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DOI: 10.1364/OE.25.003682 URL: https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-4-3682 Filiació URV: SI Memòria We report on the crystal growth, spectroscopic investigation and laser performance of Tm3+-doped monoclinic magnesium tungstate (Tm:MgWO4), for the first time, to the best of our knowledge. A high-quality crystal has been grown by the top seeded solution growth method. The relevant spectroscopic properties are characterized in terms of absorption, luminescence and Raman spectroscopy. Judd-Ofelt (J-O) analysis is performed to evaluate the spontaneous emission probabilities and the radiative lifetimes. The absorption, stimulated-emission and gain cross-section spectra are determined for the principal light polarizations. The first laser action in the 2 ¿m spectral range is demonstrated in the regime of continuous-wave operation with a maximum output power of 775 mW and a slope efficiency of 39%.

Filiació URV: SI We report on a Holmium micro-laser passively Q-switched by a semiconductor saturable absorber (SSA), for the first time to the best of our knowledge. It is based on a 1 at.% Ho:YAG ceramic with good energy storage capability and several commercial transmission-type SSAs with 0.24% modulation depth. Under in-band pumping by a Tm fiber laser at 1910 nm, the Ho micro-laser generated 450 mW at 2089 nm with 37% slope efficiency. Stable 89 ns, 3.2 ¿J pulses are achieved at a repetition rate of 141 kHz. Further shortening of the laser pulses is feasible with the increase of the modulation depth of the SSA while power scaling may lead to Q-switching at MHz-range repetition rates.

Filiació URV: SI We report on the growth and the structural, thermal, vibronic and spectroscopic properties of a complex molybdate single-crystal, Li2Mg2(MoO4)3 (LiMgMo), doped with Eu3+ or Ce3+ ions. Few cm size crystals were grown from the flux using Li2MoO4 as a solvent. Eu:LiMgMo is orthorhombic (sp. gr. Pnma, ¿=5.085 Å, b=10.482 Å¿ ¿=17.614 Å). It exhibits strongly polarized Raman spectra with the most intense band at 905.2 cm¿1. Eu:LiMgMo possesses positive thermal expansion. Using the Eu3+ ion as a structural probe, we argue its predominant accommodation in a single type of site A(3) with a trigonal prismatic coordination. The spectroscopy of Eu3+ is characterized by the lifetime measurement (¿(5D0)=537 ¿s), Judd-Ofelt modeling (¿2=21.811, ¿4=7.805 and ¿6=1.203 [10¿20 ¿m2]) and the calculation of stimulated-emission cross-sections for the 5D0¿7FJ¿ (J¿=0¿6) transitions. The LiMgMo crystals are promising for rare-earth-ion doping with application as laser materials and Raman shifters.

DOI: 10.1364/OME.7.000844 URL: https://www.osapublishing.org/ome/abstract.cfm?uri=ome-7-3-844 Filiació URV: SI Memòria We report on a detailed comparative study of the spectroscopic and thermo-optic properties of tetragonal Tm:LiLnF4 (Ln = Y, Gd, and Lu) crystals indicating their suitability for highly-efficient microchip lasers diode-pumped at ~791 nm and operating at ~1.91 ¿m. An a-cut 8 at.% Tm:LiYF4 micro-laser generated 3.1 W of linearly polarized output at 1904 nm with a slope efficiency of ¿ = 72% and a laser threshold of only 0.24 W. The internal loss for this crystal is as low as 0.0011 cm-1. For 8 at.% Tm:LiGdF4 and 12 at.% Tm:LiLuF4 lasers, the output power reached ~2 W and ¿ was 65% and 52%, respectively. The thermal lens in all Tm:LiLnF4 crystals is weak, positive and low-astigmatic. The potential for the Tm:LiLnF4 lasers to operate beyond ~2 ¿m due to a vibronic coupling has been proved. The Tm:LiYF4 vibronic laser generated 375 mW at 2026-2044 nm with ¿ = 31%. The Tm:LiLnF4 crystals are very promising for passively Q-switched microchip lasers.

DOI: 10.1016/j.jlumin.2017.04.007 URL: http://www.sciencedirect.com/science/article/pii/S0022231316312674 Filiació URV: SI Influence of pre-irradiation annealing temperature on the efficiency of the subsurface color center formation in γ-irradiated lithium fluoride nanocrystals has been studied. Increase of the annealing temperature reduces the efficiency of formation of these centers. Nanocrystals lose their ability to form subsurface color centers after pre-irradiation annealing at 623 K and higher temperatures. The formed subsurface color centers are partially transformed into the usual centers of the same composition during the post-radiation annealing at certain temperatures. It has been shown that the mechanical fragmentation of lithium fluoride crystals leads to the formation of nanosized clusters in their subsurface layer. Subsurface radiation color centers which are located near the clusters are subjected to the modified crystal field. This circumstance causes strong differences between the luminescent characteristics of subsurface color centers and usual centers of the same composition in the crystal bulk, where there are no clusters. The clusters are completely destroyed after annealing the samples at 623 K and higher temperatures. The obtained results indicate that the presence of nanoclusters is a prerequisite for the formation of subsurface radiation color centers with specific fluorescent properties. The thickness of the subsurface layer, where subsurface color centers can be formed, has been estimated.