Alexandra Peña

Laser operation of Yb3+ in the acentric RbTiOPO4 codoped with Nb5+.

We report on continuous-wave lasing of Yb(3+) at room temperature in the noncentrosymmetric RbTiOPO(4) crystal, codoped with Nb(5+), for all three possible polarizations. A maximum output power of 154 mW at 1050 nm was obtained for an absorbed power of 386 mW. The highest slope efficiency reached approximately 60% and the lowest threshold (with respect to the absorbed power) was 18 mW. The laser was tunable from 1009 to 1081 nm.

Crystal growth, spectroscopic characterization, and eye-safe laser operation of erbium- And ytterbium-codoped KLu(WO4)2

Erbium (Er)- and Ytterbium (Yb)-codoped monoclinic KLu(WO4)2 single crystals were grown by top seeded solution growth-slow cooling method for several different doping concentrations. Growth parameters have been optimized to obtain macrodefect-free single crystals. Er energy levels involved in the 4I13/2-->4I15/2 were determined by 6 K polarized optical absorption. The maximum emission cross section for this electronic transition has been evaluated, being 2.85x10(-20) cm2 for E||Nm at 1535 nm. Laser oscillation in the 1.5 microm range was obtained by pumping the Yb ion at 980 nm and sensitizing Er. The maximum output power achieved was 152 mW, with 1.2% slope efficiency.

Yb 3+ spectroscopy in (Nb or Ta):RbTiOPO 4 single crystals for laser applications

Single crystals of Yb:RbTiOPO(4) codoped with Nb(5+) or Ta(5+) were grown by the top seeded solution growth slow-cooling technique. The ytterbium concentration in the crystals varies as a function of the molar ratio of the precursor oxides and of the codopant, reaching a maximum value of 1.9x10(20) Yb(3+) ions/cm(3). The broad band near 1 mum in absorption and emission spectra at room temperature is due to the large splitting of the Yb(3+) ground state. The ytterbium (2)F(5/2) level radiative lifetime in Nb:RbTiOPO(4) (tau(rad) = 2.7 ms), was calculated and then compared to the measured fluorescence decay time (tau(em) = 2.2 ms), giving an intrinsic quantum efficiency of 81%. To evaluate the potentiality of these crystals for self-frequency doubling, preliminary results of Yb(3+) laser operation and fundamental wavelength measurements for type-II non-critical second harmonic generation ( lambda(NCPM)) are also reported.

Broad emission band of Yb 3+ in the nonlinear Nb:RbTiOPO 4 crystal: origin and applications

By means of micro-structural and optical characterization of the Yb:Nb:RbTiOPO(4) crystal, we demonstrated that the broad emission band of Yb(3+) in these crystals is due to the large splitting of the ytterbium ground state only, and not to a complex multisite occupation by the ytterbium ions in the crystals. We used this broad emission band to demonstrate wide laser tuning range and generation of femtosecond laser pulses. Passive mode-locked laser operation has been realized by using a semiconductor saturable absorber mirror, generating ultra short laser pulses of 155 fs, which were very stable in time, under Ti:sapphire laser pumping at 1053 nm.

Lattice location and short range ordering of doping ions in RbTiOPO4

By using extended x-ray absorption fine structure spectroscopy, we demonstrate that Yb3+ ions in RbTiOPO4 and RbTi1−xNbxOPO4 crystals occupy titanium sites. By comparing these results with optical spectroscopic data and the structural location of Nb5+ codopants, we concluded that Yb3+ is located in Ti(2) positions in RbTi1−xNbxOPO4 crystals. Short range ordering between Yb3+ and Nb5+ rules electrical and optical properties of these nonlinear optical materials.

Thermal stability of ferroelectric domain gratings in Rb-doped KTP

We study the thermal stability of domain walls in periodically poled Rb-doped KTP crystals. Domain-wall motion is observed after annealing the crystals above 550 °C. This motion is highly anisotropic along the a- and b- crystallographic axes. Along the b-axis domain wall motion is in the order of tens of micrometers. In the a-direction, it results in either three orders of magnitude smaller domain wall displacement or in domain merging, depending on the initial domain configuration. We show that the thermal stability of the domain gratings depends on their periodicity, resulting in complete backswitching for sub-micrometer domains annealed at 730 °C.

Intrinsic ionic screening of the ferroelectric polarization of KTP revealed by second-harmonic generation microscopy

Mobile charges and lattice polarization interact in ferroelectric materials because of the Coulomb interaction between the mobile free charges and the fixed lattice dipoles. Using SHG microscopy, w ...

Validation of the angular quasi-phase-matching theory for the biaxial optical class using PPRKTP

We report the first experimental validation of angular quasi-phase-matching (AQPM) theory in a biaxial crystal by performing second-harmonic generation (SHG) in the periodically-poled Rb-doped KTiOPO4 (PPRKTP) crystal cut as a sphere. Both AQPM and birefringence phase-matching (BPM) angles were measured thanks to a Kappa circle.

Refined Orientation of the Optical Axes as a Function of Wavelength in Monoclinic Double Tungstates

We measured the rotation of the dielectric frame and determined the orientation of the optical axes in KRE(WO4)2 (RE = Gd, Y, Lu) crystals, as a function of wavelength in the 0.4-1.6 μm range.