Effect Of Coherence Length Research Articles

Exclusive photoproduction of excited quarkonia in ultraperipheral collisions

In this paper, we discuss the exclusive photoproduction of ground and excited states of $\psi(1S,2S)$ and $\Upsilon(1S,2S)$ in ultraperipheral collisions (UPCs). Using the potential model in order to obtain the vector meson wave function, we find a good agreement of our calculations with data from the LHC and HERA colliders for $J/\psi (1S,2S) $ and $\Upsilon(1S)$ in $\gamma p$ collisions. We extend the calculations to the nuclear target case applying them to $AA$ UPCs with the use of the shadowing and finite coherence length effects fitted to the data. Our results are compared to the recent LHC data, in both incoherent ($J/\Psi(1S)$ at 2.76 TeV) and coherent ($J/\Psi(1S)$ at 2.76 and 5.02 TeV) processes. We also show the corresponding predictions for the excited states, in the hope that future measurements could provide more detailed information about the vector meson wave functions and nuclear effects.

Nuclear shadowing in DIS at electron-ion colliders

We present a revision of predictions for nuclear shadowing in deep-inelastic scattering at small Bjorken $x_{Bj}$ corresponding to kinematic regions accessible by the future experiments at electron-ion colliders. The nuclear shadowing is treated within the color dipole formalism based on the rigorous Green function technique. This allows incorporating naturally color transparency and coherence length effects, which are not consistently and properly included in present calculations. For the lowest $|q\bar q\rangle$ Fock component of the photon, our calculations are based on an exact numerical solution of the evolution equation for the Green function. Here the magnitude of shadowing is tested using a realistic form for the nuclear density function, as well as various phenomenological models for the dipole cross section. The corresponding variation of the transverse size of the $q\bar q$ photon fluctuations is important for $x_{Bj}\gtrsim 10^{-4}$, on the contrary with the most of other models, which use frequently only the eikonal approximation with the "frozen" transverse size. At $x_{Bj}\lesssim 0.01$ we calculate within the same formalism also a shadowing correction for the higher Fock component of the photon containing gluons. The corresponding magnitudes of gluon shadowing correction are compared adopting different phenomenological dipole models. Our results are tested by available data from the E665 and NMC collaborations. Finally, the magnitude of nuclear shadowing is predicted for various kinematic regions that should be scanned by the future experiments at electron-ion colliders.

Measurement of thermal effect in laser pumped silicon employing infrared digital holographic interferometry.

We present a short-coherence infrared digital holographic interferometry (IRDHI) to quantitatively measure the weak thermal effect in silicon wafer under visible laser pumping. In IRDHI, a superluminescent diode and a narrow-band filter are introduced to eliminate the self-interference fringes and suppress the noise. The effect of coherence length of the detection light source is analyzed and the optimal coherence length range in the proposed configuration is given. Meanwhile, we measure the weak thermal effect in silicon pumped by two different approaches of a continuous visible laser with different powers. The proposed configuration, which shows high stability and sensitivity, can be easily adapted and improved to measure the variation of thermal effect or refractive index in other near infrared transparent materials.

Diffraction of a partial temporal coherent beam from a single-slit and a circular aperture

We generalize the notion of the Franhoufer diffraction from a single slit and a circular aperture to the case of partially temporal coherent and quasimonochromatic light. The problem is studied analytically and the effect of coherence length on the diffraction pattern is investigated. In this case the far-field distribution of the irradiance depends on the newly introduced parameter η “decoherence parameter” which governs the deviation of the diffraction pattern from the usual one. The η-dependent corrections due to temporal decoherency on the irradiance distribution in the far field is obtained. Numerical study of the effect of decoherence parameter on the Far-field diffraction pattern is performed. In the case of a single slit, there is no noticeable deviation in the central peak, but in the higher orders of diffraction, deviation become apparent. For circular apertures, as long asη>1, the beam decoherency affects the distribution profile and the first order diffraction pattern decreases and by increasing the decoherence parameter, the first order of diffraction pattern gradually disappears.

Coherence-Length Effects in Fast Atom Diffraction at Grazing Incidence

Coherence properties of projectiles, found relevant in ion-atom collisions, are investigated by analyzing the influence of the degree of coherence of the atomic beam on interference patterns produced by grazing-incidence fast-atom diffraction (GIFAD or FAD). The transverse coherence length of the projectiles, which depends on the incidence conditions and the collimating setup, determines the overall characteristics of GIFAD distributions. We show that for atoms scattered from a LiF(001) surface after a given collimation, we can modify the interference signatures of the angular spectra by varying the total impact energy, while keeping the normal energy as a constant. Also, the role played by the geometry of the collimating aperture is analyzed, comparing results for square and circular openings. Furthermore, we study the spot-beam effect, which is due to different focus points of the impinging particles. We show that when a region narrower than a single crystallographic channel is coherently illuminated by the atomic beam, the spot-beam contribution strongly affects the visibility of the interference structures, contributing to the gradual quantum-classical transition of the projectile distributions.

Classical and quantum phenomenology in radiation by relativistic electrons in matter or in external fields

Phenomenological aspects of radiation by relativistic electrons in external field, in matter or the vicinity of matter are reviewed, among which: infrared divergence, coherence length effects, shadowing, crystal-assisted radiation, quantum recoil and spin effects, electron side-slipping, photon impact parameter and tunneling in the radiation process.

Spectrum changes of phase-locked partially coherent flat topped laser beam array propagating in turbulent atmosphere

Propagation of the phase-locked partially coherent flat topped laser beam array trough turbulent media is studied in details. Concentrating on critical radius as an important designing factor, effects of coherence length, beamlet distance and flat topped degree on this parameter are discussed. Also geometrical shape of the array is shown to be important by comparing circular and rectangular shapes.

Crystal coherence length effects on the infrared optical response of MgO thin films

The role of crystal coherence length on the infrared optical response of MgO thin films was investigated with regard to Reststrahlen band photon-phonon coupling. Preferentially (001)-oriented sputtered and evaporated ion-beam assisted deposited thin films were prepared on silicon and annealed to vary film microstructure. Film crystalline coherence was characterized by x-ray diffraction line broadening and transmission electron microscopy. The infrared dielectric response revealed a strong dependence of dielectric resonance magnitude on crystalline coherence. Shifts to lower transverse optical phonon frequencies were observed with increased crystalline coherence. Increased optical phonon damping is attributed to increasing granularity and intergrain misorientation.

Phase-matched emission of few high-harmonic orders from a helium gas cell

We report on femtosecond-laser-based generation of a few phase-matched high-order harmonics in a helium semi-infinite gas cell. The harmonic beam consists of effectively four to six intense orders with wavelengths around 9.5 nm. By varying the effective interaction length, we observe the effects of coherence length related to plasma formation and the Gouy phase shift on the output. The atomic scattering factors for photoabsorption, the effective propagation lengths (leff,He≈1 mm, leff,Ar≈7.2 mm), and the energy conversion efficiencies (εHe≈10−7, εAr≈5×10−7) are deduced for harmonic generation in helium (77th to 95th orders) and also argon (21st to 27th orders) for comparison.

Gluon shadowing in DIS off nuclei

Within a light-cone quantum-chromodynamics dipole formalism based on the Green function technique, we study nuclear shadowing in deep-inelastic scattering at small Bjorken xBj ≲ 0.01. Such a formalism incorporates naturally color transparency and coherence length effects. Calculations of the nuclear shadowing for the Fock component of the photon are based on an exact numerical solution of the evolution equation for the Green function, using a realistic form of the dipole cross section and nuclear density function. Such an exact numerical solution is unavoidable for xBj ≳ 10−4, when a variation of the transverse size of the Fock component must be taken into account. The eikonal approximation, used so far in most other models, can be applied only at high energies, when xBj ≲ 10−4 and the transverse size of the Fock component is ‘frozen’ during propagation through the nuclear matter. At xBj ⩽ 0.01, we find quite a large contribution of gluon suppression to nuclear shadowing, as a shadowing correction for the higher Fock states containing gluons. Numerical results for nuclear shadowing are compared with the available data from the E665 and NMC collaborations. Nuclear shadowing is also predicted at very small xBj corresponding to LHC kinematical range. Finally, the model predictions are compared and discussed with the results obtained from other models.

Nuclear shadowing in deep-inelastic scattering: Numerical solution of the evolution equation for the Green function

Within a light-cone QCD formalism based on the Green function technique incorporating color transparency and coherence length effects, we study nuclear shadowing in deep-inelastic scattering at moderately small Bjorken ${x}_{\mathrm{Bj}}.$ Calculations performed so far were based only on approximations leading to an analytical harmonic oscillatory form of the Green function. We present for the first time an exact numerical solution of the evolution equation for the Green function using a realistic form of the dipole cross section and nuclear density function. We compare numerical results for nuclear shadowing with previous predictions and discuss differences.

Hadron formation in high energy photonuclear reactions

We present a new method to account for coherence length effects in a semiclassical transport model. This allows us to describe photoproduction and electroproduction at large nuclei $(A>12)$ and high energies using a realistic coupled channel description of the final state interactions that goes beyond simple Glauber theory. We show that the purely absorptive treatment of the final state interactions can lead to wrong estimates of color transparency and formation time effects in particle production. As an example, we discuss exclusive ${\ensuremath{\rho}}^{0}$ photoproduction on Pb at a photon energy of 7 GeV as well as ${K}^{+}$ production in the photon energy range 1--7 GeV.

Photoproduction off nuclei and pointlike photon interactions. I. Cross sections and nuclear shadowing

High energy photoproduction off nuclear targets is studied within the Glauber-Gribov approximation. The photon is assumed to interact as a $q\bar{q}$-system according to the Generalized Vector Dominance Model and as a ``bare photon'' in direct scattering processes with target nucleons. We calculate total cross sections for interactions of photons with nuclei taking into account coherence length effects and point-like interactions of the photon. Results are compared to data on photon-nucleus cross sections, nuclear shadowing, and quasi- elastic $\rho$-production. Extrapolations of cross sections and of the shadowing behaviour to high energies are given.

Electron escape rate from coupled multiple quantum wells: Effects of coherence length and hopping.

Electron escape rates from coupled quantum wells with a small number of periods have been determined by measuring the photoluminescence decay time. In the absence of an electric field, the escape time depends strongly on the coherence length of the wave function which is estimated to extend over six well layers. The escape time of electrons localized by an electric field reflects the hopping probability which is affected by the wave-function overlap between adjacent well layers. This probability is enhanced when LO-phonon-assisted hopping is possible.

Transmission second harmonic generation in CdTe at 1.064 ?m

Transmission geometry measurements of the efficiency of second harmonic generation in various thicknesses of CdTe samples were made to determine the conversion efficiency dependence on material thickness. Neglecting pump depletion, it is found that for samples of well-defined symmetry, the second harmonic conversion efficiency scales with film thickness, with no observed enhancement owing to coherence length effects. The angular dependence of the observed second harmonic light in films of well-defined symmetry is consistent with second harmonic generation originating in the bulk.

Oscillating Flow About Smooth and Rough Cylinders

The lift, drag, and inertia coefficients and the first ten harmonics of the lift force have been determined through the use of four smooth, four sand-roughened, and one marine-roughened cylinders. The length-to-diameter ratio of the smooth and sand-roughened cylinders was kept constant (L/D = 2) in order to determine the effect of coherence length on the force coefficients. The Keulegan-Carpenter number ranged from about 1 to 60 and the Reynolds number from about 2500 to 800,000. The results have shown that (i) the smooth cylinder data agree quite well with those presented by Sarpkaya [1, 2] and Rodenbusch and Gutierrez [3]; (ii) the drag and inertia coefficients for rough cylinders (k/D = 1/50) become independent of β (= D2/vT) or of the Reynolds number (Re = UmD/v) for β larger than about 4000; (iii) the rough-cylinder data agree quite well within those reported by Sarpkaya [2] and show that the effect of roughness is indeed very profound; and (iv) the rough-cylinder drag-coefficient data of Rodenbusch and Gutierrez [3] are somewhat larger than those obtained in the present investigation.

Spatial summation for complex bar patterns

We have obtained contrast detection thresholds for spatial grating patterns of limited coherence length for square target fields subtending 2 × 2′ up to 4 × 4°. The results are consistent with a form of physiological summation in which the spatial numerical energy determines the detectability of the pattern. The limited coherence length permits us to uncouple the relationship between the target extent and the number of “coherent” periods in the pattern. Threshold is determined by the target extent, not by the number of coherent periods. A small effect of coherence length has been observed, coherent patterns being more detectable than less coherent ones, even for very long coherence lengths.

Coherence-length effects on the nucleation of superfluid transitions in liquid-helium mixtures

A theory of the nucleation of superfluid transitions near container walls of /sup 3/He-/sup 4/He mixtures is developed. The theory uses a local-continuum model, which accounts for wall-potential-induced concentration and pressure gradients, supplemented by an important coherence-length correction to account for the finite thickness of the nucleation films. An excellent one-parameter fit to the available experimental data is obtained. The theory provides support for the concept of universality in phase-transition phenomena.