Adaptive optical quantitative phase imaging based on annular illumination Fourier ptychographic microscopy

Abstract

Quantitative phase imaging (QPI) has emerged as a valuable tool for biomedical research thanks to its unique capabilities for quantifying optical thickness variation of living cells and tissues. Among many QPI methods, Fourier ptychographic microscopy (FPM) allows long-term label-free observation and quantitative analysis of large cell populations without compromising spatial and temporal resolution. However, high spatio-temporal resolution imaging over a long-time scale (from hours to days) remains a critical challenge: optically inhomogeneous structure of biological specimens as well as mechanical perturbations and thermal fluctuations of the microscope body all result in time-varying aberration and focus drifts, significantly degrading the imaging performance for long-term study. Moreover, the aberrations are sample- and environment-dependent, and cannot be compensated by a fixed optical design, thus necessitating rapid dynamic correction in the imaging process. Here, we report an adaptive optical QPI method based on annular illumination FPM. In this method, the annular matched illumination configuration (i.e., the illumination numerical aperture (NA) strictly equals to the objective NA), which is the key for recovering low-frequency phase information, is further utilized for the accurate imaging aberration characterization. By using only 6 low-resolution images captured with 6 different illumination angles matching the NA of a 10x, 0.4 NA objective, we recover high-resolution quantitative phase images (synthetic NA of 0.8) and characterize the aberrations in real time, restoring the optimum resolution of the system adaptively. Applying our method to live-cell imaging, we achieve diffraction-limited performance (full-pitch resolution of $$655\,nm$$ 655 n m at a wavelength of $$525\,nm$$ 525 n m ) across a wide field of view ($$1.77\,mm^2$$ 1.77 m m 2 ) over an extended period of time.

Transmission-Matrix Quantitative Phase Profilometry for Accurate and Fast Thickness Mapping of 2D Materials

“…To improve the phase sensitivity to ∼0.1 nm or less, common-path interferometry and/or broadband illumination have been implemented in QPM, such as epi-illumination gradient light interference microscopy (GLIM), , spatial light interference microscopy (SLIM), , quadri-wave lateral shearing interferometry (QLSI), and white-light diffraction phase microscopy (wDPM) . Intensity measurement-based computational QPM methods, such as Fourier ptychographic microscopy (FPM) , and transport of intensity equation (TIE), have recently emerged as potential solutions for material thickness profiling. These high-sensitivity QPM methods are promising candidates for characterizing monolayer atomic structures, but their capabilities are limited by several key issues: (i) the broadband illumination and associated coherence issues may result in inaccurate phase and thickness estimation; , (ii) negligence of multiple light refractions and reflection at interfaces may lead to significant errors in thickness estimations, especially in 2D materials; and (iii) further improvement in phase sensitivity and measurement throughput is limited by the interferometry design and the detection scheme.…”

Far‐Field Synthetic Aperture Imaging via Fourier Ptychography with Quasi‐Plane Wave Illumination

“…[7][8][9][10][11] It has been demonstrated for label-free imaging of biological samples without the necessity of interferometric methods to acquire phase. [12] In particular, various systems and methods have been developed for high-precision Fourier ptychographic microscopy (FPM), [13][14][15] e.g., Fourier ptychographic diffraction tomography for 3D microscopy, [16] high spatio-temporal resolution imaging over a long-time scale, [17] UV Fourier ptychographic microscopy [18] to achieve higher spatial resolution, and high-performance FP with deep learning. [19][20][21] The stability and reconstruction quality may be significantly degraded with non-negligible noise when the ptychographical iterative engine (PIE) and extended ptychographic iterative engine (ePIE) are used for phase recovery.…”

Live-cell analysis framework for quantitative phase imaging with slightly off-axis digital holographic microscopy

“…The enhancement of space-bandwidth product by the slightly off-axis DHM is necessarily accompanied by the zero-order suppression; otherwise, artifacts will be formed on the phase image due to the residual background intensity information (Pavillon et al, 2009;Pavillon et al 2010;Baek et al, 2019). In our previous work (Shen et al, 2022), we innovatively proposed a slightly off-axis holographic imaging system (FPDH) based on Fourier ptychographic reconstruction (Zheng et al, 2013;Sun et al, 2017;Shu et al, 2022). FPDH effectively breaks through the spatial bandwidth limitation of quasi-off-axis holography and reconstructs high-quality artifact-free phase images while reaching the theoretical resolution, laying the foundation for high-precision measurement of the physical properties of living cells.…”