262 research outputs found
Optical nanorod antennas modeled as cavities for dipolar emitters: Evolution of sub- and super-radiant modes
No full textOptical antennas link objects to light. Here we derive an analytical model for the interaction of dipolar transitions with radiation through nanorod antenna modes, by modeling nanorods as cavities. The model includes radiation damping, accurately describes the complete emission process, and is summarized in a phase-matching equation. We analytically discuss the quantitative evolution of antenna modes, in particular the gradual emergence of subradiant, super-radiant, and dark modes, as antennas become increasingly more bound, i.e., plasmonic. Our description is valid for the interaction of nanorods with light in general and is thus widely applicable.Fil: Taminiau, Tim H.. Institut de Ciencies Fotoniques; EspañaFil: Stefani, Fernando Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: van Hulst, Niek F.. Institució Catalana de Recerca i Estudis Avancats; España. Institut de Ciencies Fotoniques; Españ
Ultrafast Transient Holographic Microscopy
No full textNanotechnology is increasingly being applied in many emerging technologies, ranging from metamaterials to next-generation nanodrugs. A key ingredient for its success is the ability to specifically tailor ultrafast nanoscale light–matter interactions over very large areas. Unfortunately, dynamic imaging by ultrafast nanoscopy so far remains limited to very small 2D areas. This shortcoming prevents connecting single-particle observations with large-scale functionality. Here, we address this experimental challenge by combining concepts of ultrafast spectroscopy, wide-field nanoscopy, and digital holography. We introduce an ultrafast holographic transient microscope for wide-field transient nanoscale imaging with high frequency all-optical signal demodulation. We simultaneously record ultrafast transient dynamics of many individual nano-objects and demonstrate time-resolved spectroscopy of gold nanoparticles over a large volume irrespective of their x–y–z position. Our results pave the way to single-shot 3D microscopy of 2D and 3D materials on arbitrary time scales from femtosecond carrier dynamics in optoelectronic materials to millisecond dynamics in complex tissues
Widefield phototransient imaging for visualizing 3D motion of resonant particles in scattering environments
No full text: Identifying, visualising and ultimately tracking dynamically moving non-fluorescent nanoparticles in the presence of non-specific scattering is a long-standing challenge across the nano- and life-sciences. In this work we demonstrate that our recently developed ultrafast holographic transient (UHT) microscope is ideally suited for meeting this challenge. We show that UHT microscopy allows reliably distinguishing off-resonant, dielectric, from resonant, metallic, nanoparticles, based on the phototransient signal: a pre-requisite for single-particle tracking in scattering environments. We then demonstrate the capability of UHT microscopy to holographically localize in 3D single particles over large volumes of view. Ultimately, we combine the two concepts to simultaneously track several tens of freely diffusing gold nanoparticles, within a 110 × 110 × 110 μm volume of view at an integration time of 10 ms per frame, while simultaneously recording their phototransient signals. The combined experimental concepts outlined and validated in this work lay the foundation for background-free 3D single-particle tracking applications or spectroscopy in scattering environments and are immediately applicable to systems as diverse as live cells and tissues or supported heterogeneous catalysts
Escurçament de la vida útil de la fotoluminiscència de punts quàntics PbS acoblats a nanoantenes d'or
No full text[ANGLÈS] In this study we studied single PbS quantum dots (QDs) that are emitting in the visible range, 800-900 nm. We report a reduction of 20 % of the luminescence lifetime of these single PbS QDs when they are in the vicinity of a gold nanoantenna. However, the reduction of the lifetime is not translated into a brighter QD.[CASTELLÀ] En este estudio se estudiaron los puntos cuánticos (QDs) individuales de PbS que están emitiendo en el rango visible, 800-900 nm. Se presenta una reducción del 20 % de la vida útil de la fotoluminiscencia de estos puntos cuánticos (QDs) individuales de PbS cuando están en la vecindad de una nanoantena de oro. Esto podría ser explotado para obtener emisores más brillantes.[CATALÀ] En aquest estudi es van estudiar els punts quàntics (QDs) individuals de PbS que estan emetent en el rang visible, 800-900 nm. Es presenta una reducció del 20 % de la vida útil de la fotoluminiscència d'aquests punts quàntics (QDs) individuals de PbS quan estan en el veïnatge d'una nanoantena d'or. Això podria ser explotat per obtenir emissors més brillants
Ultrabroadband Optical Diffraction Tomography
No full textOptical diffraction tomography (ODT) is a powerful noninvasive 3D imaging technique, but its combination with broadband light sources is difficult. In this study, we introduce ultrabroadband ODT, covering over 150 nm of visible spectral bandwidth with a lateral spatial resolution of 150 nm. Our work addresses a critical experimental gap by enabling the measurement of broadband refractive index changes in 3D samples, crucial information that is difficult to assess with existing methodologies. We present broadband, spectrally resolved ODT images of HeLa cells, obtained via pulse-shaping-based Fourier transform spectroscopy. The spectral observations enabled by ultrabroadband ODT, combined with material-dependent refractive index responses, allow for precise three-dimensional identification of nanoparticles within cellular structures. Our work represents a crucial step toward time and spectrally resolved tomography of complex 3D structures with implications for life and materials science applications.</p
Beating spatio-temporal coupling: Implications for pulse shaping and coherent control experiments
No full textDiffraction of finite sized laser beams imposes a limit on the control that can be exerted over ultrafast pulses. This limit manifests as spatio-temporal coupling induced in standard implementations of pulse shaping schemes. We demonstrate the influence this has on coherent control experiments that depend on finite excitation, sample, and detection volumes. Based on solutions used in pulse stretching experiments, we introduce a double-pass scheme that reduces the errors produced through spatio-temporal coupling by at least one order of magnitude. Finally, employing single molecules as nanoscale probes, we prove that such a double pass scheme is capable of artifact-free pulse shaping at dimensions two orders of magnitude smaller than the diffraction limit.Fil: Brinks, Daan. Institut de Ciencies Fotoniques; EspañaFil: Hildner, Richard. Institut de Ciencies Fotoniques; España. University of Bayreuth; AlemaniaFil: Stefani, Fernando Daniel. Institut de Ciencies Fotoniques; España. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Centro de Investigaciones en Bionanociencias "Elizabeth Jares Erijman"; ArgentinaFil: Van Hulst, Niek F.. Universidad de Barcelona. Institució Catalana de Recerca i Estudis Avançats; España. Institut de Ciencies Fotoniques; Españ
Log-periodic optical antennas
No full textEnglish: In recent years optical antennas have been attracting very strong interest due to the unique possibilities they offer for manipulating light on a sub-wavelength scale. Most published work deals with relatively simple antenna designs while among the more sophisticated ones, apart from a few exceptions, the Yagi-Uda antenna has almost monopolized the field. Up to the author?s knowledge, the present work is the first systematic study of self-similar antennas of log-periodic type which, in spite of having been extensively studied at radiofrequencies, have hardly received any attention as potential optical devices. Numerical simulations using the FDTD method were performed for a number of antenna designs both in reception and emission mode thus exploring their spectral characteristics, the dynamics of their interaction with ultra-short pulses, the influence of their geometric parameters on their directivity and efficiency, the effect of using different antenna materials, the influence of the substrate etc. A series of dipole array LP antennas were fabricated by e-beam lithography and characterized experimentally by confocal microscopy and a conoscopy. A new multiple-feed configuration was implemented for driving the antennas, motivated by theoretically predicted multiband operation, and partial success was achieved for particular values of so called interelement distance which was one of the design parameters studied. Thus, a forward enhancement of about 3 dB was measured for antennas with sufficiently large interelement distance, and the possible reasons for the directivity damping observed in antennas with shorter interelement distance were discussed.Castellano: En los últimos años las antenas ópticas han atraído un gran interés debido a las únicas posibilidades que ofrecen para manipular la luz a escala inferior a la de la longitud de onda. La mayor parte de los Trabajos publicados trata principalmente de diseños relativamente simples, mientras que entre los más sofisticados, aparte de algunas excepciones, las antenas de Yagi-Uda prácticamente han monopolizado el campo. El presente trabajo es el primer estudio sistemático de antenas auto-similares log-periódicas, que a pesar de haber sido estudiadas extensamente en radiofrequencias apenas han recibido atención como potenciales dispositivos ópticos. Se realizaron simulaciones numéricas mediante el método FDTD, para una sèrie de antenas de distintos diseños operando en modo de recepción y de emisión, explorando de esta manera sus características espectrales, la dinámica de su interacción con pulsos ultracortos, la influencia de sus parámetros geométricos sobre su directividad y eficiencia, el efecto del empleo de diferentes materiales, la influencia del sustrato etc. Una sèrie de antenas log-periódicas de dipolos en serie fueron fabricadas mediante litografía de haz de electrones y fueron caracterizadas mediante microscopía confocal y conoscopía. Una nueva configuración de alimentación con múltiples fuentes fue propuesta e implementada en base a las predicciones teóricas y un éxito parcial fue conseguido para valores particulares de la distancia entre los elementos de las antenas que fue uno de los parámetros de diseño estudiados. Así, para antenas con una separación entre los elementos suficientemente grande, fue medida una intensidad de la emisión ?hacia delante? del orden de 3 dB mayor que la emisión ?hacia atrás?. Se analizaron las posibles causas de la menor directividad en el caso de las antenas de menor espaciado.Català: En els últims anys les antenes òptiques han atret un gran interès a causa de les úniques possibilitats que ofereixen per manipular la llum a escala inferior a la de la longitud d'ona. La major part dels treballs publicats tracta principalment de dissenys relativament simples, mentre que entre els més sofisticats, a part d'algunes excepcions, les antenes de Yagi-Uda pràcticament han monopolitzat el camp. El present treball és el primer estudi sistemàtic d'antenes auto-similars log-periòdiques, que malgrat haver estat estudiades extensament en radiofrequencies amb prou feines han rebut atenció com a potencials dispositius òptics. Es van realitzar simulacions numèriques mitjançant el mètode FDTD, de una sèrie d'antenes de diferents dissenys operant en modo de recepció i d'emissió, explorant d'aquesta manera les seves característiques espectrals, la dinàmica de la seva interacció amb polsos ultracortos, la influència dels seus paràmetres geomètrics sobre la seva directivitat i eficiència, l'efecte de l'ús de diferents materials, la influència del substrat etc. Una sèrie d'antenes log-periòdiques de dipols en sèrie van ser fabricades mitjançant litografia de raig d'electrons i van ser caracteritzades mitjançant microscopía confocal i conoscopía. Una nova configuració d'alimentació amb múltiples fonts va ser proposada i implementada sobre la base de les prediccions teòriques i un èxit parcial va ser aconseguit per a valors particulars de la distància entre els elements de les antenes que va ser un dels paràmetres de disseny estudiats. Així, per a antenes amb una separació entre els elements suficientment gran, va ser mesurada una intensitat de l'emissió cap a davant de l'ordre de 3 dB major que l'emissió cap a enrere. Es van analitzar les possibles causes de la menor directividad en el cas de les antenes de menor espaiat
Electronic coherences and vibrational wave-packets in single molecules studied with femtosecond phase-controlled spectroscopy
No full textEmploying femtosecond pulse-shaping techniques we investigate ultrafast, coherent and incoherent dynamics in single molecules at room temperature. In first experiments single molecules are excited into their purely electronic 0–0 transition by phase-locked double-pulse sequences with pulse durations of 75 fs and 20 nm spectral band width. Their femtosecond kinetics can then be understood in terms of a 2-level system and modelled with the optical Bloch equations. We find that we observe the coherence decay in single molecules, and the purely electronic dephasing times can be retrieved directly in the time domain. In addition, the Rabi-frequencies and thus the transition dipole moments of single molecules are determined from these data. Upon excitation of single molecules into a vibrational level of the electronically excited state also incoherent intra-molecular vibrational relaxation is recorded. Increasing the spectral band width of the excitation pulses to up to 120 nm (resulting in a transform-limited pulse width of 15 fs) coherent superpositions of excited state vibrational modes, i.e. vibrational wave packets, are excited. The wave-packet oscillations in the excited state potential energy surface are followed in time by a phase-controlled pump–probe scheme, which permits to record wave packet interference, and to determine the energies of vibrational modes and their coupling strengths to the electronic transition.Fil: Hildner, Richard. Institut de Ciencies Fotoniques; EspañaFil: Brinks, Daan. Institut de Ciencies Fotoniques; EspañaFil: Stefani, Fernando Daniel. Institut de Ciencies Fotoniques; España. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Centro de Investigaciones en Bionanociencias "Elizabeth Jares Erijman"; ArgentinaFil: van Hulst, Niek F.. Institut de Ciencies Fotoniques; Españ
Coherent control of single molecules at room temperature
No full textThe detection of individual molecules allows to unwrap the inhomogeneously broadened ensemble and reveal the spatial disorder and temporal dynamics of single entities. During 20 years of increasing sophistication this approach has provided valuable insights into biomolecular interactions, cellular processes, polymer dynamics, etc. Unfortunately the detection of fluorescence, i.e. incoherent spontaneous emission, has essentially kept the time resolution of the single molecule approach out of the range of ultrafast coherent processes. In parallel coherent control of quantum interferences has developed as a powerful method to study and actively steer ultrafast molecular interactions and energy conversion processes. However the degree of coherent control that can be reached in ensembles is restricted, due to the intrinsic inhomogeneity of the synchronized subset. Clearly the only way to overcome spatio-temporal disorder and achieve key control is by addressing individual units: coherent control of single molecules. Here we report the observation and manipulation of vibrational wave-packet interference in individual molecules at ambient conditions. We show that adapting the time and phase distribution of the optical excitation field to the dynamics of each molecule results in a superior degree of control compared to the ensemble approach. Phase reversal does invert the molecular response, confirming the control of quantum coherence. Time-phase maps show a rich diversity in excited state dynamics between different, yet chemically identical, molecules. The presented approach is promising for single-unit coherent control in multichromophoric systems. Especially the role of coherence in the energy transfer of single antenna complexes under physiological conditions is subject of great attention. Now the role of energy disorder and variation in coupling strength can be explored, beyond the inhomogeneously broadened ensemble.Fil: Brinks, Daan. Institut de Ciencies Fotoniques; EspañaFil: Hildner, Richard. Institut de Ciencies Fotoniques; EspañaFil: Stefani, Fernando Daniel. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Van Hulst, Niek F.. Institució Catalana de Recerca i Estudis Avancats; España. Institut de Ciencies Fotoniques; Españ
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