Ever since the mid-1960's, locking the phases of modes enabled the generation of laser pulses of ... more Ever since the mid-1960's, locking the phases of modes enabled the generation of laser pulses of duration limited only by the uncertainty principle, opening the field of ultrafast science. In contrast to conventional lasers, random lasers usually lack at least a mirror and generally emit broadband lowcoherence light. They have, nevertheless, cavity modes that distinguish them from amplifiers and superluminescent light sources. Mode spacing in random lasers is ill-defined because optical feedback comes from scattering centres at random positions. Although progress has been made towards locking spatial and longitudinal modes in random lasers, the literature lacks reports on transform-limited pulse generation despite the many decades of the field. Here the generation of sub-nanosecond transformlimited pulses from a mode-locked random fibre laser is described. Exceedingly weak (<-73 dB) Rayleigh backscattering from decimetre-long sections of telecom fibre serves as laser feedback, providing narrow spectral selectivity to the Fourier limit. This unique laser is adjustable in pulse duration (0.34-20 ns), repetition rate (0.714-1.05 MHz) and can be temperature tuned. The high spectral-efficiency pulses are applied in distributed temperature sensing with 9.0 cm and 3.3x10-3 K resolution, exemplifying how the results can drive advances in the fields of spectroscopy, telecommunications, and sensing. Introduction Laser light differs from spontaneous emission owing to the existence of cavity modes with welldefined and equally spaced frequencies. A mode-locked laser can generate transform-limited pulses when all modes are perfectly phase-locked to each other through a coupling mechanism such as periodic phase or amplitude modulation [1-4]. Random lasers [5,6,7] are based on a stochastic distribution of scattering centres that help form an effective cavity with laser modes, even when a laser mirror is lacking [8,9,10]. The random mode-spacing makes it difficult to lock the phases of the modes to each other [11-17]. Modelocking random lasers where the gain and scattering coexist spatially, as in dyes [6] or semiconductor powders [18], is even more challenging. For this reason, few random laser reports exist on locking the spatial modes [11-16] and the longitudinal modal distribution [17], and none to the Fourier transform limit. The generation of transform-limited pulses in random lasers can be attempted in a simplified system. In random single-mode fibre lasers [19], the complexity is reduced to one spatial dimension. Furthermore, it is possible to use lumped amplifiers to separate the section providing gain from the section with randomly distributed scatterers [20,21,22]. Random feedback from a telecom fibre lies at the
Using controlled feedback and coincident far infrared absorption, we have shown that the superrad... more Using controlled feedback and coincident far infrared absorption, we have shown that the superradiant emission process in NH3 pumped by the 9R16 line of a CO2 TEA laser has a marked effect on the absorption of laser energy and vibrational heating of the gas. Since many polyatomic molecules pumped by IR laser are efficient superradiant far infrared sources, the effect is important for laser induced fluorescence studies in these polyatomics.
We demonstrate an order-of-magnitude increase in the efficiency for first-Stokes Raman generation... more We demonstrate an order-of-magnitude increase in the efficiency for first-Stokes Raman generation in a gas cell (CH(4)) by seeding with spontaneous emission from a dye cell. Second-Stokes and first-anti-Stokes lines were also generated more efficiently. The pump energy required for production of a 1% conversion efficiency for the first-Stokes emission is reduced by a factor of 1.8 below that required without seeding.
The extraordinary component of a cw argon-ion laser beam propagating through a ruby crystal is ob... more The extraordinary component of a cw argon-ion laser beam propagating through a ruby crystal is observed to exhibit a power dependent deflection. A divergence angle of nearly 6 mrad between the ordinary and extraordinary beam is measured when 500 mW of 514.5 nm radiation is injected into the ruby rod. A simple theory for the anisotropic nonlinear index of refraction and a numerical simulation of the coupled nonlinear wave equations in (2 + 1) dimensions given good agreement with the experimental results.
Two pulse-shortening schemes based on the nonlinear propagation of picosecond pulses from a Nd: Y... more Two pulse-shortening schemes based on the nonlinear propagation of picosecond pulses from a Nd: YAG laser in single-mode optical fibres are described. In the first experiment, a spectral-windowing technique was employed to compress self-phase modulated pulses exiting 100 m of optical fibre, and compression factors of 2.5 were recorded in good agreement with theoretical predictions. The technique was adapted to enable the time-dependent frequency shift occurring after pulse propagation through 2 km of fibre to be measured. In the second experiment, cascaded stimulated Raman generation, occurring when a high-power pump pulse propagated in 4 m of fibre, was studied. Lower-order components in the cascade were severely depleted through generation of higher-order Stokes signals, leaving negatively chirped pulse fragments. These were compressed with a dispersion-tunable Gires-Tournois interferometer and compression ratios of times 4 were obtained.
2014 Fotonica AEIT Italian Conference on Photonics Technologies, 2014
ABSTRACT Waveguiding light-emitting strips have been written in a blank LiF crystal with a femtos... more ABSTRACT Waveguiding light-emitting strips have been written in a blank LiF crystal with a femtosecond laser, by translating the sample under the pulsed focused beam. Light guiding through these buried micro-structures was observed at several wavelengths between 458 and 1550 nm. Visible photoluminescence spectra of aggregate F2 and F3+ laser active color centers were measured. The refractive index increase, estimated of the order of 10-4 in the visible and near-infrared spectral intervals, is consistent with the stable formation of electronic point defects in LiF. These results are promising for the realization of miniaturized optical waveguiding solid-state amplifiers and lasers based on color centers.
In a world where convergence is becoming the new wave, nanobiophotonics sets the frame as an outs... more In a world where convergence is becoming the new wave, nanobiophotonics sets the frame as an outstanding example, as it is at the focal point of three well-established fields: nanotechnology, photonics, and biomedical sciences. The fast development of nanotechnology, from the 1980's, supported by tools that can observe and manipulate in the nanoworld has found in photonics-defined as the technology of generating, harnessing and transmitting photons-a special companion for applications. Nanophotonics is already a discipline in its own right [1]. Recent developments in nanotechnology and photonics related to biomedical sciences, both basic and applied, have led to the newly born field of nanobiophotonics. Figure 1 depicts this convergence. Notice in this figure the side roads that exist, leading to other cross-disciplinary and fertile fields, such as nanophotonics, nanomedicine and biophotonics. Fig.1. Pictorial description of the scientific convergence leading to Nanobiophotonics. Advances in nanobiophotonics are striking. Leading experts worldwide have put together multidisciplinary teams to address challenges that range from noninvasive imaging to therapies and treatment, all using photons and nanoparticles of different shapes and functionalities. This commentary focuses on two of these advances. Far-field Optical Nanoscopy. This emerging field has pushed optical microscopy to the nanoscale, providing the ability to optically observe well beyond the diffraction limit. Its main advantage for nanobiophotonics, as opposed to near-field microscopy, is the ability to see inside biological media, such as cells [2]. Several approaches have been developed to break the diffraction limit, such as optical confocal microscopy, multiphoton microscopy, and 4Pi microscopy (mainly two-photon excited). Perhaps the most exciting advances have arisen from the pioneering work of Hell and co-workers who introduced the stimulated emission depletion (STED) microscopy, providing Nanobiophotonics N a n o t e c h n o l o g y P h o t o n i c s Biomedical Sciences Nanobiophotonics N a n o t e c h n o l o g y P h o t o n i c s Biomedical Sciences
Technical Digest. CLEO/Pacific Rim '99. Pacific Rim Conference on Lasers and Electro-Optics (Cat. No.99TH8464)
ABSTRACT In this work we describe the application of the hyper-Rayleigh scattering technique (HRS... more ABSTRACT In this work we describe the application of the hyper-Rayleigh scattering technique (HRS) and the Z-scan technique to determine β and γ, the first and the second hyperpolarizabilities, respectively, of nine different mesoionic structures. The mesoionic samples were synthesized and dissolved in DMSO
I review the fast growing progress in thulium doped fiber amplifiers (TDFA) for S-band optical co... more I review the fast growing progress in thulium doped fiber amplifiers (TDFA) for S-band optical communication systems. The main results reported on pump schemes and amplifiers efficiencies are given. In particular, the characterization of TDFAs regarding distributed gain optimization using the coherent optical frequency domain reflectometry is described, from which the optimum gain-length product for a given configuration can be inferred in a non-invasive and non-destructive way.
Conference Digest. 2000 Conference on Lasers and Electro-Optics Europe (Cat. No.00TH8505)
ABSTRACT Summary form only given. The porphyrin iron complexes are important components of nature... more ABSTRACT Summary form only given. The porphyrin iron complexes are important components of nature involved in various biological processes. We report on the studies of the effect of pH and ionic strength on the equilibrium of different forms of the Fe(lII) complex of mesotetrakis(4-N-methyl-pyridiniomyl) porphyrin Fe(II)TmPyP or FeTMP in aqueous solutions by linear optical absorption, the Z-scan technique and EPR. The experimental results of Z-scan and electroparamagnetic resonance (EPR) are compared with semi-empirical quantum chemical calculations (ZINDO)
Using the hyper-Rayleigh and the Z-scan techniques, we determined the first and the second hyperp... more Using the hyper-Rayleigh and the Z-scan techniques, we determined the first and the second hyperpolarizabilities of molecules containing mesoinic rings. We also present quantum chemical calculations for both hyperpolarizabilities that are in a good qualitative agreement with experimental results. Optical Kerr gate measurements indicate response times faster than 60 fs for these compounds which possess intrinsic push-pull characteristics and are
We report on the spectroscopic characterization of infrared (1064 nm) to uv-visible up-converted ... more We report on the spectroscopic characterization of infrared (1064 nm) to uv-visible up-converted emission in multimode Tm3+-doped fluorozirconate fibers. Different excitation pathways were clearly observed for the up-converted fluorescence, which varied according to the incident pump power.
Ever since the mid-1960's, locking the phases of modes enabled the generation of laser pulses of ... more Ever since the mid-1960's, locking the phases of modes enabled the generation of laser pulses of duration limited only by the uncertainty principle, opening the field of ultrafast science. In contrast to conventional lasers, random lasers usually lack at least a mirror and generally emit broadband lowcoherence light. They have, nevertheless, cavity modes that distinguish them from amplifiers and superluminescent light sources. Mode spacing in random lasers is ill-defined because optical feedback comes from scattering centres at random positions. Although progress has been made towards locking spatial and longitudinal modes in random lasers, the literature lacks reports on transform-limited pulse generation despite the many decades of the field. Here the generation of sub-nanosecond transformlimited pulses from a mode-locked random fibre laser is described. Exceedingly weak (<-73 dB) Rayleigh backscattering from decimetre-long sections of telecom fibre serves as laser feedback, providing narrow spectral selectivity to the Fourier limit. This unique laser is adjustable in pulse duration (0.34-20 ns), repetition rate (0.714-1.05 MHz) and can be temperature tuned. The high spectral-efficiency pulses are applied in distributed temperature sensing with 9.0 cm and 3.3x10-3 K resolution, exemplifying how the results can drive advances in the fields of spectroscopy, telecommunications, and sensing. Introduction Laser light differs from spontaneous emission owing to the existence of cavity modes with welldefined and equally spaced frequencies. A mode-locked laser can generate transform-limited pulses when all modes are perfectly phase-locked to each other through a coupling mechanism such as periodic phase or amplitude modulation [1-4]. Random lasers [5,6,7] are based on a stochastic distribution of scattering centres that help form an effective cavity with laser modes, even when a laser mirror is lacking [8,9,10]. The random mode-spacing makes it difficult to lock the phases of the modes to each other [11-17]. Modelocking random lasers where the gain and scattering coexist spatially, as in dyes [6] or semiconductor powders [18], is even more challenging. For this reason, few random laser reports exist on locking the spatial modes [11-16] and the longitudinal modal distribution [17], and none to the Fourier transform limit. The generation of transform-limited pulses in random lasers can be attempted in a simplified system. In random single-mode fibre lasers [19], the complexity is reduced to one spatial dimension. Furthermore, it is possible to use lumped amplifiers to separate the section providing gain from the section with randomly distributed scatterers [20,21,22]. Random feedback from a telecom fibre lies at the
Using controlled feedback and coincident far infrared absorption, we have shown that the superrad... more Using controlled feedback and coincident far infrared absorption, we have shown that the superradiant emission process in NH3 pumped by the 9R16 line of a CO2 TEA laser has a marked effect on the absorption of laser energy and vibrational heating of the gas. Since many polyatomic molecules pumped by IR laser are efficient superradiant far infrared sources, the effect is important for laser induced fluorescence studies in these polyatomics.
We demonstrate an order-of-magnitude increase in the efficiency for first-Stokes Raman generation... more We demonstrate an order-of-magnitude increase in the efficiency for first-Stokes Raman generation in a gas cell (CH(4)) by seeding with spontaneous emission from a dye cell. Second-Stokes and first-anti-Stokes lines were also generated more efficiently. The pump energy required for production of a 1% conversion efficiency for the first-Stokes emission is reduced by a factor of 1.8 below that required without seeding.
The extraordinary component of a cw argon-ion laser beam propagating through a ruby crystal is ob... more The extraordinary component of a cw argon-ion laser beam propagating through a ruby crystal is observed to exhibit a power dependent deflection. A divergence angle of nearly 6 mrad between the ordinary and extraordinary beam is measured when 500 mW of 514.5 nm radiation is injected into the ruby rod. A simple theory for the anisotropic nonlinear index of refraction and a numerical simulation of the coupled nonlinear wave equations in (2 + 1) dimensions given good agreement with the experimental results.
Two pulse-shortening schemes based on the nonlinear propagation of picosecond pulses from a Nd: Y... more Two pulse-shortening schemes based on the nonlinear propagation of picosecond pulses from a Nd: YAG laser in single-mode optical fibres are described. In the first experiment, a spectral-windowing technique was employed to compress self-phase modulated pulses exiting 100 m of optical fibre, and compression factors of 2.5 were recorded in good agreement with theoretical predictions. The technique was adapted to enable the time-dependent frequency shift occurring after pulse propagation through 2 km of fibre to be measured. In the second experiment, cascaded stimulated Raman generation, occurring when a high-power pump pulse propagated in 4 m of fibre, was studied. Lower-order components in the cascade were severely depleted through generation of higher-order Stokes signals, leaving negatively chirped pulse fragments. These were compressed with a dispersion-tunable Gires-Tournois interferometer and compression ratios of times 4 were obtained.
2014 Fotonica AEIT Italian Conference on Photonics Technologies, 2014
ABSTRACT Waveguiding light-emitting strips have been written in a blank LiF crystal with a femtos... more ABSTRACT Waveguiding light-emitting strips have been written in a blank LiF crystal with a femtosecond laser, by translating the sample under the pulsed focused beam. Light guiding through these buried micro-structures was observed at several wavelengths between 458 and 1550 nm. Visible photoluminescence spectra of aggregate F2 and F3+ laser active color centers were measured. The refractive index increase, estimated of the order of 10-4 in the visible and near-infrared spectral intervals, is consistent with the stable formation of electronic point defects in LiF. These results are promising for the realization of miniaturized optical waveguiding solid-state amplifiers and lasers based on color centers.
In a world where convergence is becoming the new wave, nanobiophotonics sets the frame as an outs... more In a world where convergence is becoming the new wave, nanobiophotonics sets the frame as an outstanding example, as it is at the focal point of three well-established fields: nanotechnology, photonics, and biomedical sciences. The fast development of nanotechnology, from the 1980's, supported by tools that can observe and manipulate in the nanoworld has found in photonics-defined as the technology of generating, harnessing and transmitting photons-a special companion for applications. Nanophotonics is already a discipline in its own right [1]. Recent developments in nanotechnology and photonics related to biomedical sciences, both basic and applied, have led to the newly born field of nanobiophotonics. Figure 1 depicts this convergence. Notice in this figure the side roads that exist, leading to other cross-disciplinary and fertile fields, such as nanophotonics, nanomedicine and biophotonics. Fig.1. Pictorial description of the scientific convergence leading to Nanobiophotonics. Advances in nanobiophotonics are striking. Leading experts worldwide have put together multidisciplinary teams to address challenges that range from noninvasive imaging to therapies and treatment, all using photons and nanoparticles of different shapes and functionalities. This commentary focuses on two of these advances. Far-field Optical Nanoscopy. This emerging field has pushed optical microscopy to the nanoscale, providing the ability to optically observe well beyond the diffraction limit. Its main advantage for nanobiophotonics, as opposed to near-field microscopy, is the ability to see inside biological media, such as cells [2]. Several approaches have been developed to break the diffraction limit, such as optical confocal microscopy, multiphoton microscopy, and 4Pi microscopy (mainly two-photon excited). Perhaps the most exciting advances have arisen from the pioneering work of Hell and co-workers who introduced the stimulated emission depletion (STED) microscopy, providing Nanobiophotonics N a n o t e c h n o l o g y P h o t o n i c s Biomedical Sciences Nanobiophotonics N a n o t e c h n o l o g y P h o t o n i c s Biomedical Sciences
Technical Digest. CLEO/Pacific Rim '99. Pacific Rim Conference on Lasers and Electro-Optics (Cat. No.99TH8464)
ABSTRACT In this work we describe the application of the hyper-Rayleigh scattering technique (HRS... more ABSTRACT In this work we describe the application of the hyper-Rayleigh scattering technique (HRS) and the Z-scan technique to determine β and γ, the first and the second hyperpolarizabilities, respectively, of nine different mesoionic structures. The mesoionic samples were synthesized and dissolved in DMSO
I review the fast growing progress in thulium doped fiber amplifiers (TDFA) for S-band optical co... more I review the fast growing progress in thulium doped fiber amplifiers (TDFA) for S-band optical communication systems. The main results reported on pump schemes and amplifiers efficiencies are given. In particular, the characterization of TDFAs regarding distributed gain optimization using the coherent optical frequency domain reflectometry is described, from which the optimum gain-length product for a given configuration can be inferred in a non-invasive and non-destructive way.
Conference Digest. 2000 Conference on Lasers and Electro-Optics Europe (Cat. No.00TH8505)
ABSTRACT Summary form only given. The porphyrin iron complexes are important components of nature... more ABSTRACT Summary form only given. The porphyrin iron complexes are important components of nature involved in various biological processes. We report on the studies of the effect of pH and ionic strength on the equilibrium of different forms of the Fe(lII) complex of mesotetrakis(4-N-methyl-pyridiniomyl) porphyrin Fe(II)TmPyP or FeTMP in aqueous solutions by linear optical absorption, the Z-scan technique and EPR. The experimental results of Z-scan and electroparamagnetic resonance (EPR) are compared with semi-empirical quantum chemical calculations (ZINDO)
Using the hyper-Rayleigh and the Z-scan techniques, we determined the first and the second hyperp... more Using the hyper-Rayleigh and the Z-scan techniques, we determined the first and the second hyperpolarizabilities of molecules containing mesoinic rings. We also present quantum chemical calculations for both hyperpolarizabilities that are in a good qualitative agreement with experimental results. Optical Kerr gate measurements indicate response times faster than 60 fs for these compounds which possess intrinsic push-pull characteristics and are
We report on the spectroscopic characterization of infrared (1064 nm) to uv-visible up-converted ... more We report on the spectroscopic characterization of infrared (1064 nm) to uv-visible up-converted emission in multimode Tm3+-doped fluorozirconate fibers. Different excitation pathways were clearly observed for the up-converted fluorescence, which varied according to the incident pump power.
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Papers by Anderson Gomes