Abstract
The use of binary phase patterns to improve the integration and optimization of spatial light modulators (SLM) in an imaging system, especially a confocal microscope, is proposed and demonstrated. The phase masks were designed to create point spread functions (PSF), which exhibit specific sensitivity to major disturbances in the optical system. This allows direct evaluation of misalignment and fundamental aberration modes by simple visual inspection of the focal intensity distribution or by monitoring the central intensity of the PSF. The use of proposed phase masks is investigated in mathematical modelling and experiment for the use in a stimulated emission depletion (STED) microscope applying wavefront shaping by a SLM. We demonstrate the applicability of these phase masks for modal wavefront sensing of low order aberration modes up to the third order of Zernike polynomials, utilizing the point detector of a confocal microscope in a ‘guide star’ approach. A lateral resolution of ~25 nm is shown in STED imaging of the confocal microscope retrofitted with a SLM and a STED laser and binary phase mask based system optimization.
Highlights
stimulated emission depletion (STED) microscopy relies on beam shaping of a high intensity laser to create a focus featuring a central intensity zero surrounded by high intensity lobes[1,2,3]
Based on monitoring the central intensity of yielding point spread functions (PSF) in a ‘guide star’ approach[12] by the point detector of a confocal system, we demonstrate the use of binary phase mask (PM) in modal sensing of low-order aberrations and show that the method is well suited the optimization of an spatial light modulators (SLM)-STED microscope
In the case of STED microscopy, this concerns the distinction between distortions of the observed intensity PSF caused by imperfect lateral positioning of the STED PM and by aberrations due to imperfect surfaces of mirrors, lenses and the SLM itself
Summary
STED microscopy relies on beam shaping of a high intensity laser to create a focus featuring a central intensity zero surrounded by high intensity lobes[1,2,3]. The flexibility is won to apply either the vortex phase mask (PM) for ‘doughnut’ PSF creation and lateral confinement of fluorescence or the circular PM for creation of the ‘optical bottle’ PSF and axial fluorescence confinement, or both in parallel[6,7] Another crucial advantage of the adaptive optical element is that system aberration can be corrected for by the same SLM used for beam shaping. If system aberration due to imperfect surfaces of optical components are present It has been noted e.g. that PM misalignment and low-order aberrations have similar effects on the STED focus shape[8], making this correction modality based on PSF deformation error-prone. These aberrations can be corrected by applying corresponding biased Zernike polynomials
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