RESUMO
Compositional prior information is used to bridge a gap in the theory between optical coherence tomography (OCT), which provides high-resolution structural images by neglecting spectral variation, and imaging spectroscopy, which provides only spectral information without significant regard to structure. A constraint is proposed in which it is assumed that a sample is composed of N distinct materials with known spectra, allowing the structural and spectral composition of the sample to be determined with a number of measurements on the order of N. We present a forward model for a sample with heterogeneities along the optical axis and show through simulation that the N-species constraint allows unambiguous inversion of Fourier transform interferometric data within the spatial frequency passband of the optical system. We then explore the stability and limitations of this model and extend it to a general 3D heterogeneous sample.
Assuntos
Espectroscopia de Infravermelho com Transformada de Fourier/métodos , Tomografia de Coerência Óptica/métodosRESUMO
Synthetic optical holography (SOH) provides efficient encoding of the complex optical signal, both amplitude and phase, for scanning imaging methods. Prior demonstrations have synthesized reference fields with a plane-wave-like linear variation of the phase with position. To record large images without probe-mirror synchronization, a long-travel, closed-loop reference mirror stage has been required. Here we present SOH with a synthetic reference wave with sinusoidal spatial variation of the phase. This allows the use of open loop, limited mirror travel range in SOH, and leads to a novel holographic inversion algorithm. We validate the theory with scans of graphene grain boundaries from a scanning near-field optical microscope, for which SOH has been shown to drastically increase scan speeds [Nat. Commun. 5, 3499 (2014)].
RESUMO
We optically trap a single nanoparticle in high vacuum and cool its three spatial degrees of freedom by means of active parametric feedback. Using a single laser beam for both trapping and cooling we demonstrate a temperature compression ratio of four orders of magnitude. The absence of a clamping mechanism provides robust decoupling from the heat bath and eliminates the requirement of cryogenic precooling. The small size and mass of the nanoparticle yield high resonance frequencies and high quality factors along with low recoil heating, which are essential conditions for ground state cooling and for low decoherence. The trapping and cooling scheme presented here opens new routes for testing quantum mechanics with mesoscopic objects and for ultrasensitive metrology and sensing.
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Quantitative phase measurements in imaging, microscopy, and nanooptics provide information not carried in amplitude measurements alone. In this issue of ACS Nano, Honigstein et al. present a new method in phase measurement. In this Perspective, we comment on this work and more broadly on the emerging role of phase and phase measurements in nanooptics.
Assuntos
Artefatos , Cristalografia/métodos , Interpretação de Imagem Assistida por Computador/métodos , Imageamento Tridimensional/métodos , Microscopia de Varredura por Sonda/métodos , Nanopartículas/ultraestruturaRESUMO
Detection and classification of nanoparticles are important for environmental monitoring, contamination mitigation, biological label tracking, and biodefense. Detection techniques involve a trade-off between sensitivity, discrimination, and speed. This paper presents a material-specific dual-color common-path interferometric detection system. Two wavelengths are simultaneously used to discriminate between 60 nm silver and 80 nm diameter gold particles in solution with a detection time of τ ≈ 1 ms. The detection technique is applicable to situations where both particle size and material are of interest.
Assuntos
Ouro/química , Interferometria/instrumentação , Nanopartículas Metálicas/química , Prata/química , Desenho de Equipamento , Nanopartículas Metálicas/ultraestrutura , Tamanho da PartículaRESUMO
The detection and identification of nanoparticles is of growing interest in atmospheric monitoring, medicine, and semiconductor manufacturing. While elastic light scattering with interferometric detection provides good sensitivity to single particles, active optical components prevent scalability of realistic sizes for deployment in the field or clinic. Here, we report on a simple phase-sensitive nanoparticle detection scheme with no active optical elements. Two measurements are taken simultaneously, allowing the amplitude and phase to be decoupled. We demonstrate the detection of 25 nm Au particles in liquid in Δt â¼ 1 ms with a signal-to-noise ratio of â¼ 37. Such performance makes it possible to detect nanoscale contaminants or larger proteins in real time without the need of artificial labeling.
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Monitoramento Ambiental/métodos , Interferometria/métodos , Nanopartículas/análise , Monitoramento Ambiental/instrumentação , Ouro/análise , Interferometria/instrumentação , Espalhamento de RadiaçãoRESUMO
The reliable detection, sizing, and sorting of viruses and nanoparticles is important for biosensing, environmental monitoring, and quality control. Here we introduce an optical detection scheme for the real-time and label-free detection and recognition of single viruses and larger proteins. The method makes use of nanofluidic channels in combination with optical interferometry. Elastically scattered light from single viruses traversing a stationary laser focus is detected with a differential heterodyne interferometer and the resulting signal allows single viruses to be characterized individually. Heterodyne detection eliminates phase variations due to different particle trajectories, thus improving the recognition accuracy as compared to standard optical interferometry. We demonstrate the practicality of our approach by resolving nanoparticles of various sizes, and detecting and recognizing different species of human viruses from a mixture. The detection system can be readily integrated into larger nanofluidic architectures for practical applications.
Assuntos
Nanopartículas/análise , Nanotecnologia/instrumentação , Fenômenos Ópticos , Vírus/isolamento & purificação , Humanos , Nanopartículas/química , Tamanho da Partícula , Processamento de Sinais Assistido por Computador , Fatores de Tempo , Vírus/classificaçãoRESUMO
The control of optical fields on the nanometer scale is a central theme of plasmonics and nanophotonics. Methods for characterizing localized optical field distributions are necessary to validate theoretical predictions, to test nanofabrication procedures, and to provide feedback for design improvements. Typical methods of probing near fields (e.g., single molecule fluorescence and near-field microscopy) cannot probe both the complex-valued and vectorial nature of the field distributions. We demonstrate that a nanoparticle probe with isotropic polarizability in combination with polarization control of excitation and detection beams provides access to this information through the interaction tensor. For a sample consisting of a single nanoparticle we show that the recorded images correspond to maps of the local Green's function tensor elements that couple the probe and sample. The tensorial mapping of interacting nanoparticles is of interest for optical sensing, optical antennas, surface-enhanced Raman scattering, nonlinear optics, and molecular rulers.
Assuntos
Ouro/química , Nanopartículas Metálicas/química , Nanotecnologia/métodos , Algoritmos , Luz , Modelos Estatísticos , Óptica e Fotônica , Fótons , Espalhamento de Radiação , Análise Espectral Raman/métodosRESUMO
An experimental and theoretical investigation of the acoustic and vibrational properties of orchestral crotales within the range C6 to C8 is reported. Interferograms of the acoustically important modes of vibration are presented and the frequencies are reported. It is shown that the acoustic spectra of crotales are not predicted by assuming that they are either thin circular plates or annular plates clamped at the center, despite the physical resemblance to these objects. Results from finite element analysis are presented that demonstrate how changing the size of the central mass affects the tuning of the instruments, and it is concluded that crotales are not currently designed to ensure optimal tuning. The possibility of using annular plates as crotales is also investigated and the physical parameters for such a set of instruments are presented.