We report on a comparative study of a transparent Fe:MgAl2O4 (spinel) ceramics and a transparent nanophase Fe:MgAl2O4-based glass-ceramics. The 0.1 mol% Fe:MgAl2O4 ceramics was synthesized by hot ...pressing (at 1500 °C/50 MPa) of powders obtained by the sol-gel method using LiF as a sintering aid. The Fe:MgAl2O4 ceramic is a single-phase material (cubic structure, sp. gr. Fd3‾m, a = 8.083 Å) with a mean grain size of ~50 μm. The ceramic exhibits a broadband transparency of 0.2–6.0 μm and a high in-line transmission at ~1 μm of 74.4%. The iron ions are presented in the ceramics in the single state of Fe2+ species in tetrahedral (Td) sites. A broad absorption band spanning from ~1.2 to 3.7 μm assigned to the 5E → 5T2 (5D) transition of Fe2+ ions in Td sites is observed, corresponding to a ground-state absorption cross section of 0.28 × 10−18 cm2 at 1.90 μm. The glass-ceramics were prepared by secondary two-stage heat-treatments of the magnesium aluminosilicate glass nucleated by titanium oxide and doped with 0.1 mol% FeO. Transparent Fe:MgAl2O4-based glass-ceramics obtained at the temperature of the second stage of 800–1000 °C were multi-phase materials containing two crystalline nanophases, i.e., spinel (mean size: 3.7–7.4 nm) and magnesium aluminotitanate solid solution (mean size: 6.4–20.6 nm), as well as residual silica-rich glass. Glass-ceramics obtained at the temperature of the second stage of 1050 °C were transparent and based on Fe-doped sapphirine. For glass-ceramics, absorption has a much more complex character as it is caused by interplay of iron and titanium ions in different valence states, coordination sites and locations. The iron ions enter the spinel nanocrystals but unlike the ceramic, in the form of both VIFe2+ and IVFe2+ species. The developed ceramics and glass-ceramics are promising for saturable absorbers of mid-infrared (2–3 μm) lasers.
•A comparative study of Fe-doped MgAl2O4 transparent ceramics and glass-ceramics.•Ceramics synthesized by hot pressing at 1500 °C/50 MPa using a sintering aid (LiF).•GCs synthesized by heat-treatments of a MgO–Al2O3–SiO2 glass nucleated by TiO2.•The absorption of ceramics is due to the 5E. → 5T2(5D) transition of Fe2+ ions in Td sites;•For GCs, absorption is caused by iron and titanium ions in different valence states.
Transparent glass-ceramics (GCs) based on Co2+-doped γ-GaxAl2−xO3 spinel nanocrystals were developed in the lithium aluminogallosilicate glass system with TiO2 as a nucleating agent. The initial ...glass contains spinel nanocrystals with sizes less than 3 nm. Secondary heat-treatments in the temperature range of 680–800 °C result in fabrication of transparent GCs based on γ-GaxAl2−xO3 crystals enriched in aluminum with cubic spinel structure (sp. gr. Fd3m) and a mean size up to 5.5 nm. At higher temperatures, GCs become translucent and then opaque due to additional crystallization of lithium aluminosilicate solid solutions (ss) with β-quartz structure and lithium aluminogallium silicate ss with β-spodumene (keatite) structure. The introduction of gallium oxide improves the temperature stability of spinel crystals that are not decomposed at high heat-treatment temperatures when aluminosilicate crystals evolve. The Co2+ ions in GCs enter the spinel crystals predominantly in tetrahedral sites. Transparent GCs feature broadband absorption (1.15–1.7 μm) owing to the 4A2(4F) → 4T1(4F) transition of IVCo2+ species in spinel nanocrystals. They exhibit saturable absorption and high ground-state absorption (GSA) cross-section σGSA of 3.1 ± 0.4 × 10−19 cm2 at 1.54 μm. Glass-ceramic based on γ-GaxAl2−xO3 crystals is employed as a saturable absorber of an eye-safe diode-side-pumped Er3+,Yb3+:glass laser delivering 1.1 mJ/42 ns pulses at 1535 nm.
•Transparent glass-ceramics (GCs) with γ-Co2+:GaxAl2−xO3 nanocrystals were prepared.•The introduction of gallium oxide improves the temperature stability of spinel crystals.•GCs feature broadband 4A2(4F).→4T1(4F) absorption of Co2+ ions in Td sites in spinel.•The ground-state absorption cross-section of Co2+ ions is 3.1 ± 0.4 × 10−19 cm2 at 1.5 μm.•GC is employed as a saturable absorber of an eye-safe Er,Yb:phosphate glass laser.
We present a comparative study of two Lu-based oxide ceramics doped with Yb3+ ions, namely Yb:Lu3Al5O12 (garnet) and Yb:Lu2O3 (sesquioxide), promising for thin-disk lasers. The ceramics are ...fabricated using nanopowders of 3.6 at.% Yb:Lu2O3 and Al2O3 produced by laser ablation: Yb:Lu3Al5O12 – by vacuum sintering at 1800 °C for 5 h with the addition of 1 wt% TEOS as a sintering aid, and Yb:Lu2O3 – by vacuum pre-sintering at 1250 °C for 2 h followed by Hot Isostatic Pressing at 1400 °C for 2 h under Ar gas pressure of 207 MPa. The comparison includes the structure, Raman spectra, transmission, optical spectroscopy and laser operation. The crystal-field splitting of Yb3+ multiplets is revealed for Lu3Al5O12. A continuous-wave (CW) Yb:Lu3Al5O12 ceramic microchip laser generates 5.65 W at 1031.1 nm with a slope efficiency of 67.2%. In the quasi-CW regime, the peak power is scaled up to 8.83 W. The power scaling for the Yb:Lu2O3 ceramic laser is limited by losses originating from residual coloration and inferior thermal behavior.
Tm3+,Ho3+-codoped and compositionally “mixed” disordered Ca(Ga,Lu)AlO4 aluminate crystals are promising materials for ultrashort pulse generation above 2 μm. Their polarized spectroscopic properties ...are studied and the effect of Lu3+ codoping on the inhomogeneous spectral broadening is verified. The peak stimulated-emission cross-section for the 5I7 → 5I8 Ho3+ transition is 1.05 × 10−20 cm2 at 2000 nm for π-polarization. The Tm3+ ↔ Ho3+ energy-transfer parameters are P28 = 1.42 and P71 = 0.090 10−22 cm3μs−1 indicating a direct transfer with a thermal equilibrium time of 4.35 ms. The effective gain spectra for the codoped crystal are derived. For σ-polarization, the gain bandwidth at ∼2.04 μm is about 100 nm; particularly for this light polarization, Lu3+ codoping induces a noticeable red-shift of the emission spectra further beyond 2 μm. Using absorption studies at 12 K, the Stark splitting of the Tm3+ and Ho3+ multiplets is resolved. A laser-pumped Tm,Ho:Ca(Ga,Lu)AlO4 laser generated a maximum output power of 763 mW at 2078.6 nm with a slope efficiency of 26.4% and π-polarized emission. A continuous wavelength tuning between 1887.7 and 2127 nm (tuning range: 239.3 nm) was achieved for σ-polarization. Diode-pumped operation of a-cut and c-cut crystals was also studied.
•Tm3+,Ho3+-codoped “mixed” disordered Ca(Ga,Lu)AlO4 aluminate crystal.•The effect of Lu3+ codoping on the inhomogeneous spectral broadening is verified.•For σ-polarization, the gain bandwidth at ∼2.04 μm is about 100 nm.•The Tm,Ho:Ca(Ga,Lu)AlO4 laser generated 763 mW at 2078.6 nm in π-polarization.•A continuous wavelength tuning between 1887.7 and 2127 nm was achieved.
We report on the crystal growth, spectroscopy and first laser operation of a novel double molybdate compound - Tm:KY(MoO
)
. This orthorhombic (sp. gr. Pbna) crystal exhibits strong anisotropy of the ...spectroscopic properties due to its layered structure. The maximum stimulated emission cross-section for the
F
→
H
transition is 2.70×10
cm
at 1856nm with a bandwidth of >110 nm (for E || b). The lifetime of the
F
state is 2.29 ms. Crystalline films and plates (thickness down to 70 µm) of high optical quality are obtained by mechanical cleavage along the (100) plane. Continuous-wave diode-pumped laser operation is achieved in such thin films and plates yielding a maximum output power of 0.88 W at ∼1.9 µm with a slope efficiency of 65.8% and a linearly polarized laser output. Vibronic lasing is demonstrated at ∼2.06 µm. Tm:KY(MoO
)
is promising for microchip and thin-disk lasers.
We report on the crystal growth, spectroscopy characterization and first laser operation of a new tetragonal disordered "mixed" calcium aluminate crystal, Tm:Ca(Gd,Lu)AlO
. The introduction of Lu
...leads to an additional inhomogeneous broadening of Tm
absorption and emission spectra compared to the well-known Tm:CaGdAlO
. The maximum stimulated-emission cross-section for the
F
→
H
Tm
transition is 0.91 × 10
cm
at 1813 nm for σ-polarization, and the emission bandwidth is more than 200 nm. A continuous-wave diode-pumped Tm:Ca(Gd,Lu)AlO
laser generates 1.82 W at 1945 nm with a slope efficiency of 29%. Under Ti:Sapphire laser pumping, a continuous tuning of the laser wavelength from 1836 to 2083 nm (tuning range: 247 nm) is demonstrated. The Tm:Ca(Gd,Lu)AlO
crystal is promising for tunable/femtosecond lasers at ~2 μm.
A microchip laser is realized on the basis of a monoclinic Tm,Ho-codoped KLu(WO₄)₂crystal cut for light propagation along the Ng optical indicatrix axis. This crystal cut provides positive thermal ...lens with extremely weak astigmatism, S/M = 4%. High sensitivity factors, M = dD/dP(abs), of 24.9 and 24.1 m(-1)/W for the mg- and pg- tangential planes are calculated with respect to the absorbed pump power. Such thermo-optic behavior is responsible for mode stabilization in the plano-plano microchip laser cavity, as well as the demonstrated perfect circular beam profile (M(2) < 1.1). Maximum continuous-wave output power of 450 mW is obtained with a slope efficiency of 31%. A set of output couplers is employed to achieve lasing in the spectral range of 2060-2096 nm. The increase of output coupler transmission results in deterioration of the laser performance attributed to the increased up-conversion losses.
Novel multicomponent garnet phosphors, Ca2Y1–xEuxSc2GaSi2O12 (x = 0, 0.05, 0.1, 0.25 and 0.5), have been synthesized by a high-temperature solid-state reaction method using the precursors obtained ...under hydrothermal conditions. Their structures, morphology and vibronic properties have been studied by XRD, SEM methods and Raman spectroscopy. It has been found that ceramic phosphor pellets consist of microcrystals having a narrow size distribution and a mean size of 1 μm with a maximum phonon energy of 864 cm−1 for the crystal lattice of these compositions. Under UV and blue excitation, Eu3+:Ca2YSc2GaSi2O12 phosphors exhibit red f-f luminescence of Eu3+ ions at the distorted D2 site of the garnet structure and broadband blue and red emissions centered at ∼417 nm, 600 nm and 770 nm as ascribed to the defects of the garnet host. The quantum yield of luminescence reaches 26% for Ca2Y0.75Eu0.25Sc2GaSi2O12. The spectroscopic properties of Eu3+ ions have been characterized with the Judd-Ofelt (J-O) theory and luminescence decay studies. The J-O parameters are Ω2 = 2.212, Ω4 = 2.888, and Ω6 = 2.259 10−20 сm2 and the luminescence quantum efficiency for Eu3+ ions ηq is 83% in Ca2Y0.95Eu0.05Sc2GaSi2O12. The developed materials are promising as color-tunable phosphors.
•Novel multicomponent silicate garnet phosphors, Ca2Y1–xEuxSc2GaSi2O12.•Ceramic pellets synthesized by a high-temperature solid-state reaction method.•The study of structure, morphology, vibronic and luminescent properties.•The quantum yield of luminescence reaches 26% for Ca2Y0.75Eu0.25Sc2GaSi2O12.•Broadband blue and red emissions centered at ∼417 nm, 600 nm and 770 nm.
A high quality Yb
3+
-doped strontium lanthanum aluminate crystal, Yb:SrLaAlO
4
(Yb:SLA) is grown by the Czochralski method. It is tetragonal (sp. gr.
I
4/
mmm
,
a
=
b
= 3.7536 Å,
c
= 12.6253 Å). ...Room- and low-temperature spectroscopy of Yb
3+
ions in this crystal are studied. The Stark splitting is resolved. Absorption, stimulated-emission (SE) and gain cross-sections are determined with polarized light. In the spectral range of laser emission, the maximum
σ
SE
is 0.57 × 10
−20
cm
2
at 1047 nm for
σ
polarization. The polarized Raman spectra of Yb:SLA are presented. Thermal properties of Yb:SLA are characterized in terms of the linear thermal expansion, specific heat and thermal conductivity. The latter is as high as 6.06 and 4.30 W m
−1
K
−1
along the
a
- and
c
-axes, respectively (at room temperature). Broadband tuning of a continuous-wave (CW) Yb:SLA laser, from 1011 to 1082 nm has been achieved. Due to its good thermal properties, broad and smooth gain spectra, Yb:LSA is a promising material for power-scalable, broadly tunable CW and sub-100 fs mode-locked lasers at ∼1 μm.
A high quality Yb
3+
-doped strontium lanthanum aluminate crystal, Yb:SrLaAlO
4
is grown by the Czochralski method.
We report on highly-efficient laser operation in the orthorhombic Nd3+:KY(MoO4)2 (Nd:KYMo) double molybdate crystal. 2 at.% Nd:KYMo crystals were grown by the Czochralski method under low temperature ...gradients. Under Ti:Sapphire laser pumping at 874 nm (in-band, 4I9/2 → 4F3/2 transition), a compact continuous-wave (CW) c-cut Nd:KYMo laser generated 0.43 W at 1067 nm with a slope efficiency of 71% (with respect to the absorbed pump power) and a laser threshold of only 40 mW. For a standard pump wavelength of ~810 nm, the peak output was scaled to 0.55 W in a quasi-CW mode. A negative thermal lens has been detected for Nd:KYMo.
PDF
