Low Degree Of Coherence Research Articles

Pixel-super-resolved lens-free quantitative phase microscopy with partially coherent illumination

Lens-free on-chip microscopy (LFOCM) has been widely utilized in digital pathology, drug screening, point-of-care testing (POCT), and quantitative phase imaging (QPI) due to its high throughput imaging capability and compactness. Initially, coherent laser sources were used in LFOCM to generate interference fringes to reconstruct the intensity and phase information of an object. The use of partially coherent light-emitting diodes (LEDs) in LFOCM offers a more portable and cost-effective alternative to conventional coherent illumination sources. However, the coherence-gating effect from a relatively low degree of coherence may cause a blur of high-frequency information in holograms, leading to an inaccurate object recovery. Thus, we present a pixel-super-resolved lens-free quantitative phase microscopy (PSR-LFQPM) with partially coherent illumination, which not only compensates for the impact of low coherence without increasing the volume of the system but also suppresses the theoretical Nyquist-Shannon sampling resolution limit imposed by the sensor pixel size (0.9 μm). Based on the partially coherent imaging model, we integrate the spatial coherence transfer function (SCTF) obtained from the pre-calibrated LED source distribution during the iteration process to obtain an accurate high-resolution recovery. Applying PSR-LFQPM to image living HeLa cells in vitro, we achieve real-time dynamic high-throughput QPI performance (half-pitch resolution of 780 nm with a 1.41-fold improvement compared to results without considering the effect of coherence) across a wide FOV (19.53 mm2). The proposed method provides a compact, low-cost, and high-throughput lens-free on-chip microscopy system for biomedical and POCT applications.

Exergy of partially coherent thermal radiation

Exergy of electromagnetic radiation has been studied by a number of researchers for well over four decades in order to estimate the maximum conversion efficiencies of thermal radiation. As these researchers primarily dealt with solar and blackbody radiation, which have a low degree of coherence, they did not consider the partial coherence properties of thermal radiation. With the recent development of surface structures, which can emit radiation with high degree of coherence, the importance of considering the partial coherent properties in exergy calculation has become a necessity as the coherence properties directly influence the entropy of the wave field. Here in this paper we derive an expression for the exergy of quasi-monochromatic radiation using statistical thermodynamics and show that it is identical with the expressions derived using classical thermodynamics. We also present a method to calculate the entropy, thereby the exergy of partially coherent radiation using statistical thermodynamics and a method called matrix treatment of wave field.

Statistical properties of backscattered semiconductor laser radiation with different degrees of coherence

This paper compares the statistical properties of the backscatter intensity in a single-mode optical fibre for semiconductor lasers with a high and a low degree of coherence. We demonstrate that, when short probe pulses are used, shorter than the coherence times of the lasers, the statistical properties of the backscatter intensity obtained with the two lasers are identical, and the intensity distribution over an ensemble of independent fibre sections has an exponential form for both. With increasing probe pulse duration, the backscatter intensity distribution obtained with the shorter coherence time laser approaches a Gaussian one, whereas the distribution function obtained with the high-coherence laser remains nearly exponential. Reflectograms of a coherent reflectometer that relies on the detection of backscattered radiation have the highest contrast for an exponential backscatter intensity distribution over an ensemble of independent fibre sections. The reflectometer then probably has the highest sensitivity to external influences. This leads us to conclude that, when short probe pulses areused, which ensure high spatial resolution (10 m and better), one can use a laser with a short coherence time, equal to the pulse duration.

Atypical associations to abstract words in Broca’s aphasia

IntroductionLeft frontal brain lesions are known to give rise to aphasia and impaired word associations. These associations have previously been difficult to analyze. We used a semantic space method to investigate associations to cue words. The degree of abstractness of the generated words and semantic similarity to the cue words were measured. MethodThree subjects diagnosed with Broca’s aphasia and twelve control subjects associated freely to cue words. Results were evaluated with latent semantic analysis (LSA) applied to the Swedish Parole corpus. ResultsThe aphasic subjects could be clearly distinguished from controls by a lower degree of abstractness in the words they generated. The aphasic group’s associations showed a negative correlation between semantic similarity to cue word and abstractness of cue word. ConclusionsBy developing novel semantic measures, we showed that Broca’s aphasic subjects’ word production was characterized by a low degree of abstractness and low degree of coherence in associations to abstract cue words. The results support models where meanings of concrete words are represented in neural networks involving perceptual and motor areas, whereas the meaning of abstract words is more dependent on connections to other word forms in the left frontal region. Semantic spaces can be used in future developments of evaluative tools for both diagnosis and research purposes.

Rapid performance prediction for library components

Component-based programming is a methodology for designing software systems as assemblages of components with a low degree of coherence and a high degree of orthogonality. Decoupling and orthogonality, however, require coupling and assembling on the side of the component's client. This paper addresses performance problems that occur in the composition specifically of library components. We discuss the design and implementation of a composer , which assembles library components based on a classification of their declarative performance descriptions. Employing an off-the-shelf decision-tree procedure for selecting, and the C++ technique of traits for propagating the desired behavior throughout the whole library, our system allows for rapid performance predictions. It is applied to FFTL, an "STL-like" C++ library for the Fast Fourier Transform.

Advances in excimer laser technology for sub-0.25-μm lithography

There are several lasers that can provide high-power radiation at deep-UV wavelengths. The only laser that has been successfully used in semiconductor manufacturing as a source for lithography is the excimer laser Excimer lasers provide direct deep-UV light, are scalable in energy and power, and are capable of operating with narrow spectral widths. Also, by providing three wavelengths at 248, 193, and 157 nm, excimer lasers span three generations. They have large beams and a low degree of coherence. Their physics and chemistry are well understood. Thanks to major technical developments, these lasers have kept up with the ever-tightening specifications of the lithography industry. We will discuss what these specifications are and the advances that have been made in laser technology to meet these. We will also identify any possible future limitation in this technology. The success behind the microelectronics explosion is attributed to many factors. The excimer laser is one of them.

A polarisation correlation study of the excitation of the H2d3Πu(ν1=0, N1=1) level by electron impact

Full details are given of an experiment in which the three normalized Stokes' parameters characterizing the decay of the electron impact excited d3Piu (v1 = 0, N1 = 1) rotational level of H2 were determined in an electron-photon coincidence experiment at 25 eV impact energy and over the angular range of 20-60 deg. An analysis shows how these parameters are related to the state multipoles characterizing the excited state. The rather low degree of coherence which was observed is consistent with various depolarizing effects, namely the averaging over magnetic sublevels which occurred in both the excitation and decay channels and also the perturbations due to fine and hyperfine structure relaxations.

Distributed feedback dye laser pumped by a laser having a low degree of coherence

An experimental setup for pumping a distributed feedback dye laser (DFDL) is described, which ensures the creation of a perfect interference pattern even for a pump source with low spatial and temporal coherence. This property is maintained even if the DFDL laser is tuned over a 70 nm spectral range. Tuning is accomplished by rotating two mirrors. Tunable, nearly transform-limited ps pulses are generated when the pump source is a N2 laser.

Sideband and quantum-beat measurements with129mTe and57Co sources

Sideband intensities and quantum beats were measured for recoillessly emitted gamma rays as a function of the vibration frequency of quartz crystals on which sources of129mTe and57Co were deposited. At most frequencies a low degree of coherence of the vibrations of the source nuclei was observed.