26.3-W continuous-wave, diode-double-end-pumped all-solid-state Nd:GdVO4 laser operating at 1.34 μm

A high-power continuous-wave (CW) all-solid-state Nd:GdVO₄ laser operating at 1.34 μm is reported here. The laser consists of a low doped level Nd:GdVO₄ crystal double-end-pumped by two high-power fiber-coupled diode lasers and a simple plane-parallel cavity. At an incident pump power of 88.8 W, a maximum CW output of 26.3 W at 1.34 μm is obtained with a slope efficiency of 33.7%. To the best of our knowledge, this is the highest output at 1.34 μm ever generated by diode-end-pumped all-solid-state lasers.     

6.2 W laser-diode end-pumped continuous-wave Nd:YALO3 laser at 1.34 μm

We report a compact and efficient LD end-pumped linearly polarized Nd:YAP laser operating at 1.34 μm. The laser system with different crystal lengths, output couplers and cavity types were compared. Based on optimizing of the pump system and laser cavity, 6.2 W laser radiation at 1341.4 nm with c-axis polarized was achieved, corresponding to an optical conversion efficiency of about 24.8% with respect to the incident pump power. The laser threshold was only about 1.3 W and the optical slope efficiency was up to 27.2%.     

Growth, polarized spectral properties, and 1.5–1.6 μm laser operation of Er:Yb:Sr3Gd2(BO3)4 crystal

An Er:Yb:Sr₃Gd₂(BO₃)₄ crystal was grown by the Czochralski method. The polarized spectral properties of the crystal were investigated, including the polarized absorption and fluorescence spectra and fluorescence decay. The fluorescence quantum efficiency of the upper laser level ⁴I_13/2 of Er³⁺ ions and the efficiency of the energy transfer from Yb³⁺ to Er³⁺ ions were calculated. End-pumped by a diode laser at 970 nm in a hemispherical cavity, a 1.6 W quasi-cw laser at 1.5–1.6 μm with a slope efficiency of 18% and an absorbed pump threshold of 5.9 W was achieved in a 1.8-mm-thick Z-cut Er:Yb:Sr₃Gd₂(BO₃)₄ crystal. This crystal has a flat and broad gain curve at 1.5–1.6 μm and so is also a potential gain medium for tunable and short pulse lasers.     

Optical spectroscopy, 1.5 μm emission and up-conversion properties of Er-doped Li3Ba2Gd3(MoO4)8 crystal

Er³⁺:Li₃Ba₂Gd₃(MoO₄)₈ crystal has been grown from a melt of Li₂MoO₄ by the top seeded solution growth method (TSSG). The polarized spectral properties of Er³⁺:Li₃Ba₂Gd₃(MoO₄)₈ crystal were investigated and the spectroscopic parameters were calculated and analyzed based on the Judd-Ofelt (J-O) theory. The emission cross-sections were calculated by the Fuchtbauer-Ladenburg (F-L) equation and the peak values of the emission band at 1535 nm were 9.7×10⁻²¹, 7.9×10⁻²¹ and 8.4×10⁻²¹ cm² for E∥b, E∥D1 and E∥D2, respectively. Under 977 nm excitation five up-conversion fluorescence bands around 490, 530, 550, 660 and 800 nm were observed, and the possible up-conversion mechanisms were proposed.     

Magnetic,transport and microstructural properties of polycrystalline samples with nominal composition of La0.7Ca0.3Mn1−xVxO3 (0⩽x⩽0.2)

Polycrystalline samples with nominal composition of La_0.7Ca_0.3Mn_1−xV_xO₃ (0?x?0.2) sintered in air were investigated by ac susceptibility, dc magnetization, magnetoresistance (MR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and differential thermal analysis (DTA) measurements. It is found that V could not substitute for Mn to form La_0.7Ca_0.3Mn_1−xV_xO₃ phase when the samples are sintered in air. The obtained samples contain several phases such as (La, Ca)Mn_1−δO₃, LaCa₃V₃O₁₂, Mn₃O₄ phases, etc. and constitute multi-phase composites. The Curie temperature T_C and spontaneous magnetization of the composites decrease, and the resistance of the composites increases as the V content increases. The addition of V may effectively improve the low-field MR response at low temperatures due to the variation in the microstructure of the composites.     

Structural,magnetic, and transport properties in La(2+4x)/3Sr(1−4x)/3Mn1−xCuxO3 (0⩽x⩽0.20) system

A series of the double-doping samples La_(2+4x)/3Sr_(1−4x)/3Mn_1−xCu_xO₃(0?x?0.2)$(0?x?0.2)$ with the Mn³⁺/Mn⁴⁺ ratio fixed at 2:1 have been prepared. The structural, magnetic, transport properties and magnetoresistance of the series samples have been investigated. It is found that no apparent crystal structure change is introduced by Cu doping up to x=0.20$x=0.20$. But the Curie temperature _TC$T_{\mathrm{C}}$ and magnetization M   are strongly affected by Cu substitution. A remarkable magnetotransport behavior, characterized by double bumps, is observed, and an obvious low-temperature upturn is found in the range of 0.07?x?0.12$0.07?x?0.12$. As a result, the temperature range of colossal magnetoresistance (CMR) is greatly broadened. Moreover, it is found that the room temperature magnetoresistance (MR) of double-doping samples is obviously larger that the undoped La_2/3Sr_1/3Mn_1−xCu_xO₃ at 300 K, which can give a guide for the adequate selection of the room temperature CMR materials.     

Electrical conductivity and magnetic properties of La1 ? xCaxMn1 ? yFeyO3 ceramic samples (x = 0.67, y = 0, 0.05)

The temperature dependences of the magnetic susceptibility χ(T) and the electrical resistivity ρ(T) of ceramic samples of La_{1 − x} Ca _x MnO₃ with x = 0.67 (LCMO) and La_{1 − x} Ca _x Mn_{1 − y} Fe _y O₃ with x = 0.67 and y = 0.05 (LCMFO) are investigated in magnetic fields B = 50–10⁵ G and the temperature range T = 4.2–400 K. Both samples undergo a transition from the paramagnetic state to a state with charge (orbital) ordering (CO) at temperatures T _CO ≈ 272 K for LCMO and T _CO ≈ 222 K for LCMFO. The behavior of the paramagnetic phase in the temperature range 320–400 K for LCMO and 260–400 K for LCMFO is described by the Curie-Weiss law with effective Bohr magneton numbers p _eff = 4.83 μ_B (LCMO) and 4.77 μ_B (LCMFO), respectively. The disagreement between the observed positive Weiss temperatures (θ ≈ 175 K (LCMO) and θ ≈ 134 K (LCMFO)) and negative Weiss temperatures required for the antiferromagnetic ground state can be explained by the phase separation and transition to the charge-ordered state. The magnetic irreversibility for T < T _CO is accounted for by the existence of a mixture of the ferromagnetic and antiferromagnetic phases, as well as the cluster glass phase. At low temperatures, doping with iron enhances the frustration of the system, which manifests itself in a more regular behavior of the decay rate of the remanent magnetization with time. The temperature dependence of the electrical resistivity in the range of the charge-ordered phase conforms to the variable-range hopping model. The behavior of the electrical resistivity is governed by the complex structure of the density of localized states near the Fermi level, which includes a soft Coulomb gap Δ = 0.464 eV for LCMO and 0.446 eV for LCMFO. It is established that the ratio between the localization radii of charge carriers a for LCMFO and a _und for LCMO is a/a _und = 0.88. Original Russian Text ? V.S. Zakhvalinskiĭ, R. Laiho, T.S. Orlova, A.V. Khokhulin, 2008, published in Fizika Tverdogo Tela, 2008, Vol. 50, No. 1, pp. 61–68.