Design And Experiments For Diffractive Optical Elements In Beam Smoothing And Far-field Fluorescence Microscopy

The research devoted to the first part of this thesis focuses on the design and application of large aperture diffractive optical elements (DOEs) that will be used to realize uniform illumination on focal plane for inertial confinement fusion (ICF) system. The primary research and achievement are as follow:1. Theoretically, we presented the cause of generating sub-diffractive spots around the focal spot and diffraction efficiency debasement in beam shaping by320mm-diameter diffractive optical elements which is designed and fabricated in2007. Through the simulation analysis, it was suggested that, by means of adjusting the design parameters, the intensity of sub-diffractive spots can be suppressed effectually, which can ensure the effect of diffractive optical elements in beam shaping. For example, by fitting the hits, the proportion of focal spot to whole output range, named Yita, can be decreased, and the efficiency loss engendered by sub-diffractive spots would be restricted. When Yita is less than0.2, efficiency loss is only2%. Simultaneously, we propose an improvement of fabrication technology-’weakening branch cut’. The experimental results indicate the improvement with the theoretical simulation.2. The uniformity of focal-spot pattern is analyzed by the simulation of employing spectral dispersion and distributed phase plate (DPP) in the laser chain. The uncontrollability of intensity at non-sample points in DPP design causes the loss of uniformity. The simulation confirms the improvement of target irradiation by spectral dispersion; the nonuniformity of focus-spot decreases from58.30%to19.50%. The relation between nonuniformity and integration time shows that the optimal integration time is5to6modulation periods of spectral dispersion. The high spatial frequency of focus-spot caused by intensity at non-sample points is reduced by smoothing by spectral dispersion (SSD); the intensity fluctuation within26.3μm can be eliminated. 3. Design procedure of continuous phase plates (CPPs) is proposed for the indirect-drive scheme of ICF. We optimize the wrapper algorithm and spatial frequency spectrum control used in the design technology. Then a CPP with Φ240mm is designed and fabricated for experiment and achieve the design performance.The second part of this thesis presented the development of far-field superresolution fluorescence microscopy, especially the photoactivated localization microscopy (PALM). Then we propose a novel and technology to improve the z-axis resolution.1. We describe the principle of PALM and the reconstruction of superresolution image and optimize the single molecule localization algorithm. Molecules are searched by Hogbom’CLEAN’and localized by maximum likelihood estimator (MLE). To explain a novel theory of molecular biology, we reconstruct images with resolution--20nm by dual-PALM.2. Design of DOE for vector beams with vortex phase is proposed, and its application in single-molecule localization microscopy to achieve high z-axis resolution by axis selective activation of molecules is discussed. The numerical calculation demonstrated that for molecules along z axis, the probability of being active has a single peak with FWHM of only25.7nm (for R=500) and about90%of activated molecules are located in a80-nm-thick layer around zero point (for R=60).