W. F. Silva

Femtosecond-laser-written, stress-induced Nd:YVO 4 waveguides preserving fluorescence and Raman gain

We report the formation of optical waveguides in the self-Raman Nd:YVO(4) laser crystal by femtosecond laser inscription. The confocal fluorescence and Raman images have revealed that the waveguide is constituted by a locally compressed area in which the original fluorescence and Raman gains of the Nd:YVO(4) system are preserved. Thus the obtained structures emerge as promising candidates for highly efficient self-Raman integrated laser sources.

Color tunability with temperature and pump intensity in Yb3+/Tm3+ codoped aluminosilicate glass under anti-Stokes excitation

Pump and thermally induced color tunabilities were demonstrated in Yb(3+)/Tm(3+) codoped low silica calcium aluminosilicate (LSCAS) glass under anti-Stokes excitation at 1.064 microm. The effects of pump intensity and samples temperature on the upconversion emissions and mainly on the color tunabilities (from 800 to 480 nm) were investigated. The results revealed a 20- and a threefold reductions at 800/480 nm ratio as, respectively, the pump intensity and samples temperature were increased from 27 to 700 kW/cm(2) and from 296 to 577 K. These behaviors with pump intensity and temperature (a strong increase of the 480 nm emission in comparison with the 800 nm one) were attributed to the several efficient processes occurring in the LSCAS system (Yb(3+)-->Tm(3+) energy-transfer processes, easy saturations of the Yb(3+) and Tm(3+) excited states, and radiative emissions). Besides these assigns, the temperature dependence is mainly assigned to the temperature-dependent effective absorption cross section of the ytterbium sensitizer through the so-called multiphonon-assisted anti-Stokes excitation process. Theoretical analyses and fits of the experimental data provided quantitative information.

Quantum efficiencies and thermo-optical properties of Er3+-, Nd3+-, and Pr3+-single doped lead-indium-phosphate glasses

The experimental determination of thermal and optical properties, such as the fluorescence quantum efficiency (η) and temperature coefficient of the optical path length change (ds/dT) have been a challenging task. In this work, mode-mismatched thermal lens and spectroscopic measurements were performed using Er3+-, Nd3+-, and Pr3+-doped lead-indium-phosphate glasses to obtain the thermal diffusivity and conductivity, ds/dT, the thermal loading (nonradiative quantum efficiency), and η. The experimental difficulties associated with obtaining η for systems with several emitting levels, such as Er3+-doped materials were overcome. A discussion of the implications of the small η values obtained for Er3+- and Pr3+-doped glass is presented.

Luminescent and thermo-optical properties of Nd3+-doped yttrium aluminoborate laser glasses

In this work we performed a thorough spectroscopic and thermo-optical investigation of yttrium aluminoborate glasses doped with neodymium ions. A set of samples, prepared by the conventional melt-quenching technique and with Nd2O3 concentrations varying from 0.1 to 0.75 mol %, were characterized by ground state absorption, photoluminescence, excited state lifetime measurements, and thermal lens technique. For the neodymium emission at 1064 nm (F43/2→I411/2 transition), no significant luminescence concentration quenching was observed and the experimental lifetime values ranged around 70 μs. The obtained values of thermal conductivity and diffusivity of approximately 10.3×10−3 W/cm K and 4.0×10−3 cm2/s, respectively, are comparable to those of commercial laser glasses. Moreover, the fluorescence quantum efficiency of the glasses, calculated using the Judd–Ofelt formalism and luminescence decay, lies in the range from 0.28 to 0.32, larger than the typical values obtained for Nd3+ doped YAl3(BO3)4 crystals.

Thermo-optical characteristics and concentration quenching effects in Nd3+ doped yttrium calcium borate glasses.

In this work we present a comprehensive study of the spectroscopic and thermo-optical properties of a set of samples with composition xNd(2)O(3)-(5-x)Y(2)O(3-)40CaO-55B(2)O(3) (0 ≤ x ≤ 1.0 mol%). Their fluorescence quantum efficiency (η) values were determined using the thermal lens technique and the dependence on the ionic concentration was analyzed in terms of energy transfer processes, based on the Förster-Dexter model of multipolar ion-ion interactions. A maximum η = 0.54 was found to be substantially higher than for yttrium aluminoborate crystals and glasses with comparable Nd(3+) content. As for the thermo-optical properties of yttrium calcium borate, they are comparable to other well-known laser glasses. The obtained energy transfer microparameters and the weak dependence of η on the Nd(3+) concentration with a high optimum Nd(3+) concentration put this system as a strong candidate for photonics applications.

Microspectroscopy of ultrafast laser inscribed channel waveguides in Yb:tungstate crystals

We report microspectroscopy measurements of crystalline channel waveguides fabricated in Yb:KGd(WO4)2 and Yb:KY(WO4)2 using the ultrafast laser inscription technique. From these measurements we find that densification of the WO2W bridge in the double tungstate crystal lattice is responsible for the refractive index increase, which creates the waveguide confinement. We identified that shifts toward lower energies in the ∼760 cm−1 Raman mode indicate regions, which guide light polarized along the crystallographic b axis, while higher energy shifts in the 682 and 898 cm−1 Raman lines correspond to guiding regions for light polarized along the crystallographic a axis.

Influence of temperature and excitation procedure on the athermal behavior of Nd3+-doped phosphate glass: Thermal lens, interferometric, and calorimetric measurements

In this work, thermal and optical properties of the commercial Q-98 neodymium-doped phosphate glass have been measured at low temperature, from 50 to 300 K. The time-resolved thermal lens spectrometry together with the optical interferometry and the thermal relaxation calorimetry methods were used to investigate the glass athermal characteristics described by the temperature coefficient of the optical path length change, ds/dT. The thermal diffusivity was also determined, and the temperature coefficients of electronic polarizability, linear thermal expansion, and refractive index were calculated and used to explain ds/dT behavior. ds/dT measured via thermal lens method was found to be zero at 225 K. The results provided a complete characterization of the thermo-optical properties of the Q-98 glass, which may be useful for those using this material for diode-pumped solid-state lasers.

Modeling population and thermal lenses in the presence of Auger Upconversion for Nd(3+) doped materials.

We present a theoretical model to thermal (TL) and population (PL) lenses effects in the presence of Auger upconversion (AU) for analysis of Nd(3+) doped materials. The model distinguishes and quantifies the contributions from TL and PL. From the experimental and theoretical results, the AU cannot be neglected because it plays an important role on the excited state population and therefore on the temperature and polarizability difference between excited and ground states. Considering the extensive use of these techniques, the model presented here could be useful for the investigation of materials and also to avoid misleading analysis of lenses transients.

Micro-luminescence and micro-Raman mapping of ultrafast laser inscribed Yb:KGd(WO 4 ) 2 and Yb:KY(WO 4 ) 2 channel waveguides

Micro-luminescence and micro-Raman mapping has been performed on ultrafast laser inscribed channel Yb:KGd(WO<inf>4</inf>)<inf>2</inf> and Yb:KY(WO<inf>4</inf>)<inf>2</inf> waveguides. Correlation can be seen between guiding regions and shifts in micro-luminescence and micro-Raman peaks when compared to the bulk.