Backward Hemisphere Research Articles

Characterizing the Backscattered Spectrum of Mie Spheres

AbstractThis study describes both experimentally and theoretically an important hitherto undiscovered feature of the scattering of micron‐sized spherical objects when illuminated with highly focused circularly polarized light. This is a regime of high experimental relevance which has not been described in full detail. The experiments are complemented with the analytical formulas explaining the field scattered directed toward the backward hemispace. In particular, it is proven that this field shows a very regular oscillatory dependency with the optical size. This phenomenon is typically hidden in the total scattered field, as the field is scattered much less toward the backward hemisphere than toward the forward one. These regular oscillations are measured experimentally. It is proven that, by analyzing them, it is possible to determine the index of refraction of isolated micron‐sized particles, opening new paths for applications in sensing and metrology.

Large-scale and tunable transparent displays based on silver nanoparticles metasurface

We report a transparent display based on a metasurface of silver nanoparticles (Ag NPs), consisting of a transparent substrate and a layer of Ag NPs deposited by a dielectric film. The Ag NPs metasurface is prepared by a simple and direct annealing process. It presents a deep transmission valley at the wavelength of λ = 468 nm and enables desired transparent display by projecting the monochromatic image onto the metasurface. We also demonstrate that the formed Ag NPs can be approximated as truncated nanospheres, which have obvious directional scattering properties, and can radiate most of the scattered energy into the backward hemisphere with a relatively large angular beamwidth (the full width at half maximum of the scattered intensity) of ∼90°. Therefore, the fabricated displays possess wide viewing angles and high brightness characteristics. Additionally, the transmission modes can be red-shifted to the wavelength of λ = 527 nm by controlling the thickness of the deposited dielectric film. This approach using traditional thin film deposition and moderate annealing processing techniques enables simple, low-cost, and scalable fabrication in large areas for transparent displays.

Forward-backward multiplicity correlation and fluctuation in 197Au + 197Au collisions at fixed target Elab = 10A, 20A, 30A and 40A GeV in the UrQMD model

We use the ultra-relativistic quantum molecular dynamics (UrQMD) model to study the multiplicity correlations and fluctuations of charged hadrons emitted in the forward and backward rapidity hemispheres in 197Au + 197Au collisions at four different incident beam energies, namely Elab=10A,20A, 30A and 40A GeV. Dependence of the correlation and fluctuation parameters on the incident beam energy, collision centrality, rapidity gap and rapidity window size are examined. Both short and long-ranged correlations contribute to our UrQMD simulated results. In the framework of the UrQMD model the short-ranged correlations can be interpreted in terms of resonance decays and/or cluster formation. The long-ranged correlations on the other hand, perhaps originate from multiple rescattering suffered by the hadrons and decay of longitudinally stretched strings in the rapidity space. Our simulation based analysis can be used to set a reference base-line for any future experimental study on the forward-backward multiplicity correlation for the colliding system and collision energies involved in the present case.

4π light scattering flow cytometry: enhancing the identification and characterization of individual cells.

The analysis of individual particles with complex morphologies from light scattering is crucial in disperse systems studies, such as blood cells. Characterization, which assumes determining particle characteristics, has a higher likelihood of succeeding in solving the inverse light-scattering problem if an instrument provides enough light-scattering data. In this study, we demonstrate how we extend the operating angular interval for the 4π Scanning Flow Cytometer (4πSFC), which measures angle-resolved light-scattering profiles (LSPs) of individual particles. The angular interval is extended by additionally measuring light scattering for the backward hemisphere. Currently, the 4πSFC setup uses three lasers, a single optical cell, and three photomultipliers. It enables the measurement of the LSP of individual particles within the angular interval of 10 to 170° for polar angles with integration over azimuth angles, which covers the spatial angle of 98.5% of the 4π angle. We demonstrate the 4πSFC's performance in measuring LSPs from the analysis of polymer beads, mature and spherized erythrocytes, and platelets. The 4πSFC has the potential to be very useful in identifying platelet dimers and granulocytes without labels, characterizing lymphocytes, monocytes, and abnormal erythrocytes.

Emission feature of the shower particles produced in backward hemisphere in the interaction of 84Kr36 + Em at 1 A GeV

In this paper, a detailed investigation on the emission feature of the shower particles emitted in the backward hemisphere in the interaction of [Formula: see text] with emulsion at 1[Formula: see text]GeV per nucleons has been carried out. We also studied the effect of shower particles emission in backward hemisphere with composite emulsion target, AgBr target and CNO target. The results are compared with other experimental observation and found to be consistent.

Emission characteristics of the target fragments at relativistic energy

In this recent work, we present the characteristic of the emission of the black particles ejected with [Formula: see text] [Formula: see text] [Formula: see text] and [Formula: see text] [Formula: see text][Formula: see text] i.e., in the forward and backward hemispheres, respectively. For the multiplicity variation study of black particles, we have considered the interaction of [Formula: see text]Kr beam with the CNO, AgBr target present in the nuclear emulsion detector. After doing the analysis of the data, we have found that the emission possibility of black particle is greater in the forward hemisphere (FHS) angle whereas in the backward hemisphere (BHS) angle, it is quite low. Along with this, we have also found that the emission probability of black particles does not posses any relation with projectile mass as well as with the incident energy. In this work, we have also studied the characteristics of shower and et al. particles using a new parameter Q (total charge [Formula: see text] of the outgoing projectile fragments emitted in forward cone [Formula: see text], here Z denotes charge, and PF denotes Projectile Fragment) instead of impact parameter to distinguish the different type of collision for two interacting nuclei. The observation from this study suggests that the emission probability of the shower particles as well as gray particles increase as the value of Q decreasing (i.e., as we move from peripheral to central colisions). The results of this work are also compared with the context of other experimental observations and it seems to be relevant.

Characterization of angularly resolved EUV emission from 2-µm-wavelength laser-driven Sn plasmas using preformed liquid disk targets

The emission properties of tin plasmas, produced by the irradiation of preformed liquid tin targets by several-ns-long 2 µm-wavelength laser pulses, are studied in the extreme ultraviolet (EUV) regime. In a two-pulse scheme, a pre-pulse laser is first used to deform tin microdroplets into thin, extended disks before the main (2 µm) pulse creates the EUV-emitting plasma. Irradiating 30- to 300 µm-diameter targets with 2 µm laser pulses, we find that the efficiency in creating EUV light around 13.5 nm follows the fraction of laser light that overlaps with the target. Next, the effects of a change in 2 µm drive laser intensity (0.6–1.8 × 1011 W cm−2) and pulse duration (3.7–7.4 ns) are studied. It is found that the angular dependence of the emission of light within a 2% bandwidth around 13.5 nm and within the backward 2π hemisphere around the incoming laser beam is almost independent of intensity and duration of the 2 µm drive laser. With increasing target diameter, the emission in this 2% bandwidth becomes increasingly anisotropic, with a greater fraction of light being emitted into the hemisphere of the incoming laser beam. For direct comparison, a similar set of experiments is performed with a 1 µm-wavelength drive laser. Emission spectra, recorded in a 5.5–25.5 nm wavelength range, show significant self-absorption of light around 13.5 nm in the 1 µm case, while in the 2 µm case only an opacity-related broadening of the spectral feature at 13.5 nm is observed. This work demonstrates the enhanced capabilities and performance of 2 µm-driven plasmas produced from disk targets when compared to 1 µm-driven plasmas, providing strong motivation for the use of 2 µm lasers as drive lasers in future high-power sources of EUV light.

Seemingly asymmetric atom-localized electronic densities following laser-dissociation of homonuclear diatomics.

Recent experiments on laser-dissociation of aligned homonuclear diatomic molecules show an asymmetric forward-backward (spatial) electron-localization along the laser polarization axis. Most theoretical models attribute this asymmetry to interference effects between gerade and ungerade vibronic states. Presumably due to alignment, these models neglect molecular rotations and hence infer an asymmetric (post-dissociation) charge distribution over the two identical nuclei. In this paper, we question the equivalence that is made between spatial electron-localization, observed in experiments, and atomic electron-localization, alluded by these theoretical models. We show that (seeming) agreement between these models and experiments is due to an unfortunate omission of nuclear permutation symmetry, i.e., quantum statistics. Enforcement of the latter requires mandatory inclusion of the molecular rotational degree of freedom, even for perfectly aligned molecules. Unlike previous interpretations, we ascribe spatial electron-localization to the laser creation of a rovibronic wavepacket that involves field-free molecular eigenstates with opposite space-inversion symmetry i.e., even and odd parity. Space-inversion symmetry breaking would then lead to an asymmetric distribution of the (space-fixed) electronic density over the forward and backward hemisphere. However, owing to the simultaneous coexistence of two indistinguishable molecular orientational isomers, our analytical and computational results show that the post-dissociation electronic density along a specified space-fixed axis is equally shared between the two identical nuclei-a result that is in perfect accordance with the principle of the indistinguishability of identical particles.

Multiplicity characteristics of the produced shower particles in backward direction-target and projectile dependence

In the present paper a detailed investigation of the multiplicity distribution of the produced shower particles in the backward hemisphere ( $$\theta _{\mathrm {Lab}} \ge 90^{\circ }$$ ) in nuclear emulsion track detector has been carried out. The present study involves interactions of $$^{\mathrm {16}}\hbox {O}$$ and $$^{\mathrm {32}}\hbox {S}$$ projectiles with CNO, AgBr and composite emulsion target at 4.5 AGeV/c. We have compared our results with the results obtained from the analysis of modified Fritiof model. Present study reveals that the production of single shower particle is the most dominant production mode of shower particles in the backward direction. This probability increases with the increase of target mass. The percentage of events having backward shower particles remains almost independent of the projectile beam. But it increases with the increase of target size. Average multiplicity of the shower particles in the backward direction reflects a weaker dependence on the mass number of the projectile beam. Multiplicity distribution of backward shower particles for both experimental and modified Fritiof model can be described by an expression $$\mathrm {P}_{\mathrm {N}} = {\mathrm {P}_{\mathrm {s}}\mathrm {N}_{\mathrm {B}}}^{-{\uplambda }_{\mathrm {B}}}$$ . The fitting parameter $${\uplambda }_{\mathrm {B}}$$ decreases as the target size increases. The decay constant has lower value for the heavier projectile. Higher order multiplicity moments and scaled variance of multiplicity distribution for the backward shower particles showed strong target dependence. Multiplicity distributions of the backward shower particles violate KNO scaling law. Modified Fritiof model failed to reproduce the various features of the multiplicity distribution.

Role of α-Cluster Transfer in the Formation of 20Ne + 16O Cross-Sections at Backward Angles

The experimental angular distributions for 20Ne+16O elastic transfer are reanalyzed using different forms of potential both phenomenological and semi-microscopic. The significant increase in cross sections at backward hemisphere due to the contribution of alphacluster transfer is investigated using the distorted wave Born approximation (DWBA) method. The spectroscopic amplitude (SA) for the configuration 20Ne as consisting of 16O (core) and an alpha-particle orbiting this core at the different concerned energies is extracted. The agreement between the experimental data and theoretical calculations using the two considered approaches is reasonably good.

Technique for measuring of LIA spot size on target by X-rays propagating in beam backward direction

We are propose a technique for measuring of a focal spot size directly during the shot of a radiographic facility based on a linear induction accelerator. The key feature of the proposed method is the penumbral imaging in the direction backward to the electron beam propagation. Diagnostic has been installed in a backward hemisphere of the target chamber of a linear induction accelerator. It consists of two parallel edge-knife (roll-bars with 500 mm radius of curvature), a thin BGO scintillator, and a CCD camera with a 7 microseconds shutter. The performance and operability of the diagnostic was demonstrated on the linear induction accelerator with energy of electrons of 4 MeV. The first experimental results of the beam spot measurements are presented. A radiation transport modeling of the diagnostic scheme was performed using Monte-Carlo code PRIZMA. The effect of the scattered bremsstrahlung on the penumbral image in the backward direction was analyzed.

Emission Characteristics of the grey particles produced in the interaction of the 84Kr36 with nuclear emulsion detector at 1 A GeV

In the present analysis, we have studied the emission characteristics of grey particles produced from the interaction of 84Kr36 projectile at 1 A GeV with CNO target nuclei and AgBr target nuclei of nuclear emulsion detector emitted in 4π space angle, forward hemisphere (θ < 90°), and backward hemisphere (θ ≥ 90°). We have also studied the emission characteristics of grey particle with black particles. The present studies show that the emission of grey particles depends not only on the interaction of the different targets of nuclear emulsion detector but it also depends on the number of emission of the black particles. The results of the present studies are also compared with others and found to be consistent.

Mechanisms of Forward–Backward Correlations in the Multiplicity of Particles in Ultrarelativistic Heavy-Ion Collisions

The contributions of various effects to correlations of the average multiplicity of particles emitted in the forward hemisphere of heavy-ion collisions with the multiplicity of particles emitted in the backward hemisphere (forward–backward correlations) have been comparatively analyzed. It has been shown that the experimentally observed dependence of the strength of such correlations on the centrality of lead–lead ion collisions at the Large Hadron Collider energy $$\sqrt {{{s}_{{NN}}}} $$ = 2.76 TeV can be reproduced by the HYDJET++ model if the hydrodynamic particle flow, decay of resonances, and production and suppression of high-energy quarks and gluons in hot matter are taken into account. The dominant mechanism of forward–backward correlations for the most central collisions involves the production and fragmentation of quark–gluon jets.

Emission Characteristics of Charged Particle Production in Interactions of 84Kr with the Nuclear Emulsion Detector at Relativistic Energy

This article focuses on the characteristics of the charged particle produced in nucleus-nucleus collisions at relativistic energy. We have studied the emission behavior of charged particles observed in the forward hemisphere (θ < 90°) and the backward hemisphere (θ ≥ 90°). This study shows that the charged particles produced in the forward hemisphere strongly depend on the mass of the projectile beam whereas in the backward hemisphere, they show an exponential decay behavior and are independent of the mass of the projectile beam. The results are compared with other experimental observations and found to be consistent.

Lepton mass effects for beam-normal single-spin asymmetry in elastic muon-proton scattering

We estimate the beam-normal single-spin asymmetry in elastic lepton-proton scattering without employing the ultrarelativistic approximation. Our calculation is relevant for analyses of muon scattering at energies of few hundred MeV and below -- when effects of the muon mass become essential. At such energies, the transverse polarization of the muon beam is expected to contribute significantly to the systematic uncertainty of precision measurements of elastic muon-proton scattering. We evaluate such systematics using an example of the MUSE experiment at PSI. The muon asymmetry is estimated at about 0.1\% in kinematics of MUSE and it is the largest for scattering into a backward hemisphere.

Angular distribution of multiple Compton scattered gamma rays of 662 keV in tin

In multiple Compton scattering, the incident gamma photon is scattered more than once due to finite dimensions of the sample. It serves as a noise for the exact evaluation of electron momentum distribution in Compton profile, Compton cross section and non-destructive testing of in-assessable large samples. To overcome these difficulties, there is a need to characterise the contribution of multiple scattering as a function of atomic number, scattering angle and incident gamma photon energy. In the present work, measurements are carried out to investigate the multiple scattering of 662 keV photons with tin sample of different thickness in the forward and backward hemispheres. The scattered photon flux is recorded by a NaI(Tl) scintillation detector and with an HPGe solid-state detector to check for the trend of saturation thickness as a function of resolution of the detector. The number of multiply scattered photons is found to be increasing with the sample thickness up to a particular thickness value called saturation thickness beyond which it remains constant with increase in target thickness. The effect of detector collimator size on multiply scattered photons is also studied. Both the detectors show the same trend of saturation thickness as a function of thickness. Angular distribution of multiply scattered photons shows symmetry around 90° scattering angle. The low energy side of multiple scattered photon spectrums is also characterised as a function of sample thickness and order of scattering. Monte Carlo calculations support the present experimental results.

Experimental demonstration of spectrally broadband Huygens sources using low-index spheres

Manipulating the excitation of resonant electric and magnetic multipole moments in structured dielectric media has unlocked many sophisticated electromagnetic functionalities. This invited article demonstrates the experimental realization of a broadband Huygens’ source. This Huygens’ source consists of a spherical particle that exhibits a well-defined forward-scattering pattern across more than an octave-spanning spectral band at GHz frequencies, where the scattering in the entire backward hemisphere is suppressed. Two different low-index nonmagnetic spheres are studied that differ in their permittivity. This causes them to offer a different shape for the forward-scattering pattern. The theoretical understanding of this broadband feature is based on the approximate equality of the resonant electric and magnetic multipole moments in both amplitude and phase in low permittivity spheres. This is a key condition to approximate the electromagnetic duality symmetry which, together with the spherical symmetry, suppresses the backscattering. With such a configuration, broadband Huygens’ sources can be designed even if magnetic materials are unavailable. This article provides guidelines for designing broadband Huygens’ sources using low-index spheres that could be valuable to a plethora of applications.

Imaging pair-correlated reaction cross sections in F + CH3D(νb = 0, 1) → CH2D(ν4 = 1) + HF(ν).

The title reactions were studied in a crossed-beam experiment at collisional energies (Ec) from 0.5 to 4.7 kcal mol-1. The νb (ν4) vibrational mode denotes the bending (umbrella) motion of the CH3D reactant (CH2D product). Using a time-sliced, velocity-map imaging technique, we extracted the state-specific, pair-correlated integral and differential cross sections. As with other isotopically analogous ground-state reactions, an inverted vibrational population of the HF coproduct was observed. Both the step-like excitation function near the threshold and the oscillatory forward-backward peakings in the Ec-evolution of the two dominant pair-correlated angular distributions at lower Ec suggest a resonance-mediated, time-delay mechanism. As Ec increases, the angular distribution of the HF(ν = 2) product evolves into a smooth and broad swath in the backward hemisphere, indicative of a direct rebound mechanism. One quantum excitation of the bending modes of CH3D(νb = 1) promotes the reaction rate by two- to three-fold up to Ec = 2.1 kcal mol-1. Broadly speaking, all major findings are qualitatively in line with previous results in the reactions of the F atom with other isotopologues. However, the rainbow feature recently observed in the CH2D(00) + HF(ν = 3) product channel is entirely absent. A possible rationale is put forward, which reinforces the previous reactive rainbow conjecture and calls for future theoretical investigations.

Study of azimuthal correlations in the target fragmentation region in p, d, He, C+C, Ta and C+Ne, Cu collisions at momenta of 4.2, 4.5 and 10 A GeV/c

Azimuthal correlations between the same type of particles (protons or pions) in the target fragmentation region was studied in d, He, C+C, Ta (4.2A GeV/c, C+Ne, Cu (4.5A GeV/c) and p+C, Ta (10 GeV/c) interactions. The data were obtained from the SKM-200-GIBS streamer chamber and from the Propane Bubble Chamber (PBL-500) systems utilized at JINR. Study of multiparticle azimuthal correlations offers unique information about space-time evolution of the interactions. Azimuthal correlations were investigated by using correlation function $ C(\Delta\phi) = \mathrm{d} N/\mathrm{d} (\Delta\phi)$ , where $ \Delta\phi$ represents the angle between the sums of transverse momenta vectors for particles emitted in the forward and backward hemispheres. For protons “back-to-back” (“negative”) azimuthal correlations were observed in the above-mentioned interactions. The absolute values of the correlation coefficient $ \vert\xi\vert$ --the slope parameter of $ C(\Delta\phi)$, strongly depend on the mass number of the target ($ A_{T}$) nuclei in the nucleon-nucleus and nucleus-nucleus collisions. Namely, $ \vert\xi\vert$ decreases with increase of $ A_T$ in p+C and p+Ta collisions, while $ \vert\xi\vert$ initially decreases from d+C to C+Ne and then almost does not change with increase of $ A_P$, $ A_T$ in (d+He)Ta, C+Cu and C+Ta collisions. For pions “back-to-back” correlations were obtained for light targets (C, Ne), and “side-by-side” (“positive”) correlations for heavy targets (Cu, Ta). The $ \vert\xi\vert$ insignificantly changes with increase of the momenta per nucleon and almost does not change with increase of $ A_P$ and $ A_T$. Models used for description of the data, the Ultra relativistic Quantum Molecular Dynamic (UrQMD) and Quark-Gluon String Model (QGSM), satisfactorily describe the obtained experimental results.

On the origin of forward–backward multiplicity correlations in pp collisions at ultrarelativistic energies

We study multiplicity correlations of hadrons in forward and backward hemispheres in pp inelastic interactions at energies 200 GeV≤s≤13 TeV within the microscopic quark–gluon string model. The model correctly describes (i) the almost linear dependence of average multiplicity in one hemisphere on the particle multiplicity in other hemisphere in the centre-of-mass frame; (ii) the increase of the slope parameter bcorr with rising collision energy; (iii) the quick falloff of the correlation strength with increase of the midrapidity gap; (iv) saturation of the forward–backward correlations at very high multiplicities. Investigation of the sub-processes on partonic level reveals that these features can be attributed to short-range partonic correlations within a single string and superposition of several sub-processes containing different numbers of soft and hard Pomerons with different mean multiplicities. If the number of Pomerons in the event is fixed, no forward–backward correlations are observed. Predictions are made for the top LHC energy s=13 TeV.