Transverse Spatial Distribution Research Articles

Compact Partially End-Pumped Innoslab Laser Based on Micro-Cylindrical Lens Array Homogenizer

We demonstrate a compact, partially end-pumping Innoslab laser based on a micro-cylindrical lens array homogenizer. A dimension of 12 × 0.4 mm2 flat-top pumping line with a Gaussian intensity distribution across the line was simulated by the ray tracing technique. The rate equations considering the asymmetric transverse spatial distributions are theoretically developed. The simulation results are in good agreement with the experimental results. Preliminary data shows that for a pump power of 260 W, a maximum pulse energy of 15.7 mJ was obtained with a pulse width of 8.5 ns at a repetition frequency of 1 kHz. The beam quality M2 factors in the unstable and stable directions were 1.732 and 1.485, respectively. The technology has been successfully applied to temperature and humidity profiling lidar and ozone lidar and has been productized, yielding direct economic value.

Probing the spatial distribution of gluons within the proton in the coherent vector meson production at large-|t|

The coherent production of vector mesons in photon–hadron interactions is considered one of the most promising observables to probe the QCD dynamics at high energies and the transverse spatial distribution of the gluons in the hadron wave function. In this paper, we perform an exploratory study about the dependence of the transverse momentum distributions, dσ/dt\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$d\\sigma /dt$$\\end{document}, on the model assumed for the proton density profile. We consider a set of non-Gaussian profiles and include them in the forward dipole–proton scattering amplitude associated with the IP-sat model. We demonstrate that the predictions for dσ/dt\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$d\\sigma /dt$$\\end{document} are similar in the HERA kinematical range, but are very distinct for values of t that will be probed in future colliders. In particular, the presence of diffractive dips in the t-distributions associated with the production of J/Ψ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$J/\\Psi $$\\end{document} and ρ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\rho $$\\end{document} mesons is strongly dependent on the model assumed for the density profile. Similar conclusions are also derived when the non-linear effects on the dipole–target interaction are disregarded. Our results indicate that a future study of the coherent vector meson production at large-t will be useful to constrain the spatial distribution of gluons within the proton.

Temporally and longitudinally tailored dynamic space-time wave packets

In general, space-time wave packets with correlations between transverse spatial fields and temporal frequency spectra can lead to unique spatiotemporal dynamics, thus enabling control of the instantaneous light properties. However, spatiotemporal dynamics generated in previous approaches manifest themselves at a given propagation distance yet are not arbitrarily tailored longitudinally. Here, we propose and demonstrate a new versatile class of judiciously synthesized wave packets whose spatiotemporal evolution can be arbitrarily engineered to take place at various predesigned distances along the longitudinal propagation path. Spatiotemporal synthesis is achieved by introducing a 2-dimensional spectrum comprising both temporal and longitudinal wavenumbers associated with specific transverse Bessel-Gaussian fields. The resulting spectra are then employed to produce wave packets evolving in both time and axial distance – in full accord with the theoretical analysis. In this respect, various light degrees of freedom can be independently manipulated, such as intensity, polarization, and transverse spatial distribution (e.g., orbital angular momentum). Through a temporal-longitudinal frequency comb spectrum, we simulate the synthesis of the aforementioned wave packet properties, indicating a decrease in relative error compared to the desired phenomena as more spectral components are incorporated. Additionally, we experimentally demonstrate tailorable spatiotemporal fields carrying time- and longitudinal-varying orbital angular momentum, such that the local topological charge evolves every ∼1 ps in the time domain and 10 cm axially. We believe our space-time wave packets can significantly expand the exploration of spatiotemporal dynamics in the longitudinal dimension. Such wave packets might potentially enable novel applications in light-matter interactions and nonlinear optics.

LGYSB:Nd─High-Performance Lasing in the Near-Infrared Region.

Three incongruent melting LawNdxGdyYzSc4-w-x-y-z(BO3)4 (LGYSB:Nd) crystals with different Y concentrations (z = 0.15, 0.05, and 0.025) have been grown by the Czochralski method for the first time. The LGYSB:Nd-type crystals exhibit an acentric structure similar to that of the natural mineral huntite CaMg3(CO3)4, with space group R32. The composition of the LGYSB:Nd_3 (z = 0.025) crystal grown from the starting melt composition La0.628Gd0.547Y0.025Nd0.05Sc2.75(BO3)4 was measured by inductively coupled plasma mass spectrometry method, and it was found to be La0.6794Gd0.4105Y0.0178Nd0.0381Sc2.8542(BO3)4. The transversal spatial distribution of the refractive index in the LGYSB:Nd_3 crystal was investigated. Third-order nonlinear optical susceptibility χ(3) of the LGYSB:Nd_3 crystal was determined from third-harmonic generation experiments with ultrashort (fs) laser pulses. The optical transmission spectrum was measured in the range of 200-2000 nm. The absorption cross-section at 808 nm in σ-polarization was determined to be 1.18 × 10-19 cm2 for the LGYSB:Nd_3 crystal. The 10K absorption spectra revealed that the Nd3+ ions occupy only La3+ cationic sites in the LGYSB host matrix. The emission cross-section at 1064 nm in σ-polarization was determined to be σem(σ) = 1.74 × 10-19 cm2 for the LGYSB:Nd_3 crystal. The fluorescence lifetime was found to be τ = 115 μs for all of the LGYSB:Nd crystals. The LGYSB:Nd_3 laser was operated at an emission wavelength of 1062 nm with very high slope efficiencies of ηsa = 0.74 and ηsa = 0.64 in quasi-cw and cw regimes, respectively.

A Rotationally Symmetric Multifocal Pearcey Beam with a Polygonal Profile

AbstractThe polygonal multifocal propagation properties and particle trapping experiments of a new kind of power‐exponential‐phase vortex chirped circular Pearcey Gaussian beam are investigated. Theoretical and experimental results show that it is possible to adjust the position and transverse spatial distribution of the beam in focal plane, as well as to make the transverse intensity distribution emerge an arbitrary polygonal profile by changing the distribution factor and vortex topological charge. Stable trapping of multiple particles is achieved in the experiment with transverse intensity fields in the polygon plane with different topological charges.

Coherent demodulated underwater wireless optical communication system based on convolutional neural network

The optical vortex beams carrying orbital angular momentum (OAM) is a beam with a special transverse spatial distribution, which has infinite orthogonal properties and can significantly improve the channel capacity of underwater wireless optical communication (UWOC) systems. However, for the underwater wireless optical communication system based on orbital angular momentum shift keying (UWOC-OAM-SK), turbulence in the seawater channel can distort the optical vortex beam and reduce the ability of the system to demodulate the OAM-SK signal, which can reduce the reliability of the system. To improve the performance of UWOC-OAM-SK systems in the channel with different turbulence, a coherent demodulation UWOC-OAM-SK system using an image recognizer based on convolutional neural network (CNN) as demodulator is proposed in this paper. Compared with the incoherent system, the proposed system can obtain a detection image with higher image contrast and more pattern features before the OAM mode is demodulated from the OAM-SK signal at the receiver, therefore has higher reliability. Moreover, the proposed system can recognize mutually conjugate OAM modes, which can greatly save the multiplexing resources in OAM communication. With the excellent image-data processing capability of CNN, the coherent demodulator based on CNN image recognizer has higher demodulation accuracy than the incoherent demodulator in both long distance channels or strongly turbulence channels underwater. The simulation results show that the demodulation accuracy of the proposed system is still higher than 90% in channels with strong turbulence intensity Cn2=1×10−14(K2m−2/3) or transmission distance z=80m. The work done provides some theoretical basis for the design of the UWOC-OAM-SK system.

Exploring gluon tomography with polarization dependent diffractive J/ψ production

We study azimuthal asymmetries in diffractive $\mathrm{J}/\ensuremath{\psi}$ production in ultraperipheral heavy-ion collisions at RHIC and LHC energies using the color glass condensate effective theory. Our calculation successfully describes the azimuthal averaged $J/\ensuremath{\psi}$ production cross section measured by STAR and ALICE. We further predict very large $\mathrm{cos}2\ensuremath{\phi}$ and $\mathrm{cos}4\ensuremath{\phi}$ azimuthal asymmetries for diffractive $J/\ensuremath{\psi}$ production both in UPCs at RHIC and LHC energies and in eA collisions at EIC energies. These novel polarization dependent observables may provide complementary information for constraining gluon transverse spatial distribution inside large nuclei. As compared to all previous analysis of diffractive $J/\ensuremath{\psi}$ production, the essential new elements integrated in our theoretical calculations are: the double-slit interference effect, the linear polarization of coherent photons, and the final state soft photon radiation effect.

Local OAM manipulation of a terahertz wave from the air filament by chirping the few-cycle vortex pump laser

We propose a scheme to manipulate the local orbital angular momentum (OAM) of the ultra-broadband (0.1-30 THz) terahertz (THz) waves from the laser-induced short air filament via chirping the few-cycle vortex laser pump. The simulation results show that either the THz vortex pulses with linear azimuth-dependent phases or the THz angular accelerating vortex beams (AAVBs) with nonlinear azimuth-dependent phases can be produced by tuning the chirp parameter of the pump. Thus, the dominant physical mechanism for THz generation can be determined. The THz temporal and transverse spatial distributions can be also controlled by the chirp parameter. Furthermore, their local OAM density distributions present very complex structures because most of the modulated azimuthal intensity and the corresponding local angular helicity distributions are not able to cancel out completely. Via analyzing the simulated THz results at the different pump intensities, we classify the initial pump intensity into three cases. For the low intensity case, the Kerr effect comes into prominence, so the generated THz radiation shall be vortex pulses. While for the high intensity case, the leading plasma effect dominates. In contrast, when the pump intensity is at the medium level, the Kerr nonlinearity and the plasma effect may be comparable and competitive. Basically, THz AAVBs are generated for both high and medium intensity cases. Our study will provide the possibility for studying the optically induced rotation technology more intuitively from the perspective of angular momentum transfer.

Dynamics of hot refluxing electrons in ultra-short relativistic laser foil interactions

We investigate the dynamics of hot refluxing electrons in the interaction of an ultra-short relativistic laser pulse with a thin foil target via particle-in-cell (PIC) simulations, which is governed by the multidimensional spatiotemporal evolution of a self-generated sheath field. The comparison of time-integrated energy spectra of refluxing and escaping electrons indicates the refluxing efficiency is higher than 95% in average for each bounce. The characteristics of wide transverse spatial distribution and energy-resolved angular distribution caused by the refluxing electrons show a direct correlation with the angular-dependent photon yield of bremsstrahlung emission, as verified by the hybrid simulations of coupling the PIC results with Monte Carlo particle transport code. We further clarify the energy dissipation mechanisms of refluxing electrons through the recirculation in the thin target under the electron-refluxing dominated regime and conclude that the self-generated sheath field plays a dominant role over the competing processes, such as the radiation loss, collisional stopping, and anomalous inhibition via the resistive field. The lifetime of recirculation is calculated to be a few hundred femtoseconds, that is, one order of magnitude shorter than the timescale of collisional dissipation, while it is one order of magnitude longer than the laser pulse duration. The results could provide useful insights to understand the hot electron transport and stopping, secondary radiation generation, and ion acceleration in the high energy density plasmas.

Investigation of the background in coherent J/ψ production at the EIC

Understanding various fundamental properties of nucleons and nuclei are among the most important scientific goals at the upcoming Electron-Ion Collider (EIC). With the unprecedented opportunity provided by the next-generation machine, the EIC might provide definitive answers to many standing puzzles and open questions in modern nuclear physics. Here we investigate one of the golden measurements proposed at the EIC, which is to obtain the spatial gluon density distribution within a lead ($Pb$) nucleus. The proposed experimental process is the exclusive $J/\psi$ vector-meson production off the $Pb$ nucleus - $e+Pb\rightarrow e'+J/\psi+Pb'$. The Fourier transformation of the momentum transfer $|t|$ distribution of the coherent diffraction is the transverse gluon spatial distribution. In order to measure it, the experiment has to overcome an overwhelmingly large background arising from the incoherent diffractive production, where the nucleus $Pb'$ mostly breaks up into fragments of particles in the far-forward direction close to the hadron-going beam rapidity. In this paper, we systematically study the rejection of incoherent $J/\psi$ production by vetoing products from these nuclear breakups - protons, neutrons, and photons, which is based on the BeAGLE event generator and the most up-to-date EIC Far-forward Interaction Region design. The achieved vetoing efficiency, the ratio between the number of vetoed events and total incoherent events, ranges from about 80% - 99% depending on $|t|$, which can resolve at least the first minimum of the coherent diffractive distribution based on the Sar$\it{t}$re model. Experimental and accelerator machine challenges as well as potential improvements are discussed.

The spatial distribution of focal stacks within the inner enamel layer of mandibular mouse incisors.

Focal stacks are an alternative spatial arrangement of enamel rods within the inner enamel of mandibular mouse incisors where short rows comprised of 2–45 enamel rods are nestled at the side of much longer rows, both sharing the same rod tilt directed mesially or laterally. The significance of focal stacks to enamel function is unknown, but their high frequency in transverse sections (30% of all rows) suggests that they serve some purpose beyond representing an oddity of enamel development. In this study, we characterized the spatial distribution of focal stacks in random transverse sections relative to different regions of the inner enamel and to different locations across enamel thickness. The curving dentinoenamel junction (DEJ) in transverse sections complicated spatial distribution analyses, and a technique was developed to “unbend” the curving DEJ allowing for more linear quantitative analyses to be carried out. The data indicated that on average there were 36 ± 7 focal stacks located variably within the inner enamel in any given transverse section. Consistent with area distributions, focal stacks were four times more frequent in the lateral region (53%) and twice as frequent in the mesial region (33%) compared to the central region (14%). Focal stacks were equally split by tilt (52% mesial vs. 48% lateral, not significant), but those having a mesial tilt were more frequently encountered in the lateral and central regions (2:1) and those having a lateral tilt were more numerous in the mesial region (1:3). Focal stacks having a mesial tilt were longer on average compared to those having a lateral tilt (7.5 ± 5.6 vs. 5.9 ± 4.0 rods per row, p < 0.01). There was no relationship between the length of a focal stack and its location within the inner enamel. All results were consistent with the notion that focal stacks travel from the DEJ to the outer enamel the same as the longer and decussating companion rows to which they are paired. The spatial distribution of focal stacks within the inner enamel was not spatially random but best fit a null model based on a heterogenous Poisson point process dependent on regional location within the transverse plane of the enamel layer.

Laser diagnostics of atomization and combustion of kerosene in a model combustion chamber

The experimental results are presented of implementation of a built-up laser-based diagnostic system at a test rig for investigations of the flame tube heads of aircraft gas turbine engines, both existing and being under development. At this test rig the processes of liquid fuel atomization and mixing with air by flame tube heads of model combustion chambers equipped with newly-developed atomizers, and of combustion of the fuel–air mixture formed in the flow have been studied. These studies enable development and optimization of advanced low-emission engines satisfying the established environmental requirements for the levels of polluting species in the exhaust gases. By using the particle shadow velocimetry technique with a pair of 10 μs delayed 5 ns laser pulses the transverse spatial distributions of average kerosene droplet dimensions, the axial components of their average velocity, and of the average volume flux of the fuel have been measured in the mixture flow axial cross-section. By employing coherent anti-Stokes Raman scattering with 10 ns pump laser pulses at 10 Hz repetition rate during combustion of the produced kerosene–air mixture the statistical characteristics of local ‘instantaneous’ gas temperature fluctuations in the flame, slow variations of these temperatures in time during the combustion process, and transverse distributions of average temperatures in the flame axial cross-section have been measured.

Propagation properties and radiation forces of the Hermite-Gaussian vortex beam in a medium with a parabolic refractive index.

In this paper, an analytical expression with a triple sum of the Hermite-Gaussian vortex beam (HGVB) propagating in a medium with a parabolic transverse spatial distribution of the refractive index is carried out. The intensity, phase, Poynting vector, and angular momentum of the HGVB are demonstrated analytically. The parabolic parameter, orders of the HGVB, and vortex topological charge affect the propagation properties, respectively. Also, the Poynting vector and angular momentum of the HGVB are shown so that we can further discover the properties. Furthermore, radiation forces are used to demonstrate the optical trapping ability of the HGVB, and several trapping positions are formed by the beam during propagation.

Vectorized optoelectronic control and metrology in a semiconductor

The increasingly prominent role of light in information processing makes optoelectronic devices a technology of fundamental importance. Coherent control of currents in semiconductors using synthesized optical waveforms provides a sensitive and robust means to transfer information from light to an electronic circuit. Currents driven by Gaussian laser beams are spatially uniform in direction, offering limited technological utility. Full control over the transverse spatial distribution of currents excited in a material would vastly increase the versatility and impact of optoelectronic devices. Here we simultaneously control the waveform and vectorial arrangement of optical fields, enabling precise manipulation of the spatial distribution of currents in a semiconductor. As a direct application, we drive loop currents, embodying a new ultrafast magnetic field source. Subsequently, we demonstrate a scheme for generating an arbitrary superposition of two orthogonal current arrangements via subcycle adjustment of the optical waveform. Engineering of the spatial distribution of currents in a semiconductor is demonstrated using vectorial arrangement of optical fields, enabling an ultrafast magnetic field source.

Taming the swirl of self-structured liquid crystal q-plates

Spontaneously formed liquid crystal topological defects under external fields offer a nature-assisted route to the creation of geometric phase optical vortex generators (q-plates). Here we report on the consequences of the unavoidable swirled transverse spatial distribution of the optical axis of such optical elements on the beam shaping and we propose a swirl-compensation scheme based on the arithmetic of geometric phase optical elements.

Mutual transitions between stationary and moving dissipative solitons

Application of stable localized dissipative solitons as basic carriers of information promises the significant progress in the development of new optical communication networks. The success development of such systems requires getting the full control over soliton waveforms. In this paper we use the fundamental model of dissipative solitons in the form of the complex Ginzburg–Landau equation with a potential term to demonstrate controllable transitions between different types of coexisted waveforms of stationary and moving dissipative solitons. Namely, we consider mutual transitions between so-called plain (fundamental soliton), composite, and moving pulses. We found necessary features of transverse spatial distributions of locally applied (along the propagation distance) attractive potentials to perform those waveform transitions. We revealed that a one-peaked symmetric potential transits the input pulses to the plain pulse, while a two-peaked symmetric (asymmetric) potential performs the transitions of the input pulses to the composite (moving) pulse.

Gamma beam collimation system and profile imager for ELI-NP

ELI-NP-GBS is a high-brilliance gamma source that will produce monochromatic beams in the energy range 0.2–19.5 MeV through inverse Compton scattering . In order to obtain a monochromatic beam a collimation of the emission is necessary. Depending on the energy, the angular aperture required to provide the design bandwidth Δ E/E=0.5% is between 70 and 700 μ rad. This collimation is provided by a stack of 14 tungsten slits, arranged with a relative rotation around the beam axis, so that the overlap will be a continuously adjustable aperture. To monitor the operation and alignment of the collimation, a set of detectors will provide a complete characterization of the gamma beam, including the measurement of the transverse spatial distribution. For this task a gamma beam profile imager based on a thin scintillator screen and a high-resolution CCD-camera was developed. In this work we briefly present the status of the collimation system and beam profile imager, which were designed, assembled and are currently under test at INFN-Ferrara laboratories.

Spatial intensity profiling of elastic and inelastic scattering in isotropic and anisotropic liquids by immersion of a spherical silicon photocell

The transverse spatial intensity distribution of elastic and inelastic light scattering in passive and active as well as weak and strong scattering liquid media has been studied by using Sphelar One p-n junction silicon spherical photocells. We immersed a Sphelar One in these scattering solutions and measured the photoconductive response in reverse biased photodiode (PD) configuration. The passive weak scattering medium was pure ethanol (EtOH), whereas the passive strong scattering medium was 5CB nematic liquid crystal (NLC). Solutions of 0.1mM Rhodamine 640 perchlorate laser dye in EtOH and in 5CB NLC were used as active scattering media. The response of Sphelar One was strongly enhanced in 5CB NLC compared to EtOH, as well as in active solutions compared to passive solutions. The morphology of the Sphelar One is already advantageous over conventional one-sided planar PDs inside liquid solutions. This omnidirectional response of the Sphelar One can further be enhanced by optimizing the properties of the surrounding passive elastic and active inelastic scatterers.

Bose-Einstein condensates and the spectrum of excitations in a two-dimensional channel

The transverse spatial distribution of weakly interacting Bose gas in a narrow channel is found. The corresponding analytical solution of the Gross-Pitaevskii equation has the form of a cnoidal wave. The possible physical realization of the model is a system of cold atoms or quasiparticles, e.g., excitons, cavity photons, exciton polaritons. The obtained formula is used for the numerical calculation of the spectrum of excitations and the critical velocity of the condensate. These numerical results do not coincide with the Bogoliubov spectrum, and we show that the strongly inhomogeneous condensate density leads to larger values of the critical velocity. We also make numerical estimation of the critical velocity for various types of considered particles or quasiparticles.

Polarization-based control of spin-orbit vector modes of light in biphoton interference.

We report the experimental generation of a class of spin-orbit vector modes of light via an asymmetric Mach-Zehnder interferometer, obtained from an input beam prepared in a product state of its spin and orbital degrees of freedom. These modes contain a spatially varying polarization structure which may be controllably propagated about the beam axis by varying the retardance between the vertical and horizontal polarization components of the light. Additionally, their transverse spatial intensity distributions may be continuously manipulated by tuning the input polarization parameters. In the case of an analogous biphoton input, we predict that this device will exhibit biphoton (Hong-Ou-Mandel) interference in conjunction with the aforementioned tunable mode transformations.