Created by sebastien.popoff on 25/08/2020

## Using prior information for speeding up the measurement of fiber transmission matrices

[S. Li et al., arxiv, 2007.15891, (2020)]

Due to disorder and dispersion, knowing the transmission matrix of a multimode fiber is usually required to reconstruct an input image for endoscopic applications. In the general case, its characterization for a fiber allowing $$N$$ guided modes requires at least $$N$$ complex measurements. However, we usually have additional information, the most common one being that the matrix is never totally random, and usually sparse, when expressed in the mode basis. In this study, the authors use such prior information to reduce drastically the number of measurements for the transmission matrix estimation using the framework of compressed sensing. They demonstrate the validity of such an approach for endoscopic imaging through multimode fibers.

Created by sebastien.popoff on 03/08/2020

## Parallelized STED microscopy using tailored speckles

[N. Bender et al., arxiv, 2007.15491 (2020)]

Super-resolution fluorescence microscopy techniques, such as stimulated emission depletion (STED), rely on depleting fluorescence around a region smaller than the limit of diffraction. This can be achieved with a doughnut-shaped beam that is then scanned to produce an image. Such a process is time-consuming. Structured illumination techniques were proposed to parallelize the process by having multiple zeros of the field in the same image, for example with an array of doughnut beams. However, it typically limits optical sectioning as the field conserves its shape for quite large distances along the axial direction. One way to overcome this limitation is to use speckle patterns. Speckle exhibits numerous singularities, allowing parallelization of the technique, and they rapidly and non-repeatably change along the axial direction, guarantying the optical sectioning while being robust to aberrations. The issue is that speckle singularities (optical vortices) are not isotropic, leading to distortions of the image. In the present paper, N. Bender and co-authors use wavefront shaping to design ideal speckle patterns for non-linear microscopy to achieve isotropic and uniform super-resolution.

Created by sebastien.popoff on 17/07/2020

## Noninvasive incoherent imaging through scattering media based on wavefront shaping

[T. Yeminy and O. Katz., arxiv, 2007.03956 (2020)]

Wavefront shaping unlocked many exciting applications related to imaging through scattering media. However, they usually require to have some feedback from the object to observe, typically a guide-star generated by physically labeling the sample or by using ultrasound (that reduced the resolution). Other computer-based approaches recently developed relied on the memory-effect, which drastically limits the field of view, or requires a coherent illumination. In the present paper, T. Yeminy and O. Katz present a very simple approach that allows the reconstruction of an object hidden behind a scattering medium under incoherent illumination. It uses wavefront shaping of the scattered light together with an optimization procedure based on some assumptions about the object.

Created by sebastien.popoff on 04/07/2020

## Endoscopy combining photoacoustic and fluorescence imaging with a small footprint

[S. Mezil et al., arxiv, 2006.10856 (2020)]

Achieving optical-resolution photoacoustic imaging can currently only be obtained using endoscopy. It usually implies a quite bulky endoscope and/or a low signal-to-noise detection. In this paper, the authors present a technique that combines wavefront shaping through a multimode fiber, to scan the focus spot, with a single-mode fiber-based ultrasound sensor to achieve a high signal-to-noise with a small footprint (250 by 125 microns).