Jorge Sola-Pikabea

Resolution improvements in integral microscopy with Fourier plane recording.

Integral microscopes (IMic) have been recently developed in order to capture the spatial and the angular information of 3D microscopic samples with a single exposure. Computational post-processing of this information permits to carry out a 3D reconstruction of the sample. By applying conventional algorithms, both depth and also view reconstructions are possible. However, the main drawback of IMic is that the resolution of the reconstructed images is low and axially heterogeneous. In this paper, we propose a new configuration of the IMic by placing the lens array not at the image plane, but at the pupil (or Fourier) plane of the microscope objective. With this novel system, the spatial resolution is increased by factor 1.4, and the depth of field is substantially enlarged. Our experiments show the feasibility of the proposed method.

Integral Imaging Monitors with an Enlarged Viewing Angle

Enlarging the horizontal viewing angle is an important feature of integral imaging monitors. Thus far, the horizontal viewing angle has been enlarged in different ways, such as by changing the size of the elemental images or by tilting the lens array in the capture and reconstruction stages. However, these methods are limited by the microlenses used in the capture stage and by the fact that the images obtained cannot be easily projected into different displays. In this study, we upgrade our previously reported method, called SPOC 2.0. In particular, our new approach, which can be called SPOC 2.1, enlarges the viewing angle by increasing the density of the elemental images in the horizontal direction and by an appropriate application of our transformation and reshape algorithm. To illustrate our approach, we have calculated some high-viewing angle elemental images and displayed them on an integral imaging monitor.

FIMic: design for ultimate 3D-integral microscopy of in-vivo biological samples

In this work, Fourier integral microscope (FIMic), an ultimate design of 3D-integral microscopy, is presented. By placing a multiplexing microlens array at the aperture stop of the microscope objective of the host microscope, FIMic shows extended depth of field and enhanced lateral resolution in comparison with regular integral microscopy. As FIMic directly produces a set of orthographic views of the 3D-micrometer-sized sample, it is suitable for real-time imaging. Following regular integral-imaging reconstruction algorithms, a 2.75-fold enhanced depth of field and [Formula: see text]-time better spatial resolution in comparison with conventional integral microscopy is reported. Our claims are supported by theoretical analysis and experimental images of a resolution test target, cotton fibers, and in-vivo 3D-imaging of biological specimens.

Three-dimensional microscopy through liquid-lens axial scanning

In this contribution we propose the use of a liquid lens (LL) to perform three-dimensional (3D) imaging. Our proposed method consists on inserting the LL at the aperture stop of telecentric microscopes. The sequential depth images of 3D samples are obtained by tuning the focal length of LL. Our experimental results demonstrate that fast-axial scanning of microscopic images is obtained without varying neither the resolution capability nor the magnification of the imaging system. Furthermore, this non-mechanical approach can be easily implemented in any commercial optical microscope.

Evaluation of the use of wavefront encoding to reduce depth-induced aberration in structured illumination microscopy

Three-dimensional imaging is affected by depth-induced spherical aberration (SA) when imaging deep into an optically thick sample. In this work, we evaluate the impact of SA on the performance of incoherent grating-projection structured illumination microscopy (SIM). In particular, we analyze the reduction of the contrast in the structured pattern and compare the reconstructed SIM images for different amounts of SA. In order to mitigate the impact of SA, we implement and evaluate in SIM a wavefront encoded imaging system using a square cubic (SQUBIC) phase mask, an approach shown previously to be successful in conventional microscopy.

3D integral microscopy based in far-field detection

Lately, Integral-Imaging systems have shown very promising capabilities of capturing the 3D structure of micro- scopic and macroscopic scenes. The aim of this work is to provide an optimal design for 3D-integral microscopy with extended depth of field and enhanced lateral resolution. By placing an array of microlenses at the aperture stop of the objective, this setup provides a set of orthographic views of the 3D sample. Adopting well known integral imaging reconstruction algorithms it can be shown that the depth of field as well as spatial resolution are improved with respect to conventional integral microscopy imaging. Our claims are supported on theoretical basis and experimental images of a resolution test target, and biological samples.

Integral imaging with Fourier-plane recording

Integral Imaging is well known for its capability of recording both the spatial and the angular information of threedimensional (3D) scenes. Based on such an idea, the plenoptic concept has been developed in the past two decades, and therefore a new camera has been designed with the capacity of capturing the spatial-angular information with a single sensor and after a single shot. However, the classical plenoptic design presents two drawbacks, one is the oblique recording made by external microlenses. Other is loss of information due to diffraction effects. In this contribution report a change in the paradigm and propose the combination of telecentric architecture and Fourier-plane recording. This new capture geometry permits substantial improvements in resolution, depth of field and computation time

Display of travelling 3D scenes from single integral-imaging capture

Integral imaging (InI) is a 3D auto-stereoscopic technique that captures and displays 3D images. We present a method for easily projecting the information recorded with this technique by transforming the integral image into a plenoptic image, as well as choosing, at will, the field of view (FOV) and the focused plane of the displayed plenoptic image. Furthermore, with this method we can generate a sequence of images that simulates a camera travelling through the scene from a single integral image. The application of this method permits to improve the quality of 3D display images and videos.

3D Integral Microscopy with Improved Resolution and Depth of Field

In this contribution we explain two new techniques developed by our group, which permit to increase the two-dimensional spatial resolution of the computed depth images in integral microscopy.

Static real-time capture of 3D microscopy images

Two-dimensional widefield microscopy provides basic dynamic information about live biological specimens. However, it provides only a partial representation of the 3D biological processes and may be incomplete or even misleading. Current techniques, such as widefield, confocal, structured-illumination, or light-sheet microscopy cannot capture the 3D structure of a specimen in a single frame. In contrast, in 2D widefield microscopy, a stack of 2D depth images of the sample are recorded and a 3D digital image is computed from them. The different depth images are typically recorded with axial mechanical scanning. But mechanical movement could damage the sample, cause it to vibrate and hence introduce image distortions, or slow down image acquisition, which would make it impossible to record highly dynamic biological processes. The trivial solution is to use digital holographic microscopy, which permits the 3D complex distribution scattered by the sample to be rendered from a single frame.1 However, this system operates coherently and makes fluorescence imaging impossible. We have investigated using an electrically addressable liquid lens (LL) to acquire images at different depths. The lens is based on electrowetting technology: how a drop of water spreads on an electrically insulating surface can be modified by accumulating charge at the base of the drop. The optical power of the resulting LL can be tuned by an applied voltage.2 In 2010, our group proposed using an LL for parallel dynamic focusing of images obtained through an array of microlenses.3 More recently, other groups have applied LL technology in microscopy.4, 5 Our proposal is to insert an LL at the aperture stop of a widefield microscope, which is arranged as the telecentric coupling between a high-numerical-aperture (NA) infinitycorrected microscope objective and a low-NA tube lens.6 The insertion of the LL enables the axial position of the object plane to be controlled by the voltage while preserving the telecentric Figure 1. Scheme of the static axial scanning experimental setup. CCD: Charge-coupled device. Fob and FTL: Front focus of the objective and the tube lens, respectively. F0TL: Back focus of the tube lens. f0R1; R2: Focal lengths of the relay lenses.