absorption spectra using the Judd–Ofelt theory. The cross-relaxation mechanisms between Tm 3+ levels have been applied to analyze the lifetimes of the 3F 4, 3H 4, and 1G 4 manifolds. The potential for producing subpicosecond laser pulses has been discussed on the basis of the calculated emission and gain cross-sections around 2 μm wavelength. The crystal exhibits broad optical bandwidths, large absorption/emission cross sections, and a long 3F 4 fluorescence lifetime. All these features indicate that the Tm 3+:Li 2Gd 4(MoO 4) 7 crystal is a promising gain medium for tunable and ultrafast (fs) pulse lasers.