We report on the fabrication and optical properties of erbium-doped Y2O3-MgO and Gd2O3-MgO nanocomposite ceramics, with a particular focus on their mid-infrared emission. The ceramics were fabricated by a self-propagating high-temperature synthesis followed by hot pressing. The transmittance of 1.7 mm-thick 5 at.% Er:Y2O3-MgO and 7 at.% Er:Gd2O3-MgO ceramics at 3 mu m amounted to 79.4% and 21.5%, respectively. This difference in transmission, as revealed by microstructural analysis, is due to variation in the distribution of residual pore sizes, while the average grain size is almost the same for both ceramics, being similar to 200 nm. The composites exhibited luminescence in the visible, near-infrared, and mid-infrared spectral ranges attributed to electronic transitions of Er3+ ions in the cubic sesquioxide phase. Peculiarities in the Raman and luminescence spectra were identified in comparison to single-phase Er:Y2O3 and Er:Gd2O3 ceramics, which may indicate certain solubility of MgO in the sesquioxide phase of the composites.

Spectroscopy and mid-infrared laser performance are compared for Er:CaF2 single-crystal and hot-pressed transparent ceramic. The 2.8-µm Er:CaF2 crystal laser delivers 0.81 W with 32.6% slope efficiency and outperforms the ceramic due to enhanced ion clustering.

Co-doped laser materials with two active ions coupled by energy transfer is an interesting case where both ions can take part in the laser output intensity. Depending on the concentration of both co-dopants, the strength of the energy transfer coupling them or even the pumping rate, a competition between the two ions can take place which will affect the laser characteristics such as the laser wavelength. This competition between two emitting ions is illustrated here in the case of CaF2 co-doped with neodymium and ytterbium ions. The advantage of Nd3+ is that its absorption cross-section around 791nm is higher than that of Yb3+ at similar to 980nm, enabling an efficient excitation of Yb3+ by pumping Nd3+ with a subsequent Nd3+-to-Yb3+ energy transfer (ET). Combining Nd3+ and Yb3+ with Gd3+ buffer ions further enables breaking up optically-quenched Nd3+ clusters. Nd3+,Yb3+,Gd3+: CaF2 crystals exhibit broadband emission, extending the Yb3+ spectrum via the Nd3+ contribution at longer wavelengths. Before addressing the laser gain competition between Nd3+ and Yb3+ ions, the Nd3+.Yb3+ ET efficiency was estimated using two approaches based on luminescence intensity and lifetimes, showing its dependency on Yb3+ doping. We achieved an ET efficiency of 80% in 0.5%Nd,3%Yb,2%Gd:CaF2. CW laser action using different Nd,Yb,Gd:CaF2 crystals resulted in a 17% slope efficiency versus absorbed pump power and a 200mW laser threshold. The expected laser gain competition between Nd3+ and Yb3+ ions leads to a change of the laser wavelength within the 1045-1067nm range depending on the Yb3+ concentration and output coupler transmission. These results are clearly explained by investigating the respective contribution of Nd3+ and Yb3+ to the gain cross-section and its dependence on Yb3+ doping concentration and Nd3+ population inversion. The gain cross-section profile is either dominated by one of the Nd3+ emission peaks (1065nm, 1048nm), or flat across 1045-1067nm, in which case the laser oscillates randomly within this spectral range. We show how a large Nd3+ inversion ratio leads to depletion of the Yb3+2F7/2 ground state through ET, resulting in two main effects: the saturation of the ET, as the ground-state Yb3+ acceptor concentration diminishes, and a shift of the laser line towards shorter wavelengths, due to weaker Yb3+ reabsorption.

The effect of doping level (0.1-10 at.%) on mid-infrared laser performance of Er:CaF2 crystals was investigated. The Er:CaF2 laser delivered 1.17 W at 2798 nm with 35.8% slope efficiency and was tuned across 2690-2830 nm.

We report on a polarization-resolved study of mid-infrared emission properties of Er 3+ -doped orthorhombic yttrium aluminum perovskite YAlO 3 single crystal. For the 4 I 11/2 → 4 I 13/2 Er 3+ transition, the stimulated emission cross section is 0.20 × 10 −20 cm 2 at 2919 nm for light polarization E ‖ c . Pumped by an Yb-fiber laser at 976 nm, the 10 at.% Er:YAlO 3 laser delivered 1.36 W at 2919 nm with a slope efficiency of 31.4%, very close to the Stokes limit, a laser threshold as low as 33 mW and a linear polarization. Pump-induced polarization switching between E || b and E || c eigen states was observed and explained by excited-state absorption from the terminal laser level.

A GaSb-based SEmiconductor Saturable Absorber Mirror (SESAM) enables continuouswave picosecond mode -locked operation with excellent stability of a polarization -maintaining mid -infrared Er:ZBLAN fiber laser. The GaSb-based SESAM mode -locked fiber laser delivers an average output power of 190 mW at 2.76 mu m at a repetition rate of 32.07 MHz (corresponding to a pulse energy of -6 nJ) and exhibits a high signal-to-noise ratio of -80 dB. The polarization extinction ratio is more than 23 dB. By employing an intracavity diffraction grating, the laser wavelength is continuously tunable across 2.706-2.816 mu m. Passively Q -switched operation of this laser is also demonstrated. (c) 2024 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

We present sub-50 fs soliton pulse generation from a diode-pumped Kerr-lens mode-locked laser based on an Yb3+-doped BaF2 crystal. Utilizing a spatially single-mode, fiber-coupled InGaAs laser diode at 976 nm as a pump source, the Yb:BaF2 laser generates pulses as short as 46 fs at 1060.1 nm with an average output power of 45 mW at a pulse repetition rate of ~65.6 MHz via soft-aperture Kerr-lens mode locking. To the best of our knowledge, this represents the first demonstration of Kerr-lens mode-locked operation of the Yb:BaF2 crystal, as well as the shortest pulse duration ever achieved from any diode-pumped mode-locked laser based on an Yb3+-doped alkaline-earth fluoride crystal.

A diode-pumped Kerr-lens mode-locked laser generating 25 fs pulses at 1080 nm is demonstrated with an Yb3+-doped compositional mixed calcium aluminate crystal. The Yb:Ca(Gd,Y)AlO4 laser, which operates at a repetition rate of 65.6 MHz via soft-aperture Kerr-lens mode-locking, is pumped by a spatially single-mode, fiber-coupled diode laser. To the best of our knowledge, this is the first Kerr-lens mode-locked laser that utilizes an Yb3+-doped compositional mixed calcium aluminate crystal as the gain medium.

Erbium-doped “mixed” yttria-scandia (ScxY1-x)2O3 transparent laser ceramics were fabricated by vacuum sintering at 1750 °C from laser-ablated nanoparticles. Their absorption and mid-infrared emission properties were studied. The addition of Sc3+ induces a strong inhomogeneous spectral line broadening, modifies the crystal field and affects the distribution of Er3+ ions over C2 and C3i symmetry sites. Due to their broadband emission properties, Er:(ScxY1-x)2O3 ceramics are appealing for 2.8-μm lasers.

Rare-earth-doped transparent sesquioxide laser ceramics enable engineering of their gain bandwidths via solid-solution compositions exhibiting a strong inhomogeneous spectral line broadening. We report on a detailed spectroscopic study and the first mid-infrared laser operation of Erbium-doped yttria-scandia, (ScxY1-x)(2)O-3, ceramics fabricated by vacuum sintering at 1750 degrees C from laser-ablated nanoparticles. The effect of the Sc fraction on the spectral and kinetic properties of Er3+ emission around 2.8 mu m owing to the I-4(11/2) -> I-4(13/2) is revealed. The inhomogeneous spectral line broadening leading to merging of individual Stark sub-levels of Er3+ multiplets is evidenced by low-temperature spectroscopy. An original method of quantifying the distribution of dopant Er-3+ ions over C-2 and C-3i symmetry sites in the cubic bixbyite structure is suggested based on the transition probabilities derived by the Judd-Ofelt theory. In the parent Er:Y2O3 ceramic, the Er3+ ions nearly follow the ideal distribution with 3/4 of ions residing in C-2 sites, and Sc addition skews it in favor of C-3i sites. A continuous-wave Er:(Sc,Y)(2)O-3 ceramic laser generated 312 mW at 2716 nm with a slope efficiency of 18.6 % and a laser threshold of 128 mW.

We report on a mid-infrared erbium planar waveguide laser operating on the 4I11/2 → 4I13/2 transition. It employs a heavily doped 10.6 at. % Er3+:LiYF4 single-crystalline layer grown by liquid-phase epitaxy. The waveguide laser delivers a maximum output power of 191 mW at ∼2809 nm with a slope efficiency of 15%, a linear polarization, and a laser threshold of 134 mW. The waveguide propagation losses are 0.4 ± 0.2 dB/cm. The polarized spectroscopic properties of the Er3+:LiYF4 layers are also investigated. The stimulated-emission cross section of Er3+ ions amounts to 0.87 × 10−20 cm2 at 2809 nm for π-polarization. Er3+:LiYF4 epitaxial layers represent a promising platform for integrated low-loss mid-infrared light sources.

We report on polarized spectroscopic properties of Ho3+ ions in orthorhombic (sp. gr. Pnma) yttrium orthoaluminate YAlO3 crystals for laser development at 2 mu m and 3 mu m. This includes polarized Raman, absorption and luminescence spectra, fluorescence lifetime measurements and Stark energy-level study. The transition intensities for Ho3+ ions are calculated using the Judd-Ofelt theory. The peak stimulated-emission cross-sections are 2.01x10(-20) cm(2) at 1977 nm (I-5(7) -> I-5(8)) and 2.31x10(-20) cm(2) at 2918 nm (I-5(6) -> I-5(7)) for light polarization E parallel to b. For both transitions, pump-induced polarization-switching is expected. The fluorescence lifetimes of the I-5(7) and I-5(6) Ho3+ manifolds are 7.27 and 0.36 ms, respectively (for 1 at.% Ho3+-doping).

We report on polarization-resolved spectroscopy and excited-state dynamics of Er3+ ions in CALGO highlighting its potential for mid-infrared lasers. The stimulated-emission cross-section is 2.63×10-20 cm2 at 2730 nm for π-polarization (emission bandwidth: 28 nm).

We report on a detailed spectroscopic study of heavily Er3+-doped LiYF4 epitaxial layers with the goal of developing mid-infrared waveguide lasers. Layers with a doping level up to 11 at.% Er3+ were grown on (001) oriented undoped bulk LiYF4 substrates using LiF as a solvent. The absorption spectrum of Er3+ ions was measured. Under excitation at 973 nm, the layers exhibited intense and strongly polarized mid-infrared luminescence spanning from 2.65 to 2.90 mu m related to the I-4(11/2) -> I-4(13/2) Er3+ transition. The peak stimulated-emission cross-section at the expected laser wavelength was calculated to be 0.88x10(-20) cm(2) at 2809 nm for pi-polarization. By means of low-temperature (12 K) spectroscopy, the experimental crystal-field splitting of Er3+ multiplets was determined. The luminescence dynamics from Er3+ excited states were studied. For the 11 at.% Er3+ doping, the luminescence lifetimes of the I-4(13/2) and I-4(11/2) manifolds amounted to 5.54 ms and 2.66 ms, respectively.

We present the growth, spectroscopy, continuous-wave (CW) and passively mode-locked (ML) operation of a novel "mixed" tetragonal calcium rare-earth aluminate crystal, Yb3+:Ca(Gd,Y)AlO4. The absorption, stimulated-emission, and gain cross-sections are derived for π and σ polarizations. The laser performance of a c-cut Yb:Ca(Gd,Y)AlO4 crystal is studied using a spatially single-mode, 976-nm fiber-coupled laser diode as a pump source. A maximum output power of 347 mW is obtained in the CW regime with a slope efficiency of 48.9%. The emission wavelength is continuously tunable across 90 nm (1010 - 1100 nm) using a quartz-based Lyot filter. With a commercial SEmiconductor Saturable Absorber Mirror to initiate and maintain ML operation, soliton pulses as short as 35 fs are generated at 1059.8 nm with an average output power of 51 mW at ∼65.95 MHz. The average output power can be scaled to 105 mW for slightly longer pulses of 42 fs at 1063.5 nm.

A detailed spectroscopic characterization of CaF2 co-doped with neodymium and ytterbium ions is presented. The higher Nd3+ absorption cross-section around 791 nm than Yb3+ around 980 nm enables an efficient excitation of Yb3+ ions by pumping Nd3+ with a subsequent energy transfer (ET) from Nd3+ to Yb3+ ions. By combining Nd3+ and Yb3+, along with Gd3+ buffer ions Nd3+,Yb3+,Gd3+:CaF2 crystals exhibit very large emission bands extending the usual Yb3+ emission spectrum by adding the Nd3+ emission contribution at longer wave-lengths. The Nd3+ -> Yb3+ energy transfer efficiency is estimated using two different approaches based on luminescence intensity measurements and lifetimes, giving consistent results. An energy transfer efficiency of 80 % is achieved in CaF2:0.5%Nd,3%Yb,2%Gd illustrating the ET strength within Nd3+-Yb3+ clusters. Finally, a detailed study of the gain cross-sections and laser emission spectra, and their dependence with Yb3+ doping concentration and population inversion is carried out, providing a detailed model of the laser spectral dynamics in such crystals. The gain cross-section is either dominated by one of the Nd3+ peaks at 1065 nm or 1048 nm or exhibits a flat profile covering the 1045-1067 nm range, in which case the laser oscillates randomly over this spectral range. The results highlight the specifics of the Nd3+ four level laser coupled by energy transfer to the Yb3+ quasi three level laser. Among others, this study shows how a large Nd3+ inversion ratio initiates the depletion of the Yb3+ 2F7/2 ground state through the ET. This depletion then has two effects as it saturates the energy transfer since the number of Yb3+ acceptors diminishes and it also shifts the laser wavelength towards shorter wavelength as the Yb3+ laser reabsorption is weakened.

The incorporation of responsive elements into photoniccrystalsis an effective strategy for fabricating active optical componentsto be used as sensors, actuators, and modulators. In particular, thecombination of simple multilayered dielectric mirrors with opticallyresponsive plasmonic materials has proven to be successful. Recently,Tamm plasmon (TP) modes have emerged as powerful tools for these purposes.These modes arise at the interface between a distributed Bragg reflector(DBR) and a plasmonic layer and can be excited at a normal incidenceangle. Although the TP field is located usually at the DBR/metal interface,recent studies have demonstrated that nanoscale corrugation of themetal layer permits access to the TP mode from outside, thus openingexciting perspectives for many real-life applications. In this study,we show that the TP resonance obtained by capping a DBR with a nanostructuredlayer of silver is responsive to Escherichia coli. Our data indicate that the modification of the TP mode originatesfrom the well-known capability of silver to interact with bacteria,within a process in which the release of Ag+ ions leavesan excess of negative charge in the metal lattice. Finally, we exploitedthis effect to devise a case study in which we optically differentiatedbetween the presence of proliferative and nonproliferative bacteriausing the TP resonance as a read-out. These findings make these devicespromising all-optical probes for bacterial metabolic activity, includingtheir response to external stressors.

We report on the first, to the best of our knowledge, laser operation on the 4I11/2 → 4I13/2 transition of erbium-doped disordered calcium lithium niobium gallium garnet (CLNGG) crystals with broadband mid-infrared emission properties. A 41.4 at.% Er:CLNGG continuous-wave laser generated 292 mW at 2.80 µm with 23.3% slope efficiency and a laser threshold of 209 mW. Er3+ ions in CLNGG feature inhomogeneously broadened spectral bands (σSE = 1.79 × 10-21 cm2 at 2.79 µm; emission bandwidth, 27.5 nm), a large luminescence branching ratio for the 4I11/2 → 4I13/2 transition of 17.9%, and a favorable ratio of the 4I11/2 and 4I13/2 lifetimes, exhibiting values of 0.34 ms and 1.17 ms (for 41.4 at.% Er3+), respectively.