high-speed-continuous-wave-stimulated-brillouin-scattering

High-speed Continuous-wave Stimulated Brillouin Scattering Spectrometer for Material Analysis

Recent years have witnessed a significant increase in the use of spontaneous Brillouin spectrometers for non-contact analysis of soft matter, such as ...

We describe ultrawideband Raman-mediated wavelength conversion. The nonlinear conversion transfer function is calculated analytically and simulated numerically in the cw regime, and the predicted performance is confirmed experimentally. Data conversion from long- to short-wavelength bands with signal reshaping and significant noise reduction are demonstrated experimentally at 10 Gbits/s and modeled by numerical simulations. Q factors and extinction ratios that are both larger than 10 dB are possible over an effective conversion bandwidth of 35 nm.

Noise-reduction capabilities of a raman-mediated wavelength converter.

Necrotic-core fibroatheromas (NCFA) with thin, mechanically weak fibrous caps overlying lipid cores comprise the majority of plaques that rupture and cause acute myocardial infarction. Laser speckle imaging (LSI) has been recently demonstrated to enable atherosclerotic plaque characterization with high accuracy. We investigate spatio-temporal analysis of LSI data, in conjunction with diffusion theory and Monte Carlo modeling of light transport, to estimate fibrous cap thickness in NCFAs. Time-varying laser speckle images of 20 NCFAs are selected for analysis. Spatio-temporal intensity fluctuations are analyzed by exponential fitting of the windowed normalized cross-correlation of sequential laser speckle patterns to obtain the speckle decorrelation time constant, tau(rho), as a function of distance rho from the source entry location. The distance, rho', at which tau(rho) dropped to 65% of its maximum value is recorded. Diffusion theory and Monte Carlo models are utilized to estimate the maximum photon penetration depth, zmax(rho'), for a distance equal to rho', measured from LSI. Measurements of zmax(rho') correlate well with histological measurements of fibrous cap thickness (R=0.78, p<0.0001), and paired t-tests show no significant difference between the groups (p=0.4). These results demonstrate that spatio-temporal LSI may allow the estimation of fibrous cap thickness in NCFAs, which is an important predictor of plaque stability.

Measurement of fibrous cap thickness in atherosclerotic plaques by spatiotemporal analysis of laser speckle images.

Necrotic-Kern Fibroatheromas (NCFA) mit d&uuml;nnen, mechanisch schwach faserig Kappen, die dar&uuml;ber liegende Lipid-Kerne stellen die Mehrheit der Plaketten, die Bruch und akuten Myokardinfarkt. Laser-Speckle-imaging (LSI) hat k&uuml;rzlich bewiesen, atherosklerotischen Plakette Charakterisierung mit hoher Genauigkeit zu aktivieren. Wir untersuchen die r&auml;umlich-zeitliche Analyse von LSI Daten, in Verbindung mit Verbreitung Theorie und Monte-Carlo Modellierung von leichten Transport, fibr&ouml;se Kappe Dicke in NCFAs zu sch&auml;tzen. Zeitlich ver&auml;nderliche Laser-Speckle-Bilder von 20 NCFAs werden f&uuml;r die Analyse ausgew&auml;hlt. R&auml;umlich-zeitliche Intensit&auml;t Schwankungen werden durch exponentielle Einbau von den Fenstermodus normalisierte Kreuzkorrelation sequenzielle Laser-Speckle-Muster Speckle Decorrelation Zeit konstant, tau(rho), als Funktion der Entfernung Rho vom Quellspeicherort Eintrag erhalten analysiert. Die Entfernung, Rho&#39;, auf welche tau(rho) fiel auf 65 % seiner maximalen Wert aufgezeichnet wird. Verbreitung Theorie und Monte-Carlo Modelle werden eingesetzt, um die maximale Photon Eindringtiefe, zmax(rho&#39;), Rho gleich eine Strecke zu sch&auml;tzen &quot;, gemessen von LSI. Messungen der zmax(rho&#39;) korrelieren gut mit histologischen Messungen faserige GAP Dicke (R = 0,78, p &lt; 0,0001), und gepaarten t-Tests zeigen keinen signifikanten Unterschied zwischen den Gruppen (p = 0,4). Diese Ergebnisse zeigen, dass die r&auml;umlich-zeitliche LSI Absch&auml;tzung der fibr&ouml;se Kappe Dicke in NCFAs, erm&ouml;glichen kann, die ein wichtiger Pr&auml;diktor f&uuml;r Plaque-Stabilit&auml;t ist.

Messung der fibr&ouml;se Kappe Dicke in atherosklerotischen Plaques durch raumzeitliche Analyse der Laser-Speckle-Bilder.

We theoretically and experimentally illustrate a new apertured near-field scanning optical microscopy (NSOM) technique, termed differential NSOM (DNSOM). It involves scanning a relatively large (e.g., 0.3-2 mum wide) rectangular aperture (or a detector) in the near-field of an object and recording detected power as a function of the scanning position. The image reconstruction is achieved by taking a two-dimensional derivative of the recorded power map. Unlike conventional apertured NSOM, the size of the rectangular aperture/detector does not determine the resolution in DNSOM; instead, the resolution is practically determined by the sharpness of the corners of the rectangular aperture/detector. Principles of DNSOM can also be extended to other aperture/detector geometries such as triangles and parallelograms.

Differential near-field scanning optical microscopy.

Wir veranschaulichen theoretisch und experimentell eine neue apertured Nahfeld-Scannen optische Mikroskopie (NSOM) Technik, differenzielle NSOM (DNSOM) genannt. Es geht um eine relativ gro&szlig;e Scannen (z.B. 0.3-2 Mama breit) rechteckige Blende (oder einen Detektor) in das Nahfeld eines Objekts und die Aufnahme macht als eine Funktion der Scan Position erkannt. Die Bildrekonstruktion wird erreicht, indem man ein zweidimensionales Derivat der aufgenommenen Energie-Karte. Im Gegensatz zu herk&ouml;mmlichen apertured NSOM bestimmt die Gr&ouml;&szlig;e der rechteckige Blende/Detektor nicht die Aufl&ouml;sung in DNSOM; Stattdessen wird die Aufl&ouml;sung praktisch durch die Sch&auml;rfe der Ecken des rechteckigen Blende/Detektors bestimmt. Grunds&auml;tze der DNSOM k&ouml;nnen auch auf andere Blende/Detektor-Geometrien wie Dreiecke und Parallelogramme erweitert werden.

Differenzielle Nahfeld-scanning optische Mikroskopie.

Speckle noise is a ubiquitous artifact that limits the interpretation of optical coherence tomography images. Here we apply various speckle-reduction digital filters to optical coherence tomography images and compare their performance. Our results indicate that shift-invariant, nonorthogonal wavelet-transform-based filters together with enhanced Lee and adaptive Wiener filters can significantly reduce speckle and increase the signal-to-noise ratio, while preserving strong edges. The speckle reduction capabilities of these filters are also compared with speckle reduction from incoherent angular compounding. Our results suggest that by using these digital filters, the number of individual angles required to attain a certain level of speckle reduction can be decreased.

Speckle reduction in optical coherence tomography images using digital filtering.

Speckle-Rauschen ist eine allgegenw&auml;rtige Artefakt, die die Interpretation der optischen Koh&auml;renz-Tomographie-Bilder beschr&auml;nkt. Hier gelten wir verschiedene Speckle-Reduktion digitaler Filter f&uuml;r optische Koh&auml;renz-Tomographie-Bilder und ihre Leistung zu vergleichen. Unsere Ergebnisse zeigen, dass UMSCHALT-Invariant, nonorthogonal Wavelet-Transformation basierenden Filter zusammen mit verbesserten Lee und adaptive Wiener-Filter k&ouml;nnen erheblich Speckle reduzieren und das Signal-Rausch-Verh&auml;ltnis, unter Beibehaltung der starke Kanten zu erh&ouml;hen. Die Speckle-Reduktion-F&auml;higkeiten dieser Filter werden auch mit Speckle-Reduktion aus der inkoh&auml;renten eckig Aufzinsung verglichen. Unsere Ergebnisse legen nahe, dass durch die Verwendung dieser digitalen Filter, die Anzahl der einzelnen Winkel ben&ouml;tigt, um ein gewisses Ma&szlig; an Speckle Reduktion erreichen verringert werden kann.

Speckle Verringerung der optischen Koh&auml;renz-Tomographie-Bilder mit digitalen Filtern.

The use of fluorescence radiation is of fundamental importance for tackling measurement problems in the life sciences, with recent demonstrations of probing biological systems at the nanoscale. Usually, fluorescent light-based tools and techniques use the intensity of light waves, which is easily measured by detectors. However, the phase of a fluorescence wave contains subtle, but no less important, information about the wave; yet, it has been largely unexplored. Here, we introduce the concept of fluorescence interferometry to allow the measurement of phase information of fluorescent light waves. In principle, fluorescence interferometry can be considered a unique form of optical low-coherence interferometry that uses fluorophores as a light source of low temporal coherence. Fluorescence interferometry opens up new avenues for developing new fluorescent light-based imaging, sensing, ranging, and profiling methods that to some extent resemble interferometric techniques based on white light sources. We propose two experimental realizations of fluorescence interferometry that detect the interference pattern cast by the fluorescence fields. This article discusses their measurement capabilities and limitations and compares them with those offered by optical low-coherence interferometric schemes. We also describe applications of fluorescence interferometry to imaging, ranging, and profiling tasks and present experimental evidences of wide-field cross-sectional imaging with high resolution and large range of depth, as well as quantitative profiling with nanometer-level precision. Finally, we point out future research directions in fluorescence interferometry, such as fluorescence tomography of whole organisms and the extension to molecular interferometry by means of quantum dots and bioluminescence.

Fluorescence interferometry: principles and applications in biology.

Die Verwendung von Fluoreszenz-Strahlung ist von grundlegender Bedeutung f&uuml;r die Behandlung der Probleme der Messung in den Life Sciences mit j&uuml;ngsten Demonstrationen der Sondierung von biologischer Systems auf der Nanoskala. Normalerweise benutzen fluoreszierenden Licht basierende Tools und Techniken, die Intensit&auml;t der Lichtwellen, die leicht von Detektoren gemessen wird. Die Phase einer Welle Fluoreszenz enth&auml;lt jedoch subtile, aber nicht weniger wichtig, Informationen &uuml;ber die Welle; Dennoch war es weitgehend unerforscht. Hier stellen wir das Konzept der Fluoreszenz-Interferometrie erm&ouml;glichen die Messung der Phase Informationen der fluoreszierenden Lichtwellen. Im Prinzip kann Fluoreszenz-Interferometrie eine einzigartige Form der optischen Interferometrie in niedrig-Koh&auml;renz gelten, die als Lichtquelle der geringe zeitliche Koh&auml;renz Fluorophore verwendet. Fluoreszenz-Interferometrie er&ouml;ffnet neue Wege f&uuml;r die Entwicklung von neuen fluoreszierenden Licht basierende Imaging, Sensorik, bis hin und Profilerstellung Methoden, die zu einem gewissen Grad interferometrische Techniken basierend auf wei&szlig;en Lichtquellen &auml;hneln. Wir schlagen zwei experimentelle Verwirklichungen der Fluoreszenz-Interferometrie, die das Interferenzmuster umgewandelt durch die Fluoreszenz-Felder zu erkennen. Dieser Artikel beschreibt deren Messfunktionen und Einschr&auml;nkungen und vergleicht sie mit denen von optischen niedrig-Koh&auml;renz interferometrische Systeme angeboten. Wir beschreiben auch Anwendungen der Fluoreszenz-Interferometrie, Bildgebung, reichen, und Profilerstellung Aufgaben und vorliegenden experimentelle Beweise der weiten Wiese Querschnitt-Bildgebung mit hoher Aufl&ouml;sung und gro&szlig;e Auswahl an Tiefe, sowie quantitative profiling mit Nanometer-Niveau-Pr&auml;zision. Schlie&szlig;lich weisen wir darauf zuk&uuml;nftige Forschungsrichtungen in Fluoreszenz-Interferometrie, wie Fluoreszenz-Tomographie ganze Organismen und die Ausweitung auf molekulare Interferometrie durch Quantenpunkte und Biolumineszenz.

Fluoreszenz-Interferometrie: Grundlagen und Anwendungen in der Biologie.

We present a combination of self-interference microscopy with lateral super-resolution microscopy and introduce a novel approach for localizing a single nano-emitter to within a few nanometers in all three dimensions over a large axial range. We demonstrate nanometer displacements of quantum dots placed on top of polymer bilayers that undergo swelling when changing from an air to a water environment, achieving standard deviations below 10 nm for axial and lateral localization.

Three-dimensional nano-localization of single fluorescent emitters.

Photoplethysmography is a well-established technique for the noninvasive measurement of blood pulsation. However, photoplethysmographic devices typically need to be in contact with the surface of the tissue and provide data from a single contact point. Extensions of conventional photoplethysmography to measurements over a wide field-of-view exist, but require advanced signal processing due to the low signal-to-noise-ratio of the photoplethysmograms. Here, we present a noncontact method based on temporal sampling of time-integrated speckle using a camera-phone for noninvasive, widefield measurements of physiological parameters across the human fingertip including blood pulsation and resting heart-rate frequency. The results show that precise estimation of these parameters with high spatial resolution is enabled by measuring the local temporal variation of speckle patterns of backscattered light from subcutaneous skin, thereby opening up the possibility for accurate high resolution blood pulsation imaging on a camera-phone. Camera-phone laser speckle imager along with measured relative blood perfusion maps of a fingertip showing skin perfusion response to a pulse pressure applied to the upper arm. The figure is for illustration only; the imager was stabilized on a stand throughout the experiments.

Laser speckle spatiotemporal variance analysis for noninvasive widefield measurements of blood pulsation and pulse rate on a camera-phone.

Conventional low-magnification phase-contrast microscopy is an invaluable, yet a qualitative, imaging tool for the interrogation of transparent objects over a mesoscopic millimeter-scale field-of-view in physical and biological settings. Here, we demonstrate that introducing a compact, unbalanced phase-shifting Michelson interferometer into a standard reflected brightfield microscope equipped with low-power infinity-corrected objectives and white light illumination forms a phase mesoscope that retrieves remotely and quantitatively the reflection phase distribution of thin, transparent, and weakly scattering samples with high temporal (1.38 nm) and spatial (0.87 nm) axial-displacement sensitivity and micrometer lateral resolution (2.3 μm) across a mesoscopic field-of-view (2.25 × 1.19 mm(2)). Using the system, we evaluate the etch-depth uniformity of a large-area nanometer-thick glass grating and show quantitative mesoscopic maps of the optical thickness of human cancer cells without any area scanning. Furthermore, we provide proof-of-principle of the utility of the system for the quantitative monitoring of fluid dynamics within a wide region.

Quantitative reflection phase mesoscopy by remote coherence tuning of phase-shift interference patterns.

Laser speckle contrast analysis (LASCA) is an established optical technique for accurate widefield visualization of relative blood perfusion when no or minimal scattering from static tissue elements is present, as demonstrated, for example, in LASCA imaging of the exposed cortex. However, when LASCA is applied to diagnosis of burn wounds, light is backscattered from both moving blood and static burn scatterers, and thus the spatial speckle contrast includes both perfusion and nonperfusion components and cannot be straightforwardly associated to blood flow. We extract from speckle contrast images of burn wounds the nonperfusion (static) component and discover that it conveys useful information on the ratio of static-to-dynamic scattering composition of the wound, enabling identification of burns of different depth in a porcine model in vivo within the first 48 h postburn. Our findings suggest that relative changes in the static-to-dynamic scattering composition of burns can dominate relative changes in blood flow for burns of different severity. Unlike conventional LASCA systems that employ scientific or industrial-grade cameras, our LASCA system is realized here using a camera phone, showing the potential to enable LASCA-based burn diagnosis with a simple imager.

Static laser speckle contrast analysis for noninvasive burn diagnosis using a camera-phone imager.

We demonstrate the effectiveness of stimulated Brillouin scattering for background-free Brillouin spectroscopy in scattering media within the biological spectral window. Using two nearly counter-propagating continuous-wave diode laser beams at 780 nm, we acquired transmission stimulated Brillouin point spectra in 10 mm and 500 μm thick Intralipid tissue phantoms with ∼100  μm and ∼16  μm diameter focal points, respectively. Stimulated gain spectra with high signal-to-noise ratio (8.7-30.7 dB) and frequency accuracy (6-72 MHz) were obtained at 20  MHz/10  ms and 20  MHz/100  ms through 0.24-3.36 mean-free paths of tissue phantoms. Our results suggest that stimulated Brillouin gain can be useful for imaging of Brillouin resonances in submillimeter-thick scattering samples.

Article	Year
Noise-reduction capabilities of a raman-mediated wavelength converter. Optics letters\| PubMed ID: 12703924	2003
Measurement of fibrous cap thickness in atherosclerotic plaques by spatiotemporal analysis of laser speckle images. Journal of biomedical optics\| PubMed ID: 16674181	2006
Differential near-field scanning optical microscopy. Nano letters\| PubMed ID: 17090100	2006
Speckle reduction in optical coherence tomography images using digital filtering. Journal of the Optical Society of America. A, Optics, image science, and vision\| PubMed ID: 17728812	2007
Fluorescence interferometry: principles and applications in biology. Annals of the New York Academy of Sciences\| PubMed ID: 18596334	2008
Three-dimensional nano-localization of single fluorescent emitters. Optics express\| PubMed ID: 20940917	2010
Laser speckle spatiotemporal variance analysis for noninvasive widefield measurements of blood pulsation and pulse rate on a camera-phone. Journal of biophotonics\| PubMed ID: 25908015	2015
Quantitative reflection phase mesoscopy by remote coherence tuning of phase-shift interference patterns. Scientific reports\| PubMed ID: 26216719	2015
Static laser speckle contrast analysis for noninvasive burn diagnosis using a camera-phone imager. Journal of biomedical optics\| PubMed ID: 26271055	2015
Background-free Brillouin spectroscopy in scattering media at 780 nm via stimulated Brillouin scattering. Optics letters\| PubMed ID: 26974082	2016

Alberto Bilenca

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