Broadband Beam Research Articles

Multidimensional Image and Beam Splitter Based on Hyperbolic Metamaterials.

Recently, multidimensional metasurfaces, which can modulate multiple optical parameters of input and output lights simultaneously, have aroused intensive interest. Here, we demonstrate multidimensional switchable images and 3D integrated beam splitters based on hyperbolic metamaterials (HMMs). On one hand, a switchable image controlled by output helicity and input wavelengths is achieved by arranging HMMs with different polarization conversion performance. On the other hand, polarization-multiplexed broadband beam splitter is generated by spatially engineering the subunit with broadband half-plate performance. By integrating the multiplexed beam splitter with a filter metamaterial, this multidimensional beam splitter can further realize the separation of output light by space and wavelength. This cascaded multilayer metamaterial achieves a brand new optical functionality and offers more inspiring possibilities for the design of multifunctional optical devices in the future.

Narrowband nonlinear optical spectroscopy with spatially chirped broadband pulses.

Nonlinear optical vibrational spectroscopies are powerful experimental tools for inspecting material properties that are difficult to acquire otherwise. As ultrafast lasers used in such experiments are typically of much broader bandwidth than vibrational modes, narrowband filtering is usually essential, and the utility of laser energy is often highly inefficient. Here we introduce an experimental scheme to break this trade-off. A broadband beam is spatially chirped as it reaches the sample, and generates sum-frequency signals upon overlapping with another broadband, unchirped beam. A narrowband spectrum can then be retrieved from the spatially dispersed image of signals, with both broadband pulses fully utilized. The scheme is also readily employed as a spatially resolved spectroscopy technique without scanning, and can be easily extended to other wave-mixing experiments.

Two-color X-ray free-electron laser consisting of broadband and narrowband beams.

A simple scheme is proposed and experimentally confirmed to generate X-ray free-electron lasers (XFELs) consisting of broadband and narrowband beams with a controllable intensity ratio and a large photon-energy separation. This unique two-color XFEL beam will open new opportunities for investigation of nonlinear interactions between intense X-rays and matter.

Compact, Broadband and Low-Loss Polarization Beam Splitter on Lithium-Niobate-On-Insulator Using a Silicon Nanowire Assisted Waveguide

We propose a compact, broadband, and low-loss polarization beam splitter (PBS) based on an asymmetrical directional coupler on the lithium-niobate-on-insulator platform, consisting of an amorphous silicon (a-Si) assisted waveguide, and a normal waveguide. With proper design of the a-Si nanowire, and lithium niobate waveguides, the phase-matching condition is satisfied for TE polarization, while significant mismatching exists for TM polarization. A 16- $\mu$ m-long PBS (including the s-bend region) with a 200 nm gap is achieved. Numerical simulations show that the PBS exhibits a 140-nm bandwidth for extinction ratios lager than 10 dB. Moreover, the device has an ultra-low insertion loss (IL $\sim$ 0.05 dB), and maintaining ILs $ 0.5 dB over a 170 nm wavelength range.

Combining Laue diffraction with Bragg coherent diffraction imaging at 34-ID-C.

Measurement modalities in Bragg coherent diffraction imaging (BCDI) rely on finding a signal from a single nanoscale crystal object which satisfies the Bragg condition among a large number of arbitrarily oriented nanocrystals. However, even when the signal from a single Bragg reflection with (hkl) Miller indices is found, the crystallographic axes on the retrieved three-dimensional (3D) image of the crystal remain unknown, and thus localizing in reciprocal space other Bragg reflections becomes time-consuming or requires good knowledge of the orientation of the crystal. Here, the commissioning of a movable double-bounce Si (111) monochromator at the 34-ID-C endstation of the Advanced Photon Source is reported, which aims at delivering multi-reflection BCDI as a standard tool in a single beamline instrument. The new instrument enables, through rapidswitching from monochromatic to broadband (pink) beam, the use of Lauediffraction to determine crystal orientation. With a proper orientation matrixdetermined for the lattice, one can measure coherent diffraction patterns near multiple Bragg peaks, thus providing sufficient information to image the full strain tensor in 3D. The design, concept of operation, the developed procedures for indexing Laue patterns, and automated measuring of Bragg coherent diffraction data from multiple reflections of the same nanocrystal arediscussed.

Broadband and high-efficiency accelerating beam generation by dielectric catenary metasurfaces

Abstract Self-accelerating beams show considerable captivating phenomena and applications owing to their transverse acceleration, diffraction-free and self-healing properties in free space. Metasurfaces consisting of dielectric or metallic subwavelength structures attract enormous attention to acquire self-accelerating beams, owing to their extraordinary capabilities in the arbitrary control of electromagnetic waves. However, because the self-accelerating beam generator possesses a large phase gradient, traditional discrete metasurfaces suffer from insufficient phase sampling, leading to a low efficiency and narrow spectral band. To overcome this limitation, a versatile platform of catenary-inspired dielectric metasurfaces is proposed to endow arbitrary continuous wavefronts. A high diffraction efficiency approaching 100% is obtained in a wide spectral range from 9 to 13 μm. As a proof-of-concept demonstration, the broadband, high-efficiency and high-quality self-accelerating beam generation is experimentally verified in the infrared band. Furthermore, the chiral response of the proposed metasurfaces enables the spin-controlled beam acceleration. Considering these superior performances, this design methodology may find wide applications in particle manipulation, high-resolution imaging, optical vortex generation, and so forth.

Operation of a bending magnet beamline in large energy bandwidth mode for non-resonant X-ray emission spectroscopy

Two new operation modes, “pink beam” excitation, which has the energy bandwidth defined by X-ray mirrors and filters, and “broadband beam”, where the energy bandwidth is defined by the reflection from a multilayer monochromator, were implemented at the SuperXAS beamline of the Swiss Light Source (SLS). These setups allow measuring non-resonance X-ray emission spectra (XES) with 2–3 orders of magnitude higher incident flux than non-resonant XES measurements with a monochromatic incident beam. For the broadband beam mode, a Mo/Si multilayer structure was designed, with which the energy can be tuned in the 5–17 keV range. The multilayer demonstrates a relatively large energy bandwidth of 4 ± 0.2% through the whole energy range and a reflectivity of 23–60%, which increases with energy. We show that by using pink beam mode one can investigate the electronic structure of photocatalytic intermediates through time-resolved core-to-core XES experiments of diluted samples with a concentration of the element of interest of ~1 mM. Broadband beam mode is optimal for valence-to-core XES experiments and allow to avoid the excitation of additional KLβ satellites that can complicate the interpretation of spectra.

A study on the broadband beam pattern synthesis using spatial response variation

A study on the broadband beam pattern synthesis using spatial response variation

Terahertz Beam Steering Based on Trajectory Deflection in Dielectric-Free Luneburg Lens

Free-space transmission of terahertz waves opens great opportunities for wireless applications including communications and radar, enabling higher information capacity, higher spatial resolution, and yet smaller apertures than using microwaves. Nevertheless, due to the shorter wavelengths, it involves a severe path loss. To compensate for the path loss, point-to-point transmission by beam steering is indispensable. However, the implementation of broadband and low-loss beam steering is still challenging in the terahertz range due mainly to the lack of practical phase shifters. To circumvent this issue, here we demonstrate a novel approach of terahertz beam steering based on trajectory deflection in a dielectric-free Luneburg lens. It converts a point excitation into a deflected beam in the fundamental transverse electric mode inside parallel conducting plates based on graded effective refractive index, which is then launched into free-space. The absence of dielectric medium contributes to reduce the insertion loss and also enables external control of the effective refractive index. Importantly, this approach is assisted by angular leverage; a very little change of the plate tilt results in very large deflection of the beam trajectory. We demonstrate beam steering from -25° to +25° by changing the plate tilt from -25' to +25' (-0.42° to +0.42°), which is transferred to the 60 times larger angles. Such a small tilt can easily be generated, for example, by using piezo or MEMS actuators. Since the excitation point can be fixed, the proposed device can easily be coupled to a wide range of chip sources and detectors, offering waveguide integration. As an application example, we implement high-resolution radar that identifies both the direction and range toward an object.

All-Fiber Method for Real-Time Transverse-Mode Switching of Ultrashort Pulse

We demonstrate a real-time transverse-mode switching of ultrafast pulse via a cascading mode conversion. The cascading all-fiber mode converter is comprised of a mode-selective coupler (MSC) and an acoustically induced fiber grating (AIFG), which functions as a broadband and controllable beam shaper, and offers a real-time mode switching between LP11 and LP21 modes with $\sim ~190~\mu \text{s}$ switching time. Such a transverse mode-switchable all-fiber laser presents a pulse duration of 1.4 ps and flexible transverse-mode switching. We believe that this compact and robust all-fiber laser source would find promising applications in the field of ultrafast optics and structured light microscope.

Broadband transmission-type 1-bit coding metasurface for electromagnetic beam forming and scanning

Coding metasurfaces make it possible to manipulate electromagnetic (EM) waves digitally by means of several discrete particles. Hence, there have been rapid advances in this field recently. Here we propose a novel design of a broadband transmission-type coding metasurface, which is valid to both x - and y -polarized EM incidences from 8.1-12.5 GHz while satisfies the requirements of 1-bit coding without changing the polarization. Two types of multi-layer coding particles with different geometrical parameters are adopted to represent the digital states “0” and “1”, which are easily promoted to terahertz and optics through modifying the size scale. To verify the ability to manipulate the EM waves, we first adopt the coding metasurface to achieve broadband beam forming by converting spherical waves to plane waves and realize high-directivity pencil beam in far field with low side lobes. We further arrange the particles according to the coding sequence 010101… to steer two symmetrical beams in different directions controlled by frequencies with the maximum range of the scanning angle of 30°-50.5°. The good agreements between the simulated and measured results validate the proposed broadband coding metasurface, indicating its huge potential in communication and radar imaging systems.

Photopatterned liquid crystal mediated terahertz Bessel vortex beam generator [Invited

In this Letter, we propose that the photopatterned liquid crystal (LC) can act as a broadband and efficient terahertz (THz) Bessel vortex beam (BVB) generator. The mechanism lies in the frequency-independent geometric phase modulation induced by the spatially variant LC directors. By adopting large birefringence LCs and optimizing the cell gap, the maximized mode conversion efficiency can be continuously adjusted in broadband. Furthermore, the LC patterns can be designed and fabricated at will, which enables the THz BVBs to carry various topological charges. Such a THz LC BVB generator may facilitate the advanced THz imaging and communication apparatus.

Metasurface-enabled broadband beam splitters integrated with quarter-wave plate functionality.

Conventional beam splitters and wave plates, while being essential components in diverse optical systems, require considerable space, especially when used in combination. Here, we designed and experimentally demonstrated metasurface-enabled efficient broadband beam splitters integrated with quarter-wave plate (QWP) functionality for simultaneous power splitting and circular-to-linear polarization conversion in the near-infrared range. By utilizing two different gap-plasmon meta-atoms, which function as QWPs performing efficient circular-to-linear polarization conversion and provide the phase difference of π between reflected linearly polarized beams, we designed a metasurface that completely suppress the specular reflection (zero-order diffraction) and second-order diffraction, while ensuring efficient and equal beam splitting of a circularly polarized wave into two reflected beams with predesigned directions and well-defined linear-polarization states in the wavelength range of 750-950 nm. The fabricated metasurface exhibits excellent performance of circular-to-linear conversion and power splitting, with efficient suppression of specular reflection (<1%) and splitting efficiencies above 50% for both right and left circularly polarized excitation at the design wavelength of λ = 850 nm. By enabling the combined functionalities of a conventional beam splitter and a QWP, our approach opens up new prospects for advanced research and applications targeting photonics integration and miniaturization.

An active set approximation method for the design of broadband beam former

The microphone array beam former design problem in far-field environment is to design the coefficients of FIR filters such that the maximum error between the actual response and the desired response in a specified domain is minimized. The specified domain is always very large and this problem is a large scale optimization problem. In general the complexity of the optimal method for solving this problem is very expensive. In this paper, we apply an active set approximation method to solve this problem. First, we transform this problem into a semi-infinite programming problem. Next, we find an approximate active set such that the scale of the problem can be mostly reduced. Then, this problem can be solved efficiently and the approximate solution is very close to the optimal solution. Numerical experiments are illustrated to show the efficiency of the proposed method.

Design of far field beamforming problem by window function

The design of the broadband beam former problem is to find the coefficients vector for all FIR filters such that output fits to a given target spatial directivity pattern in a specified domain. This problem is always very complicated. In this paper, we propose a fast window function method to solve this problem. First, we formulate a simplified optimization problem, where the frequency response function is the decision function. Then an optimal frequency response vector can be obtained by solving this problem. Next we apply the window function to cut off the infinite length of the coefficient. The window function method is efficient and can be applied in real time applications. Numerical example is illustrated to show the efficiency of the method.

Third-order double-achromat bunch compressors for broadband beams

Many state-of-the-art applications for linear accelerators, such as free-electron lasers (FELs) and plasma-wakefield accelerators (PWFAs), require small normalized emittances, and PWFAs in particular are very sensitive to transverse slice offsets along the beam. Dispersive systems, such as bunch compressors, can cause different chromatic aberrations, one of which yields transverse slice offsets. In this paper, we show a design approach to double-achromat bunch compressors which greatly reduces different chromatic aberrations and mitigates coherent synchrotron radiation effects.

Broadband and compact polarization beam splitter based on an asymmetrical directional coupler with extra optimizing designs.

In this paper, a novel, to the best of our knowledge, polarization beam splitter (PBS) based on an asymmetrical directional coupler (DC) was proposed, which consists of a strip waveguide (WG) and a ${{\rm Si}_3}{{\rm N}_4}$Si3N4 loaded horizontal slot WG. By carefully adjusting the geometric parameters of the DC, the phase match condition between these two WGs can be satisfied for the transverse magnetic (TM) polarization, while the coupling efficiency of the transverse electric (TE) polarization is frustrated due to the large phase mismatch. The extra optimizing designs include adding filters to the output ports as well as introducing the tapered structure into the DC, which is settled by the particle swarm optimizing (PSO) algorithm so that the performance of the proposed PBS is improved over a broadband range. Numerical simulations show that the bandwidths for the extinction ratio (ER) $ \gt {20}\;{\rm dB}$>20dB, 30 dB, and 40 dB are 160 nm, 95 nm, and 50 nm, respectively, with insertion loss (IL) $ \lt {1}\;{\rm dB}$<1dB for the wavelength of 1.49-1.58 µm. The analysis of the deviations demonstrates that the proposed PBS allows high fabrication tolerances.

A broadband beam scanning antenna array based on substrate integrated coaxial line Butler matrix for Q‐band application

AbstractIn this article, a broadband beam scanning antenna array is proposed in Q‐band attributed to miniaturized size, wideband and high integration. A patch antenna element is utilized with a back cavity, which is formed by metallic via holes and ground plane. A 1 × 4 series fed sub‐array is implemented by the patch element using multilayer PCB. Four symmetrical sub‐arrays and Butler matrix feeding network are used to form the antenna array with high gain and decrease side lobes. The Butler matrix is implemented by substrate integrated coaxial line, which provides low loss of around 0.09 dB/mm from 40 to 50 GHz. The measured antenna array bandwidth is 9.8 GHz (21.8%) under the condition of voltage standing wave ratio less than 2. The main beam of the antenna array in azimuth direction is tilted to −28.5°, −14.1°, 18.4° and 35.6° and the gains are 13.11, 13.88, 14.02 and 11.78 dBi at 45 GHz, respectively. Both the measured and simulated results agree well.

Design and Simulation of Broadband Beam Splitter on a Silicon Nitride Platform for Optical Coherence Tomography

ABSTRACTIntegrated photonics enables the miniaturization of bulk optical components for biosensing applications such as optical coherence tomography (OCT) and is therefore promising for future lab-on-chip solutions. Here, we report the design and simulation of a compact low loss broadband beam splitter with arbitrary coupling ratios on silicon nitride platform for OCT systems. The reported coupler uses asymmetric waveguide-based phase control section for 10:90, 20:80, 30:70, 40:60, and 50:50 splitting ratios and is broadband over 100 nm with the central wavelength of 850 nm. The couplers are realized for transverse electric, transverse magnetic, and fully vectorial modes, and maximum excess loss for all mode types is reported to be less than 0.19 dB. The design tolerance of waveguide width and thickness of the designed coupler is further calculated and is within fabrication limit.

Recent upgrades of the multiple-reflection time-of-flight mass spectrometer at TITAN, TRIUMF

A multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS) has been installed and integrated into the TITAN experiment at TRIUMF. The MR-TOF-MS extends the capabilities and improves the performance of the TITAN experiment, for instance it provides fast isobar separation, short measurement cycles, yield measurements and broad-band beam diagnosis, and enhanced rate capabilities and dynamic range. Thereby, even more exotic nuclides become accessible at TITAN for experiments. Such improved capabilities of TITAN have been used in first experiments to investigate the sub-shell closure of neutron-rich nuclides at N = 32 and the r-process nucleo-synthesis for masses at A ∼ 85. The vacuum system, electronics and data-acquisition hardware and software have been recently upgraded. For the first time an isomeric state has been measured with TITAN′s MR-TOF-MS, 84mRb (excitation energy: 464 keV). The accurate measurement of excitation energies of low-lying isomeric states is possible due to the high mass resolving power of TITAN′s MR-TOF-MS and a specialized data-analysis procedure.