Generating Electromagnetic Nonuniformly Correlated Beams

We develop a method to generate electromagnetic nonuniformly correlated (ENUC) sources from vector Gaussian Schell-model (GSM) beams. Having spatially varying correlation properties, ENUC sources are more difficult to synthesize than their Schell-model counterparts (which can be generated by filtering circular complex Gaussian random numbers) and, in past work, have only been realized using Cholesky decomposition—a computationally intensive procedure. Here we transform electromagnetic GSM field instances directly into ENUC instances, thereby avoiding computing Cholesky factors resulting in significant savings in time and computing resources. We validate our method by generating (via simulation) an ENUC beam with desired parameters. We find the simulated results to be in excellent agreement with the theoretical predictions. This new method for generating ENUC sources can be directly implemented on existing spatial-light-modulator-based vector beam generators and will be useful in applications where nonuniformly correlated beams have shown promise, e.g., free-space/underwater optical communications

Experimentally Generating Any Desired Partially Coherent Schell-model Source Using Phase-only Control

A technique is presented to produce any desired partially coherent Schell-model source using a single phase-only liquid-crystal spatial light modulator (SLM). Existing methods use SLMs in combination with amplitude filters to manipulate the phase and amplitude of an initially coherent source. The technique presented here controls both the phase and amplitude using a single SLM, thereby making the amplitude filters unnecessary. This simplifies the optical setup and significantly increases the utility and flexibility of the resulting system. The analytical development of the technique is presented and discussed. To validate the proposed approach, experimental results of three partially coherent Schell-model sources are presented and analyzed. A brief discussion of possible applications is provided in closing

Generating Partially Coherent Schell-Model Sources Using a Modified Phase Screen Approach

A significant improvement to the recently introduced complex screen (CS) method for generating partially coherent Schell-model sources is presented. The method, called the modified phase screen (MPS) technique, applies a deterministic amplitude and the phase portion of a CS to an initially coherent light source using a single phase-only spatial light modulator. The MPS technique, unlike the CS approach from which it is derived, does not produce a fully developed speckle pattern in the source plane, and therefore converges faster and more uniformly to the desired partially coherent source. The analytical development of the MPS method is presented. Experimental results of a Bessel-Gaussian-correlated Schell-model source, generated using the CS and MPS approaches, are compared to demonstrate the validity and utility of the MPS technique

Modeling Random Screens for Predefined Electromagnetic Gaussian-Schell Model Sources

In a previous paper [Opt. Express 22, 31691 (2014)] two different wave optics methodologies (phase screen and complex screen) were introduced to generate electromagnetic Gaussian Schell-model sources. A numerical optimization approach based on theoretical realizability conditions was used to determine the screen parameters. In this work we describe a practical modeling approach for the two methodologies that employs a common numerical recipe for generating correlated Gaussian random sequences and establish exact relationships between the screen simulation parameters and the source parameters. Both methodologies are demonstrated in a wave-optics simulation framework for an example source. The two methodologies are found to have some differing features, for example, the phase screen method is more flexible than the complex screen in terms of the range of combinations of beam parameter values that can be modeled. This work supports numerical wave optics simulations or laboratory experiments involving electromagnetic Gaussian Schell-model sources

Generation of Vector Partially Coherent Optical Sources Using Phase-Only Spatial Light Modulators

A simple and flexible optical system for generating electromagnetic or vector partially coherent sources or beams is presented. The alternative design controls field amplitude (beam shape), coherence, and polarization using only spatial light modulators. This improvement makes the apparatus simpler to construct and significantly increases the flexibility of vector partially coherent source generators by allowing many different types of sources to be produced without changing the physical setup. The system’s layout and theoretical foundations are thoroughly discussed. The utility and flexibility of the proposed system are demonstrated by producing a vector Schell-model and non-Schell-model source. The experimental results are compared to theoretical predictions to validate the design. Lastly, design aspects, which must be considered when building a vector partially coherent source generator for a specific application, are discussed. Abstract (c) APS

Computational Approaches for Generating Electromagnetic Gaussian Schell-model Sources

Two different methodologies for generating an electromagnetic Gaussian-Schell model source are discussed. One approach uses a sequence of random phase screens at the source plane and the other uses a sequence of random complex transmittance screens. The relationships between the screen parameters and the desired electromagnetic Gaussian-Schell model source parameters are derived. The approaches are verified by comparing numerical simulation results with published theory. This work enables one to design an electromagnetic Gaussian-Schell model source with pre-defined characteristics for wave optics simulations or laboratory experiments. © 2014 Optical Society of Americ

Synthesizing Time-evolving Partially-coherent Schell-model Sources

Time-evolving simulation of sources with partial spatial and temporal coherence is sometimes instructive or necessary to explain optical coherence effects. Yet, existing time-evolving synthesis techniques often require prohibitive amounts of computer memory. This paper discusses three methods for the synthesis of continuous or pulsed time-evolving sources with nearly arbitrary spatial and temporal coherence. One method greatly reduces computer memory requirements, making this type of synthesis more practical. The utility of all three methods is demonstrated via a modified form of Young\u27s experiment. Numerical simulation and laboratory results for time-averaged irradiance are presented and compared with theory to validate the synthesis techniques

SKIL/SnoN attenuates TGF-β1/SMAD signaling-dependent collagen synthesis in hepatic fibrosis

The ski-related novel gene (SnoN), encoded by the SKIL gene, has been shown to negatively regulated transforming growth factor-β1 (TGF-β1) signaling pathway. However, the roles of SnoN in hepatic stellate cell (HSC) activation and hepatic fibrosis (HF) are still unclear. To evaluate the role of SnoN in HF, we combined bulk RNA sequencing analysis and single-cell RNA sequencing analysis to analyse patients with HF. The role of SKIL/SnoN was verified using liver samples from rat model transfected HSC-T6 and LX-2 cell lines. Immunohistochemistry, immunofluorescence, PCR, and western blotting techniques were used to demonstrate the expression of SnoN and its regulatory effects on TGF-β1 signaling in fibrotic liver tissues and cells. Furthermore, we constructed competitive endogenous RNA regulatory network and potential drug network associated with the SnoN gene. We identified SKIL gene as a differentially expressed gene in hepatic fibrosis. SnoN protein was found to be widely expressed in the cytoplasm of normal hepatic tissues, whereas it was almost absent in HF tissues. In the rat group subjected to bile duct ligation (BDL), SnoN protein expression decreased, while TGF-β1, collagen III, tissue inhibitor of metalloproteinase 1 (TIMP-1), and fibronectin levels increased. We observed the interaction of SnoN with p-SMAD2 and p-SMAD3 in the cytoplasm. Following SnoN overexpression, apoptosis of HSCs was promoted, and the expression of HF-associated proteins, including collagen I, collagen III, and TIMP-1, was reduced. Conversely, downregulation of SnoN inhibited HSC apoptosis, increased collagen III and TIMP-1 levels, and decreased matrix metalloproteinase 13 (MMP-13) expression. In conclusion, SnoN expression is downregulated in fibrotic livers, and could attenuate TGF-β1/SMADs signaling-dependent de-repression of collagen synthesis

The effect of cubic stiffness nonlinearity on the vortex-induced vibration of a circular cylinder at low Reynolds numbers

The vortex-induced vibration (VIV) of a circular cylinder elastically supported by linear and cubic springs is investigated numerically at low Reynolds numbers. The cylinder has a low mass ratio and zero structural damping. Nine dimensionless cubic stiffness nonlinearity strength values are considered. It is found that within the parameter space examined, the VIV response for the linear and softening springs can be divided into four regimes, namely the initial, upper, lower and desynchronised regimes. When the softening spring nonlinearity gets stronger, there exist a reduction in the peak amplitude and shifts in the initial-upper branch and upper-lower branch transitions to lower Reynolds number ranges. In contrast, as the hardening spring nonlinearity increases, the response envelope moves to a higher Reynolds number range and the profile of the initial and upper branches becomes smoother with the lower branch gradually disappearing. In the hardening spring case, the beating response is observed near the low end of the initial branch up to the high end of the initial branch. The modulations in the vibration amplitude gradually diminish with increasing Reynolds number. The cubic spring results coincide with those of the linear spring when they are presented with the equivalent reduced velocity. Due to the low Reynolds number range considered, the majority of the vortex shedding is in the 2S mode. The wake in the cases with smaller vibration amplitudes exhibits a single-row configuration. Whereas, a double-row vortex street is mainly observed in the upper branch. Disorders in the wake are found to be associated with beating responses which have larger vibration amplitudes