Osip Schwartz - Academia.edu (original) (raw)

Papers by Osip Schwartz

Breaking the diffraction limit in microscopy by utilizing quantum properties of light has been th... more Breaking the diffraction limit in microscopy by utilizing quantum properties of light has been the goal of intense research in the recent years. We propose a quantum superresolution technique based on non-classical emission statistics of fluorescent markers, routinely used as contrast labels for bio-imaging. The technique can be readily implemented using standard fluorescence microscopy equipment.

Optics Express, 2011

Probing the evolution of physical systems at the femto- or attosecond timescale with light requir... more Probing the evolution of physical systems at the femto- or attosecond timescale with light requires accurate characterization of ultrashort optical pulses. The time profiles of such pulses are usually retrieved by methods utilizing optical nonlinearities, which require significant signal powers and operate in a limited spectral range\cite{Trebino_Review_of_Scientific_Instruments97,Walmsley_Review_09}. We present a linear self-referencing characterization technique based on time domain localization of the pulse spectral components, operated in the single-photon regime. Accurate timing of the spectral slices is achieved with standard single photon detectors, rendering the technique applicable in any spectral range from near infrared to deep UV. Using detection electronics with about 707070 ps response, we retrieve the temporal profile of a picowatt pulse train with sim10\sim10sim10 fs resolution, setting a new scale of sensitivity in ultrashort pulse characterization.

Physical Review Letters, 2010

The observed intermittent light emission from colloidal semiconductor nanocrystals has long been ... more The observed intermittent light emission from colloidal semiconductor nanocrystals has long been associated with Auger recombination assisted quenching. We test this view by observing transient emission dynamics of CdSe/CdS/ZnS semiconductor nanocrystals using time-resolved photon counting. The size and intensity dependence of the observed decay dynamics seem inconsistent with those expected from Auger processes. Rather, the data suggest that in the "off" state the quantum dot cycles in a three-step process: photoexcitation, rapid trapping, and subsequent slow nonradiative decay.

Nano Letters, 2009

Surface plasmon resonance exhibited by noble metal nanoparticles makes them attractive agents for... more Surface plasmon resonance exhibited by noble metal nanoparticles makes them attractive agents for advanced microscopic imaging applications. In this work we study third harmonic generation in gold nanorods under conditions of resonance of the laser frequency with the longitudinal plasmon mode. Large resonant enhancement and the symmetry properties of third harmonic generation allow for background-free, orientation sensitive optical imaging of individual nanoparticles.

Physical Review Letters, 2011

The waveforms of attosecond pulses produced by high-harmonic generation carry information on the ... more The waveforms of attosecond pulses produced by high-harmonic generation carry information on the electronic structure and dynamics in atomic and molecular systems. Current methods for the temporal characterization of such pulses have limited sensitivity and impose significant experimental complexity. We propose a new linear and all-optical method inspired by widely used multidimensional phase retrieval algorithms. Our new scheme is based on the spectral measurement of two attosecond sources and their interference. As an example, we focus on the case of spectral polarization measurements of attosecond pulses, relying on their most fundamental property—being well confined in time. We demonstrate this method numerically by reconstructing the temporal profiles of attosecond pulses generated from aligned CO2 molecules.

Advanced Functional Materials, 2010

Biological photonic systems composed of anhydrous guanine crystals evolved separately in several ... more Biological photonic systems composed of anhydrous guanine crystals evolved separately in several taxonomic groups. Here, two such systems found in fish and spiders, both of which make use of anhydrous guanine crystal plates to produce structural colors, are examined. Measurements of the photonic-crystal structures using cryo-SEM show that the crystal plates in both fish skin and spider integument are ∼20-nm thick. The reflective unit in the fish comprises stacks of single plates alternating with ∼230-nm-thick cytoplasm layers. In the spiders the plates are formed as doublet crystals, cemented by 30-nm layers of amorphous guanine, and are stacked with ∼200 nm of cytoplasm between crystal doublets. They achieve light reflective properties through the control of crystal morphology and stack dimensions, reaching similar efficiencies of light reflectivity in both fish skin and spider integument. The structure of guanine plates in spiders are compared with the more common situation in which guanine occurs in the form of relatively unorganized prismatic crystals, yielding a matt white coloration.

A linear self-referenced technique for temporal characterization of ultraweak pulse trains is pre... more A linear self-referenced technique for temporal characterization of ultraweak pulse trains is presented. Shot-noise limited time-resolved single photon detection enables temporal resolution down to 10fs for pulse trains with ~ 1 photon per pulse.

Probing the evolution of physical systems at the femto- or attosecond timescale with light requir... more Probing the evolution of physical systems at the femto- or attosecond timescale with light requires accurate characterization of ultrashort optical pulses. The time profiles of such pulses are usually retrieved by methods utilizing optical nonlinearities, which require significant signal powers and operate in a limited spectral range\cite{Trebino_Review_of_Scientific_Instruments97,Walmsley_Review_09}. We present a linear self-referencing characterization technique based on time domain localization of the pulse spectral components, operated in the single-photon regime. Accurate timing of the spectral slices is achieved with standard single photon detectors, rendering the technique applicable in any spectral range from near infrared to deep UV. Using detection electronics with about 707070 ps response, we retrieve the temporal profile of a picowatt pulse train with sim10\sim10sim10 fs resolution, setting a new scale of sensitivity in ultrashort pulse characterization.

The observed intermittent light emission from colloidal semiconductor nanocrystals has long been ... more The observed intermittent light emission from colloidal semiconductor nanocrystals has long been associated with Auger recombination assisted quenching. We test this view by observing transient emission dynamics of CdSe/CdS/ZnS semiconductor nanocrystals using time-resolved photon counting. The size and intensity dependence of the observed decay dynamics are inconsistent with the those expected from Auger processes. Moreover, the data suggests that in the `off' state the quantum dot cycles in a three-step process: photoexcitation, rapid trapping and subsequent slow nonradiative decay.

Optics Letters, 2009

Pupil filters are widely used to improve the resolution of confocal microscopes. We analyze the p... more Pupil filters are widely used to improve the resolution of confocal microscopes. We analyze the possibilities of applying them to N-photon microscopy. We find that taking a linear combination of images obtained with several pupil filters can improve the resolution by a factor of N (compared to a conventional microscope). When applied to saturable fluorescence, this technique allows one to observe fluorescent objects with, in principle, unlimited spatial resolution.

Light is the tool of the 21st century. New photosensitive tools offer the possibility to monitor ... more Light is the tool of the 21st century. New photosensitive tools offer the possibility to monitor and control neuronal activity from the sub-cellular to the integrative level. This ongoing revolution has motivated the development of new optical methods for light stimulation. Among them, it has been recently demonstrated that a promising approach is based on the use of wavefront shaping to generate optically confined extended excitation patterns. This was achieved by combining the technique of temporal focusing with different approaches for lateral light shaping including low numerical aperture Gaussian beams, holographic beams and beams created with the generalized phase contrast mthod. What is needed now is a precise characterization of the effect of scattering on hese different methods in order to extend their use for in depth excitation. Here we present a theoretical and experimental study on the effect of scattering on the propagation of wavefront shaped beams. Results from fixed and acute cortical slices show that temporally focused spatial patterns are extremely robust against the effects of scattering and this permits their three-dimensional confinement for depths up to 550 {\mu}m.

Breaking the diffraction limit in microscopy by utilizing quantum properties of light has been th... more Breaking the diffraction limit in microscopy by utilizing quantum properties of light has been the goal of intense research in the recent years. We propose a quantum superresolution technique based on non-classical emission statistics of fluorescent markers, routinely used as contrast labels for bio-imaging. The technique can be readily implemented using standard fluorescence microscopy equipment.

Optics Express, 2011

Probing the evolution of physical systems at the femto- or attosecond timescale with light requir... more Probing the evolution of physical systems at the femto- or attosecond timescale with light requires accurate characterization of ultrashort optical pulses. The time profiles of such pulses are usually retrieved by methods utilizing optical nonlinearities, which require significant signal powers and operate in a limited spectral range\cite{Trebino_Review_of_Scientific_Instruments97,Walmsley_Review_09}. We present a linear self-referencing characterization technique based on time domain localization of the pulse spectral components, operated in the single-photon regime. Accurate timing of the spectral slices is achieved with standard single photon detectors, rendering the technique applicable in any spectral range from near infrared to deep UV. Using detection electronics with about 707070 ps response, we retrieve the temporal profile of a picowatt pulse train with sim10\sim10sim10 fs resolution, setting a new scale of sensitivity in ultrashort pulse characterization.

Physical Review Letters, 2010

The observed intermittent light emission from colloidal semiconductor nanocrystals has long been ... more The observed intermittent light emission from colloidal semiconductor nanocrystals has long been associated with Auger recombination assisted quenching. We test this view by observing transient emission dynamics of CdSe/CdS/ZnS semiconductor nanocrystals using time-resolved photon counting. The size and intensity dependence of the observed decay dynamics seem inconsistent with those expected from Auger processes. Rather, the data suggest that in the "off" state the quantum dot cycles in a three-step process: photoexcitation, rapid trapping, and subsequent slow nonradiative decay.

Nano Letters, 2009

Surface plasmon resonance exhibited by noble metal nanoparticles makes them attractive agents for... more Surface plasmon resonance exhibited by noble metal nanoparticles makes them attractive agents for advanced microscopic imaging applications. In this work we study third harmonic generation in gold nanorods under conditions of resonance of the laser frequency with the longitudinal plasmon mode. Large resonant enhancement and the symmetry properties of third harmonic generation allow for background-free, orientation sensitive optical imaging of individual nanoparticles.

Physical Review Letters, 2011

The waveforms of attosecond pulses produced by high-harmonic generation carry information on the ... more The waveforms of attosecond pulses produced by high-harmonic generation carry information on the electronic structure and dynamics in atomic and molecular systems. Current methods for the temporal characterization of such pulses have limited sensitivity and impose significant experimental complexity. We propose a new linear and all-optical method inspired by widely used multidimensional phase retrieval algorithms. Our new scheme is based on the spectral measurement of two attosecond sources and their interference. As an example, we focus on the case of spectral polarization measurements of attosecond pulses, relying on their most fundamental property—being well confined in time. We demonstrate this method numerically by reconstructing the temporal profiles of attosecond pulses generated from aligned CO2 molecules.

Advanced Functional Materials, 2010

Biological photonic systems composed of anhydrous guanine crystals evolved separately in several ... more Biological photonic systems composed of anhydrous guanine crystals evolved separately in several taxonomic groups. Here, two such systems found in fish and spiders, both of which make use of anhydrous guanine crystal plates to produce structural colors, are examined. Measurements of the photonic-crystal structures using cryo-SEM show that the crystal plates in both fish skin and spider integument are ∼20-nm thick. The reflective unit in the fish comprises stacks of single plates alternating with ∼230-nm-thick cytoplasm layers. In the spiders the plates are formed as doublet crystals, cemented by 30-nm layers of amorphous guanine, and are stacked with ∼200 nm of cytoplasm between crystal doublets. They achieve light reflective properties through the control of crystal morphology and stack dimensions, reaching similar efficiencies of light reflectivity in both fish skin and spider integument. The structure of guanine plates in spiders are compared with the more common situation in which guanine occurs in the form of relatively unorganized prismatic crystals, yielding a matt white coloration.

A linear self-referenced technique for temporal characterization of ultraweak pulse trains is pre... more A linear self-referenced technique for temporal characterization of ultraweak pulse trains is presented. Shot-noise limited time-resolved single photon detection enables temporal resolution down to 10fs for pulse trains with ~ 1 photon per pulse.

Probing the evolution of physical systems at the femto- or attosecond timescale with light requir... more Probing the evolution of physical systems at the femto- or attosecond timescale with light requires accurate characterization of ultrashort optical pulses. The time profiles of such pulses are usually retrieved by methods utilizing optical nonlinearities, which require significant signal powers and operate in a limited spectral range\cite{Trebino_Review_of_Scientific_Instruments97,Walmsley_Review_09}. We present a linear self-referencing characterization technique based on time domain localization of the pulse spectral components, operated in the single-photon regime. Accurate timing of the spectral slices is achieved with standard single photon detectors, rendering the technique applicable in any spectral range from near infrared to deep UV. Using detection electronics with about 707070 ps response, we retrieve the temporal profile of a picowatt pulse train with sim10\sim10sim10 fs resolution, setting a new scale of sensitivity in ultrashort pulse characterization.

The observed intermittent light emission from colloidal semiconductor nanocrystals has long been ... more The observed intermittent light emission from colloidal semiconductor nanocrystals has long been associated with Auger recombination assisted quenching. We test this view by observing transient emission dynamics of CdSe/CdS/ZnS semiconductor nanocrystals using time-resolved photon counting. The size and intensity dependence of the observed decay dynamics are inconsistent with the those expected from Auger processes. Moreover, the data suggests that in the `off' state the quantum dot cycles in a three-step process: photoexcitation, rapid trapping and subsequent slow nonradiative decay.

Optics Letters, 2009

Pupil filters are widely used to improve the resolution of confocal microscopes. We analyze the p... more Pupil filters are widely used to improve the resolution of confocal microscopes. We analyze the possibilities of applying them to N-photon microscopy. We find that taking a linear combination of images obtained with several pupil filters can improve the resolution by a factor of N (compared to a conventional microscope). When applied to saturable fluorescence, this technique allows one to observe fluorescent objects with, in principle, unlimited spatial resolution.

Light is the tool of the 21st century. New photosensitive tools offer the possibility to monitor ... more Light is the tool of the 21st century. New photosensitive tools offer the possibility to monitor and control neuronal activity from the sub-cellular to the integrative level. This ongoing revolution has motivated the development of new optical methods for light stimulation. Among them, it has been recently demonstrated that a promising approach is based on the use of wavefront shaping to generate optically confined extended excitation patterns. This was achieved by combining the technique of temporal focusing with different approaches for lateral light shaping including low numerical aperture Gaussian beams, holographic beams and beams created with the generalized phase contrast mthod. What is needed now is a precise characterization of the effect of scattering on hese different methods in order to extend their use for in depth excitation. Here we present a theoretical and experimental study on the effect of scattering on the propagation of wavefront shaped beams. Results from fixed and acute cortical slices show that temporally focused spatial patterns are extremely robust against the effects of scattering and this permits their three-dimensional confinement for depths up to 550 {\mu}m.