E. A. Gouveia

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 23–155 °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.

Pump-power-controlled luminescence switching in Yb3+/Tm3+ codoped water-free low silica calcium aluminosilicate glasses

Intense infrared-to-visible upconversion emissions in Tm3+∕Yb3+ codoped water-free low silica calcium aluminosilicate glasses have been obtained under excitation at 976nm. The results showed that as the pump power/intensity is increased, a reduction of up to one order of magnitude at the 800∕480nm emitted intensity ratio is observed; characterizing what can be denominated as luminescent switching. The physical origin of this switching is discussed and explained in terms of the tailoring of luminescent switchers to operate in a large range of pump powers, what could be used in the development of sensors and networks for optical processing and optical communications.

Twentyfold blue upconversion emission enhancement through thermal effects in Pr3+/Yb3+-codoped fluoroindate glasses excited at 1.064 μm

Infrared-to-visible upconversion emission enhancement through thermal effects in Yb3+-sensitized Pr3+-doped fluoroindate glasses excited at 1.064 μm is investigated. A twentyfold increase in the 485 nm blue emission intensity as the sample temperature was varied from 20 to 260 °C was observed. The visible upconversion fluorescence enhancement is ascribed to the temperature dependent multiphonon-assisted anti-Stokes excitation of the ytterbium sensitizer and excited-state absorption of the praseodymium acceptor. A model based upon conventional rate equations considering a temperature dependent effective absorption cross section for the 2F7/2→2F5/2 transition of the Yb3+ and 1G4→3P0 excited-state absorption of the Pr3+, agrees very well with the experimental results.

Infrared-to-visible frequency upconversion in Pr3+/Yb3+- and Er3+/Yb3+-codoped tellurite glasses

Abstract Upconversion luminescence and thermal effects in Pr 3+ /Yb 3+ - and Er 3+ /Yb 3+ -codoped 60TeO 2 –10GeO 2 –10K 2 O–10Li 2 O–10Nb 2 O 5 tellurite glasses excited by CW infrared radiation at 1.064 μm is reported. Generation of intense green and red fluorescence emission in Er 3+ /Yb 3+ -codoped samples and appreciable upconversion luminescence in the wavelength region of 450–680 nm in Pr 3+ /Yb 3+ -codoped samples is observed. Temperature-induced enhancement of ×12 in the upconversion efficiency in Er 3+ /Yb 3+ - and ×10 in the Pr 3+ /Yb 3+ -doped samples is demonstrated.

Blue cooperative luminescence in Yb3+-doped tellurite glasses excited at 1.064 μm

Blue luminescence emission around 480 nm through cooperative upconversion from pairs of Yb3+ ions implanted into 60TeO2–10GeO2–10K2O–10Li2O–10Nb2O5 tellurite glasses and excited by a cw laser at 1.064 μm is demonstrated. Cooperative luminescence emission enhancement owing to the temperature dependent multiphonon-assisted anti-Stokes excitation process of the ytterbium ions is also observed. The experimental results revealed a fourfold enhancement in the cooperative luminescence emission when the sample was heated in the temperature range of 20 °C–260 °C. The thermally induced enhancement is assigned to the effective absorption cross-section for the ytterbium ions which is an increasing function of the medium temperature.

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 mol %, 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.

Efficient energy upconversion emission in Tm3+/Yb3+-codoped TeO2-based optical glasses excited at 1.064 μm

Efficient energy upconversion of cw radiation at 1.064 μm into blue, red, and near infrared emission in Tm3+-doped Yb3+-sensitized 60TeO2-10GeO2-10K2O-10Li2O-10Nb2O5 glasses is reported. Intense blue upconversion luminescence at 485 nm corresponding to the Tm3+ 1G4→3H6 transition with a measured absolute power of 0.1 μW for 800 mW excitation power at room temperature is observed. The experimental results also revealed a sevenfold enhancement in the upconversion efficiency when the sample was heated from room temperature to 235 °C yielding 0.7 μW of blue absolute fluorescence power for 800 mW pump power. High brightness emission around 800 nm (3F4→3H6) in addition to a less intense 655 nm (1G4→3H4 and 3F2,3→3H6) fluorescence is also recorded. The energy upconversion excitation mechanism for thulium emitting levels is assigned to multiphonon-assisted anti-Stokes excitation of the ytterbium-sensitizer followed by multiphonon-assisted sequential energy-transfer processes.

Optical characterization of Nd3+- and Er3+-doped lead-indium-phosphate glasses

In this work, Judd–Ofelt analysis is applied to rare-earth-doped lead-indium-phosphate glasses (RE-PbInPO4, where RE=Er3+ and Nd3+) in order to evaluate their potential as both glass laser systems and amplifier materials. The phenomenological Judd–Ofelt parameters Ω(2), Ω(4), and Ω(6) are determined for both rare-earth ions together with their quality factors and compared with the equivalent parameters for several other host glasses. The spontaneous emission probabilities and the lifetimes of the Nd3+ F43/2 laser transitions are determined and analyzed as a function of the optical quality factor. For Nd3+-PbInPO4, glass fluorescence emission (890, 1058, and 1330 nm) lines are observed. Highly efficient infrared-to-visible frequency up-conversion at 530, 550, and 670 nm as well as an intense infrared fluorescence emission (∼1540 nm) is observed in Er3+-doped PbIn(PO4) glasses pumped using 800 nm radiation excitation.