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Originating from the stochastic nature of the photon emission process, the diffusion of the electron longitudinal coordinate exists even if the global phase slippage of a storage ring is zero, as we cannot zero all the local phase slippages simultaneously. This quantum diffusion is viewed as the most fundamental limit of the lowest bunch length realizable in an electron storage ring from the single-particle dynamics perspective. Here, we present an analysis of this effect using the Courant-Snyder parametrization in the longitudinal dimension. Analytical formulas for the longitudinal emittance, energy spread, and bunch length are derived. The same formalism is used to discuss the application of multiple radio frequency systems for longitudinal strong focusing. The presented work is expected to be useful in the development of novel light source mechanisms like steady-state microbunching, where a short bunch length or small longitudinal emittance is needed.

In Harbin, the 300 MeV proton microprobe system with long-length quadrupole lenses, as a component of the Space Environment Simulation Research Infrastructure (SESRI), is under development driven by many applications in space science and proton therapy. Significant challenges have previously been addressed including minimization of ion scattering from collimators and the development of promising focusing systems compatible with the large beam magnetic rigidity. Here the intrinsic aberrations contributed by the fringe field regions of quadrupole lenses in the probe forming lens system are investigated with respect to the model used for the fringe field profile. The investigation compares the rectangular model, commonly used with the matrix method, and a more sophisticated model employing a multiphysics code for the full field profile used with a numerical raytracing method. For computational and constructional efficiency the proposed triplet system of long-length quadruple lenses required to achieve strong focusing was split into three pairs of two identical short quadrupole lenses, forming a sextuplet microprobe system. The comparison of the two fringe field models show large variations in the aberration coefficients of this system, however the rectangular model is suitable for a broad survey of possible systems to identify promising configurations for further optimization.

Twisting behaviors of the optical vortices and the intensity patterns of a strongly focused, circularly polarized field with two off-axis vortices are investigated in this article. The transverse focal shift (TFS) which is mainly caused by the off-axis vortices and the strong focusing effect is also studied. It is very interesting to find that in the focal region the two off-axis vortices can coil many circles with each other as the beam propagates, and their trajectories form a double helical structure. Three factors for this twisting behavior are analyzed. It is also found that the intensity maxima of the total field are not strongly influenced by the twisting behavior of the vortices and rotate only a quarter circle (90°) to the focal plane. In contrast to the TFS in the linearly polarized field, the ‘actual focus/foci’ in this circularly polarized field does/do not move between the + y s axis and the − y s axis or the y s axis and the x s axis, but is/are always confined on the + y s ∕ y s axis. These results will be useful in understanding the general rotational behaviors in optical fields with off-axis vortices and can have applications in optical manipulations.

The fast beam ion instability (FBII) in electron storage ring is widely studied by solving two coupled equations of motion for electrons and ions. The instability growth rate was estimated from the analytical method and also from the numerical method using strong–weak and strong–strong interactions among the electrons and ions. In a storage ring, several ion species exists, and each of them have different ion frequencies at different locations along the circumference, due to strong focusing lattice. This creates a spread in ion frequencies, and that helps in damping the instability effect via Landau damping . In essence, ions couple the electron beam with different oscillating frequencies. The combined contributions of multi-gas species and optics variation in the lattice are taken care by solving the fast ion instability in the wake function formalism. Here, the wake field produced by the ions is estimated following a similar procedure, which is being used for the cavity like structure inside the vacuum chamber. Since the associated wake function due to ions last for duration more than the bunch to bunch separation duration, it drives multi-bunch instability. We investigate the possibility of FBII for the Indus-2 storage ring using the growth rate formulation of conventional multi-bunch instability, and the results are presented. Also a suitable bunch filling pattern is mooted for suppression of the FBII.

The ARTEMIS model is used to numerically analyze the wave conditions near the Sabetta-Utrenniy port of different layouts. Monochromatic and spectral waves were considered. The results show that a navigation channel can not only cause strong focusing of wave energy, but also give rise to zones of reduced waves. It is important to recognize these effects and use them to optimize the project.

Structured light applications [1] , [2] require introducing a phase aberration to shape the beam for a specific purpose and with these applications, often strong focusing is involved. The demand for modeling algorithms to handle every regime of propagation is increasing. Geometrical optics do not require the full sampling of the electromagnetic field in contrast to physical optics methods, as such, beams with strong phase factors are managed more efficiently. Although it is not accurate near the focal regions, geometrical optics can be used for regions with spatial variations of the refractive index. All necessary information is the mapping function from the input to the output plane, which can be acquired via ray-tracing. Propagation to the focal plane especially in a non-paraxial regime can be realized using Debye-Wolf (DW) integral; this solution is suited for well-designed systems since does approximate the amplitude strength factor as for an ideal lens. By strength factor of a ray, first defined in [3] , we refer to the Jacobian determinant of the ray mapping from the input to the output plane. A generalized version of DW that evaluates the amplitude strength factor numerically from the second-order derivatives of the phase function was described in [4] , this being valid also when stronger aberrations are present.

International Congress of Applications of Lasers & Electro-Optics, ICALEO 2020, online, 18 Oct 2021 - 20 Oct 2021; Journal of laser applications : JLA 33(4), 042013 (2021). doi:10.2351/7.0000532 special issue: "Proceedings of the International Congress of Applications of Lasers & Electro-Optics (ICALEO 2020)", Published by Laser Inst. of America, Orlando, Fla.

Radially polarized field under strong focusing has emerged as a powerful manner for fluorescence microscopy. However, the refractive index (RI) mismatch-induced aberrations seriously degrade imaging performance, especially under high numerical aperture (NA). Traditional adaptive optics (AO) method is limited by its tedious procedure. Here, we present a computational strategy that uses artificial neural networks to correct the aberrations induced by RI mismatch. There are no requirements for expensive hardware and complicated wavefront sensing in our framework when the deep network training is completed. The structural similarity index (SSIM) criteria and spatial frequency spectrum analysis demonstrate that our deep-learning-based method has a better performance compared to the widely used Richardson-Lucy (RL) deconvolution method at different imaging depth on simulation data. Additionally, the generalization of our trained network model is tested on new types of samples that are not present in the training procedure to further evaluate the utility of the network, and the performance is also superior to RL deconvolution.

Physical review accelerators and beams 23(5), 052802 (2020). doi:10.1103/PhysRevAccelBeams.23.052802, Matching to small beta functions is required to preserve emittance in plasma accelerators. The plasma wake provides strong focusing fields, which typically require beta functions on the mm-scale, comparable to those found in the final focusing of a linear collider. Such beams can be time consuming to experimentally produce and diagnose. We present a simple, fast, and noninvasive method to measure Twiss parameters in a linac using two beam position monitors only, relying on the similarity of the beam phase space and the jitter phase space. By benchmarking against conventional quadrupole scans, the viability of this technique was experimentally demonstrated at the FLASHForward plasma-accelerator facility., Published by American Physical Society, College Park, MD

A plasma sheath inside an ion source has a strong focusing effect on the formation of an ion beam from the plasma. Properties of the beam depend on the shape and location of the plasma sheath inside the source. The most accessible experimental data dependent on the plasma sheath are the beam phase space distribution. Variation of beam emittance is a reflection of the properties of the plasma sheath, with minimum emittance for the optimal shape of the plasma sheath. The location and shape of the plasma sheath are governed by complex physics and can be understood by simulations using plasma models in particle tracking codes like IBSimu. In the current study, a model of the D-Pace’s TRIUMF licensed filament powered volume-cusp negative ion source is made using the IBSimu code. Beam emittance trends are compared between experiments and simulations. peerReviewed

In the context of extended theories of teleparallel gravity $f(T)$ we derive the focusing conditions for a one-parameter dependent congruence of timelike auto-parallels of the Levi-Civita connection. We also consider the $f(T)$ field equations for a general metric tensor before moving on to consider a spatially flat Robertson-Walker space-time. Following this, we study the expansion rate for a one-parameter dependent congruence of timelike auto-parallel curves of the Levi-Civita connection. Given the fact that test particles follow auto-parallels of the Levi-Civita connection, the torsion-free Raychaudhuri equation is used in order to determine the desired focusing conditions. Finally we study the obtained focusing conditions for three $f(T)$ paradigmatic cosmological models and discuss the satisfaction or violation of these conditions. Through this, we find $f(T)$ models that allow for the weak and strong focusing conditions to be satisfied or violated. It is mentioned that this behaviour can also be found in the so-called $f(R)$ and $f(Q)$ theories., Comment: 31 pages, 9 figures, JCAP format, minor changes, matches published version in JCAP

The paper addresses the creation of strong circular dichroism from a femtosecond laser light with a linear polarization strongly focused in silica glass and perpendicular incidence. All aspects of the experiment are therefore achiral and should not give rise to chiral property creation if taken themselves alone. We investigate the laser-induced circular dichroism according to orientation of the laser polarization, pulse energy and focusing depth. It appears that deep focusing under high numerical aperture conditions leads to higher ellipticity when compared to shallow focusing or low numerical aperture focusing. Strong circular dichroism can be imprinted when polarization is at ±45° of the horizontal scanning direction in reference to the laser plan. In addition the generation of circular dichroism appears to be closely related to the spatial aberration, spatial chirp and beam elongation under strong focusing conditions.

Microscopic lenses are paramount in solar energy harvesting, optical devices, and imaging technologies. This work reports an extraordinary focusing effect exhibited by a surface nanolens (i.e., with at least one dimension of subwavelength) that is situated in an evanescent field from the total internal reflection (TIR) of light illuminated to the supporting substrate above the critical angle. Our measurements show that the position, shape, and size of the surface area with enhanced light intensity are determined by the geometry of the nanolens and the incident angle, in good agreement with simulation results. This strong focusing effect of the surface nanolens is shown to significantly promote the plasmonic effect of deposited gold nanoparticles on the lens surface inlight conversion and to vaporize surrounding water to microbubbles by using low laser power. This work further demonstrates that the light redistribution by the surface nanolens in TIR enables a range of novel applications in selectively local visualization of specimens in fluorescence imaging, optical trapping of colloids from an external flow, and selective materials deposition from photoreactions., Small scale lenses demonstrated a remarkable focusing effect when illuminated near the critical angle. This attribute yielded an enhanced plasmonic bubble formation, fluorescence signal, and local photoreaction.

Advanced diagnostic tools for high brightness electron beams are mandatory for the proper optimization of plasma-based accelerators. The accurate measurement of beam parameters at the exit of the plasma channel plays a crucial role in the fine tuning of the plasma accelerator. Electron beam diagnostics will be reviewed with emphasis on emittance measurement, which is particularly complex due to large energy spread and strong focusing of the emerging beams.

Journal of synchrotron radiation 24(2), 498 - 505 (2017). doi:10.1107/S160057751700128X, In X-ray holographic near-field imaging the resolution and image quality depend sensitively on the beam. Artifacts are often encountered due to the strong focusing required to reach high resolution. Here, two schemes for reconstructing the complex-valued and extended wavefront of X-ray nano-probes, primarily in the planes relevant for imaging (i.e. focus, sample and detection plane), are presented and compared. Firstly, near-field ptychography is used, based on scanning a test pattern laterally as well as longitudinally along the optical axis. Secondly, any test pattern is dispensed of and the wavefront reconstructed only from data recorded for different longitudinal translations of the detector. For this purpose, an optimized multi-plane projection algorithm is presented, which can cope with the numerically very challenging setting of a divergent wavefront emanating from a hard X-ray nanoprobe. The results of both schemes are in very good agreement. The probe retrieval can be used as a tool for optics alignment, in particular at X-ray nanoprobe beamlines. Combining probe retrieval and object reconstruction is also shown to improve the image quality of holographic near-field imaging., Published by IUCr, Chester

In this paper, a recently-proposed pure-phase optical element, the fractal conical lens (FCL), is introduced for the regulation of strongly-focused circularly-polarized optical vortices in a high numerical aperture (NA) optical system. Strong focusing characteristics of circularly polarized optical vortices through a high NA system in cases with and without a FCL are investigated comparatively. Moreover, the conversion between spin angular momentum (SAM) and orbital angular momentum (OAM) of the focused optical vortex in the focal vicinity is also analyzed. Results revealed that a FCL of different stage S could significantly regulate the distributions of tight focusing intensity and angular momentum of the circularly polarized optical vortex. The interesting results obtained here may be advantageous when using a FCL to shape vortex beams or utilizing circularly polarized vortex beams to exploit new-type optical tweezers.

In our previous publications, we introduced a concept of complex bend, which is a bending element consisting of dipole poles, interleaved with strong focusing and defocusing quadrupole poles. An electron ring built from such elements features low emittance while preserving substantial room for insertion devices and associated lattice elements. In this paper, we present two new optics solutions for the complex bend which offer to substantially reduce the device length by removing the dipole poles. In the first of the solutions, the bending is realized by shifting the quadrupole poles along the curved horizontal axis. For the second solution, we use permanent magnet quadrupole poles installed into a wide gap of the conventional electromagnet. In this case, the resulting bending field in the magnet gap is a superposition of the quadrupole field from the poles and the dipole field from the conventional magnet. We present an analysis of the particle motion and synchrotron radiation emitted in such fields, as well as an assessment of the ring linear lattice that is composed of complex bend elements.

Plasma-based accelerators offer accelerating fields orders of magnitude higher than conventional radio-frequency cavities. However, these accelerating fields are typically coupled with strong focusing fields, which can result in significant radiative energy loss at high energies. In this work, we present a new accelerator configuration, the Matryoshka channel, a hollow plasma channel stabilized by a hollow plasma filament. We demonstrate that the absence of on-axis focusing plasma fields greatly reduces radiation losses, allowing acceleration to the TeV frontier., 4 pages, 3 figures

Scanning Acoustic Microscopes for nondestructive imaging commonly use strong focusing single element probes with center frequencies up to 230 MHz. Depending on the test scenario and the materials a resolution down to 10 µm is reachable. This high resolution means a small extension of the sensitivity zone in lateral and axial direction and leads to the necessity of multiple C-Scans for the inspection of a volume. Using an annular-array transducer, the focal point can be shifted in axial direction. Thus, multiple scans in different depth can be replaced by a single scan. To achieve a comparable resolution to strong focused single element transducers it is necessary to increase the center frequency of annular-array transducers. So we present a prototype of a probe, that contains a planar annular-array transducer with a center frequency of 20 MHz and an aperture of 5.4 mm, separated into four quartered rings (16 elements). The characterization of the sound field, using a spherical reflector, shows a sensitivity zone with a lateral extension of 300 µm for focusing without a lens.

A current challenge that is facing the plasma wakefield accelerator (PWFA) community is transverse beam emittance preservation. This can be achieved by balancing the natural divergence of the beam against the strong focusing force provided by the PWFA plasma source in a scheme referred to as beam matching. One method to accomplish beam matching is through the gradual focusing of a beam with a plasma density ramp leading into the bulk plasma. Here, the beam dynamics in a Gaussian plasma density ramp are considered, and an empirical formula is identified that gives the ramp length and beam vacuum waist location needed to achieve near-perfect matching. The method uses only the beam vacuum waist beta function as an input. Numerical studies show that the Gaussian ramp focusing formula is robust for beta function demagnification factors spanning more than an order of magnitude with experimentally favourable tolerances for future PWFA research facilities. This article is part of the Theo Murphy meeting issue ‘Directions in particle beam-driven plasma wakefield acceleration’.

A hybrid seven-bend-achromat lattice that features very strong focusing elements and a relatively small vacuum chamber has been proposed for the Advanced Photon Source (APS) upgrade. The design lattice parameters during commissioning will need to be quickly achieved in order to minimize the interruption of user operation. This paper describes start-to-end simulation of the machine commissioning beginning from first-turn trajectory correction, progressing to orbit correction, and culminating in lattice correction and coupling adjustment. The automated commissioning procedure shows that the rapid commissioning of the ultralow emittance lattice is possible. It also enables a more rigorous statistical evaluation of expected performance of proposed lattices.

Laser-wakefield accelerators (LWFAs) are high acceleration-gradient plasma-based particle accelerators capable of producing ultra-relativistic electron beams. Within the strong focusing fields of the wakefield, accelerated electrons undergo betatron oscillations, emitting a bright pulse of X-rays with a micrometer-scale source size that may be used for imaging applications. Non-destructive X-ray phase contrast imaging and tomography of heterogeneous materials can provide insight into their processing, structure, and performance. To demonstrate the imaging capability of X-rays from an LWFA we have examined an irregular eutectic in the aluminum-silicon (Al-Si) system. The lamellar spacing of the Al-Si eutectic microstructure is on the order of a few micrometers, thus requiring high spatial resolution. We present comparisons between the sharpness and spatial resolution in phase contrast images of this eutectic alloy obtained via X-ray phase contrast imaging at the Swiss Light Source (SLS) synchrotron and X-ray projection microscopy via an LWFA source. An upper bound on the resolving power of 2.7 ± 0.3 μm of the LWFA source in this experiment was measured. These results indicate that betatron X-rays from laser wakefield acceleration can provide an alternative to conventional synchrotron sources for high resolution imaging of eutectics and, more broadly, complex microstructures.

International audience; The laser plasma accelerator has shown a great promise where it uses plasma wakefields achieving gradients as high as GeV/cm. With such properties, one would be able to build much more compact accelerators, compared to the conventional RF ones, that could be used for a wide range of fundamental research and applied applications. However, the electron beam properties are quite different, in particular, the high divergence, leading to a significant growth of the emittance along the transport line. It is, thus, essential to mitigate it via a strong focusing of the electron beam to enable beam transport. High-gradient quadrupoles achieving a gradient greater than 100 T/m are key components for handling laser plasma accelerator beams. Permanent magnet technology can be used to build very compact quadrupoles capable of providing a very large gradient up to 500 T/m. We present different designs, modeled with a 3D magnetostatic code, of fixed and variable systems. We also review different quadrupoles that have already been built and one design is compared to measurements.

Electro-optic (EO) Bragg deflectors have been extensively used in a variety of applications. Recent developments show that bandwidths and deflection efficiencies, as well as angular bandwidths, would significantly limit the utilization of EO Bragg deflectors, especially for applications which need strong focusing, such as intra-cavity applications. In this paper, we introduce a broadband EO Bragg deflector based on periodically-poled lithium niobate with a monolithic dual-grating design. We analyzed the deflection properties of this device by using a modified coupled wave theory and showed that this device can be still efficient for a small beam radius under strong focusing, whereas a single-grating one becomes very inefficient. Using a 1064-nm laser beam with a 100-μm beam radius, we obtained a 74% deflection efficiency with a 190-V bias voltage with a 0.5-mm-thick and 7.5-mm-long dual-grating sample. The acceptance angle for the Bragg condition of this device is as large as a few tens of mrad. The potential bandwidth of this device exceeds 500 nm if the proper operation region is chosen.

Wavelength shift of modified second-harmonic bandwidth in a 20-mm-long engineered chirped periodically poled lithium niobate is experimentally demonstrated by focal-point displacement of a strongly focused pump beam of a 30- $\mu \text{m}$ beam waist. Utilizing this non-confocal arrangement in a cascaded second harmonic generation and difference frequency generation process, a CW probe as a signal wavelength is variably shifted within an 8-nm span by pump tuning using a $\sim 7$ -nm second-harmonic bandwidth.

Because circularly polarized vortex beam can be characterized as the linear superposition of radially polarized and azimuthally polarized components in the cylindrical coordinate. When investigating the focusing properties of the circularly polarized vortex beam, we must consider radially polarized vortex beam has azimuthal component and azimuthally polarized vortex beam has radial component after focusing. Due to this reason, the focusing properties of the circularly polarized vortex beams have been restudied based on the amending the tightly focusing formula of the circularly polarized vortex beam. The results show that not only the focusing of the single handedness of the circularly polarized vortex beam but also the focusing of superposition of two circularly polarized vortex beams with different topological charges and different handedness can generate the flat-top intensity shape. We also investigate the influence of amplitude ratio, waist radius and the aperture blocking on the flat-topped focus size.

A description is given on the methods used for field analysis of magnets and the extracted parameters used for accurate beam simulations of the fragment separator. For the strong focusing magnets, Fourier decomposition is used in order to extract induced fields associated with higher order multipoles. For dipoles, a 2D field map model is used instead in order to emulate complex field distributions. The theory of the models and the techniques chosen are described, along with results from Monte Carlo beam simulations up to 5th order. The n = 6 multipole induced by the quadrupole is the most significant component. The effects on separator performance with and without this component in the model are demonstrated.

Setting up collisions in high energy circular colliders requires beam acceleration and “beta-squeeze”. The latter produces small beam sizes, and hence, high luminosity by applying strong focusing with quadrupoles near the interaction points. At the Relativistic Heavy Ion Collider (RHIC), these two processes, beam acceleration and beta-squeeze, have been performed simultaneously during recent years. In the past, beam optics correction at RHIC has only taken place at injection and at final energy, with interpolation of corrections partially into the acceleration cycle. Recent measurements of the beam optics during acceleration and squeeze have evidenced significant beta-beats that, if corrected, could minimize undesirable emittance dilutions and maximize the spin polarization of polarized proton beams by avoiding the high-order multipole fields sampled by particles within the bunch. We recently demonstrated beam optics corrections during acceleration at RHIC. As a valuable by-product, these corrections minimized the beta-beat at the profile monitors, so providing more accurate measurements of the evolution of the beam emittances during acceleration.

The basic ion-optical characteristics of the luminosity and the high-resolution of kinematic separator COMBAS realized for the first time on the strong focusing principle are presented. The developed facility allows to separate the high-intensity secondary radioactive beams in a wide range of mass numbers A and atomic numbers Z which are produced in heavy ion reactions in the energy range of 20 ≤ E ≤ 100 MeV/A (Fermi energy domain). Two distinct detector systems such as realized Si strip detector telescope and the promising development of the three dimension time-projection chamber are discussed. Program of the investigations of nuclear reaction mechanisms at intermediate energies of 20–100 MeV/A, measurement of the radii of unstable nuclei, study of the cluster structure of light nuclei near the nuclear drip-line and search of 26,28O resonances in exchange reactions is proposed. The upgrading of experimental facility by the integration of COMBAS separator with the Ion Catcher is discussed.

The development of new clinical applications of therapeutic ultrasound has been accompanied by efforts to standardize simulation methods for predicting nonlinear ultrasound fields. Although software tools for simulating nonlinear ultrasound propagation are increasingly available, computational burdens remain high, especially for fields characterized by strong focusing and significant harmonic content. Because nonlinear effects in such fields accumulate primarily over a short axial distance within the focal lobe, the nonlinear field can be approximated by considering an equivalent source with a similarly shaped focal lobe in the linearly focused beam. If an axisymmetric equivalent source can be identified, even strongly nonlinear fields can be accurately simulated with minimal computational burden using the Khokhlov-Zabolotskaya- Kuznetsov model. This approach has been implemented and validated in water for several real sources using only a simple set of linear field measurements to characterize the focal lobe of each source. To demonstrate the breadth of utility of this approach, holograms of non-axisymmetric fields distorted by phantoms were also used to define equivalent sources and estimate in situ nonlinear fields. Fast holography measurements combined with equivalent-source simulations can efficiently characterize the impact of different phantom geometries on nonlinear fields. [Work supported by NIH R01EB025187 and R01EB007643, and RSF 19-12-00148.]

We report the method of producing a spatio-temporal (ST) wave packet carrying pure transverse orbital angular momentum (OAM) with subwavelength spatial sizes. Due to the lack of temporal focusing, an ST wave packet focused by a high numerical aperture (NA) objective lens experiences a “spatio-temporal astigmatism” effect similar to the focusing action of a cylindrical lens on the transverse profile of optical field. Thus an ST vortex with a spiral phase in the ST domain focused through a high NA objective will be distorted and lose the ST characteristic spiral phase pattern. With the understanding of such an ST astigmatism, the ST wave packet can be pre-conditioned such that an ST vortex carrying OAM with subwavelength transverse sizes can be obtained after strong focusing. This is the first revelation that a tightly focused ST vortex beam with transverse OAM can be realized, paving the way for potential applications including microscopy, optical trapping, laser machining, nonlinear light-matter interactions, and so on. The ST astigmatism effect also offers insights for the focusing and propagation studies of other types of ST wave packets.

White-light super-resolution imaging, proposed in 2011, has been achieved by combining the transparent microspheres of the micron scale with an ordinary optical microscope. At present, in most of the researches employed is the way of spreading microspheres directly onto the surface of sample, which causes the randomness and discontinuity of microspheres. It is impossible to achieve the complete imaging of specific regions, which greatly limits the application scope of this technology. Such an issue can be solved by using microprobes or micro-cantilevers to precisely transfer the location of microsphere, but for doing so, a sophisticated controlling system is required, which is costly and not user-friendly. In this paper, a robust, controllable, easy-to-use integrated design which can efficiently consolidate microsphere and objective together is demonstrated for super-resolution imaging. The PDMS and customized metal sleeve are used to encapsulate the microsphere semi-submerged on the ordinary objective lens to achieve an integrated design. In this system, the distances among the microsphere, objective lens and the sample are controlled accurately by building a side-view imaging and position feedback system. With the help of a universal microscopic imaging system, the super-resolution imaging of specific controlled areas is realized. Based on theoretical analysis, the semi-submerged structure of the 100-μm-diameter BaTiO3 microsphere has a strong focusing effect, which can form the so-called ‘photonic nanojet’ on a micro-scale in length and on a sub-diffraction scale in waist to possess the ability to break through the diffraction limit within the range of focal length. At the same time, experiments are carried out for investigating imaging performances at various working distances in the air. According to the experimental results, the system can clearly distinguish between the CPU lattice features of 200 nm and the Blu-ray disc fringe of 100 nm, which means that the resolution of the ordinary microscopic objective lens (40×, NA 0.6) is significantly enhanced by 4.78×. In addition, with the increase of working distance, the magnification factor increases gradually, but the image contrast becomes worse, and the super-resolution effect fades. The integrated design which can match with ordinary optical microscope to achieve super resolution imaging has universality of installation and operation, and greatly conduces to super-resolution imaging of sub-diffraction limit samples.

In spectral diagnostic physics experiments of inertial confinement fusion, the spectral signal is weak due to the low diffraction efficiency when using bent crystals. A spectral diagnostic instrument with high efficiency and wide spectral range is urgently needed. A multi-curvature bent crystal with multi-energy focusing ability is proposed based on the traditional conical crystal geometry. It has advantages of wide spectral range, strong focusing ability, and high spectral resolution. It also can eliminate the imaging aberration in principle due to rotational symmetry for the incoming X rays. A spectral diagnostic experiment based on a fabricated multi-curvature α-quartz crystal was accomplished using a titanium X-ray tube of the bent crystal, and the corresponding experimental data using a plane α-quartz crystal was also acquired to demonstrate the strong focusing ability. The result shows that the Kα intensity of the multi-curvature α-quartz crystal is 157 times greater than that of the plane crystal, and the corresponding energy range is about 4.51–5.14 keV. This diagnostic instrument could be combined with a streak camera at a vertical direction so as to intensify the diffracted X-ray signal with a wide spectral range.

Laser wakefield accelerators (LWFA) hold great potential to produce high-quality high-energy electron beams (e beams), and wiggling of these LWFA e beams either in the Conventional period magnetic field structure (undulator radiations), strong focusing laser wakefield (betatron radiation), or intense laser fields (Compton scattering) can emit high-energy x-ray photons. By experimentally generating the high-quality LWFA e beams with a good stability and repeatability, we have recently produced tunable quasi-monochromatic ultrahigh brilliance MeV γ-ray via the self-synchronized all-optical Compton scattering scheme and realized a scheme to enhance betatron radiation by manipulating transverse oscillation of electrons in a deflected wakefield with a tilted shock front. The concurrent generation of high-quality e beams and bright x-rays in a compact LWFA may provide practical applications in ultrafast pump-probe study and x-ray radiology fields.

Modern synchrotron light sources are competing intensively to increase x-ray brightness and, eventually, approach the diffraction limit, which sets the final goal of lattice emittance. All recent synchrotron facility upgrades follow the multibend achromat approach by arranging small horizontal beta function and dispersion inside discrete bending dipoles. In this paper we propose a concept of a lattice element that we call ``complex bend,'' which has the potential of becoming a main building block for low emittance lattices. The complex bend is a sequence of dipole poles interleaved with strong alternate focusing so as to maintain the beta function and dispersion oscillating at low values. Comprising the ring lattice with complex bends, instead of regular dipoles, will minimize the $H$-function and reduce horizontal emittance while localizing bending to a small fraction of the storage ring circumference, which should provide more space for insertion devices. In this paper we present the details of the complex bend, considerations regarding the choice of optimal parameters, and thoughts for its practical realization. We focus here on complex bend physics and engineering design, rather than integration of this complex bend into a specific ring lattice.

We derive a set of azimuthally polarized hollow beam solutions in free space. These solutions are exact vector solutions to Maxwell's and Poynting's equations with the electric- and magnetic-field components expressed as linear combinations of the partial derivatives of a sinc function. They depict beams the intensity of which vanishes everywhere on the beam axis, forming dark hollow channels. There is one adjustable dimensionless parameter $Q$ in the formulation which governs the degree of focusing of a beam. In the weak focusing limit $(Q\ensuremath{\gg}1)$, a beam shows a doughnut-shaped intensity profile while a multiple-ring intensity distribution is found for the strong focusing case with $Q\ensuremath{\le}1$.

Physical review letters 121(19), 194801 (2018). doi:10.1103/PhysRevLett.121.194801, Active plasma lensing is a compact technology for strong focusing of charged particle beams, which has gained considerable interest for use in novel accelerator schemes. While providing $kT/m$ focusing gradients, active plasma lenses can have aberrations caused by a radially nonuniform plasma temperature profile, leading to degradation of the beam quality. We present the first direct measurement of this aberration, consistent with theory, and show that it can be fully suppressed by changing from a light gas species (helium) to a heavier gas species (argon). Based on this result, we demonstrate emittance preservation for an electron beam focused by an argon-filled active plasma lens., Published by APS, College Park, Md.

We describe an approach for the automated design of photonic crystals for various applications. Our approach includes gradient-based optimization for arbitrary objective functions, with the electromagnetic fields calculated by an accurate multiple-scattering approach. An example of a two-color silicon photonic crystal demultiplexer designed by our method is presented, with dozens of parameters chosen automatically in reasonable time. The optimized device exhibits strong focusing with low crosstalk for both frequencies.

Beam-driven, underdense thin plasma lenses are a compact and tunable means of providing strong focusing to relativistic electron beams. It is necessary to focus electron beams to small sizes in a beam-driven plasma wakefield accelerator to preserve the beam emittance, or volume in phase space. The thin plasma lens can be used to achieve these small beam sizes that are otherwise out of reach of conventional electromagnetic beam delivery systems. Ultrashort (~ 30 fs), low energy (~ 10 mJ) laser pulses can be used to ionize a small region of gas to generate the thin plasma lens. The interplay between the ionized gas and the focusing of the laser pulse are modeled in detail to calculate experimentally achievable 3-D plasma lens profiles, which are then used in simulations of beam focusing. Plasma lens focal lengths and minimum beam sizes achievable are estimated, considering the effects of radiation reaction in both the classical and quantum regimes.

we study the sum frequency generation from high gain parametric down conversion with broadband spectrum in the absence of the phase matching. In the case of strong focusing, a set of interference spectral peaks in the spectrum of the second harmonic appear without the phase matching. Experimental data supported by theoretical modeling reveal the influence of correlation effects on non-phase matched sum frequency generation.