E. Martín Rodríguez

Optical trapping of NaYF4:Er3+,Yb3+ upconverting fluorescent nanoparticles

We report on the first experimental observation of stable optical trapping of dielectric NaYF4:Er(3+),Yb(3+) upconverting fluorescent nanoparticles (~26 nm in diameter) using a continuous wave 980 nm single-beam laser. The laser serves both to optically trap and to excite visible luminescence from the nanoparticles. Sequential loading of individual nanoparticles into the trap is observed from the analysis of the emitted luminescence. We demonstrate that the trapping strength and the number of individual nanoparticles trapped are dictated by both the laser power and nanoparticle density. The possible contribution of thermal effects has been investigated by performing trapping experiment in both heavy water and into distilled water. For the case of heavy water, thermal gradients are negligible and optical forces dominate the trap loading behaviour. The results provide a promising path towards real three dimensional manipulation of single NaYF4:Er(3+),Yb(3+) nanoparticles for precise fluorescence sensing in biophotonics experiments.

Time resolved confocal luminescence investigations on Reverse Proton Exchange Nd:LiNbO 3 channel waveguides

In this work we report on the time and spatial resolved fluorescence of Neodymium ions in LiNbO(3) channel waveguides fabricated by Reverse Proton Exchange. The analysis of the fluorescence decay curves obtained with a sub-micrometric resolution has evidenced the presence of a relevant fluorescence quenching inside the channel waveguide. From the comparison between diffusion simulations and the spatial dependence of the (4)F(3/2) fluorescence decay rate we have concluded that the observed fluorescence quenching can be unequivocally related to the presence of H+ ions in the LiNbO(3) lattice. Nevertheless, it turns out that Reverse Proton Exchange guarantees a fluorescence quenching level significantly lower than in similar configurations based on Proton Exchange waveguides. This fluorescence quenching has been found to be accompanied by a relevant red-shift of the (4)F(3/2)?(4)I(9/2) fluorescence band.

Multicolour second harmonic generation by strontium barium niobate nanoparticles

Infrared to visible second harmonic generation (SHG) has been demonstrated from 40 nm Sr0.6Ba0.4Nb2O6 nanoparticles in a broad spectral range of infrared fundamental wave excitation (800–1200 nm). The efficiency for SHG is compared with that obtained from powdered samples of larger crystallite sizes so that the mechanism leading to optical frequency conversion is discussed. The obtained results point out the possibility of using nonlinear nanoparticles for multifrequency optical imaging.

Laser action from Yb3+ ions in the ferroelectric and paraelectric phases of strontium barium niobate

We report on continuous wave laser oscillation of trivalent ytterbium ions in the frequency converter Yb3+:Sr0.6Ba0.4Nb2O6 ferroelectric laser crystal. Pump induced thermal loading has been used to drive the crystal from its ferroelectric to paraelectric phase. Stable laser radiation at 1070nm was found in both phases while a bistable laser output is observed through phase transition. In addition, diffuse green (535nm) radiation was generated by self-frequency doubling of the fundamental laser radiation because of the random distribution of microferroelectric domains existing in the ferroelectric as grown crystal.

Optical distortions through phase transition in the Nd3+:SBN laser crystal

We report on the polarization and temperature dependence of optical distortions of beams passing through a Nd3+-doped Sr0.61Ba0.39Nb2O6 laser crystal. For temperatures close to TC (≈70oC), a strong enhancement in the optical distortion of a nonabsorbed beam takes place, related to the temperature dependence of the r33 electro-optical coefficient during phase transition. From pump and probe experiments, we have concluded that the traditional 808nm Nd3+ pumping radiation also causes optical distortions, especially for extraordinary polarized radiation.

Gold nanorod assisted intracellular optical manipulation of silica microspheres.

We report on the improvement of the infrared optical trapping efficiency of dielectric microspheres by the controlled adhesion of gold nanorods to their surface. When trapping wavelength was equal to the surface plasmon resonance wavelength of the gold nanorods (808 nm), a 7 times improvement in the optical force acting on the microspheres was obtained. Such a gold nanorod assisted enhancement of the optical trapping efficiency enabled the intracellular manipulation of the decorated dielectric microsphere by using a low power (22 mW) infrared optical trap.

Improvement of laser gain by microdomain compensation effects in Nd:SrBa(Nb3O)2 lasers

The laser performance of poled and unpoled neodymium-doped strontium barium niobate crystals has been compared. We have found that the random distribution of microferroelectric domains, characteristic of as-grown crystals, leads to a relevant improvement in the laser performance. From the analysis of the optical distortion effects induced by both poled and unpoled crystals we have concluded that the compensation effects taking place between adjacent microdomains inside the active volume are at the origin of this improvement.

Optical Spectroscopy of YPO4 Single Crystals Doped with Ho3

ABSTRACT Crystal field absorption and emission spectra originated by 5I8 ↔ 5F5 transitions, due to Ho3+ (1% molar fraction) in a YPO4 single crystal, were investigated in the 15000 to 16000 cm−1 range. Fourier Transform high resolution absorption measurements, performed in the 9 to 300 K range, and photoluminescence, monitored at 10 K upon 540 nm excitation, supplied the sublevel separations within both 5I8 and 5F5 manifolds. The sublevel positions were compared to those calculated by diagonalization of the full 4f-configuration matrix in the framework of a single-ion model. The results are discussed also in relation with experimental data previously reported for similar systems containing Ho3+.

Phase transition induced gain depression in Nd3+:SBN lasers

In this work the origin of the phase transition induced gain depression in diode pumped Nd3+ doped Sr0.6Ba0.4(NbO3)2 lasers has been systematically investigated. The mechanisms capable of intracavity beam distortions are discussed and their relative contribution to the gain depression is investigated. We also provide evidence of two effects: a phase transition induced polarization switching and an enhancement in the laser performance when phase transition is overcome.