Spiral Phase Research Articles

Spatial shaping of low- and high-order harmonics generated using vortex beams

We demonstrate the generation of the low- and high-order harmonic vortex beams from a single spiral phase plate illuminated by different laser wavelengths. The second harmonic (532 nm) originates from the application of the wavefront-structured 1064 nm femtosecond pulses with fractional orbital angular momentum (OAM) during propagation through a lithium triborate crystal, while the third harmonic (500 nm) originates from the application of the wavefront-structured near-IR (1500 nm) femtosecond pulses with integer OAM during propagation through a 150 μm thick fused silica plate. The topological charges (TCs) of the second and third harmonics are measured and compared. The increase in TC and the peculiarities in OAM variations during modification of the polarisation of the incident radiation are analysed and discussed. The two-colour-pump-driven second-harmonic vortex radiation interacted with an Ar gas jet to generate vortex harmonics up to the 14th order with double-lobe complex spatial profiles in the extreme ultraviolet region.

Improving millimeter-wave imaging quality using the vortex phase method

This paper investigates a new vortex wave imaging approach to improve the imaging quality of small metal targets of size less than 1.5 mm. Antennas with different spiral phase plates are designed to efficiently transmit vortex beams with orbital angular momentums (OAMs). By analyzing the OAM spectrum of the target, it was discovered that the predominant reflection contains a particular OAM mode that carries abundant azimuthal information. This can be explained by the OAM selectivity of the target and the guidance of the vortex transmitting beam. A simple reflection vortex imaging system was designed to capture the phase information. Measurement results show that the high image contrast reaches 14.9%, which is twice as high as that of the imaging without OAM. Both of simulations and experiments demonstrate that the vortex phase imaging approach proposed in this paper can effectively improve the imaging quality at 80 GHz. This approach is suitable for other millimeter wave imaging systems and is helpful to improve the resolution in anti-terrorism security checks.

Isolated attosecond electron and hard x-ray pulse generation by ultra-intense spatiotemporal vortex laser

The spatiotemporal optical vortex (STOV) laser pulse, characterized by containing a space-time dependent spiral phase structure and intrinsic transverse orbital angular momentum (OAM), has been of much recent research interest for basic physics as well as potential applications in optical communication and manipulation, as well as the attosecond sciences. Here we consider electron acceleration and generation of attosecond hard x-rays by irradiating a thin foil with intense STOV laser pulse. It is found that the affected foil electrons can be trapped and acquire transverse OAM, or synchrotron-like motion, from the STOV, as well as accelerated forward by the transverse and enhanced axial laser electric fields to form a tiny energetic bunch at the front of the laser pulse and emit short ( ∼400 attosecond) high-flux ( >109 photons per pulse) hard (100–1000 keV) x rays.

Optical vortices by an adaptive spiral phase plate

An Adaptive Spiral Phase Plate (ASPP) based on liquid crystal (LC) and the transmission electrode technique is theoretically and experimentally demonstrated. This ASPP design enables the generation of high-quality optical vortices with topological charges ranging from ±1 to ±4 using a single device, with higher charges being directly achievable by employing higher-birefringence LC or thicker cells. The continuous reconfigurability of the optical phase shift, achieved through a simple control mechanism involving only two low voltages and 100 electrodes that distribute the voltage, sets this device as an accurate approximation to a continuous ASPP. The measured conversion efficiency ranges between almost 100% and 95% for the first and fourth topological charges, respectively. This device offers remarkable advantages, such as complete reconfigurability, allowing adjustment of operating wavelengths and topological charges. The fabrication process mirrors that of a standard LCD cell, ensuring a cost-effective and reliable solution. In summary, the proposed ASPP is a key advancement, providing superior light conversion efficiency, simplicity, and the capability for on-the-fly reconfiguration in various optical applications.

Multioptical bottles from the chirped circular Bessel Gaussian beams carrying annular spiral-zone power-exponent-phase

In this paper, we introduce a new structure of multioptical bottles formed by the chirped circular Bessel Gaussian beams carrying annular spiral-zone power-exponent-phase (ASP). The ASP is a general term for complex phases composed of the radial phase, equiphase, and power spiral phase. By combining the influence of autofocusing properties, chirp factor, and ASP mode, the propagation dynamics of the proposed multioptical bottles beam such as the sizes, lengths, number and locations can be flexibly manipulated. Intriguingly, the effect of the power order of ASP mode on the beam propagation dynamics is firstly introduced and examined. The proposed beams can enable diversification the optical tweezers system in multiparticle manipulation, which is verified by the radiation force analysis on a Rayleigh particle.

Observation of spatiotemporal optical vortices enabled by symmetry-breaking slanted nanograting

Providing additional degrees of freedom to manipulate light, spatiotemporal optical vortex (STOV) beams carrying transverse orbital angular momentum are of fundamental importance for spatiotemporal control of light-matter interactions. Unfortunately, existing methods to generate STOV are plagued by various limitations such as inefficiency, bulkiness, and complexity. Here, we theoretically propose and experimentally demonstrate a microscale singlet platform composed of a slanted nanograting to generate STOV. Leveraging the intrinsic topological singularity induced by C2 symmetry and z-mirror symmetry breaking of the slanted nanograting, STOV is generated through the Fourier transform of the spiral phase in the momentum-frequency space to the spatiotemporal domain. In experiments, we observe the space-time evolution of STOV carried by femtosecond pulses using a time-resolved interferometry technique and achieve a generation efficiency exceeding 40%. Our work sheds light on a compact and versatile platform for light pulse shaping, and paves the way towards a fully integrated system for spatiotemporal light manipulation.

Compact meta-differentiator for achieving isotropically high-contrast ultrasonic imaging

Ultrasonic imaging is crucial in the fields of biomedical engineering for its deep penetration capabilities and non-ionizing nature. However, traditional techniques heavily rely on impedance differences within objects, resulting in poor contrast when imaging acoustically transparent targets. Here, we propose a compact spatial differentiator for underwater isotropic edge-enhanced imaging, which enhances the imaging contrast without the need for contrast agents or external physical fields. This design incorporates an amplitude meta-grating for linear transmission along the radial direction, combined with a phase meta-grating that utilizes focus and spiral phases with a first-order topological charge. Through theoretical analysis, numerical simulations, and experimental validation, we substantiate the effectiveness of our technique in distinguishing amplitude objects with isotropic edge enhancements. Importantly, this method also enables the accurate detection of both phase objects and artificial biological models. This breakthrough creates new opportunities for applications in medical diagnosis and nondestructive testing.

Hollow vortex Gaussian beam expressed in terms of cylindrical wave

The electrical field of hollow vortex Gaussian beam (HVGB) with an arbitrary combination of the beam order and topological charge is formulated by using the cylindrical wave spectrum representation (CWSR), which satisfies Maxwell’s equations rigorously and allows to study analytically and numerically the evolution of the beam along its propagation in the source region and the near/far- field regions. It is found that in the source region there exists a sharp and very narrow peak, due to the contribution of evanescent waves when the beam order and the topological charge satisfy specific relations. The effect of the spiral phase plate (SPP) in generating a non-vortex Gaussian beam to a vortex one is explained. Besides, it is found that the divergence of the beam is mainly determined by the topological charge and the hollow structure is mainly determined by the beam order.

Electron paramagnetic resonance probing of the spin fluctuation transition in the conical spiral phase of MnSi

In the spiral conical phase of manganese monosilicide, MnSi, the EPR spectra are studied at a frequency of 9.3 GHz in the temperature range of 5–30 K for an external magnetic field oriented along the crystallographic direction [100]. It is found that in the temperature range T < T* = 25 K, located 4 K below the paramagnetic phase-conical phase transition temperature TC = 29 K, a complex EPR spectrum consisting of several lines appears. A procedure is proposed for decomposing experimental spectra into components, which makes it possible to find for each spectral line the temperature dependences of the resonance magnetic field, line width, and integrated intensity. At Tf ∼16 K, one of the main lines in the EPR spectrum with the highest integrated intensity demonstrates a maximum in the temperature dependence of the line width W(T), corresponding to a change in W by a factor of ∼2.8. We argue that this unusual behavior appears as a consequence of a spin fluctuation transition in the conical spiral magnetic phase with long range magnetic order.

Double iris image asymmetric encryption mechanism using rear mounted spiral phase mask in hybrid transform domain

Double iris image asymmetric encryption mechanism using rear mounted spiral phase mask in hybrid transform domain

Abruptly autofocusing of polycyclic tornado symmetric Pearcey vortex beams in the fractional Schrödinger equation

In this paper, we study polycyclic tornado symmetric Pearcey (PTSP) vortex beam induced by superimposing spiral phase and vortex, and its propagation dynamics in the fractional Schrödinger equation (FSE). We find that the autofocusing of the symmetric Pearcey beam is enhanced and the autofocus length is shorten with the increase of Lévy index α. Polycyclic tornado phase will form a dark tornado ring (DTR) on the basis of PTSP vortex beam, and the radius of the DTR will also change with the increase of the propagation distance. Finally, the divergence force and gradient force of the PTSP vortex beam in FSE are displayed during transmission. The development of these special properties in FSE has important implications for optical tweezers, medical and military applications.

A High Extinction Ratio Silicon Thermo-Optic Switch With Variable Splitter and Spiral Phase Shifters

A High Extinction Ratio Silicon Thermo-Optic Switch With Variable Splitter and Spiral Phase Shifters

3D printable PLA spiral phase plate with horn feed for OAM beam generation for 6G communication

3D printable PLA spiral phase plate with horn feed for OAM beam generation for 6G communication

Divide and structure: generating and interswitching orthogonal eigenstates of complementary petal beams using a π-shifted Sagnac interferometer.

One of the many facets of structured light are Ferris wheel/petal beams that can be generated by the addition/superposition of two beams with opposite vorticity/orbital angular momentum (OAM). We demonstrate a simple scheme employing a π-shifted Sagnac interferometer (SI) containing a spiral phase plate (SPP) that divides and structures an incoming beam into two azimuthally complementary petal beams representing orthogonal eigenstates. The half-wave plate in the SI can interswitch/route these intensity patterns between the two outputs of the interferometer. The results are interpreted as a double symmetry breaking--that of helicity due to SPP and handedness due to HWP--experienced by counterpropagating beams in the π-shifted SI. In general, for a Laguerre-Gaussian (LG) incoming mode, the SI produces two orthogonal output states, each consisting of a sum or difference of distinct SPP-modified LG modes and resulting in complementary petal beams convoluted with the incoming mode. We also introduce a three-mirror π-shifted SI that can switch on and switch off opposite sign vortices into different SI arms. The scheme can find applications in particle trapping, information transmission/development of communications protocols, and signal processing (i.e.,multiplexing/demultiplexing when using beams with high vorticity/OAM).

Dual-channel polarization-modulated metasurface

Metasurfaces provide excellent design flexibility, allowing for the creation of versatile integrated designs with significant potential for practical applications. This paper proposes a dual-channel polarization-modulated metasurface, which realizes the modulation of line-polarized light (LP) to circularly polarized light (CP) with opposite rotation. The polarization state of the dual channels can be changed by adjusting the polarization angle of the line-polarized light. Through the reasonable selection of element atoms, the function of the quarter waveplate is combined with the wavefront control of the general metalens, and the spiral phase can be arbitrarily added to the two channels to realize the simultaneous generation of multi-mode vortex beams. This work achieves functional integration on a single-layer metasurface, enabling its application in polarization imaging and other areas. This work achieves functional integration on a single-layer metasurface, enabling its application in polarization imaging and other areas.

Manipulating the Generation of Photonic Moiré Lattices Using Plasmonic Metasurfaces.

The generation of moiré lattices by superimposing two identical sublattices at a specific twist angle has garnered significant attention owing to its potential applications, ranging from two-dimensional materials to manipulating light propagation. While macroscale moiré lattices have been widely studied, further developments in manipulating moiré lattices at the subwavelength scale would be crucial for miniaturizing and integrating platforms. Here, we propose a plasmonic metasurface design consisting of rotated nanoslits arranged within N + N' round apertures for generating focused moiré lattices. By introducing a spin-dependent geometric phase through the rotated nanoslits, an overall lens and spiral phase can be achieved, allowing each individual set of round apertures to generate a periodic lattice in the focal plane. Superimposing two sets of N and N' apertures at specific twist angles and varying phase differences allows for the superposition of two sublattices with different periods, leading to the formation of diverse moiré patterns. Our simulations and theoretical results demonstrate the feasibility of our proposed metasurface design. Due to their compactness and tunability, the utilization of metasurfaces in creating nanoscale photonic moiré lattices is anticipated to find extensive applications in integrated and on-chip optical systems.

Photo-Aligned Ferroelectric Liquid Crystal Fork Grating-Mediated Fast Switchable Spiral Phase Contrast Imaging

Extensive research has been devoted to spiral phase contrast imaging because of its notable capacity to enhance the edges of both phase and amplitude objects. We demonstrate a setup using ferroelectric liquid crystal (FLC) fork grating (FG) to enable switchable spiral phase contrast imaging within sub-milli-second responses. This system enables the electrical toggling between images featuring edge enhancement and those without it. The specially designed FLC FG generates a vortex beam while in a diffractive state and transmits a Gaussian beam when in a transmissive state. Using a two-step photo-alignment method, the produced FLC FG exhibits exceptional efficiency at approximately 35% and impressively rapid switching at around 307 μs. By introducing this method, we expand the potential applications of spiral phase contrast imaging, particularly in fields such as bio-sensing and photonics.

Optothermal shaping of lamb waves with square and spiral phase fronts

We introduce a Lamb-wave medium with tunable propagation velocities, which are controlled by a two-dimensional heating pattern produced by a laser beam. We utilized it to demonstrate that waves in an appropriately designed medium can propagate in the form of concentric squares, in contrast to the circular patterns typically emitted by a point source in a homogeneous two-dimensional medium. In order to avoid the concentration of wave energy in the middle of the sides of the squares, we propose two alternatives: a square wave that either rotates or exponentially decelerates as it expands. Additionally, we present how circular waves can be transformed into spiral waves utilizing the same tunable medium. The described experimental platform offers a new tool to generate shaped pulses for ultrasonic applications, which has the potential to improve the efficiency of energy and information transport.

Edge enhancement in three-dimensional vortex imaging based on FINCH by Bessel-like spiral phase modulation.

Edge enhancement, as an important part of image processing, has played an essential role in amplitude-contrast and phase-contrast object imaging. The edge enhancement of three-dimensional (3D) vortex imaging has been successfully implemented by Fresnel incoherent correlation holography (FINCH), but the background noise and image contrast effects are still not satisfactory. To solve these issues, the edge enhancement of FINCH by employing Bessel-like spiral phase modulation is proposed and demonstrated. Compared with the conventional spiral phase modulated FINCH, the proposed technique can achieve high-quality edge enhancement 3D vortex imaging with lower background noise, higher contrast and resolution. The significantly improved imaging quality is mainly attributed to the effective sidelobes' suppression in the generated optical vortices with the Bessel-like modulation technique. Experimental results of the small circular aperture, resolution target, and the Drosophila melanogaster verify its excellent imaging performance. Moreover, we also proposed a new method for selective edge enhancement of 3D vortex imaging by breaking the symmetry of the spiral phase in the algorithmic model of isotropic edge enhancement. The reconstructed images of the circular aperture show that the proposed method is able to enhance the edges of the given objects selectively in any desired direction.

PROPAGATION OF VECTOR VORTEX BEAMS EXCITED BY A TERAHERTZ LASER DIELECTRIC RESONATOR

In this paper, analytical expressions for the nonparaxial mode diffraction of a terahertz laser dielectric waveguide resonator are derived. It is assumed that the modes interact with a spiral phase plate. The cases of different topological charges (n) are considered. Also, using numerical simulations, the physical features of emerging vortex beams are studied when they propagate in free space. The Rayleigh-Sommerfeld vector theory is used to study propagation of the vortex laser beams in different diffraction zones excited by the modes of a dielectric waveguide quasi-optical resonator upon incidence on a spiral phase plate. It is shown that the interaction of a spiral phase plate with a linearly polarized EH&lt;sub&gt;11&lt;/sub&gt; mode forms a ring (n &amp;#61; 1, 2) due to field structure with an intensity maximum at the center (n &amp;#61; 0). For the azimuthally polarized TE&lt;sub&gt;01&lt;/sub&gt; mode, the ring (n &amp;#61; 0) field structure transforms into a field distribution with an intensity maximum at the center (n &amp;#61; 1) and then back to a ring (n &amp;#61; 2). In this case, the phase front of the EH&lt;sub&gt;11&lt;/sub&gt; mode beam turns from a spherical shape to a spiral one with one singularity point on the axis, while a region with two singularity points appears off the axis for the phase structure of the TE&lt;sub&gt;01&lt;/sub&gt; mode beam.