To extend the imaging depth of high-resolution optical microscopy, various gating operations-confocal, coherence, and polarization gating-have been devised to filter out the multiply scattered wave. ...However, the imaging depth is still limited by the multiply scattered wave that bypasses the existing gating operations. Here, we present a space gating method, whose mechanism is independent of the existing methods and yet effective enough to complement them. Specifically, we reconstruct an image only using the ballistic wave that is acousto-optically modulated at the object plane. The space gating suppresses the multiply scattered wave by 10-100 times in a highly scattering medium, and thus enables visualization of the skeletal muscle fibers in whole-body zebrafish at 30 days post fertilization. The space gating will be an important addition to optical-resolution microscopy for achieving the ultimate imaging depth set by the detection limit of ballistic wave.
Light in biological media is known as freely diffusing because interference is negligible. Here, we show Anderson light localization in quasi-two-dimensional protein nanostructures produced by ...silkworms (Bombyx mori). For transmission channels in native silk, the light flux is governed by a few localized modes. Relative spatial fluctuations in transmission quantities are proximal to the Anderson regime. The sizes of passive cavities (smaller than a single fibre) and the statistics of modes (decomposed from excitation at the gain-loss equilibrium) differentiate silk from other diffusive structures sharing microscopic morphological similarity. Because the strong reflectivity from Anderson localization is combined with the high emissivity of the biomolecules in infra-red radiation, silk radiates heat more than it absorbs for passive cooling. This collective evidence explains how a silkworm designs a nanoarchitectured optical window of resonant tunnelling in the physically closed structures, while suppressing most of transmission in the visible spectrum and emitting thermal radiation.
The original PDF version of this Article contained errors in Equations 1 and 2. Both equations omitted all Γ terms. This has been corrected in the PDF version of the Article. The HTML version was ...correct from the time of publication.
Optical microscopy suffers from a loss of resolving power when imaging targets are embedded in thick scattering media because of the dominance of strong multiple-scattered waves over waves scattered ...only a single time by the targets. Here, we present an approach that maintains full optical resolution when imaging deep within scattering media. We use both time-gated detection and spatial input-output correlation to identify those reflected waves that conserve in-plane momentum, which is a property of single-scattered waves. By implementing a superradiance-like collective accumulation of the single-scattered waves, we enhance the ratio of the single scattering signal to the multiple scattering background by more than three orders of magnitude. An imaging depth of 11.5 times the scattering mean free path is achieved with a near-diffraction-limited resolution of 1.5 μm. Our method of distinguishing single- from multiple-scattered waves will open new routes to deep-tissue imaging and studying the physics of the interaction of light with complex media.
Optical imaging of objects embedded within scattering media such as biological tissues suffers from the loss of resolving power. In our previous work, we proposed an approach called collective ...accumulation of single scattering (CASS) microscopy that attenuates this detrimental effect of multiple light scattering by combining the time-gated detection and spatial input-output correlation. In the present work, we perform a rigorous theoretical analysis on the effect of multiple light scattering to the optical transfer function of CASS microscopy. In particular, the spatial frequency-dependent signal to noise ratio (SNR) is derived depending on the intensity ratio of the single- and multiple-scattered waves. This allows us to determine the depth-dependent resolving power. We conducted experiments using a Siemens star-like target having various spatial frequency components and supported the theoretical derived SNR spectra. Our study provides a theoretical framework for understanding the effect of multiple light scattering in high-resolution and deep-tissue optical imaging.
Various external gating approaches, based on position, time, and polarization, have proven to be effective in selectively rejecting multiply scattered waves, thereby extending the imaging depth of ...deep-tissue optical microscopy. However, in a highly scattering medium, a significant portion of multiply scattered waves can bypass these gating operations because of the dissociation between the wave properties inside and outside the scattering medium. Here, we propose a method, termed volumetric gating, that introduces ultrasound focus to confocal reflectance imaging to directly suppress the multiply scattered waves traveling outside the imaging volume. The volumetric gating axially rejects the multiply scattered wave traveling to a depth shallower than the object plane while simultaneously suppressing the deeper penetrating portion extended beyond the transverse area of the ultrasonic focus of 30 × 90 μm2. These joint gating actions along the axial and lateral directions attenuate the multiply scattered waves by a factor of 1/1000 or smaller, thereby extending the imaging depth to 12.1 times the scattering mean free path with a diffraction-limited resolution of 1.5 μm. We showed that volumetric gating enables noninvasive imaging of the internal microscopic structures inside tubular organs such as the mouse colon and small intestine. We further developed theoretical and experimental frameworks to characterize the axial distribution of optical energy within scattering media. The volumetric gating will serve as an important addition to deep-tissue imaging modalities and a useful tool for studying wave propagation in scattering media.
Imaging systems targeting macroscopic objects tend to have poor depth selectivity. In this Letter, we present a 3D imaging system featuring a depth resolution of 200µm, depth scanning range of more ...than 1m, and view field larger than 70×70mm2. For depth selectivity, we set up an off-axis digital holographic imaging system using a light source with a coherence length of 400µm. A prism pair was installed in the reference beam path for long-range depth scanning. We performed imaging macroscopic targets with multiple different layers and also demonstrated imaging targets hidden behind a scattering layer.
•Imaging systems targeting macroscopic objects tend to have poor depth selectivity.•In this Letter, we present a 3D imaging system featuring a depth resolution of 200µm, and depth range of more than 1m.•For depth selectivity, an off-axis digital holographic imaging system was set up using a low-coherence light source.•A prism pair was installed in the reference beam path for long-range depth scanning.•We performed imaging macroscopic objects hidden behind a scattering layer.
We present an approach that maintains full optical resolution in imaging deep within scattering media. Imaging depth of 11.5 times the scattering mean free path was achieved with ...near-diffraction-limit resolution of 1.5 μm.
The imaging depth of deep-tissue optical microscopy is governed by the performance of the gating operation that suppresses the multiply scattered waves obscuring the ballistic waves. Although various ...gating operations based on confocal, time-resolved/coherence-gated, and polarization-selective detections have proven to be effective, each has its own limitation; certain types of multiply scattered waves can bypass the gating. Here, we propose a method, volumetric gating, that introduces ultrasound focus to confocal reflectance imaging to suppress the multiply scattered waves traveling outside the ultrasonic focal volume. The volumetric gating axially rejects the multiply scattered wave traveling to a depth shallower than the object plane while suppressing the deeper penetrating portion that travels across the object plane outside the transversal extent of the ultrasonic focus of 30\({\times}\)90\( {\mu}m^2\). These joint gating actions along the axial and lateral directions attenuate the multiply scattered waves by a factor of 1/1000 or smaller, thereby extending the imaging depth to 12.1 times the scattering mean free path while maintaining the diffraction-limited resolution of 1.5 \({\mu}\)m. We demonstrated an increase in the imaging depth and contrast for internal tissue imaging of mouse colon and small intestine through their outer walls. We further developed theoretical and experimental frameworks to characterize the axial distribution of light trajectories inside scattering media. The volumetric gating will serve as an important addition to deep-tissue imaging modalities and a useful tool for studying wave propagation in scattering media.
High-resolution optical microscopy suffers from a low contrast in scattering media where a multiply scattered wave obscures a ballistic wave used for image formation. To extend the imaging depth, ...various gating operations - confocal, coherence, and polarization gating - have been devised to filter out the multiply scattered wave. However, these gating methods are imperfect as they all act on the detection plane located outside a scattering medium. Here, we present a new gating scheme, called 'space' gating, that rejects the multiply scattered wave directly at the object plane inside a scattering medium. Specifically, we introduced a 30 \(\mu\)m-wide acoustic focus to the object plane and reconstructed a coherent image only with the ballistic wave modulated by acousto-optic interaction. This method allows us to reject the multiply scattered wave that the existing gating methods cannot filter out and improves the ratio of the ballistic wave to the multiply scattered wave by more than 100 times for a scattering medium more than 20 times thicker than its scattering mean free path. Using the coherent imaging technique based on space gating, we demonstrate the unprecedented imaging capability - phase imaging of optically transparent biological cells fully embedded within a scattering medium - with a spatial resolution of 1.5 \(\mu\)m.
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