Transverse Size Research Articles

Narrow transverse‐size compact vertically polarized end‐fire antenna using dual‐hat composite elements

A narrow transverse-size compact end-fire antenna with vertical polarization (VP) is presented in this paper. The antenna working in the 433 MHz band is constructed based on a dual-hat composite element, which consists of a rectangular and a pentagon top hat. This is operated in terms of capacitive coupling and inductive loading. Two dual-hat composite elements are, respectively, applied as the driven and the reflector elements in a Yagi array layout, and they are arranged in a noncommon ground manner. The main radiators are the posts with VP radiation fields, which are readily affected by electromagnetic coupling from the adjacent elements. The radiation fields are constructively guided and overlapped to generate an end-fire radiation. The resonant length of the antenna is stretched due to a folded current path with a reduced profile height. The measured |S11| < −10 dB impedance bandwidth (IMBW) for the fabricated antenna ranges from 419 to 444 MHz (5.7%) and the measured end-fire peak gain can go up to 2.2 dBi at 433 MHz. The antenna dimensions can be maintained at 0.37λ0 × 0.16λ0 × 0.051λ0, where λ0 is the free-space wavelength at the center frequency. It exhibits narrow transverse size and compact structure.

Mechanical damage thresholds for hematomas near gas-containing bodies in pulsed HIFU fields

Objective. Boiling histotripsy (BH) is a novel high intensity focused ultrasound (HIFU) application currently being developed for non-invasive mechanical fractionation of soft tissues and large hematomas. In the context of development of BH treatment planning approaches for ablating targets adjacent to gas-containing organs, this study aimed at investigation of the ultrasound pressure thresholds of atomization-induced damage to the tissue-air interface and correlation of the danger zone dimensions with spatial structure of nonlinear HIFU field parameters. Approach. A flat interface with air of freshly clotted bovine blood was used as an ex vivo model due to its homogenous structure and higher susceptibility to ultrasound-induced mechanical damage compared to soft tissues. Three 1.5 MHz transducers of different F-numbers (0.77, 1 and 1.5) were focused at various distances before or beyond a flat clot surface, and a BH exposure was delivered either at constant, high-amplitude output level, or at gradually increasing level until a visible damage to the clot surface occurred. The HIFU pressure field parameters at the clot surface were determined through a combination of hydrophone measurements in water, forward wave propagation simulation using ‘HIFU beam’ software and an image source method to account for the wave reflection from the clot surface and formation of a standing wave. The iso-levels of peak negative pressure in the resulting HIFU field were correlated to the outlines of surface erosion to identify the danger zone around the BH focus. Main results. The outline of the danger zone was shown to differ from that of a typical BH lesion produced in a volume of clot material. In the prefocal area, the zone was confined within the 4 MPa contour of the incident peak-to-peak pressure; within the main focal lobe it was determined by the maximum BH lesion width, and in the postfocal area—by the transverse size of the focal lobe and position of the first postfocal pressure axial null. Significance. The incident HIFU pressure-based danger zone boundaries were outlined around the BH focus and can be superimposed onto in-treatment ultrasound image to avoid damage to adjacent gas-containing bodies.

Visual learning graph convolution for multi-grained orange quality grading

The quality of oranges is grounded on their appearance and diameter. Appearance refers to the skin’s smoothness and surface cleanliness; diameter refers to the transverse diameter size. They are visual attributes that visual perception technologies can automatically identify. Nonetheless, the current orange quality assessment needs to address two issues: 1) There are no image datasets for orange quality grading; 2) It is challenging to effectively learn the fine-grained and distinct visual semantics of oranges from diverse angles. This study collected 12 522 images from 2 087 oranges for multi-grained grading tasks. In addition, it presented a visual learning graph convolution approach for multi-grained orange quality grading, including a backbone network and a graph convolutional network (GCN). The backbone network’s object detection, data augmentation, and feature extraction can remove extraneous visual information. GCN was utilized to learn the topological semantics of orange feature maps. Finally, evaluation results proved that the recognition accuracy of diameter size, appearance, and fine-grained orange quality were 99.50, 97.27, and 97.99%, respectively, indicating that the proposed approach is superior to others.

Ultimate bunch length and emittance performance of an MeV ultrafast electron diffraction apparatus with a dc gun and a multicavity superconducting rf linac

We present the design of a high repetition rate MeV energy ultrafast electron diffraction instrument based on a DC photoelectron gun and an SRF linac with multiple independently controlled accelerating and bunching cavities. The design is based on the existing Cornell photoinjector, which can readily be applied to the presented findings. Using particle tracking simulations in conjunction with multiobjective genetic algorithm optimization, we explore the smallest bunch lengths, emittance, and probe spot sizes achievable. We present results for both stroboscopic conditions (with single electrons per pulse) and with $10^5$ electrons/bunch which may be suitable for single-shot diffraction images. In the stroboscopic case, the flexibility provided by the many-cavity bunching and acceleration allows for longitudinal phase space linearization without a higher harmonic field, providing sub-fs bunch lengths at the sample. Given low emittance photoemission conditions, these small bunch lengths can be maintained with probe transverse sizes at the single micron scale and below. In the case of $10^5$ electrons per pulse, we simulate state-of the art 5D brightness conditions: rms bunch lengths of 10 fs with 3 nm normalized emittances, while now permitting repetition rates as high as 1.3 GHz. Finally, to aid in the design of new SRF-based UED machines, we simulate the trade-off between the number of cavities used and achievable bunch length and emittance.

Boron nitride nanosheets: Large-scale exfoliation in NaOH-LiCl solution and their highly thermoconductive insulating nanocomposite paper with PI via electrospinning-electrospraying

The miniaturisation of electronic components requires high-performance materials with insulating and thermal conductive properties for electronic packaging and thermal management. Boron nitride nanosheets (BNNS) are a desirable thermal conductive filler due to their excellent thermal stability, chemical stability, and high thermoconductivity. However, it remains challenging to mass produce ultra-thin large-scale BNNS and combine them with small amounts of polymers to fabricate malleable thermoconductive composites for flexible electronic devices. Herein, we report a new method to prepare BNNS at high yield by high-temperature oxidation treatment followed by hydrothermal exfoliation in NaOH-LiCl solution. We further fabricated flexible, insulating, and highly thermoconductive BNNS/PI (polyimide) nanocomposite paper, via a scalable layer-by-layer process that involves electrospinning of PI fibres and eletrospraying of BNNS. The prepared BNNS have a transverse size of 1.18 µm and a thickness of 1–2.9 nm, with a high yield of 75.48% at a concentration of 3.38 mg mL− 1. The BNNS/PI nanocomposite paper exhibited an ultrahigh in-plane thermal conductivity (7.58 W m−1 K−1), 2005% higher than that of the pure PI nanofibre composite. This simple method has wide application potential in next-generation electronic devices to design thermal interface materials with excellent electrical insulation, thermostability, and flexibility.

Magnetosheath Filamentary Structures Driven by Foreshock Energetic Ions

AbstractPrevious simulation studies have revealed the formation of magnetosheath filamentary structures by foreshock energetic ions. We report Cluster and Double Star observations of three such events triggered by a foreshock bubble, a hot flow anomaly and a traveling foreshock, respectively. In each case, in association with the onset of foreshock energetic ions, the magnetosheath energetic ion fluxes have quasi‐periodic modifications. Their azimuthal and pitch angular distributions indicate that these populations flow into the magnetosheath along the magnetic field lines. As a result, filamentary plasma structures form and display as a series of ion density and pressure oscillations anticorrelated to temperature oscillations. Moreover, our statistical analyses of their properties show that filamentary structures primarily form in the magnetosheath with the magnetic field lines connecting to the quasi‐parallel bow shock and under favorable formation conditions similar to those of foreshock transients. The distributions of the angles between the filamentary structure normals and the local magnetic field directions peak at 80°–90°. The transverse sizes of those filaments are in the range of 0.2–1.6 RE. Magnetosheath filamentary structures are often associated with large‐amplitude ion density and temperature perturbations comparable to the unperturbed background levels.

Improved SCRLH ZOR‐based compact microstrip bandpass filter with wide upper stopband

AbstractA novel compact microstrip bandpass filter (BPF) based on an improved simplified composite right‐/left‐handed (SCRLH) zeroth‐order resonator (ZOR) is presented in this paper. The improved SCRLH ZOR (ISZOR) can substantially simplify the filter configuration and shrink the filter size as well as ensure a wide upper stopband. A certain orientation of two ISZORs allows a larger gap to produce the specified interstage capacitive coupling, easing the requirement for fabrication precision. Starting from the purely lumped circuit model, the microstrip ISZOR is efficiently generated by utilizing the implicit space mapping technique, with which the microstrip BPF is then constructed and optimized by the Nelder–Mead simplex algorithm. A three‐pole filter with a center frequency of 3.1 GHz and a relative bandwidth of 5% is exemplified to illustrate the design process. The measurement shows that the filter is of good bandpass selectivity, with a transversal size reduction of more than 64% compared to a former counterpart and a rejection level better than 30 dB up to 11.76 GHz (close to 4f0).

Major haemorrhage after non-surgical management of oropharyngeal squamous cell carcinoma.

Major haemorrhage is a rare complication after chemoradiotherapy for oropharyngeal squamous cell carcinoma. This is managed by interventional neuroradiology with endovascular embolisation of the bleeding vessel. This study aimed to describe radiological and clinical predictors of haemorrhage. A retrospective case series was conducted of all patients with oropharyngeal squamous cell carcinomas who suffered a major haemorrhage requiring embolisation during or after treatment with chemoradiotherapy or radiotherapy alone, between 2013 and 2021, in Western Australia. This study included 14 patients, in two groups: haemorrhage group (n = 70) and tumour stage matched non-haemorrhage group (n = 7). Patients who haemorrhaged had a larger average transverse axial tumour size on pre-treatment computed tomography (38 mm vs 22 mm; p = 0.02) and tumours tended to involve the proximal aspect of the offending bleeding vessel. All patients who haemorrhaged developed deep cavitating or ulcerative tumour bed changes on post-treatment imaging (p < 0.0001). Tumour bed ulceration or cavitation appears to be highly predictive of haemorrhage in this patient cohort.

Synchrotron radiation interferometry for beam size measurement at low current and in large dynamic range

The Synchrotron Radiation Interferometry (SRI) has become a widely used technique to measure the small transverse size of the electron beam in the storage ring. In a typical SRI system for the routine storage ring operation, synchrotron radiation from a dipole magnet is used to illuminate a double slit with a small slit opening and a relatively large slit separation to form a large number of interference fringes on the observation plane. However, a different type of SRI is needed for intrabeam scattering (IBS) research to measure the beam size at ultralow currents and in a wide dynamic range. Such a system requires a double slit with a large slit opening to increase the light input while having the capability of accurately measuring the beam size with a range of visibility. By examining the impact of the nonuniform wave amplitude of synchrotron radiation and that of the varying visibility (due to a changing beam size) on the beam size measurement, we propose a new physics model for this type of SRI. This new model is validated using simulation, showing significantly improved results when compared with the conventional model. Based on this new model, we have developed and tested an SRI system dedicated to the IBS study on the Duke storage ring. This system has been used successfully to measure electron beams with about $10\text{ }\text{ }\ensuremath{\mu}\mathrm{A}$ of current and with a higher current but a variable size. This new physics model can also improve the measurement accuracy and consistency of the conventional SRIs, especially at low visibility.

Friction-induced motion evolution of reduced graphene oxide-Al2O3 at contact interface to achieve superior lubrication performance

Reduced graphene oxide-Al2O3 (rGO-Al2O3) nanoparticle (NP) was synthesized and applied as additive in water-based lubricants. Pin-on-disk tribological experiments indicated that rGO-Al2O3 nanofluid exhibited reinforced lubricity due to the formation of a double-layer tribofilm, contributing to 34.8 % ± 2.3 % and 78.2 % ± 2.5 % reduction in friction coefficient and wear rate. Combined with nonequilibrium molecular dynamics (NEMD) simulation, rGO-Al2O3 NP exerted synergistic effects of interlayer sliding, rolling, polishing and self-mending to obtain higher surface quality. A new parameter (p) was proposed to determine the motion modes of Al2O3. Al2O3 NP exhibited both rolling and sliding motion. The synergy of rGO and Al2O3 NPs increased the rolling motion proportion of Al2O3 from 78 % to 91 % compared to using alone. Similarly, about 12.6 % of the friction force in friction system was shared by the interlayer sliding of rGO monolayers in the presence of Al2O3 than the system with only rGO (9.5 %). Besides, rGO-Al2O3 had higher diffusion coefficient, which was more conducive to the formation of tribofilm. rGO nanosheets with large transverse size adsorbed on the Fe surface to prevent the embedding of high hardness Al2O3 to maintain its rolling effect. Meanwhile, Al2O3 can reversely stimulate the interlaminar sliding of rGO to enhance the lubrication performance of rGO-Al2O3 nanofluid.

ACCELERATION OF A HIGH-CURRENT PROTON BEAM IN A LINEAR INDUCTION ACCELERATOR AT ITS COMPENSATION BY ELECTRON BEAMS

The dynamics of a high-current proton beam in the cusp magnetic field and in the uniform magnetic field of the drift region in the presence of an accelerating field in the cusp region and of two types of compensating electron beams (before and after the cusp) has been studied. It is shown that for the taken beam parameters and magnetic field it is impossible to accelerate a proton beam of the density higher than 1012 cm-3 with maintaining its initial transverse size and monoenergeticity.

Effect of driver charge on wakefield characteristics in a plasma accelerator probed by femtosecond shadowgraphy

We report on experimental investigations of plasma wave structures in a plasma wakefield acceleration (PWFA) stage which is driven by electron beams from a preceding laser plasma accelerator. Femtosecond optical probing is utilized to allow for direct visualization of the plasma dynamics inside the target. We compare two regimes in which the driver propagates either through an initially neutral gas, or a preformed plasma. In the first case, plasma waves are observed that quickly damp after a few oscillations and are located within a narrow plasma channel ionized by the driver, having about the same transverse size as the plasma wakefield cavities. In contrast, for the latter robust cavities are recorded sustained over many periods. Furthermore, here an elongation of the first cavity is measured, which becomes stronger with increasing driver beam charge. Since the cavity length is linked to the maximum accelerating field strength, this elongation implies an increased field strength. This observation is supported by 3D particle-in-cell simulations performed with PIConGPU. This work can be extended for the investigation of driver depletion by probing at different propagation distances inside the plasma, which is essential for the development of high energy efficiency PWFAs.

Tempforming Strengthening of a Low-Alloy Steel.

Low-alloy structural steels subjected to quenching and tempering to achieve high strength possess a common drawback associated with low-impact toughness at low temperatures. An additional warm rolling, i.e., tempforming, is a promising approach to strengthen the rolled semi-products along with increasing their impact toughness. The effect of tempforming at 823–923 K on the microstructures and the mechanical properties of a low-alloy steel was studied in comparison with ordinary tempering at the same temperatures. The tempformed microstructures consisted of highly flattened grains with a transverse grain size of 245 nm to 360 nm depending on tempering temperature. A decrease in the transverse grain size with a decreasing temperature was accompanied by an increase in the total dislocation density (including sub-boundary dislocations) from 3.3 × 1015 m−2 to 5.9 × 1015 m−2. The steel samples subjected to tempforming exhibited enhanced mechanical properties. The yield strength increased by more than 300 MPa, approaching about 1200–1500 MPa depending on tempforming temperature. Moreover, strengthening by tempforming was accompanied by an increase in the impact toughness, especially inthe low temperature range down to 77 K, where the impact toughness was above 80 J cm−2.

DIAGNOSTIC VALUE OF MULTIPARAMETRIC ULTRASOUND EXAMINATION IN PATIENTS WITH RECURRENT TONSILITIS

The problem of recurrent tonsillitis in the world is still highly relevant. A clear algorithm for the diagnosis and treatment of patients with this pathology is still being developed and improved. Thanks to the latest technologies, modernization of equipment and improvement of knowledge of medical workers, it is possible to diagnose this disease better and, consequently, to decide on further treatment.&#x0D; Aim. Determine the informative value of shear wave elastography as an additional objective method for the diagnostics of recurrent tonsillitis.&#x0D; Materials and methods. 24 participants were enrolled in the research. Age structure: children of primary school age (6-10 years) - 14 people, teenagers (10-15 years) - 6 people, high school age (15-17 years) - 2 people, adults (22-35 years) - 2 people. Criteria for inclusion in the research - from 4 to 6 episodes of tonsillitis per year for the last 2 years. The patients' anamnesis was carefully collected, and ENT examination, paying special attention to the presence of symptoms of "underactivity" of the tonsils, shear wave elastometry and elastography of the palatine and peritoneal tonsils were performed as one of the newest methods of ultrasound examination. Longitudinal and transverse scans of the palatine tonsils and surrounding structures were performed. The obtained data were recorded in the patient's examination card for further analysis.&#x0D; In general, the main indicators were identified, which were further analyzed - the size of the tonsils, transverse size and stiffness of the paratonsillar space, colors, which mapped the examined structures, the size of regional maxillary lymph nodes.&#x0D; Results. After collecting the participants’ anamnesis, the main common feature was identified - experiencing 4 to 6 episodes of tonsillitis per year for the past 2 years, and on ENT examination – fixation of the tonsils, which indicated fibrotic changes in the paratonsillar space, which became one of the main criteria for inclusion of patients in this research. It is an objective criterion for recurrent tonsillitis. Elastometry and elastography of peritonsillar structures revealed other important objective features of recurrent tonsillitis - the shear waves velocity (stiffness of the peritonsillar space) higher than 2.0 m/sec which is mapped in red and burgundy color. Mapping of the tonsils themselves was less informative due to insignificant clinical significance. More important was the mapping of paratonsillar spaces. An additional objective criterion was the size of the maxillary lymph nodes as regional lymph nodes for the palatine tonsils. They ranged from 10.5 mm to 20.5 mm, which is larger than normal values.&#x0D; Conclusions. According to the result of the research, the following signs of recurrent tonsillitis were identified: fixation of the palatine tonsils, increased shear wave velocity (stiffness index) in the peritonsillar space on elastometry (higher than 2 m/sec), that hypothetically, can be considered as indicating fibrosis of the peritonsillar space, mapping of peritonsillar space structures with colors from green and blue to red with areas of burgundy (in normal tissues green, blue, sometimes yellow colors are seen), enlarged maxillary lymph nodes, as regional for the palatine tonsils.&#x0D; Thus, we can confirm the high informative value of shear wave elastometry and elastography as an additional objective method of visualization in patients with recurrent tonsillitis.

Modeling the Solar Wind Turbulent Cascade Including Cross Helicity: With and Without Expansion

Simulations of the turbulent cascade forming in the solar wind, including cross helicity, commonly adopt a homogeneous setup, not taking into account wind expansion. Here we want to assess the predictions of decaying 3D compressible (low Mach number) MHD simulations, respectively homogeneous and with expansion, in order to examine which is the most fruitful approach to understanding the turbulent cascade in the solar wind. We follow turbulent evolution during 10 nonlinear turnover times, considering several initial values of the initial spectral slope and cross helicity. In the expanding case, the transverse sizes of the plasma volume are stretched by a factor of 5 during the simulation, corresponding to traveling from 0.2 up to 1 au. In homogeneous simulations, the relative cross helicity rises, and the Elsässer spectra E ± show “pinning,” with a steep dominant spectrum and flat subdominant spectrum, the final spectral indices depending on cross helicity but not initial indices. With expansion, the relative cross helicity decreases, and dominant and subdominant spectra share the same index, with the index relaxing to an asymptotic value that generally depends on the initial index. The absence of pinning, as well as the decrease of relative cross helicity, probably both rely on the permanent injection by expansion of an excess of magnetic energy at the largest scales, equivalent to injecting subdominant energy. Also, spectra generally steepen when initially starting flatter than k −5/3 but stop evolving at a finite time/distance.

Differential Diagnosis Value of Shear-Wave Elastography for Superficial Enlarged Lymph Nodes.

ObjectivesTo evaluate the diagnostic efficiency and diagnostic threshold of conventional US and shear-wave elastography (SWE) in superficial enlarged lymph nodes (LNs).MethodsA total of 204 patients with superficial enlarged LNs were enrolled in this retrospective study aged 46.0 ± 15.2 years from March 2020 to March 2021. LNs with a long axis larger than 0.7 cm were considered as superficial enlarged. Before the histological biopsy, LNs that were considered suspicious according to both conventional US and SWE were included, while LNs with no or unclear pathological results, or with no satisfactory SWE images, were excluded. The conventional and 2-D SWE examinations were performed with Aplio i800 and Acuson sequoia equipped with i18LX5 linear-array transducer (5-18 MHz) and 10L4 linear-array transducer (4-10 MHz), respectively. Both E Median and Vs Median parameters were investigated by two senior ultrasound physicians. The pathological results were performed as the gold standard.ResultsVariables including transverse axis size, lymphatic hilum, L/T ratio, echogenicity, and color Doppler pattern were considered significant. The mean E Median value in benign, metastatic LNs, and lymphoma were 28.26 ± 8.87 kPa, 77.46 ± 22.85 kPa, and 50.37 ± 5.41 kPa (p <0.001), while Vs Median values were 3.02 ± 0.50 m/s, 4.87 ± 0.90 m/s, and 4.09 ± 0.22 m/s, respectively (p < 0.001). The diagnostic performance indicated the high sensitivity, specificity, PPV, NPV, and overall accuracy of conventional US combined with SWE. The optimal cutoff values of E Median and Vs Median for predicting malignant LNs were 42.90 kPa and 3.73 m/s, respectively. As AUC value, sensitivity, specificity, accuracy, PPV, and NPV revealed, the indexes of E Median were 0.976, 0.927, 0.975, 0.946, 0.983, and 0.897, respectively, while Vs Median were 0.970, 0.927, 0.963, 0.941, 0.975, and 0.895, respectively (p <0.001). The ROC curves of both E Median (AUC=0.976) Vs Median (AUC=0.970) suggested the remarkable diagnostic efficiency in distinguishing benignity between suspected malignant LNs.ConclusionsAbove results indicated that conventional US together with 2-D SWE could elevate the diagnostic performance. Meanwhile, the parameters of 2-D SWE including E Median and Vs Median could effectively assess malignant LNs, which provide valuable differentiating information in superficial enlarged LNs.

Experience of pancreaticodigestive anastomosis performing in pancreaticoduodenectomy

The aim of the study was to analyze the short-term and long-term results of pancreaticoduodenectomy (PD) on condition of performing different types of pancreaticodigestive anastomoses. The results of 108 PD of the period from 2008 to 2021 performed in the Department of Surgery N 2 on the basis of the Dnipro Regional Hospital named after І. Mechnikov were analyzed. Pancreatojejunostomy (PJ) was formed in 88 (81.5%) cases, pancreaticogastrostomy (PG) ‒ in 20 (18.5%). Depending on the transverse size of pancreatic isthmus and body, diameter of the pancreatic duct the method of PJ was chosen: telescope-type PJ «end-to-end» (n=26), Wirsung-jejunostomy (n=28), original method (n=34). In the PJ group the dense parenchyma of the pancreas was in 51 (58.0%) cases, soft parenchyma ‒ in 37 (42.0%), and in the PG group the dense gland was observed in 12 (60%) cases, soft ‒ in 8 (40%) patients (p&gt;0,05). The number of the early postoperative complications was 43 (39,8±4,7%), among them there were (15,7±3,5%) patients with severe complications who required additional interventions. Mortality was 6.5±2.4%. The best results for the early postoperative complications were obtained in the groups of PG and original PJ. There were statistically significant differences in the total number of cases of the early postoperative complications between the groups of PG (20.0±8.9%) and telescope-type PJ (50.0±9.8%, p=0.037) and Wirsung-jejunostomy (50.0±9.4%, p=0.034), as well as while comparing the total number of patients with complications in the groups of PG and PJ (44.3±5.3%, p=0.045). There were not any statistically significant differences among the late postoperative complications (p&gt;0.05).

A novel sequential‐phase quad‐feed circularly polarized microstrip antenna for INMARSAT and GPS applications

In this letter, a compact circularly polarized microstrip antenna has been developed with a new type of feed structure. The key feature of the antenna is the integrated design of the quad-feed network coplanar with the driven patch, which makes the antenna simple in structure and has good circular polarization performance. A parasitic patch is used to expand the impedance bandwidth, while a round hole in the center of the driven patch is used to improve impedance matching. In addition, a cavity is utilized to reduce the transverse size of the antenna and improve the front-to-back ratio. The simulation and experimental results show that the VSWR of the antenna is lower than 1.5 and the average gain is higher than 8dBic in the L-band for International Maritime Satellite applications. Due to the centrosymmetric feed configuration, the antenna can also be used as a global positioning system antenna, which requires high stability of the phase center.

Light propagation in a random three-dimensional ensemble of point scatterers in a waveguide: Size-dependent switching between diffuse radiation transfer and Anderson localization of light

Light transport in a disordered ensemble of resonant atoms placed in a waveguide is found to be very sensitive to the sizes of the cross section of a waveguide. Based on a self-consistent quantum microscopic model treating atoms as coherent radiating dipoles, we have shown that the nature of radiation transfer changes from Anderson localization regime in a single-mode waveguide to a traditional diffuse transfer in a multimode one. Moreover, the transmittance magnitude undergoes complicated steplike nonmonotonic dependence on the transverse sizes of a waveguide.

Severing the Link between Modal Order and Group Index Using Hybrid Guided Space-Time Modes

The structure of an optical waveguide determines the characteristics of its guided modes, such as their spatial profile and group index. General features are shared by modes regardless of the waveguiding structure; for example, modal dispersion is inevitable in multimode waveguides, every mode experiences group-velocity dispersion, and higher-order modes are usually slower than their lower-order counterparts. We show here that such trends can be fundamentally altered -- altogether severing the link between modal order and group index hybrid and eliminating dispersion -- by exploiting hybrid guided space-time modes in a planar multimode waveguide. Such modes are confined in one-dimension by the waveguide and in the other by the spatio-temporal spectral structure of the field itself. Direct measurements of the modal group delays confirm that the group index for low-loss, dispersion-free, hybrid space-time modes can be each tuned away from the group index of the conventional mode of same order, and that the transverse size of these hybrid modes can be varied independently of the modal order and group index. These findings are verified in a few-mode planar waveguide consisting of a 25.5-mm-long, 4-$\mu$m-thick silica film deposited on a MgF$_2$ substrate.