Macarena Barredo-Zuriarrain

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.

Random laser action in stoichiometric Nd3Ga5O12 garnet crystal powder

This work explores the room temperature infrared random laser (RL) performance of Nd3+ ions in a new stoichiometric Nd3Ga5O12 crystal powder. The time-resolved measurements show that the RL pulse is able to follow the subnanosecond oscillations of the pump pulse profile. The pump threshold energy and the absolute stimulated emission energy have been measured using a method developed by the authors. The laser slope efficiency is the highest compared to other Nd3+ stoichiometric RL crystals.

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.

Influence of Upconversion Processes in the Optically-Induced Inhomogeneous Thermal Behavior of Erbium-Doped Lanthanum Oxysulfide Powders

The efficient infrared-to-visible upconversion emission present in Er-doped lanthanum oxysulfide crystal powders is used as a fine thermal sensor to determine the influence of upconversion processes on the laser-induced thermal load produced by the pump laser and to assess the potentialities of this material in order to obtain anti-Stokes laser-induced cooling. The analysis of the upconversion emission and excitation spectra as well as the decay curves indicates that energy transfer upconversion is the main mechanism responsible for the green (4S3/2) and red (4F9/2) upconversion luminescence. The dependence on temperature of the intensity ratio of upconversion emission from thermally-coupled 2H11/2 and 4S3/2 levels of Er3+ in the 240–300 K temperature range has been used to estimate a relative sensitivity of 1.09 × 10−2 K−1. Thermal measurements performed on the powder samples by using a thermal infrared camera exhibit a very inhomogeneous heat distribution at the sample surface due to the random distribution of the pumping energy inside the sample as well as to the random properties of the thermal field. The analysis of both spectroscopic and thermal measurements show that after a transient heating induced by the background absorption, cooling of discrete regions by means of anti-Stokes processes can be observed.

Random Laser Action in Nd:YAG Crystal Powder

This work explores the room temperature random stimulated emission at 1.064 μm of a Nd:YAG crystal powder (Neodymium-doped yttrium aluminum garnet) in a very simple pump configuration with no assistance from an internal mirror. The laser threshold energy as a function of pump beam area and pump wavelength has been measured, as well as the temporal dynamics of emission pulses. The absolute energy of stimulated emission and the absolute laser slope efficiency have been measured by using a method proposed by the authors. The results show a surprising high efficiency that takes the low Nd3+ ion concentration of the crystal powder into account.

Spectral dynamics of a diffusive random laser under two photon pumping

Abstract The spectral dynamics of a diffusive random laser under two photon excitation is investigated by using an experimental set-up which allows for fine mode discrimination and time resolution. The diffusive scattering system consists of a di-ureasil hybrid matrix powder doped with Rhodamine B. The anti-Stokes random laser emission obtained by pumping at 1064 nm shows a larger output pulse duration, build-up time, and threshold than the one produced under one photon pumping at 532 nm using the same experimental conditions. The time resolved analysis of the single shot emission pulse demonstrates the inherent stochastic nature of its lasing modes as well as the existence of modal relaxation oscillations. The outcome of our experiments also suggests that mode saturation appears with the increase of pump power.

Site symmetry and host sensitization-dependence of Eu 3+ real time luminescence in tin dioxide nanoparticles

The present work gives a detailed investigation of the dependence of the real time luminescence of Eu3+-doped tin dioxide nanopowder on rare earth (RE) site symmetry and host defects. Ultrafast time-resolved analysis of both RE-doped and undoped nanocrystal powder emissions, together with electronic paramagnetic resonance studies, show that host-excited RE emission is associated with RE-induced oxygen vacancies produced by the non-isoelectronic RE-tin site substitution that are decoupled from those producing the bandgap excited emission of the SnO2 matrix. A lower limit for the host-RE energy transfer rate and a model for the excitation mechanism are given.

Random lasing of LiLa 1−x Nd x P 4 O 12 crystal powders

We report random laser action, for the first time to our knowledge, in crystalline powders of LiLa1-xNdxP4O12 (x = 0.5 and 1) by using a pulsed Ti-sapphire pumping. The effect of grain size on slope efficiency and threshold energy is investigated. The absolute slope efficiencies are similar for all samples studied whereas the lowest threshold pump energy corresponds to the stoichiometric sample with an average grain size of around 10 μm. The grain size also affects the emitting surface and therefore the diffusive length which is reduced as the grain size decreases.

Progress in the spectroscopic and thermal studies of Er-doped oxysulfide crystal powders

Gadolinium oxysulfide crystal is a wide-gap semiconductor material known as an excellent host for trivalent rare-earth ions. The present investigation explores the upconversion and thermal properties of Er3+-doped Gd2O2S crystal powders as well as their potentiality for anti-Stokes cooling. A detailed study of the wavelength and pumping power dependence of the spectroscopic properties and temperature field for samples of various erbium concentrations is presented.

Spectroscopic and thermal study of Er-doped oxysulfide crystal powders

The present investigation explores the upconversion properties of Er3+- doped La2O2S crystal powder as well as its potentiality for anti-Stokes cooling. A detailed study of the wavelength and pumping power dependence of the spectroscopic properties and of the temperature field of samples with various erbium concentrations is presented. The analysis of both spectroscopic and thermal measurements shows that after a transient heating induced by the background absorption, cooling can be attained by means of anti-Stokes processes.