Mode-locked laser operation of epitaxially grown Yb:Klu(WO4)2 composites

Mode locking based on an epitaxial composite of the monoclinic double tungstate crystal Yb:KLu(WO4)2 is realized. A 100 microm thin Yb:KLu(WO4)2 layer grown on a KLu(WO4)2 substrate is used as an active medium in a laser passively mode locked by a semiconductor saturable absorber. Pulse durations of 114 fs have been achieved for an average power of 31 mW at 1030 nm. Results in the femtosecond and picosecond regimes of the Yb:KLu(WO4)2/KLu(WO4)2 laser are presented. The great potential of Yb-doped tungstate composite structures as active elements for mode-locked laser systems is demonstrated.     

Intermittency and deterministic diffusion in chaotic ratchets

We consider the problem of deterministic transport of particles in an asymmetric periodic ratchet potential of the rocking type. When the inertial term is taken into account, the dynamics can be chaotic and modify the transport properties. We calculate the bifurcation diagram as a function of the amplitude of forcing and analyze in detail the crisis bifurcation that leads to current reversals. Near this bifurcation we obtain intermittency and anomalous deterministic diffusion.     

A straightforward and versatile synthetic approach to 1-azabicyclic alkaloids

A very straightforward route to 1-azabicyclo alkaloid scaffolds with several ring sizes is reported. The final bicyclic structures were built through a synthetic scheme that involved (i) the construction of dienic 4-piperidone systems by an imino-Diels-Alder reaction between aminotrienes and N-omega-vinylimines, in the presence of Yb(OTf)(3), and (ii) the ring-closing metathesis reaction of these cyclic dienes, under the influence of the first-generation Grubbs' Ru-complex catalyst. During this investigations, various polysubstituted azabicyclic ring skeletons, including several examples of the quinolizidine alkaloids, are reported, and their relative stereochemistry is adequately discussed.     

Improvement of the analysis of dansylated derivatives of polyamines and their conjugates by high-performance liquid chromatography.

The paper described a method for improving the hydrolysis of conjugated polyamines in PH fraction, isolated from the lichen Evernia prunastri, as well as the optimization of dansylation procedure of these polyamines on the basis of the pH value to which derivatization is achieved. Dansylated polyamines have been later separated by high-performance liquid chromatography (HPLC) using a gradient elution. Hydrolysis of conjugates requires acid treatment at room temperature rather than at 110 degrees C, as usually described. Dansylation is improved at high pH values, whereas removal of phenolics (mainly evernic acid), from the conjugates requires low pH values.     

Kink fluctuation asymptotics and zero modes

In this paper we propose a refinement of the heat-kernel/zeta function treatment of kink quantum fluctuations in scalar field theory, further analyzing the existence and implications of a zero-energy fluctuation mode. Improved understanding of the interplay between zero modes and the kink heat-kernel expansion delivers asymptotic estimations of one-loop kink mass shifts with remarkably higher precision than previously obtained by means of the standard Gilkey–DeWitt heat-kernel expansion.     

Crystal growth,optical spectroscopy,and continuous-wave laser operation of Ho:KLu(WO4)2 crystals

We present the crystal growth, optical spectroscopy, and room temperature continuous-wave (CW) laser operation of monoclinic Ho:KLu(WO₄)₂ crystals. Macro defect-free crystals of several dopant concentrations were grown by top-seeded solution growth slow-cooling method. The evolution of unit cell parameters with holmium doping level and temperature was studied using X-ray powder diffraction. The spectroscopic properties were characterized in terms of room- and low-temperature optical absorption and photoluminescence. From low-temperature optical absorption measurements, the energy of the Stark levels was determined. Calculation of the emission and gain cross sections is presented. CW laser action was realized for 3 and 5 at. % Ho-doped KLu(WO₄)₂ by in-band pumping using a Tm:KLu(WO₄)₂ pump laser. A maximum output power of 507 mW with a slope efficiency of ~38 % with respect to the incident power was achieved at 2,080 nm with the Ho:KLu(WO₄)₂ laser.     

Experimental control of transport and current reversals in a deterministic optical rocking ratchet

We present an experimental demonstration of a deterministic optical rocking ratchet. A periodic and asymmetric light pattern is created to interact with dielectric microparticles in water, giving rise to a ratchet potential. The sample is moved with respect to the pattern with an unbiased time-periodic rocking function, which tilts the potential in alternating opposite directions. We obtain a current of particles whose direction can be controlled in real time and show that particles of different sizes may experience opposite currents. Moreover, we observed current reversals as a function of the magnitude and period of the rocking force.