Omer Wagner

Superresolved imaging based on wavelength multiplexing of projected unknown speckle patterns

We propose a method for resolution enhancement of a diffraction limited optical system based on the capture of a set of low resolution images. These images are obtained after projection of an ensemble of unknown speckle patterns on top of the high resolution object that is to be imaged. Each speckle pattern is generated by the same thin (and unknown) diffuser, but illuminated with a slightly different wavelength. From the ensemble of low resolution images, we obtain a system of equations that can be solved in an iterative manner that enables reconstruction of the high resolution object. As a result, we also achieve the projected high resolution speckle patterns used for the encoding.

Optical-tweezing-based linear-optics nanoscopy.

Previous works reported that linear optics could be used to observe sub-wavelength features with a conventional optical microscope. Yet, the ability to reach a sub-200 nm resolution with a visible light remains limited. We present a novel widely-applicable method, where particle trapping is employed to overcome this limit. The combination of the light scattered by the sample and by the trapped particles encodes super-resolution information, which we decode by post image processing, with the trapped particle locations predetermined. As the first proof of concept our method successfully resolved sample characteristic features down to 100 nm. Improved performance is achieved with the fluorescence of the trapped particles employed. Further improvement may be attained with trapped particles of a smaller size.

Superresolved nanoscopy using Brownian motion of fluorescently labeled gold nanoparticles

The fundamental limit set by the wavelength of light can be overcome using methods of superresolution localization microscopy. These methods require labeling of the sample with fluorescent molecules and are time consuming as repeated cycles of activation and photobleaching of the sample are required. Alternatively, we propose a simplified approach that is free from direct labeling with fluorescence molecules and does not require the repeated cycles of activation and photobleaching. The method uses fluorescently labeled gold nanoparticles in an aqueous solution that are distributed on top of the sample. The nanoparticles move in random Brownian motion and obscure different areas of the sample, while the scene is being imaged sequentially. By conducting the proper postprocessing, a superresolution image can be generated. The method is validated both by numerical simulations as well as by experimental data.

Super-Resolving Approaches Suitable for Brain Imaging Applications

Usage of imaging in the optical regime in biological research established itself as a fundamental tool to reveal answers to critical scientific questions in that field. Specialized techniques such as Golgi’s method, the Nissl staining technique, and others led further to remarkable findings in the fields of brain imaging and neuroscience research. Pushing modern research to the next level requires spatial and temporal resolution capabilities which are better than the conventional limits of optical imaging. Hence, a fascinating new world of super-resolved imaging that achieves higher-resolving capabilities, while still using the same wavelengths, has emerged. This chapter will first cover the historical development of super-resolution microscopy, while relating it to applications and development in brain imaging and neuroscience research. Further, we cover many of the current promising super-resolution methods and point to applicative achievements that may prove to be highly useful in the field of brain imaging. The super-resolving concept we aim to address includes among others structured illumination microscopy, stimulated emission depletion microscopy, photo-activated localization microscopy, stochastic optical reconstruction microscopy, near-field scanning microscopy, and alternative new labeled and label-free concepts.

Synthesis of 3-D amplitude distribution through layer of discrete scatterers for photo-acoustic excitation

Many imaging applications rely on sample illumination with known 3-D light distributions. As these 3-D light distributions must satisfy the wave equation, many variables such as the geometry and reflectance of the sample and its environment may cause changes. While in most applications this change is neglected, for many scanning applications where the scanning beam should preserve its characteristics over a large distance it could become significant. Moreover, the environment scatters may also be used to generate desirable 3-D light distributions that may not be realizable using a single optical element. We propose a method that provides a solution for an optical element which modulates a physical beam in the presence of discrete scatters. This solution will generate a beam with optimal 3-D distribution in comparison with a desired one in the sense of minimal mean-square error. Specifically, the proposed concept is applicable for enhancing photo-acoustic imaging where the projected photonic excitation patterns need to be obtained inside a body after passing through scattering biological tissue.

Label free microscopy with enhanced localization performance based upon temporally modulated polarization

Recent microscopy techniques use nanoparticles as contrast agents that assist in realizing super resolved imaging of the inspected sample. While the sample itself is not labelled, its optical properties and form are revealed from the agents location and movement. Gold nanoparticles are frequently used for compound cellular imaging due to their plasmonic resonance that occurs in the visible regime. While the effect dramatically enhances their effective absorption cross-section, additional enhancement techniques are still needed in order to reach adequate signal-to-noise levels and differentiate between adjacent nanoparticles. In this paper we demonstrate an effective way to image a sample using specialized eccentric gold nanoparticles while exploiting the polarization dependency of their plasmonic resonance. Temporal modulation of the illumination polarization induces a corresponding temporal flickering of the nanoparticles. The method enhances localization by eliminating noise that differs in frequency from the temporal modulation. Differentiation between nanoparticles is concurrently gained as the flickering is changed in relation with the angle between their eccentric axis and the polarization angle.

Time multiplexing super-resolution nanoscopy based on the Brownian motion of gold nanoparticles

Super-resolution localization microscopy can overcome the diffraction limit and achieve a tens of order improvement in resolution. It requires labeling the sample with fluorescent probes followed with their repeated cycles of activation and photobleaching. This work presents an alternative approach that is free from direct labeling and does not require the activation and photobleaching cycles. Fluorescently labeled gold nanoparticles in a solution are distributed on top of the sample. The nanoparticles move in a random Brownian motion, and interact with the sample. By obscuring different areas in the sample, the nanoparticles encode the sub-wavelength features. A sequence of images of the sample is captured and decoded by digital post processing to create the super-resolution image. The achievable resolution is limited by the additive noise and the size of the nanoparticles. Regular nanoparticles with diameter smaller than 100nm are barely seen in a conventional bright field microscope, thus fluorescently labeled gold nanoparticles were used, with proper

Non-labeled lensless micro-endoscopic approach for cellular imaging through highly scattering media

We describe an imaging approach based on an optical setup made up of a miniature, lensless, minimally invasive endoscope scanning a sample and matching post processing techniques that enable enhanced imaging capabilities. The two main scopes of this article are that this approach enables imaging beyond highly scattering medium and increases the resolution and signal to noise levels reaching single cell imaging. Our approach has more advantages over ordinary endoscope setups and other imaging techniques. It is not mechanically limited by a lens, the stable but flexible fiber can acquire images over long time periods (unlike current imaging methods such as OCT etc.), and the imaging can be obtained at a certain working distance above the surface, without interference to the imaged object. Fast overlapping scans enlarge the region of interest, enhance signal to noise levels and can also accommodate post-processing, super-resolution algorithms. Here we present that due to the setup properties, the overlapping scans also lead to dramatic enhancement of non-scattered signal to scattered noise. This enables imaging through highly scattering medium. We discuss results obtained from in vitro investigation of weak signals of ARPE cells, rat retina, and scattered signals from polydimethylsiloxane (PDMS) microchannels filled with hemoglobin and covered by intralipids consequently mimicking blood capillaries and the epidermis of human skin. The development of minimally invasive procedures and methodologies for imaging through scattering medium such as tissues can vastly enhance biomedical diagnostic capabilities for imaging internal organs. We thereby propose that our method may be used for such tasks in vivo.