Degree Of Coherence Research Articles

Coherence phase spectrum analyzer for a randomly fluctuated fractional vortex beam

Fractional vortex beams exhibit a higher degree of modulation dimensions than conventional vortices, thus inheriting superior anti-turbulent transmission properties through the incorporation of additional coherence modulation. However, aliasing the mixed modes induced by coherence degradation makes the quantitative measurement of the topological charge in fractional vortex beams challenging. In this study, a coherence phase spectrum was introduced, and experimental demonstrations to quantitatively determine the fractional topological charge of partially coherent fractional vortex beams were performed. By leveraging the four-dimensional measurement of a partially coherent light field, the source coherence function was inversely reconstructed, and fractional topological charges were determined with high precision by extracting the phase spectrum of the coherence function. Laguerre–Gaussian, elliptical Gaussian, and plane-wave-fraction vortex beams with various degrees of coherence were used to demonstrate measurement precision. The proposed method is applicable to X-rays and electron vortices. It has potential applications in optical encryption, high-capacity optical communication, and quantum entanglement.

Propagation Properties of Generalized Schell-Model Pulse Sources in Dispersive Media

A model of a generalized pulse source, whose complex degree of temporal coherence is described by a function of the nth power difference of two instants, was constructed. As examples, we consider the generalized Gaussian and multi-Gaussian Schell-model pulse sources and study their propagation in dispersive media. It is indicated that such pulse beams present unique self-focusing, off-axis self-shifting and asymmetric self-splitting characteristics by adjusting the power exponent and phase parameters. Further, we explicitly discuss how the coherence time, summation factor as well as the dispersive coefficient significantly affect the self-focusing and self-shifting behaviors of the pulse beam. The results will benefit some applications involving pulse shaping, optical trapping and remote sensing.

Longitudinal spatial coherence of computational ghost imaging through atmospheric turbulence

The resolution and imaging quality of ghost imaging is determined by the longitudinal spatial coherence (LSC) of speckle beams on the signal and reference arms. Based on the cross-correlation function, long-exposure and short-exposure computational ghost imaging through turbulent atmosphere is investigated analytically and numerically in the framework of the traditional imaging theory. According to the point spread function (PSF), the modulation transfer function (MTF) is derived, both of which are utilized to evaluate imaging resolution and imaging quality of computational ghost imaging (CGI), respectively. By simulating long-exposure and short-exposure ghost imaging through atmospheric turbulence, the comprehensive effects of atmospheric turbulence and beam initial parameters on the complex degree of coherence (CDC), PSF, and MTF are studied, respectively. It is found that the degradation of LSC between the two planes on the reference and signal path implies a narrower PSF and increased MTF values, which represent the better resolution and imaging quality. Thus, reducing the atmospheric turbulence strength, the speckle particle size, the wavelength and the propagation distance, and increasing the source size contribute to improving resolution and image quality of CGI because of the degradation of LSC. Furthermore, short-exposure CGI can provide imaging performance superior to long-exposure CGI in terms of resolution and imaging quality due to the decrease of LSC.

Структурные уровни глобальной экономической системы и цифровая трансформация кофейной индустрии Вьетнама

Agriculture is one of the eight important economic sectors identified by the Government of Vietnam as requiring digital transformation in accordance with Decision 749/QD-TTg dated June 3, 2020, as an integral component of the digital economy development strategy in the context of globalization. Coffee is an agricultural product that has high economic value and is a key export product with an annual export turnover exceeding US$3 billion for the Vietnamese economy. Entities involved in the coffee industry, namely farmers, coffee businesses and government, are key players in the digital transformation process. Each entity has different resources in terms of capital, technology, labor levels and production and business goals, but between them there are always intermediate levels, closely linked by economic interests in the development of the coffee industry. To realize the digital transformation of the Vietnamese coffee industry, it is necessary to identify the factors influencing the implementation process. Therefore, the purpose of this study is to analyze the relationship between the main structural levels of the system under study, the resources and goals of the participants, and the intermediate levels in the global economic system to identify the factors influencing the digital transformation of the Vietnamese coffee industry. The results of the study show that in order for the Vietnamese coffee industry to continue to develop and be able to realize digital transformation, it is necessary to focus on the nano-level of the economy and make special demands on the degree of coherence and goals of economic and social policies at all levels of government. Significant barriers to digitalization for farmers need to be addressed through the effective implementation of policies to support concessional loans for the purchase of machinery and technologies for coffee production. To effectively apply digital technologies in production, it is necessary to have a sufficiently large area of ​​land and to encourage farmers to cooperate. Policies should be formulated to encourage the development of agricultural cooperative models to expand coffee plantation area in line with high-tech applications, large enterprises should strengthen their connections and provide more support to coffee farmers to create a sustainable source of high-quality raw materials.

Propagation properties of partially coherent radially polarized rotationally-symmetric power-exponent-phase vortex beams in turbulent atmosphere

In this paper, the propagation properties of partially coherent radially polarized rotationally-symmetric power-exponent-phase vortex beams (RP-RSPEPVBs) in turbulent atmosphere were investigated. Based on the extended Huygens-Fresnel principle and unified theory of coherence and polarization, the theoretical propagation model was established. Then, the numerical simulations were carried out to reveal the evolution of intensity distribution, spectral degree of coherence (DOC) and spectral degree of polarization (DOP) in turbulent atmosphere. The results showed that although the partially coherent RP-RSPEPVBs diverged during the propagation, the spatial structure remains analogous, and the relatively larger waist widths gain smaller divergence. Moreover, the optical pattern can be evidently modulated by optical parameters, as the number of sidelobes can be changed with topological charge l, and the continuity of the light spot as well as the rotating speed around the optical axis can be influenced by power exponent n. Besides, the spectral DOC and DOP would decrease with larger propagation distance and refractive-index structure constant, but decrease less with a shorter coherence width. This work may be helpful in fields such as remote sensing and optical communication.

Propagation of generalized multi-Gaussian correlated Schell-model beams in electromagnetically induced transparency atomic vapor

Propagation of generalized multi-Gaussian correlated Schell-model (GMGCSM) beams through four-level electromagnetically induced transparency (EIT) atomic vapor is investigated for the first time. Analytical expression for the GMGCSM beam passing through an ABCD optical system of EIT vapor is deduced and employed to analyze its propagation properties. It is demonstrated that intensity evolution of the targeted GMGCSM beam through EIT atomic vapor is dependent on the coupling Rabi frequency of the control light, the beam index and coherence length. Moreover, analysis shows that degree of coherence of the beam can also be regulated by the coupling Rabi frequency. Additionally, it is shown that, selecting appropriate coherence length, GMGCSM beams of the first kind would form a shift from a dark-centered distribution known as “optical cage”, to a peak-centered distribution; GMGCSM beams of the second kind would shift from a flat-topped distribution to a Gaussian distribution. Therefore, EIT atomic vapor provides a method to regulate the coherence of partially coherent beams. Results obtained here could be expected applications in free-space optical communications, material thermal processing, and optical trapping.

Coherent properties of partially coherent vortex beam with nonuniform polarization propagating in turbulent atmosphere

The spectral degree of coherence (SDOC) evolution of partially coherent vortex beam with radially and azimuthally polarized (RPV and APV) beams in atmospheric turbulence have been studied and the results indicate that SDOC distribution will gradually appear dark ring and finally evolve into quasi-Gaussian-like form. In addition, we have simulated this process by muti-phase screen method and the simulation results are consistent well with the theoretical predictions. What’s more, we have emphatically investigated the phase evolution of SDOC and the dynamic evolution of correlation singularities of partially coherent RPV and APV beams in turbulent atmosphere in detail. The results indicate that the correlation singularity of the beam will first split, and then generate new correlation singularity, finally vanish. Both of stronger atmospheric turbulence and lower correlation length make the beam generate a pair of correlation singularities with opposite sign. Our findings can provide reference for free space communication.

Tight Focusing of Circular Partially Coherent Radially Polarized Circular Airy Vortex Beam

The tight focusing properties of circular partially coherent radially polarized circular Airy vortex beams (CPCRPCAVBs) are theoretically studied in this paper. After deriving the cross-spectral density matrix of CPCRPCAVBs in the focal region of a high-NA objective, numerical calculations were performed to indicate the influence of the topological charge of the vortex phase on intensity distribution, degree of coherence and degree of polarization of the tightly focused beam. An intensity profile along the propagation axis shows that a super-length optical needle (~15 λ) can be obtained with a topological charge of 1, and a super-length dark channel (~15 λ) is observed with a topological charge of 2 or 3. In the focal plane, the rise in the number of topological charge does not distort the shapes of the coherence distribution pattern and the polarization distribution pattern, but enlarges their sizes.

Implementation gaps of the Portuguese Nacional Health Plan 2012-2021: evidence mapping analysis

Abstract Background The National Institute of Health Doutor Ricardo Jorge (INSA) is responsible for carrying out the evaluation of the Portuguese National Health Plan (PNS) 2012-2016, extended to 2020 (and later to 2021). As part of PNS evaluation, this study aims to identify gaps in the implementation of the PNS 2012-2021, and to identify the degree of alignment and coherence between the strategic axis, goals, and monitoring framework issued by the PNS at different levels of implementation (national, regional, local and municipal). Methods A mix study, employing both qualitative and quantitative approaches was performed based upon a modified scoping review. Portuguese healthcare institutional websites and municipality websites were identified as the main data sources and secondary data were gathered. Evidence (plans, programs, or strategies) with publication date between 2015 and 2020 were included. A data collection matrix was validated by a group of experts from major stakeholders from academia and public health services. The matrix included 3 main categories following the PNS intervention logic (5 strategic axis, 4 goals and 37 monitoring indicators). Results A total of 204 documents met the inclusion criteria. Evidence from national level (55%) and local level (35%) represented about 90% of the sample. Overall, three implementation gaps were identified: 1) absence of two Regional Health Plans (in a total of 5 mainland health regions); 2) lack of about 1/3 of the expected Local Health Plans (16 out of 53) and, 3) low transposition (or approximation) of the PNS monitoring framework into the hospital and primary care contract-programs, one of the main management tools for planning. Conclusions The identification and analysis of implementation gaps contribute to the final evaluation of the PNS. Moreover, the results can guide the next planning cycle pointing out sensitive areas of implementation which need more attention from various stakeholders. Key messages • Implementation gaps can compromise the impact of PNS as the strategic tool to set the necessary health interventions and their alignment at national, regional and local level of implementation. • The next planning cycle should tackle the identified implementation gaps with the purpose of strengthen PNS as a strategic planning platform and with the aim of maximize population health gains.

Active-illumination extension to the Priest and Meier pBRDF.

This paper develops a 3D vector solution for the scattering of partially coherent laser-beam illumination from statistically rough surfaces. Such a solution enables a rigorous comparison to the well-known Priest and Meier polarimetric bidirectional reflectance distribution function (pBRDF) [Opt. Eng.41(5), 988 (2002)10.1117/1.1467360]. Overall, the comparison shows excellent agreement for the normalized spectral density and the degree of polarization. Based on this agreement, the 3D vector solution also enables an extension to the Priest and Meier pBRDF that accounts for the effects of active illumination. In particular, the 3D vector solution enables the development of a closed-form expression for the spectral degree of coherence. This expression provides a gauge for the average speckle size based on the spatial-coherence properties of the laser source. Such an extension is of broad interest to long-range applications that deal with speckle phenomena.

Quantum Dynamics of Oblique Vibrational States in the Hénon-Heiles System.

In this paper, we study the quantum time evolution of oblique nonstationary vibrational states in a Hénon-Heiles oscillator system with two dissociation channels, which models the stretching vibrational motions of triatomic molecules. The oblique nonstationary states we are interested in are the eigenfunctions of the anharmonic zero-order Hamiltonian operator resulting from the transformation to oblique coordinates, which are defined as those coming from nonorthogonal coordinate rotations that express the matrix representation of the second-order Hamiltonian in a block diagonal form characterized by the polyadic quantum number n = n1 + n2. The survival probabilities calculated show that the oblique nonstationary states evolve within their polyadic group with a high degree of coherence up to the dissociation limits on the short time scale. The degree of coherence is certainly much higher than that exhibited by the local nonstationary states extracted from the conventional orthogonal rotation of the original normal coordinates. We also show that energy exchange between the oblique vibrational modes occurs in a much more regular way than the exchange between the local modes.

New insight into the strengthening mechanism of AlCoCrFeNi2.1 eutectic high-entropy alloy with dual-phase nanolamellar structures achieved via laser powder bed fusion

Recently, the AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA) prepared by laser powder bed fusion (LPBF) could reach a good balance of strength and ductility. The strengthening effect was only qualitatively clarified, however, quantitative analysis remained unclear. In this study, the quantitative analysis of strengthening mechanisms and the relationship between microstructural characteristics and tensile properties were revealed in depth. The AlCoCrFeNi2.1 EHEA with FCC and BCC dual-phase nanolamellar structures (interlamellar spacings of 200–300 nm) fabricated by LPBF achieved an excellent combination of high yield strength (1116 MPa) and fracture elongation (20.3 %). Compared with as-cast EHEA samples, the FCC/BCC nanolamellar interfaces in the LPBF-printed AlCoCrFeNi2.1 EHEA were still semi-coherent but with a higher degree of coherency, and the Al concentration in the FCC phase increased. Post-deformation analysis showed that there were high-density dislocation pile-up and slip, stacking faults (SFs), and Lomer-Cottrell (L-C) locks in the FCC phase, and there were deformation nano-twins and SFs in the BCC phase. The back stress generated in FCC/BCC phases during tensile deformation could maintain the plastic co-deformation of the two phases. The theoretical calculation revealed that the strengthening mechanisms mainly stemmed from the nanolamellar structures, dislocation strengthening, and the solution strengthening induced by the increased Al concentration in the FCC phase. The calculated result (1096.3 MPa) was consistent with the experimental value, and the nanolamellar structures strengthening (∼720.7 MPa) was the main contributor. This work provides a theoretical quantitative understanding of the strengthening mechanism of the AlCoCrFeNi2.1 EHEA fabricated by LPBF and references for the strengthening mechanism of additively manufactured EHEAs.

Low temperature sintering of high performance Al2O3/ZrO2 ceramics with ultra-fine nanoparticles strengthening

In this work, we propose a novel amorphous/solid solution Al2O3/ZrO2 powder with a low sintering temperature, capable of precipitating many ultra-fine nanoparticles in the ceramics. The powder was prepared by combustion synthesis assisted with rapid cooling in water, and then subjected to grinding for further refinement. The high preparation temperature and the rapid cooling process resulted in the formation of solid solutions and partially amorphous structures in the powder, which leads to a metastable state in the powder. The transformation of the metastable state and the presence of oxygen vacancies in the powder can accelerate mass transfer during sintering. Therefore, the powder can be densified through hot press at temperature as low as 1300 °C. During sintering, a large number of ultra-fine nanoparticles (∼5 nm) were precipitated from the solid solution and evenly dispersed throughout the matrix. The nanoparticles exhibit a high degree of coherence with the matrix due to the similarities in crystal structure between t-ZrO2 and α-Al2O3. The presence of nanoparticles shifts the fracture mode from intergranular to transgranular, and effectively improve the mechanical properties of the ceramics. Consequently, the bending strength, hardness and fracture toughness of the ceramic can reach up to 749 ± 43 MPa, 16.2 ± 0.24 GPa and 10.3 ± 0.53 MPa·m0.5, respectively. To compare the sintering capabilities and the performance of the ceramics, commercial powders were also sintered at the same temperature. This research may offer a new instruction for the low temperature fabrication of nanoparticles-strengthened ceramics.

Ідентичність та суверенітет в системі інституційних ресурсів національно укоріненого економічного розвитку України

The author shows that identity as a historically given social reality develops under the inverse influence of the entire set of value-institutional resources of society generated by it, including its active subjectivity, integrating potential of national interest, process sovereignty, stable institutional structure and dynamic factor of exogenous reforms. The conclusion is substantiated that the imprint of relevance on the historical essence of the national identity adapts it to today’s needs, but at the same time there are limits of adaptation that the society cannot cross without losing its identity. Based on such an understanding, the author proves the possibility of consistently developing criteria for the coordinated use of internal trust tools as those that should be directly correlated with national identity: stability of the monetary unit, stability of the tax regime, stimulating state investment policy, social guarantee policy, and foreign economic strategy. This provides an opportunity to significantly increase the degree of coherence of the main areas of state regulatory policy.

Enhancing plantain epicarp active edible coating performance through investigation of optimal spray coating conditions

The current research presents a comprehensive investigation aimed at predicting and optimizing the adhesion characteristics of Nanoemulsion coatings sprayed onto plantains epicarps. To achieve this, a full factorial experimental design and an artificial neural network model were deployed. The process parameters, consisting of the height of the nozzle, pressure, and time, served as inputs for the artificial neural network model, while the coating amount and thickness were measured and treated as targets for both models. Through meticulous training, the artificial neural network model demonstrated remarkable efficiency and reliability, evident in the high degree of coherence between predicted and experimental results (R² = 0.99 and MSE = 1.98 %). The study identified a critical sequence of variables (height/pressure/time: 0.15 m / 0.6 MPa / 5 s) that yielded optimal coating characteristics, including a thickness of 38.5 µm, permeance of 1.388 × 10–05 kg s−1 m−1 Pa−1, and water vapor permeability of 2.7 × 10–09 kg s−1 m−1 Pa−1, along with a contact angle of 11.3° indicative of enhanced wettability. Significantly, the coated epicarps exhibited lower water vapor permeability, implying an extended shelf life. This promising technology of edible coatings not only contributes to preserving fruit quality and prolonging shelf life for plantainss but also holds potential for application in other food products and fortifying food packaging practices. The current findings shed light on the valuable role of active edible coatings in advancing food preservation methods and sustainability within the food industry.

Coherence and polarization behaviors of partially coherent circular edge dislocation beam in biological tissue

The effects of the several factors on the changes in spectral degree of polarization P(ρ,-ρ,z) and spectral degree of coherence μ(ρ,-ρ,z), μ(ρ,0,z) for the partially coherent circular edge dislocation beam propagating in biological tissue have been studied. It is shown that both beam wavelength λ and dislocation number n have no effect on the initial values of the three, while the values of field points distance ρx and spatial self-correlation length σyy play a significant role. During the propagation, the curves of P(ρ,-ρ,z), μ(ρ,-ρ,z) and μ(ρ,0,z) with different beam parameters will undergo different fluctuation, eventually the former tends to be a certain value less than its initial one and the latter two tend to zero. The smaller ρx is, the higher the coherence of the beam is. The visible light is more suitable for biological tissue disease diagnosis compared to the far infrared and ultraviolet light. The beam with larger n will possess more richer optical distribution when propagating in biological tissues. The difference value between σyy and σxx will significantly influence the change range of P(ρ,-ρ,z), μ(ρ,-ρ,z) and μ(ρ,0,z).

Image plane digital holography for simultaneous measurement of temporal and spatial coherence

In this work, we propose and validate the Image Plane Digital Holography (IPDH) with laminar illumination technique for measuring the complete coherence degree, the temporal coherence length and the spatial coherence area (transversal coherence radius), of a light source at the same time and from a single measurement. This holographic technique has been used before as a fluid velocimetry technique that allows measuring the three components of the fluid velocity in a plane. Since its performance is limited by the temporal and spatial coherence of the laser, we can take advantage of this and make IPDH with laminar illumination a means of obtaining these laser properties. The proposed method could be of interest for the optics community since it could be used for any type of light source, presenting some advantages by comparing it with other well-established techniques. It has been tested by using a high repetition rate laser commonly used in velocimetry and the results have been compared to those obtained with other standard techniques, verifying the well-functioning of the IPDH-based technique.

Spin-flip dynamics in core-excited states in the basis of irreducible spherical tensor operators.

Recent experimental advances in ultrafast science have put different processes occurring on the electronic timescale below a few femtoseconds in focus. In the present theoretical work, we demonstrate how the transformation and propagation of the density matrix in the basis of irreducible spherical tensors can be conveniently used to study sub-few fs spin-flip dynamics in core-excited transition metal compounds. With the help of the Wigner-Eckart theorem, such a transformation separates the essential dynamical information from the geometric factors governed by the angular momentum algebra. We show that an additional reduction can be performed by the physically motivated truncation of the spherical tensor basis. In particular, depending on the degree of coherence, the ultrafast dynamics can be considered semi-quantitative in the notably reduced spherical basis when only the total populations of the basis states of the given spin are of interest. Such truncation should be especially beneficial when the number of high-spin basis states is vast, as it reduces computational costs.

Evolution properties of a complex coherent square Gaussian-Schell-model beam in a uniaxial crystal orthogonal to the optical axis.

The analytical formulas for spectral density, degree of coherence, and effective beam widths of complex coherent square Gaussian-Schell-model (GSM) beams in a uniaxial crystal orthogonal to the optical axis are derived. Based on these analytical formulas, the evolution properties are investigated by a set of numerical examples. It is demonstrated that the complex coherent square GSM beams spread at different rates in the directions parallel and orthogonal to the optical axis due to the anisotropic crystal, but the self-shift effect of the light field is almost unaffected by the fact that the uniaxial crystal is anisotropic. The effect of anisotropy of the uniaxial crystal on the effective width of the beam in the x direction and that in the y direction is completely opposite. The results provide a way for the modulation of the complex coherent square GSM beams and enrich the propagation theory of uniaxial crystal.

Propagation Characteristics of a Partially Coherent Gaussian Schell‐model Array Vortex Beam in the Joint Turbulence Effect of a Jet Engine and Atmosphere

AbstractThis work investigates the joint effects of jet engine exhaust‐induced turbulence and atmospheric turbulence on the propagation of a partially coherent Gaussian Schell‐model Array (GSMA) vortex beam. Using the two‐process propagation method, analytical formulae are derived for the cross‐spectral density, spectral density, degree of coherence, and beam width of the considered beam. The results show that the considered beam takes different shapes; when the spatial coherence is large, the spectral density of the GSMA vortex beam takes an elliptical shape, whereas when the spatial coherence is smaller, the spectral density remains a Gaussian shape. The evolution profile of the degree of coherence weakens gradually when the propagation distance, topological charge, and turbulence strength increase. Moreover, the profile of the degree of coherence takes the Gaussian profile when the propagation distance is longer or turbulence atmospheric is stronger. Furthermore, the results reveal that the corresponding beam spreads faster with a larger propagation distance, lower spatial coherence, and high‐strength turbulence. This study also concludes from the results that the beam is affected more when its propagation is near the jet engine exhaust, which means that this latter has a significant impact.