Beam Phase Research Articles

Optimization and multiphysics analysis of high-performance lithium niobate modulators

Thin-film lithium niobate electro-optic modulators (TFLN EOMs) are widely utilized across various fields due to their exceptional performance. In this theoretical study, we optimized a TFLN EOM featuring a multimode interference coupler, cosine-curved waveguides, and a modulating arm straight waveguide structure. By tuning the etching depth, waveguide width, and geometric parameters of the traveling wave electrodes, we achieved a half-wave voltage-length product of 1.6V⋅cm and a 3 dB bandwidth of approximately 140 GHz. Additionally, we performed a multiphysics analysis to investigate the temperature characteristics of the modulator. The results indicate that increased temperature induces thermal-optic effects in the material, leading to changes in the waveguide’s refractive index and the optical beam phase, which results in increased insertion loss. Moreover, the stress generated by thermal expansion is concentrated in the modulator’s waveguide, representing a weak point that is prone to failure.

Enhancement of beam quality and transmission using phase bunching in the central region of a cyclotron

Phase bunching in the central region of an azimuthally varying field (AVF) cyclotron contributed significantly to the improvement of the extracted beam quality. The phase bunching effect was demonstrated by measurements of the accelerated and extracted beam properties and by a theoretical analysis using the upgraded geometric trajectory model of the AVF cyclotron at the facility of Takasaki Ion accelerators for Advanced Radiation Application. The phase bunching effect on the beam extraction efficiency and emittance was estimated by a comparison between the 260 MeV 20Ne7+ beam of harmonic number h = 2 in the phase-bunching condition (PBC) and the 107 MeV 4He2+ beam of h = 1 in the non-phase-bunching condition (NBC). The PBC narrowed beam phase width and produced near-single-turn extraction, resulting in high extraction efficiency more than twice as high as that for the NBC. It was proved by beam current measurements. Reduction of the beam phase width was confirmed by the theoretical and experimental analysis of correlation between the radial positions at the phase-defining slits and the phase distribution of the particles passing through the slits. The theoretical analysis also showed that the beam emittance before extraction under the PBC is reduced to less than half of the NBC case. Furthermore, the measured normalized beam emittance in the horizontal direction after the extraction for the PBC was remarkably improved to 0.054π mm mrad nearly one-fourth of the emittance of 0.20π mm mrad for the NBC.

Measuring the topological charge of a vortex beam via the self-rotating beam phase

We proposed a method to measure the topological charge of a vortex beam by using the self-rotating beam phase in this Letter. We investigated the far-field intensity patterns of the vortex beams passing through a phase hologram of the self-rotating beam with n = +2 theoretically and experimentally. The results demonstrate that the far-field intensity patterns cannot exhibit bright stripes when the topological charge of the vortex is positive (i.e., n ⋅ l > 0) and the calculated ratio relationship ξ can be used to identify the topological charge of the vortex beam. Differently, it can be found that the far-field intensity patterns exhibit several bright stripes when the topological charge of the vortex is negative (i.e., n ⋅ l < 0) and the number N of the bright stripes is equal to |l|−1(l represents the topological charge of the vortex beam). The experimental results are in good agreement with the theoretical ones. This method may inspire further research in the field of self-rotating beams.

Optically Controlled Fine-Tuning Phase Shift Cell Based on Thin-Film Ge2Sb2Te5 for Light Beam Phase Modulation

We present the experimental study of free-space optical control of the optical beam phase shift caused by the formation of a layered structure in an elementary controllable cell made of phase-change material Ge2Sb2Te5 subjected to the controlling effect of pulsed laser radiation. The phase change of the signal optical beam passing through the controlled cell from phase-change material relative to the control beam in the Jamin interferometer is demonstrated.

Holographic encryption with power-exponent helicon-conical optical vortices

We present a holographic encryption technique that combines the orbital angular momentum (OAM) multiplexing method with power-exponent helico-conical (PEHC) optical vortices. By incorporating the power exponent and normalization factor of the PEHC beam's phase into the selective modulation of OAM modes, we unlock their potential as encoding degrees of freedom in holographic multiplexing. Through the integration of these parameters with the topological charge, we develop an approach to OAM multiplexing for encryption, increasing both the storage capacity of holographic information and data security. To validate our proposed method, we conducted numerical simulations and optical experiments, which confirmed the promising potential of utilizing the adopted noncanonical vortices as an efficient and reliable strategy for achieving holographic encryption.

Mode matching with a phase camera for gravitational-wave detectors

Mode mismatch causes a large fraction of optical losses in gravitational-wave detectors. This effect will need to be considerably reduced in next generation detectors in order to fully exploit advanced techniques such as squeezing. Phase cameras are wavefront sensors capable of imaging the amplitude and phase of a laser beam. We simulate a measurement scheme with the phase camera and show that the two resulting error signals can be used to act on the two mismatch degrees of freedom in a closed loop.

Low cross-talk optical addressing of trapped-ion qubits using a novel integrated photonic chip

Individual optical addressing in chains of trapped atomic ions requires the generation of many small, closely spaced beams with low cross-talk. Furthermore, implementing parallel operations necessitates phase, frequency, and amplitude control of each individual beam. Here, we present a scalable method for achieving all of these capabilities using a high-performance integrated photonic chip coupled to a network of optical fibre components. The chip design results in very low cross-talk between neighbouring channels even at the micrometre-scale spacing by implementing a very high refractive index contrast between the channel core and cladding. Furthermore, the photonic chip manufacturing procedure is highly flexible, allowing for the creation of devices with an arbitrary number of channels as well as non-uniform channel spacing at the chip output. We present the system used to integrate the chip within our ion trap apparatus and characterise the performance of the full individual addressing setup using a single trapped ion as a light-field sensor. Our measurements showed intensity cross-talk below ~10–3 across the chip, with minimum observed cross-talk as low as ~10–5.

Two fast multiturn injection models for synchrotron injection efficiency optimization

A multiturn injection scheme is used in the XiPAF-Upgrading synchrotron, with beam loss mainly occurring at the injection septum. The paper presents two theoretical models for calculating the efficiency of multiturn injection in compact synchrotrons, with a focus on the situation of dispersion mismatch at the injection point. The first model is the beam phase ellipse rotation model, which is based on the beam projection distribution. The second model is the injection septum rotation model, which is based on the particle coordinate criterion. The deviation in efficiency between both injection models and the simulation results is less than 5%, and the calculation speed has increased by a factor of 1000 compared to PyORBIT simulations. The models are used to optimize the multiturn injection efficiency of the XiPAF-Upgrading synchrotron, resulting in an optimal injection efficiency of 92%.

Propagation dynamics of orbital angular momentum beams under the hazy scattering environment

The disturbance of the scattering medium, such as hazy, can affect the propagation of vortex beams and induce cross−talk within the orbital angular momentum (OAM) spectrum in optical communications based on vortex beams. This paper first validates the integrated scattering phase screen model through experimental beam phase measurements using a simple interferometer. Then, the influence of macroscopic physical parameters of the scattering medium on the OAM spectrum is investigated based on the hazy scattering phase model. It is demonstrated that the larger particle radius, concentration, and thickness will result in a greater cross−talk of the OAM spectrum. Moreover, the behavior of multiplexed vortex beams influenced by the hazy environment is also studied. The results may be a powerful tool to estimate the effect of the scattering medium on beam quality in optical communication based on vortex beams.

Exploring single-shot propagation and speckle based phase recovery techniques for object thickness estimation by using a polychromatic X-ray laboratory source.

Propagation and speckle-based techniques allow reconstruction of the phase of an X-ray beam with a simple experimental setup. Furthermore, their implementation is feasible using low-coherence laboratory X-ray sources. We investigate different approaches to include X-ray polychromaticity for sample thickness recovery using such techniques. Single-shot Paganin (PT) and Arhatari (AT) propagation-based and speckle-based (ST) techniques are considered. The radiation beam polychromaticity is addressed using three different averaging approaches. The emission-detection process is considered for modulating the X-ray beam spectrum. Reconstructed thickness of three nylon-6 fibers with diameters in the millimeter-range, placed at various object-detector distances are analyzed. In addition, the thickness of an in-house made breast phantom is recovered by using multi-material Paganin's technique (MPT) and compared with micro-CT data. The best quantitative result is obtained for the PT and ST combined with sample thickness averaging (TA) approach that involves individual thickness recovery for each X-ray spectral component and the smallest considered object-detector distance. The error in the recovered fiber diameters for both techniques is , despite the higher noise level in ST images. All cases provide estimates of fiber diameter ratios with an error of 3% with respect to the nominal diameter ratios. The breast phantom thickness difference between MPT-TA and micro-CT is about 10%. We demonstrate the single-shot PT-TA and ST-TA techniques feasibility for thickness recovery of millimeter-sized samples using polychromatic microfocus X-ray sources. The application of MPT-TA for thicker and multi-material samples is promising.

Transfer of optical vortices in a coherently-prepared rare-earth-ion-doped solid

Optical vortices carrying orbital angular momentum (OAM) of light have earned much attention due to their potential applications in the classical and quantum physics. Quantum coherence has been proved to be an important tool for controlling the behavior of light fields. Developing the manipulation method of optical vortices is very useful for high-dimensional information processing encoded with OAM. In this paper, we experimentally investigate the transfer of optical vortices between different light modes in a coherently-prepared solid-state medium. Utilizing the technique of fractional stimulated Raman passage (f-STIRAP), the experimental medium is prepared into a coherent superposition of two ground states. By applying a probe vortex beam to scatter the induced atomic coherence, a new signal is generated with the same vorticity as that of the input probe field. Furthermore, the vortex beams are used as the f-STIRAP preparation pulses, and the helical phases of the vortex beams are mapped into the coherent superposition state. Subsequently, the optical vortices of the preparation pulses are transferred to a new light mode by using the probe beam to interact with the coherent medium. The new signal field accumulates the total topological charges of the applied fields in this coherent process. Such an experimental demonstration will enrich the interactions between optical vortices and matter, and can be helpful in further information processing.

Accelerator beam phase space tomography using machine learning to account for variations in beamline components

We describe a technique for reconstruction of the four-dimensional transverse phase space of a beam in an accelerator beamline, taking into account the presence of unknown errors on the strengths of magnets used in the data collection. Use of machine learning allows rapid reconstruction of the phase-space distribution while at the same time providing estimates of the magnet errors. The technique is demonstrated using experimental data from CLARA, an accelerator test facility at Daresbury Laboratory.

“Two-dimensional distribution reconstruction and emittance diagnostics of proton beam phase space using tomography”

A two-dimensional distribution of a proton beam in phase space was reconstructed using beam profile data and a tomography technique in this study. These beam profile data were acquired by a wire scanner under various beam optics conditions, employing an experimental procedure identical, in principle, to the quadrupole magnet (QM) scan method to diagnose beam parameters. According to beam optics, beam profile data measured while changing the QM current is the same as that measured while rotating the beam distribution in the phase space. Thus, the set of the beam profile data can be converted into a sinogram, serving as source data for tomography. A filtered-back-projection (FBP) method is applied to reconstruct the beam distribution from this sinogram. However, if the range and distribution of the rotation angle are not sufficient, the reconstructed distribution data will be inaccurate, which will negatively affect beam parameter evaluation. To solve this limitation, a simulator incorporating the beam optics theory with the tomography was developed to derive an efficient experimental condition. The beam distribution in the phase space was successfully reconstructed, and the beam parameters evaluated from this were also confirmed to match well with the values obtained from the QM scan.

Simple 3D PIC Analysis for Beam Phase Space Oscillation in RF Driven Negative Hydrogen Ion Source

Temporal oscillation of the negative hydrogen ion (H−) beam in the Radio Frequency (RF) ion source is investigated by a simple 3D3V Particle-In-Cell (PIC) model. The model solves electron, proton, and H− transport processes in the extraction region. The calculation domain is from the vicinity of the beam aperture to the ground electrode. To understand the relation between the plasma density oscillation and the extracted H− beam characteristics, the input electron and proton fluxes from the driver region are varied parametrically with the fundamental J-PARC RF frequency (2 MHz). The numerical results give an idea of the main physical processes between the oscillations of the plasma parameters and the extracted H− ion trajectories depending on the plasma meniscus shape in the different RF phases.

Research and development of a muon entrance trigger for the muEDM experiment at PSI

The muEDM experiment at the Paul Scherrer Institute (PSI) in Switzerland aims to probe the muon electric dipole moment (EDM) using the frozen-spin technique in a compact storage ring, with a sensitivity of 6×10−23 e⋅cm. A fast entrance detector is expected to work in concert with a magnetic pulse generator to direct muons into the desired orbit. Simultaneously, the entrance detector is designed to veto muons that exceed the apparatus's admittance without introducing significant multiple scatterings. We developed a prototype entrance trigger detector consisting of a thin scintillator for detecting incoming muons and four wall scintillators as veto detectors. The prototype was tested at 27.5 MeV/c at the πE1 beamline at PSI. A total of 7×105 events were collected, which were read out by SiPMs coupled to the plastic scintillators under two different beam tunes. These events were analyzed to characterize the detector's performance, which was also cross-checked with Monte Carlo simulations that took into account the beam phase space and scintillation processes.

Generation of auto-focusing vortex beam via segment vortex phase for imaging edge-enhancement

The auto-focusing beam based on the circular Airy beam and segmented vortex phase, termed circular Airy segmented vortex beam (CASVB), was generated. During propagation, the focusing properties of the CASVB can be flexibly tunable for multiple degrees of freedom. The results show that the segmentation type of the vortex phase are determined by the number and position of phase jumps, which results in the beam split. Moreover, the number and position of the CASVB gaps coincide with the number and position of the phase jumps. In addition, the edge images can be enhanced by combining the phase of the beam with the phase of the lens. Due to its adjustable number and position of gaps, the CASVB will likely give rise to potential applications in manipulating particles along different segmented intensity trajectories.

Analysis of single particle and collective beam effects in high intensity beams in a periodic quadrupole channel

In high intensity proton accelerators, there are two main mechanisms that can cause beam degradation: incoherent and coherent effects due to nonlinear space charge forces. The incoherent effects represent the single particle dynamics while the coherent effects represent the collective response of the beam. Of particular interest is the region above a zero current phase advance (σ0) of 90° where the (coherent) second-order envelope instability and the (incoherent) fourth-order particle resonance are seen to lead to emittance growth. Large emittance growth is also seen below the envelope instability region as the full current beam phase advance (σ) decreases. In the present study, we have studied the nonlinear effects in a high intensity beam propagating through a focusing-defocusing (FD) quadrupole channel for σ0 greater than 90°, both analytically, by studying the solutions of Kapchinsky-Vladimirsky (KV) equation and the particle core model, and through detailed particle-in-cell (PIC) simulations using the code. The KV envelope equation gives the collective response of the beam while the particle core model gives the contribution of the single particle effects. With pic simulations, which resemble the behavior of the real beams more closely as compared to envelope calculations or the particle core model, it is possible to study the evolution of the beam in a self-consistent manner. Our studies show, that it is possible to identify the specific process responsible for beam degradation in high intensity beams. It is also possible to identify which process dominates under different conditions. We further show that the width of the emittance increase stop band calculated from PIC simulations is wider than that calculated by the envelope equations and that the width depends on the length of the channel being studied. Published by the American Physical Society 2024

Two-photon coherence in a DROP-FWM medium

In this work, we report experimental studies on coherence in a medium exhibiting DROP (Double Resonance Optical Pumping)-FWM (Four Wave Mixing). Here 5S1/2(F) → 5P3/2(F/) → 5D (F//) two photon transition of hot 87Rb atoms is used. The 5S→5P connection is modified by introducing an additional beam phase coupled to the original beam linking F = 2 → F/ transition. The frequency of the additional beam is offset from that of the original beam by ≈ +10Γ (Γ is natural linewidth). Such a two-beam configuration in F→F/ manifold effectively satisfies conditions of Vee (V) linkage or degenerate two-level connection (DTLC), depending on the detuning of the 780nm laser. This transformation profoundly affects the behavior of the ensuing Ladder (Ξ) system. While the (I) Ξ +V condition is favorable for Electromagnetically Induced Transparency (EIT), the (ii) Ξ + DTLC brings in the effect of Electromagnetically Induced Absorption (EIA). The EIT-dominated situation is helpful for FWM to take place, and the EIA effect augments the stronger presence of DROP. This condition is verified by monitoring the blue fluorescence emanating from the 5D→6P3/2→5S1/2 decay route. The DROP effect follows the Amplified Spontaneous Emission (ASE) pattern in the media. The origin of blue photons is also due to FWM under EIT conditions. In the case of EIA, the dominant condition increment in blue fluorescence is due to increased stimulated emission. The blue photons mainly contributed by (i) FWM and (ii) increased participation of stimulated emission are directional in nature and phase coherent.

RF direct sampling and processing electronics for SHINE cavity BPM system

Cavity BPMs are crucial for achieving submicron beam alignment in X-ray Free-Electron Lasers (XFEL), particularly in undulator sections. These monitors typically generate RF signals in the S, C, or X band regions. Due to the limitations of analog-to-digital converter's (ADC) bandwidth and sampling rates, and digital signal processing capabilities, heterodyne and homodyne receivers are often employed to down-convert the RF signal to an intermediate frequency (IF) or baseband (Zero IF) respectively before digital sampling. The digitized signal is then processed by Field Programmable Gate Array (FPGA) to get the beam position and phase information. An RF direct-sampling beam signal processor has been developed using ADCs with a bandwidth of 9 GHz and a sampling rate of 2.6 GSPS, and a powerful system-on-chip FPGA. In addition, a prototype RF module without complex down conversion devices has been designed for the SHINE (Shanghai High Repetition Rate XFEL and Extreme Light Facility) cavity BPM. The processor and the RF module make a novel RF direct sampling and processing cavity BPM electronics for SHINE. This is the first attempt to use direct sampling electronics in the C band cavity BPM system. The analog signal processing chain is greatly simplified compared to the down-conversion structure. The performance of this electronics has been analyzed and evaluated in laboratory. The amplitude relative error is 2.0 × 10-4, surpassing the required accuracy of 1 × 10-3 for cavity BPM systems. The phase error is 14 femtoseconds (fs), which also meets the requirements for an RF Beam Arrival Time Monitor (BAM) system. Additionally, the paper introduces the cavity BPM signal processing algorithms and their implementation in FPGA. The processor can deliver pulse-to-pulse beam position measurement above 1 MHz. The RF direct-sampling electronics represents significant advancements in cavity BPM system, large-scale application can be carried out in accelerator facilities like SHINE.

Photon subtraction with a Mach–Zehnder interferometer and its application to entanglement enhancement

Photon subtraction (PS) is an important operation for optic quantum information processing. Conventional PS is implemented using a single linear beam splitter (BS) and photon detector. However, in this study, we show that the PS effect can be enhanced using two beam splitters and an optional phase modulator. This can be considered PS with an extended version of the well-known Mach–Zehnder (MZ) interferometer. By tuning the transmittance of the two beam splitters and phase modulator, the probability of success can be considerably improved over that of the original PS scheme with a single BS and photon detector. Moreover, if applied to a single-photon input, our proposed scheme can even implement deterministic PS, which is almost impossible for the original scheme with a single BS and photon detector. Owing to the higher probability of success, applying the PSMZ method to the entanglement enhancement of a very weak two-mode squeezed vacuum state is straightforward. Our result is helpful for improving the yield of output entanglement.