Optical gain on the 476.5 nm Argon-ion laser line in a gas-target excited by a heavy ion beam

Optical gain on the 476.5 nm Ar II 4p–4s ion laser transition has been observed in argon-gas excited by 2.5 ns pulses of 90 MeV³²S ions with a repetition rate of 4883 Hz. The energy per pulse was 23 J. The projectiles were stopped in the target at pressures between 5 and 20 kPa. Gain was determined from a measured transient increase of the intensity of a 476.5 nm probe laser beam sent along the ion beam axis and back reflected by an aluminum foil. The maximum gain observed was (0.4±0.1)×10^–3 at a target-gas pressure of 5 kPa. Control experiments using krypton as target-gas were performed and yielded a null result. The optical gain observed in argon is consistent with the result from an analysis of spectroscopic studies of rare-gas targets excited by heavy ion beams.Dedicated to Prof. Dr. P. Kienle on the occasion of his 60th birthday. This work has been funded by the German Federal Ministry for Research and Technology (BMFT) under contract No. 06 TM 310 I, Gesellschaft für Schwerionenforschung (GSI), Darmstadt, and the Tandem accelerator laboratory, Munich     

Isotropic Evolution of a JBD Anisotropic Bianchi Universe

I study the dynamical effects due to the Brans-Dicke scalar -field at the early stages of a supposedly anisotropic Universe expansion in the scalar-tensor cosmology of Jordan-Brans-Dicke. This is done considering the behaviour of the general solutions for the homogeneous model of Bianchi type VII in the vacuum case. I conclude that the Bianchi-VII₀ model shows an isotropic expansion and that its only physical solution is equivalent to a Friedman-Robertson-Walker spacetime whose evolution can, depending on the value of the JBD coupling constant, begin in a singularity and, after expanding (inflating, if > 0), shrink to another, or starting in a non-singular state, collapse to a singularity. I also conclude that the general Bianchi-VII _h (with h 0) models show strong curvature singularities producing a complete collapse of the homogeneity surfaces to 2D-manifolds, to 1D-manifolds or to single points. Our analysis depends crucially on the introduction of the so-called intrinsic time, , as the product of the JBD scalar field times a mean scale factor a ³ = a ₁ a ₂ a ₃, in which the finite-cosmological-time evolution of this universe unfolds into an infinite -range. These universes isotropize from an anisotropic initial state, thence I conclude that they are stable against anisotropic perturbations.     

Time-reversal symmetry violation and the oscillating universe

The expressions for the fractional number ofK ⁰'s and¯K ⁰'s in a neutral kaon beam are discussed with reference to time-reversal asymmetry. The suggested relation between the sign of Re ( is the Lee-WuT-violation parameter) and the cosmological arrow of time ifCPT is broken is further clarified.Research sponsored by the Air Force Office of Scientific Research, Office of Aerospace Research, U.S. Air Force, under AFOSR grant number EOOAR-68-0010, through the European Office of Aerospace Research.     

Compatibility of higher rho-resonances with the pion form factor data

A realistic pion form factor model respecting the usual fundamental principles supplemented by reasonable assumptions is constructed by means of conformai mapping having some specific uniformization properties. The model includes the contributions of higher rho-resonances without any conflict with analyticity, provides a certain flexibility for the asymptotic behaviour and depends just on the physical parameters. The best fit of all existing data is achieved with(770),'(1600) and the asymptoticst ^–3/2. The predicted values of the pion charge radius, P-wave isovector scattering length, as well as theI=J = 1 scattering amplitude at the experimental measurable region coincide with the world averaged data.Dedicated to the 30th anniversary of the Joint Institute of Nuclear Research.The authors are indebted to Prof. V. A. Meshcheryakov, Dr. S. B. Gerasimov and Dr. D. Krupa for many stimulating and illuminating discussions.     

Light transformers with photon multiplication

Conclusions Crystal phosphors with photon multiplication in the optical range can be used as efficient light transformers. Their use in mercury-free luminescent gas-discharge lamps is especially promising. Analysis of the present position as regards neon discharges indicates that by using phosphors with _t=2–3 it might be possible to create light sources with an efficiency of 30–50 1m/W which would operate solely under outdoor lighting conditions. Evaluation of the prospects of developing light transformers with _t=2–3 indicates that this problem is solvable in principle.We are grateful to the staff of the Ionic Crystal Physics Sector of the Institute of Physics and Astronomy, AS Estonian SSR, and especially to G. Liid'ya, R. Kink, N. Lushchik, I. Meriloo, N. Rooze, and R. Milenina for taking part in our discussions of the problem of transformers with photon multiplication. We also wish to thank V. V. Fedorov and F. A. Butaeva of the All-Union Scientific Institute of Lighting Engineering, who drew our attention to the importance of developing luminophors with>1 for new light sources.Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 10, No. 1, pp. 127–133, January, 1969.     

Reflection of superlong waves from the terminator in the earth — Ionosphere waveguide

Results are offered of an experimental study of reflection of vlf radio signals from the day-night transition region of the earth-ionosphere waveguide. The reflected signal was distinguished and detected by the Doppler shift in its frequency produced by terminator motion. Reflection coefficient values on the order of magnitude of 10^–2–10^–3 were determined. Estimates were performed which indicate that the observed reflection cannot be described within the framework of smooth change of the waveguide parameters in the terminator region. In correspondence with this, the statistical problem of vlf wave scattering by terminator roughness was solved. Using transition region inhomogeneity characteristics consistent with data in the literature, calculated reflection coefficient values close to those observed experimentally were obtained.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 21, No. 11, pp. 1582–1590, November, 1978.In conclusion, the authors wish to express their sincere gratitude to B. N. Gershman, I. M. Fuks, and V. D. Freilikher for their study of the preliminary draft of the study and many valuable suggestions, and to their colleagues in the radiophysics faculty of at Leningrad State University for participating in the evaluation of the results.     

On the Reflection Coefficient in a Superbarrier Passage of a Quantum Particle

The problem on the reflection coefficient is considered for a quantum particle passing over a potential barrier. A rigorous treatment of this problem is not available in the literature. We have developed a consecutive method of finding the pre-exponential multiplier in solving the problem on the probability of the passage in a quasiclassical case, including a correct choice of the singular point. Its novelty in comparison to the earlier used methods is that it involves some rules for the most expedient analytic continuation of the wave function to the complex region. Our method does not use the conventional subdivision of the incident wave function into two ones: penetrating and reflected. When considering the action integral L = pdx = L ₁ + iL ₂, we obtain a bundle of trajectories with L ₂ = const: one extreme member of this bundle is the real axis and the other extreme member is a curve which is indefinitely close to one of the singular points. This singular point plays the leaging role in finding the asymptote of the reflection coefficient R having a physical meaning. Five examples that explain the theory are considered.     

The real part of the amplitude of proton-proton scattering at an energy of 3 GeV

Measurement of the differential cross-sections of proton-proton scattering at an energy of 3 GeV is described. The measurement was performed in the region of angles from 2·4° to 16·2°. Analysis of the experimental data shows that besides the imaginary scattering amplitude a real part is also necessary in order to describe elastic scattering at an energy of 3 GeV; the magnitude of the real part is 24% of the magnitude of the imaginary part.It is the authors' pleasant duty to thank V. Sviridov, V. Nikitin, M. afranova and L. Kirillova from the High Energy Laboratory of the Joint Institute of Nuclear Research in Dubna for their help in irradiating the emulsions and monitoring the primary proton beam, and also to Prof. V. Petrílka for stimulating interest and suport in the work.     

Coefficient of reflection of laser radiation from a dense plasma and the region of anomalous absorption

The time dependence of the coefficient of reflection of laser radiation from a dense plasma is studied in this paper for reverse stopping and anomalous (decay of pumping wave by ionic sound and electron Langmuir oscillation,tl+s) mechanisms, and the region of anomalous absorption is determined.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 79–82, November, 1976.The author thanks E. E. Lovetskti, V. S. Fetisov, and V. T. Tikhonchuk for useful discussions.     

Imaging and focusing of an atomic beam with a large period standing light wave

A novel atomic lens scheme is reported. A cylindrical lens potential was created by a large period ( 45 m) standing light wave perpendicular to a beam of metastable He atoms. The lens aperture (25 m) was centered in one antinode of the standing wave; the laser frequency was nearly resonant with the atomic transition 2³ S ₁–2³ P ₂ (=1.083 m) and the interaction time was significantly shorter than the spontaneous lifetime (100 ns) of the excited state. The thickness of the lens was given by the laser beam waist (40 m) in the direction of the atomic beam. Preliminary results are presented, where an atomic beam is focused down to a spot size of 4 m. Also, a microfabricated grating with a period of 8 m was imaged. We discuss the principle limitations of the spatial resolution of the lens given by spherical and chromatic aberrations as well as by diffraction. The fact that this lens is very thin offers new perspectives for deep focusing into the nm range.     

Polarization correlation in the scattering of polarized nucleons

Experiments concerning the spin correlation tensorC _pqik in the scattering of polarized nucleons on polarized nucleons are discussed. Relativistic formulae are derived for the experimental quantities. The scattering matrix is directly reconstructed with the help of experimentally measured quantities. The components ofC _pqik are predicted for np-scattering at 630 MeV and are given on graphs.On leave from Faculty of Technical and Nuclear Physics, Czech Technical University, Behová 7, Praha 1, Czechoslovakia.On leave from Nuclear Research Institute, Czechosl. Acad. Sci., e, Czechoslovakia.The authors are indebted to S. M. Bilenskij, J. Bystrický, I. M.Kazarinov, L. I. Lapidus, R. M. Ryndin and Ja. A. Smorodinskij for stimulating discussions and valuable comments and to L. I. Graeva and A. M. Fulkina for their assistance.     

Special Features of the Reflection Coefficient in (Pb0.78Sn0.22)1–xInxTe (x = 0.05–0.20)

Spectral dependences of the reflection coefficient R are studied in solid solutions of (Pb_0.78Sn_0.22)_1–x In _x Te with indium content in the mixture x = 0.05–0.20 at T = 300 K. In the R() spectra of each of the examined specimens, two minima of the reflection coefficient are revealed: one in the short-wavelength region at = 1–2 m, and the other – in the long-wavelength region at = 25–30 m, the latter being due to plasma vibrations of free electrons. Peculiar features of the short-wavelength minima in the R() dependences are analyzed. It is shown that these minima are likely to be associated with heterogeneities formed by the nonuniform spatial distribution of indium in the specimen.     

Reflection of a focused light beam in a medium with Kerr nonlinearity. I. Estimates in the paraxial-beam approximation

The reflection intensity in a nonlinear dielectric layer is calculated in the approximation of paraxial incident and reflected light beams. It is shown that reflection is mainly determined by discontinuities of the refractive-index on the boundaries. Unlike reflection by a linear dielectric layer, reflection by a nonlinear layer occurs with a three-time decrease in the effective reflection area and the corresponding broadening of the angular spectrum. The intensity of the reflected wave is comparable to that of an incident wave with nearly critical beam power.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 7, pp. 867–875, July, 1996.This work was supported by the International Science Foundation and the Russian Federation Government (projects MR1000 and MR1300).     

The reflection of relativistic electron beam by virtual cathode

We studied the formation of Virtual Cathode (VC) by a Relativistic Electron Beam (REB) propagating through a terminating foil into a vacuum region in experimental devices REBEX. The beam properties (homogeneity and angular spread of particle velocities) and arising electromagnetic fields (e.g. equipotentials of VC, internal azimuthal magnetic field) were determined numerically with the help of 2d relativistic electromagnetic currentline code POISSON 2. We were interested in obtaining the dependence of the reflection coefficient of the scattered REB by the created VC on the total beam current, beam energy, external magnetic field and on the length of vacuum drift tube. The results obtained are useful for an additional plasma heating mechanism via a two stream instability generated by the oscillating REB.     

Nonlinear effects and the transformation of wave energy in an inhomogeneous plasma

This paper discusses the problem: under what conditions does the quasilinear transformation of waves in plasma with an inhomogeneous beam remain a dominant effect if the nonlinear interaction of waves is respected. It is shown that in the region of densities _p ² _B ² the nonlinear interaction between the high-frequency and the newly excited waves can already affect the initial stage of the process and can result in the establishment of the Rayleigh-Jeans distribution for the two groups of waves. If, on the other hand, the low-frequency waves grow first with a quasilinear increment, the nonlinear transformation of energy inside a group of low-frequency waves is again apt to affect substantially their final amplitude and thus also the total amount of energy that can be transformed into those waves. The conditions under which a particular nonlinear effect predominates are derived for various characteristic values of the density of a cold plasma.     

Nonlocality as a feature of the physical world

Aprediction puzzle leads to a form ofnecessary realism which forces the rejection of a central tenet of the Copenhagen interpretation. This leads to reconsidering conceptual difficulties related to Bell's locality premise. It is shown that aparadox of elementary probability theory puts new light on Bell's assumption that causality and statistical independence are mutually incompatible. Nemo dat quod non habet : No one can offer more than he has ability to give; in that spirit, this paper is dedicated to the memory of J.S. Bell.     

Specific Features of Light Scattering in [N(CH3)4]2CuCl4 Crystals with an Incommensurable Phase

We present the results of investigation of the optical birefringence and intensity of the main light beam that passed through an [N(CH₃)₄]₂CuCl₄ crystal under the conditions of viscous interaction of the incommensurable structure with defects. A nonmonotonic temperature dependence of the basic signal is revealed. The observed temperature dependence of the intensity (in the form of irregular steps) is related to different periods of the incommensurable structure. In transitions between adjacent metastable states the periodicity of the incommensurable structure changes. It is shown that in transition regions for the central beam one observes an anomalous decrease in the light intensity due to the appearance of a perturbation lattice with the wave vector q.     

Thermal blooming in gases

The absorption of light and subsequent thermalisation of the absorbed energy can be significantly affected by the presence of non-equilibrium population distributions in gases. The phenomenon of thermal blooming in gases is discussed from this standpoint. It is shown that a transient phenomenon of absorption cooling can occur, leading to a focusing rather than defocusing of an incident laser beam. Flux densities causing saturation in air and pure CO₂ are calculated. For vibrational saturation in air, I > 3.66 kw/cm², for pure CO₂, I > 4.58 kw/cm². For rotational saturation, in either gas, I > 840 kw/cm².     

The ground state energy of a Bose gas with Coulomb interaction II

LetH _N be the quantum mechanical Hamiltonian for a neutral system of 2_N charged particles, each of unit charge. The HamiltonianH _N is assumed to act on wave functions inL ²(^6N ) which satisfy Bose statistics. It is shown that if the kinetic energy of is sufficiently small, then |H _N |–CN ^7/5 for some universal constantC.Research supported by U.S. National Science Foundation Grant DMS 8600748     

Probabilistic bond percolation in random arrays

We consider the problem of percolation in a system having sites distributed at random, but in which only a fractionh of the physical overlaps form viable links. We convert this to a site problem on the covering lattice, and then show that in two dimensionsh - 1/S ⁴ forh - 1, andh - 4)S² forh 1, whereS is proportional to the critical percolation radius in the original array. This result reproduces the T^–1/3 behavior for log(conductivity) expected of variable-range hopping and found by numerical methods. It also accounts for the region of transition tor-percolation asT . We make a prediction that in three dimensions,h = 1/8S³ + const/S⁶, but numerical confirmation is lacking for this case. While the argument is not exact, we have demonstrated a novel approach to random systems.Supported by the National Research Council of Canada.