R. Vilaseca - Academia.edu (original) (raw)

Papers by R. Vilaseca

Optica Pura y Aplicada

ABSTRACT

Cornell University - arXiv, Oct 22, 2010

In this letter we experimentally demonstrate second harmonic conversion in the opaque region of a... more In this letter we experimentally demonstrate second harmonic conversion in the opaque region of a GaAs cavity with efficiencies of the order of 0.1% at 612nm, using 3ps pump pulses having peak intensities of order of 10MW/cm 2. We show that the conversion efficiency of the inhomogeneous, phase-locked second harmonic component is a quadratic function of the cavity factor Q.

In this Letter, we experimentally demonstrate the enhancement of the inhomogeneous second harmoni... more In this Letter, we experimentally demonstrate the enhancement of the inhomogeneous second harmonic conversion in the opaque region of a GaAs cavity with efficiencies of the order of 0.1% at 612 nm, using 3 ps pump pulses having peak intensities of the order of 10 MW=cm 2. We show that the conversion efficiency of the inhomogeneous, phase-locked second harmonic component is a quadratic function of the cavity factor Q.

We study the enhancement of the second and third harmonic generation using ultra short pulses in ... more We study the enhancement of the second and third harmonic generation using ultra short pulses in a cavity environment, focusing on the role of the phase locking phenomena. Despite the fact that the cavity is only resonant at the fundamental frequency and the harmonics are tuned in a spectral range of huge nominal absorption, we predict and experimentally observe the harmonics become localized inside the cavity leading to relatively large conversion efficiencies. This unique behavior reveals new optical phenomena and new applications for opaque nonlinear materials (i.e. semiconductors) in the visible and UV ranges.

ABSTRACT We analyze different possibilities to control and modify the optical response of a photo... more ABSTRACT We analyze different possibilities to control and modify the optical response of a photonic crystal via nonlinear effects induced by an external optical control beam. We consider two different nonlinear schemes in which such active optical control may be achieved. The first one is based on the second order nonlinear interaction within a one-dimensional photonic structure with a defect. We show that using a control beam at the second harmonic frequency we can induce important changes in the reflection and transmission of a signal at the fundamental frequency. In the second scheme, the nonlinearity is achieved via electronically resonant optical Kerr effect, through optical injection of carriers. We report on wide wavelength tuning of a non defective two-dimensional photonic crystal resonance observed in reflectivity. Moreover, we prove that the same structure shows different optical functions such as frequency shifting, switching, amplification and lasing, if it is used under appropriate stimulus. These very fast effects may be used for the design of an ultra-fast all-optical modulator or switching device to be integrated in a photonic circuit.

Journal of Applied Physics, 2000

A method for generating second-harmonic light from silica glass by doping its surface layer with ... more A method for generating second-harmonic light from silica glass by doping its surface layer with ions is presented. When anions CO32-, OH- or Cl- are introduced from the cathodic surface during poling, the second-harmonic signal generated near that surface is enhanced by two orders of magnitude with respect to the case of poling without doping. The penetration depths of CO32-, OH- and Cl- have been measured by the etching technique. In contrast, by doping the anodic surface with cations Li+, Na+ or K+, the second-harmonic signal drops to one tenth of that corresponding to the case of poling without doping. This indicates that in the anodic surface the main charges are negative, and the positive charges neutralize them to decrease the strength of the electric field that is at the origin of the second-order susceptibility. Secondary ion mass spectroscopy detection shows the concentration distribution of the injected lithium in the surface layer. The second-harmonic signal from the anodic surface decreases monotonically with increasing poling-doping time up to 300 min. Doping from interfaces far from the electrodes is inefficient for influencing the second-harmonic generation.

The absorption of a weak laser beam probing a Doppler-broadened three-level system saturated by a... more The absorption of a weak laser beam probing a Doppler-broadened three-level system saturated by a standing-wave pump is studied theoretically for the case of small saturator detunings. The features of the obtained absorption spectra are analysed by means of the dressed-atom approach. A strong influence of radiative and high-order multi-photon processes is showed. The influence of saturator tuning fluctuations on the narrow Doppler-free peak which appears in the resonant case is analysed and its consequences for high-resolution applications are considered.

i tantes cerveses al voltant d'una taula parlant de tots els temes haguts i per haver, que m'han ... more i tantes cerveses al voltant d'una taula parlant de tots els temes haguts i per haver, que m'han animat i esperonat quan ho he necessitat i que m'han fet sentir estimat i valorat. Sempreés reconfortant tornar-te a sentir com a casa. Agraeixo a la meva família la fe cega que han tingut en la meva feina. Sempre Agraiments iii s'han preocupat per mi i m'han ajudat en tot allò que han pogut amb abnegació i amor. Qui més ha sofert tots els meus mal de caps i dubtes probablement ha estat la Mariona. M'ha aconsellat amb seny i objectivitat i sempre ha intentat animar-me quan les coses no anaven bé. Sense ella, no hauria arrivat al final d'aquest camí. L'altre persona que sempre he tingut com a referència ha estat la Maite, qui ha cregut sempre en mi i les meves possibilitats, més fins i tot, que jo mateix. Sempre disposada a escoltar-me, ha aguantat estoicament les meves explicacions sobre la recerca que estava fent. A elles dues, les dues dones de la meva vida, a les que admiro i venero els hi dedico la meva Tesi.

Optics Communications, 1981

The narrow peak appearing at the center of the velocity distribution of the populations for satur... more The narrow peak appearing at the center of the velocity distribution of the populations for saturation by a detuned standing-wave laser is analysed theoretically as a function of the relaxation parameters and the pump laser intensity. This peak allows high-resolution spectroscopic measurements when a frequency-unstabilized pump laser and a low intensity high-stability probe laser are used.

Coherence and Quantum Optics VI, 1989

Coherently pumped lasers (CPL) operating in the far-infrared spectral region shown a wealth of in... more Coherently pumped lasers (CPL) operating in the far-infrared spectral region shown a wealth of instabilities1, including a behavior remarkably similar2,3 with the predictions of the paradigmatic Lorenz-Haken model of a single-mode homogeneously broadened laser4,5. The qualitative agreement; between theory and experiments2,3 was rather surprising, for the model4,5 refers to a two-level system whereas the CPL operate on a three-level scheme, where the pumping and lasing transitions share a common upper level. Dupertuis et al.6 have identified conditions for the mathematical reduction of the CPL equations to the Lorenz-Haken equations4, but these conditions were not all fulfilled in the experiments of Weiss and collaborators2,3.

Physical Review E, 1997

ABSTRACT A topological analysis has been carried out on time series generated from a Doppler broa... more ABSTRACT A topological analysis has been carried out on time series generated from a Doppler broadened three-level model, which has been proposed to describe optically pumped lasers, in particular the far-infrared ammonia laser. In certain parameter ranges it is known that the experimental findings and the predictions from the Doppler broadened optically pumped laser model closely agree and show features that follow the dynamics of the Lorenz model. By means of a suitable symmetry adapted differential phase space embedding, the present analysis shows that, in fact, the embedded data sets are topologically equivalent to the Lorenz attractor. This equivalence essentially remains upon variation of a laser control parameter within a certain range.

Examines the dynamic behaviour of lasers and other optical systems from the point of view of the ... more Examines the dynamic behaviour of lasers and other optical systems from the point of view of the nonlinear dynamics of dissipative systems, discussing temporal and spatio-temporal instabilities and characterizing periodic and chaotic behaviours. Other contributions consider the quantum properties of electromagnetic radiation, in particular the generation and properties of squeezed states of light. In the discussion of above-threshold ionization emphasis is placed on the modeling and interpretation of observed features and the prediction of new phenomena. The combination of longer reviews and shorter research reports aims to provide the reader with a clear picture of the current status of these areas of otpics.

Physical Review E - PHYS REV E, 1996

Suppression of chaos and stabilization of an unstable steady state in a dissipative nonlinear sys... more Suppression of chaos and stabilization of an unstable steady state in a dissipative nonlinear system are demonstrated numerically by means of large-amplitude slow (nonresonant) modulation of a control parameter. A wide domain of modulation amplitudes and frequencies is allowed. The steady state becomes influenced by the slow modulation, although in some cases this influence is very small. It can be said that suppression of chaos occurs, naturally, without any further action, in slowly modulated systems.

We present an experimental study of the second harmonic light generated at a slab of nonlinear mo... more We present an experimental study of the second harmonic light generated at a slab of nonlinear molecules embedded in a 1D periodic structure, truncated by the introduction of a defect in the central period. We have observed an enhancement of the nonlinear interaction in the vicinity of the defect, when the second harmonic wave is excited for modes within the forbidden zone or stop band. We have also observed an enhancement near the band edge, where the group velocity approaches zero. Second harmonic generation is completely suppressed for local modes within the forbidden band other than the defect mode.

Physical Review A, 1992

ABSTRACT

Physical Review A, 1993

The inhuence of light polarization on the dynamics of an optically pumped single-mode laser with ... more The inhuence of light polarization on the dynamics of an optically pumped single-mode laser with a homogeneously broadened four-level medium is theoretically investigated in detail. Pump and laser fields with either parallel or crossed linear polarizations are considered, as are typical in far-infraredlaser experiments. Numerical simulations reveal dramatically different dynamic behaviors for these two polarization configurations. The analysis of the model equations allows us to find the physical origin of both behaviors. In particular, the crossed-polarization configuration is shown to be effective in decoupling the pump and laser fields, thus allowing for the appearance of Lorenz-type dynamics.

Optics Letters, 1995

We present an experimental study of the generation of second-harmonic light in a one-dimensional ... more We present an experimental study of the generation of second-harmonic light in a one-dimensional periodic structure truncated by the introduction of a defect in the central period. We observed an enhancement of the nonlinear interaction in the vicinity of the defect when the second-harmonic wave was excited for modes within the forbidden zone or stop band. We also observed an enhancement near the band edge, where the group velocity approaches zero. Second-harmonic generation is completely suppressed for local modes within the forbidden band other than the defect mode.

Journal of Physics D: Applied Physics, 1988

Summary form only given. In a cascaded configuration, the quadratic nonlinear interaction can be ... more Summary form only given. In a cascaded configuration, the quadratic nonlinear interaction can be used to induce a change in the effective index of refraction of a nonlinear material. When this change is induced within a microcavity the enhanced interaction within the structure may lead to a large change in the transmission or reflection properties of that material. The use

Optica Pura y Aplicada

ABSTRACT

Cornell University - arXiv, Oct 22, 2010

In this letter we experimentally demonstrate second harmonic conversion in the opaque region of a... more In this letter we experimentally demonstrate second harmonic conversion in the opaque region of a GaAs cavity with efficiencies of the order of 0.1% at 612nm, using 3ps pump pulses having peak intensities of order of 10MW/cm 2. We show that the conversion efficiency of the inhomogeneous, phase-locked second harmonic component is a quadratic function of the cavity factor Q.

In this Letter, we experimentally demonstrate the enhancement of the inhomogeneous second harmoni... more In this Letter, we experimentally demonstrate the enhancement of the inhomogeneous second harmonic conversion in the opaque region of a GaAs cavity with efficiencies of the order of 0.1% at 612 nm, using 3 ps pump pulses having peak intensities of the order of 10 MW=cm 2. We show that the conversion efficiency of the inhomogeneous, phase-locked second harmonic component is a quadratic function of the cavity factor Q.

We study the enhancement of the second and third harmonic generation using ultra short pulses in ... more We study the enhancement of the second and third harmonic generation using ultra short pulses in a cavity environment, focusing on the role of the phase locking phenomena. Despite the fact that the cavity is only resonant at the fundamental frequency and the harmonics are tuned in a spectral range of huge nominal absorption, we predict and experimentally observe the harmonics become localized inside the cavity leading to relatively large conversion efficiencies. This unique behavior reveals new optical phenomena and new applications for opaque nonlinear materials (i.e. semiconductors) in the visible and UV ranges.

ABSTRACT We analyze different possibilities to control and modify the optical response of a photo... more ABSTRACT We analyze different possibilities to control and modify the optical response of a photonic crystal via nonlinear effects induced by an external optical control beam. We consider two different nonlinear schemes in which such active optical control may be achieved. The first one is based on the second order nonlinear interaction within a one-dimensional photonic structure with a defect. We show that using a control beam at the second harmonic frequency we can induce important changes in the reflection and transmission of a signal at the fundamental frequency. In the second scheme, the nonlinearity is achieved via electronically resonant optical Kerr effect, through optical injection of carriers. We report on wide wavelength tuning of a non defective two-dimensional photonic crystal resonance observed in reflectivity. Moreover, we prove that the same structure shows different optical functions such as frequency shifting, switching, amplification and lasing, if it is used under appropriate stimulus. These very fast effects may be used for the design of an ultra-fast all-optical modulator or switching device to be integrated in a photonic circuit.

Journal of Applied Physics, 2000

A method for generating second-harmonic light from silica glass by doping its surface layer with ... more A method for generating second-harmonic light from silica glass by doping its surface layer with ions is presented. When anions CO32-, OH- or Cl- are introduced from the cathodic surface during poling, the second-harmonic signal generated near that surface is enhanced by two orders of magnitude with respect to the case of poling without doping. The penetration depths of CO32-, OH- and Cl- have been measured by the etching technique. In contrast, by doping the anodic surface with cations Li+, Na+ or K+, the second-harmonic signal drops to one tenth of that corresponding to the case of poling without doping. This indicates that in the anodic surface the main charges are negative, and the positive charges neutralize them to decrease the strength of the electric field that is at the origin of the second-order susceptibility. Secondary ion mass spectroscopy detection shows the concentration distribution of the injected lithium in the surface layer. The second-harmonic signal from the anodic surface decreases monotonically with increasing poling-doping time up to 300 min. Doping from interfaces far from the electrodes is inefficient for influencing the second-harmonic generation.

The absorption of a weak laser beam probing a Doppler-broadened three-level system saturated by a... more The absorption of a weak laser beam probing a Doppler-broadened three-level system saturated by a standing-wave pump is studied theoretically for the case of small saturator detunings. The features of the obtained absorption spectra are analysed by means of the dressed-atom approach. A strong influence of radiative and high-order multi-photon processes is showed. The influence of saturator tuning fluctuations on the narrow Doppler-free peak which appears in the resonant case is analysed and its consequences for high-resolution applications are considered.

i tantes cerveses al voltant d'una taula parlant de tots els temes haguts i per haver, que m'han ... more i tantes cerveses al voltant d'una taula parlant de tots els temes haguts i per haver, que m'han animat i esperonat quan ho he necessitat i que m'han fet sentir estimat i valorat. Sempreés reconfortant tornar-te a sentir com a casa. Agraeixo a la meva família la fe cega que han tingut en la meva feina. Sempre Agraiments iii s'han preocupat per mi i m'han ajudat en tot allò que han pogut amb abnegació i amor. Qui més ha sofert tots els meus mal de caps i dubtes probablement ha estat la Mariona. M'ha aconsellat amb seny i objectivitat i sempre ha intentat animar-me quan les coses no anaven bé. Sense ella, no hauria arrivat al final d'aquest camí. L'altre persona que sempre he tingut com a referència ha estat la Maite, qui ha cregut sempre en mi i les meves possibilitats, més fins i tot, que jo mateix. Sempre disposada a escoltar-me, ha aguantat estoicament les meves explicacions sobre la recerca que estava fent. A elles dues, les dues dones de la meva vida, a les que admiro i venero els hi dedico la meva Tesi.

Optics Communications, 1981

The narrow peak appearing at the center of the velocity distribution of the populations for satur... more The narrow peak appearing at the center of the velocity distribution of the populations for saturation by a detuned standing-wave laser is analysed theoretically as a function of the relaxation parameters and the pump laser intensity. This peak allows high-resolution spectroscopic measurements when a frequency-unstabilized pump laser and a low intensity high-stability probe laser are used.

Coherence and Quantum Optics VI, 1989

Coherently pumped lasers (CPL) operating in the far-infrared spectral region shown a wealth of in... more Coherently pumped lasers (CPL) operating in the far-infrared spectral region shown a wealth of instabilities1, including a behavior remarkably similar2,3 with the predictions of the paradigmatic Lorenz-Haken model of a single-mode homogeneously broadened laser4,5. The qualitative agreement; between theory and experiments2,3 was rather surprising, for the model4,5 refers to a two-level system whereas the CPL operate on a three-level scheme, where the pumping and lasing transitions share a common upper level. Dupertuis et al.6 have identified conditions for the mathematical reduction of the CPL equations to the Lorenz-Haken equations4, but these conditions were not all fulfilled in the experiments of Weiss and collaborators2,3.

Physical Review E, 1997

ABSTRACT A topological analysis has been carried out on time series generated from a Doppler broa... more ABSTRACT A topological analysis has been carried out on time series generated from a Doppler broadened three-level model, which has been proposed to describe optically pumped lasers, in particular the far-infrared ammonia laser. In certain parameter ranges it is known that the experimental findings and the predictions from the Doppler broadened optically pumped laser model closely agree and show features that follow the dynamics of the Lorenz model. By means of a suitable symmetry adapted differential phase space embedding, the present analysis shows that, in fact, the embedded data sets are topologically equivalent to the Lorenz attractor. This equivalence essentially remains upon variation of a laser control parameter within a certain range.

Examines the dynamic behaviour of lasers and other optical systems from the point of view of the ... more Examines the dynamic behaviour of lasers and other optical systems from the point of view of the nonlinear dynamics of dissipative systems, discussing temporal and spatio-temporal instabilities and characterizing periodic and chaotic behaviours. Other contributions consider the quantum properties of electromagnetic radiation, in particular the generation and properties of squeezed states of light. In the discussion of above-threshold ionization emphasis is placed on the modeling and interpretation of observed features and the prediction of new phenomena. The combination of longer reviews and shorter research reports aims to provide the reader with a clear picture of the current status of these areas of otpics.

Physical Review E - PHYS REV E, 1996

Suppression of chaos and stabilization of an unstable steady state in a dissipative nonlinear sys... more Suppression of chaos and stabilization of an unstable steady state in a dissipative nonlinear system are demonstrated numerically by means of large-amplitude slow (nonresonant) modulation of a control parameter. A wide domain of modulation amplitudes and frequencies is allowed. The steady state becomes influenced by the slow modulation, although in some cases this influence is very small. It can be said that suppression of chaos occurs, naturally, without any further action, in slowly modulated systems.

We present an experimental study of the second harmonic light generated at a slab of nonlinear mo... more We present an experimental study of the second harmonic light generated at a slab of nonlinear molecules embedded in a 1D periodic structure, truncated by the introduction of a defect in the central period. We have observed an enhancement of the nonlinear interaction in the vicinity of the defect, when the second harmonic wave is excited for modes within the forbidden zone or stop band. We have also observed an enhancement near the band edge, where the group velocity approaches zero. Second harmonic generation is completely suppressed for local modes within the forbidden band other than the defect mode.

Physical Review A, 1992

ABSTRACT

Physical Review A, 1993

The inhuence of light polarization on the dynamics of an optically pumped single-mode laser with ... more The inhuence of light polarization on the dynamics of an optically pumped single-mode laser with a homogeneously broadened four-level medium is theoretically investigated in detail. Pump and laser fields with either parallel or crossed linear polarizations are considered, as are typical in far-infraredlaser experiments. Numerical simulations reveal dramatically different dynamic behaviors for these two polarization configurations. The analysis of the model equations allows us to find the physical origin of both behaviors. In particular, the crossed-polarization configuration is shown to be effective in decoupling the pump and laser fields, thus allowing for the appearance of Lorenz-type dynamics.

Optics Letters, 1995

We present an experimental study of the generation of second-harmonic light in a one-dimensional ... more We present an experimental study of the generation of second-harmonic light in a one-dimensional periodic structure truncated by the introduction of a defect in the central period. We observed an enhancement of the nonlinear interaction in the vicinity of the defect when the second-harmonic wave was excited for modes within the forbidden zone or stop band. We also observed an enhancement near the band edge, where the group velocity approaches zero. Second-harmonic generation is completely suppressed for local modes within the forbidden band other than the defect mode.

Journal of Physics D: Applied Physics, 1988

Summary form only given. In a cascaded configuration, the quadratic nonlinear interaction can be ... more Summary form only given. In a cascaded configuration, the quadratic nonlinear interaction can be used to induce a change in the effective index of refraction of a nonlinear material. When this change is induced within a microcavity the enhanced interaction within the structure may lead to a large change in the transmission or reflection properties of that material. The use