Combined Beam Research Articles

Simple approach for spectral beam combination of narrowband laser sources for spectroscopic applications.

Spectral beam combination of multiple single mode laser sources employing narrowband spectral filters which are arranged on the perimeter of regular polygons is demonstrated. With this simple geometric design, co-alignment and co-propagation of the individual laser beams can be reasonably achieved. Spectroscopic applicability is displayed by spatial filtering, mode-matching, and subsequent coupling of the combined beams into a 76 m astigmatic mirror multipass cell.

Study on Overburden Fracture and Structural Distribution Evolution Characteristics of Coal Seam Mining in Deep Large Mining Height Working Face

Coal mining has gradually entered the deep mining era, and large-height mining is an important way to mine thick coal seams in the deep. The high coal wall will inevitably make the distribution of the overburden structure in the coal mining face more complicated, and the large buried depth will also cause more intense mine pressure. The study of the distribution and evolution of the overburden structure and stress in the mining site can provide theoretical guidance for safe mining. In this work, a physical similarity modeling test was carried out based on the physical–mechanical parameters of overburden rock and similarity theory, taking the mining of a deep, large-height working face in Pingdingshan Coal Mine as an example. The results show that the deformation and breakage of overburden rock in deep, large-height workings occurring during mining is persistent and not only in a short period of time. The breakage form of overburden can be categorized into two types based on the deformation characteristics: (I) non-separation-induced type, and (II) separation-induced type. Among these, the breakage induced by separation can be divided into two categories: (i) dominated by self-weight stress, and (ii) affected by shear cracks. It also summarizes the form of the overburden structure and the structural morphology of the stope. The overburden structure shows a “combined cantilever beam structure-articulated rock-slab structure-non-articulated rock-slab structure”. Among these, the periodic breakage of the upper cantilever beam evolved articulated and non-articulated rock-slab structure in the lower part, which weakened the supporting effect of the lower gangue and further aggravated the breakage of the upper overburden rock. The shape of the main structure of the stope mainly depends on the fracture line from the advancing coal wall to the upper overburden: from a rectangular shape without collapse to a trapezoidal shape at the initial stage of collapse, to a trapezoidal shape with multiple steps after the main roof collapse.

Dual-parameter femtosecond mode-locking pulse generation in partially shared all-polarization-maintaining fiber Y-shaped oscillator with a single saturable absorber

We present a design of a mode-locked fiber laser based on a polarization-maintaining (PM) Y-shaped fiber structure, which employs a single semiconductor saturable absorber mirror (SESAM) and a common polarization beam combiner (PBC) to achieve dual- parameter mode-locking femtosecond pulse in two orthogonal polarization states. The two output pulses have different characteristics, such as repetition frequency (87.3 MHz and 91.3 MHz), average output powers (2.1 mW and 1.9 mW), pulse durations (299 fs and 377 fs) and spectral profiles (centered at 1565.6 nm and 1563.6 nm with spectral width of 9.96 nm and 9.93 nm). The properties of the two pulses are experimentally characterized and their potential applications in areas such as bistable frequency lasers and dual femtosecond optical frequency comb is discussed.

Multiple beam coherent combination via an optical ring resonator.

Future gravitational wave detectors (GWDs) require low noise, single frequency, continuous wave lasers with excellent beam quality and powers in excess of 500 W. Low noise laser amplifiers with high spatial purity have been demonstrated up to 300 W. For higher powers, coherent beam combination can overcome scaling limitations. In this Letter we introduce a new, to the best of our knowledge, combination scheme that uses a bow-tie resonator to combine three laser beams with simultaneous spatial filtering performance.

Development of an anti-vibration aircraft model support system with magnetorheological annular squeeze dampers for wind tunnel

Sting support is an important equipment in wind tunnel test and is also vulnerable to resonance under the influence of wind flow, which will reduce the accuracy of test data and even pose a hazard to the wind tunnel. To address the vibration problem, an innovative magnetorheological sting support (MRSS) was proposed in this paper. Specifically, the vibration reduction mechanism was explained by using a combination of Euler-Bernoulli beam and Kelvin-Voigt element. Furthermore, the relationship between the stiffness and damping of the magnetorheological damper (MRD) and the natural frequency (NF) and damping ratio (DR) characteristics of the MRSS was illustrated. To provide controllable damping and stiffness for the support system, an MRD with annular squeeze mode was designed, taking into account various factors such as low influence on wind flow, sting shape, and magnetic circuit requirements, and was also optimized by considering target magnetic field and low power consumption as the objectives. Tests on the manufactured MRD demonstrate the effectiveness of the structure design and optimization. Also, the response time characteristic satisfies the system vibration control. Subsequently, the controllability and superior fail-safe property of MRSS were verified through laboratory and wind tunnel tests. Finally, an on–off control logic was developed, and real-time vibration control tests were conducted in various impulse excitation, the resonance peak was significant attenuated by 27.1 dB. Additionally, the resonance peak was attenuated by 17.6 dB in the passive state. The experimental results showed that the MRSS was able to suppress the vibration with efficiency and reliability.

Refining the Stellar Parameters of τ Ceti: a Pole-on Solar Analog

To accurately characterize the planets a star may be hosting, stellar parameters must first be well determined. τ Ceti is a nearby solar analog and often a target for exoplanet searches. Uncertainties in the observed rotational velocities have made constraining τ Ceti’s inclination difficult. For planet candidates from radial velocity (RV) observations, this leads to substantial uncertainties in the planetary masses, as only the minimum mass () can be constrained with RV. In this paper, we used new long-baseline optical interferometric data from the CHARA Array with the MIRC-X beam combiner and extreme precision spectroscopic data from the Lowell Discovery Telescope with EXPRES to improve constraints on the stellar parameters of τ Ceti. Additional archival data were obtained from a Tennessee State University Automatic Photometric Telescope and the Mount Wilson Observatory HK project. These new and archival data sets led to improved stellar parameter determinations, including a limb-darkened angular diameter of 2.019 ± 0.012 mas and rotation period of 46 ± 4 days. By combining parameters from our data sets, we obtained an estimate for the stellar inclination of 7° ± 7°. This nearly pole-on orientation has implications for the previously reported exoplanets. An analysis of the system dynamics suggests that the planetary architecture described by Feng et al. may not retain long-term stability for low orbital inclinations. Additionally, the inclination of τ Ceti reveals a misalignment between the inclinations of the stellar rotation axis and the previously measured debris disk rotation axis (i disk = 35° ± 10°).

NUMERICAL AND THEORETICAL INVESTIGATION ON COMPOSITE COLD-FORMED STEEL JOINTS WITH LIGHTWEIGHT CONCRETE

This research intends to investigate behaviour of composite cold-formed steel joint numerically through finite element analysis by using ABAQUS and theoretically by referring to BS 5950-1:2000 and Green book P213 “Joint in Steel Construction-Composite Connection”. A composite joint is modelled by combination of composite beam and steel column with connection of HRS gusset plate and M12 bolts. The significant failure mode is local buckling in CFS column web which similar in experimental study, FEM numerical simulation and theoretical component calculation. The behaviour of the cold-formed steel composite joint will be expressed in moment-rotational and load-deflection relationship to determine the initial rotational stiffness and ultimate moment resistance. The findings from numerical and theoretical investigations are compared with the full-scale experimental study in three different thicknesses of gusset plate. A correlation in stiffness ratio and strength ratio are obtained in the range of 1.76 to 2.25, and 1.00 to 1.60 respectively indicating that the numerical modelling tends to underpredict the behaviour of the composite structures.

Energy focusability of spatial incoherent beam combining for pulse laser propagation in marine atmosphere.

In this study, we have deduced the generalized scintillation index of the plane wave and plane wave structure function based on the modified non-Kolmogorov power spectrum of atmospheric refractive index with the spectrum power index α. In addition, we have analyzed the fluctuation of atmospheric density due to thermal blooming. Based on the interaction of six beams in thermal blooming, the thermal phase screening and intensity distribution are simulated. Under the influence of atmospheric turbulence and thermal blooming, the six-beam combination is then simulated numerically to obtain the equivalent radius with long exposure (RL), power in the bucket (PIB), Strehl ratio (SR), and peak value of intensity (Ip). Results show that PIB, Ip, and SR of the pulse beam combination decrease with an increase in α; however, RL operates in reverse mode and the short pulse durations reduce the thermal blooming. Moreover, laser of short duration cannot generate high ring energy on the target.

A hybrid mechanism of 3D optical trapping of particles immersed in a cold buffer gas

A novel mechanism of the formation of a deep optical superlattice (OSL) for three-dimensional (3D) trapping of resonant impurity atoms immersed in a transparent cold buffer gas is proposed and investigated theoretically. This mechanism is associated with the joint action of two factors of different physical nature: rectification effect of the gradient force of light pressure and effect of the light induced drift (LID) of atoms (a consequence of the difference in gas-kinetic cross sections of excited and unexcited atoms). Such a situation can be realised when a gas mixture is irradiated by a bichromatic combined light beam which is a special coaxial superposition of cosine-Gaussian optical beams. Here, the RcGF creates a periodic 1D array of deep potential wells (OSL) along the beam axes, and an effective force, causing LID, pulls resonant particles into the combined light beam and provides their transverse (with respect to the beam axes) confinement in OSL. As a result, there can occur a giant accumulation of impurity particles in the OSL cells, accompanied by a strong spatial particle localization far away from the walls of the reservoir, in which the gas mixture is located.

Fast Beam Search Based on Recorded Combinations for Distributed Massive MIMO Systems Using Sub-THz Wave Bands

Massive multiple-input multiple-output (mMIMO) systems using sub-Terahertz (sub-THz) wave bands are viewed as a promising way to increase greatly the capacity of future mobile communications because they can provide a wider bandwidth than conventional wireless communications. Distributed mMIMO systems can improve the spatial multiplexing transmission performance by reducing spatial correlations among the MIMO channels in line-of-sight environments. Unfortunately, beam search is more complex than in conventional wireless communications, because each access point (AP) requires a very narrow beamwidth to compensate for the significant propagation attenuation in sub-THz waves and beam search must involve all distributed APs. To address this problem, this paper proposes a fast beam search method to limit the beam-sweep directions of beam sweep based on the beam combinations selected for the distributed APs in the past. Simulations show that the proposed method maintains the transmission capacity while greatly reducing the number of search beams compared to conventional all-AP exhaustive beam search. The results show based on 16 APs that while matching the transmission capacity attained by all-AP exhaustive or two-stage beam search methods, the proposed method reduces the number of search beams by APs (excluding the initial AP executed exhaustive beam search) by 90.8% at the 50th percentile and 62.5% at the 95th percentile compared to two-stage beam search for 50,000 sets of user equipment used for recording beam combinations before evaluating the performance.

Null Space Projection-Based Design of Multibeam for Joint Communication and Sensing Systems

This paper proposes a multibeam combining method for joint communication and sensing (JCAS) systems. A sensing beamforming (BF) vector is designed to have components only in the orthogonal subspace of the communication BF vector by using a null space projection. In addition, a sensing beam-centric coherence combining is adopted to align the phases of the communication beam and the sensing beam at the sensing beam direction. The proposed approach allows the communication channel to remain stable while scanning the region of interest with the combined beams. The sensing BF gain is also improved by making the sidelobe of the communication beam contribute to increasing the BF gain of the sensing beam. Simulation results are provided to verify the effectiveness of the proposed method.

Hybrid topological photonic crystals

Topologically protected photonic edge states offer unprecedented robust propagation of photons that are promising for waveguiding, lasing, and quantum information processing. Here, we report on the discovery of a class of hybrid topological photonic crystals that host simultaneously quantum anomalous Hall and valley Hall phases in different photonic band gaps. The underlying hybrid topology manifests itself in the edge channels as the coexistence of the dual-band chiral edge states and unbalanced valley Hall edge states. We experimentally realize the hybrid topological photonic crystal, unveil its unique topological transitions, and verify its unconventional dual-band gap topological edge states using pump-probe techniques. Furthermore, we demonstrate that the dual-band photonic topological edge channels can serve as frequency-multiplexing devices that function as both beam splitters and combiners. Our study unveils hybrid topological insulators as an exotic topological state of photons as well as a promising route toward future applications in topological photonics.

DOSIMETRIC EVALUATION OF POST-MASTECTOMY THREE-DIMENSIONAL CONFORMAL RADIATION THERAPY (3DCRT) BREAST CANCER TREATMENT PLANS

Breast cancer is the most diagnosed cancer in women globally. External beam radiotherapy is one method to treat breast cancer, which can be given to the patients after mastectomy. The changes in anatomy of breast tissues after mastectomy makes the radiotherapy treatment very challenging to ensure the prescribed dose delivered to the tumour target while the radiation to the surrounding critical organs is kept to be low. This study aims to evaluate the dosimetric parameters of radiotherapy treatment plans for breast cancer patients after mastectomy delivered using 3DCRT technique. The evaluation includes the target coverage to the PTV, defined as the volume of PTV receiving 95% of the prescribed dose and the volume of PTV receiving 107% of the prescribed dose. The min, max and mean dose to the PTV were also recorded. The dosimetric parameters to the OARs were Dmean and V20 to the lung, Dmean and V25 to the heart, Dmean to esophagus and Dmax to the spinal cord. The result shows that target coverage is fulfilled in most of the plans, however the host spot in the PTV also observed in the most of the plans. Dose to heart, left lung, esophagus and spinal cord are relatively low and below the constraint recommended by QUANTEC, however the V20 to the right lung exceeded the constraint in the most of the plans. The combination of photon and electron beam might be useful to reduce the excessive dose to the right lung.

Accurate Estimation of Inter-Story Drift Ratio in Multistory Framed Buildings Using a Novel Continuous Beam Model

This study presents a novel method for accurately predicting the dynamic behavior of multistory frame buildings under earthquake ground motion. The proposed method allows approximately estimating the inter-story drift ratio, a crucial parameter strongly associated with building damage, its distribution along the building height, and its maximum value location. An equivalent continuous beam model with a rotation at the base, consisting of a combination of a shear beam and a flexural beam, is proposed to achieve this. This model derives closed-form solutions for the building’s dynamic characteristics. The lateral deformations along the height of frame buildings subjected to a given earthquake load, particularly the inter-story drift ratio profiles, and the maximum inter-story drift ratio parameter, are investigated. The proposed continuous model requires two dimensionless parameters: the lateral stiffness ratio (α) and the rotation at the base (θ), representing the drift ratio of the first story. For the expression of the lateral stiffness ratio (α) coefficient, a simple equation is also proposed using the beam-to-column stiffness ratio (ρ, or Blume coefficient) associated with the framed (discrete) system. Various building models are employed to validate the proposed method, demonstrating its applicability to both high-rise and low-rise building configurations. With the results obtained, it is shown that the proposed continuous model can be used not only for high-rise or multistory building models but also for low-rise building models.

First white beam on a von Hámos spectrometer at the PolyX beamline of SOLARIS

Synchrotrons are brilliant sources of X-ray radiation used in a variety of methods to study the structure of matter and dynamics of processes on the atomic scale. X-ray spectroscopy methods at synchrotrons are typically combined with the beam monochromatization which guarantees better energy resolution but also reduces orders of magnitude the photon flux incident on the sample and thus wastes the vast majority of the photons produced. Here we report on the commissioning of an X-ray spectrometer at the PolyX beamline of SOLARIS specialized in application of white, broadband and monochromatic X-ray beam in multimodal microimaging, microtomography and microscpectroscopic studies. The spectrometer was used to acquire good quality Fe K-edge X-ray absorption spectrum over about 120 eV-range within seconds. In this work we present the first X-ray absorption spectrum measured using a synchrotron white beam in combination with a von Hámos geometry-based spectrometer.

A Machine-Vision Approach to Transmission Electron Microscopy Workflows, Results Analysis and Data Management.

Transmission electron microscopy (TEM) enables users to study materials at their fundamental, atomic scale. Complex experiments routinely generate thousands of images with numerous parameters that require time-consuming and complicated analysis. AXON synchronicity is a machine-vision synchronization (MVS) software solution designed to address the pain points inherent to TEM studies. Once installed on the microscope, it enables the continuous synchronization of images and metadata generated by the microscope, detector, and in situ systems during an experiment. This connectivity enables the application of machine-vision algorithms that apply a combination of spatial, beam, and digital corrections to center and track a region of interest within the field of view and provide immediate image stabilization. In addition to the substantial improvement in resolution afforded by such stabilization, metadata synchronization enables the application of computational and image analysis algorithms that calculate variables between images. This calculated metadata can be used to analyze trends or identify key areas of interest within a dataset, leading to new insights and the development of more sophisticated machine-vision capabilities in the future. One such module that builds on this calculated metadata is dose calibration and management. The dose module provides state-of-the-art calibration, tracking, and management of both the electron fluence (e-/Å2·s-1) and cumulative dose (e-/Å2) that is delivered to specific areas of the sample on a pixel-by-pixel basis. This enables a comprehensive overview of the interaction between the electron beam and the sample. Experiment analysis is streamlined through a dedicated analysis software in which datasets consisting of images and corresponding metadata are easily visualized, sorted, filtered, and exported. Combined, these tools facilitate efficient collaborations and experimental analysis, encourage data mining and enhance the microscopy experience.

PAWS and POCO: NIR Astrophotonic Instruments for Astronomy

AbstractFor near‐infrared ground and space‐based astronomy, compact photonic devices can replace the large bulk optical components in spectrographs, frequency combs, beam combiners, and sky subtraction filters, thus saving cost, reducing volume, weight, and power requirements. Photonic integrated circuits (PICs), analogous to integrated circuits (IC) in electronics, are particularly powerful to address innovative miniaturized solutions. Here, we demonstrate two new instrument prototypes: the Potsdam Arrayed Waveguide Spectrograph (PAWS) built around an array waveguide grating (AWG) PIC and Hawaii2RG detector, and the Potsdam Comb (POCO), a frequency comb generated by nonlinear processes in a micro‐ring resonator photonic chip. PAWS is calibrated by the remotely located POCO via the fiber optic communication network of the Leibniz‐Institute for Astrophysics Potsdam (AIP). The vision of future astrophotonic solutions for instrumentation is pointing toward hybrid solutions of PIC and detector arrays that hold the promise to dramatically change the layout of telescope focal plane instrumentation.

Dual-ring parity-time symmetric brillouin fiber laser with an unbalanced polarization Mach-Zehnder interferometer.

A dual-ring parity-time (PT) symmetric Brillouin fiber laser (BFL) with an unbalanced polarization Mach-Zehnder interferometer (UP-MZI) is proposed and experimentally investigated. An UP-MZI consisting of optical coupler, polarization beam combiner (PBC) and two asymmetric length arms with 10 km and 100 m single-mode fiber, is used to achieve Vernier effect and PT symmetry. Due to the orthogonally polarized lights created in the PBC, the dual-ring PT symmetry BFL with an UP-MZI implements two unbalanced length feedback rings that are connected to one another, one long length ring with a Brillouin gain and the other short length ring with a loss of the same magnitude, to break a PT symmetric and maintain the Vernier effect. By contrast with existing PT symmetry BFL studies, this design does not require same lengths of the gain and loss loops, but can manipulate freely PT symmetry status in accordance with a rational scaling factor between them. Experimental results reveal that the 3-dB linewidth of dual-ring PT symmetry BFL with an UP-MZI is about 4.85 Hz with the threshold input power of 9.5 mW, in accordance with the 97 Hz measured linewidth at the -20 dB power point. Within 60 mins of the stability experiment, the power and frequency stability fluctuation are ±0.02 dB and ±0.137 kHz, respectively. Thanks to the two asymmetric ring lengths, the sidemode suppression ratio (SMSR) is optimized by 54 dB compared to that with the only long ring structure, 26 dB when using only the Vernier effect or 12 dB for existing PT symmetry BFL. This BFL design with single longitudinal mode and high SMSR output can be applied to high coherent communication and Brillouin-based microwave photonics systems with low phase noise.

Coupling nonlinearities investigation and dynamic modeling of a tristable combined beam rotational energy harvesting system

Energy harvesting system is regarded as major units in self-powering of massive sensors of Artificial Internet of Things, whose mechanical dynamics play a crucial role in energy conversion efficiency and overall service performance. During rotational motion, periodic disturbances near resonant regions may lead to a large-amplitude oscillation of the harvesters. Due to the coupling effect of rotation and vibration, the distributions of mass and stiffness are related with local deformation and nonlinear rotational frequency in harvesting system, which are yet to be well understood and it is still an open issue. In this paper, a tristable combined beam rotational energy harvester is proposed to obtain higher energy conversion efficiency. Based on the extended Hamilton’s principle, a comprehensive coupling nonlinearities dynamic model is established with consideration of strain distributions, geometric nonlinearity, centrifugal effect, gravitation effect, and nonlinear rotational frequency. The effect of geometric nonlinearity and gravity on the synergistic transition and form mechanism of the tristable harvesting system is explored under the guidance of the static bifurcation, and the influence mechanism of the geometric nonlinearity and nonlinear rotational frequency on the mechanic and energetic characteristics of the system are thoroughly revealed. Numerical and experimental studies are performed to validate the effectiveness of the established model. Results show that geometric nonlinearity and nonlinear rotational frequency lead to a wider frequency bandwidth and a more complex inter-well snap-through motion. Meanwhile, the established model provides a theoretical fundamental framework of high-performance harvester’s design in large-amplitude complex excitation scenarios, which is conducive to control harvester in actual engineering applications.

Symplectic space wave propagation method for forced vibration of acoustic black hole assemblies

Recently, acoustic black holes (ABHs) have been widely used for vibration and noise reduction. Compared with a single ABH, multiple ABHs embedded in a structure can achieve better vibration suppression. However, most of the current research focuses on embedding a single ABH. In this study, a symplectic space wave propagation method was proposed for the forced vibration of ABH assemblies. The governing differential equations based on the Euler-Bernoulli beam model of the ABH beam for vibration were first converted into Hamiltonian canonical equations. A symplectic eigenvalue problem was then formed, and the wave propagation parameters and wave shapes were obtained analytically. A Gaussian-discretization scheme was used to discretize the ABH beam, whereas the proposed method was used to evaluate the wave amplitude at each point. Second, a combination of the ABH beams of various forms was considered, in which the ABH beams are coupled directly or through a joint. A semi-analytical solution for the forced vibration of ABH assemblies was established by satisfying the dynamic coupling between the ABH beams and the joint. Because the proposed method utilizes symplectic analytical solutions of wave modes, its computational efficiency and precision are high.