We investigated in-band pumping of Tm,Ho,Lu:CaGdAlO4 (CALGO) using a Raman shifted Er-fiber laser (1678 nm) in the continuous-wave (CW) and mode-locked (ML) regimes. The 6-mm long, antireflection-coated, a-cut CALGO was doped with 4.48at.% Tm (sensitizer), 0.54at.% Ho (emission) and 5.51at.% Lu (compositional disorder). For mode-locking we employed a GaSb SESAM and chirped mirrors (round-trip group-delay dispersion: -1250 fs2). Pumping with 5.5 W (unpolarized), the average output power (0.2% output coupler) was 148 mW at ⁓96 MHz. The spectrum was centered at 2071.5 nm with a FWHM of 21.5 nm (sigma-polarization) and the pulse duration was 218 fs (time-bandwidth product: 0.327).
Yb3+,Li+ -codoped monoclinic zinc tungstate (ZnWO4) crystals with optimized Li+ content providing efficient local charge compensation were grown by the Czochralski method. Heavy Li+ codoping makes the Yb3+-doped ZnWO4 crystals less prone to cracking, improves the Yb3+ segregation, reduces the melting point and induces inhomogeneous spectral line broadening. The polarized absorption and stimulated-emission cross-sections of Yb3+ in ZnWO4 were determined. The maximum stimulated-emission cross-section σSE is 2.94×10-20 cm2 at 1055.5 nm corresponding to an emission bandwidth of 12.2 nm for light polarization E || Np. The formation of Yb3+ optical centers in singly Yb3+-doped and Yb3+,Li+ -codoped zinc monotungstate crystals is revealed by low-temperature spectroscopy. The Yb,Li:ZnWO4 laser pumped by a commercial 976-nm Yb-fiber laser generated 2.41 W at approximately 1.06 μm with a slope efficiency of 76.4%, a laser threshold of 143 mW and linear polarization.
We report on polarized spectroscopic properties of Ho3+ ions in orthorhombic (sp. gr. Pnma) yttrium orthoaluminate YAlO3 crystals for laser development at 2 μm and 3 μm. 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 2.01×10-20 cm2 at 1977 nm (5 I7 → 5 I8) and 2.31×10-20 cm2 at 2918 nm (5 I6 → 5 I7) for light polarization E || b. For both transitions, pump-induced polarization-switching is expected. The fluorescence lifetimes of the 5 I7 and 5 I6 Ho3+ manifolds are 7.27 and 0.36 ms, respectively (for 1 at.% Ho3+ -doping).
We demonstrate a diode-pumped SESAM mode-locked Yb:(Y,Gd)AlO3 laser delivering soliton pulses as short as 28-fs at 1063 nm with an average output power of 21 mW. The maximum average output power is scaled to 135 mW for a pulse duration of 37 fs.
Lasers emitting in the visible find applications in biology and medicine. Considering the success of near-infrared fiber lasers, the possibility to optically pump rare-earth-doped fibers in the blue to directly obtain visible emission is attractive. The recent progress in the field of GaN-based blue laser diodes offers new scopes. Dy3+-doped materials have received much interest because of their intense yellow emission originating from the 4F9/2→6H13/2 transition. An involvement of a glass matrix benefiting from enhanced thermo-mechanical properties would ease diode pumping. We report on the synthesis of a series of novel phosphate glasses in the system P2O5-Al2O3–BaO-K2O doped with Dy2O3. The Dy3+ concentrations were 0.05, 0.21, 0.83 and 2.5 [1020 ions/cm3]. The glasses were synthesized by the standard melt-quenching technique and thoroughly characterized in their physical, thermo-mechanical and optical properties. A Dy3+-doped optical fiber was drawn by preform drawing from the developed glasses, with the preform being obtained by rod-in tube technique, combining a cast core and an extruded cladding. Preliminary emission results in the visible from the fabricated fiber will be reported.
We report on the growth, structure and spectroscopy of an Er3+ -doped Na5Y9F32 (5NaF∙9YF3) crystal featuring significant inhomogeneous spectral broadening. Single-crystals of Na5Y9F32 doped with 0.22 – 9.63 at.% Er3+ were grown by the Czochralski method. Er:Na5Y9F32 exhibits a cubic fluorite-type structure (a = 5.4881(2) Å for 5.59 at.% Er3+ doping). The most intense Raman band of this material is found at ~404 cm-1 . Er3+ ions in Na5Y9F32 exhibit a broad and smooth emission band owing to the 4 I11/2 → 4 I13/2 transition with a maximum stimulated-emission cross-section of 0.42×10-20 cm2 at 2708 nm. According to the Judd-Ofelt analysis, the radiative lifetime of the 4 I11/2 multiplet is 10.0 ms and the luminescence branching ratio β( 4 I11/2 → 4 I13/2) is 17.6%. The luminescence lifetimes of the 4 I11/2 and 4 I13/2 Er3+ states were studied as a function of the doping concentration. For 5.59 at.% Er doping, they are 7.72 ms and 6.69 ms, respectively, representing a favorable ratio for mid-infrared laser operation.
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