Sara García-Revilla

Spectroscopy and concentration quenching of the infrared emissions in Tm 3+ -doped TeO 2 -TiO 2 -Nb 2 O 5 glass

In this work, we report the optical properties of Tm(3+) ions in tellurite glasses (TeO(2)-TiO(2)-Nb(2)O(5)) for different Tm(3+) concentrations ranging between 0.05 and 1 wt%. Judd-Ofelt intensity parameters have been determined to calculate the radiative transition probabilities and radiative lifetimes of excited states. The stimulated emission cross-sections of the infrared emissions at 1487 nm and 1800 nm have been determined from the line shape of the emission spectra and the lifetimes of levels (3)H(4) and (3)F(4) respectively. The emission spectra obtained under 793 nm excitation reveal the existence of energy transfer via cross-relaxation among Tm(3+) ions. As a result, the intensity of the infrared (3)H(4)?(3)F(4) emission at 1487 nm decreases in relation to the one at 1800 nm, as concentration increases. The non-exponential character of the decays from the (3)H(4) level with increasing concentration indicates the presence of a dipole-dipole quenching process assisted by energy migration. The self-quenching of the (3)F(4)?(3)H(6) emission at 1800 nm can be attributed to limited diffusion within the active centers.

Ultrafast random laser emission in a dye-doped silica gel powder

We report efficient random lasing in a ground powder of a novel solid-state material based on silica gel containing SiO(2) nanoparticles embedding rhodamine 6G (Rh6G) dye. Basic properties of random lasing such as emission kinetics, emission spectrum, and threshold of stimulated emission are investigated by using real-time spectroscopy. The laser-like emission dynamics can be accurately described by a light diffusive propagation model. The device behavior is close to a conventional ultrafast Q-switched laser, which is an interesting fact aimed to further applications.

Real time random laser properties of Rhodamine-doped di-ureasil hybrids.

This investigation explores, for the first time, the random laser behavior of ground powder obtained from organic-inorganic hybrid materials based on Rhodamine 6G incorporated into a di-ureasil matrix. The experimental results, both in the spectral and temporal domains, obtained by pumping with picosecond laser pulses, show the existence of efficient random laser emission in this system. Finally, the random laser performance is compared with the one of other Rhodamine-doped solid state silica compounds.

Random lasing in Nd:LuVO4 crystal powder

Room temperature random lasing action is demonstrated for the first time in a low concentrated neodymium doped vanadate crystal powder. Laser threshold and emission efficiency are comparable to the ones obtained in stoichiometric borate crystal powders. The present investigation provides a complete picture of the random lasing characteristics of Nd-doped vanadate powder both in the spectral and temporal domain, together with a simplified model which accounts for the most relevant features of the random laser.

Broadband laser tunability of Nd 3+ ions in 0.8CaSiO 3 -0.2Ca 3 (PO 4 ) 2 eutectic glass

Site-selective spectroscopy and stimulated emission experiments performed in the (4)F(3/2)-->(4)I(11/2) laser transition of Nd(3+)-doped 0.8CaSiO(3-) 0.2Ca(3)(PO(4))(2) eutectic glass are presented. The spectral features of the excitation spectra and those of spontaneous and stimulated emissions reveal the existence of a very complex crystal field site distribution for Nd(3+) ions. As a consequence, the stimulated emission of Nd(3+) in this glass shows a tunability of about 10 nm as a function of excitation wavelength.

1Low threshold random lasing in dye-doped silica nano powders

Random laser action is demonstrated in two kinds of powder samples containing rhodamine 6G (Rh6G) doped SiO2 nanoparticles which are either directly dispersed within pure silica particles or embedded in a silica gel matrix which is subsequently ground. Both organic-inorganic hybrid materials present different laser thresholds and emission features which are systematically studied and compared. The dependence of the emission kinetics, emission spectrum, random laser threshold and slope efficiency on the dye doped nanoparticles concentration is investigated in both cases. We also explore if the incorporation of additional TiO2 scatterers could enhance the random laser operation of the studied systems.

Effects of pumping wavelength and pump density on the random laser performance of stoichiometric Nd crystal powders.

Laser slope and threshold properties have been investigated in Nd stoichiometric crystal powders as a function of pump wavelength and pump beam size. Above a given pumped area, the laser slope and the threshold pump energy per unit area are invariant and the known theoretical expressions are well fulfilled. Likewise, the size of the stimulated emission zone as a function of the pump beam area has been measured, also showing a different behavior above or below a given pumped area value which coincides with the one mentioned above. In conclusion, two different operating regimes with different performances are clearly observed as a function of the pump beam area.

On the temporal behavior of Nd 3+ random lasers

The temporal dynamics of random laser emission from Nd-doped crystal powders has been investigated by using an improved detection device. The precise conditions to detect high contrast, fast oscillations are described. The measured period is about one order of magnitude shorter than the one given in the literature for relaxation oscillations in these materials. The origin of these differences is discussed.

Diffusive random laser modes under a spatiotemporal scope

At present the prediction and characterization of the emission output of a diffusive random laser remains a challenge, despite the variety of investigated materials and theoretical interpretations given up to now. Here, a new mode selection method, based on spatial filtering and ultrafast detection, which allows to separate individual lasing modes and follow their temporal evolution is presented. In particular, the work explores the random laser behavior of a ground powder of an organic-inorganic hybrid compound based on Rhodamine B incorporated into a di-ureasil host. The experimental approach gives direct access to the mode structure and dynamics, shows clear modal relaxation oscillations, and illustrates the lasing modes stochastic behavior of this diffusive scattering system. The effect of the excitation energy on its modal density is also investigated. Finally, imaging measurements reveal the dominant role of diffusion over amplification processes in this kind of unconventional lasers.

Two-photon pumped random lasing in a dye-doped silica gel powder

We report the first observation of two-photon pumped random laser action in the ground powder of a silica gel containing rhodamine 6G doped silica nanoparticles. When this solid-state dye system is pumped with 800 nm femtosecond-lasing pulses, random laser-like effects such as spectral narrowing and temporal shortening are observed with a laser-like emission peak centered around 598 nm. A comparison between the emission features, random laser behavior and threshold of random laser action, following one- and two-photon excitations is also performed.