M. D. Serrano

Nonlinear Refractive Indices in Disordered NaT(XO 4 ) 2 T = Y, La, Gd, Lu and Bi, X = Mo, W Laser Crystals

Nonlinear index has been measured using z-scan technique in tetragonal disordered double tungstate and molybdate laser crystals. The n2is comparable or larger than in monoclinic double tungstates, with substantial enhancement found in NaBi(WO4)2.

Tm-doped disordered molybdate crystals for ultrashort mode-locked solid state lasers

5 at% Tm-doped NaGd(MoO4)2 laser crystal operated in CW conditions provided up to 641 mW of output power at λ ≈ 1910 nm with a slope efficiency of 50.8% and a pump power laser threshold of 166 mW. 10 at% Tm-doped Li3Ba2Lu3(MoO4)8 laser operated in quasi-CW conditions provided up to 510 mW of output power at λ ≈ 1950 nm with a slope efficiency of 71.4% and a pump power laser threshold of 125 mW. Both crystals were grown by the Top Seeded Solution Growth method at about two hundreds degrees below their melting points. The structural disorder of these crystals confers inhomogenous broadening to the Tm3+ electronic transitions. Slightly broader laser tuning range and laser emission bandwidths are observed in the Li3Ba2Lu3(MoO4)8 crystal despite of the lower expected degree of crystalline disorder. The crystals are promising for the development of mode locked ultrafast (fs) lasers with emission close to λ = 2 μm.

Continuous-wave and mode-locked operation of diode-pumped Yb-NaY(WO4)2

We studied diode pumping of the locally disordered Yb-doped NaY(WO4)2 crystal. An a-cut 1.514-mm thick sample (6.9 at % Yb doping or 4.52×1020 cm-3) was placed under Brewster angle in a z-shaped astigmatically compensated cavity, without any active cooling. It was oriented for pumping and emission in π-polarization (E//c). Laser experiments were performed applying a high brightness laser diode as a pump source. The laser diode delivered up to 2.1 W of input power and the emission wavelength was selected in the broad absorption peak of Yb:NaY(WO4)2 around 961nm. Continuous-wave operation in the 1-μm range was obtained for output coupler transmission between 1% and 10%. A maximum output power of ≈180 mW and slope efficiencies up to 30%, related to the absorbed power, were achieved. For femtosecond mode-locked operation, a semiconductor saturable absorber mirror as well as two SF10 prisms were included in the cavity. Aligning the cavity for shortest pulses, we obtained stable passive mode-locking with pulse durations as short as 97 fs directly from the oscillator. Applying external compression, the pulse duration could be further reduced to 90 fs with a corresponding time-bandwidth-product of 0.321. The average output power amounted to 59 mW at a repetition rate of 90 MHz and the corresponding output spectrum was centered at 1044 nm.

Z-scan measurements of nonlinear refractive indices of NaT(XO4)2 T= Y, La, Gd, Lu and Bi, X= Mo, W, femtosecond laser crystals

The characterization of the coefficient of the nonlinear optical Kerr effect, the nonlinear refractive index (n2), of several femtosecond laser crystals with compositions derived by total or partial replacement of D2+ in DXO4, X = Mo or W, is presented. Tetragonal (space group I4) Na-based double tungstates NaT(WO4)2 (T = Y, La, Gd, Lu and Bi) and double molybdate NaY(MoO4)2, as well as the monoclinic (space group C2/c) Li3Gd3Ba2(MoO4)8 crystals, have been measured by the z-scan technique. All these crystals present structural local disorder, and among them the tetragonal ones exhibit significant n2 values, which should allow their efficient laser pulsed operation by Kerr-lens mode locking, especially NaBi(WO4)2, 68x10-16 cm2/W (for σ light), which is about twice than for the others. This feature is attributed to the high polarizability associated to the lone electron pair of Bi3+.

Tunable CW laser operation of Tm 3+ in locally disordered NaLa(WO 4 ) 2

We report now on lasing of Tm³⁺ in the isostructural host NaLa(WO₄)₂, shortly NaLaW, which was grown for the present work by the Czochralski method, with 5 mol % Tm substitution in the melt.

Mode-locking of the Yb:NaY(WO 4 ) 2 laser

Mode-locking of the Yb:NaY(WO4)2 laser is reported. Pulse durations as short as 53 fs are achieved using a semiconductor saturable absorber mirror (SESAM) and additional extracavity compression. Autocorrelation trace of the shortest pulse is obtained.