1991 EGAS Conference

1991 EGAS Conference Torun, Poland / 10-13 July 1991 The 23rd annual meeting of the European Group for Atomic Spectroscopy (EGAS) was held this year inTorun, Poland, on 10-13 July. Originally planned for Vilnius, Lithua nia, the EGAS Board decided in the spring to shift the meeting because of the unpredic table political situation. In spite of the short notice, the local organizers, S. Legowski and his coworkers, with the help of the orga nizers from Vilnius, Z. Rudzikas and coworkers, were able to complete all the ne cessary arrangements. More than 170 scientists and students from 19 different countries came together at Nicolas Coper nicus University and benefited from the informal style and relaxing atmosphere. The scientific programme consisted of 11 invited lectures and about 120 contribu tions, some of which were presented orally, while the majority was given as posters. The invited lectures, most of them in a tuto rial style, emphasized highlights in recent results in atomic physics, their impact on different areas of physics as well as future developments. The conference began with a review by B.W. Petley (NPL, UK) of the present status of the system of fundamental constants, where accurate comparisons provide strin gent tests of our knowledge of the physical world. Some of the relevant measurements are firmly spectroscopic and are now ap proaching the 10-10 level of precision. The progress may, in some cases, end when, Fig. 1— The accuracy of measurements of the Rydberg constant, of the speed of light and of the reproducibility of the metre during this century (Courtesy B.W. Petley). 178 Europhys. News 22 (1991) Fig. 2 — Experimental setup for an atomic interferometer to record optical Ramsay fringes in a calcium atomic beam by means of four travelling waves (Courtesy F. Riehle et al., Proc. 10th Int. Conf. on Laser Spectro scopy). B.G. Wybourne (Canterbury, New Zea land) discussed a technologically advanced ring laser with a supercavity, having a fi nesse of 100000 and being able to ultima tely observe frequency differences δf/f of 7.10-20. Applications of such a device in clude detecting the earth's rotation to about 10-14 rad/s, the investigation of nonlinear optical effects giving rise to phase shifts of only 10-10 rad, and the observation of opti cal activity induced in the vacuum by elec tric and magnetic fields or in an atomic gas by Coriolis effects. Knystautas (Laval University, Quebec) described the application of atomic physics to plasma physics. Fluorescence from NII or Ο II spectra induced by the impact of 10 keV/q Ar9+ ions in a Tokamak plasma allows one to monitor purification of the plasma by boron, enabling substantial progress in the performance and control of high tempera ture plasmas. D. Stacey (Oxford, UK) spoke on weak interaction effects in atomic physics. He stressed, in particular, that experiments to detect changes in the optical rotation indu ced by parity violating weak currents (PNC) at the 10-6 level place enormous demands on our knowledge of systematic effects as well as requiring an atomic theory of the same level of precision, thus pushing both experimental and theoretical atomic phy sics to their limits. Fig. 3 gives an example of the status of our understanding of com plex spectra. He summarized the results of many different experiments on different atomic systems to show that theory and experiment, after several years of discus sion and continuous improvement, now agree very well. Also, the extracted value of sin2θwvia the standard model of the electroweak interaction, agrees with the values obtained from high energy experiments. Since the prediction of atomic PNC effects are very sensitive to the mass of the Z-boson, any discrepancy would imply phy- e.g., weak interaction comes into play or QED effects from the conducting surfaces of the apparatus shift spectral lines. Petley pointed out the lack of precision and the need for further improvements in some other cases such as Avogadro's constant and the proton magnetic moment. Evolu tion inthe accuracy of measurements of the Rydberg constant, of the speed of light and of the reproducibility of the metre is illus trated in Fig. 1. W. Ertmer (Bonn, Germany) reviewed techniques to cool, focus and manipulate atomic beams by laser light. Atomic beams of very low velocity, small velocity spread and very high collimation offer further im provements to both spectroscopic measu rements and fundamental investigations. One area is interferometry using cold atoms — a topic also reviewed by J. Helmcke (PTB Braunschweig, Germany) who showed that an atomic beam excited in resonance by four travelling laser wave fields in an optical Ramsey geometry (Fig. 2) acts as an atomic interferometer, and that shifts of the fringes under rotation of the interferometer may be interpreted in terms of the Sagnac effect known from optics. Rectified dipole forces in standing wave laser fields, another as pect of light-atom interaction, was discus sed by A. Sidorov (Troisk, USSR). The complexity of the emission and ab sorption spectra of hot plasmas (unresolved transition arrays) has revealed a need for new theoretical approaches to interpret observations. C. Bauche-Arnoult (Orsay, France) gave a number of examples to illus Fig. 3 — Optical rotation measured in the trate the different parameters which can be vicinity of the 876 nm M1 transition in used to describe groups of lines in place of atomic bismuth. The dominant effect is the individual features and, as a second step, nuclear spin-independent PNC interaction, the application of statistical arguments to which consists of a series of dispersiondescribe the shapes of some contributions. shaped curves, one centred on each hyperA review of model studies on threshold fine component. The signal/noise ratio is phenomena in photodetachment and pho poorest near the component centres be toionization (J. Zaremba, Torun) presented a cause these are the regions of high absorp detailed non-perturbative description of tion. The continuous line is the best fit theo photoionization as well as typical approxi retical curve (Courtesy M.J. Macpherson et al., submitted to Phys. Rev. Lett.). mations and their limitations. sics beyond the standard model, e.g., extra heavy bosons. The general behaviour and recent results of spectroscopic experiments using laser cooled highly charged Ions travelling at high speed in a storage ring at GSI, Darmstadt, were presented by Th. Kühl. Different velo city classes of a circulating Li+ beam can be excited by lasers (Fig. 4) and an experi ment Involving a precision test of special relativity Is underway. Afascinating and rapidly developing field deals with the properties and applications of squeezed states of light, where the un certainty of the photon number in a light beam Is reduced at the expense of phase fluctuations. H.A. Bachor (Canberra, Aus tralia) discussed experimental setups to produce such states and to improve the deg (...truncated)