FOTONICA - Grup de Recerca de Fotònica
http://hdl.handle.net/2117/3270
2018-02-17T23:35:07ZSTED imaging performance estimation by means of Fourier transform analysis
http://hdl.handle.net/2117/113009
STED imaging performance estimation by means of Fourier transform analysis
Merino, David; Mallabiabarrena, Arrate; Andilla, Jordi; Artigas García, David; Zimmermann, Timo; Loza Alvarez, Pablo
Due to relatively high powers used in STED, biological samples may be affected by the illumination in the process of image acquisition. Similarly, the performance of the system may be limited by the sample itself. Optimization of the STED parameters taking into account the sample itself is therefore a complex task as there is no clear methodology that can determine the image improvement in an objective and quantitative manner. In this work, a method based on Fourier transform formalism is presented to analyze the performance of a STED system. The spatial frequency distribution of pairs of confocal and STED images are compared to obtain an objective parameter, the Azimuth Averaged Spectral Content Spread (AASCS), that is related to the performance of the system in which the sample is also considered. The method has been first tested on samples of beads, and then applied to cell samples labeled with multiple fluorescent dyes. The results show that a single parameter, the AASCS, can be used to determine the optimal settings for STED image acquisition in an objective way, only by using the information provided by the images from the sample themselves. The AASCS also helps minimize the depletion power, for better preservation of the samples.
2018-01-19T15:34:23ZMerino, DavidMallabiabarrena, ArrateAndilla, JordiArtigas García, DavidZimmermann, TimoLoza Alvarez, PabloDue to relatively high powers used in STED, biological samples may be affected by the illumination in the process of image acquisition. Similarly, the performance of the system may be limited by the sample itself. Optimization of the STED parameters taking into account the sample itself is therefore a complex task as there is no clear methodology that can determine the image improvement in an objective and quantitative manner. In this work, a method based on Fourier transform formalism is presented to analyze the performance of a STED system. The spatial frequency distribution of pairs of confocal and STED images are compared to obtain an objective parameter, the Azimuth Averaged Spectral Content Spread (AASCS), that is related to the performance of the system in which the sample is also considered. The method has been first tested on samples of beads, and then applied to cell samples labeled with multiple fluorescent dyes. The results show that a single parameter, the AASCS, can be used to determine the optimal settings for STED image acquisition in an objective way, only by using the information provided by the images from the sample themselves. The AASCS also helps minimize the depletion power, for better preservation of the samples.Bound states in the continuum in anisotropic structures
http://hdl.handle.net/2117/112926
Bound states in the continuum in anisotropic structures
Gomis Bresco, Jordi; Artigas García, David; Pujol Closa, Pilar; Torner Sabata, Lluís
We report theoretical and experimental observation of radiationless bound states
in the continuum (BIC) in waveguiding anisotropic structures. BICs may have all
possible polarizations and be the only possible boundstates in the structure.
2018-01-17T21:24:36ZGomis Bresco, JordiArtigas García, DavidPujol Closa, PilarTorner Sabata, LluísWe report theoretical and experimental observation of radiationless bound states
in the continuum (BIC) in waveguiding anisotropic structures. BICs may have all
possible polarizations and be the only possible boundstates in the structure.Bound states in the continuum in spin-orbit-coupled atomic systems
http://hdl.handle.net/2117/108096
Bound states in the continuum in spin-orbit-coupled atomic systems
Kartashov, Yaroslav V.; Konotop, Vladimir V; Torner Sabata, Lluís
We show that the interplay between spin-orbit coupling and Zeeman splitting in atomic systems can lead to the existence of bound states in the continuum (BICs) supported by trapping potentials. Such states have energies falling well within the continuum spectrum, but nevertheless they are localized and fully radiationless. We report the existence of BICs, in some cases in exact analytical form, in systems with tunable spin-orbit coupling and show that the phenomenon is physically robust. We also found that BIC states may be excited in spin-orbit-coupled Bose-Einstein condensates, where under suitable conditions they may be metastable with remarkably long lifetimes.
2017-09-28T15:13:59ZKartashov, Yaroslav V.Konotop, Vladimir VTorner Sabata, LluísWe show that the interplay between spin-orbit coupling and Zeeman splitting in atomic systems can lead to the existence of bound states in the continuum (BICs) supported by trapping potentials. Such states have energies falling well within the continuum spectrum, but nevertheless they are localized and fully radiationless. We report the existence of BICs, in some cases in exact analytical form, in systems with tunable spin-orbit coupling and show that the phenomenon is physically robust. We also found that BIC states may be excited in spin-orbit-coupled Bose-Einstein condensates, where under suitable conditions they may be metastable with remarkably long lifetimes.Gap solitons on a ring
http://hdl.handle.net/2117/107785
Gap solitons on a ring
Kartashov, Yaroslav V.; Malomed, B A; Vysloukh, Victor A.; Torner Sabata, Lluís
We introduce a new species of gap solitons (GSs) supported by an azimuthally modulated guiding ring in defocusing cubic media. The periodicity in the azimuthal direction strongly modifies properties and existence domains of GSs. In addition to the fundamental solitons, we report even and twisted bound states. The former type is found to be stable, while the twisted states are always unstable in defocusing media.
2017-09-19T15:56:40ZKartashov, Yaroslav V.Malomed, B AVysloukh, Victor A.Torner Sabata, LluísWe introduce a new species of gap solitons (GSs) supported by an azimuthally modulated guiding ring in defocusing cubic media. The periodicity in the azimuthal direction strongly modifies properties and existence domains of GSs. In addition to the fundamental solitons, we report even and twisted bound states. The former type is found to be stable, while the twisted states are always unstable in defocusing media.Four-wave mixing of light beams with engineered orbital angular momentum in cold cesium atoms
http://hdl.handle.net/2117/107784
Four-wave mixing of light beams with engineered orbital angular momentum in cold cesium atoms
Barreiro, S; Tabosa, J W R; Pérez Torres, Juan; Deyanova, Y; Torner Sabata, Lluís
We report an experimental demonstration that shows that the spatial structure carried by engineered coherent superpositions of light beams with orbital angular momentum can be mapped into the nonlinear polarization induced in a cloud of cold cesium atoms. The structure of such polarization was revealed by nearly degenerate four-wave-mixing processes.
2017-09-19T15:55:34ZBarreiro, STabosa, J W RPérez Torres, JuanDeyanova, YTorner Sabata, LluísWe report an experimental demonstration that shows that the spatial structure carried by engineered coherent superpositions of light beams with orbital angular momentum can be mapped into the nonlinear polarization induced in a cloud of cold cesium atoms. The structure of such polarization was revealed by nearly degenerate four-wave-mixing processes.Orbital angular momentum of entangled counterpropagating photons
http://hdl.handle.net/2117/107783
Orbital angular momentum of entangled counterpropagating photons
Pérez Torres, Juan; Osorio Tamayo, Clara Inés; Torner Sabata, Lluís
We elucidate the paraxial orbital angular momentum of entangled photon pairs generated by spontaneous parametric downconversion in different noncollinear geometries in which the entangled photons counterpropagate. We find, in particular, the orbital angular momentum of entangled pairs generated in transverse-emitting configurations, in which none of the known rules for selecting orbital angular momentum holds.
2017-09-19T15:54:33ZPérez Torres, JuanOsorio Tamayo, Clara InésTorner Sabata, LluísWe elucidate the paraxial orbital angular momentum of entangled photon pairs generated by spontaneous parametric downconversion in different noncollinear geometries in which the entangled photons counterpropagate. We find, in particular, the orbital angular momentum of entangled pairs generated in transverse-emitting configurations, in which none of the known rules for selecting orbital angular momentum holds.Soliton eigenvalue control in optical lattices
http://hdl.handle.net/2117/107782
Soliton eigenvalue control in optical lattices
Kartashov, Yaroslav V.; Crasovan, L C; Zelenina, A; Vyslokh, V V; Sanpera, Anna; Lewenstein, Maciej; Torner Sabata, Lluís
We address the dynamics of higher-order solitons in optical lattices, and predict their self-splitting into the set of their single-soliton constituents. The splitting is induced by the potential introduced by the lattice, together with the imprinting of a phase tilt onto the initial multisoliton states. The phenomenon allows the controllable generation of several coherent solitons linked via their Zakharov-Shabat eigenvalues. Application of the scheme to the generation of correlated matter waves in Bose-Einstein condensates is discussed.
2017-09-19T15:53:36ZKartashov, Yaroslav V.Crasovan, L CZelenina, AVyslokh, V VSanpera, AnnaLewenstein, MaciejTorner Sabata, LluísWe address the dynamics of higher-order solitons in optical lattices, and predict their self-splitting into the set of their single-soliton constituents. The splitting is induced by the potential introduced by the lattice, together with the imprinting of a phase tilt onto the initial multisoliton states. The phenomenon allows the controllable generation of several coherent solitons linked via their Zakharov-Shabat eigenvalues. Application of the scheme to the generation of correlated matter waves in Bose-Einstein condensates is discussed.Second harmonic generation tuning curves in quasiphase-matched potassium titanyl phosphate with narrow, high-intensity beams
http://hdl.handle.net/2117/107781
Second harmonic generation tuning curves in quasiphase-matched potassium titanyl phosphate with narrow, high-intensity beams
Katz, M; Eger, D; Kim, H; Jankovic, L; Stegeman, G; Carrasco Rodríguez, Sílvia; Torner Sabata, Lluís
The second harmonic generation (SHG) tuning curves with temperature and angle of incidence were measured in periodically poled KTiOPO4 for narrow fundamental beams at intensities typical of quadratic soliton generation. Mutual self-focusing of the fundamental and harmonic, cascading, and walk-off for light incidence away from the poling axis drastically distorted the SHG response curves, in good agreement with theory.
2017-09-19T15:34:15ZKatz, MEger, DKim, HJankovic, LStegeman, GCarrasco Rodríguez, SílviaTorner Sabata, LluísThe second harmonic generation (SHG) tuning curves with temperature and angle of incidence were measured in periodically poled KTiOPO4 for narrow fundamental beams at intensities typical of quadratic soliton generation. Mutual self-focusing of the fundamental and harmonic, cascading, and walk-off for light incidence away from the poling axis drastically distorted the SHG response curves, in good agreement with theory.Observation of optical vortex streets in walking-second harmonic generation
http://hdl.handle.net/2117/107779
Observation of optical vortex streets in walking-second harmonic generation
Molina Terriza, Gabriel; Dmitri, V Petrov; Recolons Martos, Jaume; Torner Sabata, Lluís
We report what is believed to be the first experimental observation of spontaneous nucleation of arrays of optical vortices in the process of second-harmonic generation in a crystal with moderate Poynting vector walk-off, pumped with focused beams containing screw phase dislocations. Our experiments were conducted in lithium triborate under conditions of small-efficiency second-harmonic generation pumped by nanosecond pulses at 1064 nm.
2017-09-19T15:29:16ZMolina Terriza, GabrielDmitri, V PetrovRecolons Martos, JaumeTorner Sabata, LluísWe report what is believed to be the first experimental observation of spontaneous nucleation of arrays of optical vortices in the process of second-harmonic generation in a crystal with moderate Poynting vector walk-off, pumped with focused beams containing screw phase dislocations. Our experiments were conducted in lithium triborate under conditions of small-efficiency second-harmonic generation pumped by nanosecond pulses at 1064 nm.Continuous-wave self-pumped optical parametric oscillator based on Yb3+-doped bulk periodically-poled LiNbO3 (Mg0)
http://hdl.handle.net/2117/107777
Continuous-wave self-pumped optical parametric oscillator based on Yb3+-doped bulk periodically-poled LiNbO3 (Mg0)
Capmany, J; Callejo, D; Bermúdez, V; Diéguez, E; Artigas García, David; Torner Sabata, Lluís
We present experimental evidence of continuous-wave self-pumped parametric oscillation in Yb3+-doped periodically poled lithium niobate co-doped with MgO. A single bulk crystal of periodically poled lithium niobate containing Yb3+ laser-active ions performs as a singly resonant parametric oscillator generating a signal wave at 1360 nm. The optical parametric oscillator is intracavity pumped by the laser emission at 1063 nm produced by the Yb3+ ions in the crystal. The whole system is end pumped at 980 nm.
2017-09-19T15:24:27ZCapmany, JCallejo, DBermúdez, VDiéguez, EArtigas García, DavidTorner Sabata, LluísWe present experimental evidence of continuous-wave self-pumped parametric oscillation in Yb3+-doped periodically poled lithium niobate co-doped with MgO. A single bulk crystal of periodically poled lithium niobate containing Yb3+ laser-active ions performs as a singly resonant parametric oscillator generating a signal wave at 1360 nm. The optical parametric oscillator is intracavity pumped by the laser emission at 1063 nm produced by the Yb3+ ions in the crystal. The whole system is end pumped at 980 nm.