Structured illumination generation with an integrated optical chip

Structured illumination is a widely used technique in fluorescence microscopy that allows for super-resolution imaging. In this paper, a brief introduction to the topic will be presented, together with a compact and integrated optical device that can generate and spatially translate a structured light pattern suitable for SIM microscopy. The device uses optical waveguides and directional couplers made with femtosecond laser micromachining. The beams are directed through an optical coupler to create the illumination pattern after interfering. The phase of the beams in the waveguides can be adjusted using thermal phase-shifters so that it is possible to shift the illumination pattern over the field of view of the microscope, enabling the acquisition of multiple phase images for SIM reconstruction without the need for additional optical elements. The effectiveness of the device is demonstrated by showing its use in a commercially available inverted microscope for superresolution imaging of Bovine Pulmonary Artery Endothelial Cells (BPAE Line) deposited on a commercial glass slide

Compressed sensing in fluorescence microscopy.

Compressed sensing (CS) is a signal processing approach that solves ill-posed inverse problems, from under-sampled data with respect to the Nyquist criterium. CS exploits sparsity constraints based on the knowledge of prior information, relative to the structure of the object in the spatial or other domains. It is commonly used in image and video compression as well as in scientific and medical applications, including computed tomography and magnetic resonance imaging. In the field of fluorescence microscopy, it has been demonstrated to be valuable for fast and high-resolution imaging, from single-molecule localization, super-resolution to light-sheet microscopy. Furthermore, CS has found remarkable applications in the field of mesoscopic imaging, facilitating the study of small animals' organs and entire organisms. This review article illustrates the working principles of CS, its implementations in optical imaging and discusses several relevant uses of CS in the field of fluorescence imaging from super-resolution microscopy to mesoscopy

Spatially modulated illumination allows for light sheet fluorescence microscopy with an incoherent source and compressive sensing

Light sheet fluorescence microscopy has become one of the most widely used techniques for three-dimensional imaging due to its high speed and low phototoxicity. Further improvements in 3D microscopy require limiting the light exposure of the sample and increasing the volumetric acquisition rate. We hereby present an imaging technique that allows volumetric reconstruction of the fluorescent sample using spatial modulation on a selective illumination volume. We demonstrate that this can be implemented using an incoherent LED source, avoiding shadowing artifacts, typical of light sheet microscopy. Furthermore, we show that spatial modulation allows the use of Compressive Sensing, reducing the number of modulation patterns to be acquired. We present results on zebrafish embryos which prove that selective spatial modulation can be used to reconstruct relatively large volumes without any mechanical movement. The technique yields an accurate reconstruction of the sample anatomy even at significant compression ratios, achieving higher volumetric acquisition rate and reducing photodamage biological samples. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreemen

A novel approach to online Physics refresher courses at Politecnico di Milano

Among the challenges that universities are facing nowadays, one that deserves special attention is the increasing number of dropouts. Refresher courses for perspective freshmen have regularly been organised at Politecnico di Milano over the last years as a means to tackle this issue. Due to the Covid-19 pandemic, the present situation posed serious limitations to traditional teaching methods this year, especially for long (3-4 hours) lectures which may be difficult to follow online. In this paper we present a novel approach based on a blend of non-interactive conventional lectures in large groups and interactive lessons in smaller groups. The course was delivered online using the Microsoft Teams software according to the following structure: first, a live video of a 1-hour lecture was streamed by a single tutor for the whole pool of approximately 1000 students. During this streaming, the students were not allowed to interact with the tutor or with one another by any means. Afterwards, 8 teams of students were formed and assigned to different tutors for the following three hours of more interactive lectures. Each tutor presented examples and exercises of their own choice (mainly on the same topic as the streamed video) and delivered guided solutions while promoting the interaction among students. Furthermore, a common set of short problems was given to each team: this activity could be performed at any time during the second part of the block, as decided by each tutor. In order to span among different teaching styles, the student teams were assigned to a different tutor every day for the interactive part of the lesson. As an additional resource, an online forum was activated on a dedicated website, which allowed students to ask questions on the course topics in an asynchronous way. At the end of the course, every student was invited to fill in an anonymous survey to express their satisfaction with the course. The results of the survey indicate an overall degree of satisfaction with a mean rating over 75%

Enlarged Field of View in Spatially Modulated Selective Volume Illumination Microscopy

Three-dimensional fluorescence microscopy is a key technology for inspecting biological samples, ranging from single cells to entire organisms. We recently proposed a novel approach called spatially modulated Selective Volume Illumination Microscopy (smSVIM) to suppress illumination artifacts and to reduce the required number of measurements using an LED source. Here, we discuss a new strategy based on smSVIM for imaging large transparent specimens or voluminous chemically cleared tissues. The strategy permits steady mounting of the sample, achieving uniform resolution over a large field of view thanks to the synchronized motion of the illumination lens and the camera rolling shutter. Aided by a tailored deconvolution method for image reconstruction, we demonstrate significant improvement of the resolution at different magnification using samples of varying sizes and spatial features