Artur S. Gouveia-Neto

Optical temperature sensing using upconversion fluorescence emission in Er3+/Yb3+-codoped chalcogenide glass

Optical temperature sensing using upconversion fluorescence emission in Er3+/Yb3+-codoped Ga2S3:La2O3 chalcogenide glass excited at 1.06 μm is reported. Temperature measurements in the region of 20–225u2009°C with a resolution of approximately 0.5u2009°C using excitation powers of a few tens of milliwatts were obtained. The temperature sensing mechanism is independent of variations in the excitation intensity, possible fluctuations of transmission, and utilizes a simple signal detection and processing system. The results also revealed that the glass host material plays an important role in the performance of the sensing system.

Thermally induced threefold upconversion emission enhancement in nonresonant excited Er3+/Yb3+-codoped chalcogenide glass

Thermally induced threefold infrared-to-visible upconversion emission enhancement in Er3+/Yb3+-codoped Ga2S3:La2O3 chalcogenide glasses excited at 1.064 μm is reported. The times three upconversion efficiency enhancement was achieved by heating the sample in the temperature range of 23–155u200a°C, and is assigned to the temperature-dependent multiphonon-assisted anti-Stokes sideband excitation process of the ytterbium sensitizer. A theoretical analysis based upon rate equations considering the sensitizer absorption cross section as a function of the phonon occupation number in the host material exhibited very good agreement with experimental data.

Unveiling in Vivo Subcutaneous Thermal Dynamics by Infrared Luminescent Nanothermometers

The recent development of core/shell engineering of rare earth doped luminescent nanoparticles has ushered a new era in fluorescence thermal biosensing, allowing for the performance of minimally invasive experiments, not only in living cells but also in more challenging small animal models. Here, the potential use of active-core/active-shell Nd(3+)- and Yb(3+)-doped nanoparticles as subcutaneous thermal probes has been evaluated. These temperature nanoprobes operate in the infrared transparency window of biological tissues, enabling deep temperature sensing into animal bodies thanks to the temperature dependence of their emission spectra that leads to a ratiometric temperature readout. The ability of active-core/active-shell Nd(3+)- and Yb(3+)-doped nanoparticles for unveiling fundamental tissue properties in in vivo conditions was demonstrated by subcutaneous thermal relaxation monitoring through the injected core/shell nanoparticles. The reported results evidence the potential of infrared luminescence nanothermometry as a diagnosis tool at the small animal level.

Infrared to visible up-conversion fluorescence spectroscopy in Er3+-doped chalcogenide glass

Abstract Infrared to visible frequency up-conversion fluorescence spectroscopy in erbium-doped chalcogenide glass samples excited at 1.06 and 1.54xa0μm, is experimentally investigated. For 1.06xa0μm pumping, two-photon absorption and phonon-assisted energy transfer account for the excitation of the 2 H 11/2 , 4 S 3/2 and 4 F 9/2 emitting levels, yielding intense green emission at 530 and 555xa0nm and low intensity light at 670xa0nm, respectively. For excitation at 1.54xa0μm, much higher up-conversion efficiencies were obtained with the red emission signal around 670xa0nm presenting higher intensity than the green fluorescence signals. At this excitation wavelength the population of the 2 H 11/2 , 4 S 3/2 and 4 F 9/2 excited-state emitting levels is accomplished via energy-transfer and phonon-assisted decays. Saturation of the up-conversion efficiency for 1.54xa0μm pumping was also observed.

Modulational instability in semiconductor-doped glass fibers with saturable nonlinearity

Modulational instability in doped glass fibers is analyzed theoretically in a steady-state regime, taking into account a saturable nonlinearity. The results have shown that the critical modulation frequency and modulation gain increase with input power, reaching a maximum value at the saturation power. This leads to a unique value of the critical modulation frequency for two different input powers so that two solutions will experience a maximum gain at the same frequency.

Fourfold output power enhancement and threshold reduction through thermal effects in an Er 3+ /Yb 3+ -codoped optical fiber laser excited at 1.064 µm

Thermally induced output power enhancement and threshold reduction in an Er(3+)/Yb(3+) -codoped optical fiber laser at 1.54mum pumped by 1.064-mu;m cw radiation is demonstrated. Steady fourfold output power increase and threshold decrease were achieved by heating of the Yb(3+) -sensitized Er(3+) -doped fiber laser medium in the temperature range 23-150 degrees C degrees . The laser efficiency thermal behavior is assigned to the temperature-dependent effective absorption cross section of the ytterbium sensitizer through the so-called multiphonon-assisted anti-Stokes excitation process.

Third‐harmonic generation in GeO2‐doped silica single‐mode optical fibers

Third‐harmonic generation of 1.319 μm Nd:YAG laser pulses in circular‐core GeO2‐doped silica single‐mode fibers is reported. The experimental results have shown that the blue‐violet light generated at 439 nm is less than 0.2 nm wide and its intensity depends strongly upon GeO2‐doping concentration for fixed fiber length and pump power. It has been observed that for GeO2‐doping concentrations greater than 9 molu2009%, the third‐harmonic signal was the unique visible wavelength line exiting the fiber span throughout the spectral region of 400–800 nm. The frequency tripling process started immediately with fiber pump light illumination, i.e., no previous long‐time preparation mechanism was required in order to have appreciable third‐harmonic generation.

Two-photon-resonant photoinduced second-harmonic generation in Er 3+ -doped germano-aluminosilicate optical fibers pumped at 1.319 μm

The growth of a two-photon-resonant photoinduced second-harmonic signal at 660 nm in Er(3+)-doped GeO(2)-Al(2)O(3)-SiO(2) single-mode optical fibers pumped by a Nd:YAG laser at 1.319 microm is reported. Defect states in the band gap are optically excited through a resonant two-photon absorption process connecting the (4)I(15/2)-(4)F(9/2) energy levels of the erbium ions present in the fiber core. As a result a periodic X((2)) grating is formed, and efficient second-harmonic generation takes place. For erbium-free GeO(2)-doped silica test fibers no second-harmonic signal has been detected, even after hours of seeded preparation process.

Self-phase modulation of incoherent pulses in single-mode optical fibers

An experimental observation of self-phase-modulation-induced spectral broadening and coherence-time shortening of incoherent pulses in single-mode optical fibers is reported for the first time to our knowledge. Reduction of the field correlation time by a factor greater than 2.5 was observed in both normal and anomalous dispersive regimes.

Infrared to visible frequency upconversion in erbium-doped Ga2S3–La2O3 chalcogenide glass

Abstract Infrared to visible frequency upconversion in an erbium-doped lanthanum-oxide chalcogenide glass excited at 1.06 μ m, is reported for the first time. Intense green upconversion emission lines at 525 and 550 nm of the thermally coupled excited state levels 2 H 11/2 and 4 S 3/2 , respectively, is observed. A much lower intensity emission band around 670 nm corresponding to the 4 F 9/2 – 4 I 15/2 transition, is also observed. Two-photon absorption and phonon-assisted energy transfer account for the upconversion excitation mechanism.