Investigations of aluminum films with synchrotron radiation of wavelengths 500 to 1000 Å

Measurements of the photocurrent from thin Al cathodes in a windowless electron multiplier as a function of wavelength, polarization, angle of incidence, and film thickness have been carried out in the extreme vacuum ultraviolet. A normal incidence monochromator utilizing synchrotron radiation provided highly polarized light. A marked difference is found between the photocurrent measured during irradiation of thin films with “s” and “p” polarized light at wavelengths near the Al plasma wavelength (835 Å). For films thicker than about 500 Å pronounced interference effects are found in both “p” and “s” light at wavelengths less than the plasma wavelength. The observations can be explained by assuming the photocurrent is related to the photon density (electromagnetic energy density) in the photocathode. Calculations of the energy density in films irradiated with light give the structure found in the measured photocurrent. The measurements indicate our monochromator yields light with a degree of polarization consistent with the calculated polarization of the synchrotron radiation incident upon our grating (about 85%).     

Self field electromagnetism and quantum phenomena

Abstract

Quantum Electrodynamics (QED) has been extremely successful inits predictive capability for atomic phenomena. Thus the greatest hope for any alternative view is solely to mimic the predictive capability of quantum mechanics (QM), and perhaps its usefulness will lie in gaining a better understanding of microscopic phenomena. Many “paradoxes” and problematic situations emerge in QED. To combat the QED problems, the field of Stochastics Electrodynamics (SE) emerged, wherein a random “zero point radiation” is assumed to fill all of space in an attmept to explain quantum phenomena, without some of the paradoxical concerns. SE, however, has greater failings. One is that the electromagnetic field energy must be infinit eto work. We have examined a deterministic side branch of SE, “self field” electrodynamics, which may overcome the probelms of SE. Self field electrodynamics (SFE) utilizes the chaotic nature of electromagnetic emissions, as charges lose energy near atomic dimensions, to try to understand and mimic quantum phenomena. These fields and charges can “interact with themselves” in a non-linear fashion, and may thereby explain many quantum phenomena from a semi-classical viewpoint. Referred to as self fields, they have gone by other names in the literature: “evanesccent radiation”, “virtual photons”, and “vacuum fluctuations”. Using self fields, we discuss the uncertainty principles, the Casimir effects, and the black-body radiation spectrum, diffraction and interference effects, Schrodinger's equation, Planck's constant, and the nature of the electron and how they might be understood in the present framework. No new theory could ever replace QED. The self field view (if correct) would, at best, only serve to provide some understanding of the processes by which strange quantum phenomena occur at the atomic level. We discuss possible areas where experiments might be employed to test SFE, and areas where future work may lie.     

Leading large N modification of QCD2 on a cylinder by dynamical fermions

We consider two-dimensional QCD on a cylinder, where space is a circle. We find the ground state of the system in case of massless quarks in a 1/Nexpansion. We find that coupling to fermions nontrivially modifies the large N saddle point of the gauge theory due to the phenomenon of “decompactification” of eigenvalues of the gauge field. We calculate the vacuum energy and the vacuum expectation value of the Wilson loop operator both of which show a nontrivial dependence on the number of quarks flavours at the leading order in 1/N.     

Investigating the QED vacuum with ultra-intense laser fields

In view of the increasingly stronger available laser fields it is becoming feasible to employ them to probe the nonlinear dielectric properties of the vacuum as predicted by quantum electrodynamics (QED) and to test QED in the presence of intense laser beams. First, we discuss vacuum-polarization effects that arise in the collision of a high-energy proton beam with a strong laser field. In addition, we investigate the process of light-by-light diffraction mediated by the virtual electron-positrons of the vacuum. A strong laser beam “diffracts” a probe laser field due to vacuum polarization effects, and changes its polarization. This change of the polarization is shown to be in principle measurable. Also, the possibility of generating harmonics by exploiting vacuum-polarization effects in the collision in vacuum of two ultra-strong laser beams is discussed. Moreover, when two strong parallel laser beams collide with a probe electromagnetic field, each photon of the probe may interact through the “polarized” quantum vacuum with the photons of the other two fields. Analogously to “ordinary” double-slit set-ups involving matter, the vacuum-scattered probe photons produce a diffraction pattern, which is the envisaged observable to measure the quantum interaction between the probe and strong field photons. We have shown that the diffraction pattern becomes visible in a few operating hours, if the strong fields have an intensity exceeding 10²⁴W/cm².     

On synchrotron radiation in non-uniform magnetic fields

We study the conditions in which a charged particle in an inhomogeneous magnetic field (particularly at the edges of a “long” uniform magnet or in a “short” magnet) can emit synchrotron radiation with a spectrum extending beyond the “critical frequency”. We suggest that this effect should be clearly visible (and also useful) in the case of very high energy proton storage rings.     

电子磁矩对同步辐射频谱的修正

本文从偶极子辐射场的Heaviside-Feynman表达式出发, 用经典的电动力学方法推导了考虑内禀磁矩影响后的相对论电子辐射频谱分布的表达式, 并对做匀速圆周运动的极端相对论性电子的同步辐射, 计算了两个偏振方向上的考虑磁矩修正后的辐射谱. 计算结果表明对于特征频率为ω_c的同步辐射, 如果ħω_c≥10 keV, 内禀磁矩对辐射的修正是可观的. 通过同步辐射的内禀磁矩修正, 本文讨论了电子束极化度与辐射场偏振度的依赖关系, 并基于此关系提出一种测量电子束极化度的新方法. 关键词： 同步辐射 电子内禀磁矩 同步辐射偏振度 束流极化度     

Fission of bags by spontaneous quark-antiquark pair production in supercritical colour fields

We describe the fission of heavy quarkonia as the decay of the bag vacuum state by spontaneous creation of a light quark-antiquark pair due to super-critical colour-electric fields. In the adiabatic approximation the heavy quarks are reduced to two point charges fixed at the foci of a prolate ellipsoidal MIT bag. We solve the Dirac equation with the corresponding quasi-abelian potential numerically and estimate the critical heavy-quark separation, at which the energy needed to produce the light quark pair approaches zero, to be 2.2 fm for the value 4α _s /3=0.385 of the strong coupling constant and the vacuum pressureB ^1/4=235 MeV. These values have been used previously by Hasenfratz et al. to reproduce the spectra of heavy quarkonia. We show that this “critical distance” lies just above the classical turning point of thosec \(\bar c\) - andb \(\bar b\) -resonances which are presently known.     

Light from cascading partons in relativistic heavy-ion collisions

We calculate the production of high energy photons from Compton and annihilation processes as well as fragmentation off quarks in the parton cascade model. The multiple scattering of partons is seen to lead to a substantial production of high energy photons, which rises further when parton multiplication due to final state radiation is included. The photon yield is found to be directly proportional to the number of hard collisions and thus provides valuable information on the preequilibrium reaction dynamics.     

Experimental aspects of synchrotron-Čerenkov radiation

Various features of synchrotron-?erenkov radiation are illustrated in the context of the following situations: (1) The passage of high energy electrons through gases, liquids, solids, and plasmas in the presence of magnetic fields. (2) The suppression of synchrotron X-rays from high energy electrons in the earth's atmosphere and extraterrestrial environs. (3) The detection of the real part of the Delbrück scattering amplitude. (4) Vacuum polarization effects on radiation by ultra-high energy electrons in intense magnetic fields. (5) Synchrotron-?erenkov radiation by charged particles heavier than electrons.     

Streuung von Laserphotonen an schnellen Elektronen

The high laser intensity allows colliding-beam Compton scattering experiments of high-energy electrons with the photons of the red ruby laser light by which the latter are transformed intoγ-radiation photons. Detailed calculations are given in this paper for the “average” polarization over the scattered beam and for the energy spectrum of theγ-rays.     

Pointlike gamma ray sources as signatures of distant accelerators of ultrahigh energy cosmic rays

We discuss the possibility of observing distant accelerators of ultrahigh energy cosmic rays in synchrotron gamma rays. Protons propagating away from their acceleration sites produce extremely energetic electrons during photopion interactions with cosmic microwave background photons. If the accelerator is embedded in a magnetized region, these electrons will emit high energy synchrotron radiation. The resulting synchrotron source is expected to be pointlike, steady, and detectable in the GeV-TeV energy range if the magnetic field is at the nanoGauss level.     

Four-photon correlations in parametric down-conversion

Four-photon correlations of the output radiation of a parametric amplifier with a vacuum at the input are considered for an arbitrary parametric gain coefficient. Such states are interpreted in the literature as four-photon states. It is shown that the fourth-order correlation function for such states in the limit of a small number of photons has an asymptotics typical of two-photon states. Nevertheless, even in the “classical” limit of high intensities, the level of four-photon correlations, i.e., the value of the normalized fourth-order correlation function, is substantially greater than that for coherent and even thermal fields.     

Probing vacuum birefringence by phase-contrast Fourier imaging under fields of high-intensity lasers

In vacuum high-intensity lasers can cause photon–photon interaction via the process of virtual vacuum polarization which may be measured by the phase velocity shift of photons across intense fields. In the optical frequency domain, the photon–photon interaction is polarization-mediated described by the Euler–Heisenberg effective action. This theory predicts the vacuum birefringence or polarization dependence of the phase velocity shift arising from nonlinear properties in quantum electrodynamics (QED). We suggest a method to measure the vacuum birefringence under intense optical laser fields based on the absolute phase velocity shift by phase-contrast Fourier imaging. The method may serve for observing effects even beyond the QED vacuum polarization.     

Effect of synchrotron radiation on nuclear beta decay

The stimulation of the endothermic beta decay of stable nuclei by the field of synchrotron radiation has been analyzed theoretically in the framework of the photobeta decay mechanism. In contrast to works devoted to the effect of laser fields on beta decay, the action of the field directly on a nucleus rather than on a beta electron is considered (a sufficiently intense flux of hard photons whose energies exceed 60 keV allows this action). The rates of such a beta decay are calculated for a number of “parent nucleus-daughter nucleus” pairs for the relativistic case including Coulomb effects. For the most intense available sources of synchrotron radiation, the rate of stimulated beta decay for most nuclei under investigation appears to be characteristic of third-forbidden β^? transitions. The effect of synchrotron radiation on highly forbidden natural nuclear β^? decays is also analyzed. In particular, irradiation increases the rate of the β^? decay of the ₃₇ ⁸⁷ Rb and ₄₉ ¹¹⁵ In nuclei by 2% and by almost two orders of magnitude, respectively.     

Anomalous vortices and electromagnetism

We examine the electromagnetic interactions of the fermion-vortex system and elucidate how photons can charge the vortex and surrounding vacuum via the anomaly. We find that the charge of the fermions trapped on the vortex is anti-screened by vacuum polarization so that external electromagnetic fields fall off more slowly than 1/r.     

Magnetic Dichroism in the Reflectivity of Linearly Polarized Synchrotron Radiation from a Ti(10 nm)/Gd<Subscript>0.23</Subscript>Co<Subscript>0.77</Subscript>(250 nm)/Ti(10 nm) Sample

The dichroic effect (“rotated” polarization) in the reflectivity from a magnetically ordered sample is experimentally studied at the station PHASE of the Kurchatov Synchrotron Radiation Source. The experiments are performed for the Gd_0.23Co_0.77 film, which has a compensation temperature T_comp ≈ 433 K, using linearly polarized radiation of the photon energy of 7930 eV (L₂ absorption edge of gadolinium) at room temperature. The developed theory of reflectivity accounted for the magnetic contributions to the scattering amplitude predicts the appearance of a peak for the orthogonal (to the incident polarization) polarization of the reflected radiation near the critical angle of the total external reflection. The experiment reveals the significant difficulties because of the incomplete σ polarization of the synchrotron beam, the beam instability, and so on. Therefore, a rotated-polarization peak has been detected near the critical angle but at the limits of the measurement accuracy. In principle, our experimental technique could be an alternative to circular polarization experiments, which are widely used at synchrotrons to study magnetic ordering. However, as we have shown, it makes high demands of the radiation source parameters.     

Baryons as quarks in a skyrmion bubble

We suggest a model for baryons with quarks populating an unbroken vacuum bubble in the center of a topological soliton (“skyrmion”). The problems involved in such an introduction of quarks into the Skyrme-Witten soliton are investigated. The SU(3) generalization of the model is briefly discussed.     

Accelerators and x-rays in cultural heritage investigations

In the following article a review is given on the use of accelerators in studies connected to our cultural heritage. It focuses on making use of the production and detection of x-rays as a general tool. At “small accelerators”, the proton induced x-ray emission (PIXE), especially when combined with Rutherford backscattering spectroscopy (RBS), has been developed to a very versatile and powerful technique for near-surface investigations. It is well complemented by larger facilities, synchrotron radiation sources as well as medium energy ion accelerators for high energy PIXE. With the development of small compact electron accelerators, a new generation of mono-energetic high-energy high-intensity x-ray sources will add a very comfortable complement in cultural heritage studies. To cite this article: H.-E. Mahnke et al., C. R. Physique 10 (2009).     

DISCO: a low‐energy multipurpose beamline at synchrotron SOLEIL

DISCO, a novel low‐energy beamline covering the spectrum range from the VUV to the visible, has received its first photons at the French synchrotron SOLEIL. In this article the DISCO design and concept of three experimental stations serving research communities in biology and chemistry are described. Emphasis has been put on high flux generation and preservation of polarization at variable energy resolutions. The three experiments include a completely new approach for microscopy and atmospheric pressure experiments as well as a `classical' synchrotron radiation circular dichroism station. Preliminary tests of the optical design and technical concept have been made. Theoretical predictions of the beam have been compared with the first images produced by the first photons originating from the large‐aperture bending‐magnet source. Results are also reported concerning the cold finger used to absorb hard X‐ray radiation in the central part of the synchrotron beam and to avoid heavy thermal load on the following optics. Wavelength selection using monochromators with different gratings for each experimental set‐up as well as beam propagation and conditioning throughout the optical system are detailed. First photons comply very well with the theoretical calculations.     

Sea quark effects in non-topological chiral soliton models and the Nambu-Jona-Lasinio approach

The Nambu-Jona-Lasinio model (NJL) in the chiral invariant SU (2)-sector with scalar couplings is solved numerically in the Hartree approximation (zero boson loop) for baryon number B=1. To this end first the polarized vacuum solution (B=0) is constructed using appropriately parametrized non-dynamic meson fields on the chiral circle. The cut-off Λ is fixed to reproduce the pion decay constant. With this choice a full treatment of the polarized vacuum is shown in second-order gradient expansion to be equivalent to considering kinetic energies of the mesons. Solutions of the NJL model with baryon number B=1 are obtained by adding N_c=3 valence quarks to the full polarized vacuum and subjecting them to the same meson fields. If one adds the valence quarks to the kinetic energy of the mesons the usual chiral soliton model with valence quarks (CSM) is obtained. For both, NJL and CSM, the equilibrium radii of the B=1 solution are evaluated and shown to be rather close to each other. The present approach shows no vacuum instabilities. The resulting radii are different from those of the renormalized one-quark-loop model.