Beam Transmission Research Articles

Ultra-precision optical processing technology for large-aperture laser optics: Polishing path and technical parameter of arrayed magnetorheological finishing (AMRF)

With the continuous development of high-power laser systems, laser optics gradually changed towards large-aperture, high-quality. To adapt to the fabrication of large-aperture laser optics, a new-type array magnetorheological finishing (AMRF) technique was developed and had made initial progress. However, AMRF technique would introduce more obvious ripple structures (such as 1 mm−1 of spatial frequency) compared to original MRF technique while adopting conventional raster path, and the ripple structures might affect laser beam transmission. For the further application of AMRF technique, the formation mechanism of ripple structures was studied, and a method based on the contour of removal function was proposed to analyze the changes of spatial frequency and evaluate the effect of different polishing paths. According to the analysis method, non-equal-interval parallel raster path was chosen and applied into AMRF process, along with maintaining efficiency while controlling ripple structures. In general, this work could provide a valuable support for the AMRF process of large-aperture laser optics and had a certain significance for the high-power laser system.

Beam Transmission (BTR) Software for Efficient Neutral Beam Injector Design and Tokamak Operation

BTR code (originally—“Beam Transmission and Re-ionization”, 1995) is used for Neutral Beam Injection (NBI) design; it is also applied to the injector system of ITER. In 2008, the BTR model was extended to include the beam interaction with plasmas and direct beam losses in tokamak. For many years, BTR has been widely used for various NBI designs for efficient heating and current drive in nuclear fusion devices for plasma scenario control and diagnostics. BTR analysis is especially important for ‘beam-driven’ fusion devices, such as fusion neutron source (FNS) tokamaks, since their operation depends on a high NBI input in non-inductive current drive and fusion yield. BTR calculates detailed power deposition maps and particle losses with an account of ionized beam fractions and background electromagnetic fields; these results are used for the overall NBI performance analysis. BTR code is open for public usage; it is fully interactive and supplied with an intuitive graphical user interface (GUI). The input configuration is flexibly adapted to any specific NBI geometry. High running speed and full control over the running options allow the user to perform multiple parametric runs on the fly. The paper describes the detailed physics of BTR, numerical methods, graphical user interface, and examples of BTR application. The code is still in evolution; basic support is available to all BTR users.

Vortex Beam Transmission Compensation in Atmospheric Turbulence Using CycleGAN

To improve the robustness of vortex beam transmission and detection in the face of atmospheric turbulence and to guarantee accurate recognition of orbital angular momentum (OAM), we present an end-to-end dynamic compensation technique for vortex beams using an improved cycle-consistent generative adversarial network (CycleGAN). This approach transforms the problem of vortex beam distortion compensation into one of image translation. The Pix2pix and CycleGAN models were extended with a structural similarity loss function to constrain turbulence distortion compensation in luminance, contrast and structure. Experiments were designed to evaluate the compensation performance from subjective and objective indicators. The simulation results demonstrate that the optical OAM intensity map is very similar to that of the target OAM light after compensation. The mean value of structural similarity is close to 1. The recognition accuracy of the OAM is improved by 4.4% compared to no distortion compensation, demonstrating that the improved CycleGAN-based compensation scheme can guarantee excellent detection accuracy without reconstructing the wavefront and saving optical hardware. The method can be implemented in real-time optical communications in atmospheric turbulence environments.

Effect of cooling rate on the composition and chemical heterogeneity of quench-induced grain boundary η-phase precipitates in 7xxx aluminium alloys

The mechanical properties and stress corrosion cracking (SCC) resistance of 7xxx series aluminium alloys are significantly affected by the composition and distribution of precipitates formed during heat treatment. In particular, their quench sensitivity is related to the formation of η-phase precipitates that nucleate heterogeneously on grain boundaries at lower cooling rates after solution treatment, which has been a key factor restricting the gauge of hot rolled plates in the aerospace industry. To better understand the effects of slower cooling rates on the composition of quench-induced grain boundary precipitates (Q-GBPs) found in thick plate 7xxx alloys, plasma focused ion beam and high-resolution scanning transmission electron microscopy were used to obtain accurate composition data. The η-phase Q-GBPs have a complex- branched morphology, which develops higher aspect ratios and secondary arms as the cooling rate is reduced. Only a small change in average composition of Q-GBPs was found with cooling rate; but a large scatter was observed. This is caused by significant Zn/Cu/Al composition gradients developing along their principal growth directions in both AA7050 and AA7085 alloys. This concentration gradient did not reduce significantly after a T76 treatment. Simulations of Q-GBP growth with different cooling rates using a CALPHAD-informed phase-field model, with the η-phase represented by a two-sublattice model, gave results consistent with experimental observations. Chemical gradients were predicted to develop in the Q-GBPs due to the changing local equilibrium at the growth front during the cooling. The influence of this non-homogeneous microchemistry on the SCC behaviour of 7xxx alloys is briefly discussed.

Direct prediction and compensation of atmospheric turbulence for free-space integer and fractional order OAM multiplexed transmission links.

Atmospheric turbulence has an adverse impact on orbital angular momentum (OAM) beam transmission, resulting in power fluctuations and mode crosstalk. These challenges are particularly pronounced in OAM multiplexing links. In this paper, we propose and demonstrate a novel network architecture that integrates convolutional layers and residual structures to address the issue of turbulence phase compensation. By harnessing the local feature learning capability of convolutional layers and the information-preserving function of residual structures, we aim to mitigate the adverse effects of network depth on information loss. By employing the proposed network, we compensate the turbulence phase directly using the received intensity distributions for free space multiplexed integer and fractional order OAM links, respectively. The obtained results show that the received optical power can be improved for more than 10 dB for integer order OAM multiplexed FSO links under weak to strong turbulence conditions, while 9 dB for fractional-order OAM multiplexed FSO links. Moreover, mode crosstalk can be reduced for about 10 dB under 4 OAM modes multiplexed links under turbulence strength D/r0=5. The proposed deep learning based atmospheric turbulence compensation method can predict phase screens rapidly and accurately, thus enhancing the dependability of future OAM multiplexing technology.

Dual-mode vortex beam transmission metasurface antenna based on linear-to-circular polarization converter.

The generation of multi-mode vortex beams at the same aperture is currently emerging as a research hotspot. In this paper, a method based on a linearly polarized-circularly polarized translational transmission metasurface (TM) is proposed to enable a dual-circularly polarized dual-mode vortex beam generation. Through the judicious implementation of an additional rotational phase and the combination of the initial transmission phase, the phases of the left-hand circularly polarized (LHCP) and right-hand circularly polarized (RHCP) waves can be manipulated arbitrarily and independently. Meanwhile, the design of the array phase is utilized for the dual-mode dual-circularly polarized beam generation. Simulation and sample measurements provide validation data for the feasibility of this method, in which the measurement results are in excellent consistency with the simulation ones. This proposed method paves the way toward the enhancement of the channel capacity of mobile communication.

Indoor millimeter wave D2D communication resource optimization based on improved PMVC and CTRA algorithms

In order to improve the quality of millimeter wave communication in indoor environment and ensure the maximum use of link resources. It is proposed to construct indoor communication transmission characteristics through multi sphere link model and indoor millimeter wave reflection blocking model. At the same time, the improved PMVC algorithm and CTRA algorithm are used to optimize the resource scheduling of links in indoor central scenes and edge scenes respectively. The simulation results show that compared with the original PVC algorithm and greedy algorithm, PMVC has a maximum link throughput of 5.01 Gbps under the optimized scheduling of the improved vertex coloring algorithm, while the maximum throughput of the traditional vertex coloring algorithm and greedy algorithm are 4.73 Gbps and 4.57 Gbps respectively. In the case of fixed link transmission beam width, as the number of link flows increases, the slot throughput of the link decreases continuously. Under the width of 30, the maximum slot throughput of PMVC algorithm is 2.75 Gbps, and the maximum slot throughput of greedy algorithm is 2.48 Gbps; When the beam width is 60, the maximum slot throughput of PMVC algorithm and greedy algorithm is 2.25 Gbps and 1.55 Gbps respectively. The proposed PMVC resource scheduling method can effectively alleviate the shortage of indoor spectrum resources and reduce indoor transmission interference of millimeter wave.

A Comprehensive Survey on Transmitting Antenna Systems With Synthesized Beams for Microwave Wireless Power Transmission

A Comprehensive Survey on Transmitting Antenna Systems With Synthesized Beams for Microwave Wireless Power Transmission

Clustering fusion algorithm for selection of historical beam steady-state transmission data in CAFe facility

Accelerator-driven systems (ADS) are promising technologies for nuclear waste transmutation and energy production. The China ADS Front-end Superconducting Demo Linac (CAFe) is a prototype of the China Initiative Accelerator Driven System (CiADS), which aims to verify the feasibility of key technologies of CiADS. In this article, a novel method for historical data screening of the beam transport in the medium energy beam transport (MEBT) section of CAFe is presented. A clustering fusion algorithm based on unsupervised learning and beam transmission characteristics is designed to extract a large number of samples with the beam in steady-state transmission from historical beam data. A deep neural network model was constructed to fit the beam transport characteristics and verify the reliability of the screened data samples. The method can improve the efficiency and accuracy of data analysis and provide valuable insights for the optimization and control of beam transport in CAFe.

The Investigation Optical, X/γ-Rays and Neutrons Shielding Properties of BaO Based on Steel Slag Glass System

For BaO based on steel slag glass system (BaSSG) in chemical composition (50-x)B2O3: 20steel slag: 20Na2O: 10CaO: xBaO (x = 0, 5, 10, 15, 20, 25 wt%) were prepared by melt quenching technique at 1,200 °C and investigated optical, X/γ-rays, fast and thermal neutrons shielding properties. The optical properties were measured and explained on transmission (T%) value. The X/γ-rays shielding properties were experimented with and explained on mass attenuation coefficients (µm ) for X-rays which were measured using a high-frequency digital X-rays machine while γ-rays were measured using the narrow beam transmission method. In addition, half value layer (HVL), mean free path (MFP) and transmission factor (TF) values were evaluated and discussed. Also, fast and thermal neutron shielding properties of BaSSG have been evaluated and discussed. The results found that the BaSSG6 glass sample had the highest T% and µm values, while HVL, MFP and TF were the lowest. These results indicated that the BaSSG6 glass sample offers excellent X/γ-rays and fast neutron shielding compared to other samples. Whereas the BaSSG1 glass sample provided superb thermal neutron shielding. These reflected that the BaSSG glass system had the potential to develop transparent and Pb-free shielding material.

Highly nonlinear tellurite photonic crystal fiber for supercontinuum generation: Design and quantitative performance analysis

This research study proposes a unique photonic crystal fiber (PCF) consisting of a solid core and a hexa-spiral shape, using tellurite as the background material. The proposed PCF exhibits numerous significant optical guiding properties, such as nonlinearity, dispersion, effective index, effective mode area, etc. Simulated findings from COMSOL Multiphysics v5.5 confirm that the PCF can achieve high nonlinearity and zero-dispersion at 1650 nm. The base material is tellurite, which has a significant nonlinear refractive index (RI) of 5.11 × 10−19 m2 W−1. The resultant wave has a bandwidth of 562.65 nm when pumped at a wavelength of 1650 nm. Additionally, a continuum can be produced by pumping at 1500 and 1550 nm. The designed PCF can generate a broad spectrum of supercontinuum with a pulse duration of 200 fs and 10 kW input power. Here is also performed measurements and inspections on the impact of higher-order Taylor series dispersion coefficients, pulse width, input power, etc. The proposed PCF has many potential applications, including nonlinear optics, high dispersion characteristics, infinitely single-mode fibers, high wattage beam transmission, particle trapping, and sensing. To address these applications, here is used COMSOL Multiphysics to generate data, such as propagation constants, attenuations, effective area, and fields, which were used by Optisystem. To the best of our knowledge, this is the first investigation to verify the performance of our designed PCF in Optisystem, for modeling signal transmission for supercontinuum generation and Raman shift.

UAV-Assisted Wideband Terahertz Wireless Communications with Time-Delay Phased UPA under Beam Squint

Future Unmanned Aerial Vehicle (UAV)-assisted wireless communication systems are expected to utilize wide bandwidths available at terahertz (THz) frequencies to enhance system throughput. To compensate for the severe path loss in the THz band, it is essential to have a multitude of antennas in the UAV to generate narrow beams for directional transmission. However, narrow beams severely limit its spatial coverage, which greatly affects the efficiency of large-scale access UAV-assisted THz systems. Moreover, the combination of massive antennas and large bandwidth at THz makes the misalignment of the beams caused by beam squint non-negligible and also high energy consumption. UAV-assisted communication technology can effectively increase spatial coverage and provide reliable LoS communication links. In addition, reducing the number of radio frequency (RF) chains while ensuring the number of transmitted data streams and space division multiplexing capability is also an effective way to reduce energy consumption in the UAV communication. In this paper, a single RF chain uniform planar array (UPA) with true-time-delays (TTDs) is equipped on the UAV to achieve two dimensional (2D) beams and split spatial beams to improve transmission efficiency. We analyze the 2D beam squint of the UPA and design a time-delay phased UPA for UAV-assisted THz communication systems. By introducing TTDs between the single RF chain and phase shifters, the beam squint can be controlled flexibly by introducing the delay between each antenna. When TTDs are arranged in both the horizontal and vertical dimensions, the coverage of the beams becomes more complicated compared to uniform linear arrays (ULA). Simulation results show that the proposed time-delay phased UPA can achieve better performance in both single-beam and multi-beam modes for single user and multi-user scenarios compared with conventional phased UPA, respectively. In addition, we propose frequency division beam multiple access (FDBMA) multi access technology, which achieves more efficient multi access by reusing resources from different frequency beam pairs. Finally, the results also show that the enlargement of the beamwidth through the proposed FDBMA strategy can also increase the performance in multi-user scenarios.

Adapting the Time-Domain Synthetic Aperture Focusing Technique (T-SAFT) to Laser Ultrasonics for Imaging the Subsurface Defects.

Traditional ultrasonic testing uses a single probe or phased array probe to investigate and visualize defects by adapting certain imaging algorithms. The time-domain synthetic aperture focusing technique (T-SAFT) is an imaging algorithm that employs a single probe to scan along the test specimen in various positions, to generate inspection images with better resolution. Both the T-SAFT and phased array probes are contact methods with limited bandwidth. This work aims to combine the advantages of the T-SAFT and phased array in a noncontact way with the aid of laser ultrasonics. Here, a pulsed laser beam is employed to generate ultrasonic waves in both thermoelastic and ablation regimes, whereas the laser Doppler vibrometer is used to acquire the generated signals. These two lasers are focused on the test specimen and, to avoid the plasma and crater influence in the ablation regime, the transmission beam and reception beam are separated by 5 mm. By moving the test specimen with a step size of 0.5 mm, a 1D linear phased array (41 and 43 elements) with a pitch of 0.5 mm was synthesized, and three side-drilled holes (Ø 8 mm-thermoelastic regime, Ø 10 mm and Ø 2 mm-ablation regime) were introduced for inspection. The A-scan data obtained from these elements were processed via the T-SAFT algorithm to generate the inspection images in various grid sizes. The results showed that the defect reflections obtained in the ablation regime have better visibility than those from the thermoelastic regime. This is due to the high-amplitude signals obtained in the ablation regime, which pave the way for enhancing the pixel intensity of each grid. Moreover, the separation distance (5 mm) does not have any significant effect on the defect location during the reconstruction process.

A combined periodic acoustic black hole beams with wide vibration attenuation bands

An acoustic black hole (ABH) structure has a gradual impedance gradient due to the thickness of the section decreasing as a power law, which shows excellent wave gathering and energy dissipation effect. To enhance the vibration suppression ability, periodic ABHs are proposed recently. A virtual spring-energy method (VEM) is adopted to handle the periodic boundary condition of periodic ABHs. The accuracy of the method is verified through the finite element method. The band gap of infinite periodic ABH beam and vibration transmission of finite periodic ABH beam are analyzed. For finite periodic ABH beams, the size of cells affects the attenuation band of vibration transmission, and the number of cells affects the amplitude. There is a linear superposition characteristic between the attenuation amplitude and the number of cells. The effect of damping layer on beams with different cross sections is also discussed. Finally, a combined ABH beam with damping layers of different cell sizes is proposed to achieve wide transmission attenuation bands.

2.2 kW single-mode narrow-linewidth laser delivery through a hollow-core fiber

Antiresonant hollow-core fibers (AR-HCFs) have opened up exciting possibilities for high-energy and high-power laser delivery because of their exceptionally low nonlinearities and high damage thresholds. While these fiber designs offer great potential for handling kilowatt-class powers, it is crucial to investigate their performance at multi-kW power levels. Until now, transmission of narrow-linewidth single-mode lasers at multi-kW power levels through a HCF has not been demonstrated, to our knowledge. Here, we present the delivery of a record 2.2 kW laser power with an input spectral linewidth of 86 GHz, centered at 1080 nm, while maintaining 95% transmission efficiency and beam quality (M2) of 1.03. This was achieved via a 104.5 m single-mode five-tube nested AR-HCF with 0.79 dB/km loss. Furthermore, we show power delivery of 1.7 kW with a spectral linewidth as narrow as 38 GHz through the same fiber. Our results could lead to a new generation of fiber-based laser beam delivery systems with applications in precision machining, nonlinear science, directed energy, and power beaming over fiber.

Lead-free bismuth glass system towards eco-friendly radiation shielding applications

In this study, the gamma-ray photon, electron, proton, helium ion, carbon ion, thermal neutron, and fast neutron interaction parameters of the (70-x)(Bi2O3 + ZnO) + x(V2O5 + TeO2) + 20B2O3 + 6.5SiO2 + 2.5Al2O3 + 1(CeO2 + Sb2O3) glass system were estimated with the aim of assessing their radiation shielding potentials. The mass attenuation coefficients (MACs) of the glasses were estimated for photon energies between 0.015 and 15 MeV using the PHITS simulation code and XCOM software. The stopping powers of charged radiation such as electrons, protons, α-particles, and carbon ions were also estimated by Monte Carlo simulation of particle transport using PHITS. The narrow beam transmission simulated using PHITS yielded values of MAC that were not so different from those from XCOM. The MACs of B/V-ZBVSA1 vary from 0.039–90.747 cm2/g, while those of B/V-ZBVSA2, B/V-ZBVSA3, and B/V-ZBVSA4 vary from 0.035–69.724, 0.036–73.088, and 0.037–70.597 cm2/g, respectively. The HVL of the glasses varied from 0.011–2.56 cm, 0.019–3.69 cm, 0.017–3.31 cm, and 0.017–3.36 cm for B/V-ZBVSA1 – B/V-ZBVSA4, respectively The effective atomic number varied within the limits: 28.36–76.06, 19.67–67.91, 22.14–68.70, and 22.39–68.08 for BV-ZBVSA1 – BV-ZBVSA4, respectively. The stopping powers (Sp) of electrons in BV-ZBVSA1, BV-ZBVSA2, BV-ZBVSA3, and BV-ZBVSA4 were in the range 1.219–8.043 MeVcm2/g, 1.295–9.306 MeVcm2/g, 1.264–8.859 MeVcm2/g, and 1.257–8.793 MeVcm2/g correspondingly. Comparatively, the Sp of protons, α-radiation, and carbon ions follows the order: BV-ZBVSA2 > BV-ZBVSA3 > BV-ZBVSA4 > BV-ZBVSA1. Also, the value of ΣR for BV-ZBVSA1, BV-ZBVSA2, BV-ZBVSA3, and BV-ZBVSA4 was 0.1171, 0.1126, 0.1133, and 0.1103 cm−1 accordingly, while the corresponding total cross-section of thermal neutrons was 67.6227, 46.8356, 59.1179, and 56.6994 cm−1. The present glasses showed superiority in absorbing photons and neutrons compared to some existing shields and previously recommended glasses. The present glassy samples, thus, can be adopted for radiation protection purposes, among others in radiation facilities.

Measurement device-independent quantum key distribution with vector vortex modes under diverse weather conditions

Most quantum key distribution schemes exploiting orbital angular momentum-carrying optical beams are based on conventional set-ups, opening up the possibility of detector side-channel attacks. These optical beams also suffer from spatial aberrations due to atmospheric turbulence and unfavorable weather conditions. Consequently, we introduce a measurement device-independent quantum key distribution implemented with vector vortex modes. We study the transmission of vector vortex and scalar beams through a turbulent atmospheric link under diverse weather conditions such as rain or haze. We demonstrate that a maximum secure key transmission distance of 178 km can be achieved under clear conditions by utilizing the vector vortex beams, which have been mainly ignored in the literature. When raindrops have a diameter of 6 mm and fog particles have a radius of 0.5 upmum, the signals can reach 152 km and 160 km, respectively. Since these distances are comparable, this work sheds light into the feasibility of implementing measurement device-independent quantum key distribution using vector vortex modes under diverse weather conditions. Most significantly, this opens the door to practical secure quantum communications.

Design and Waveguide Measurement of 2-Bit Reconfigurable Amplification Metasurface Cell

This letter presents a novel 2-bit amplification metasurface cell (APMC) for nonreciprocal reflection of linearly polarized EM waves into high-intensity orthogonal waves. The 2-bit APMC consists of four parts, a reconfigurable receiving patch, a reconfigurable phase shifter, a power amplifier circuit, and a reradiating patch. By tuning the bias voltage of the p-i-n diodes mounted on the receiving patch and the phase shifter, the APMC could manipulate reflected waves with four discrete phase states. A power amplifier is placed between the receiving patch and the phase shifter to increase the energy intensity of the reflected wave. In addition, an orthomode transducer (OMT) waveguide is designed and fabricated for measurement of the performance of the 2-bit APMC. From the measurement results, the maximum phase variation of the APMC is less than 25.5°, and the saturation reflected power is 27dBm, indicating good phase stability and high energy transfer capability. The proposed APMC could be used as a metasurface unit cell to provide arbitrary microwave beams for wireless power transmission.

Microstructural study on the effect of thermo-physical properties for plasma sprayed Ni and Ni[sbnd]20Cr splats formed on Cu substrates

Ni and Ni20Cr powder particles were air plasma sprayed onto polished copper substrates to gain insight into the flattening behaviour of both Ni and Ni20Cr particles (splats) formed on a relatively low melting point material (i.e. copper) substrate. The extent of any interfacial bonding, along with any splat-substrate intermixing derived from the different thermo-physical properties of the sprayed particles were characterised. The plan-view features of the splats were captured using scanning electron microscopy (SEM), while splat-substrate interfacial properties were examined using focused ion beam microscopy (FIB) and transmission electron microscopy (TEM). The chemical characteristics of the splat and substrate were analyzed using energy-dispersive X-ray spectroscopy (EDS). The addition of ∼20 wt% chromium to Ni (i.e the Ni20Cr particles) was observed to significantly influence the spreading behaviour of the particles on impact with the substrate, both the extent of any splat splashing and the splat flattening ratio, as well as the microstructure of the splat-substrate interface, including the degree of substrate melting and the likelihood of material from the substrate jetting into the body of the splat. The evidence of intermixing between the splat and the copper substrate for both feedstocks is an intriguing feature of this study. The presence of a thermodynamically formed copper oxide layer during substrate preheating also influenced both the splat formation behaviour and substrate melting as observed by both microstructural examination and investigation through numerical models.

Intensity correlation properties of x-ray beams split with Laue diffraction

Beam splitting is one of the main approaches to achieving x-ray ghost imaging, and the intensity correlation between diffraction beam and transmission beam will directly affect the imaging quality. In this paper, we investigate the intensity correlation between the split x-ray beams by Laue diffraction of stress-free crystal. The analysis based on the dynamical theory of x-ray diffraction indicates that the spatial resolution of diffraction image and transmission image are reduced due to the position shift of the exit beam. In the experimental setup, a stress-free crystal with a thickness of hundred-micrometers-level is used for beam splitting. The crystal is in a non-dispersive configuration equipped with a double-crystal monochromator to ensure that the dimension of the diffraction beam and transmission beam are consistent. A correlation coefficient of 0.92 is achieved experimentally and the high signal-to-noise ratio of the x-ray ghost imaging is anticipated. Results of this paper demonstrate that the developed beam splitter of Laue crystal has the potential in the efficient data acquisition of x-ray ghost imaging.