Marcos Vinícius Dias Vermelho | UFAL - Universidade Federal de Alagoas (original) (raw)

Papers by Marcos Vinícius Dias Vermelho

Research paper thumbnail of Modeling population and thermal lenses in the presence of Auger Upconversion for Nd^3+ doped materials

Optics Express, 2015

We present a theoretical model to thermal (TL) and population (PL) lenses effects in the presence... more 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.

Research paper thumbnail of Blue upconversion in Tm3+-Yb3+-phosphosilicate rib waveguide generated by a CW pump at 980 nm

Nonlinear Guided Waves and Their Applications, 1999

Research paper thumbnail of Ghost resonance in the chaotic Chua's circuit

Physical Review E, 2012

We experimentally investigate the ghost resonance phenomenon in the electronic circuit of Chua op... more We experimentally investigate the ghost resonance phenomenon in the electronic circuit of Chua operating in the chaotic regime. The circuit can be stimulated to jump between two single-scroll attractors by an external periodic signal with an amplitude above an intrinsic threshold. For subthreshold signals, jumps between the chaotic attractors can be promoted by a superposed white noise. We show that the circuit output can exhibit a well-defined ghost resonance signature, i.e., a resonance on a frequency that is absent in a multicomponent input signal, when the amplitudes of the input components are properly related. Further, we show that ghost resonance can be induced by the Chua's circuit's own chaotic dynamics when it is driven by a suprathreshold multicomponent signal without the need of an external noise source.

Research paper thumbnail of Analog study of the first passage time problem driven by power-law distributed noise

Physica A: Statistical Mechanics and its Applications, 2005

In this work, we develop an analog circuit to generate a stochastic signal with stationary distri... more In this work, we develop an analog circuit to generate a stochastic signal with stationary distribution exhibiting a tunable power-law tail. The proposed circuit design is a variant of a recently introduced one based on a differential equation with both multiplicative and additive noises. Here, the circuit is carefully designed in order to ensure that all components operate within their specific regimes. We provide a detailed characterization of the output signal, including the power-law exponent dependence on the tunable component. We apply the present circuit to study the first passage time problem in a simple integrate-fire model of neural dynamics driven by a non-Gaussian noise. r

Research paper thumbnail of Red–green–blue upconversion emission and energy-transfer between Tm3+ and Er3+ ions in tellurite glasses excited at 1.064μm

Journal of Solid State Chemistry, 2003

Red, green, and blue emission through frequency upconversion and energy-transfer processes in tel... more Red, green, and blue emission through frequency upconversion and energy-transfer processes in tellurite glasses doped with Tm 3+ and Er 3+ excited at 1.064 mm is investigated. The Tm 3+ /Er 3+ -codoped samples produced intense upconversion emission signals at around 480, 530, 550 and 660 nm. The 480 nm blue emission was originated from the 1 G 4 -3 H 6 transition of the Tm 3+ ions excited by a multiphoton stepwise phonon-assisted excited-state absorption process. The 530, 550 nm green and 660 nm red upconversion luminescences were identified as originating from the 2 H 11/2 , 4 S 3/2 -4 I 15/2 and 4 F 9/2 -4 I 15/2 transitions of the Er 3+ ions, respectively, populated via efficient cross-relaxation processes and excited-state absorption. White light generation employing a single infrared excitation source is also examined. r

Research paper thumbnail of Temperature investigation of infrared-to-visible frequency upconversion in erbium-doped tellurite glasses excited at 1540nm

Journal of Luminescence, 2003

Temperature investigation of infrared-to-visible frequency upconversion in erbium-doped tellurite... more Temperature investigation of infrared-to-visible frequency upconversion in erbium-doped tellurite glasses excited by CW laser radiation at 1540 nm and under cryogenic temperatures is reported. Intense upconversion emission signals around 530, 550 and 660 nm ...

Research paper thumbnail of Simple and accurate procedure for modeling erbium-doped waveguide amplifiers with high concentration

Journal of Lightwave Technology, 2000

We present an accurate, fast, and easily implemented procedure for modeling erbium-doped waveguid... more We present an accurate, fast, and easily implemented procedure for modeling erbium-doped waveguide amplifiers (EDWAs) with high concentration doping level. The model is shown to be in a very good agreement when compared with experimental results, and is used in a detailed analysis of a waveguide amplifier with 980-nm pumping

Research paper thumbnail of Energy upconversion luminescence in neodymium-doped tellurite glass

Journal of Alloys and Compounds, 2002

Luminescence Luminescence D 6540 Energy Upconversion Luminescence in Neodymium-Doped Tellurite Gl... more Luminescence Luminescence D 6540 Energy Upconversion Luminescence in Neodymium-Doped Tellurite Glass. -Nd 3+ -doped 60TeO 2 -10GeO 2 -10K 2 O-10Li 2 O-10Nb 2 O 5 glasses exhibit blue (430 and 475 nm), green (530 nm), and yellow-orange (590 nm) IR-to-VIS upconversion luminescence emissions under continuous-wave laser excitation around 800 nm. The upconversion excitation mechanism responsible for the observed emission signals is attributed to stepwise multiphoton absorption. -(AMORIM, H. T.; VERMELHO, M. V. D.; GOUVEIA-NETO*, A. S.; CASSANJES, F. C.; RIBEIRO, S. J. L.; MESSADDEQ, Y.; J. Alloys Compd. 346 (2002) 1-2, 282-284; Dep. Fis., Univ. Fed.

Research paper thumbnail of Fluorescence lifetime measurements of aerosol doped erbium in phosphosilicate planar waveguides

Fluorescence lifetimes and scatter losses for Er 3q doped, silica waveguides formed by aerosol do... more Fluorescence lifetimes and scatter losses for Er 3q doped, silica waveguides formed by aerosol doping and flame hydrolysis deposition are reported. The fast decay component and out of plane scatter decreased markedly with optimisation of the deposition technique, sintering process and co-doping regime. q 1998 Elsevier Science B.V.

Research paper thumbnail of All optical integrated upconversion fluorescence-based point temperature sensing system using< equation>< font face='verdana'> Er</font>< sup> 3+</sup></equation>-doped silica-on-silicon waveguides

In this work an optically integrated and compact point temperature sensor based upon upconversion... more In this work an optically integrated and compact point temperature sensor based upon upconversion fluorescence emission in an Er3+-doped silica-on-silicon waveguide is proposed. The sensing system relies upon the temperature information residing in the intensity ratio of two thermally coupled upconversion excited fluorescence emission signals around 530 and 550 nm due to the Er3+ transitions 2H11/2-->4I15/2 and 4S3/2-->4I15/2, respectively. The system was tested in the range of temperature from 20 °C to 140 °C. Under this circumstance the system have shown sensitivity close to 9.0×10-3/°C with a coupled pump power around 800 nm as low as 7 mW and a maximum sensitivity of 0.010/°C is expected at 250 °C.

Research paper thumbnail of Efficient third-harmonic blue-violet light generation in bulk germanosilicate and Er/sup 3+/-doped germanosilicate glasses pumped at 1.319 /spl mu/m

Quaternary International, 1996

Summary form only given. There has been a widespread interest in research and development of soli... more Summary form only given. There has been a widespread interest in research and development of solid-state blue-light sources, owing to their potential applications in optical-data storage, undersea communications, and displays. In this work we report on the generation of third-harmonic 120 /spl mu/W average power light at 440 nm in bulk GeO/sub 2/-SiO/sub 2/ and Er/sup 3+/-doped GeO/sub 2/-SiO/sub 2/

Research paper thumbnail of Blue light emission in thulium doped silica-on-silicon waveguides

Optics Communications, 1997

We report the experimental observation of up-conversion in an integrated silica-on-silicon wavegu... more We report the experimental observation of up-conversion in an integrated silica-on-silicon waveguide. Blue light at 455 nm and 475 nm was observed. In addition to the strong blue emission near infrared ( N 800 nm), visible (648 nm) and UV (366 nm) lines were also detected. We investigated the excitation mechanisms by using different pumping wavelengths. 0 1997 Elsevier Science B.V.

Research paper thumbnail of Bright visible upconversion emission and thermally enhanced cooperative energy-transfer in Tb/sup 3+//Yb/sup 3+/-codoped tellurite glass

2003 Conference on Lasers and Electro-Optics Europe (CLEO/Europe 2003) (IEEE Cat. No.03TH8666), 2003

In this work, bright visible upconversion emission excited through cooperative energy-transfer an... more In this work, bright visible upconversion emission excited through cooperative energy-transfer and thermal effects in Tb3+/Yb3+-codoped 60TeO2-10GeO2-10K2O-10Li2O-10Nb2O5glasses excited at 1.064 μm is investigated. Bright upconversion luminescence around 485, 550, 590, 625 and 655 nm, identified as due to the 5D4→7FJ(J= 6, 5, 4, 3, and 2) transitions of the terbium-ions, respectively, was generated.

Research paper thumbnail of Second-Harmonic Generation in Pr/sup 3+/-Doped Gallium-Lanthanum- Sulphide Glasses for Optical Fiber Amplifiers at 1.3/spl mu/m

Proceedings of European Meeting on Lasers and Electro-Optics CLEOE-96, 1996

Pmwdymiumdaped gallium-lanthanum-sulphide (Ga:La:S) glaaes are oue of the most promising candidat... more Pmwdymiumdaped gallium-lanthanum-sulphide (Ga:La:S) glaaes are oue of the most promising candidates for fabrication of Optical fiber amplifiers in the wavelength region of 1.3 pm, due to their low phononenergy and high quantum efficiency as compared to fluoride glasses 11.21. The experimental investigation of Ga:La:S glasses under conditions of high oplical powers around I 3 pm and 1.0 lun is important because uonlinear

Research paper thumbnail of Stochastic resonance of a periodically driven neuron under non-Gaussian noise

Physica A: Statistical Mechanics and its Applications, 2008

ABSTRACT We investigate the first-passage-time statistics of the integrate–fire neuron model driv... more ABSTRACT We investigate the first-passage-time statistics of the integrate–fire neuron model driven by a sub-threshold harmonic signal superposed with a non-Gaussian noise. Here, we considered the noise as the result of a random multiplicative process displaced from the origin by an additive term. Such a mechanism generates a power-law distributed noise whose characteristic decay exponent can be finely tuned. We performed numerical simulations to analyze the influence of the noise non-Gaussian character on the stochastic resonance condition. We found that when the noise deviates from Gaussian statistics, the resonance condition occurs at weaker noise intensities, achieving a minimum at a finite value of the distribution function decay exponent. We discuss the possible relevance of this feature to the efficiency of the firing dynamics of biological neurons, as the present result indicates that neurons would require a lower noise level to detect a sub-threshold signal when its statistics departs from Gaussian.

Research paper thumbnail of Efficient frequency upconversion of 1319-Mum radiation into intense yellow light at 580 nm in pure SiO2-core monomode optical fiber

Optics Letters, 1993

Generation of intense visible light at 580 nm with peak powers as high as 20 W through efficient ... more Generation of intense visible light at 580 nm with peak powers as high as 20 W through efficient frequency upconversion of 1.319-,m Nd:YAG laser pulses in a single span of pure SiO 2 -core single-mode optical fiber is reported. The yellow-light signal generated at 580 nm propagates in the LP 02 mode and exhibits an asymmetrical 3.5-nm bandwidth spectrum with a long tail toward high frequencies. The frequency upconversion process presents a threshold power, which depends on the fiber length, and a critical length of a few meters, at which the mechanism starts to build up. A conversion efficiency of fundamental radiation at 1.319 ,um into visible light at 580 nm of approximately 0.5% in a 20-m length of pure silica-core fiber at 5.0-kW peak pump power was measured.

Research paper thumbnail of Thermal lens study of energy transfer in Yb^3+/Tm^3+-co-doped glasses

Optics Express, 2007

Energy transfer (ET) and heat generation processes in Yb 3+ /Tm 3+ -co-doped low-silica calcium-a... more Energy transfer (ET) and heat generation processes in Yb 3+ /Tm 3+ -co-doped low-silica calcium-aluminosilicate glasses were investigated using thermal lens and photoluminescence measurements.

Research paper thumbnail of Deep and shallow trap contributions to the ionic current in the thermal-electric field poling in soda-lime glasses

Optics Express, 2007

In this paper, we investigate the contribution of deep and shallow trapped ions on the second-ord... more In this paper, we investigate the contribution of deep and shallow trapped ions on the second-order nonlinearity during typical poling procedures in soda-lime glass. The zero-electric field potential barriers of each contribution were estimated. The shallow traps, measured through the electrical ionic current, was determined as ~0.34 eV; while deep trap activation energy, measured by means of the thermal/electric field activated luminescence, was estimated ~3.8 eV. The traps show different dependence on its thermal energy onset for different applied electric field. The ionic current is linearly dependent on the electric field. The luminescence has a minimum electric field ~3.6 kV/cm and thermal energy ~31 meV (~87 o C) to occur. The average ionic jump lengths for both processes are also estimated, and the deep trap length is about ten times shorter than the shallow trap one. Samples poled at the border of the luminescence onset parameters revealed that the higher its contributions the more stable the induced second order nonlinearity.

Research paper thumbnail of Harmonic generation and frequency upconversion in Pr3+-doped germanosilicate optical fibers pumped at 1.319 μm

Optics Communications, 1997

We report on the generation of visible light signals through harmonic generation and frequency up... more We report on the generation of visible light signals through harmonic generation and frequency upconversion in Pr3+-doped germanosilicate single-mode optical fibers pumped by a Q-switched and modelocked Nd:YAG laser operated at 1.319 μm. Growth rate of the frequency-doubling process seeded by upconversion fluorescence signal and instantaneous efficient frequency-tripling is also demonstrated.

Research paper thumbnail of Efficient frequency upconversion of 1064- and 1319-µm Nd:YAG laser pulses into intense visible light in silica-based optical fibers

Journal of the Optical Society of America B, 1993

Single-pass efficient frequency upconversion of 1.064-and 1.319-,m Q-switched and mode-locked Nd:... more Single-pass efficient frequency upconversion of 1.064-and 1.319-,m Q-switched and mode-locked Nd:YAG laser pulses into visible-wavelength light in the range 450-600 nm in silica-based monomode optical fibers is reported. The visible upconverted signal propagates in the LP 0 2 fiber mode and exhibits an asymmetrical widebandwidth spectrum of several nanometers with a long tail toward high frequencies. At both pump wavelengths the upconversion process presents a critical fiber length of a few meters and a threshold power that depends on the fiber length and the pump wavelength. It is also observed that the visible light signal has its peak wavelength centered on higher frequencies for fibers with longer minimum dispersion wavelengths. In pure SiO2-core fibers pumped at 1.319 Am, conversion efficiencies of approximately 0.5% were obtained, and a 20-W peak power upconversion signal was generated at 580 nm.

Research paper thumbnail of Modeling population and thermal lenses in the presence of Auger Upconversion for Nd^3+ doped materials

Optics Express, 2015

We present a theoretical model to thermal (TL) and population (PL) lenses effects in the presence... more 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.

Research paper thumbnail of Blue upconversion in Tm3+-Yb3+-phosphosilicate rib waveguide generated by a CW pump at 980 nm

Nonlinear Guided Waves and Their Applications, 1999

Research paper thumbnail of Ghost resonance in the chaotic Chua's circuit

Physical Review E, 2012

We experimentally investigate the ghost resonance phenomenon in the electronic circuit of Chua op... more We experimentally investigate the ghost resonance phenomenon in the electronic circuit of Chua operating in the chaotic regime. The circuit can be stimulated to jump between two single-scroll attractors by an external periodic signal with an amplitude above an intrinsic threshold. For subthreshold signals, jumps between the chaotic attractors can be promoted by a superposed white noise. We show that the circuit output can exhibit a well-defined ghost resonance signature, i.e., a resonance on a frequency that is absent in a multicomponent input signal, when the amplitudes of the input components are properly related. Further, we show that ghost resonance can be induced by the Chua's circuit's own chaotic dynamics when it is driven by a suprathreshold multicomponent signal without the need of an external noise source.

Research paper thumbnail of Analog study of the first passage time problem driven by power-law distributed noise

Physica A: Statistical Mechanics and its Applications, 2005

In this work, we develop an analog circuit to generate a stochastic signal with stationary distri... more In this work, we develop an analog circuit to generate a stochastic signal with stationary distribution exhibiting a tunable power-law tail. The proposed circuit design is a variant of a recently introduced one based on a differential equation with both multiplicative and additive noises. Here, the circuit is carefully designed in order to ensure that all components operate within their specific regimes. We provide a detailed characterization of the output signal, including the power-law exponent dependence on the tunable component. We apply the present circuit to study the first passage time problem in a simple integrate-fire model of neural dynamics driven by a non-Gaussian noise. r

Research paper thumbnail of Red–green–blue upconversion emission and energy-transfer between Tm3+ and Er3+ ions in tellurite glasses excited at 1.064μm

Journal of Solid State Chemistry, 2003

Red, green, and blue emission through frequency upconversion and energy-transfer processes in tel... more Red, green, and blue emission through frequency upconversion and energy-transfer processes in tellurite glasses doped with Tm 3+ and Er 3+ excited at 1.064 mm is investigated. The Tm 3+ /Er 3+ -codoped samples produced intense upconversion emission signals at around 480, 530, 550 and 660 nm. The 480 nm blue emission was originated from the 1 G 4 -3 H 6 transition of the Tm 3+ ions excited by a multiphoton stepwise phonon-assisted excited-state absorption process. The 530, 550 nm green and 660 nm red upconversion luminescences were identified as originating from the 2 H 11/2 , 4 S 3/2 -4 I 15/2 and 4 F 9/2 -4 I 15/2 transitions of the Er 3+ ions, respectively, populated via efficient cross-relaxation processes and excited-state absorption. White light generation employing a single infrared excitation source is also examined. r

Research paper thumbnail of Temperature investigation of infrared-to-visible frequency upconversion in erbium-doped tellurite glasses excited at 1540nm

Journal of Luminescence, 2003

Temperature investigation of infrared-to-visible frequency upconversion in erbium-doped tellurite... more Temperature investigation of infrared-to-visible frequency upconversion in erbium-doped tellurite glasses excited by CW laser radiation at 1540 nm and under cryogenic temperatures is reported. Intense upconversion emission signals around 530, 550 and 660 nm ...

Research paper thumbnail of Simple and accurate procedure for modeling erbium-doped waveguide amplifiers with high concentration

Journal of Lightwave Technology, 2000

We present an accurate, fast, and easily implemented procedure for modeling erbium-doped waveguid... more We present an accurate, fast, and easily implemented procedure for modeling erbium-doped waveguide amplifiers (EDWAs) with high concentration doping level. The model is shown to be in a very good agreement when compared with experimental results, and is used in a detailed analysis of a waveguide amplifier with 980-nm pumping

Research paper thumbnail of Energy upconversion luminescence in neodymium-doped tellurite glass

Journal of Alloys and Compounds, 2002

Luminescence Luminescence D 6540 Energy Upconversion Luminescence in Neodymium-Doped Tellurite Gl... more Luminescence Luminescence D 6540 Energy Upconversion Luminescence in Neodymium-Doped Tellurite Glass. -Nd 3+ -doped 60TeO 2 -10GeO 2 -10K 2 O-10Li 2 O-10Nb 2 O 5 glasses exhibit blue (430 and 475 nm), green (530 nm), and yellow-orange (590 nm) IR-to-VIS upconversion luminescence emissions under continuous-wave laser excitation around 800 nm. The upconversion excitation mechanism responsible for the observed emission signals is attributed to stepwise multiphoton absorption. -(AMORIM, H. T.; VERMELHO, M. V. D.; GOUVEIA-NETO*, A. S.; CASSANJES, F. C.; RIBEIRO, S. J. L.; MESSADDEQ, Y.; J. Alloys Compd. 346 (2002) 1-2, 282-284; Dep. Fis., Univ. Fed.

Research paper thumbnail of Fluorescence lifetime measurements of aerosol doped erbium in phosphosilicate planar waveguides

Fluorescence lifetimes and scatter losses for Er 3q doped, silica waveguides formed by aerosol do... more Fluorescence lifetimes and scatter losses for Er 3q doped, silica waveguides formed by aerosol doping and flame hydrolysis deposition are reported. The fast decay component and out of plane scatter decreased markedly with optimisation of the deposition technique, sintering process and co-doping regime. q 1998 Elsevier Science B.V.

Research paper thumbnail of All optical integrated upconversion fluorescence-based point temperature sensing system using< equation>< font face='verdana'> Er</font>< sup> 3+</sup></equation>-doped silica-on-silicon waveguides

In this work an optically integrated and compact point temperature sensor based upon upconversion... more In this work an optically integrated and compact point temperature sensor based upon upconversion fluorescence emission in an Er3+-doped silica-on-silicon waveguide is proposed. The sensing system relies upon the temperature information residing in the intensity ratio of two thermally coupled upconversion excited fluorescence emission signals around 530 and 550 nm due to the Er3+ transitions 2H11/2-->4I15/2 and 4S3/2-->4I15/2, respectively. The system was tested in the range of temperature from 20 °C to 140 °C. Under this circumstance the system have shown sensitivity close to 9.0×10-3/°C with a coupled pump power around 800 nm as low as 7 mW and a maximum sensitivity of 0.010/°C is expected at 250 °C.

Research paper thumbnail of Efficient third-harmonic blue-violet light generation in bulk germanosilicate and Er/sup 3+/-doped germanosilicate glasses pumped at 1.319 /spl mu/m

Quaternary International, 1996

Summary form only given. There has been a widespread interest in research and development of soli... more Summary form only given. There has been a widespread interest in research and development of solid-state blue-light sources, owing to their potential applications in optical-data storage, undersea communications, and displays. In this work we report on the generation of third-harmonic 120 /spl mu/W average power light at 440 nm in bulk GeO/sub 2/-SiO/sub 2/ and Er/sup 3+/-doped GeO/sub 2/-SiO/sub 2/

Research paper thumbnail of Blue light emission in thulium doped silica-on-silicon waveguides

Optics Communications, 1997

We report the experimental observation of up-conversion in an integrated silica-on-silicon wavegu... more We report the experimental observation of up-conversion in an integrated silica-on-silicon waveguide. Blue light at 455 nm and 475 nm was observed. In addition to the strong blue emission near infrared ( N 800 nm), visible (648 nm) and UV (366 nm) lines were also detected. We investigated the excitation mechanisms by using different pumping wavelengths. 0 1997 Elsevier Science B.V.

Research paper thumbnail of Bright visible upconversion emission and thermally enhanced cooperative energy-transfer in Tb/sup 3+//Yb/sup 3+/-codoped tellurite glass

2003 Conference on Lasers and Electro-Optics Europe (CLEO/Europe 2003) (IEEE Cat. No.03TH8666), 2003

In this work, bright visible upconversion emission excited through cooperative energy-transfer an... more In this work, bright visible upconversion emission excited through cooperative energy-transfer and thermal effects in Tb3+/Yb3+-codoped 60TeO2-10GeO2-10K2O-10Li2O-10Nb2O5glasses excited at 1.064 μm is investigated. Bright upconversion luminescence around 485, 550, 590, 625 and 655 nm, identified as due to the 5D4→7FJ(J= 6, 5, 4, 3, and 2) transitions of the terbium-ions, respectively, was generated.

Research paper thumbnail of Second-Harmonic Generation in Pr/sup 3+/-Doped Gallium-Lanthanum- Sulphide Glasses for Optical Fiber Amplifiers at 1.3/spl mu/m

Proceedings of European Meeting on Lasers and Electro-Optics CLEOE-96, 1996

Pmwdymiumdaped gallium-lanthanum-sulphide (Ga:La:S) glaaes are oue of the most promising candidat... more Pmwdymiumdaped gallium-lanthanum-sulphide (Ga:La:S) glaaes are oue of the most promising candidates for fabrication of Optical fiber amplifiers in the wavelength region of 1.3 pm, due to their low phononenergy and high quantum efficiency as compared to fluoride glasses 11.21. The experimental investigation of Ga:La:S glasses under conditions of high oplical powers around I 3 pm and 1.0 lun is important because uonlinear

Research paper thumbnail of Stochastic resonance of a periodically driven neuron under non-Gaussian noise

Physica A: Statistical Mechanics and its Applications, 2008

ABSTRACT We investigate the first-passage-time statistics of the integrate–fire neuron model driv... more ABSTRACT We investigate the first-passage-time statistics of the integrate–fire neuron model driven by a sub-threshold harmonic signal superposed with a non-Gaussian noise. Here, we considered the noise as the result of a random multiplicative process displaced from the origin by an additive term. Such a mechanism generates a power-law distributed noise whose characteristic decay exponent can be finely tuned. We performed numerical simulations to analyze the influence of the noise non-Gaussian character on the stochastic resonance condition. We found that when the noise deviates from Gaussian statistics, the resonance condition occurs at weaker noise intensities, achieving a minimum at a finite value of the distribution function decay exponent. We discuss the possible relevance of this feature to the efficiency of the firing dynamics of biological neurons, as the present result indicates that neurons would require a lower noise level to detect a sub-threshold signal when its statistics departs from Gaussian.

Research paper thumbnail of Efficient frequency upconversion of 1319-Mum radiation into intense yellow light at 580 nm in pure SiO2-core monomode optical fiber

Optics Letters, 1993

Generation of intense visible light at 580 nm with peak powers as high as 20 W through efficient ... more Generation of intense visible light at 580 nm with peak powers as high as 20 W through efficient frequency upconversion of 1.319-,m Nd:YAG laser pulses in a single span of pure SiO 2 -core single-mode optical fiber is reported. The yellow-light signal generated at 580 nm propagates in the LP 02 mode and exhibits an asymmetrical 3.5-nm bandwidth spectrum with a long tail toward high frequencies. The frequency upconversion process presents a threshold power, which depends on the fiber length, and a critical length of a few meters, at which the mechanism starts to build up. A conversion efficiency of fundamental radiation at 1.319 ,um into visible light at 580 nm of approximately 0.5% in a 20-m length of pure silica-core fiber at 5.0-kW peak pump power was measured.

Research paper thumbnail of Thermal lens study of energy transfer in Yb^3+/Tm^3+-co-doped glasses

Optics Express, 2007

Energy transfer (ET) and heat generation processes in Yb 3+ /Tm 3+ -co-doped low-silica calcium-a... more Energy transfer (ET) and heat generation processes in Yb 3+ /Tm 3+ -co-doped low-silica calcium-aluminosilicate glasses were investigated using thermal lens and photoluminescence measurements.

Research paper thumbnail of Deep and shallow trap contributions to the ionic current in the thermal-electric field poling in soda-lime glasses

Optics Express, 2007

In this paper, we investigate the contribution of deep and shallow trapped ions on the second-ord... more In this paper, we investigate the contribution of deep and shallow trapped ions on the second-order nonlinearity during typical poling procedures in soda-lime glass. The zero-electric field potential barriers of each contribution were estimated. The shallow traps, measured through the electrical ionic current, was determined as ~0.34 eV; while deep trap activation energy, measured by means of the thermal/electric field activated luminescence, was estimated ~3.8 eV. The traps show different dependence on its thermal energy onset for different applied electric field. The ionic current is linearly dependent on the electric field. The luminescence has a minimum electric field ~3.6 kV/cm and thermal energy ~31 meV (~87 o C) to occur. The average ionic jump lengths for both processes are also estimated, and the deep trap length is about ten times shorter than the shallow trap one. Samples poled at the border of the luminescence onset parameters revealed that the higher its contributions the more stable the induced second order nonlinearity.

Research paper thumbnail of Harmonic generation and frequency upconversion in Pr3+-doped germanosilicate optical fibers pumped at 1.319 μm

Optics Communications, 1997

We report on the generation of visible light signals through harmonic generation and frequency up... more We report on the generation of visible light signals through harmonic generation and frequency upconversion in Pr3+-doped germanosilicate single-mode optical fibers pumped by a Q-switched and modelocked Nd:YAG laser operated at 1.319 μm. Growth rate of the frequency-doubling process seeded by upconversion fluorescence signal and instantaneous efficient frequency-tripling is also demonstrated.

Research paper thumbnail of Efficient frequency upconversion of 1064- and 1319-µm Nd:YAG laser pulses into intense visible light in silica-based optical fibers

Journal of the Optical Society of America B, 1993

Single-pass efficient frequency upconversion of 1.064-and 1.319-,m Q-switched and mode-locked Nd:... more Single-pass efficient frequency upconversion of 1.064-and 1.319-,m Q-switched and mode-locked Nd:YAG laser pulses into visible-wavelength light in the range 450-600 nm in silica-based monomode optical fibers is reported. The visible upconverted signal propagates in the LP 0 2 fiber mode and exhibits an asymmetrical widebandwidth spectrum of several nanometers with a long tail toward high frequencies. At both pump wavelengths the upconversion process presents a critical fiber length of a few meters and a threshold power that depends on the fiber length and the pump wavelength. It is also observed that the visible light signal has its peak wavelength centered on higher frequencies for fibers with longer minimum dispersion wavelengths. In pure SiO2-core fibers pumped at 1.319 Am, conversion efficiencies of approximately 0.5% were obtained, and a 20-W peak power upconversion signal was generated at 580 nm.