Diffractive Processes Research Articles

On obtaining high spectral resolution in extreme ultraviolet/soft X-ray monochromators operating off-plane diffraction in a divergent incident beam.

When the trajectory of an incident beam is oriented parallel to the grooves of a periodic grating structure the radiation beam is diffracted off-plane orthogonal to the plane of incidence. The diffraction efficiency in this condition is very high and in a grating with a sawtooth profile it can approach the reflection coefficient for a simple mirror, when the diffraction order of interest follows the direction for specular reflection at the flat part of the steps. When this concept is used in a plane grating in a monochromator for synchrotron radiation sources, the incident beam is almost always collimated in order to minimize any deterioration of the beam properties due to aberrations, which will be introduced in the diffraction process when an uncollimated beam is used. These aberrations are very severe when the groove density is constant. It will be shown that the effect of these aberrations can be corrected after the diffraction by the use of astigmatic focusing. The latter can be provided by a crossed mirror pair with different focal lengths in the corresponding orthogonal directions. Then a monochromator based on this concept can provide source size limited spectral resolution in an uncollimated incident beam. This is identical to the spectral resolution that can be provided by the same grating when operated at the same position in a collimated incident beam. The source size limited spectral resolution in this case corresponds to a high spectral resolving power of better than ΔE/E = 10 000 for photon energies around 300 eV in the soft X-ray range.

Multi-crystal data collection using synchrotron radiation as exemplified with low-symmetry crystals of Dps.

Multi-crystal data collection using synchrotron radiation was successfully applied to determine the three-dimensional structure of a triclinic crystal form of Dps from Escherichia coli at 2.0 Å resolution. The final data set was obtained by combining 261 partial diffraction data sets measured from crystals with an average size of approximately 5 µm. The most important features of diffraction data measurement and processing for low-symmetry crystals are discussed.

A study on detonation-diffraction reflection point distances in H2/O2, C2H2/O2, and C2H4/O2 systems

Recently, Kawasaki and Kasahara (2019) reported that reflection point distance, which is a detonation characteristic length relevant to the diffraction process, is a useful measure; i.e., the critical condition for detonation diffraction can be universally expressed in terms of the diffraction point distance, independent of mixture stability. However, their findings were limited to their experimental conditions only. In this study, we performed high-speed visualization of processes of cylindrical (line-symmetric) detonation diffraction around a 90-degree corner for two series of experiments to obtained reflection point distances, lr, as a novel characteristic length, and examined critical conditions of reinitiation expressed in terms of the reflection point distance. In the first experimental series, stoichiometric C2H2/O2 mixtures with 50% Ar dilution were employed, and the channel width lc was varied to 5, 10, 15, and 20 mm to investigate the influences of the boundary condition of the flow field. In the second experimental series, H2/O2, C2H2/O2, or C2H4/O2 mixtures with different equivalence ratios were employed to investigate influences of the reaction systems. Our results confirmed that the channel width does not affect the reflection point distance or the critical condition. The critical condition was also independent of fuel species and equivalence ratio, and can be uniquely expressed as lr / lc = 4.0 ± 0.6 in terms of the reflection point distance.

A flexible and standalone forward simulation model for laboratory X-ray diffraction contrast tomography.

Laboratory X-ray diffraction contrast tomography (LabDCT) has recently been developed as a powerful technique for non-destructive mapping of grain microstructures in bulk materials. As the grain reconstruction relies on segmentation of diffraction spots, it is essential to understand the physics of the diffraction process and resolve all the spot features in detail. To this aim, a flexible and standalone forward simulation model has been developed to compute the diffraction projections from polycrystalline samples with any crystal structure. The accuracy of the forward simulation model is demonstrated by good agreements in grain orientations, boundary positions and shapes between a virtual input structure and that reconstructed based on the forward simulated diffraction projections of the input structure. Further experimental verification is made by comparisons of diffraction spots between simulations and experiments for a partially recrystallized Al sample, where a satisfactory agreement is found for the spot positions, sizes and intensities. Finally, applications of this model to analyze specific spot features are presented.

Analytic theory for Bragg atom interferometry based on the adiabatic theorem

High-fidelity Bragg pulses are an indispensable tool for state-of-the-art atom interferometry experiments. In this paper, we introduce an analytic theory for such pulses. Our theory is based on the pivotal insight that the physics of Bragg pulses can be accurately described by the adiabatic theorem. We show that efficient Bragg diffraction is possible with any smooth and adiabatic pulse shape and that high-fidelity Gaussian pulses are exclusively adiabatic. Our results give strong evidence that adiabaticity according to the adiabatic theorem is a necessary requirement for high-performance Bragg pulses. Our model provides an intuitive understanding of the Bragg condition, also referred to as the condition on the "pulse area". It includes corrections to the adiabatic evolution due to Landau-Zener processes as well as the effects of a finite atomic velocity distribution. We verify our model by comparing it to an exact numerical integration of the Schr\"odinger equation for Gaussian pulses diffracting four, six, eight and ten photon recoils. Our formalism provides an analytic framework to study systematic effects as well as limitations to the accuracy of atom interferometers employing Bragg optics that arise due to the diffraction process.

Spin-dependent two-photon Bragg scattering in the Kapitza-Dirac effect

We present the possibility of spin-dependent Kapitza-Dirac scattering based on a two-photon interaction only. The interaction scheme is inspired from a Compton scattering process, for which we explicitly show the mathematical correspondence to the spin-dynamics of an electron diffraction process in a standing light wave. The spin effect has the advantage that it already appears in a Bragg scattering setup with arbitrary low field amplitudes, for which we have estimated the diffraction count rate in a realistic experimental setup at available X-ray free-electron laser facilities.

Diffractive gamma gamma production in pp collisions at the LHC

In this letter we estimate the contribution of the double diffractive processes for the diphoton production in pp collisions at the large hadron collider (LHC). The acceptance of the central and forward LHC detectors is taken into account and predictions for the invariant mass, rapidity and, transverse momentum distributions are presented. A comparison with the predictions for the light-by-light (LbL) scattering and exclusive diphoton production is performed. We demonstrate that the events associated to double diffractive processes can be separated and its study can be used to constrain the behavior of the diffractive parton distribution functions.

Readout system of the ALICE Fast Interaction Trigger

The Fast Interaction Trigger (FIT) detector will be essential for the operation of the ALICE experiment at CERN during Run 3 and 4 of the LHC . FIT will serve as an interaction trigger, luminometer, the first indicator of the vertex position, and the forward multiplicity counter. It will also provide the precise collision time for the TOF-based particle identification, yield the centrality and interaction plane for flow measurements, and measure cross sections of diffractive processes. In order to cope with an increased interaction rate of up to 1 MHz in proton-proton (pp) collisions and up to 50 kHz in Pb-Pb collisions, a new readout system for the ALICE FIT detector has been designed and implemented. FIT readout system is compatible both with the triggered and continuous (triggers-less) ALICE readout modes. The GBT-FPGA based FIT readout and trigger systems allow to stream data up to 5.5 MHz event rate with 3.2 Gbps data rate. The trigger processing time is only 225 ns. With the additional 200 ns delay along the connecting signal cables, the total latency of the FIT trigger is 425 ns.

A novel terbium doping effect on physical properties of lead sulfide nanostructures: A facile synthesis and characterization

Abstract

Diffraction and ‘In-Visible Light’

Feminism and Physics underpin the theory of Diffraction. Re-turning as a multiplicity of processes is central to the work of diffractive theorists like Karen Barad and Donna J. Haraway. This paper explores diffraction from the perspective of the dancing and performing body, using as a case study Vertical Dance Kate Lawrence’s (VDKL) Yn y Golau/In-visible Light (YYG). Diffractive principles inspired VDKL and the Photonics Academy of Wales Bangor (PAWB) to discover how invisible aspects of light might be made visible to audience members, particularly those who had visual impairments. We will argue that a diffraction process occurs for audiences as YYG requires them to make meaningful correspondences between phenomena in different mediums: dance/objects/scientific ideas/spoken word/music. We draw on Barad’s (2003) notion of ‘correspondences’ to highlight the connections between the various components in the performance space.

Multigap diffraction cross sections: Problems in eikonal methods for the Pomeron unitarization

Large rapidity gap diffraction processes are considered in multi-channel eikonal models. It is shown that shadow corrections to over-fast rising contribution of the input supercritical pomeron (with $\alpha(0)>1$), originating from the pomeron rescatterings or, equivalently, accounting survival probability factor, do not solve the Finkelstein-Kajantie problem. Therefore, in our opinion, another methods of unitarization of supercritical pomeron should be developed.

The natural grating method in determining family heredity

Human hair is one of material used to identify heredity of an individual. There has been a lot of researches done by scientists in sophisticated ways to test inheritance based on hair characteristics. However, to teach this uniqueness at the school level can be done with a simple test. One of them with natural grating method. This study aims to analyze the interference patterns produced by hair from the diffraction process. Five non-blood related families were examined. A beam of 800 nm wavelength from the laser is passed through the hair and its lattice width is calculated. Lattice gap data obtained are then calculated the correlation value between mother and child father. The results of this simple analysis are not enough to support the inheritance relationship of one family. Obtained mystery figures that still need to be studied further. But found one family with twins who have the same width of hair gap. This finding is certainly very interesting to be taught to students at the school level.

Investigation of the interaction of the ion beams with deuterated crystal structures at the HELIS facility

The paper reviews results obtained in the course of low energy nuclear reactions experimental study using the HELIS facility (LPI). The analysis of DD-reaction yields in deuterated crystalline structures at deuteron energies of 10–25 keV has shown a significant amplification effect. It was found that the exposure of deuterated targets both to 10–25 keV H+ and Ne+ ion beams and 20–30 keV X-ray radiation beams results in stimulation of DD-reaction yield. For CVD diamond and PdDx targets, it was shown that the magnitude of the neutron yield is affected by the orientation of the sample with respect to the deuteron beam. The possible explanation of the said effect may be attributed to the channeling of deuterium ions and neutron (DD reaction products) in textured targets. It was found that the heat release is much higher when D+ ion beams act upon the TiDx target than in case with H+ and Ne+ beams. The heat release depends upon the deuterium concentration in the target and the deuteron beam current density. “Additional peaks” were observed in the X-ray fluorescence spectra, but those are not related to any element and are seemingly associated with diffraction processes in deuterated palladium and CVD diamond.

Subwavelength self-imaging in cascaded waveguide arrays

Self-imaging is an important function for signal transport, distribution, and processing in integrated optics, which is usually implemented by multimode interference or diffractive imaging process. However, these processes suffer from the resolution limit due to classical wave propagation dynamics. We propose and demonstrate subwavelength optical imaging in one-dimensional silicon waveguide arrays, which is implemented by cascading straight and curved waveguides in sequence. The coupling coefficient between the curved waveguides is tuned to be negative to reach a negative dispersion, which is an analog to a hyperbolic metamaterial with a negative refractive index. Therefore, it endows the waveguide array with a superlens function as it is connected with a traditional straight waveguide array with positive dispersion. With a judiciously engineered cascading silicon waveguide array, we successfully show the subwavelength self-imaging process of each input port of the waveguide array as the single point source. Our approach provides a strategy for dealing with optical signals at the subwavelength scale and indicates functional designs in high-density waveguide integrations.

Inclusive diffractiveηcproduction in pp, pA, and AA modes at the LHC

In this paper, the inclusive Pomeron-Pomeron, Reggeon-Reggeon, Pomeron-Reggeon as well as gluon-Pomeron(-Reggeon) and photon-Pomeron(-Reggeon) interactions for the $\rm \eta_{c}$ at the LHC energies have been examined in proton-proton, proton-nucleus and nucleus-nucleus collision modes. The cross section has been computed based on the NRQCD factorization and Regge theory formalism. The cross exchange of Pomeron-Reggeon contribution is important in $\rm pp$ and $\rm pA$ modes. The Pomeron-Pomeron contribution is significant in $\rm AA$ mode. The Pomeron contribution is considerable for $\rm AA$ and $\rm pA$ modes in single diffractive process where $\rm A$ undergoes the diffractive process. Reggeon contribution is sizable in $\rm pp$ and $\rm pA$ modes where $\rm p$ only undergoes the diffractive process. The Pomeron and Reggeon contributions in photon-Pomeron and-Reggeon process remain smaller than that of gluon-Pomeron and-Reggeon processes. Our results show that the experimental study of Reggeon, Pomeron and their cross exchange can be carried out in certain kinematic windows with the specific choice of the mode at the LHC. The investigation can be useful to better constrain the Reggeon and Pomeron parton content. The inclusive process serves as the background to related exclusive processes which should be predicted.

Contribution of exclusive diffractive processes to the measured azimuthal asymmetries in SIDIS

Hadron leptoproduction in Semi-Inclusive measurements of Deep-Inelastic Scattering (SIDIS) on unpolarised nucleons allows one to get information on the intrinsic transverse momentum of quarks in a nucleon and on the Boer-Mulders function through the measurement of azimuthal modulations in the cross section. These modulations were recently measured by the HERMES experiment at DESY on proton and deuteron targets, and by the COMPASS experiment using the CERN SPS muon beam and a 6LiD target. In both cases, the amplitudes of the cos⁡ϕh and cos⁡2ϕh modulations show strong kinematic dependences for both positive and negative hadrons. It has been known since some time that the measured final-state hadrons in those SIDIS experiments receive a contribution from exclusive diffractive production of vector mesons, particularly important at large values of z, the fraction of the virtual photon energy carried by the hadron. In previous measurements of azimuthal asymmetries this contribution was not taken into account, because it was not known that it could distort the azimuthal modulations. Presently, a method to evaluate the contribution of the exclusive reactions to the azimuthal asymmetries measured by COMPASS has been developed. The subtraction of this contribution results in a better understanding of the kinematic effects, and the remaining non-zero cos⁡2ϕh modulation gives indication for a non-zero Boer-Mulders effect.

Optimization of phase masks using simulated annealing algorithm for mode conversion

The simulated annealing algorithm was applied for optimizing binary phase masks used in the conversion of optical modes through spatial light modulation in free space. The method changes the phase distribution to be displayed on a spatial light modulator, in such a way maximizes the correlation between de converted mode and the theoretical mode. The method allowed the optimal conversion of the linearly polarized modes through a diffractive process. The analysis of the correlations between obtained and theoretical modes showed the effectiveness of the method and its capability to generate optical modes similar to those in an optical fiber. The optimized phase masks could be applied in a dynamic and arbitrary mode converter.

Herwig 7.2 release note

A new release of the Monte Carlo event generator Herwig (version 7.2) is now available. This version introduces a number of improvements over the major version 7.0, notably: multi-jet merging with the dipole shower at LO and NLO QCD; spin correlations in both the dipole and angular-ordered parton showers; an improved choice of evolution variable in the angular-ordered parton shower; improvements to mass effects and top decays in the dipole shower, improvements to the simulation of multiple-parton interactions, including diffractive processes; a new model for baryonic colour reconnection; improvements to strangeness production; as well as a new tune of the hadronisation parameters and support for generic Lorentz structures in BSM models. This article illustrates new features of versions 7.1 and 7.2.

Exclusive and diffractive gamma gamma production in PbPb collisions at the LHC, HE-LHC and FCC

In this paper we present a detailed analysis of the contribution of the Light-by-Light (LbL), Durham and double diffractive processes for the diphoton production in ultraperipheral PbPb collisions at the Large Hadron Collider (LHC), High-Energy LHC (HE-LHC) and Future Circular Collider (FCC). The acceptance of the central and forward LHC detectors is taken into account and predictions for the invariant mass, rapidity, transverse momentum and acoplanarity distributions are presented. Our results indicate that the contribution of the Durham process is negligible and that the double diffractive process can be strongly suppressed by the exclusivity cuts, which will allow to perform a precise analysis of the LbL scattering, as well the search of beyond Standard Model physics in this final state.

X-ray diffraction on La3Ga5SiO14 crystal modulated by SAW near the K absorption edge of Ga

The process of x-ray diffraction on the La3Ga5SiO14 (LGS) crystal modulated by surface acoustic waves (SAWs) near the K absorption edge of Ga (E=10 367 eV) was studied. A redistribution of the diffracted x-ray intensity between the diffraction satellites occurs at the absorption edge due to the change in the x-ray penetration depth into the crystal and an effective change in the interaction of x-ray radiation with the near-surface crystal region modulated by SAW. The intensity distribution of the diffraction satellites starts to change smoothly immediately after the K absorption edge of Ga with a decrease in the x-ray penetration depth into the crystal.