In point-scanning microscopy, such as confocal laser scanning microscopy (CLSM), the imaging resolution is limited by the size of the focal spot. Breaking through the diffraction limit by inserting a modulation phase mask in the objective pupil plane is a compact, high efficiency and adaptable scheme. Here, we propose a feedback phase design method based on genetic algorithm to control the 3D shape of the focal spot. The lateral and axial size can be jointly designed for various usages. Simulation and experimental results present the feasibility of this method. The axial size can be decreased by 50% while the lateral size is decreased by 15% simultaneously. This method of 3D super-diffraction limit focusing may potentially be used in CLSM for 3D super resolution imaging.
Optical microscopy is an indispensable imaging tool in life science. However, light cannot be focused owing to high scattering, and hence, the imaging depth and spatial resolution are restricted. Here, we propose an imaging method that combines wavefront shaping and image scanning microscopy. The reflected signal is used as feedback to acquire an optimal phase that can refocus the scattered light behind the scattering media. The experimental results show that the proposed method works in multilayer scattering media and can improve both the resolution and imaging depth of optical microscopy.
Fourier ptychography (FP) is a promising computational imaging technique that overcomes the physical space-bandwidth product (SBP) limit of a conventional microscope by applying angular diversity illuminations. However, to date, the effective imaging numerical aperture (NA) achievable with a commercial LED board is still limited to the range of 0.3–0.7 with a 4×/0.1NA objective due to the constraint of planar geometry with weak illumination brightness and attenuated signal-to-noise ratio (SNR). Thus the highest achievable half-pitch resolution is usually constrained between 500–1000 nm, which cannot fulfill some needs of high-resolution biomedical imaging applications. Although it is possible to improve the resolution by using a higher magnification objective with larger NA instead of enlarging the illumination NA, the SBP is suppressed to some extent, making the FP technique less appealing, since the reduction of field-of-view (FOV) is much larger than the improvement of resolution in this FP platform. Herein, in this paper, we initially present a subwavelength resolution Fourier ptychography (SRFP) platform with a hemispherical digital condenser to provide high-angle programmable plane-wave illuminations of 0.95NA, attaining a 4×/0.1NA objective with the final effective imaging performance of 1.05NA at a half-pitch resolution of 244 nm with a wavelength of 465 nm across a wide FOV of 14.60 mm2 , corresponding to an SBP of 245 megapixels. Our work provides an essential step of FP towards high-NA imaging applications without scarfing the FOV, making it more practical and appealing.
We present an improved iteration algorithm for speckle-correlation imaging through scattering media. We employ an approximate solution obtained from a bispectrum-analysis method as the initial condition of the iterative process. This method avoids several different runs performed with different random initial conditions in the traditional iteration algorithm and reduces the execution time in comparison with the conventional bispectrum-analysis method. Therefore, we obtain a balance between image quality and reconstruction speed. The feasibility of the proposed method is proved by the experimental results.
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