Wavefront-sensing with a thin diffuser

We propose and implement a broadband, compact, and low-cost wavefront sensing scheme by simply placing a thin diffuser in the close vicinity of a camera. The local wavefront gradient is determined from the local translation of the speckle pattern. The translation vector map is computed thanks to a fast diffeomorphic image registration algorithm and integrated to reconstruct the wavefront profile. The simple translation of speckle grains under local wavefront tip/tilt is ensured by the so-called "memory effect" of the diffuser. Quantitative wavefront measurements are experimentally demonstrated both for the few first Zernike polynomials and for phase-imaging applications requiring high resolution. We finally provided a theoretical description of the resolution limit that is supported experimentally

Reference-less complex wavefields characterization with a high-resolution wavefront sensor

Wavefront sensing is a widely-used non-interferometric, single-shot, and quantitative technique providing the spatial-phase of a beam. The phase is obtained by integrating the measured wavefront gradient. Complex and random wavefields intrinsically contain a high density of singular phase structures (optical vortices) associated with non-conservative gradients making this integration step especially delicate. Here, using a high-resolution wavefront sensor, we demonstrate experimentally a systematic approach for achieving the complete and quantitative reconstruction of complex wavefronts. Based on the Stokes' theorem, we propose an image segmentation algorithm to provide an accurate determination of the charge and location of optical vortices. This technique is expected to benefit to several fields requiring complex media characterization

Chromato-axial memory effect in step index multimode fibers

Multimode fibers (MMF) are used in many applications from telecomunications to minimally invasive micro-endoscopic imaging. However, the numerous modes and their coupling make light-beam control and imaging a delicate task. To circumvent this difficulty, recent methods exploit priors about the transmission of the system, such as the so-called optical memory effect. Here, we quantitatively characterize a chromato-axial memory effect in step-index MMF, characterized through its slope $\delta z/\delta \lambda$ and its spectral and axial widths. We propose a theoretical model and numerical simulations in good agreement with experimental observations

Supplementary document for Multiplexed wavefront sensing with a thin diffuser - 6774961.pdf

Revised supplemental informatio

Codes_v2.rar

This supplementary Material includes: •The raw data corresponding to the multiplexed speckle maps for the two experiments shown in Figure 2 (3 multiplexed wavefronts) and Figure 3 (5 multiplexed wavefronts) of the article. •The Matlab codes used to reconstruct the various multiplexed wavefronts from these speck-le maps (MAIN1_Multiplex.m) which is the heart of this article. This code will allow readers to check the impact of each reconstruction parameter (e.g. number of iterations, macropix-el size…) •The raw data corresponding to each wavefront, acquired individually using a standard non-multiplexed method . •A Matlab code (MAIN2_Comparison.m) allowing a quantitative comparison of the wave-fronts reconstructed using our multiplexing method to wavefronts acquired individually. •A Matlab code (MAIN3_Multiplex_AO.m) is an modification of (MAIN1_Multiplex.m), in which the direct DIC (T=1) is used with big phase-pixel to reconstruct the wavefront. Parfor loop is used for processing each GS running in a parallelization mode

Supplementary document for Multiplexed wavefront sensing with a thin diffuser - 6856404.pdf

Supplemental documen

Data.rar

Dataset for validating multiplexed wavefront sensing with a thin diffuser

Topological transformations of speckles

Deterministic control of coherent random light is highly important for information transmission through complex media. However, only a few simple speckle transformations can be achieved through diffusers without prior characterization. As recently shown, spiral wavefront modulation of the impinging beam allows permuting intensity maxima and intrinsic $\pm 1$-charged optical vortices. Here, we study this cyclic-group algebra when combining spiral phase transforms of charge $n$, with $D_3$- and $D_4$-point-group symmetry star-like amplitude modulations. This combination allows statistical strengthening of permutations and controlling the period to be 3 and 4, respectively. Phase saddle-points are shown to complete the cycle. These results offer new tools to manipulate critical points in speckles

3955552.pdf

Supplementary informatio

Single-shot Digital Optical Fluorescence Phase Conjugation Through Forward Multiply Scattering Samples

Aberrations and multiple scattering in biological tissues critically distort light beams into highly complex speckle patterns. In this regard, digital optical phase conjugation (DOPC) is a promising technique enabling in-depth focusing. However, DOPC becomes challenging when using fluorescent guide-stars for four main reasons: The low photon budget available, the large spectral bandwidth of the fluorescent signal, the Stokes shift between the emission and the excitation wavelength, and the absence of reference beam preventing holographic measurement. Here, we demonstrate the possibility to focus a laser beam through multiple-scattering samples by measuring speckle fields in a single acquisition step with a reference-free and high-resolution wavefront sensor. By taking advantage of the large spectral bandwidth of forward multiply scattering samples, Digital Fluorescence Phase Conjugation (DFPC) is achieved to focus a laser beam at the excitation wavelength while measuring the broadband speckle field arising from a micron-sized fluorescent bead