Structured illumination microscopy is able to improve the spatial resolution of wide-field fluorescence imaging by applying sinusoidal stripe pattern illumination to the sample. The corresponding computational image reconstruction requires precise knowledge of the pattern's parameters, which are its phase (ϕ) and wave vector (p). Here, a computationally inexpensive method for estimation of p from the raw data is proposed and illustrated with simulations. The method estimates p through a selective discrete Fourier transform at tunable subpixel precision. This results in an accurate p estimation for all the illumination patterns and subsequently improves the superresolution image recovery by a factor of 10 around sharp edges as compared to an integer pixel approach. The technique as presented here is of major interest to the large variety of custom-build systems that are used. The feasibility of the presented method is proven in comparison with published data.
Applying structured instead of plane illumination in widefield optical fluorescence microscopy can improve the spatial resolution beyond what is known as the Abbe limit. In general it is not only the resolution of an imaging system that is of interest but also its field of view (FOV). These two parameters are expressed in the space-bandwidth product (SBP). Here we introduce a modified structured illumination microscopy (SIM) approach that offers a larger SBP than any other available implementation. This is achieved through a transillumination geometry instead of the typical epifluorescent configuration. Compared to conventional SIM, the illumination path is decoupled from the objective lens by using a multi-mirror setup to generate the sinusoidal interference pattern for structured illumination in transmission mode. The spatial frequency of the illumination pattern can be controlled by changing the angle of the mirrors, achieving comparably fine patterns over a large FOV. In this work simulation results demonstrate the potential resolution improvement to be expected by the suggested implementation. Preliminary experimental results demonstrate phase-shifting ability and the stability of fringe frequencies over a large FOV of (
16 mm2) at different numerical apertures, fulfilling the prerequisites for SIM acquisition.
Photonic-chip-based light illumination has recently found applications in optical microscopy and nanoscopy methodologies. The photonic chip removes the dependency on imaging objective lenses to generate the required illumination patterns for different microscopy methods. Until now, all the reported chip-based optical microscopy methods exploit the evanescent field present on top of a waveguide surface and are thus inherently limited to two-dimensional microscopy. Here, we perform systematic simulation studies to investigate different chip-based waveguide designs for static and dynamic shaping of light beams in the free-space. The simulation studies have been carefully designed considering the photo-lithography limitations and wavelength spectrum (405 nm to 660 nm) that is of interest in fluorescence based optical microscopy and nanoscopy. We first report the generation of a quasi-Bessel beam (QBB) using an on-chip axicon made at the end facet of a planar waveguide to mimic light sheet illumination. This is extended to the implementation of a counter propagating QBB for lattice light-sheet applications. The double axicon, a derivative of the axicon generates superimposed Bessel beams (SBB). Its waveguide-based implementation is proposed and analyzed. Finally, we investigate an optical phased array (OPA) approach to allow dynamic steering of the output light in the free-space. The aim of this study is to find suitable waveguide design parameters for free-space beam shaping operating in the visible spectrum opening possibilities for three-dimensional chip-based optical microscopy.
A photonic chip-based approach is shown as alternative to conventional super-resolution fluorescence microscopy. By making use of photonic circuits, more compact, cost-effective and higher resolving setups can allow for a wider implementation of these techniques.
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