A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

We report an imaging method, termed Fourier ptychographic microscopy (FPM), which iteratively stitches together a
number of variably illuminated, low-resolution intensity images in Fourier space to produce a wide-field, high-resolution
complex sample image. By adopting a wavefront correction strategy, the FPM method can also correct for aberrations and
digitally extend a microscope’s depth of focus beyond the physical limitations of its optics. As a demonstration, we built a
microscope prototype with a resolution of 0.78 µm, a field of view of ∼120 mm^2 and a resolution-invariant depth of focus
of 0.3 mm (characterized at 632 nm). Gigapixel colour images of histology slides verify successful FPM operation. The
reported imaging procedure transforms the general challenge of high-throughput, high-resolution microscopy from one
that is coupled to the physical limitations of the system’s optics to one that is solvable through computation.

Wide-field, high-resolution Fourier ptychographic microscopy

A self-scanned 1024 element photodiode array and minicomputer are used to measure the phase (wavefront) in the interference pattern of an interferometer to lambda/100. The photodiode array samples intensities over a 32 x 32 matrix in the interference pattern as the length of the reference arm is varied piezoelectrically. Using these data the minicomputer synchronously detects the phase at each of the 1024 points by a Fourier series method and displays the wavefront in contour and perspective plot on a storage oscilloscope in less than 1 min (Bruning et al. Paper WE16, OSA Annual Meeting, Oct. 1972). The array of intensities is sampled and averaged many times in a random fashion so that the effects of air turbulence, vibrations, and thermal drifts are minimized. Very significant is the fact that wavefront errors in the interferometer are easily determined and may be automatically subtracted from current or subsequent wavefrots. Various programs supporting the measurement system include software for determining the aperture boundary, sum and difference of wavefronts, removal or insertion of tilt and focus errors, and routines for spatial manipulation of wavefronts. FFT programs transform wavefront data into point spread function and modulus and phase of the optical transfer function of lenses. Display programs plot these functions in contour and perspective. The system has been designed to optimize the collection of data to give higher than usual accuracy in measuring the individual elements and final performance of assembled diffraction limited optical systems, and furthermore, the short loop time of a few minutes makes the system an attractive alternative to constraints imposed by test glasses in the optical shop.

Digital wavefront measuring interferometer for testing optical surfaces and lenses

Have you ever felt that the very title, Progress in Optics, conjured an image in your mind? Don’t you see a row of handsomely printed books, bearing the editorial stamp of one of the most brilliant members of the optics community, and chronicling the field of optics since the invention of the laser? If so, you are certain to move the bookend to make room for Volume 16, the latest of this series. It contains seven chapters on widely diverging topics, written by well-known authorities in their fields. These are: 1) Laser Selective Photophysics and Photochemistry by V. S. Letokhov, 2) Recent Advances in Phase Profiles (sic) Generation by J. J. Clair and C. I. Abitbol, 3 ) Computer-Generated Holograms: Techniques and Applications by W.-H. Lee, 4) Speckle Interferometry by A. E. Ennos, 5 ) Deformation  Invariant, Space-Variant Optical  Pattern Recognition by D. Casasent and D. Psaltis, 6) Light Emission from High-Current Surface-Spark Discharges by R. E. Beverly, and 7) Semiclassical Radiation  Theory within a  QuantumMechanical Framework by I. R. Senitzkt. The  breadth of topic  matter  spanned  by  these  chapters makes it impossible, for this reviewer at least, to pass judgement on the comprehensiveness, relevance, and completeness of every chapter. With an editorial board as prominent as that of Progress in Optics, however, it seems hardly likely that such comments should be necessary. It should certainly be possible to take the authority of each author as credible. The only remaining judgment to be  made on these chapters is their readability. In short, what are they like to read? The first sentence of the first chapter greets the eye with an obvious typographical error: “The creation of coherent laser light source, that have tunable radiation, opened the . . . .” Two pages later we find: “When two types of atoms or molecules of different isotopic composition ( A and B ) have even one spectral line that does not overlap with others, it is pos-

Progress in optics

Quantitative phase imaging (QPI) has emerged as a valuable method for investigating cells and tissues. QPI operates on unlabelled specimens and, as such, is complementary to established fluorescence microscopy, exhibiting lower phototoxicity and no photobleaching. As the images represent quantitative maps of optical path length delays introduced by the specimen, QPI provides an objective measure of morphology and dynamics, free of variability due to contrast agents. Owing to the tremendous progress witnessed especially in the past 10–15 years, a number of technologies have become sufficiently reliable and translated to biomedical laboratories. Commercialization efforts are under way and, as a result, the QPI field is now transitioning from a technology-development-driven to an application-focused field. In this Review, we aim to provide a critical and objective overview of this dynamic research field by presenting the scientific context, main principles of operation and current biomedical applications. Over the past 10–15 years, quantitative phase imaging has moved from a research-driven to an application-focused field. This Review presents the main principles of operation and representative basic and clinical science applications.

Quantitative phase imaging in biomedicine

In this paper we start by presenting one recent development in the field of near field imaging where a lensless
microscope is introduced. Its operation principle is based upon wavelength encoding of the spatial information through
non periodic holes array and right after decoding the spatial information using a spectrometer. In the second part of the
paper we demonstrate a remote super sensing technique allowing monitoring, from a distance, the glucose level in the
blood stream of a patient by tracking the trajectory of secondary speckle patterns reflected from the skin of the wrist.

Novel approaches for near and far field super-resolved imaging

In a computer experiment we prove shift and scale invariant pattern recognition abilities of an elliptic coordinate transformed phase-only filter. The filter is built in the following way: from the classical matched filter we take the phase component only and then the elliptic coordinate transformation is made. We analyze performance of the filter for different semiaxes ratios and on-axis stops of several diameters. Discrimination ability of the filter is calculated. The filter allows good recognition of objects with change of scale by a factor of 1.5.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Elliptical coordinate transformed phase-only filter for shift and scale invariant pattern recognition

Invariant optical correlation method for 3D target detection is addressed. Tridimensionality is expressed in terms of range images. The recognition model is based on a vector space representation using an orthonormal image basis. The recognition method proposed is based on the calculation of the angle between the vector associated with a certain 3D object and a vector subspace. Scale and rotation invariant 3D target detection are obtained using the phase Fourier transform (PhFT) of the range images. In fact, when the 3D object is scaled, the PhFT becomes a distribution multiplied by a constant factor. On the other hand a rotation of the 3D object around the z axis, implies a shift in the PhFT. So, changes of scale and rotation of 3D objects are replaced by changes of intensity and position of PhFT distributions. We applied intensity invariant correlation methods for recognition. In addition to tolerance to scale and rotation, high discrimination against false targets is also achieved.

Improved invariant optical correlations for 3D target detection

Cardiovascular disease is America’s number one killer, accounting for more than 41% of deaths each year.1 Furthermore, 61 million Americans have some form of the condition, including heart disease, stroke, high blood pressure, congestive heart failure, congenital heart defects, and hardening of the arteries. Early detection of abnormality is the key to treating cardiovascular disease and reducing the death toll. However, some conditions, such as myocardial ischemia (reduced blood supply to the heart), can be difficult to establish in the early stages, which is when treatment is most effective. Cardiac ischemia is currently diagnosed by measuring electrical signals from the heart, or by using ultrasound waves to analyze heart contractions.2, 3 Our study aims to understand the contraction behavior of cardiac myocytes (muscle cells) in their simplest form: in a culture. We propose a robust way to test the influence of certain substances on the rate and magnitude of those contractions. Our work enables precise measurement (with nanometer accuracy) of the propagation of electronic stimulation waves within the culture. Such capability could be useful for studying re-entrant arrhythmias, when the electrical signal travels in a circle, instead of propagating in a linear fashion. Reentrant arrhythmias can be detected on the pericardium (outer wall) of the heart. We propose a very simple configuration to assess the statistics of cell contractions by measuring their physical contraction and expansion following illumination and analysis of the resulting secondary speckle patterns.4–7 Our system provides an ‘instant snapshot’ of the sample, enabling the study of numerous cells, and obtains statistics of their contractions. We illuminate the culture with a laser, while a camera positioned at a given distance from the culture collects the Figure 1. Results from measuring simultaneous contractions of muscle cells without using an imaging lens.

Photonic inspection of cardiac myocyte cell contractions

The main advantage of optical image processing with respect to its electronic counterpart is the high degree of parallelism. This characteristic can be boosted by feeding an optical system with several channels simultaneously. Several ways to perform this multiplexing can be devised. In this talk we focus on the spatial multiplexing, were several channels share the spatial bandwidth of the system input and wavelength multiplexing, were the channels are input in different wavelengths simultaneously. Principle and applications are discussed, along with several possible architectures for image processing systems.

Javier Garcia

Papers

Novel approaches for near and far field super-resolved imaging

Elliptical coordinate transformed phase-only filter for shift and scale invariant pattern recognition

Improved invariant optical correlations for 3D target detection

Photonic inspection of cardiac myocyte cell contractions

Image processing using spatial and wavelength multiplexing