Articles de revista
http://hdl.handle.net/2117/3215
Fri, 20 Apr 2018 00:08:44 GMT
20180420T00:08:44Z

Comparative analysis of ferroelectric domain statistics via nonlinear diffraction in random nonlinear materials
http://hdl.handle.net/2117/116337
Comparative analysis of ferroelectric domain statistics via nonlinear diffraction in random nonlinear materials
Wang, Bin; Switowski, K; Cojocaru, Crina; Roppo, V; Sheng, Yan; Escalora, M.; Kisielewski, J.; Pawlak, D.; Vilaseca Alavedra, Ramon; Akhouayri, H.; Krolikowski, Wieslaw; Trull Silvestre, José Francisco
We present an indirect, nondestructive optical method for domain statistic characterization in disordered nonlinear crystals having homogeneous refractive index and spatially random distribution of ferroelectric domains. This method relies on the analysis of the wavedependent spatial distribution of the second harmonic, in the plane perpendicular to the optical axis in combination with numerical simulations. We apply this technique to the characterization of two different media, Calcium Barium Niobate and Strontium Barium Niobate, with drastically different statistical distributions of ferroelectric domains.
© 2018 [Optical Society of America]. Users may use, reuse, and build upon the article, or use the article for text or data mining, so long as such uses are for noncommercial purposes and appropriate attribution is maintained. All other rights are reserved.
Mon, 16 Apr 2018 13:10:57 GMT
http://hdl.handle.net/2117/116337
20180416T13:10:57Z
Wang, Bin
Switowski, K
Cojocaru, Crina
Roppo, V
Sheng, Yan
Escalora, M.
Kisielewski, J.
Pawlak, D.
Vilaseca Alavedra, Ramon
Akhouayri, H.
Krolikowski, Wieslaw
Trull Silvestre, José Francisco
We present an indirect, nondestructive optical method for domain statistic characterization in disordered nonlinear crystals having homogeneous refractive index and spatially random distribution of ferroelectric domains. This method relies on the analysis of the wavedependent spatial distribution of the second harmonic, in the plane perpendicular to the optical axis in combination with numerical simulations. We apply this technique to the characterization of two different media, Calcium Barium Niobate and Strontium Barium Niobate, with drastically different statistical distributions of ferroelectric domains.

Directionality fields generated by a local Hilbert transform
http://hdl.handle.net/2117/116325
Directionality fields generated by a local Hilbert transform
Ahmed, W. W.; Herrero Simon, Ramon; Botey Cumella, Muriel; Hayran, Zeki; Kurt, Hamza; Staliunas, Kestutis
We propose an approach based on a local Hilbert transform to design nonHermitian potentials generating arbitrary vector fields of directionality, ¿p(¿r), with desired shapes and topologies. We derive a local Hilbert transform to systematically build such potentials by modifying background potentials (being either regular or random, extended or localized). We explore particular directionality fields, for instance in the form of a focus to create sinks for probe fields (which could help to increase absorption at the sink), or to generate vortices in the probe fields. Physically, the proposed directionality fields provide a flexible mechanism for dynamical shaping and precise control over probe fields leading to novel effects in wave dynamics.
©2018 American Physical Society
Mon, 16 Apr 2018 12:12:33 GMT
http://hdl.handle.net/2117/116325
20180416T12:12:33Z
Ahmed, W. W.
Herrero Simon, Ramon
Botey Cumella, Muriel
Hayran, Zeki
Kurt, Hamza
Staliunas, Kestutis
We propose an approach based on a local Hilbert transform to design nonHermitian potentials generating arbitrary vector fields of directionality, ¿p(¿r), with desired shapes and topologies. We derive a local Hilbert transform to systematically build such potentials by modifying background potentials (being either regular or random, extended or localized). We explore particular directionality fields, for instance in the form of a focus to create sinks for probe fields (which could help to increase absorption at the sink), or to generate vortices in the probe fields. Physically, the proposed directionality fields provide a flexible mechanism for dynamical shaping and precise control over probe fields leading to novel effects in wave dynamics.

Persistence and stochastic periodicity in the intensity dynamics of a fiber laser during the transition to optical turbulence
http://hdl.handle.net/2117/116178
Persistence and stochastic periodicity in the intensity dynamics of a fiber laser during the transition to optical turbulence
Carpi, Laura C.; Masoller Alonso, Cristina
Many natural systems display transitions among different dynamical regimes, which are difficult to identify when the data are noisy and high dimensional. A technologically relevant example is a fiber laser, which can display complex dynamical behaviors that involve nonlinear interactions of millions of cavity modes. Here we study the laminarturbulence transition that occurs when the laser pump power is increased. By applying various data analysis tools to empirical intensity time series we characterize their persistence and demonstrate that at the transition temporal correlations can be precisely represented by a surprisingly simple model.
Wed, 11 Apr 2018 13:16:13 GMT
http://hdl.handle.net/2117/116178
20180411T13:16:13Z
Carpi, Laura C.
Masoller Alonso, Cristina
Many natural systems display transitions among different dynamical regimes, which are difficult to identify when the data are noisy and high dimensional. A technologically relevant example is a fiber laser, which can display complex dynamical behaviors that involve nonlinear interactions of millions of cavity modes. Here we study the laminarturbulence transition that occurs when the laser pump power is increased. By applying various data analysis tools to empirical intensity time series we characterize their persistence and demonstrate that at the transition temporal correlations can be precisely represented by a surprisingly simple model.

Collective excitability in a mesoscopic neuronal model of epileptic activity
http://hdl.handle.net/2117/113120
Collective excitability in a mesoscopic neuronal model of epileptic activity
Jedynak, Maciej; Pons Rivero, Antonio Javier; García Ojalvo, Jordi
At the mesoscopic scale, the brain can be understood as a collection of interacting neuronal oscillators, but the
extent to which its sustained activity is due to coupling among brain areas is still unclear. Herewe address this issue
in a simplified situation by examining the effect of coupling between two cortical columns described via JansenRit
neural mass models. Our results show that coupling between the two neuronal populations gives rise to stochastic
initiations of sustained collective activity, which can be interpreted as epileptic events. For large enough coupling
strengths, termination of these events results mainly from the emergence of synchronization between the columns,
and thus it is controlled by coupling instead of noise. Stochastic triggering and noiseindependent durations are
characteristic of excitable dynamics, and thus we interpret our results in terms of collective excitability.
Tue, 23 Jan 2018 18:49:57 GMT
http://hdl.handle.net/2117/113120
20180123T18:49:57Z
Jedynak, Maciej
Pons Rivero, Antonio Javier
García Ojalvo, Jordi
At the mesoscopic scale, the brain can be understood as a collection of interacting neuronal oscillators, but the
extent to which its sustained activity is due to coupling among brain areas is still unclear. Herewe address this issue
in a simplified situation by examining the effect of coupling between two cortical columns described via JansenRit
neural mass models. Our results show that coupling between the two neuronal populations gives rise to stochastic
initiations of sustained collective activity, which can be interpreted as epileptic events. For large enough coupling
strengths, termination of these events results mainly from the emergence of synchronization between the columns,
and thus it is controlled by coupling instead of noise. Stochastic triggering and noiseindependent durations are
characteristic of excitable dynamics, and thus we interpret our results in terms of collective excitability.

Generation of extreme pulses on demand in semiconductor lasers with optical injection
http://hdl.handle.net/2117/112898
Generation of extreme pulses on demand in semiconductor lasers with optical injection
Tian, Jin; Chen, Siyu; Masoller Alonso, Cristina
The generation of extreme intensity pulses in an optically injected semiconductor laser is studied numerically by using a wellknown rate equation model. We show that stepup perturbations of the laser pump current can trigger extreme pulses. We study the perturbation parameters (amplitude, duration) that are more likely to trigger a extreme pulse, and compare the properties of the generated extreme pulses with those spontaneous emitted, which are due to the intrinsic deterministic dynamics of the laser. We study how the phase of the optical field evolves during the pulses and compare both types of pulses (generated by external perturbations and generated by intrinsic nonlinear dynamics). We find that in both cases the phase dynamics is similar with an abrupt rise and fall: as an extreme pulse begins, the phase grows abruptly and reaches a local maximum at the peak of the pulse, then, when the pulse is over, the phase falls down to a value which is similar to the one before the pulse started.
© 2017 [Optical Society of America]. Users may use, reuse, and build upon the article, or use the article for text or data mining, so long as such uses are for noncommercial purposes and appropriate attribution is maintained. All other rights are reserved.
Wed, 17 Jan 2018 14:19:23 GMT
http://hdl.handle.net/2117/112898
20180117T14:19:23Z
Tian, Jin
Chen, Siyu
Masoller Alonso, Cristina
The generation of extreme intensity pulses in an optically injected semiconductor laser is studied numerically by using a wellknown rate equation model. We show that stepup perturbations of the laser pump current can trigger extreme pulses. We study the perturbation parameters (amplitude, duration) that are more likely to trigger a extreme pulse, and compare the properties of the generated extreme pulses with those spontaneous emitted, which are due to the intrinsic deterministic dynamics of the laser. We study how the phase of the optical field evolves during the pulses and compare both types of pulses (generated by external perturbations and generated by intrinsic nonlinear dynamics). We find that in both cases the phase dynamics is similar with an abrupt rise and fall: as an extreme pulse begins, the phase grows abruptly and reaches a local maximum at the peak of the pulse, then, when the pulse is over, the phase falls down to a value which is similar to the one before the pulse started.

Monolithic CIGSPerovskite tandem cell for optimal light harvesting without current matching
http://hdl.handle.net/2117/112461
Monolithic CIGSPerovskite tandem cell for optimal light harvesting without current matching
Mantilla Perez, Paola; Correa Baena, Juan Pablo; Liu, Quan; Colodrero, Silvia; Toudert, Johann; Saliba, Michale; Hagfeldt, Anders; Martorell Pena, Jordi
We present a novel monolithic architecture for optimal light harvesting in multijunction thin film solar cells. In the configuration we consider, formed by a perovskite (PVK) cell overlying a CIGS cell, the current extracted from the two different junctions is decoupled by the insertion of a dielectric nonperiodic photonic multilayer structure. This photonic multilayer is designed by an inverse integration approach to confine the incident sunlight above the PVK band gap in the PVK absorber layer, while increasing the transparency for sunlight below the PVK band gap for an efficient coupling into the CIGS bottom cell. To match the maximum power point voltages in a parallel connection of the PVK and CIGS cells, the latter is divided into two subcells by means of a standard threelaser scribing connection. Using realistic parameters for all the layers in the multijunction architecture we predict power conversion efficiencies of 28%. This represents an improvement of 24% and 26% over the best CIGS and PVK singlejunction cells, respectively, while at the same time outperforms the corresponding currentmatched standard tandem configuration by more than two percentage points.
Mon, 08 Jan 2018 13:43:22 GMT
http://hdl.handle.net/2117/112461
20180108T13:43:22Z
Mantilla Perez, Paola
Correa Baena, Juan Pablo
Liu, Quan
Colodrero, Silvia
Toudert, Johann
Saliba, Michale
Hagfeldt, Anders
Martorell Pena, Jordi
We present a novel monolithic architecture for optimal light harvesting in multijunction thin film solar cells. In the configuration we consider, formed by a perovskite (PVK) cell overlying a CIGS cell, the current extracted from the two different junctions is decoupled by the insertion of a dielectric nonperiodic photonic multilayer structure. This photonic multilayer is designed by an inverse integration approach to confine the incident sunlight above the PVK band gap in the PVK absorber layer, while increasing the transparency for sunlight below the PVK band gap for an efficient coupling into the CIGS bottom cell. To match the maximum power point voltages in a parallel connection of the PVK and CIGS cells, the latter is divided into two subcells by means of a standard threelaser scribing connection. Using realistic parameters for all the layers in the multijunction architecture we predict power conversion efficiencies of 28%. This represents an improvement of 24% and 26% over the best CIGS and PVK singlejunction cells, respectively, while at the same time outperforms the corresponding currentmatched standard tandem configuration by more than two percentage points.

Nanoparticle assisted mechanical delamination for freestanding high performance organic devices
http://hdl.handle.net/2117/112460
Nanoparticle assisted mechanical delamination for freestanding high performance organic devices
Colodrero, Silvia; Romero Gómez, Pablo; Mantilla Perez, Paola; Martorell Pena, Jordi
Organic electronics has the potential to be incorporated in any kind of surface morphology for wearable or fully portable applications. Unfortunately when organic devices, such as solar cells, are fabricated on flexible substrates, the device performance is severely limited unless the physical properties of such substrates are carefully chosen. Here, it is demonstrated that layers of nanoparticles with a size gradient distribution can be used to obtain high performance solar cell devices that can be effectively delaminated from an original flat and rigid glass substrate. Such sacrificial nanoparticles layers are incorporated in between the glass substrate and the semitransparent electrode of a polymer:fullerene (PTB7:PC71BM) cell. After the cell delamination, freestanding flexible devices with power conversion efficiencies as high as 7.12% are obtained, which corresponds to 90% of the performance of the same cell fabricated on a standard glass smooth surface.
Mon, 08 Jan 2018 13:22:44 GMT
http://hdl.handle.net/2117/112460
20180108T13:22:44Z
Colodrero, Silvia
Romero Gómez, Pablo
Mantilla Perez, Paola
Martorell Pena, Jordi
Organic electronics has the potential to be incorporated in any kind of surface morphology for wearable or fully portable applications. Unfortunately when organic devices, such as solar cells, are fabricated on flexible substrates, the device performance is severely limited unless the physical properties of such substrates are carefully chosen. Here, it is demonstrated that layers of nanoparticles with a size gradient distribution can be used to obtain high performance solar cell devices that can be effectively delaminated from an original flat and rigid glass substrate. Such sacrificial nanoparticles layers are incorporated in between the glass substrate and the semitransparent electrode of a polymer:fullerene (PTB7:PC71BM) cell. After the cell delamination, freestanding flexible devices with power conversion efficiencies as high as 7.12% are obtained, which corresponds to 90% of the performance of the same cell fabricated on a standard glass smooth surface.

Attosecond sublevel beating and nonlinear dressing on the 3dto5p and 3pto5s coretransitions at 91.3 eV and 210.4 eV in krypton
http://hdl.handle.net/2117/111732
Attosecond sublevel beating and nonlinear dressing on the 3dto5p and 3pto5s coretransitions at 91.3 eV and 210.4 eV in krypton
Seres, Enikoe; Seres, Jozsef; Namba, Shinichi; Afa, Iduabo John; Serrat Jurado, Carles
Applying extreme ultraviolet (XUV) transient absorption spectroscopy, the dynamics of the two laser dressed transitions 3d5/2to5p3/2 and 3p3/2to5s1/2 at photon energies of 91.3 eV and 210.4 eV were examined with attosecond temporal resolution. The dressing process was modeled with density matrix equations which are found to describe very accurately both the experimentally observed transmission dynamics and the linear and nonlinear dressing oscillations at 0.75 PHz and 1.5 PHz frequencies. Furthermore, using Fourier transform XUV spectroscopy, quantum beats from the 3d5/23d3/2 and 3p3/23p1/2 sublevels at 0.3 PHz and 2.0 PHz were experimentally identified and resolved.
© 2017 Optical Society of America. Users may use, reuse, and build upon the article, or use the article for text or data mining, so long as such uses are for noncommercial purposes and appropriate attribution is maintained. All other rights are reserved.
Mon, 11 Dec 2017 17:59:25 GMT
http://hdl.handle.net/2117/111732
20171211T17:59:25Z
Seres, Enikoe
Seres, Jozsef
Namba, Shinichi
Afa, Iduabo John
Serrat Jurado, Carles
Applying extreme ultraviolet (XUV) transient absorption spectroscopy, the dynamics of the two laser dressed transitions 3d5/2to5p3/2 and 3p3/2to5s1/2 at photon energies of 91.3 eV and 210.4 eV were examined with attosecond temporal resolution. The dressing process was modeled with density matrix equations which are found to describe very accurately both the experimentally observed transmission dynamics and the linear and nonlinear dressing oscillations at 0.75 PHz and 1.5 PHz frequencies. Furthermore, using Fourier transform XUV spectroscopy, quantum beats from the 3d5/23d3/2 and 3p3/23p1/2 sublevels at 0.3 PHz and 2.0 PHz were experimentally identified and resolved.

Scattering properties of a PT dipole
http://hdl.handle.net/2117/111185
Scattering properties of a PT dipole
Staliunas, Kestutis; Markos, P.; Kuzmiak, V.
Electromagnetic response of a PT dipole is studied both analytically and numerically. In the analytical approach, the dipole is represented by two point scatterers. Within the first Born approximation, the asymmetry of the scattering field with respect to the orientation of the dipole is proven. In numerical simulations, the dipole is represented by two infinitely long, parallel cylinders with opposite sign of the imaginary part of a refractive index. Numerical data confirm the validity of the Born approximation in the weak scattering limit, while significant deviations from the Born approximation were observed for stronger scatterers and in the nearfield range.
Fri, 24 Nov 2017 17:38:21 GMT
http://hdl.handle.net/2117/111185
20171124T17:38:21Z
Staliunas, Kestutis
Markos, P.
Kuzmiak, V.
Electromagnetic response of a PT dipole is studied both analytically and numerically. In the analytical approach, the dipole is represented by two point scatterers. Within the first Born approximation, the asymmetry of the scattering field with respect to the orientation of the dipole is proven. In numerical simulations, the dipole is represented by two infinitely long, parallel cylinders with opposite sign of the imaginary part of a refractive index. Numerical data confirm the validity of the Born approximation in the weak scattering limit, while significant deviations from the Born approximation were observed for stronger scatterers and in the nearfield range.

Experimental characterization of the transition to coherence collapse in a semiconductor laser with optical feedback
http://hdl.handle.net/2117/111176
Experimental characterization of the transition to coherence collapse in a semiconductor laser with optical feedback
Panozzo, M.; Quintero Quiroz, Carlos Alberto; Tiana Alsina, Jordi; Torrent Serra, Maria del Carmen; Masoller Alonso, Cristina
Semiconductor lasers with timedelayed optical feedback display a wide range of dynamical regimes, which have found various practical applications. They also provide excellent testbeds for data analysis tools for characterizing complex signals. Recently, several of us have analyzed experimental intensity timetraces and quantitatively identified the onset of different dynamical regimes, as the laser current increases. Specifically, we identified the onset of lowfrequency fluctuations (LFFs), where the laser intensity displays abrupt dropouts, and the onset of coherence collapse (CC), where the intensity fluctuations are highly irregular. Here we map these regimes when both, the laser current and the feedback strength vary. We show that the shape of the distribution of intensity fluctuations (characterized by the standard deviation, the skewness, and the kurtosis) allows to distinguish among noise, LFFs and CC, and to quantitatively determine (in spite of the gradual nature of the transitions) the boundaries of the three regimes. Ordinal analysis of the interdropout time intervals consistently identifies the three regimes occurring in the same parameter regions as the analysis of the intensity distribution. Simulations of the wellknown timedelayed LangKobayashi model are in good qualitative agreement with the observations.
Fri, 24 Nov 2017 15:37:16 GMT
http://hdl.handle.net/2117/111176
20171124T15:37:16Z
Panozzo, M.
Quintero Quiroz, Carlos Alberto
Tiana Alsina, Jordi
Torrent Serra, Maria del Carmen
Masoller Alonso, Cristina
Semiconductor lasers with timedelayed optical feedback display a wide range of dynamical regimes, which have found various practical applications. They also provide excellent testbeds for data analysis tools for characterizing complex signals. Recently, several of us have analyzed experimental intensity timetraces and quantitatively identified the onset of different dynamical regimes, as the laser current increases. Specifically, we identified the onset of lowfrequency fluctuations (LFFs), where the laser intensity displays abrupt dropouts, and the onset of coherence collapse (CC), where the intensity fluctuations are highly irregular. Here we map these regimes when both, the laser current and the feedback strength vary. We show that the shape of the distribution of intensity fluctuations (characterized by the standard deviation, the skewness, and the kurtosis) allows to distinguish among noise, LFFs and CC, and to quantitatively determine (in spite of the gradual nature of the transitions) the boundaries of the three regimes. Ordinal analysis of the interdropout time intervals consistently identifies the three regimes occurring in the same parameter regions as the analysis of the intensity distribution. Simulations of the wellknown timedelayed LangKobayashi model are in good qualitative agreement with the observations.