Partially coherent light beam shaping via complex spatial coherence structure engineering

Bacterial populations often have complex spatial structures, which can impact their evolution. Here, we study how spatial structure affects the evolution of antibiotic resistance in a bacterial population. We consider a minimal model of spatially structured populations where all demes (i.e., subpopulations) are identical and connected to each other by identical migration rates. We show that spatial structure can facilitate the survival of a bacterial population to antibiotic treatment, starting from a sensitive inoculum. Specifically, the bacterial population can be rescued if antibiotic resistant mutants appear and are present when drug is added, and spatial structure can impact the fate of these mutants and the probability that they are present. Indeed, the probability of fixation of neutral or deleterious mutations providing drug resistance is increased in smaller populations. This promotes local fixation of resistant mutants in the structured population, which facilitates evolutionary rescue by drug resistance in the rare mutation regime. Once the population is rescued by resistance, migrations allow resistant mutants to spread in all demes. Our main result that spatial structure facilitates evolutionary rescue by antibiotic resistance extends to more complex spatial structures, and to the case where there are resistant mutants in the inoculum.

Optical coherence is becoming an efficient degree of freedom for light field manipulations and applications. In this work, we show that the image information hidden a distance behind a random scattering medium is encoded in the complex spatial coherence structure of a partially coherent light beam that generates after the random scatterer. We validate in experiment that the image information can be well recovered with the spatial coherence measurement and the aid of the iterative phase retrieval algorithm in the Fresnel domain. We find not only the spatial shape but also the position including the lateral shift and longitudinal distances of the image hidden behind the random scatterer can be reconstructed, which indicates the potential uses in three-dimensional optical imaging through random scattering media.

The propagation performance of high-power partially coherent fibre laser beams in a real environment is investigated and the theoretical model of a high-power fibre laser propagating in a real environment is established. The influence of a collimating system and thermal blooming is considered together with atmospheric turbulence and mechanical jitter. The laser energy concentration of partially coherent beams in the far field is calculated and analysed based on the theoretical model. It is shown that the propagation performance of partially coherent beams depends on the collimating system, atmospheric turbulence, mechanical jitter and thermal blooming. The propagation performance of partially coherent beams and fully coherent beams is studied and the results show that partially coherent beams are less sensitive to the influence of thermal blooming, which results in that the energy degeneration for partially coherent beams is only 50% of that for fully coherent beams. Both partially coherent beams and fully coherent beams become less sensitive to thermal blooming when the average structural constant of the refraction index fluctuations increases to 1.7 × 10−14m−2/3. The investigation presents a reference for applications of a high-power fibre laser system.

In this work we report on a novel optical design for beam shaping and focalization of high-power diode laser bars. The goals of our study are: the increase the optical throughput of the beam shaping device with respect to standard solutions and either to enhance the irradiance on a target or to inject the laser beam into a smaller fibre than with respect to beam shaping system based on plane surfaces. The high power diode laser bars pose serious difficulties in their optical handling due to their strong difference between the two transverse axes, which induce a strong astigmatic and asymmetric output radiation. As is well known, the beam quality is very different in the two axes called slow axis and fast axis, and in particular the slow axis is composed by the superposition of several multimodal sources. The beam quality in this axis is very low (its etendue may exceed 2000 mm mrad). On the other hand, the fast axis has a very high beam quality, near diffraction limited, although with very high divergence (30°-50°). The common solution for the application of the laser radiation is a fast axis aspheric micro lens in front of the emitters, in order to achieve its collimation. Typical values of the fast axis collimated beam are 0.7mm and less than 6mrad. However, the so obtained collimated beam is poorly focusable with a standard lens, and a few methods were proposed to overcome the problem. The more relevant solutions include: the stepped mirror technique, the plane parallel mirrors pair, micro prisms array and confocal micro lens array. Each of these techniques is based on the equalization of the beam parameter product by the subdivision of the beam in the slow axis and its reshaping. For all these techniques the efficiency spans from 50% to 70%. The best focalization results allow the coupling in a fibre of 400μm diameter, with NA-0.22. The aim of this work is the design and the realization of a new device, that is considered as target the following aspects: 1) the maximum optical efficiency in the beam shaping process, 2) the optimal equalization of the beam parameter product for the two axes, 3) the use of few optical elements and 4) a very compact size. These goals are addressed by a scheme that splits the collimated beam from the laser diode into different portions while the length of the optical paths of each sub element is kept constant, and by the subsequent use of short focal length aspheric lenses for the focalization of the transformed beam. Each sub-beam is deflected by a couple of plane parallel mirrors, whose normal is directed to equalize the BPP without any mutual shadowing. An optimal solution can be easily envisaged for a laser source of common size of 0.7 x 10 mm. The condition on equal optical path length has the noticeable property of placing the virtual position of the individual portions into which the original beam is split at the same distance with respect to target. Thanks to this, their subsequent focusing is unaffected by the axial displacement of the common solution by the stepped mirrors. In fact, to correct this effect, this latter technique requires the use of a prism pair, involving complexity, size enlargement and higher costs. In this work both an extensive ray tracing and optical analysis is presented as well as the experimental characterization of an experimental model. Moreover, we also report on the technique for the realization of th tilted-face plane mirrors of which is composed our beam shaping device. The scheme of beam shaping here reported can be extended to higher power beam by means of the technique of the beam combination by polarization coupling or that of the optical beam compression. Examples of theses developments are discussed in the paper, and experimental results presented. The most direct applications of the class of optical devices here reported are the high power diode laser direct application in material processing or manufacturing, the coupling into multimode optical fiber of the diode laser radiation as well as the fiber laser end pumping.

A high-power laser beam profiling system was set up to investigate the influence of the interaction between the laser beam and the process emissions during welding with a shaped beam profile. A positional instability of the beam on the workpiece in the order of magnitude of tens of µm and noticeable distortions of the beam shape were observed when no cross jet was used. Both perturbations were reduced when a cross jet was applied to remove the process emissions from the beam path and minimized when the cross jet was positioned closest to the workpiece.

By using numerical simulation, the propagation of pseudo-partially coherent Gaussian-Schell model beam in atmospheric turbulence is simulated. The properties of intensity fluctuation of different receiving aperture and aperture averaging factors are statistically analyzed. And the influence of relative changing frequency of the modulating phase which models the partial coherence of beam source on scintillation index is also discussed. The simulation results of pseudo-partially coherent beam are compared with those of the well-developed partially coherent beam and fully coherent Gaussian beam. It is found that the reduction of coherence degree may cause scintillation index to decrease. However, the aperture averaging effect is weakened at the same time. At the same receiving aperture diameter, the aperture averaging factor of pseudo-partially coherent beam is greater than that of the fully coherent beam. The increase of relative changing frequency of modulating phase may cause a reduction of scintillation index to some degree. And with the increase of relative changing frequency, the scintillation index of pseudo-partially coherent beam tends to be coincident with that of the partially coherent beam.

We study the spectral density of partially coherent vortex beams propagating in atmospheric turbulence by numerical simulation and experiments with a spatial light modulator. On the basis of the new simulation method proposed in our previous work, we extend the research objective from coherent beams to partially coherent beams. The spectral density of partially coherent vortex beams propagating in Kolmogorov and non-Kolmogorov turbulence is studied by further optimization of the simulation method with beam wander. Consistent results between numerical simulation and experiments are obtained to prove our standpoint. The study of the spectral density of partially coherent beams propagating in a turbulent environment with the improved simulation method proposed by us is helpful for improving the accuracy of simulating partially coherent beams in optical study. It is of great significance for the comprehensive research of beam propagation in turbulence.

Compared with coherent laser beams, partially coherent beams have advantages of effectively reducing turbulence-induced extra beam spreading, beam wander and intensity scintillation on propagation through turbulent atmosphere, and have promising applications in free-space optical communications, laser radar and remote sensing. Recently, more and more attention was paid to the propagation of partially coherent beams through turbulent atmosphere. In this article, we first review historically the research progress of the propagation of partially coherent beams in atmospheric turbulence. And we describe in detail the basic theory for the calculation of average intensity, second-order moment and scintillation index of partially coherent beams in turbulence based on the extended Huygens-Fresnel principle and Rytov method. We also present a phase screen method of numerically simulating the propagation of coherent beams through turbulent atmosphere, and then extend such a method to treating the propagation of partially coherent beams.

Analysis to beam quality of partially coherent flat-topped vortex beams propagating through atmospheric turbulence

Natural microbial populations often have complex spatial structures. This can impact their evolution, in particular the ability of mutants to take over. While mutant fixation probabilities are known to be unaffected by sufficiently symmetric structures, evolutionary graph theory has shown that some graphs can amplify or suppress natural selection, in a way that depends on microscopic update rules. We propose a model of spatially structured populations on graphs directly inspired by batch culture experiments, alternating within-deme growth on nodes and migration-dilution steps, and yielding successive bottlenecks. This setting bridges models from evolutionary graph theory with Wright-Fisher models. Using a branching process approach, we show that spatial structure with frequent migrations can only yield suppression of natural selection. More precisely, in this regime, circulation graphs, where the total incoming migration flow equals the total outgoing one in each deme, do not impact fixation probability, while all other graphs strictly suppress selection. Suppression becomes stronger as the asymmetry between incoming and outgoing migrations grows. Amplification of natural selection can nevertheless exist in a restricted regime of rare migrations and very small fitness advantages, where we recover the predictions of evolutionary graph theory for the star graph.

Ever since vortex beams were proposed, they are known for owning phase singularity and carrying orbital angular momentum (OAM). In the past decades, coherent optics developed rapidly. Vortex beams have been extended from fully coherent light to partially coherent light, from scalar light to vector light, from integral topological charge (TC) to fractional TC. Partially coherent vortex beams have attracted tremendous interest due to their hidden correlation singularity and unique propagation properties (e.g., beam shaping, beam rotation and self-reconstruction). Based on the sufficient condition for devising a genuine correlation function of partially coherent beam, partially coherent vortex beams with nonconventional correlation functions (i.e., non-Gaussian correlated Schell-model functions) were introduced recently. This timely review summarizes basic concepts, theoretical models, generation and propagation of partially coherent vortex beams.

It has been established that in order to study thermo- and electrophysical phenomena in wet steam turbines, studies of the wet steam flow volume charge effect on its dielectric and thermophysical properties have recently been carried out at A. Pidhornyi Institute of Mechanical Engineering Problems of the National Academy of Sciences of Ukraine. According to their results, it was established that the most representative electrophysical parameter, which allows to evaluate changes in the thermophysical properties of steam, which occur under the action of its own volume charge, is its dielectric constant. It is assumed that the value of the dielectric constant of an electrified steam can be significantly different from the value for a neutral steam, and a mathematical assessment of its possible change is made. It has been confirmed that the influence of electrophysical phenomena caused by the wet steam flow electrification is significant, but is not taken into account in the existing physical and mathematical thermodynamic models of the steam expansion process. It is proved that in order to clarify the main thermodynamic parameters and calculated characteristics of the electrified wet steam flow, it is necessary to determine how its dielectric constant changes. On the basis of the analysis, the relevance of experimental determination of the dielectric constant of a wet steam flow with a volume charge in order to obtain the dependence of its change on the temperature and pressure of the flow, as well as the density of the volume charge, is substantiated. To perform the research, a gas dynamic laboratory plant, which allows to obtain a wet steam flow with a volume charge, was used. The internal space of the flow part of a real wet steam turbine has a significant size and allows the formation of a flow with a volume charge of a complex spatial configuration and structure. It is emphasized that in the flow part of the plant of a small volume, in contrast to the turbine flow part, significant technical difficulties arise when organizing the conditions for the occurrence of a wet steam flow with a volume charge. Taking this into account, at the first stage, it was decided to conduct a study of a steam flow with a volume charge flowing into the atmosphere in a laboratory room with a sufficient volume to form its spatial structure. To estimate the value of its dielectric constant, the inductive method (L-method) of determining dielectric properties, in which the substance under study is introduced into the inductive solenoid cell, was chosen. Experiments were conducted and, according to the obtained data, it is possible to make a preliminary assessment of the change in dielectric constant in the presence of a volume electric charge in the steam flow

In recent years, emerging sequencing technologies and computational tools have driven a tidal wave of research on host-associated microbiomes, particularly the gut microbiome. These studies demonstrate numerous connections between the gut microbiome and vital host functions, primarily in humans, model organisms, and domestic animals. As the adaptive importance of the gut microbiome becomes clearer, interest in studying the gut microbiomes of wild populations has increased, in part due to the potential for discovering conservation applications. The study of wildlife gut microbiomes holds many new challenges and opportunities due to the complex genetic, spatial, and environmental structure of wild host populations, and the potential for these factors to interact with the microbiome. The emerging picture of adaptive coevolution in host-microbiome relationships highlights the importance of understanding microbiome variation in the context of host population genetics and landscape heterogeneity across a wide range of host populations. We propose a conceptual framework for understanding wildlife gut microbiomes in relation to landscape variables and host population genetics, including the potential of approaches derived from landscape genetics. We use this framework to review current research, synthesize important trends, highlight implications for conservation, and recommend future directions for research. Specifically, we focus on how spatial structure and environmental variation interact with host population genetics and microbiome variation in natural populations, and what we can learn from how these patterns of covariation differ depending on host ecological and evolutionary traits.

Structuring and patterning of thin layer via selective laser ablation is one of the key technologies in production of display and photovoltaic. Concurrently, there are two ablation processes used in production of thin film solar: Scribing via selective ablation and edge isolation via deletion. Beside the wave length, the pulse length and the peak power, the beam profile of the laser is of essential importance for the efficiency of the ablation process and for the productivity. The most currently lasers of high beam quality have Gaussian beam profile with circular cross section. Because of threshold behaviour Gaussian beam profile is not favourable for ablation process. On the other side there are emerging laser concepts which deliver rectangular or square top-hat beams with high beam quality. In this paper we will discuss and compare ablation processes with circular Gaussian beams, one dimensional top-hat beams and two dimensional top-hat beams. The major concern will be the effective energy efficiency of the process and the over filling factor obtainable the different beam profiles.Structuring and patterning of thin layer via selective laser ablation is one of the key technologies in production of display and photovoltaic. Concurrently, there are two ablation processes used in production of thin film solar: Scribing via selective ablation and edge isolation via deletion. Beside the wave length, the pulse length and the peak power, the beam profile of the laser is of essential importance for the efficiency of the ablation process and for the productivity. The most currently lasers of high beam quality have Gaussian beam profile with circular cross section. Because of threshold behaviour Gaussian beam profile is not favourable for ablation process. On the other side there are emerging laser concepts which deliver rectangular or square top-hat beams with high beam quality. In this paper we will discuss and compare ablation processes with circular Gaussian beams, one dimensional top-hat beams and two dimensional top-hat beams. The major concern will be the effective energy efficiency of...

Flat optical components, or metasurfaces, have transformed optical imaging, data storage, information processing, and biomedical applications by providing unprecedented control over light-matter interactions. These nano-engineered structures enable compact, multidimensional manipulation of light's amplitude, phase, polarization, and wavefront, producing scalar and vector beams with unique properties such as orbital angular momentum and knotted topologies. This flexibility has potential applications in optical communication and imaging, particularly in complex environments such as atmospheric turbulence and undersea scattering. However, designing metasurfaces for shorter wavelengths, such as visible and ultraviolet light, remains challenging due to fabrication limitations and material absorption. Here, we introduce an innovative concept called topology imprinting using judiciously designed all-dielectric nonlinear optical metasurfaces to replicate desired waveforms at fundamental and harmonic frequencies, opening promising avenues for advanced photonic applications.