Table of contents

The Seventh General Conference of the European Physical Society "Trends in Physics" was held in Finland, August 10–14, 1987. The conference sites were the Finlandia Hall in Helsinki and the Helsinki University of Technology in Espoo. Seventy-five plenary and invited talks were presented together with about hundred and forty posters. In this special issue we have been able to include the majority of the plenary and invited talks. They cover a large area of contemporary physics from cosmology to biophysics. In addition a section has been devoted to the role of physics in our human society. In our compilation of the papers we have not attempted to follow the organisation of the conference, but the contributions are arranged so that the readers can find their way through the material in as easy a way as we have been able to achieve.

We are very grateful to the authors for their contributions to these Proceedings, which in many ways reflect the exciting progress physics has made during recent years. It is, of course, impossible to cover all aspects of the development of physics in a five days conference. Nevertheless after having had access to all the manuscripts we feel that the international programme committee did an excellent job. This successful result was achieved largely through the efforts of the Program Committee Chairman, Professor Klaus Dransfeld. We think that it is a remarkable achievement of the European Physical Society to run these general physics conferences, where physicists representing widely diverse fields can meet and discover that they still share a common language.

Recent research indicates that cosmology is connected to particle physics in the same way as astrophysics is connected to nuclear physics. A well-established example of this is the calculation of the ⁴He abundance in the universe, which constrains the number of neutrino species and gives us a window to the 1 s old and 10⁹ K hot universe.

Still earlier, about 10^-5 s after the big bang, an important phase transition took place in the universe. Quarks and gluons, which formed a colour plasma earlier at high temperature, were then confined into nucleons, pions and other hadrons. The high temperature phase, the quark gluon plasma phase, is a new phase of matter, which so far is experimentally unobserved. Theoretically, however, much work has been devoted to predicting its properties. One may attempt to probe the quark → hadron transition as well as the behaviour of the quark gluon plasma by a little bang, an ultra-relativistic nucleus–nucleus collision. The systems are vastly different in size, but the cosmologically relevant temperature, more than 200 MeV, should be attainable in the little bang too.

The first experiments with a ¹⁶O beam of an energy 3200 GeV/nucleus colliding on heavy nuclei with A ≈ 200 were carried out at CERN in November 1986. Large multiplicities of produced particles, large energy densities and indications of collective flow have been observed. For a study of quark gluon plasma and its transition to hadrons one would still prefer larger beam nuclei and higher energies. Experiments with ³²S beams will be carried out at CERN in September 1987 and plans for beams up to Pb have been presented. In the US a plan to build a 100 GeV + 100 GeV relativistic heavy ion collider RHIC in Brookhaven is progressing.

Berry's work on quantum systems described by adiabatically varying Hamiltonians is introduced. Some simple systems exhibiting the "Berry phase" phenomenon are discussed, including: a spin-½ particle in a slowly varying magnetic field, linearly polarised light propagating down a helically wound optical fibre, and dynamic Jahn-Teller E ⊗ systems. The way in which the Berry phase concept illuminates the origin of anomalies in chiral gauge field theories, and the fermionic behaviour of solitons in certain scalar field theories (skyrmions), is also indicated.

A rapid review for non-accelerator physicists of work on linear electron-positron colliders. Various ideas and problems associated with them are discussed in a phenomenological way, without any detailed theoretical background.

The Fermilab Tevatron is a proton accelerator designed for research into the properties of fundamental forces and particles. The Tevatron is based upon a superconduction magnet ring 1 km in radius. It operates in two modes, both providing the highest energy particles in the world. In the fixed target mode, 800 GeV protons are extracted and distributed as primary, secondary or tertiary particles to fifteen experiments. In the collider mode, protons are brought in headon-collisions with antiprotons at a total energy of 1.8 TeV. The detectors and scientific goals are also briefly described.

In recent years significant advances in the field of high spin gamma-ray spectroscopy have been made. These advances are the result of a new generation of gamma-ray spectrometers that have extended the spin range for which detailed nuclear structure information can be obtained. This paper concentrates on results obtained from the TESSA spectrometers at the Nuclear Structure Facility, Daresbury Laboratory. Two topics will be covered in detail. Firstly, evidence for a phase change at high spin in light rare-earth nuclei, e.g. ¹⁵⁸Er, will be presented. This phase change involves a transition from a prolate nucleus rotating collectively about one of its minor axes to an oblate-shaped nucleus with the spin generated by single particle motion. Secondly, the observation of highly deformed prolate or superdeformed nuclei at high spin will be discussed. This observation represents detailed spectroscopy within the second minimum of the nuclear potential energy at large deformation and a quantum leap forward in high spin gamma-ray spectroscopy.

A unified description of alpha decay, heavy cluster radioactivities and the new type of symmetric fission with compact shapes in which one or both fragments have magic numbers or almost magic numbers - magic radioactivity is presented. We consider mainly the static aspects of the nuclear evolution based essentially on the shell effects in the potential. Simple assumptions are made for the inertia parameters. No dissipation has been introduced.

In nuclear physics the limits of the traditional framework in which non-relativistic nucleons interact through potentials have become apparent. The role of the underlying quark substructure of the nucleons in determining the properties of nuclear forces and the structure of atomic nuclei has to be uncovered. Experiments using the new electron facilities will provide important insights for advancing nuclear physics along these new directions.

The discovery of the icosahedral phase, which marked the start of the new science of quasicrystals, has posed several intriguing questions for the scientific community. Verification of the unique quasiperiodic character of quasicrystals has been obtained through a series of experiments, and the nature of its structure has been studied with a variety of experimental tools. This article briefly introduces quasiperiodicity and outlines some of the crystallographic properties of the icosahedral phase.

A tutorial review is given of some of the basic electronic properties of two-dimensional systems and their physical realisations.

We discuss the absorption and luminescence properties of simiconductor quantum wells and superlattices from simple models of their electronic structures. The electron or hole confinement in quantum well is derived from the effective mass approximation. Excitonic effects are discussed with emphasis on their quasi-two-dimensional properties. The electronic structure of superlattices is described from a tight binding approach, and the optical properties are classified according to the respective location of electrons and holes: type I (both particles mainly in the same layer), type II (electrons and holes in different layers), and type III (interface states).

Far-infrared spectroscopy of cyclotron resonance in quasi two-dimensional electron systems on III-V semiconductors is discussed and special emphasis is laid on the consequences of band nonparabolicity and polar nature of these materials on the subband structure and cyclotron masses. Experimental results obtained for metal-oxide-semiconductor structures on InSb and GaAs/Ga_1-xAl_xAs heterojunctions are explained with the aid of simple pictures. Recent experiments on subband-shifted cyclotron resonance in quasi one-dimensional electron systems are also addressed.

The perturbing effect of electron-LO phonon interaction on the Landau level energies of an electron bound to a surface which is perpendicular to the applied magnetic field becomes more pronounced as the binding of the electron to the surface increases. Second-order perturbation calculations of this effect will be discussed. In the two-dimensional limit (infinite binding), exact fourth-order perturbation theory results have recently been obtained by a novel method. These results are used to study the accuracy of energies obtained from approximate theories - especially the generalized Feynman theory of Peeters, Devreese and co-workers. The effect of finite electron density on the polaron anticrossing (or "pinning") is discussed in the two-dimensional limit. A generalized Fröhlich hamiltonian is introduced which is appropriate for studying polaron energy levels in nonparabolic bands. Weak-coupling results are discussed for the cyclotron energies and the polaron "radiative" correction to the electron g-factor is presented.

The electron-optic phonon coupling in semiconductor heterostructures has been investigated in cyclotron and magnetophonon resonance experiments. Measurements of the energy dependence of the cyclotron mass show that polaron effects are small relative to bulk semiconductors at low temperatures, contrary to theoretical expectations. However, the coupling reappears at very low electron densities or at high temperatures, and this is attributed to temperature dependent screening of the interaction. Resonant polaron cyclotron resonance and magnetophonon resonance measurements of the frequencies of the phonons coupling to the electrons show that in single heterojunctions the electrons interact with a phonon mode close in frequency to the TO phonons. In contrast, quantum well samples show coupling at the LO frequencies. A magnetic field in the plane of the two-dimensional electron gas suppresses the TO frequency coupling in the heterojunctions to reveal a weaker interaction near the LO frequency. Possible interpretations of these results in terms of screened phonons, interface modes and finite size TO phonons are discussed.

The magnetic field dependence of the polaron cyclotron resonance mass in a GaAs-Al_xGa_{1 - x}As heterostructure is investigated theoretically for different electron densities. The polaron effects in real two-dimensional (2D) systems are found to be smaller than the one-polaron correction for an ideal 2D system. The reduction of the polaron effect is attributed to: (1) the non-zero width of the 2D electron layer, and (2) the many-particle aspects of the system like (i) the occupation effect which is a result of the Pauli exclusion principle and (ii) screening of the electron-phonon interaction. It is found that the non-zero width of the 2D electron layer and the blocking effect due to the Fermi-Dirac statistics are the main cause for the reduction. Screening leads to a further reduction of the polaron effect but it is found to be only of secondary importance. A good agreement is found between the theoretical results and the experimental data in the magnetic quantum limit (i.e., for filling factor ν < 1). For ν > 1 the experimental tendency of a magnetic field independent mass is corroborated by our theoretical analysis.

The main physical properties of point contact spectroscopy of solids are reviewed. The spectra of metals, alloys, semiconductors and other systems are discussed.

An overview is given on the application of scanning tunneling microscopy for a study of clean semiconductor faces, in particular, of Si(111). The theoretical models for interpretation of the measurements are discussed briefly and the experimental techniques are summarized. Results will be presented on different samples of Si(111). In addition to large scale 7 × 7 reconstructed Si(111), images are shown of (111) terraces, which develop a variety of reconstructions. For an interpretation of the results in terms of the topography of the surface the local electronic structure has to be considered. Information on the atomically resolved surface electronic structure may be obtained by scanning tunneling spectroscopy, where the tunneling current is determined locally as a function of sample bias voltage. The influence of energy and position on the tunneling probability is discussed.

A number of models are discussed for the normal state and superconducting properties of the high-T_c copper based oxide systems.

Heavy-Fermion superconductivity has been viewed by us theorists as a marvellous new area in which we could practice once more our celebrated skills in the standard theory of superconductivity. Many exotic and fascinating aspects of standard theory seemed to accumulate in Heavy-Fermion superconductors. Available data indicated unconventional pairing, strong Fermi-liquid effects, resonant impurity scattering, multi-band effects or other subtleties and needed support and explanation by theory. Now that most of us have quickly moved to a new field, it is fair to ask whether we have left the theory of Heavy-Fermion superconductivity well understood and under control.

Normal heavy fermion systems may be assumed to have infinitely strong short range electron-electron interaction U within the f-orbital. Formulating the Anderson lattice model in terms of slave bosons and working in mean field approximation the very high masses, high specific heats and high susceptibilities of these materials may be simply understood. Allowing U to be large but finite, a generalisation of the theory allows for the possibility of superconductivity. In an isotropic model estimates of T_c give values close to experiment. Gap and H_c take BCS values in the weak coupling limit. In a more realistic model, the gap is found to be anisotropic with zeros and other nonuniversal features developing. The model is also applied to high-T_c oxide superconductors.

Elastic properties of the high temperature superconductors La_{2 - x}Ba_xCuO₄ (LABCO), La_{2 - x}Sr_xCuO₄ (LASCO) and Y₁Ba₂Cu₃O_{7 - δ} (YBCO) are reviewed. The changes in sound velocity and the jump in specific heat are analysed. Using thermodynamic relations these results are compared with measured values of dT_c/dp and B_c(0) obtained from the literature.

Since the discovery of superconductivity in high effective mass electrons, so-called "heavy fermions", in CeCu₂Si₂, many experiments have been carried out to try to understand these newly discovered phenomena. Despite a number of remaining puzzles, it has become ever clearer that magnetism and the heavy fermion ground state are closely connected in heavy fermion compounds.

Electron-phonon effects are briefly discussed. Details can be found in the list of references.

Recent experiments to study e⁺-e^- paircreation in heavy ion atom collisions at energies close to the Coulomb barrier are reviewed. For high combined charges of the collision system Z_u = Z₁ + Z₂ one finds pairs produced by the strong time changing Coulomb field with cross sections rising proportional to Z¹⁶_u. The characteristics of the e⁺ production line Z_u and scattering angle dependence as well as their spectral distribution is well understood theoretically. Superimposed on the e⁺ continua, e⁺ lines were discovered with energies independent on Z_u but with cross sections which rise with Z²²_u.

The line energies are grouped around 250 and 340 keV for all systems with 164 < Z_u < 184. For heavy systems (U-Th) and U-U) a third line at about 400 keV is seen.

There is strong indication that these positron lines have a common source namely neutral particles produced in the high Coulomb fields, which decay into e⁺-e^- pairs. This is indicated by e⁺-e^- coincidence experiments which show evidence for energy and angle correlated e⁺-e^- emission expected for a particle decay.

The paper reviews the present understanding of the mechanisms and collision dynamics responsible for excitation of outer shell electrons in atomic collisions. Experimental and theoretical results at increasing levels of sophistication are presented for selected model systems, culminating in so-called perfect scattering experiments which determine the quantum-mechanical state of the system completely. When theory and experiment agree at this level, one can go no further.

We discuss some recent theoretical as well as experimental advances in collisions involving Rydberg atoms. We recall some basic properties of Rydberg atoms before showing that in most cases a simplified theoretical treatment of Rydberg collisions is possible. On the experimental side, special attention is paid to the opportunity offered by Rydberg states for the study of quasi-resonant processes.

One of the most important energy loss mechanisms for very slow electrons travelling through molecular gases is the excitation of rotational states and, less frequently, of vibrational states of the ambient molecules. In this short review the main theoretical aspects of the problem are discussed and the computational methods which have recently produced very good accord with the existing, accurate measurements are presented. The important role played by low-energy, open-channel shape resonances in enhancing the energy transfer mechanism is underlined and shown with computational examples for the polyatomic methane molecule.

An approximate three-dimensional quantum mechanical method for the calculation of atom-diatom reactive scattering cross sections and rate constants is described. The method is known as the Fixed Angle Reactor Model (FARM). Its key features are that it uses information from both classical trajectory and simplified quantum mechanical calculations to compute vibrational state-to-state reactive scattering cross sections. The classical trajectory calculations are used to estimate the degree to which torques acting during the approach of the collision partners are able to successfully reorient them into the most favorable geometry for subsequent reaction. This information is then used, together with fixed angle quantum reactive scattering calculations to approximate a full three-dimensional quantum reactive scattering calculation. Test results are presented for the reactions: H + H₂(ν = 0) → H₂(ν' = 0) + H and D + H₂(ν = 1) → HD + H and comparison is made with other methods.

Mode selective excitation to high overtone vibrational states in ion-polyatomic molecule collisions can be particularly well studied in the case of the H⁺ + CF₄ model system. Results are summarized which demonstrate that only the infrared-active modes ν₃ and ν₄ participate in the excitation process, while their relative contributions are determined by the corresponding infrared line strengths. The vibrational transition probabilities agree with a Poisson distribution which is expected if the collision dynamics can be described by a forced oscillator mechanism. This is supported by classical trajectory calculations which provide good agreement with the measured average energy transfers even for the separately observed contributions from the three different impact parameters below the rainbow scattering angle. Very recent measurements with a new scattering apparatus reveal a significantly improved energy resolution of better than 15 meV. This promises interesting future information on the spectroscopic nature of the high overtone states excited in proton collisions.

For studying the chemical reaction occurring when one of the collision partner is electronically excited, one can use the unique property of the intermolecular interaction: at long distance the potential is attractive and often present a small minimum, the van der Waals minimum. It is then possible by cooling the gas mixture of the reactives in a supersonic expansion to freeze the collisional complex into this van der Waals potential depth. The reactive process is triggered by an optical excitation, which promotes the system onto the reactive surface and the products obtained are analysed by laser induced fluorescence.

In this technique all the entrance channel parameters are known: the kinetic energy is zero, and the partner are initially oriented. Moreover the spectroscopic studies of the complex give direct grasp of the potential energy surface, and on the alignment of the electronic orbitals upon the intermolecular axis.

The onset of deterministic chaos in lasers is studied by referring to low dimensional systems, in order to isolate the characteristics of chaos from the random fluctuations due to the coupling with a thermal reservoir. For this purpose, attention is focused on single mode homogeneous line lasers, whose dynamics is ruled by a low number of coupled variables. In the examined cases, experiments and theoretical model are in close agreement. In particular I describe Shilnikov chaos, how it can be characterized, and the strong resulting coupling between nonlinear dynamics and statistical mechanics.

Experiments on the interaction of a single atom with a single mode of a resonant electromagnetic field in a cavity are reviewed. The atoms used in these experiments were Rydberg atoms with a very large principal quantum number. Another important ingredient is a superconductivity cavity, the quality factor of which is high enough for a periodic energy exchange between atom and cavity field to be observed. The dynamics of the atom-field interaction predicted by theory was measured. Some of the features are explicitly a consequence of the quantum nature of the electromagnetic field: The statistical and discrete nature of the photon field leads to new dynamic characteristics such as collapse and revivals in the Rabi nutation.

Ion traps and cw dye lasers allow one to prepare small clouds of ions, or single ions. They can be detected even by absorptive techniques, such that the information is contained in one field mode only, the mode of the irradiating light. The noise can approach the quantum limit. For excitation on weak and narrow lines, random breaks of the scattering on a competing resonance line can reveal the quantized signal absorption. These interruptions are the signature of "quantum jumps" which characterize the internal dynamics of a single atomic particle under quasi-continuous observation.

The advantages of collimated cold supersonic beams for sub-Doppler laser spectroscopy of molecules and small clusters are discussed and illustrated by several examples. These include sub-Doppler spectroscopy of the SO₂ molecule in the ultraviolet and of NO₂ in the visible region. Lifetime measurements under collision-free conditions, stepwise excitation of high lying molecular Rydberg states, and sub-Doppler double resonance spectroscopy of Na₃ demonstrate the achievements possible by combining molecular beam techniques with various methods of laser spectroscopy. The relevance of the experimental results for our understanding of the dynamics of molecules in excited states and for the development of new theoretical approaches is emphasized. Some sensitive detection techniques are presented which are in particular useful when cw lasers are used for spectroscopy in cw molecular beams at low densities.

The subject of this presentation is to show how molecular cluster calculations can lead to a deeper understanding of laser induced processes at surfaces of ionic crystals. Molecular cluster calculations were performed for bulk BaF₂ and for different clusters modelling the (111) surface of BaF₂. The effect of the surrounding crystal ions have been included by an embedding crystal potential. Calculations for a stoichiometric surface give an electronic structure similar to the bulk, while calculations for a local non-stoichiometric surface show the existence of occupied surface states in the upper half of the bandgap, followed by unoccupied states extending above the ionization limit. These calculations give a qualitative understanding of the experimentally observed resonantly enhanced multiphoton processes of electron and ion emission from the (111) surface of BaF₂.

Femtosecond time-resolved transient grating experiments on liquid CS₂ and C₆H₆ clearly show the delayed appearance of an anisotropy of molecular origin, with respect to the electronic nonlinear signal. We emphasize the optimal accuracy obtained from the measurement of this temporal shift, by using properties associated with the polarization of the incoming and outcoming pulses. A discussion of the mathematical models available is given, in connection with the various processes involved in the molecular nonlinearities.

Soliton-Raman processes are described in single pass and synchronously pumped ring geometries using standard single-mode, silica based fibres for the generation of kilowatt pulses with durations of 100 fs-200 fs tunable from 1.3-1.45 μm. Using dispersion shifted fibres, similar operation has been demonstrated with a cascade-Raman soliton shaping mechanism in fibre ring oscillators, providing tunability to similar 1.7 μm.

For ultrashort pulses the small core of an optical single mode fiber leads to enormous peak intensities even for moderate input pulse energies. At these high intensities a multitude of optical nonlinear processes modify light transmission severely but in a very controlled way. This has led to several interesting discoveries:

(i) the spectral broadening and frequency chirping of pulses which subsequently can be compressed to pulse durations of only a few femtoseconds

(ii) the undisturbed propagation of pulses as optical solitons

(iii) the continuous red shift of the pulse centre frequency (soliton self-frequency-shift)

(iv) the disintegration of pulses into a set of fragments of soliton nature Theory and corresponding experiments to the above phenomena will be presented.

Multiphoton coherent interaction effects are investigated in atoms and molecules. It is demonstrated theoretically as well as experimentally that, in the presence of a two photon resonance, maximum conversion efficiency can be achieved using energy preserving pulse sequences, in condition of coherent interaction. However, highest conversion efficiencies are obtained with weak two photon resonances. A study of four photon resonant coherent interaction in mercury points to a peculiar quenching of the interaction by the generated third harmonic. Four photon resonant coherent interaction is also investigated in molecules, where it is shown that an input signal can be found that results in selective excitation of the upper levels.

Optical parametric emission produces light in which photons are created in highly correlated pairs. This feature is formalized through the concept of quadratic coherence. We study the correlation between twin photons through a spectral and temporal analysis of the second-harmonic of the parametric light.

The application of ps laser controlled optoelectronic semiconductor switching for the generation of ps electrical pulses with μV, V or kV amplitudes is considered. Methods and experimental conditions, e.g., the use of a partly covered gap end of finger structures, are described.

The central problem of any theoretical approach in hot carrier transport is the calculation of the energy distribution function, which no longer resembles the equilibrium shape. In this paper we survey the main results obtained on the subject in these last years through the use of Monte Carlo simulations. Recent advances concerning the development of a quantum kinetic equation accounting for intra-collisional field effects and/or collisional broadening are emphasized.

We present new physical methods to obtain population inversion and electromagnetic wave generation in semiconductors based on deformation of the carrier distribution function in momentum space, and also laser action on optical transitions between light and heavy hole subbands, and NEMAG on a heavy hole cyclotron resonance, the inversion of the light hole population of Landau levels.

We discuss kinematic and dynamical constrains in design of useful unipolar hot electron transistors. In addition, we demonstrate room temperature operation of a double heterojunction hot electron transistor with a two-dimensional electron gas forming the base region. Our test structure has the narrowest ever reported base width at a mere 100 Å and is the first such transistor to show current gain in excess of 10 at room temperature. The device uses an indirect, wide bandgap AlSb_0.92As_0.08 emitter and the transistor base is a thin InAs layer.

The electron transport in the base of a double barrier transistor structure is investigated by the Monte Carlo particle technique. The possibility of excitation of plasma waves due to the streaming instability is considered. The results of the simulation show that the electron velocity distribution is strongly broadened due to the injected electron interaction with plasma waves. The calculated distribution function is in agreement with the experimental data.

Internal photoemission for transport analysis (IPTA) and low energy electron transmission (LEET) experiments allow the determination of energy dependent quasi-elastic (acoustic phonon) and inelastic (LO-phonon) scattering rates of hot electrons in wide bandgap insulators for energies smaller than the electron excitation threshold. A model for the analysis of experimental data is presented. The model is used to analyse IPTA and LEET experiments in a variety of insulators such as rare gas solids, amorphous SiO₂ and organic dielectrics. The results are compared to scattering rates obtained from electron-phonon interaction theory. The implications of the energy dependence of scattering rates on high field electron transport are discussed.

This paper describes the Joint European Torus (JET) device which was built as a European collaboration effort, with the aim of testing the scientific feasibility of producing controlled thermonuclear reactions between light nuclei with a net yield of energy.

JET is the largest magnetic confinement machine in the world both in physical size and in the magnitude of the plasma current (5 × 10⁶ Amperes). The machine came into operation in mid-1983 and has followed the first stages of a planned evolution, in which the performance is progressively increased mainly by adding more heating power and which will culminate in eventual operation in a deuterium-tritium mixture. This will permit study of the plasma performance when there is a substantial power input from the α-particle fusion products. So far operating in deuterium gas with 8 MW of additional heating by neutral beams, a peak ion temperature of 12 keV has been obtained with a corresponding fusion product (density × confinement time) of 8 × 10¹⁸ m^-3 s. If the same conditions were to be achieved in a deuterium-tritium mixture, then the ratio of thermonuclear power output to the heating power input, Q, would be ∼ 0.1. It is expected that following further technical improvements to JET, "scientific breakthrough" (namely Q = 1) will be achieved.

The next step after JET will be to study a burning or ignited plasma in which no power input is required because energy losses are balanced by α-particle heating. The requirements for such an experiment will become increasingly clear as more data is obtained from JET. At present it seems likely that a larger apparatus will be needed with a plasma current capability of 12-15 MA. These requirements for the thermonuclear furnace remain broadly consistent with the known technological constraints on an eventual power reactor.

Plasmas are examples of non-equilibrium phenomena which are being used increasingly for the synthesis and modification of materials impossible by conventional routes. This paper introduces methods available by describing the construction and characteristics of some equipment used for the production of different types of plasmas and other non-equilibrium phenomena. This includes high energy ion beams. The special features, advantages and disadvantages of the techniques will be described. There are a multitude of potential applications relevant to electronic, metallic, ceramic, and polymeric materials.

However, scale-up from the laboratory to production equipment depends on establishing a better understanding of both the physics and chemistry of plasmas as well as plasma-solid interactions. Examples are given of how such an understanding can be gained. The chemical analysis of polymer surfaces undergoing modification by inert gas, hydrogen or oxygen plasmas is shown to give physical information regarding the relative roles of diffusion of active species, and direct and radiative energy transfer from the plasma. Surface modification by plasma depositing a new material onto an existing substrate is discussed with particular reference to the deposition of amorphous carbon films. Applications of the unique properties of these films are outlined together with our current understanding of these properties based on chemical and physical methods of analysis of both the films and the plasmas producing them.

Finally, surface modification by ion beams is briefly illustrated using examples from the electronics and metals industries where the modification has had a largely physical rather than chemical effect on the starting material.

The role of energetic ion bombardment in causing directionality in plasma-assisted etching is well established. However, the detailed mechanisms by which ion bombardment accelerates etching reactions are not well understood. Experiments have been carried out using controlled beams of particles representative of a plasma-assisted etching environment and the results of these experiments can be qualitatively related to plasma-assisted etching phenomena. The results of these controlled beam experiments also provide some insight concerning the basic mechanisms responsible for ion-assisted etching. Evidence will be summarized which indicates that, for the silicon-halogen system, the primary role of energetic ion bombardment is to accelerate the formation of a volatile product from a partially reacted surface layer. This conclusion cannot be extended in general to other gas-solid combinations and some data obtained from metal-halogen systems will be noted.

The paper deals with microphysical modelling the low pressure reactive r.f. plasmas which are widely used in plasma technology particularly for etching of thin solid films in microelectronic pattern replication and plasma enhanced deposition of solid films. To model these types of plasma processing in addition to the complex discharge physics the production of chemically active species by electron impact reactions with the feed gas, the gas phase reactions and the transport of active species to the discharge surface as well as the surface reactions must be adequately described. The objective of the paper is to present the basic ideas which are applied when modelling the mentioned processes, to illustrate the complicated interplay of these processes in a real reactive r.f. discharge and to give some outlooks on future activities needed for improving the modelling.

Why? It is fun to challenge a giant. And we believe that optics is better suited than electronics for super parallel computing.

How? By a very large number of small optical processors, tied together by a powerful connecting network. The optical signals travel as light rays in free space. Many independent rays may traverse the same portion of the 3D-space, without "crosstalk". By contrast, electronic connections are confined to material guides, usually in planar topology.

If? We believe we will succeed if nonlinear optical effects and devices are improved, if our architectures utilize the benefits of optics, if enough users are dissatisfied with all-electronic computers.

There has been much recent interest in certain organic materials for applications in the field of nonlinear optics, where they have been shown to have significant advantages over the inorganic compounds that are used at present. A brief review of nonlinear optical effects is given, along with a description of the role of the new organic materials, including their design, fabrication and characterisation. Applications of these materials in optical signal processing and optical computing are outlined.

Laser spectroscopy provides powerful means for advanced diagnostics and sample analysis. Applications of laser spectroscopy in the fields of energy, environmental and medical research are discussed. Emphasis is given to diagnostics of combustion processes, to remote monitoring of atmospheric trace gases and to various applications of laser-induced fluorescence. These latter applications include marine pollution analysis, industrial surface characterization and medical tissue diagnostics. Cancer tumours and atherosclerotic plaque in vessels can be detected. Illustrations from work performed at the Lund Institute of Technology are used and references to books, reviews and selected papers are given.

After a brief review of the lasers available for metal-working processes an analysis of the interaction of laser radiation with matter is provided in the power density ranges of practical use namely:

(a) High energy density processes (10⁶-10⁷ W/cm²) exploiting focused beams to induce solid to liquid or to vapour state changes to allow the material removal for cutting or the formation of molten an resolidified material channels for welding and joining.

(b) Medium energy density processes (10⁴-10⁵ W/cm²) exploiting unfocused beams with a suitable spatial distribution to provide surface treatments without change of state or with surface melting for hardening and cladding.

Class (a) processes require a more complex analysis taking into account both the direct energy transfer from the beam to the workpiece by direct absorption and the coupling of the energy via the plasma generated by the interaction.

Class (b) processes can be treated with simpler models under the assumption of constant values for the absorption and for the thermal parameters of the target. Temperature dependent parameters can also be considered with added complexity.

Finally a short outline will be provided of the systems which can implement in practice the laser metalworking process.

Sensors are one of the key elements for the automation in the manufacturing and process technology. The sensor field is presently within a restructuring process, directed to a stronger utilization of solid state technologies. This restructuring is governed by the utilization of solid state physical effects, by the use of reproducible fabrication techniques, and by the market driving forces.

The state of the art of sensors in modern fabrication techniques will be demonstrated in examples, namely for sensors in silicon technology, in thin film technology and in thick film/screen printing technology.

Some important physical and technological problems to be solved for the development of new and advanced sensor families will be outlined. Sensor development is strongly directed to the minaturization of devices and to the integration of different sensors to multisensors, as well as the integration between sensors and microelectronics.

Liquid crystal (LC) polymers can be divided into two kinds of compounds: main chain and side chain LC polymers. These two kinds of polymers exist as lyotropic or thermotropic LC polymers. In this report we will describe some properties and applications of main chain and side chain LC polymers.

Main chain LC polymers, mainly composed of rigid mesogenic moieties, are used for high modulus fibres, reinforcement of optical fibres or specific molded parts.

Side chain LC polymers can be used in optics and optoelectronics. Due to the combination of properties of liquid crystals and polymers they can be oriented, in the nematic phase, by an electric or magnetic field and frozen into a glassy state. In this state they show interesting properties like matrix for orientation of non linear optic moities (χ₂ coefficient). We will describe in this field the properties of LC polyacrylates copolymer. Chiral smectic C* LC polymers have also been obtained in this family, they are pyroelectric and potentially piezoelectric.

These LC polymers have also several interesting applications like information storage media. These applications will also be described.

Some of the basic concepts of magnetoencephalography (MEG) and neuromagnetic instrumentation are reviewed. Examples of multichannel SQUID magnetometers and results of measurements with them are presented. Current trends in MEG instrument development are discussed.

The techniques developed to obtain localized NMR spectra from living substances are reviewed, and the methods are illustrated by examples.

After a plea for more research workers to devote themselves to fundamental thinking about how physics should be taught, and how it should be presented to students who have no intention of becoming professional physicists, the lecture is devoted to a specific problem - the encouragement of imaginative thinking about physical situations that are beyond the range of the student's formal technique. A number of example are given to indicate the wide range of topics available for seminar discussion - an educational process that the author considers to justify by its results the time spent in making the discussions lively and interesting.

From 26 till 29 October 1986 the second Europhysics Study Conference on the Employment of Physicists in Europe was held in Bad Honnef (FRG). A wealth of data, published in the proceedings of this study conference [5] was collected about Education, Recruitment and Employment of physicists in 15 European countries. At the conference these data were compared and discussed. The main conclusions of this study conference were:

(i) in future there should and can be much better data than presented at this Europhysics study conference;

(ii) there is no significant unemployment of physicists in Europe;

(iii) due to demographic reasons there will be a shortage of physicists at the end of the century all over Europe;

(iv) in the lesser developed countries of Europe the employment situation compared to that presented at the 1981 Erice study conference, has been much more improved than foreseen at the Istanbul meeting [4];

(v) in the near future there will be a shortage of physics teachers in the secondary schools (already imminent in the UK), which will affect the future production of physicists;

(vi) as European industries will continue to hire physicists at a constant rate, due to the reduction of physics students, a shortage of University research physicists is foreseen.

The talk takes up the need for physics as basis for technology transfer and development. It indicates ways in which EPS physicists may take part in the development process.

Research activities in the department of physics, University of Khartoum, Sudan are briefly described as an example of physics research in the developing countries. Difficulties and problems faced by the researchers in the department are highlighted and means of overcoming them via the departmental foreign links are discussed.

This workshop was held in Geneva in October 1986 and was attended by invited delegates from both East (14) and West (13), members of the ACPS (5) and the President. Relevant disciplines as well as Physics were represented which lead to comprehensive discussions.

The factors which have a bearing on the probabilities of a nuclear winter were reviewed using the SCOPE-ENUWAR studies as a basis. These covered the nature of a possible nuclear war; the quantities of dust and smoke thrown into the atmosphere, its particle size, height and lifetime; the resulting effects on sunlight and temperature; and the consequences for vegetation and animal life both terrestrial and marine.

There are many uncertainties in such analyses. Much more work is needed on many facets. The more important were highlighted as further topics for East-West collaboration. Never the less it was concluded that:-

Climatic effects involving temperature falls of only three or four degrees below normal combined with a large fall in light intensity during the growing season of cereal crops would have disastrous consequences.