Ramzi N. Zahreddine

Electrowetting lenses for compensating phase and curvature distortion in arrayed laser systems

We have demonstrated a one-dimensional array of individually addressable electrowetting tunable liquid lenses that compensate for more than one wave of phase distortion across a wavefront. We report a scheme for piston control using tunable liquid lens arrays in volume-bound cavities that alter the optical path length without affecting the wavefront curvature. Liquid lens arrays with separately tunable focus or phase control hold promise for laser communication systems and adaptive optics.

Simultaneous quantitative depth mapping and extended depth of field for 4D microscopy through PSF engineering

An extended depth of field (EDF) microscope that allows for quantitative axial positioning has been constructed. Past work has shown that EDF microscopy allows for features in varying planes to appear sharply focused simultaneously, however an inherent consequence of this is that depth information is lost. Here, a specifically engineered phase plate is used to create a point spread function (PSF) that contains both of the necessary attributes for extended depth of field and quantitative depth mapping. A two-camera solution is used to separate and capture the information for individualized post processing. The result is a microscope that can serve as an essential tool for full 3D, real-time imaging.

Simulation of electrowetting lens and prism arrays for wavefront compensation

A novel application of electrowetting devices has been simulated: wavefront correction using an array of electrowetting lenses and prisms. Five waves of distortion can be corrected with Strehl ratios of 0.9 or higher, utilizing piston, tip-tilt, and curvature corrections from arrays of 19 elements and fill factors as low as 40%. Effective control of piston can be achieved by placing the liquid lens array at the focus of two microlens arrays. Seven waves of piston delay can be generated with variation in focal length between 1.5 and 500 mm.

Noise removal in extended depth of field microscope images through nonlinear signal processing

Extended depth of field (EDF) microscopy, achieved through computational optics, allows for real-time 3D imaging of live cell dynamics. EDF is achieved through a combination of point spread function engineering and digital image processing. A linear Wiener filter has been conventionally used to deconvolve the image, but it suffers from high frequency noise amplification and processing artifacts. A nonlinear processing scheme is proposed which extends the depth of field while minimizing background noise. The nonlinear filter is generated via a training algorithm and an iterative optimizer. Biological microscope images processed with the nonlinear filter show a significant improvement in image quality and signal-to-noise ratio over the conventional linear filter.

Reducing noise in extended depth of field microscope images by optical manipulation of the point spread function

This work describes improved methods and algorithms for implementing extended depth of field (EDF) microscopy through point spread function (PSF) engineering. It utilizes adaptive optics to create a test bed on which to evaluate new phase shapes for EDF. Being able to quickly and cheaply design novel PSFs is essential to overcome limitations of EDF that have prevented the technology from reaching mainstream use. Further improvement is made by reducing the noise normally seen in EDF images. Computational optics principles are used to first encode the noise with an identifiable pattern and a specially-tailored non-linear algorithm then removes the noise. This approach improves a microscopes imaging capabilities in photon-starved applications such as live-cell fluorescence and object tracking.

Total variation regularized deconvolution for extended depth of field microscopy.

The depth of field of an optical system can be extended through a combination of point spread function (PSF) engineering and image processing. A phase mask inserted in the back aperture of the system creates a PSF that is focus-invariant over an extended depth. A digital deconvolution is then used to restore transverse resolution. The application and analysis of this technique to fluorescence microscopy is limited in the literature. In this paper we formalize a microscopy specific imaging model, and experimentally demonstrate a total variation regularized deconvolution approach. Results are compared to the Wiener filter.

Real-time quantitative differential interference contrast (DIC) microscopy implemented via novel liquid crystal prisms

A phase shifting differential interference contrast (DIC) microscope, which provides quantitative phase information and is capable of imaging at video rates, has been constructed. Using a combination of phase shifting and bi-directional shear, the microscope captures a series of eight images which are then integrated in Fourier space. In the resultant image the intensity profile linearly maps to the phase differential across the object. The necessary operations are performed by various liquid crystal devices (LCDs) which can operate at high speeds. A set of four liquid crystal prisms shear the beam in both the x and y directions. A liquid crystal bias cell delays the phase between the e- and o-beams providing phase-shifted images. The liquid crystal devices are then synchronized with a CCD camera in order to provide real-time image acquisition. Previous implementation of this microscope utilized Nomarski prisms, a rotation stage and a manually operated Sénarmont compensator to perform the necessary operations and was only capable of fixed sample imaging. In the present work, a series of images were taken using both the new LCD prism based microscope and the previously implemented Sénarmont compensator based system. A comparison between these images shows that the new system achieves equal and in some cases superior results to that of the old system with the added benefit of real-time imaging.

Binary phase modulated partitioned pupils for extended depth of field imaging

A new of extended depth of field phase mask based on incoherent pupil partitioning with binary phase modulation is proposed. The mask creates a maximally flat PSF with no zeros in the MTF so its ideal in applications that require post-processing.

A new expanded point information content design approach for 3D live-cell microscopy at video rates

Through a combination of optical design and algorithm development, a new expanded point information content (EPIC) microscope has been developed that is capable of extending the depth of field while simultaneously super locating the depth position of complex biological objects to within an accuracy of 75 nm. The data is then combined to form 3D animations of live-cell biological specimens. This is accomplished without the need to acquire multi-focal image stacks and is thus well suited for high-speed imaging.

Total Variation Regularized Deconvolution of Extended Depth of Field Microscope Images

Total variation regularized deconvolution provides a highly accurate reconstruction of extended depth of field microscopy images. Several versions of the deconvolution problem, tailored for specific noise distributions, are presented. Results are compared with linear filters.