Spectro-temporal behavior of dye-based solid-state random lasers under a picosecond pumping regime: Part III.

In two recent works, the authors have investigated the spectro-temporal properties of the random laser emission from solid state dye-doped powders in picosecond pumping regime. Each emission pulse consists, both above and below threshold, in a collection of narrow peaks of a spectro-temporal width at the theoretical limit (ΔωΔt≅1). The distribution of path lengths traveled inside the diffusive active medium by photons that can be amplified by stimulated emission explains this behavior, as demonstrated by a simple theoretical model developed by the authors.

Spectro-temporal behavior of dye-based solid-state random lasers under picosecond pumping regime: part II.

In a very recent work the spectral and temporal properties of the random laser emission from solid state dye-doped powders have been investigated by the authors in picosecond pumping regime. The emission shows within each pulse, peaks of more intensity than background, and of a spectro-temporal width at the theoretical limit (ΔωΔt≅1), even in conditions well below the threshold. The relationship between the distribution of paths lengths traveled by photons inside the active medium, and the amplification by stimulated emission explains this behavior.

Spectro-temporal behavior of dye-based solid-state random lasers under picosecond pumping regime.

In this work, the spectral and temporal properties of the random laser emission from dye-doped solid state powders are investigated in picosecond pumping regime. Ultrafast time-resolved spectroscopy achieved with a streak-camera has been used to perform a detailed study of the temporal evolution of the spectrum of their single pulses. Under conditions of low population inversion density, it is observed that the detected radiation occurs as isolated peaks with a very narrow spectro-temporally spread (ΔωΔt≅1).

Input/output energy in solid state dye random lasers.

A new approach to the problem of energy in solid state dye random lasers is presented. The measurements performed in terms of absolute energy show that the slope efficiency depends on the measurement conditions. In particular, in lasers with pumping in the picoseconds range, the result is really different if measured by recording the emission in the same time range or in a longer one (nanoseconds range).

Random laser model for Nd-doped powders and its application to stimulated emission cross-section calculations.

A new theoretical approach for random lasing of Nddoped powders is presented. The model's singularity lies in the fact that it proposes a probability distribution of the stimulated photon paths lengths in the sample, as well as a population inversion shared by different photon paths. The model's predictions satisfactorily compare with the results of laser threshold and absolute input/output energy slope of a real Random Laser.

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

The present work gives a detailed investigation of the dependence of the real time luminescence of Eu-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 SnO matrix. A lower limit for the host-RE energy transfer rate and a model for the excitation mechanism are given.

Random laser properties of Nd crystal powders.

This work presents an overview of near infrared random lasing emitters based on a variety of neodymium (Nd)-doped crystal powders with different Nd concentrations and different grain sizes. The pump-configuration used allows for an absolute measurement of both pumping and emitted energies. The results provide an absolute measure of the random laser efficiency and prove a relation of direct proportionality between the absorbance of the material and the laser slope efficiency.

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.

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 (⁴S) and red (⁴F) upconversion luminescence. The dependence on temperature of the intensity ratio of upconversion emission from thermally-coupled ²H and ⁴S levels of Er in the 240-300 K temperature range has been used to estimate a relative sensitivity of 1.

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.

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.

On the temporal behavior of Nd3+ 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.

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.

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.

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.

Broadband laser tunability of Nd3+ ions in 0.8CaSiO3-0.2Ca3(PO4)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.

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.

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.