Resolution limit in opto-digital systems revisited.

The resolution limit achievable with an optical system is a fundamental piece of information when characterizing its performance, mainly in case of microscopy imaging. Usually this information is given in the form of a distance, often expressed in microns, or in the form of a cutoff spatial frequency, often expressed in line pairs per mm. In modern imaging systems, where the final image is collected by pixelated digital cameras, the resolution limit is determined by the performance of both, the optical systems and the digital sensor.

Machine Learning-Based View Synthesis in Fourier Lightfield Microscopy.

Current interest in Fourier lightfield microscopy is increasing, due to its ability to acquire 3D images of thick dynamic samples. This technique is based on simultaneously capturing, in a single shot, and with a monocular setup, a number of orthographic perspective views of 3D microscopic samples. An essential feature of Fourier lightfield microscopy is that the number of acquired views is low, due to the trade-off relationship existing between the number of views and their corresponding lateral resolution.

Fourier lightfield microscopy: a practical design guide.

In this work, a practical guide for the design of a Fourier lightfield microscope is reported. The fundamentals of the Fourier lightfield are presented and condensed on a set of contour plots from which the user can select the design values of the spatial resolution, the field of view, and the depth of field, as function of the specifications of the hardware of the host microscope. This work guides the reader to select the parameters of the infinity-corrected microscope objective, the optical relay lenses, the aperture stop, the microlens array, and the digital camera.

Handheld and Cost-Effective Fourier Lightfield Microscope.

In this work, the design, building, and testing of the most portable, easy-to-build, robust, handheld, and cost-effective Fourier Lightfield Microscope (FLMic) to date is reported. The FLMic is built by means of a surveillance camera lens and additional off-the-shelf optical elements, resulting in a cost-effective FLMic exhibiting all the regular sought features in lightfield microscopy, such as refocusing and gathering 3D information of samples by means of a single-shot approach. The proposed FLMic features reduced dimensions and light weight, which, combined with its low cost, turn the presented FLMic into a strong candidate for in-field application where 3D imaging capabilities are pursued.

Three-dimensional real-time darkfield imaging through Fourier lightfield microscopy.

We report a protocol that takes advantage of the Fourier lightfield microscopy concept for providing 3D darkfield images of volumetric samples in a single-shot. This microscope takes advantage of the Fourier lightfield configuration, in which a lens array is placed at the Fourier plane of the microscope objective, providing a direct multiplexing of the spatio-angular information of the sample. Using the proper illumination beam, the system collects the light scattered by the sample while the background light is blocked out.

Fast and robust phase-shift estimation in two-dimensional structured illumination microscopy.

A method of determining unknown phase-shifts between elementary images in two-dimensional Structured Illumination Microscopy (2D-SIM) is presented. The proposed method is based on the comparison of the peak intensity of spectral components. These components correspond to the inherent structured illumination spectral content and the residual component that appears from wrongly estimated phase-shifts.

Improvement of two-dimensional structured illumination microscopy with an incoherent illumination pattern of tunable frequency.

In two-dimensional structured illumination microscopy (2D-SIM), high-resolution images with optimal optical sectioning (OS) cannot be obtained simultaneously. This tradeoff can be overcome by using a tunable-frequency 2D-SIM system and a proper reconstruction method. The goal of this work is twofold.

Mapping electron-beam-injected trapped charge with scattering scanning near-field optical microscopy.

Scattering scanning near-field optical microscopy (s-SNOM) has been demonstrated as a valuable tool for mapping the optical and optoelectronic properties of materials with nanoscale resolution. Here we report experimental evidence that trapped electric charges injected by an electron beam at the surface of dielectric samples affect the sample-dipole interaction, which has direct impact on the s-SNOM image content. Nanoscale mapping of the surface trapped charge holds significant potential for the precise tailoring of the electrostatic properties of dielectric and semiconductive samples, such as hydroxyapatite, which has particular importance with respect to biomedical applications.

Free-depths reconstruction with synthetic impulse response in integral imaging.

Integral Imaging provides spatial and angular information of three-dimensional (3D) objects, which can be used both for 3D display and for computational post-processing purposes. In order to recover the depth information from an integral image, several algorithms have been developed. In this paper, we propose a new free depth synthesis and reconstruction method based on the two-dimensional (2D) deconvolution between the integral image and a simplified version of the periodic impulse response function (IRF) of the system.

Resolution enhancement in integral microscopy by physical interpolation.

Integral-imaging technology has demonstrated its capability for computing depth images from the microimages recorded after a single shot. This capability has been shown in macroscopic imaging and also in microscopy. Despite the possibility of refocusing different planes from one snap-shot is crucial for the study of some biological processes, the main drawback in integral imaging is the substantial reduction of the spatial resolution.

Off-axis digital holographic microscopy: practical design parameters for operating at diffraction limit.

The utilization of microscope objectives (MOs) in digital holographic microscopy (DHM) has associated effects that are not present in conventional optical microscopy. The remaining phase curvature, which can ruin the quantitative phase imaging, is the most evident and analyzed. As phase imaging is considered, this interest has made possible the development of different methods of overcoming its undesired consequences.

Accurate single-shot quantitative phase imaging of biological specimens with telecentric digital holographic microscopy.

The advantages of using a telecentric imaging system in digital holographic microscopy (DHM) to study biological specimens are highlighted. To this end, the performances of nontelecentric DHM and telecentric DHM are evaluated from the quantitative phase imaging (QPI) point of view. The evaluated stability of the microscope allows single-shot QPI in DHM by using telecentric imaging systems.

Enhancing spatial resolution in digital holographic microscopy by biprism structured illumination.

A novel and efficient architecture of a structured-illumination digital holographic microscope (DHM) is presented. As the DHM operates at the diffraction limit, its spatial resolution on label-free imaging of transparent samples is improved by illuminating the sample with a structured illumination produced by a Fresnel's biprism. The theoretical analysis of the method forecasts a twofold improvement of the spatial resolution.

Aberration compensation for objective phase curvature in phase holographic microscopy: comment.

In a recent Letter by Seo et al. [Opt. Lett.

Shift-variant digital holographic microscopy: inaccuracies in quantitative phase imaging.

Inaccuracies introduced in quantitative phase digital holographic microscopy by the use of nontelecentric imaging systems are analyzed. Computer modeling of the experimental result shows that even negligible errors in the radius and center of curvature of the numerical compensation needed to get rid of the remaining quadratic phase factor introduce errors in the phase measurements; these errors depend on the position of the object in the field-of-view. However, when a telecentric imaging system is utilized for the recording of the holograms, the numerical modeling and experimental results show the shift-invariant behavior of the quantitative-phase digital holographic microscope.

Axial resonance of periodic patterns by using a Fresnel biprism.

This paper proposes a method for the generation of high-contrast localized sinusoidal fringes with spatially noncoherent illumination and relatively high light throughput. The method, somehow similar to the classical Lau effect, is based on the use of a Fresnel biprism. It has some advantages over previous methods for the noncoherent production of interference fringes.

Multispectral integral imaging acquisition and processing using a monochrome camera and a liquid crystal tunable filter.

This paper presents an acquisition system and a procedure to capture 3D scenes in different spectral bands. The acquisition system is formed by a monochrome camera, and a Liquid Crystal Tunable Filter (LCTF) that allows to acquire images at different spectral bands in the [480, 680]nm wavelength interval. The Synthetic Aperture Integral Imaging acquisition technique is used to obtain the elemental images for each wavelength.

Subtractive imaging in confocal scanning microscopy using a CCD camera as a detector.

We report a scheme for the detector system of confocal microscopes in which the pinhole and a large-area detector are substituted by a CCD camera. The numerical integration of the intensities acquired by the active pixels emulates the signal passing through the pinhole. We demonstrate the imaging capability and the optical sectioning of the system.

Digital holographic microscopy with pure-optical spherical phase compensation.

Telecentric architecture is proposed for circumventing, by the pure-optical method, the residual parabolic phase distortion inherent to standard configuration of digital holographic microscopy. This optical circumvention produces several important advantages. One is that there is no need for computer compensation of the parabolic phase during the phase map recovering procedure.