http://hdl.handle.net/2117/3271 Fri, 24 May 2013 15:06:21 GMT 2013-05-24T15:06:21Z webmaster.bupc@upc.edu Universitat Politècnica de Catalunya. Servei de Biblioteques i Documentació no http://hdl.handle.net/2117/19143 Title: Weak measurements with orbital-angular-momentum pointer states Authors: Puentes, G.; Hermosa, N.; Pérez Torres, Juan Abstract: Weak measurements are a unique tool for accessing information about weakly interacting quantum systems with minimal back action. Joint weak measurements of single-particle operators with pointer states characterized by a two-dimensional Gaussian distribution can provide, in turn, key information about quantum correlations that can be relevant for quantum information applications. Here we demonstrate that by employing two-dimensional pointer states endowed with orbital angular momentum (OAM), it is possible to extract weak values of the higher order moments of single-particle operators, an inaccessible quantity with Gaussian pointer states only. We provide a specific example that illustrates the advantages of our method both in terms of signal enhancement and information retrieval. Wed, 08 May 2013 18:22:45 GMT http://hdl.handle.net/2117/19143 2013-05-08T18:22:45Z Puentes, G.; Hermosa, N.; Pérez Torres, Juan no Weak measurements are a unique tool for accessing information about weakly interacting quantum systems with minimal back action. Joint weak measurements of single-particle operators with pointer states characterized by a two-dimensional Gaussian distribution can provide, in turn, key information about quantum correlations that can be relevant for quantum information applications. Here we demonstrate that by employing two-dimensional pointer states endowed with orbital angular momentum (OAM), it is possible to extract weak values of the higher order moments of single-particle operators, an inaccessible quantity with Gaussian pointer states only. We provide a specific example that illustrates the advantages of our method both in terms of signal enhancement and information retrieval. http://hdl.handle.net/2117/17791 Title: Practical dyakonons Authors: Takayama, Osamu; Artigas García, David; Torner Sabata, Lluís Abstract: We show that engineered photonic metamaterials composed of alternating layers of suitable dielectrics and metals can support different kinds of surface waves (SWs) under robust and readily achievable experimental conditions. The supported SWs include Dyakonov SWs, hybrid plasmons, and Dyakonov plasmons. In particular, in contrast to conventional physical settings, we show that the high form birefringence exhibited by the metamaterials allows Dyakonov SWs, or dyakonons, to exist within large angular existence domains and levels of localization similar to plasmons, thus making dyakonons available for practical applications Fri, 15 Feb 2013 12:47:40 GMT http://hdl.handle.net/2117/17791 2013-02-15T12:47:40Z Takayama, Osamu; Artigas García, David; Torner Sabata, Lluís no We show that engineered photonic metamaterials composed of alternating layers of suitable dielectrics and metals can support different kinds of surface waves (SWs) under robust and readily achievable experimental conditions. The supported SWs include Dyakonov SWs, hybrid plasmons, and Dyakonov plasmons. In particular, in contrast to conventional physical settings, we show that the high form birefringence exhibited by the metamaterials allows Dyakonov SWs, or dyakonons, to exist within large angular existence domains and levels of localization similar to plasmons, thus making dyakonons available for practical applications http://hdl.handle.net/2117/17691 Title: Digital coherent receiver for orbital angular momentum demultiplexing Authors: Belmonte Molina, Aniceto; Pérez Torres, Juan Abstract: We put forward a type of receiver for coherent detection of the photon orbital angular momentum (OAM). A coherent array receiver, consisting of multiple subapertures, with each subaperture coupled to a single-mode fiber, maps the complex optical field in the image plane. Using digital samplers connected to each array element, the local electrical signals resulting from the detection process can be measured coherently, moving the complexity of the full OAM measurement from the optical domain to the digital domain. By computer processing the coherent electrical patterns obtained, one can retrieve full information (amplitude and phase) of the different OAM components that constitute any incoming beam Tue, 12 Feb 2013 18:28:00 GMT http://hdl.handle.net/2117/17691 2013-02-12T18:28:00Z Belmonte Molina, Aniceto; Pérez Torres, Juan no We put forward a type of receiver for coherent detection of the photon orbital angular momentum (OAM). A coherent array receiver, consisting of multiple subapertures, with each subaperture coupled to a single-mode fiber, maps the complex optical field in the image plane. Using digital samplers connected to each array element, the local electrical signals resulting from the detection process can be measured coherently, moving the complexity of the full OAM measurement from the optical domain to the digital domain. By computer processing the coherent electrical patterns obtained, one can retrieve full information (amplitude and phase) of the different OAM components that constitute any incoming beam http://hdl.handle.net/2117/16749 Title: Characterization of dielectric spheres by spiral imaging Authors: Petrov, Dimitri; Rahuel, Nicolás; Molina Terriza, Gabriel; Torner Sabata, Lluís Abstract: We study the spiral spectra scattered off transparent dielectric spheres when probed by different Laguerre–Gaussian light beams, carrying nested topological wavefront dislocations. We show that such scattering data may be employed to determine geometrical properties of the spheres, such as their position. The technique is a generalization of standard Mie scattering, and it can be extended to study and to characterize nanospheres. Description: This paper was published in Optics Letters and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://dx.doi.org/10.1364/OL.37.000869. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law. Thu, 18 Oct 2012 08:30:21 GMT http://hdl.handle.net/2117/16749 2012-10-18T08:30:21Z Petrov, Dimitri; Rahuel, Nicolás; Molina Terriza, Gabriel; Torner Sabata, Lluís no We study the spiral spectra scattered off transparent dielectric spheres when probed by different Laguerre–Gaussian light beams, carrying nested topological wavefront dislocations. We show that such scattering data may be employed to determine geometrical properties of the spheres, such as their position. The technique is a generalization of standard Mie scattering, and it can be extended to study and to characterize nanospheres. http://hdl.handle.net/2117/16629 Title: Measurement of the temperature of atomic ensembles via which-way information Authors: León Montiel, R.D.J.; Pérez Torres, Juan Abstract: We unveil the relationship existing between the temperature of an ensemble of three-level atoms in a configuration, and the width of the emission cone of Stokes photons that are spontaneously emitted when atoms are excited by an optical pulse. This relationship, which is based on the amount of which-way information available about where the Stokes photon originated during the interaction, allows us to put forward a scheme to determine the temperature of atomic clouds by measuring the width of the emission cone. Unlike the commonly used time-of-flight measurements, with this technique, the atomic cloud is not destroyed during each measurement. Thu, 04 Oct 2012 09:02:40 GMT http://hdl.handle.net/2117/16629 2012-10-04T09:02:40Z León Montiel, R.D.J.; Pérez Torres, Juan no We unveil the relationship existing between the temperature of an ensemble of three-level atoms in a configuration, and the width of the emission cone of Stokes photons that are spontaneously emitted when atoms are excited by an optical pulse. This relationship, which is based on the amount of which-way information available about where the Stokes photon originated during the interaction, allows us to put forward a scheme to determine the temperature of atomic clouds by measuring the width of the emission cone. Unlike the commonly used time-of-flight measurements, with this technique, the atomic cloud is not destroyed during each measurement. http://hdl.handle.net/2117/16509 Title: Observation of the gradual transition from one-dimensional to two-dimensional Anderson localization Authors: Naether, U.; Kartashov, Yaroslav; Vysloukh, Victor A.; Nolte, S.; Tünnermann, A.; Torner Sabata, Lluís; Szameit, A. Abstract: We study the gradual transition from one-dimensional to two-dimensional Anderson localization upon transformation of the di-mensionality of disordered waveguide arrays. An effective transition from one- to two-dimensional system is achieved by increas-ing the number of rows forming the arrays. We observe that, for a given disorder level, Anderson localization becomes weaker with increasing number of rows, hence the effective dimension. Mon, 17 Sep 2012 12:05:29 GMT http://hdl.handle.net/2117/16509 2012-09-17T12:05:29Z Naether, U.; Kartashov, Yaroslav; Vysloukh, Victor A.; Nolte, S.; Tünnermann, A.; Torner Sabata, Lluís; Szameit, A. no We study the gradual transition from one-dimensional to two-dimensional Anderson localization upon transformation of the di-mensionality of disordered waveguide arrays. An effective transition from one- to two-dimensional system is achieved by increas-ing the number of rows forming the arrays. We observe that, for a given disorder level, Anderson localization becomes weaker with increasing number of rows, hence the effective dimension. http://hdl.handle.net/2117/16463 Title: Stable vortex-soliton tori with multiple nested phase singularities in dissipative media Authors: Borovkova, Olga V.; Lobanov, Valery E.; Kartashov, Yaroslav; Torner Sabata, Lluís Abstract: We show the existence of stable two- and three-dimensional vortex solitons carrying multiple, spatially separated, single-charge topological dislocations nested in a common vortex-ring core. Such nonlinear states are supported by elliptical gain landscapes in focusing nonlinear media with two-photon absorption. The separation between the phase dislocations is dictated mostly by the geometry of the gain landscape, and it only slightly changes upon variation of the gain or absorption strength. Mon, 10 Sep 2012 12:15:56 GMT http://hdl.handle.net/2117/16463 2012-09-10T12:15:56Z Borovkova, Olga V.; Lobanov, Valery E.; Kartashov, Yaroslav; Torner Sabata, Lluís no We show the existence of stable two- and three-dimensional vortex solitons carrying multiple, spatially separated, single-charge topological dislocations nested in a common vortex-ring core. Such nonlinear states are supported by elliptical gain landscapes in focusing nonlinear media with two-photon absorption. The separation between the phase dislocations is dictated mostly by the geometry of the gain landscape, and it only slightly changes upon variation of the gain or absorption strength. http://hdl.handle.net/2117/16403 Title: Compact ultrafast semiconductor disk laser: targeting GFP based nonlinear applications in living organisms Authors: Loza Álvarez, Pablo; Artigas García, David; Santos, Susana I.C.O.; Aviles Espinosa, Rodrigo; Filippidis, George; Hamilton, Craig; Malcolm, Graeme; Weingarten, Kurt J.; Südmeyer, Thomas; Barbarin, Yohan; Keller, Ursula Abstract: We present a portable ultrafast Semiconductor Disk Laser (SDL) (or vertical extended cavity surface emitting laser—VECSELs), to be used for nonlinear microscopy. The SDL is modelocked using a quantum-dot semiconductor saturable absorber mirror (SESAM), delivering an average output power of 287 mW, with 1.5 ps pulses at 500 MHz and a central wavelength of 965 nm. Specifically, despite the fact of having long pulses and high repetition rates, we demonstrate the potential of this laser for Two-Photon Excited Fluorescence (TPEF) imaging of in vivo Caenorhabditis elegans (C. elegans) expressing Green Fluorescent Protein (GFP) in a set of neuronal processes and cell bodies. Efficient TPEF imaging is achieved due to the fact that this wavelength matches the peak of the two-photon action cross section of this widely used fluorescent marker. The SDL extended versatility is shown by presenting Second Harmonic Generation images of pharynx, uterus, body wall muscles and its potential to be used to excite other different commercial dyes. Importantly this non-expensive, turn-key, compact laser system could be used as a platform to develop portable nonlinear bio-imaging devices. Wed, 29 Aug 2012 12:11:18 GMT http://hdl.handle.net/2117/16403 2012-08-29T12:11:18Z Loza Álvarez, Pablo; Artigas García, David; Santos, Susana I.C.O.; Aviles Espinosa, Rodrigo; Filippidis, George; Hamilton, Craig; Malcolm, Graeme; Weingarten, Kurt J.; Südmeyer, Thomas; Barbarin, Yohan; Keller, Ursula no SATURABLE ABSORBER, 2-PHOTON EXCITATION, FLUORESCENCE MICROSCOPY, MULTIPHOTON MICROSCOPY, SCANNING MICROSCOPY, PULSE SOURCE, FEMTOSECOND, DIODE, GENERATION, NEURONS We present a portable ultrafast Semiconductor Disk Laser (SDL) (or vertical extended cavity surface emitting laser—VECSELs), to be used for nonlinear microscopy. The SDL is modelocked using a quantum-dot semiconductor saturable absorber mirror (SESAM), delivering an average output power of 287 mW, with 1.5 ps pulses at 500 MHz and a central wavelength of 965 nm. Specifically, despite the fact of having long pulses and high repetition rates, we demonstrate the potential of this laser for Two-Photon Excited Fluorescence (TPEF) imaging of in vivo Caenorhabditis elegans (C. elegans) expressing Green Fluorescent Protein (GFP) in a set of neuronal processes and cell bodies. Efficient TPEF imaging is achieved due to the fact that this wavelength matches the peak of the two-photon action cross section of this widely used fluorescent marker. The SDL extended versatility is shown by presenting Second Harmonic Generation images of pharynx, uterus, body wall muscles and its potential to be used to excite other different commercial dyes. Importantly this non-expensive, turn-key, compact laser system could be used as a platform to develop portable nonlinear bio-imaging devices. http://hdl.handle.net/2117/16402 Title: Measurement and correction of in vivo sample aberrations employing a nonlinear guide-star in two-photon excited fluorescence microscopy Authors: Aviles Espinosa, Rodrigo; Andilla, Jordi; Porcar-Guezenec, Rafael; Olarte, Omar E.; Nieto, Marta; Levecq, Xavier; Artigas García, David; Loza Álvarez, Pablo Abstract: We demonstrate that sample induced aberrations can be measured in a nonlinear microscope. This uses the fact that two-photon excited fluorescence naturally produces a localized point source inside the sample: the nonlinear guide-star (NL-GS). The wavefront emitted from the NL-GS can then be recorded using a Shack-Hartmann sensor. Compensation of the recorded sample aberrations is performed by the deformable mirror in a single-step. This technique is applied to fixed and in vivo biological samples, showing, in some cases, more than one order of magnitude improvement in the total collected signal intensity. Wed, 29 Aug 2012 11:59:45 GMT http://hdl.handle.net/2117/16402 2012-08-29T11:59:45Z Aviles Espinosa, Rodrigo; Andilla, Jordi; Porcar-Guezenec, Rafael; Olarte, Omar E.; Nieto, Marta; Levecq, Xavier; Artigas García, David; Loza Álvarez, Pablo no Adaptative optics, Multiphoton microscopy, Spherical-aberration, Deep-Tissue We demonstrate that sample induced aberrations can be measured in a nonlinear microscope. This uses the fact that two-photon excited fluorescence naturally produces a localized point source inside the sample: the nonlinear guide-star (NL-GS). The wavefront emitted from the NL-GS can then be recorded using a Shack-Hartmann sensor. Compensation of the recorded sample aberrations is performed by the deformable mirror in a single-step. This technique is applied to fixed and in vivo biological samples, showing, in some cases, more than one order of magnitude improvement in the total collected signal intensity. http://hdl.handle.net/2117/16401 Title: Light localization in nonuniformly randomized lattices Authors: Kartashov, Yaroslav; Konotop, Vladimir V; Vysloukh, Victor A.; Torner Sabata, Lluís Abstract: We address Anderson localization of light in disordered optical lattices where the disorder strength varies across the transverse direction. Such variation changes the preferred domains where formation of localized eigenmodes is most probable, hence drastically impacting light localization properties. Thus, step-like disorder results in formation of modes with different decay rates at both sides of the interface, while a smoothly varying disorder yields appearance of modes that are extended within weakly disordered domains and rapidly fade away in strongly disordered domains. Wed, 29 Aug 2012 11:52:54 GMT http://hdl.handle.net/2117/16401 2012-08-29T11:52:54Z Kartashov, Yaroslav; Konotop, Vladimir V; Vysloukh, Victor A.; Torner Sabata, Lluís no We address Anderson localization of light in disordered optical lattices where the disorder strength varies across the transverse direction. Such variation changes the preferred domains where formation of localized eigenmodes is most probable, hence drastically impacting light localization properties. Thus, step-like disorder results in formation of modes with different decay rates at both sides of the interface, while a smoothly varying disorder yields appearance of modes that are extended within weakly disordered domains and rapidly fade away in strongly disordered domains. http://hdl.handle.net/2117/16082 Title: Dyakonov surface wave resonant transmission Authors: Takayama, Osamu; Nikitin, A. Yu; Martin-Moreno, Luis; Torner Sabata, Lluís; Artigas García, David Abstract: The role of Dyakonov surface waves in the transmission through structures composed of birefringent media is theoretically explored. In the case of structures using prisms, unexpected high transmission above the critical angle due to resonant excitation of Dyakonov surface waves is predicted. This transmission is produced only when TE polarized incident wave reaches the interface supporting the surface waves within a narrow interval of angles, for both the angle of incidence and the angle with respect to the optic axis of the birefringent media. As a result, over 90% transmission for a single and isolated peak confined in the two transversal directions, with hybrid TE and TM polarization, can be obtained. Mon, 18 Jun 2012 14:43:24 GMT http://hdl.handle.net/2117/16082 2012-06-18T14:43:24Z Takayama, Osamu; Nikitin, A. Yu; Martin-Moreno, Luis; Torner Sabata, Lluís; Artigas García, David no The role of Dyakonov surface waves in the transmission through structures composed of birefringent media is theoretically explored. In the case of structures using prisms, unexpected high transmission above the critical angle due to resonant excitation of Dyakonov surface waves is predicted. This transmission is produced only when TE polarized incident wave reaches the interface supporting the surface waves within a narrow interval of angles, for both the angle of incidence and the angle with respect to the optic axis of the birefringent media. As a result, over 90% transmission for a single and isolated peak confined in the two transversal directions, with hybrid TE and TM polarization, can be obtained. http://hdl.handle.net/2117/16061 Title: Negative Goos-Hanchen shift in periodic media Authors: Rechtsman, Mikael C.; Kartashov, Yaroslav; Setzpfandt, Frank; Trompeter, Henrik; Torner Sabata, Lluís; Pertsch, T.; Peschel, Ulf; Szameit, A. Abstract: We show that, under certain conditions, a negative Goos–Hänchen shift—a longitudinal displacement of a totally internally reflected wave packet—occurs in periodic media such as waveguide arrays. Fri, 15 Jun 2012 17:04:27 GMT http://hdl.handle.net/2117/16061 2012-06-15T17:04:27Z Rechtsman, Mikael C.; Kartashov, Yaroslav; Setzpfandt, Frank; Trompeter, Henrik; Torner Sabata, Lluís; Pertsch, T.; Peschel, Ulf; Szameit, A. no We show that, under certain conditions, a negative Goos–Hänchen shift—a longitudinal displacement of a totally internally reflected wave packet—occurs in periodic media such as waveguide arrays. http://hdl.handle.net/2117/15863 Title: Topological light bullets supported by spatiotemporal gain Authors: Lobanov, Valery E.; Borovkova, Olga V.; Kartashov, Yaroslav; Vysloukh, Victor A.; Torner Sabata, Lluís Abstract: We reveal that the competition among diffraction, cubic nonlinearity, two-photon absorption, and gain localized in both space and time results in arrest of collapse, suppression of azimuthal modulation instabilities for spatiotemporal wave packets, and formation of stable three-dimensional light bullets. We show that Gaussian spatiotemporal gain landscapes support bright, fundamental light bullets, while gain landscapes featuring a ringlike spatial and a Gaussian temporal shapes may support stable vortex bullets carrying topological phase dislocations. Tue, 15 May 2012 17:48:22 GMT http://hdl.handle.net/2117/15863 2012-05-15T17:48:22Z Lobanov, Valery E.; Borovkova, Olga V.; Kartashov, Yaroslav; Vysloukh, Victor A.; Torner Sabata, Lluís no We reveal that the competition among diffraction, cubic nonlinearity, two-photon absorption, and gain localized in both space and time results in arrest of collapse, suppression of azimuthal modulation instabilities for spatiotemporal wave packets, and formation of stable three-dimensional light bullets. We show that Gaussian spatiotemporal gain landscapes support bright, fundamental light bullets, while gain landscapes featuring a ringlike spatial and a Gaussian temporal shapes may support stable vortex bullets carrying topological phase dislocations. http://hdl.handle.net/2117/15862 Title: Enhancing the sensitivity and robustness of label-free imaging systems via stimulated Raman adiabatic passage Authors: León Montiel, R.D.J.; Pérez Torres, Juan Abstract: We show that the sensitivity and robustness of a label-free optical imaging technique based on stimulated Raman scattering (SRS) can be enhanced by using resonant optical transitions in a Raman adiabatic passage scheme. Our approach is based on the consideration that any enhancement of the flow of energy between two light beams involved in the SRS process is related to an increase in atomic population transfer between the energy levels of interest. One can thus profit from techniques developed in quantum optics to maximize such atomic population transfer for enhancing the sensitivity and robustness of optical imaging techniques. Tue, 15 May 2012 17:41:28 GMT http://hdl.handle.net/2117/15862 2012-05-15T17:41:28Z León Montiel, R.D.J.; Pérez Torres, Juan no We show that the sensitivity and robustness of a label-free optical imaging technique based on stimulated Raman scattering (SRS) can be enhanced by using resonant optical transitions in a Raman adiabatic passage scheme. Our approach is based on the consideration that any enhancement of the flow of energy between two light beams involved in the SRS process is related to an increase in atomic population transfer between the energy levels of interest. One can thus profit from techniques developed in quantum optics to maximize such atomic population transfer for enhancing the sensitivity and robustness of optical imaging techniques. http://hdl.handle.net/2117/15859 Title: Solitons supported by spatially inhomogeneous nonlinear losses Authors: Borovkova, Olga V.; Kartashov, Yaroslav; Vysloukh, Victor A.; Lobanov, Valery E.; Malomed, Boris A.; Torner Sabata, Lluís Abstract: We uncover that, in contrast to the common belief, stable dissipative solitons exist in media with uniform gain in the presence of nonuniform cubic losses, whose local strength grows with coordinate η (in one dimension) faster than |η| . The spatially-inhomogeneous absorption also supports new types of solitons, that do not exist in uniform dissipative media. In particular, single-well absorption profiles give rise to spontaneous symmetry breaking of fundamental solitons in the presence of uniform focusing nonlinearity, while stable dipoles are supported by double-well absorption landscapes. Dipole solitons also feature symmetry breaking, but under defocusing nonlinearity. Tue, 15 May 2012 17:08:47 GMT http://hdl.handle.net/2117/15859 2012-05-15T17:08:47Z Borovkova, Olga V.; Kartashov, Yaroslav; Vysloukh, Victor A.; Lobanov, Valery E.; Malomed, Boris A.; Torner Sabata, Lluís no We uncover that, in contrast to the common belief, stable dissipative solitons exist in media with uniform gain in the presence of nonuniform cubic losses, whose local strength grows with coordinate η (in one dimension) faster than |η| . The spatially-inhomogeneous absorption also supports new types of solitons, that do not exist in uniform dissipative media. In particular, single-well absorption profiles give rise to spontaneous symmetry breaking of fundamental solitons in the presence of uniform focusing nonlinearity, while stable dipoles are supported by double-well absorption landscapes. Dipole solitons also feature symmetry breaking, but under defocusing nonlinearity.