Label-free microscopy that does not require the staining of weakly absorbing samples circumvent the adverse effects of exogenous dyes on the biological sample, and thus have received much attention in recent years. Among them, non-interferometric optical diffraction tomography microscopy has become a hot topic in the direction of label-free three-dimensional microscopy due to its system simplicity, ease of integration and independence from scattering noise. We recently designed a refractive index and fluorescence dual-modality microscopy system based on the transport of intensity diffraction tomography microscopy, which solves the absorption and phase information of the sample separately with the help of two illuminating apertures, and optimizes the imaging speed by applying an electrically tunable lens.
Wigner distribution function (WDF) is a complete representation of the optical field with arbitrary coherent state and can be regarded as a local spectrum. It has unique advantages for representation, measurement and manipulation of partially coherent fields. Image sensors can only obtain the two-dimensional intensity data, which is the shearing projection of WDF. The shearing of WDF, which equals to the propagation of optical field, embodies the coherent properties of optical field. In this paper, a phase space retrieval method based on three-dimensional (3D) intensity focus stack combined with an iterative optimization is proposed. WDF with arbitrary coherent state can be reconstructed by 3D intensity sequences, which can realize the local spectrum retrieval and the analysis of spatial partially coherent fields.
We present a 3D label-free refractive index (RI) imaging technique based on single-exposure intensity diffraction tomography (sIDT) utilizing a color-multiplexed illumination scheme. In our method, the chromatic LEDs corresponding R/G/B channels in an annular programmable array provide oblique illumination geometry which matches the numerical aperture of the objective precisely to maximize the spectrum coverage. A color intensity image encoding the scattering field of the specimen from different directions is captured, and monochromatic intensity images with respect to three color channels were separated and then used to recover the 3D RI distribution of the object following the process of IDT. In addition, the axial chromatic dispersion of focal lengths at different wavelengths introduced by the chromatic aberration of the objective lens and the spatial position misalignment of the ring LED source in the imaging system’s transfer functions modeling are both corrected to significantly reduce the artifacts in slice-based deconvolution procedure for the reconstruction of 3D RI distribution. Experimental results on MCF-7, Spirulina algae, and live C. elegans samples demonstrate the solid performance of the sIDT method in label-free, high-throughput, and real-time (∼ 24 fps) 3D volumetric biological imaging applications.
Phase space optics allows the four-dimensional simultaneous visualization of both space and spatial frequency optical information. The Wigner distribution function (WDF) is a common characterization of the phase space. Compared with the two-dimensional complex amplitude coherent optical field, the WDF can characterize optical field with arbitrary coherent states due to its higher dimensions. It is especially advantageous for the representation of partially coherent optical fields. The WDF is real and may have negative values, which are the result of phase-space interference. In this paper, an improved phase-space retrieval method is demonstrated. First, capture three-dimensional intensity focal stack. Then, phase space tomography (PST) combined with a non-linear iterative projection algorithm is conducted to reconstruct the whole WDF. We further analyzed the effect of the microscopy imaging system, i.e., the illumination aperture and the aperture of objective lens effect.
Phase space optics allows the four-dimensional (4D) simultaneous visualization of both space (x) and spatial frequency (u) information. The Wigner distribution function (WDF) is commonly used to represent the phase space characterization. Compared with the coherent optical field expressed by two-dimensional (2D) complex amplitude, the 4D WDF (2D space and 2D spatial frequency) can characterize optical field with arbitrary coherent state. It is especially advantageous for the characterization of partially coherent optical fields. The WDF is real and may have negative values, which are the result of phase-space interference. In this paper, an improved phase-space retrieval method is demonstrated. First, capture three-dimensional intensity focal stack by camera sensors. Then, phase space tomography (PST) combined with a non-linear iterative algorithm is conducted to reconstruct the whole WDF. We further analyzed the effect of the imaging system, i.e., the illumination aperture and the aperture of objective lens effect.
Phase space is an artificially structured space jointly represented by the space and spatial frequency variables, and the Wigner distribution function (WDF) is widely used to describe the phase space. Compared with the coherent optical field expressed by two-dimensional (2D) complex amplitude, the four-dimensional WDF (2D space and 2D spatial frequency) can characterize optical field with arbitrary coherent state (coherent, partially coherent and incoherent). It is especially advantageous for the characterization of partially coherent optical fields. The WDF is real and may have negative values, which are the result of phase-space interference. The direct measurement of phase space can only obtain the absolute value of the whole WDF because the camera sensors can only obtain intensity, therefore, the negative values of measured WDF are mixed with positive values. In this paper, an improved phase-space retrieval method is demonstrated. First, capture three-dimensional intensity focal stack by camera sensors. Then, phase space tomography (PST) combined with a non-linear iterative algorithm is conducted to reconstruct the whole WDF.
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