Tunable Beam Research Articles

Achievement of tunable vortex beams with dual index by intra-cavity multi-surface construction modulation

Tunable vortex beams with dual index and high power potential have been widely applied in various fields. However, due to the trade-off between the adjustment flexibility and the power damage threshold of the adopted elements, the generation of tunable vortex beams with dual index and high power potential remains a challenge. The deformable mirror (DM) with high power damage threshold and flexible adjustment ability, has the potential for generating vortex beams with the capability to high power, but vortex beams with only single index have been realized. Herein, the method based on intra-cavity multi-surface construction modulation with DM and extra-cavity conversion, is first proposed to generate tunable vortex beams with dual index. The vortex beams could be achieved by extra-cavity conversion of the Hermite-Gaussian (HG) beams generated from a resonant cavity. In this work, a designed Z-shaped resonant cavity is used, and the modulation conditions for generating HG beams and vortex beams with dual index are investigated based on four classic surface construction methods. The dual single piezoelectric (PZT) DM with a simple manufacturing process and low manufacturing cost, is adopted and has been proven to generate tunable HG beams and vortex beams with dual index. For the adopted dual single-PZT modulation method, the influence of parameters (i.e., cavity structure parameters, DM assembly parameters and DM structure parameters) on the generated laser beams have been further investigated in simulation to ensure the selection of suitable parameters. The experiment has been conducted and the experimental results have been proven the feasibility of the proposed method, which is of great significance for generating tunable vortex beams with dual index in various applications.

Generation of Multi-Photon Catalyzed Coherent States with Conditional Measurement on a Tunable Beam Splitter

Generation of Multi-Photon Catalyzed Coherent States with Conditional Measurement on a Tunable Beam Splitter

Tunable Bessel beam generator based on a 3D-printed helical axicon on a fiber tip.

We demonstrate a tunable and fully enclosed fiber-based Bessel beam generator that has the potential for applications in a tough environment. This generator consists of a few-mode fiber (FMF), a short section of graded index fiber (GIF), and a 3D-printed helical axicon. The FMF provides tunable modes that carry an orbital angular momentum (OAM). The GIF was fused to the FMF to expand and collimate the generated modes. The helical axicon was 3D-printed on the GIF tip without any holes or gaps, which reshapes the OAM modes into Bessel modes and adds an additional helical phase structure to them, resulting in the generation of zeroth-order, first-order, and second-order Bessel beams. The fully enclosed structure provides high mechanical strength and optical stability, which enable the generator to be suitable for imaging or particle manipulation in a complex liquid or air environment.

Inverse-designed flexural wave metamaterial beams with thermally induced tunability

Elastic metamaterials (EMMs) have been developed for more than two decades, but their practical applications have been scarcely reported due to their narrow bandgaps, relatively high working frequency ranges, poor load-bearing capabilities, and other implementation-related issues. As an attempt to solve some of these problems, in this work, a novel kind of tunable metamaterial beams is proposed to mitigate or isolate low-frequency and broadband flexural waves, where the integrated tunable elements made of a 3D-printed thermally sensitive material are inversely designed. The tunability is further achieved through the thermal-driving on the tunable elements. The optimized tunable elements are fabricated independently and have pretty good load-bearing capabilities under quasi-static uniaxial compression tests. They are directly glued on the host beams to form simple structured metamaterial beams without destruct the host beams. The experimentally measured transmission spectra under different thermal loadings demonstrate that the third pass-bands of the optimized three metamaterial beams at room temperature (RT) are changed to bandgaps or stop-bands as the temperature increases to about 60 °C, and vice versa. In addition, this temperature change induced bandgap is concatenated to the optimization obtained bandgap to form a wider bandgap. The good thermal reversibility is also validated by experimental tests under several thermal-loading cycles. Our present work suggests a dual-technique combined method to design low-frequency and broadband EMMs.

Generation and Manipulation of Tunable Chiral Structured Light Beams

Generation and Manipulation of Tunable Chiral Structured Light Beams

Tunable achromatic metalens for generating focused vortex beam in the near-infrared range

Highly precise and controllable focusing of optical vortex beams in the NIR range is essential for applications in biological imaging, nanomanipulation, and other fields. However, achieving tunable vortex beams across a broad spectrum remains a significant challenge. Herein, we propose a varifocal and broadband achromatic metalens capable of effectively correcting chromatic aberration, achieving a maximum focusing efficiency of 40.0% over 1400–1700 nm. Furthermore, through adjustments to the crystalline fraction of Ge2Sb2Te5 (GST), it offers the ability to vary focal lengths from 6.90 to 10.73 μm. This study may further advance NIR communication and imaging systems.

Tunable vortex beams generation in visible band via Pr3+:YLF laser with a spot defect

The generation of optical vortex beams with user-configurable topological charge and spatial profile is a topic of intense research due to the numerous potential applications for these types of laser beams. In this work, we demonstrate the direct generation of vortex laser beams with controllable topological charge and tunable spatial profile from a Pr3+:YLF laser cavity using a spot-defect technique. A theoretical model is established to examine the relationship between the topological charge of the generated vortex beam and how this relates to laser cavity parameters. Experimentally, the selective operation of first- and second-order vortex beams and tunable optical vortex lattices with one to four singularities at 607 nm can be achieved by adjusting the position of the defect spot. This work offers insight into methods for the generation of visible optical vortex beams with controllable topological charge and tunable singularities for a range of applications.

Coin-structured tunable beam shaping assembly design for accelerator-based boron neutron capture therapy for tumors at different depths and sizes

Coin-structured tunable beam shaping assembly design for accelerator-based boron neutron capture therapy for tumors at different depths and sizes

Tunable low-frequency broadband metamaterial beams composed of hierarchical annular cantilevers

Tuning the resonance frequency of the local resonators in an active way and obtaining a broad bandgap at low frequency is a long-lasting challenge for traditional elastic metamaterials. This work proposes a kind of tunable metamaterial beam to isolate flexural waves, which are composed of hierarchical annular cantilevers with a steel mass block embedded in the center of each unit cell. To obtain a broad low-frequency bandgap, a genetic algorithm-based size optimization is utilized to determine the optimal geometry parameters of the unit cell. The tunability of the metamaterial beam is realized by attaching different numbers of permanent magnets to the embedded mass block. Such a tuning approach makes the change of the resonator’s mass available. Moreover, based on the rainbow effect, ultra-broadband flexural wave attenuation is realized by forming a gradient metamaterial beam. Both numerical and experimental results verify the good flexural wave attenuation ability of our proposed tunable metamaterial beam.

Tunable spectrally-flat multi-wavelength cylindrical vector beam fiber laser by using a re-circulating frequency shifter loop with two external injections

We experimentally demonstrate a tunable spectrally -flat multi-wavelength cylindrical vector beam (CVB) fiber laser based on a two-mode long-period fiber grating (TM-LPFG) and a re-circulating frequency shifter loop with two external injections. The TM-LPFG is utilized as a mode converter in the re-circulating frequency shifter loop to excite the LP11 mode in the two-mode fiber. By adjusting the wavelength interval of the two injected seed signals, the power of the injected seed signals, and the pump power can produce a flat intensity envelope between the two injected wavelengths. Multi-wavelength CVBs of 12, 18, or 30 channels with a peak-to-peak power variation lower than 2 dB between the two injected wavelengths are obtained with a wavelength spacing of approximately 0.08 nm. The wavelength spacing can be adjusted by changing the frequency of the radio frequency signal. Multi-wavelength CVBs of 14 channels with a peak-to-peak power variation lower than 2 dB between the two injected wavelengths are obtained with a wavelength spacing of approximately 0.2 nm. The purity of the generated multi-wavelength CVBs is higher than 98%. Due to the absence of interference-type filter elements, the multi-wavelength CVB fiber laser exhibits excellent stability. The maximum wavelength deviation of each channel is less than 6.5 pm, and the maximum intensity fluctuation is less than 0.7 dB over a period of one hour.

Controlling the Glassy State toward Structural and Mechanical Enhancement: Additive Manufacturing of Bulk Metallic Glass Using Advanced Laser Beam Shaping Technology

AbstractBulk metallic glasses (BMGs) offer exceptional physical/mechanical properties enabling them to be highly desirable for a variety of applications. Laser powder bed fusion (LPBF) has great promise for producing large and intricate BMG structures. However, using non‐optimal energy distribution in current additive manufacturing machines leads to extensive reheating of previously solidified layers. As a result, the mechanical characteristics can be significantly impacted by structural relaxation and partial crystallization. Here, a tunable advanced laser beam shaping technology is employed to overcome the difficulties originating from non‐optimal energy distribution in current additive manufacturing machines. This study fabricates fully amorphous/dense BMG samples using the shaped laser beam and established optimized atomic‐scale short‐and medium‐range ordering along with improved yield/fracture compressive strength. Formation of a shallow and wide melting pool geometry using the beam shaping allows to increase hatching distances to better control the thermal history introducing improved amorphicity and rejuvenation. This higher rejuvenation and disordering allow for increased atomic mobility, which facilitates the creation and spread of shear bands, thus enhancing the mechanical strength and ductility of the material. The current work demonstrates that BMG parts can be fabricated using flexible beam‐shaping technology allowing to go beyond the capabilities of state‐of‐the‐art additive manufacturing techniques.

Hybrid control method for generating airy beam in wavefront sensorless adaptive optics system

In order to reduce the complexity of Airy beams generation based on adaptive optics with a wavefront sensor, a wavefront sensorless adaptive optics system, which employs a camera to measure the far-field intensity distribution as the feedback for optimizing the control voltages of the deformable mirror, is proposed for generating high-quality Airy beams. A hybrid control method combining hill-climbing algorithm and open-loop control method is developed to correct the aberrations of the system and produce the cubic phases. High-quality tunable Airy beams were generated successfully. The properties of the generated Airy beams, such as non-diffraction, self-acceleration and self-healing, were verified. The experimental results coincide with the theoretical results, showing the proposed method has potential applications such as Airy beam light-sheet microscope and optical manipulation.

An active tunable piezoelectric metamaterial beam for broadband vibration suppression by optimization

An active tunable piezoelectric metamaterial beam for broadband vibration suppression by optimization

Tunable broadband terahertz beam splitting using gated graphene metasurfaces [Invited

Active control of split ratios in terahertz (THz) beam splitters holds substantial potential for applications in imaging and spectroscopy. In this study, we introduce an approach for electrically controlling THz beam splitting with near non-dispersive characteristics, using the metasurface hybridized with single-layer graphene. Specifically, the resonant frequency of the metasurface is meticulously chosen to provide an enhanced effective conductivity that is almost frequency-independent. Furthermore, the split ratio can be manipulated by adjusting the gate voltage applied to graphene, thereby altering the effective conductivity of the hybrid metasurface without affecting its non-dispersive transmission and reflection characteristics. The feasibility of our approach is confirmed by the near non-dispersive split ratio across a wide operating frequency range, from 0.5 to 1.5 THz. The demonstration of this efficient, broadband, and tunable beam splitting ability validates the potential of gated graphene metasurfaces for advanced THz applications.

Coupled bandgap properties and wave attenuation in the piezoelectric metamaterial beam on periodic elastic foundation

In recent years, the innovative design of metamaterials and the study of bandgap characteristics have become the focus of research. The flexible setting of small added mass in locally resonant metamaterials can effectively regulate bandgap characteristics and wave transmission. In this paper, a novel tunable piezoelectric metamaterial beam on periodic elastic foundation is proposed for realizing the wider bandgap region and the stronger attenuation capability. Based on Timoshenko beam theory, wave equation of the metamaterial beam considering the piezoelectric and the inertial amplification effects is obtained from the transfer matrix method, and the calculational results are compared to that of numerical simulation. The results show that periodic elastic foundation can improve the overall stiffness of the structure, and the bending wave attenuation frequency domain will broaden with the increase of the elastic foundation stiffness. The metamaterial beam exhibits the strong wave attenuation in the bandgap induced by external negative capacitance shunt circuit, and the wave transmission loss is improved about 20 dB than the short circuit case. The coupling effects between the local resonance and the inertial amplification mechanism can cause the coupled bandgaps, which expand the original bandgap range by at least 25%. In addition, the coupled bandgaps boundary can be extended to lower frequencies by adjusting the angle of rigid rod and the additional mass separately, resulting in broadband wave attenuation. This work will provide valuable ideas for the design of advanced smart materials and structures in the field of vibration and noise reduction.

Plasmonic vortex beam emitter

Terahertz vortices prompt numerous advanced applications spanning classical and quantum communications, sensing, and chirality-based detection, owing to the inherent physical properties of terahertz waves and orbital angular momentum (OAM). Nonetheless, existing methodologies for generating terahertz vortices face challenges such as unalterable topological charges and intricate feed networks. To address these limitations, we propose a novel approach to generate multi-mode and tunable vortex beams based on chiral plasmons. Through eigenmode analysis, the uniform helical gratings are demonstrated to support chiral plasmons carrying OAM. By leveraging their vortex characteristics and introducing modulation into the periodic system, these chiral plasmons are alternatively diffracted into high-purity vortex radiations according to the Bragg law. To validate the theory, the vortex beam emitter is fabricated and measured in the microwave regime based on the modulated scheme. Experimental results confirm the emission of vortex beams with desirable phase distributions and radiation patterns. Our findings highlight the potential of chiral plasmons as seeds for tunable and compact vortex radiation, offering promising applications in tunable vortex sources.

Broadband ultrafast ultraviolet laser output by using β-BaB2O4 crystal

In this paper, a broadband ultrafast ultraviolet (UV) laser was generated through sum-frequency method with β-BaB2O4 (BBO) crystal by using a femtosecond (fs) Ti:sapphire laser as the fundamental laser source. We studied the influence of the power ratio between the fundamental frequency and second harmonic laser beams on output power and conversion efficiency of UV laser. The time delay method was used to change the optical path difference in the sum-frequency generation (SFG). At the same time, the cutting angle of the crystal was optimized and the effect of different focal lengths of lenses on the experimental results was studied. Finally, we obtained a tunable UV laser beam with a tuning range from 226.7 nm to 360 nm generated by the BBO crystal. The laser had high conversion efficiency, and the maximum output power was 540 mW at 270 nm.

Wireless at the Nanoscale: Toward Magnetically Tunable Beam Steering

Plasmonic wireless nanolinks hold great promise to overcome limitations from conventional metallic wires, namely narrow bandwidths, Ohmic losses, dispersion and cross-talking. However, current developments are limited to the wireless communication between two fixed points, i.e., a fixed transmitter with a fixed receiver, which in turn limits the energy efficiency and integration levels. In this work, we propose the use of magnetic fields for the active tuning of the radiation beam steering of plasmonic nanoantennas. The physical principle behind our concept is shown with a rigorous solution of the radiation pattern of a radiating dipole source in the presence of magnetic fields. The results indicate that the proposal of this work is feasible with magnetoplasmonic nanoantennas, which can be fabricated using available ferromagnetic materials.

Continuously Tunable Optical Modulation Using Vanadium Dioxide Huygens Metasurfaces.

Efficient and dynamic light manipulation at small scale is highly desirable for many photonics applications. Active optical metasurfaces represent a useful way of achieving this due to their creative design potential, compact footprint, and low power consumption, paving the way toward the realization of chip-scale photonic devices with tunable optical functionality on demand. Here, we demonstrate a dynamically tunable, dual-function metasurface based on dielectric resonances in vanadium dioxide that is capable of independent active amplitude and phase control without the use of mechanical parts. Significant developments in the nanofabrication of vanadium dioxide have been shown to enable this metasurface. Gradual thermal control of the metasurface yields a computationally predicted continuously tuned amplitude modulation of 19 dB with negligible phase modulation and a continuously tuned phase modulation of 228° with negligible amplitude modulation, both at near-infrared wavelengths. Experimentally, a maximum continuously tuned amplitude modulation of 9.6 dB and phase modulation of 120° are shown, along with demonstration of stable intermediate states and repeated modulation without degradation. Reprogrammable optical functionality can thus be achieved in precisely engineered nanoantenna arrays for adaptive modulation of amplitude and phase of light for applications such as tunable holograms, lenses, and beam deflectors.

A compact dication source for Ba2+ tagging and heavy metal ion sensor development

We present a tunable metal ion beam that delivers controllable ion currents in the picoamp range for testing of dry-phase ion sensors. Ion beams are formed by sequential atomic evaporation and single or multiple electron impact ionization, followed by acceleration into a sensing region. Controllability of the ionic charge state is achieved through tuning of electrode potentials that influence the retention time in the ionization region. Barium, lead, and cadmium samples have been used to test the system, with ion currents identified and quantified using a quadrupole mass analyzer. Realization of a clean Ba2+ ion beam within a bench-top system represents an important technical advance toward the development and characterization of barium tagging systems for neutrinoless double beta decay searches in xenon gas. This system also provides a testbed for investigation of novel ion sensing methodologies for environmental assay applications, with dication beams of Pb2+ and Cd2+ also demonstrated for this purpose.