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A cost-effective stereolithography for medium-scale components is developed to fabricate 3D components with high build speed and resolution from photo-curable resin. The developed SLA utilizes a focused light beam of wavelength range (300 nm–700 nm) coming from the DLP projector and passes through the objective lens and finally imposed on the platform containing a layer of photo-curable resin. After focusing the light beam on the liquid resin layer, the photo-polymerization reaction occurs and the liquid resin becomes solid. Thus, the 3D object is fabricated layer by layer curing of liquid resin. The photopolymer used in this experimentation is polyethylene glycol di-acrylate and Irgacure 784 as photo-initiator. The Creo 3.0 software is used for modelling of 3D objects. A special MATLAB code is developed for slicing of the 3D model and displaying the sliced image one by one through DLP projector. The Arduino microcontroller with stepper motor and ball screw is used to control the motion of Z-stage platform. The Creation workshop software is also used to control motion of the Z-stage and period to display the sliced images through DLP projector. The medium-scale 3D objects with rectangular, square, and circular cross-sections are obtained by curing the aforementioned photo-curable resin. It is observed that the 3D objects are best cured for two seconds curing time with 0.1 mm curing depth along Z-axis.

In this research, a free rotation and distortion projector doublet electromagnetic lens was designed by computer-aided using electron optical design (EOD) program. This lens consists of two identical lenses. This lens's focal and projector characteristics were calculated in the two max magnification regions by changing the axial magnetic flux density in one of the two single lenses by changing its axial bore diameter. The results showed the possibility of obtaining a free rotation and distortion projector doublet electromagnetic lens in the first max magnification regions, and it has the min magnitude for the projector focal length.

Two dimensional (2D) Photonic crystals (PhCs) based cross waveguide structure (CWs) consisting of resonant cavity is investigated in this paper. Investigations are done using Two Dimensional Finite Difference Time Domain (2DFDTD) method. Transmission characteristics have been obtained for different radii of central rod placed at crossing point of two waveguides and number of regular rods surrounding central rod. Nonlinear behavior is also studied for different operating wavelengths.

Reliable spatially resolved compositional analysis through atom probe tomography requires an accurate placement of the detected ions within the three-dimensional reconstruction. Unfortunately, for heterogeneous systems, traditional reconstruction protocols are prone to position some ions incorrectly. This stems from the use of simplified projection laws which treat the emitter apex as a spherical cap, although the actual shape may be far more complex. For instance, sampled materials with compositional heterogeneities are known to develop local variations in curvature across the emitter due to their material phase specific evaporation fields. This work provides three pivotal precursors to improve the spatial accuracy of the reconstructed volume in such cases. First, we show scanning probe microscopy enables the determination of the local curvature of heterogeneous emitters, thus providing the essential information for a more advanced reconstruction considering the actual shape. Second, we demonstrate the cyclability between scanning probe characterization and atom probe analysis. This is a key ingredient of more advanced reconstruction protocols whereby the characterization of the emitter topography is executed at multiple stages of the atom probe analysis. Third, we show advances in the development of an electrostatically driven reconstruction protocol which are expected to enable reconstruction based on experimental tip shapes.

Tunable lens technology inspired by the human eye has opened a new paradigm of smart optical devices for a variety of applications due to unique characteristics such as lightweight, low cost, and facile fabrication over conventional lens assemblies. The fast-growing demands for tunable optical lenses in consumer electronics, medical diagnostics, and optical communications require the lens to have a large focal length modulation range and high compactness. Herein, for the first time, an all-solid tunable soft lens driven by highly transparent dielectric elastomer actuators (DEAs) based on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and waterborne polyurethane (PEDOT:PSS/WPU) transparent electrodes is developed. The deformation of the tunable soft lens is achieved by the actuation of DEAs, mimicking the change of the surface profile of the human eye to achieve remarkable focal length variations. Upon electrical activation, this tunable soft lens can vary its original focal length by 209%, which is one of the highest among current tunable soft lenses and far beyond that of the human eye. This study demonstrates that transparent DEAs are capable of achieving focus-variation functions, and potentially useful in artificial robotic vision, visual prostheses, and adjustable glasses, which will induce significant effects on the future development of tunable optics.

A line laser with high power as the background light source for the design of a new photoelectric detection target is proposed in this paper, aiming to improve the detection ability of the traditional photoelectric detection target under low background illumination. The laser emitted pulse waveform function and the laser echo pulse response function were used to establish the mathematical model of the reflected echo power of projectile in the detection area and derive the calculation function of minimum detectable echo power in the line laser detection screen, according to information of the line laser emitted power, incident angle of projectile, duration time and detection distance of projectile passing through the line laser detection screen. Calculations and experimental results showed that the design method of line laser detection screen and calculation model of laser echo power are reasonable, and the detection ability of line laser detection screen is obviously higher than that of traditional photoelectric detection screen, especially in low background illumination; at the same time, the designed line laser detection screen was used to combine a six line laser detection screen intersection test system, based on live ammunition for shooting. The test system is stable and able to obtain the dynamic parameters of the flying projectile, verifying that the design of the line laser detection screen in new photoelectric detection target can be suitable for shooting range test applications.

The influence of neutron and gamma radiation on single mode fiber cables is experimentally conducted. Attenuation due to incident radiation is measured. Attenuation is determined by laser source and power meter in Africa Teleco Company, besides attenuation recovery is attained. The Gamma experiment is carried out within Egypt Mega Gamma1 in National Center for Radiation Research and Technology of Egyptian Atomic Energy Authority (EAEA). In this experiment, the cable is degraded by gamma radiation of doses 5KGy, 10KGy, 15KGy and 25KGy and dose rate of 1KGy/26.4 min. However the attenuation based on neutron degradation is executed in the second Egyptian Training Research Reactor (ETRR-2), in front of neutron beam facility (NBF) in ETRR-2 which has a flux of 1.5x107(n/cm2.sec). For both experiments, the experimental measurements are done at two different spectral wavelengths of 1310 nm and 1550 nm. A comparison between obtained results is investigated.

Photovoltaic (PV) system's performance is significantly affected by its orientation and tilt angle. Experimental investigation (indoor and outdoor) has been carried out to trace the variation in PV performance and electrical parameters at varying tilt angles in Malaysian conditions. There were two experimental modus: 1) varying module tilt under constant irradiation level, 2) varying irradiation intensity at the optimum tilt set up. For the former scheme, the irradiation level was maintained at 750 W/m2, and for the later arrangement, the module tilt angle was varied from 0o to 80o by means of a single-axis tracker. Results show that under constant irradiation of 750 W/m2, every 5o increase in tilt angle causes a power drop of 2.09 W at indoor and 3.45 W at outdoor. In contrast, for the same condition, efficiency decreases by 0.54% for indoor case and by 0.76% at outdoor. On the other hand, for every 100 W/m2 increase in irradiation, solar cell temperature rises by 7.52°C at indoor and by 5.67°C at outdoor. As of module electrical parameters, open-circuit voltage, short-circuit current, maximum power point voltage and maximum power point current drops substantially with increasing tilt angle, whereas fill factor drops rather gradually. Outdoor experimental investigation confirms that the optimum tilt angle at Malaysian conditions is 15o and orienting a PV module this angle will maximize the sun's energy captured and thereby enhance its performance.

This chapter gives a complete but concise introduction to electron cryomicroscopy. The theoretical and practical background is discussed together with a review of applications to the three-dimensional structural analysis of biological macromolecules or macromolecular assemblies. It includes basic descriptions of how to analyse the structures of molecules arranged in the form of two-dimensional crystals, helical arrays or as single particles with or without symmetry. The chapter concludes by anticipating trends towards increased automation, development of better electronic cameras and increasing use of electron tomography for analysis of cell structure. Keywords: cryoTEM; electron cryomicroscopy; electron microscopy; electron scattering; helical particles; icosahedral particles; image processing in cryoTEM; phasing; radiation damage; three-dimensional image reconstruction; two-dimensional crystals

Optical coherence tomography (OCT) is a novel imaging modality that provides volumetric in-vivo high-resolution (1-15μm) images in real-time. Multi-channel OCT (MOCT) imaging utilizes many imaging channels simultaneously yielding several advantages over single-channel OCT. The benefits of MOCT are at the cost of the added requirement of several imaging beams, which demands high power output from the laser source. Dual-core Ytterbium (Yb) doped fiber was used in two configurations to demonstrate its use as a MOCT light source gain medium: 1) within a ring cavity resonator and 2) in a post-amplification regime with a low powered seed-laser. The amplification wavelength range was tailored to be centered at ~1060nm, where light absorption and scattering is at a minimum in water. In the post-amplification configuration, the output power was increased from 5mW to >200mW, with the axial resolution reducing from 10μm to 12μm. We also present initial in-vivo MOCT imaging of a tadpole.

We show theoretically and experimentally how a flat-top second-order response can be achieved with a self-coupled single add-drop ring resonator based on two couplers with different splitting ratios. The resulting device is a 1x1 filter, reflecting light back in the input waveguide at resonating wavelengths in the passbands, and transmitting light in the output waveguide at all other non-resonating wavelengths. Different implementations of the filter have been designed and fabricated on a micron-scale silicon photonics platform. They are based on compact Euler bends - either U-bends or L-bends - and Multi-Mode Interferometers as splitters for the ring resonators. Different finesse values have been achieved by using either 50:50 MMIs in conjunction with 85:15 MMIs or 85:15 MMIs in conjunction with 95:05 double MMIs. Unlike ordinary lowest order directional couplers, the MMIs couple most of the power in the cross-port which make them particularly suitable for the topology of the self-coupled ring, which would otherwise require a waveguide crossing. Experimental results are presented, showing good agreement with simulations. The proposed devices can find applications as wavelength-selective reflectors for relatively broad-band lasers or used as 2x2 add-drop filters when two exact replicas of the device are placed on the arms of a Mach-Zehnder interferometer., 9 pages, 17 references, 12 figures

Fiber Optic Network is an advanced and modern system technology, which is used in sending pulses of laser light inside a glass of fiber over long distances, widely used in every environment with various sorts of applications in a different field. It is well-known that the main material of fiber optics is glass, therefore it is typical that the temperature can affect the glass during the thermal expansion. This effect will be applied to the properties of the optical components such as refractive index, radius curvature of the fiber optics layers, and also there is an effect on the data transfer through the fiber optics network units. In this paper, the effect of temperature degree on the optical signal and the functions of the fiber optic network will be simulated, measured, and analyzed. The result will be discussed and the conclusion will show the serious points of thermal effects on the optical signal of a fiber-optic network.

A new kind of metamaterial (MTM) leaky wave antenna (LWA) integrated with a super-regenerative oscillator (SRO) architecture is proposed for the first time. As a proof of concept, the proposed radar sensor, including a one-dimensional (1D) MTM LWA and a tunable voltage-controlled oscillator (VCO), is designed to perform frequency-dependent space mapping with the main-beam angle sweeping from −50 $^\circ $ to +30 $^\circ $ with respect to the varying frequency from 1.85 to 2.85 GHz. The proposed SRO-integrated MTM LWA system is operated in the logarithmic mode with a quench signal imposed at the drain port of transistor. Experiments have been conducted to show that vital sign information for two human targets can be successfully detected when they are located along different scanning angles of −10 $^\circ $ and −30 $^\circ $ , respectively. Furthermore, compared with MTM LWA radar sensor based on the self-injection-locked (SIL) architecture, vibrating motion at a farther distance can be detected accurately using the proposed radar sensor, indicating a higher sensitivity with reduced system complexity.

In this paper, we present the design, development, and characteristics of the novel aerosol mass spectrometer ERICA (ERC Instrument for Chemical composition of Aerosols; ERC – European Research Council) and selected results from the first airborne field deployment. The instrument combines two well-established methods of real-time in situ measurements of fine particle chemical composition. The first method is the laser desorption and ionization technique, or laser ablation technique, for single-particle mass spectrometry (here with a frequency-quadrupled Nd:YAG laser at λ = 266 nm). The second method is a combination of thermal particle desorption, also called flash vaporization, and electron impact ionization (like the Aerodyne aerosol mass spectrometer). The same aerosol sample flow is analyzed using both methods simultaneously, each using time-of-flight mass spectrometry. By means of the laser ablation, single particles are qualitatively analyzed (including the refractory components), while the flash vaporization and electron impact ionization technique provides quantitative information on the non-refractory components (i.e., particulate sulfate, nitrate, ammonia, organics, and chloride) of small particle ensembles. These techniques are implemented in two consecutive instrument stages within a common sample inlet and a common vacuum chamber. At its front end, the sample air containing the aerosol particles is continuously injected via an aerodynamic lens. All particles which are not ablated by the Nd:YAG laser in the first instrument stage continue their flight until they reach the second instrument stage and impact on the vaporizer surface (operated at 600 ∘C). The ERICA is capable of detecting single particles with vacuum aerodynamic diameters (dva) between ∼ 180 and 3170 nm (d50 cutoff). The chemical characterization of single particles is achieved by recording cations and anions with a bipolar time-of-flight mass spectrometer. For the measurement of non-refractory components, the particle size range extends from approximately 120 to 3500 nm (d50 cutoff; dva), and the cations are detected with a time-of-flight mass spectrometer. The compact dimensions of the instrument are such that the ERICA can be deployed on aircraft, at ground stations, or in mobile laboratories. To characterize the focused detection lasers, the ablation laser, and the particle beam, comprehensive laboratory experiments were conducted. During its first deployments the instrument was fully automated and operated during 11 research flights on the Russian high-altitude research aircraft M-55 Geophysica from ground pressure and temperature to 20 km altitude at 55 hPa and ambient temperatures as low as −86 ∘C. In this paper, we show that the ERICA is capable of measuring reliably under such conditions.

Here, we report measurements made with an external vibration-insensitive single-shot interferometer, which is applicable for on-machine measurement. Previously, we developed a simple single-shot interferometry method in which the optical intensities of interference fringes appear not as sinusoidal distributions but have a sawtooth-like distribution, and the peak distortion direction depicts the slope of the measured surfaces. These properties allow use of this method in vibration-insensitive interferometry. In this study, we have experimentally confirmed this concept through measurement of a quarter of a Si wafer specimen 50 mm in diameter. The vibration source was a motorized linear stage the surface of which fluctuated between ±400 nm in height. The obtained surface profiles of the Si wafer were consistent with measurements made with a commercial interferometer within 30 nm.

Intentional electromagnetic interference is a serious threat to the safety of electronic devices. Multiple electromagnetic pulses will be coupled and transmitted to electronic devices through the cables. Accumulative effects are generated, which make it easier for damage to occur in the electronic devices. In this article, the working principle of micro-silicon acceleration sensors is introduced. The accumulative effects of multiple pulses on acceleration sensors is studied by a large number of injection experiments. The accumulation trends of multiple pulses with different pulse numbers and intervals are analyzed. The damaged structures inside abnormal sensor amplifiers were observed via optical microscopy and scanning electron microscopy. The experimental results show that the accumulative effect is strengthened with increased pulse number or decreased pulse interval, and the threshold voltage for multiple pulses on the acceleration sensor decreases. The threshold voltage for a single pulse is 321.57 V. When the pulse interval is 1 μs and the pulse number is 5, the threshold voltage for multiple pulses is 163.42 V, which is reduced by 49.12% compared with a single pulse. These results provide a reference for the damage design of electromagnetic pulse weapons.

The rapid detection of microparticles exhibits a broad range of applications in the field of science and technology. The proposed method differentiates and identifies the 2 µm and 5 µm sized particles using a laser light scattering. The detection method is based on measuring forward light scattering from the particles and then classifying the acquired data using support vector machines. The device is composed of a microfluidic chip linked with photosensors and a laser device using optical fiber. Connecting the photosensors and laser device using optical fibers makes the device more diminutive in size and portable. The prepared sample containing microspheres was passed through the channel, and the surrounding photosensors measured the scattered light. The time-domain features were evaluated from the acquired scattered light, and then the SVM classifier was trained to distinguish the particle's data. The real-time detection of the particles was performed with an overall classification accuracy of 96.06%. The optimum conditions were evaluated to detect the particles with a minimum concentration of 0.2 µg/mL. The developed system is anticipated to be helpful in developing rapid testing devices for detecting pathogens ranging between 2 µm to 10 µm.

In this paper, a compact and low-profile beam steering circularly polarized folded reflectarray antenna (CPFRA) with low scan loss for wide-angle coverage is proposed and designed. In order to obtain lower scan loss over a wider beam coverage range (BCR), a multibeam optimization method considering the illumination weighting factor is introduced to obtain minimum phase errors for the designed beam direction. To improve antenna compactness and alleviate the mutual couplings among multiple feeding sources, small-size substrate integrated waveguide (SIW) cavity-backed slot antennas are employed as the feeding sources, which are integrated with the single-layer reflector board. An incident angle insensitive circular polarizer is designed and integrated over the antenna aperture to achieve circularly polarized (CP) radiation over a wide BCR. At last, a 15-beam CPFRA working at Ka-band, with size 140 mm × 140 mm is designed, manufactured, and measured to validate the proposed design method. Measurement results show that the designed CPFRA can achieve a rather flat gain, with only a 2.1 dB scan loss, across the wide 3-dB BCR of ±29°. The good CP beams are formed over the entire coverage range without any blind zone. With the advantages of wide-angle coverage, low scan loss, and high integration, the proposed beam steering antenna is promising in applications such as 5G communication, radar imaging, and target recognition.

This paper reports the control method for the core power of the China initiative Accelerator Driven System (CiADS) facility. In the CiADS facility, an intense external neutron source provided by a proton accelerator coupled to a spallation target is used to drive a sub-critical reactor. Without any control rod inside the sub-critical reactor, the core power is controlled by adjusting the proton beam intensity. In order to continuously change the beam intensity, an adjustable aperture is considered to be used at the Low Energy Beam Transport (LEBT) line of the accelerator. The aperture size is adjusted based on the Proportional Integral Derivative (PID) controllers, by comparing either the setting beam intensity or the setting core power with the measured value. To evaluate the proposed control method, a CiADS core model is built based on the point reactor kinetics model with six delayed neutron groups. The simulations based on the CiADS core model have indicated that the core power can be controlled stably by adjusting the aperture size. The response time in the adjustment of the core power depends mainly on the adjustment time of the beam intensity.

In this communication, a low-profile circularly polarized (CP) staircase curl antenna array with 2:1 impedance bandwidth and 50% axial ratio bandwidth is proposed for 5G millimeter-wave (mmW) communications. It overcomes a vital drawback of complex multi-layer structure of the wideband CP antenna array. By fully taking advantage of 3D staircase layout, the curl element achieves 2:1 impedance bandwidth, 57.9% axial ratio (AR) bandwidth, and a maximum gain of 7.4 dBic. Accordingly, benefiting from the tapered matching transformer, a singlelayer full-corporate microstrip feeding network with 111.4% impedance bandwidth is constructed. For demonstration, an 8 × 8 staircase curl antenna array is designed on three-layer PCB laminates. The proposed antenna array is measured with impedance bandwidth of 76.9% (20.0-45.0 GHz), AR bandwidth of 53.6% (23.1-40.0 GHz), demonstrating a promising candidate to be used in 5G mmW communications.

A liquid crystal-based beam-steering leaky-wave holographic antenna is designed with decoupling structure. Since the distance between elements in holographic antennas is inevitably small (< λ /5), the mutual coupling is strong and should be compensated for the accurate implementation of the excitation amplitude and phase of each element. The performance degradation of a holographic antenna due to mutual coupling is estimated and a decoupling structure is proposed, fabricated, and inserted into the designed antenna. The operating principle of the decoupling structure is explained with circuit model and the simulation confirms the enhanced gain and sidelobe performance when steered from -60° to 60° in 20° intervals. Compared to the antenna without the decoupling structure, the maximum improvement of the gain and the sidelobe level are 3.93 dB and 7.7 dB, respectively, in the simulation. The experimental results are consistent with the simulation results.

Uniquely capable of simultaneous imaging of the hemoglobin concentration, blood oxygenation, and flow speed at the microvascular level in vivo, multi-parametric photoacoustic microscopy (PAM) has shown considerable impact in biomedicine. However, the multi-parametric PAM acquisition requires dense sampling and thus a high laser pulse repetition rate (up to MHz), which sets a strict limit on the applicable pulse energy due to safety considerations. A similar limitation is shared by high-speed PAM, which also uses lasers with high pulse repetition rates. To achieve high quantitative accuracy besides good structural visualization at low levels of laser fluence in PAM, we have developed a new, sparse coding-based two-step denoising technique. In the setting of intravital brain imaging, we demonstrated that this unsupervised learning approach enabled the reduction of the laser fluence in PAM by 5 times without compromise of the image quality (structural similarity index measure or SSIM: >0.92) and the quantitative accuracy (errors

A wideband omnidirectional circularly polarized (CP) antenna using a conformal artificial anisotropic polarizer is proposed for millimeter-wave applications. The antenna consists of three parts: an omnidirectional linearly polarized (LP) radiator, an annular hyperbolic lens, and a conformal anisotropic polarizer. The annular hyperbolic lens regulates the spherical wavefront from the LP radiator into a cylindrical shape prior to propagating into the conformal artificial anisotropic polarizer. Each curved slab of the polarizer is conformally tilted 45 degrees to the incident electric field. Therefore, the conformal polarizer is the three-dimensionalization of the two-dimensional planar artificial anisotropic polarizer. The polarizer designing methodology is the first of its kind to generate wideband CP wave omnidirectionally. The hyperbolic lens and the conformal polarizer are fabricated together using stereolithography (SLA) 3D printing technology. Measurement results show that the antenna has a wide operating bandwidth of 45% (from 24 to 38 GHz), which completely covers potential 5G 28-GHz spectra. The proposed design has a low fabrication complexity and brings possibilities for high-speed wireless communications utilizing circular polarization.

This paper presents a high-gain slotted ridge waveguide array antenna (SRWAA) with inductive diaphragms, which can realize a wide-sector beam with a low sidelobe simultaneously. The proposed antenna can cover a wide detection range and avoid interference from other directions. The expected excitation distribution for the antenna array is extracted through a beamforming method. To reduce the influence of the dispersion phenomenon on signal quality, inductive diaphragms are inserted into the sidewall of the ridge waveguide, which is fully analyzed from the point of the equivalent circuit. A cut-off-mode power divider is utilized, which can control the power ratio flexibly. A SRWAA working at 24.125 GHz, including a six-way feeding network, and a 6×24 slot array with the size of 330 mm × 66.8 mm is designed and fabricated. The measured sidelobe level (SLL) and half-power beamwidth (HPBW) in the elevation plane are -19.6 dB and 54.41°, with the counterparts in the azimuth plane -29.8 dB and 3.15°, respectively. The measured peak gain is 22.3 dBi at 24.125 GHz. The measured results are in good agreement with the simulated ones. This work has the potential to be applied in air detection, anti-unmanned aerial vehicles (UAVs), meteorological radar, and imaging radar.

We treat whistler mode radiation from a dipole antenna in a cold magnetized plasma based on the Fresnel zone construction theory. Radiated waves from the antenna with different propagation directions interfere in space. Regions of enhanced waves are formed when the interference is predominantly constructive at the observing point. The coherently enhanced wave propagates at the group velocity. If the antenna is perpendicular to the background magnetic field, the regions of strong waves form two back-to-back Fresnel zones that are parabolic-shaped cones along the background magnetic field from the antenna. The power within each cone drops with distance at a rate of 1/r much more slowly than the 1/r2 thinning of a spherical wave as in vacuum. The total radiation can be approximately derived by the total energy flux integrated over the Fresnel zone. The derived radiation resistance is much greater than that in vacuum. It is proportional to frequency as 1/f2 and proportional to the antenna length as d2. To radiate more power a longer antenna is preferred, a result that is opposite to some previous theoretical studies.

This paper proposes a design of waveguide slot arrays with asymmetric Iris to achieve broadband properties with high polarization isolation for E-band wireless backhaul systems. The proposed subarray of 2 × 2 radiating slots is excited by two-layered feeding networks carrying two orthogonal waves, and the asymmetric Iris is inserted at the intersection where the waves merge. For verification, a prototype with 16 × 16 radiating slots is fabricated, and its antenna characteristics are measured in an anechoic chamber. The fabricated antenna has a bandwidth of 13 GHz at Port 1 and 10.5 GHz at Port 2 for VSWR ≤ 2.6, and the isolation between two ports is greater than 30 dB within the target frequency bands. The average bore-sight gains of the two ports are 30.85 dBi and 31.67 dBi, and the half-power beam widths are 3.5° and 3.25°. We also fabricate another prototype with 64 × 64 radiating slots for a field test. The proposed prototype is capable of maintaining the received power to be greater than 15 dB for an effective isotropic radiated power of 40.7 dBm at 25 m, which demonstrates that the proposed antenna is suitable to replace current parabolic dish antennas with a reduced profile.

Type II fiber Bragg gratings (FBGs) inscribed with femtosecond (fs) laser possess significant potential for high temperature sensing. In this work, we propose and demonstrate a method for fabricating a parallel-integrated ultra-short type II FBG (PI-US-FBG) by using an fs laser point-by-point technology. The PI-US-FBG, featuring by an ultra-short grating length of 80 m, consists of six identical FBGs parallel-inscribed into a fiber core at different radial positions in the same cross section. The fabricated PI-US-FBG exhibits a broadband Gaussian-shape spectrum with a low reflectivity of ~10%, an ultra-low out-of-band insertion loss of 0.01 dB, and a large full width at half maximum bandwidth of 9.4 nm. Moreover, this PI-US-FBG could be used as a high temperature sensor with a wide measurement range from 25 to 1000 C, and an excellent linearity was achieved with a dual-wavelength differential detection. The temperature sensitivity could be increased from 0.00316 to 0.00945 (dB/C) by enlarging the wavelength spacing of the tunable laser. In addition, two cascaded PI-US-FBGs were used to precisely measure the temperature field distribution in a CO2 laser spot with a very high spatial resolution of 100 m. Hence, the proposed PI-US-FBGs could be used for a large-scale fiber sensor network, especially in future distributed temperature measurement with a high spatial resolution.

We propose and demonstrate an overall non-mechanical spectrally steered laser rangefinder using the dispersion-tuned swept laser (DTSL) and a passive diffractive element. The DTSL has no mechanical moving parts, making it possible to achieve an inertial-free high wavelength sweeping speed. The inherent intensity-modulation characteristic of the DTSL allows the modulation phase-shift method to be applied, similar to that used for an amplitude-modulated continuous-wave (AMCW) rangefinder. Since the pulse repetition rate of the DTSL is chirped, standard signal processing techniques for AMCW are not applicable. In this paper, we propose a novel chirped amplitude-modulated phase-shift (CAMPS) method with a signal processing technique to obtain the phase-shift information from a chirped amplitude-modulated signal. As a proof of concept, we demonstrated the CAMPS LiDAR with an axial ranging resolution of ~50 m at a scanning speed of 10 kHz.

Theoretical limit of solar cell conversion efficiency given by Shockley and Queisser is calculated for the case that the cell is illuminated by solar radiation. If the input radiation is monochromatic, the efficiency can exceed the limit. The aim of our study is to experimentally demonstrate this theoretical prediction and to obtain the experimental results of spectral dependence of photovoltaic cell conversion efficiency. Conversion efficiencies of two types of Si photodiodes (equivalent to solar cells) are determined through the measurements of current–voltage characteristics as a function of the wavelength and the incident radiant power. As the theory predicts, it has been confirmed that the conversion efficiency is almost proportional to the wavelength and also to the logarithm of the incident radiant power. Also, it has been experimentally confirmed that the power conversion efficiency for long wavelength monochromatic radiation is higher than that for white radiation.

A novel miniature THz resonator consisting of a finite-length slotted graphene cylinder wrapped around an infinite circular dielectric rod is proposed. A full-wave 3D electromagnetic scattering model is built using the method of moments (MoM) solution of the electric-field integral equation (EFIE) in the spectral domain. In order to gain better understanding of the associated physical effects, the obtained results are compared with a 2D model where the slotted graphene cylinder is assumed infinite. A good agreement between the 3D and 2D models if found. The dependence of the backscattering radar cross-section on the frequency is analyzed. It is found that in both cases this scatterer displays quasi-static Helmholtz resonance response in the sub-THz frequency range, a behavior previously known for perfectly electrically conducting (PEC) slotted cylinders. For both models, in-resonance surface current distributions and far-zone radiation patterns are given. The most important innovation is that due to the use of graphene the Helmholtz-mode resonance becomes electrically tunable.

The evolution of a C-antidipole and a C-dipole embedded in Gaussian beams in the presence of an astigmatic lens is studied, respectively. After the passage of the beams carrying a C-antidipole through the lens, four C-points with the same topological charges appear in the fields. Their position and degree of polarization may change, but their number and the handedness don't change with variations of the propagation distance, the off-axis parameter and the astigmatic coefficient. On the other hand, the evolution of the C-dipole passing through the lens is more complicated. In addition to the change of their position and degree of polarization, the handedness of the same C-point may change, and the creation or disappearance of C-dipoles may occur by varying the relevant parameters.

This letter presents a reconfigurable antenna that uses gravity to control the self-circulation of liquid metal (LM), thereby realizing an adaptive reconstruction method. Then the polydimethylsiloxane (PDMS) structure with a square ring channel is loaded on the microstrip antenna, and the contact position between the liquid metal and the patch is controlled by gravity, which provides conditions for reconfiguration. The antenna has four reconfigurable frequency bands, which can be switched between the dual circle polarization (left-and right-hand circular polarization) mode and the linear polarization (LP) mode without additional mechanical adjustment structures, radio frequency circuits or related components. The measured results show that the proposed antenna has -10 dB impedance band of 1.2-1.6 GHz, 2.5-2.75 GHz, 4.2-4.55 GHz and 5-5.4 GHz and peak gain of 3.6 dBi, 5.07 dBi, 2.68 dBi and 3.25 dBi within passband, which agree well with the simulated results.

Femtosecond laser processing is a non-thermal process with less heat effect on a target material and is applied to dielectric and difficult-to-machine materials, such as titanium alloy and diamond. Femtosecond laser processing has been used for 3-dimensional shape generation in recent years, and increasing accuracy and productivity are required for such generation by femtosecond lasers. However, a 2.5-dimensional computer-aided manufacturing (CAM) system, which is mainly used in femtosecond laser processing, does not satisfy the requirement for complicated 3-dimensional shape generation. Therefore, there is a need for the development of a 3-dimensional CAM system for high-precision and productive 3-dimensional processing. Furthermore, for the 3-dimensional CAM system, quantitative identification of a 3-dimensional removal shape through ablation is necessary. This study proposes the development of a simulation method to accurately predict the 3-dimensional removal shape through femtosecond laser processing, including the piecewise approximation of the ablation rate and absorptance correction. At the same time, a similar 3-dimensional shape as that found through the experimental results was obtained during the simulation by considering the mechanical errors of the laser processing machine in the simulation model. Furthermore, an on-machine measurement system was developed to efficiently identify the ablation parameters.

Energetic materials have extremely high volumetric and specific energy densities, making them attractive and important in combustion systems. To improve their combustion performance, reliable temperature acquirement method is highly demanded. A laser sensor was developed for in situ and quantitative measurements of gas temperature. Scanned-wavelength direct absorption spectroscopy was used for line-of-sight temperature measurements. Multiple absorption features in the near-infrared combination band (v1+v3) and mid-infrared fundamental band (v3) were selected to establish four absorption line pairs with good temperature sensitivity. Three infrared distributed feedback lasers (DFB) were used to cover the selected absorption lines. The accuracy and uncertainty of the sensor were first numerically evaluated in a wide temperature range of 1000–3000 K under different Gaussian white noise levels (5–20%). A free-space optical setup was established to experimentally evaluate the sensor performance by measuring benchmark laminar premixed flames, which were compared with additional thermocouple measurements, chemical kinetic modeling and computational fluid dynamics simulations. The good performance of the current sensor indicates the potential of being used in non-intrusive, in-situ and quantitative diagnostics of the energetic materials combustion.

This paper presents a gain-equalized Ka-band Rotman lens-fed antenna by using phase gradient transmission lines (PGTLs). With PGTLs, the variation trend of the output progressive phase differences among the feeding ports are inverted. The aperture loss of the planar antenna array is then partially compensated by the efficiency of the lens when performing a wide-angle beam scanning. Hence, gain equalization is achieved among multiple beams with an acceptable gain degradation. To reduce the total size, the Rotman lens with PGTLs, the feeding networks, and the antenna array are stacked vertically. Meanwhile, the feeding network is implemented with substrate integrated coaxial lines, suppressing the parallel-plate-mode inside the multilayer structure. In order to validate the proposed design, a compact Rotman lens fed antenna operating at 24.75-27.5 GHz (FBW=10.5%) is designed and fabricated. The results show that the gain drop of the Rotman lens-fed multibeam antenna is reduced from 4.4 dB to 1.5 dB at the design frequency of 26 GHz, covering a wide angular range between ±56∘.

Surface aberrations of transport mirrors within Inertial Confinement Fusion laser facility have significant impacts on system's optical and physical performances. Mounting design of transport mirrors is challenging for the critical specifications of mirror surface aberration under extreme operation environment. This paper presents a novel and general flexure mounting method and structure for transport mirrors with various-axis towards gravity to minimize the mirror surface aberration. Key techniques involved in mirror mounting design, including theoretical modeling, numerical optimization, optomechanical structure design and analysis, and optical testing are explored. The relationship between mirror surface aberration and its use angle θ subject to gravity is clarified using thin elastic plate theory. The mounting configuration is parametrically optimized with a more comprehensive mathematical model. Optomechanical structure design and analysis of the flexure mirror mount are detailed and accomplished. The performance of the proposed mount is experimentally validated by interferometric measurements. Experimental results indicate that the designed mirror mount potentially provides the transport mirrors (with 45° ≤ θ ≤ 90° and no screw pretension) a peak-to-valley aberration level about λ/3 (λ = 632.8 nm) of the total aberration and ∼λ/4 of the residual aberration, respectively. The proposed mounting method and structure provide a feasible and promising method and technique scheme to minimize the transport mirror surface aberrations for the next generation Inertial Confinement Fusion laser facility. The paper work also represents a design effort and a beneficial attempt for analyzing and minimizing gravity aberration for large-aperture, various-axis, and rectangular flat mirrors.

We report the characterization of an achromatic focusing metasurface at oblique incident angles. We show that in addition to the inherent off-axis aberrations that occurs due to the hyperbolic phase profile of the metasurface, the focusing performance is significantly degraded due to the meta-atoms' angular dispersion. To obtain insights into how the angular and spectral bandwidth of meta-atoms relate to the metasurface focusing performance, point-dipole models are used which incorporate different aspect's of the meta-atoms' angular response. It is emphasized that despite the meta-atoms being designed under the assumption that they support a single dipolar resonance, other resonances exist within the meta-atom geometry and become stronger at oblique incidence. These resonances disturb the designed phase and amplitude responses, resulting in lower focusing efficiency at higher incident angles. The modelling of higher order modes leads to good agreement with the experimental measurements, confirming that angular dispersion of the meta-atoms is the dominant mechanism in determining off-axis aberrations.

A novel reflectarray (RA) with ultra-low-profile and 2-bit phase quantization beam-steering ability is presented in this paper. To reduce the profile, a Leaky-wave feed is used to excite the RA with enhanced illumination efficiency. Moreover, simultaneous sum and difference patterns are also obtained to provide beam flexibility. The entire thickness of the proposed RA is less than 3% of that of the conventional front-fed RA with the same aperture. To increase the efficiency of the RA, a novel unit cell consisting of a polarizer layer and a reflection layer is developed, which is configured to provide polarization rotation and 2-bit phase shifts by using a hybrid of tunable polarization and discrete resonator. The operation principle, theoretical explanation, and implementation of the proposed antenna are elaborated in this work. To prove the design concept and beam scanning performance, an array with 9×7 unit cells operating at Ka-band is designed and simulated firstly. 2-D beam scanning within the range of ±30° has been verified. Then, a passive prototype with 9×67 unit cells is designed, fabricated and measured. Experimental results show aperture efficiency of 35.1% and illumination efficiency of 43.4%. The developed RA is scalable, and it provides a viable low-cost solution to develop low-profile, high-gain and beam-steering array antennas for satellite applications.

A light beam scanning technology for 3D sensing has been attracting much interest thanks to its signal-to-noise-ratio merit compared to conventional flash 3D sensing. A Solid-state beam scanner based on a vertical cavity surface emitting laser (VCSEL) with amplification function was invented. In this paper, though enlarging the length of scanner to 6mm, a narrow beam divergence of 4000 was obtained. Its intensity variation is < 40% and could be further improved by better DOE design and fabrication process. The DOE could be simply stacked on the scanner and thus the submodule size of the scanner could be managed within 7mm 1mm 1mm. We also discussed its integrability with a tunable seed laser and its application in 2D beam scanning for better signal to noise ratios.

This study systematically investigated the influence of the position and inclination angle of an externally mounted hollow cathode in 1.35 kW magnetically shielded Hall thrusters to establish the r...

In this work, we establish a comprehensive spectral model to realize effective design of high-power ytterbium-Raman fiber amplifiers (YRFAs) employing different types of Raman-pump lasers, and propose an intuitive approach for the optimization of high-power YRFAs. Quantitative comparisons with the experimental results are given in two high-power YRFAs employing Raman-pump lasers with different spectral linewidth. The consistency of measured and simulated power ratios and spectral properties of different components in the two YRFAs confirms the fidelity of the spectral model. Further theoretical analysis reveals that the impact of Raman-pump lasers on YRFAs is mainly determined by the relative intensity noise (RIN) of Raman-pump lasers up to the cutoff frequency of the pump RIN transfer function of the YRFA. Notably, the RIN of Raman-pump lasers could provide a well reference for the superior design of Raman-pump lasers in high-power YRFAs.

We present the structural design and polarization-maintaining performance of solid-core anti-resonant fiber with two nested circular tubes in 3 m wavelength for the first time, to the best of our knowledge. Numerical simulation results indicated that laser fundamental mode could be obtained by filling the specially designed fiber model with materials of different refractive indices to form the completely solid configuration. We calculated the bend loss of fiber to demonstrate the preferable birefringence performance and outstanding light-confining ability. With the structural deformations from resonant tubes, the birefringence coefficient was enhanced significantly from 210-5 to 6.9310-5, which was of great importance in the polarization sensitive systems. In particular, when nested circular tubes were moved to introduce deformations, the confined loss difference in two orthogonal polarizations was calculated more than two orders of magnitude, which was the desirable result to promote the fabrication of the linear polarizer in 3 m wavelength.

Backscattering noise is a key factor to restrict the performance of resonant fiber optic gyroscopes(RFOG). In order to improve the accuracy of RFOG, this paper proposes a scheme with heterodyne optical phase-locked loop(HOPLL) technique based on acousto-optic modulation(AOM) to suppress backscattering noise. In this scheme, the main light source is divided into three output lights, two of which are frequency-shifted by the AOM, and then they are phase-locked with the third light, using the HOPLL technique. The two channels of frequency-shifted light are respectively used as the clockwise (CW) and counterclockwise(CCW) light of the RFOG, and are locked on the resonance peak. The transmissive fiber resonator can be regarded as a band-pass filter. By adjusting the reference signal in the HOPLL, the carrier of the two frequency-shifted lights can be moved away from the resonance peak. The carrier light intensity of the frequency-shifted light is suppressed by the cavity itself. The suppression ratio(SPR) reaches 15.83dB. The experimental results illustrate that the bias stability of RFOG is 3.8/h based on the Allan deviation, strongly proving the effectiveness of this scheme in suppressing backscattering noise in practical applications.