Enhancing the isotropy of lateral resolution in coherent structured illumination microscopy

Joo Hyun Park,Eun Seong Lee,Jae Yong Lee

doi:10.1364/boe.5.001895

Abstract

We present a method to improve the isotropy of spatial resolution in a structured illumination microscopy (SIM) implemented for imaging non-fluorescent samples. To alleviate the problem of anisotropic resolution involved with the previous scheme of coherent SIM that employs the two orthogonal standing-wave illumination, referred to as the orthogonal SIM, we introduce a hexagonal-lattice illumination that incorporates three standing-wave fields simultaneously superimposed at the orientations equally divided in the lateral plane. A theoretical formulation is worked out rigorously for the coherent image formation with such a simultaneous multiple-beam illumination and an explicit Fourier-domain framework is derived for reconstructing an image with enhanced resolution. Using a computer-synthesized resolution target as a 2D coherent sample, we perform numerical simulations to examine the imaging characteristics of our three-angle SIM compared with the orthogonal SIM. The investigation on the 2D resolving power with the various test patterns of different periods and orientations reveal that the orientation-dependent undulation of lateral resolution can be reduced from 27% to 8% by using the three-angle SIM while the best resolution (0.54 times the resolution limit of conventional coherent imaging) in the directions of structured illumination is slightly deteriorated by 4.6% from that of the orthogonal SIM.

Highlights

Optical microscopy has been widely used in the biological sciences for its ability to visualize the fine interiors of specimens and biomolecules [1]
The high-frequency contents can be extracted from a series of images with different phases of the illumination pattern, which allows, after appropriate back-shifting of the high-frequency contents in frequency space, reconstruction of an image with resolution improved in a direction perpendicular to the illumination pattern
We present a modified framework to improve the isotropy of lateral resolution in the 2014 dimensions (2D) coherent structured illumination microscopy (SIM)

Summary

Introduction

Optical microscopy has been widely used in the biological sciences for its ability to visualize the fine interiors of specimens and biomolecules [1]. Diffraction of light, has long been imposing a critical limitation on the spatial resolution attainable with conventional optical microscopy, which often precludes its use in the observation of many biologically relevant structures at scales beyond the diffraction limit [2]. This has prompted challenging attempts to surpass the optical diffraction limit, leading eventually to a number of superresolution techniques, such as stimulated emission depletion (STED) microscopy [3,4], photoactivated localization microscopy (PALM) [5], stochastic optical reconstruction microscopy (STORM) [6], structured illumination microscopy (SIM) [7,8,9,10,11], etc. The results clearly demonstrate the benefit of our effort to improve isotropy of the 2D resolution in coherent SIM over the existing scheme

Principle of coherent SIM with isotropic 2D resolution

Mathematical formulation

Numerical simulation

Findings

Conclusion