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We report on the experimental measurement of the backscattering matrix of a weakly scattering medium in optics, composed of a few dispersed gold nanobeads. The decomposition of the time-reversal operator is applied to this matrix and we demonstrate selective and efficient focusing on individual scatterers, even through an aberrating layer. Moreover, we show that this approach provides the decomposition of the scattering pattern of a single nanoparticle. These results open important perspectives for optical imaging, characterization, and selective excitation of nanoparticles.
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Oro/química , Nanopartículas del Metal/química , Fenómenos Ópticos , Rayos Láser , Microesferas , Factores de TiempoRESUMEN
Acousto-optical coherence tomography (AOCT) is a variant of acousto-optic imaging (also called ultrasonic modulation imaging) that makes it possible to get the z resolution with acoustic and optic continuous wave beams. We describe here theoretically the AOCT effect, and we show that the acousto-optic "tagged photons" remain coherent if they are generated within a specific z region of the sample. We quantify the z selectivity for both the "tagged photon" field and for the Lesaffre et al. [Opt. Express 17, 18211 (2009)] photorefractive signal.
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Luz , Modelos Teóricos , Tomografía de Coherencia Óptica , Ultrasonido , Fantasmas de Imagen , FotonesRESUMEN
We introduce a method to experimentally measure the monochromatic transmission matrix of a complex medium in optics. This method is based on a spatial phase modulator together with a full-field interferometric measurement on a camera. We determine the transmission matrix of a thick random scattering sample. We show that this matrix exhibits statistical properties in good agreement with random matrix theory and allows light focusing and imaging through the random medium. This method might give important insight into the mesoscopic properties of a complex medium.
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We propose an original adaptive wavefront holographic setup based on the photorefractive effect (PR), to make real-time measurements of acousto-optic signals in thick scattering media, with a high flux collection at high rates for breast tumor detection. We describe here our present state of the art and understanding on the problem of breast imaging with PR detection of the acousto-optic signal.
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Acústica , Holografía/métodos , Fenómenos Ópticos , Fotones , Dispersión de Radiación , Animales , Mama/citología , Pollos , HumanosRESUMEN
The measurement of optical contrasts within thick biological tissues can be performed with the hybrid technique of acousto-optic imaging, but it has been shown that an acquisition rate in the 1-10kHz range is required for a good efficiency. This comes from the interferometric nature of the signal, blurred by speckle decorrelation in a time t(c), due to a decrease of the speckle pattern contrast at the exit of the sample. An holographic setup that associates a fast and large area single photodetector and a photorefractive crystal, can measure in real-time the acousto-optic signal: this is the so-called self-adaptive wavefront holography technique. Nevertheless, it is essential to size the photorefractive response time ( t(PR)) of the crystal with t(c) in order to optimize the signal-to-noise ratio of the measurement. This time mainly depends on the overall light intensity within the crystal. We have developed an original in situ method to determine t(PR) with the combination of acoustic pulses and a frequency de-tuning of the reference beam. We can measure precisely this time but also monitor it according to a theoretical model that we have previously described. We are able to adapt the response time of the setup to the decorrelation time of the medium under study.
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We present a new and simple method to obtain ultrasound modulated optical tomography images in thick biological tissues with the use of a photorefractive crystal. The technique offers the advantage of spatially adapting the output speckle wavefront by analysing the signal diffracted by the interference pattern between this output field and a reference beam, recorded inside the photorefractive crystal. Averaging out due to random phases of the speckle grains vanishes, and we can use a fast single photodetector to measure the ultrasound modulated optical contrast. This technique offers a promising way to make direct measurements within the decorrelation time scale of living tissues.
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An ultrahigh-resolution full-field optical coherence tomography (OCT) system has been developed for cellular-level imaging of biological media. The system is based on a Linnik interference microscope illuminated with a tungsten halogen lamp, associated with a high-resolution CCD camera. En face tomographic images are produced in real time, with the best spatial resolution ever achieved in OCT (0.7 microm x 0.9 microm, axial x transverse). A shot-noise limited detection sensitivity of 80 dB can be reached with an acquisition time per image of 1 s. Images of animal ophthalmic biopsies and vegetal tissues are shown.
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Ojo/citología , Aumento de la Imagen/métodos , Interpretación de Imagen Asistida por Computador/métodos , Imagenología Tridimensional/métodos , Microscopía de Interferencia/métodos , Hojas de la Planta/citología , Tomografía de Coherencia Óptica/métodos , Animales , Ratas , Nicotiana/citologíaRESUMEN
We report experimental evidence and correction of defocus in full-field optical coherence tomography of biological samples owing to mismatch of the refractive index of biological tissues and water. Via a metric based on the image quality, we demonstrate that we are able to compensate this index-induced defocus and to recover a sharp image in depth.
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Tomografía de Coherencia Óptica/métodos , Análisis de Fourier , Aumento de la Imagen , Ganglios Linfáticos , AguaRESUMEN
An interferometric method for parallel optical spectroscopy in the kilohertz range is reported, as well as its experimental validation in the context of high-speed laser Doppler imaging in vivo. The interferometric approach enables imaging in the low light conditions of a 2 kHz frame rate recording with a complementary metal-oxide semiconductor camera. Observation of mice craniums with near-infrared (lambda=785 nm) laser light in reflection configuration is reported. Doppler spectral images allegedly sensitive to blood flow are sequentially measured at several optical frequency detunings, to shift the spectral range of analysis in the radio-frequency spectrum.
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Rayos Láser , Cráneo/anatomía & histología , Animales , Efecto Doppler , Ratones , Cráneo/irrigación sanguíneaRESUMEN
We describe a novel method for localizing a fluorescent inclusion in a homogeneous turbid medium through the use of time-resolved techniques. Based on the calculation of the mean time of the fluorescence curves, the method does not require a priori knowledge of either the fluorescence lifetime or the mean time of the instrument response function since it adopts a differential processing approach. Theoretical expressions were validated and experiments for assessing the accuracy of localization were carried out on liquid optical phantoms with a small fluorescent inclusion. The illumination and detection optical fibers were immersed in the medium to achieve infinite medium geometry as required by the model used. The experimental setup consisted of a time-correlated single-photon counting system. Submillimeter accuracy was achieved for the localization of the inclusion.
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Interpretación de Imagen Asistida por Computador/métodos , Microscopía Fluorescente/instrumentación , Nanopartículas/ultraestructura , Nefelometría y Turbidimetría/instrumentación , Microscopía Fluorescente/métodos , Nefelometría y Turbidimetría/métodos , Tamaño de la Partícula , Fantasmas de ImagenRESUMEN
We present a technique for imaging fluorescent particles based on the axial modulation of the objective's focal plane position. This technique provides full-field optical sectioning and can be used to localize the fluorophores in three dimensions. We describe the technique and apply it to image 200 nm diameter fluorescent beads immobilized in a gel. We show that full-field optical sectioning is obtained and that the beads are localized with a precision of 10 nm in the transverse plane and 14 nm in the axial direction.
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We present a new technique that produces en face tomographic images with a 10-micros acquisition time per image. The setup consists of an interference microscope with stroboscopic illumination provided by a xenon arc flash lamp (10-micros flashes at 15 Hz). The tomographic images are obtained from two phase-opposed interferometric images recorded simultaneously by two synchronized CCD cameras. Transverse resolution better than 1.0 microm is achieved by use of high-numerical-aperture microscope objectives. The short coherence length of the source yields an axial resolution of 0.9 microm. 3 x 3 pixel binning leads to a detection sensitivity of 71 dB. Our system is suitable for various applications, particularly in biology for in vivo cellular-level imaging.
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Ojo/citología , Aumento de la Imagen/instrumentación , Microscopía de Interferencia/instrumentación , Procesamiento de Señales Asistido por Computador/instrumentación , Estroboscopía/instrumentación , Tomografía de Coherencia Óptica/instrumentación , Animales , Diseño de Equipo , Análisis de Falla de Equipo , Aumento de la Imagen/métodos , Microscopía de Interferencia/métodos , Estroboscopía/métodos , Tomografía de Coherencia Óptica/métodos , Xenopus laevisRESUMEN
We present a new detection scheme for acousto-optic tomography based on pulsed-wave ultrasound and illumination combined with heterodyne parallel speckle detection. This setup can perform tomographies inside several-centimeter-thick scattering samples. Test experiments confirm the suitability of this method for performing tomographies inside various types of optically scattering media, including liquids.
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Aumento de la Imagen/instrumentación , Procesamiento de Señales Asistido por Computador/instrumentación , Tomografía Óptica/instrumentación , Ultrasonografía/instrumentación , Acústica , Diseño de Equipo , Análisis de Falla de Equipo , Aumento de la Imagen/métodos , Luz , Óptica y Fotónica/instrumentación , Fantasmas de Imagen , Dispersión de Radiación , Tomografía Óptica/métodos , Ultrasonografía/métodosRESUMEN
A new technique is presented for measuring the spectral broadening of light that has been multiply scattered from scatterers in motion. In our method the scattered light is detected by a heterodyne receiver that uses a CCD as a multipixel detector. We obtain the frequency spectrum of the scattered light by sweeping the heterodyne local oscillator frequency. Our detection scheme combines a high optical etendue (product of the surface by the detection solid angle) with an optimal detection of the scattered photons (shot noise). Using this technique, we measure, in vivo, the frequency spectrum of the light scattered through the breast of a female volunteer.
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Mama/citología , Refractometría/instrumentación , Procesamiento de Señales Asistido por Computador/instrumentación , Tomografía de Coherencia Óptica/instrumentación , Transductores , Diseño de Equipo , Análisis de Falla de Equipo , Femenino , Humanos , Luz , Fantasmas de Imagen , Refractometría/métodos , Dispersión de Radiación , Tomografía de Coherencia Óptica/métodosRESUMEN
We present the application of a compact setup for real-time in situ trace-gas detection based on photothermal beam deflection (mirage-effect) spectroscopy to environmental monitoring and chemical analysis. The setup provides many advantages for local (nonremote) detection applications, such as rapid response and high sensitivity under true in situ conditions. The detection limit of C(2)H(4) in open air is estimated to be 0.25 parts in 10(9), based on concentration calibration with the dominant noise that is due to atmospheric turbulence on a time scale of 1 s. Detection limits are extrapolated for other species, and applications are explored by real-time measurements of gas emissions from a variety of solid and semisolid samples.
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A visible and near-infrared (0.36-3-microm) Michelson interferometer has been built to perform Fourier transform photoacoustic spectroscopy. The scanning (step and integrate) and the internal modulation are obtained with only one active element: the moving mirror holder driven by a linear motor. The signal-to-improvement and the performance of the spectrometer are compared with other photoacoustic methods and illustrated by various spectra.
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We have constructed an interference microscope that produces, in real time, reflectivity and topography images of surfaces with depth discrimination better than 1>mu;m . Intensity and phase images are obtained at the rate of 50 per second by use of a multiplexed lock-in detection and MMX assembler-optimized calculation routines. With a wavelength of 0.84microm , depth discrimination of 0.7microm and lateral resolution of 0.3microm were demonstrated, in good agreement with theory. Two-dimensional cross-sectional reflectivity and topography images taken at different depths in an integrated circuit are presented.
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We have built a high-resolution optical coherence tomography (OCT) system, based on a Linnik-type interference microscope, illuminated by a white-light thermal lamp. The extremely short coherence length of the illumination source and the large aperture of the objectives permit resolution close to 1 microm in three dimensions. A parallel detection scheme with a CCD camera provides cross-section (x-y) image acquisition without scanning at a rate of up to 50 Hz. To our knowledge, our system has the highest resolution demonstrated to date for OCT imaging. With identical resolution in three dimensions, realistic volume rendering of structures inside biological tissues is possible.
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We describe an interference microscope that produces topographic images with a minimum acquisition time of 20 ms. The system is based on phase-shifting interferometry with sinusoidal phase modulation induced by the oscillation of an interferometric objective (Michelson or Mirau). A CCD camera captures four images per oscillation period to produce a phase map in real time. The system is installed on a commercial microscope.
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Using a two-dimensional CCD array, a photoelastic modulator, and a commercial Nomarski microscope, we built a differential polarization interferometer. Multichannel lock-in detection of the signal allowed us to reach a shot-noise limit corresponding to 5-pm path differences for a few seconds of recording time. This interferometer was used as a surface profilometer as well as a system for imaging through scattering media.