M. Al-Saleh

Infrared to visible upconversion in Pr3+-doped KPb2Cl5 crystal

Abstract In this work we report the infrared to visible upconversion luminescence in the low phonon-energy host material KPb2Cl5 doped with Pr3+ ions. A strong orange luminescence from the 1D2 level, and less intense blue, green, and red emissions from the 3P0,1 levels have been observed under infrared excitation inside the 1G4 level and compared with those obtained under one photon excitation. The upconverted fluorescence from the 1D2 level shows a quadratic dependence on the pump power indicating a two photon process, whereas the pump power dependence of the blue fluorescence from level 3P0 is nearly cubic, which indicates a three photon mechanism. The possible excitation mechanisms responsible for these upconversion processes are discussed.

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.

Light propagation in optical crystal powders: effects of particle size and volume filling factor

In this work, we analyse the light propagation in some laser and nonlinear crystal powders. In particular, we study the dependence of the diffusive absorption lengths and the transport lengths on particle size and volume filling factor. The theoretical calculations have been made by assuming a diffusive propagation of light in these materials.

Spontaneous and stimulated emission spectroscopy of a Nd 3+ -doped phosphate glass under wavelength selective pumping

The influence of the host matrix on the spectroscopic and laser properties of Nd(3+) in a K-Ba-Al phosphate glass has been investigated as a function of rare-earth concentration. Site-selective time resolved laser spectroscopy and stimulated emission experiments under selective wavelength laser pumping show the existence of a very complex crystal field site distribution of Nd(3+) ions in this glass. The peak of the broad stimulated (4)F(3/2)→(4)I(11/2) emission shifts in a non monotonous way up to 3 nm as a function of the excitation wavelength. This behavior can be explained by the relatively moderate inter-site energy transfer among Nd(3+) ions found in this system and measured by using fluorescence line narrowing spectroscopy. The best slope efficiency obtained for the laser emission was 40%.

Laser properties of Nd3+ in K5Nd(MoO4)4 stoichiometric disordered crystal

Abstract The spectroscopic and laser properties of K5Nd(MoO4)4 crystal have been thoroughly investigated to show the relationship between the optical properties of Nd3+ ions and the crystal structure. High-resolution site-selective excitation spectroscopy performed at low temperature has demonstrated the existence of two broad crystal field site distributions for Nd3+. In agreement with this result, a broad laser emission has been observed. The shape and width of the laser line strongly depend on the polarization of the pump pulse. The temporal evolution of the laser spectrum shows remarkable changes in its spectral structure.

Time-resolved fluorescence line-narrowing of Eu3+ in biocompatible eutectic glass-ceramics

The spectroscopic properties of Eu(3+) in biocompatible glass and glass-ceramic eutectic rods of composition 0.8CaSiO(3)-0.2Ca(3)(PO(4))(2) doped with 0.5 wt% of Eu(2)O(3) are investigated to explore their potential applications as optical probes. The samples were obtained by the laser floating zone technique. Depending on the growth rate, they exhibit three (two crystalline and one amorphous) or two (one crystalline and one amorphous) phases. The crystalline phases correspond to Ca(2)SiO(4) and apatite-like structures. At high growth rates the system presents an amorphous arrangement which gives a glass phase. The results of time-resolved fluorescence line narrowing spectroscopy obtained under excitation within the inhomogeneous broadened (7)F(0)→(5)D(0) absorption band allow to isolate the emission from Eu(3+) ions in the crystalline and amorphous environments and to accurately correlate the spectroscopic properties with the microstructure of these eutectics.

Origin of laser-induced internal cooling of Yb3+ -doped systems

Laser induced internal cooling has been investigated in a new fluorochloride glass (CNBZn) and a fluoride glass (BIG) doped with 2.1x1020 Yb3+ ions/cm3 and in a Kpb2Cl5 crystal doped with 5x1019 Yb3+ by using collinear photothermal deflection and conventional laser excitation spectroscopies under high photon irradiances. The cooling efficiency for CNBZn glass which is approximately 2% relative to the absorbed laser power at 1010 nm and 300 K falls about 20% at 77 K. The cooling efficiency for BIG glass was only approximately 6% at room temperature. For the Yb3+ doped Kpb2Cl5 crystal we have shown internal laser cooling with a cooling efficiency of about 0.2% at room temperature. This is the third ytterbium-doped crystal, after Kgd(WO4) (Ref.10) and YAG (Ref.11), in which anti-Stokes laser-induced internal cooling has been demonstrated. The observed temperature dependence of the cooling process can be explained by a simple model accounting for the photon-ion- photon interaction.

Spectroscopy and frequency upconversion in KPb2Cl5:Pr3+ crystal

In this work we report the upconversion luminescence of Pr3+ doped Kpb2Cl5 crystal upon excitation in the near infrared region inside the 1G4 level. Direct excitation in the visible region has been also carried out. A strong orange luminescence from the 1D2 leve, and a less intense blue, green, and red emission from the 3P0,1 levels have been observed under infrared excitation and compared with those obtained under one photon excitation. The upconverted fluorescence from the 1D2 level shows a quadratic dependence on the pump power indicating a two photon process, whereas the pump power dependence of the blue fluorescence from level 3P0 is nearly cubic (2.62), which indicates a three photon mechanism. Emission from levels 3P0,1 is also observed under pulsed excitation in the 1D2 state. The possible excitation mechanisms responsible for these upconversion processes are discussed.

Transport mean free path in K5Bi1- xNdx(MoO4)4 laser crystal powders

In this work, we calculate in two different ways the transport mean free paths in K5Bi1−xNdx(MoO4)4 (x = 0.05, 0.2, 1) laser crystal powders by using the diffuse spectral reflectance and transmittance of the powders and the absorption coefficient of the crystal materials. The theoretical calculations have been made by assuming a diffusive propagation of light in these materials. Similar results have been obtained from both methods.

Upconversion processes and laser action in K5Nd(MoO4)4 stoichiometric crystal

In this work we report the upconversion processes that produce blue, green, orange, and red emission in K5Nd(MoO4)4 stiochiometric crystal together with the dynamics and spectral properties of the laser emission. It was found that upconversion energy transfer processes reduce the energy storage capacity through the reduction of the fluorescence lifetimes of the metastable 4F3/2 level. The experiments were conducted in such a way that the dynamics of the IR and visible fluorescence was performed under lasing and nonlasing conditions. The dynamics of the unconverted emission shows that both upconversion energy transfer and excited state absorption of the laser emission occur.