Phone: + 46 33 16 54 44, Telefax: + 46 10 69 73,
E-mail: Leslie.Pendrill @ sp.se
At the foundations of physics lie objective experimentation and the ability to relate measurements made at different times, places or laboratories. This concerns the universality of physical laws as well as the engineering of physical measurement. The fundamental symmetries of the universe, as investigated at the highest accuracy levels with the best instrumentation, are ultimately expressed in terms of the natural fundamental physical constants.
Throughout much of the 20th Century, atomic physics has provided the most accurate values of the majority of these fundamental (or 'atomic') constants, such as the Planck constant, h; the elementary charge, e; the electromagnetic fine-structure constant, alpha, ... (even though this has in some instances been challenged recently with the observation of mesoscopic quantum phenomena in solids). I have given a review of this field in my paper 42. "Some comments on Fundamental Constants...".
My scientific career started in the mid-70's when the tunable dye laser was being introduced to atomic spectroscopy, enabling the high-resolution study of in some cases very highly excited "Rydberg" atoms. My thesis supervisor was Professor G W Series FRS. Symmetry in the spectra of 'simple' atoms, such as the one- and two-electron, alkali and alkaline earth and the inert gases, as expressed by the Rydberg formula, enables a succinct description of long series of energy levels in terms of a few, physically meaningful parameters.
During my postdoctoral work at a number of the world's leading spectroscopy laboratories, I performed precise measurements of atomic energy levels and splittings, choosing always the simplest atoms. Of particular interest has been the semi-empirical formulation of results: a recent paper summarises a "fine structure quantum defect theory" which I have developed, applying to energy intervals a similar approach as applied to energy levels in QDT (49."Isotope shifts of Rydberg... ").
The laser spectroscopy of atomic isotope shifts, in particular, led to our revival of an old technique of extracting "level" isotope shifts from Rydberg atom measurements (6. "Isotope shifts of individual ..."). These level shifts were much more useful than the traditionally determined transition shifts (i.e. the difference of two level shifts), revealing as much about atomic structure as nuclear structure. The study has also formed the basis for a fruitful collaboration with the theoretical division (my wife, docent Ann-Marie Mårtensson-Pendrill) of the Atomic Physics group at Chalmers University of Technology (CTH) in Gothenburg, Sweden where the Many-Body Perturbation Theory could be readily applied to our experimental results. During my time at Chalmers (1981 - 5), I led the high-resolution laser spectroscopy group there.
My work in laser spectroscopy has also included another influence of the atomic nucleus on the optical spectra of various elements, namely, that of parity nonconservation. The standard model of weak and electromagnetic interactions predicts parity violation even at the few volts of energy with which atomic electrons are bound. The atomic experiments make a relatively inexpensive complement to high-energy elementary particle experiments but an exacting test of the standard electro-weak theory. In 1980 - 1, I worked in the group of Professor P G H Sandars, at the Clarendon Laboratory in Oxford, on parity non-conservation in atomic bismuth. In the spring of 1990 I worked with Professor E N Fortson, at the University of Washington in Seattle, on parity non-conservation in lead and thallium.
Highly excited Rydberg atoms are extremely sensitive to external perturbation, principally owing to their appreciable size (typically mm). Some rich physics has been revealed in my studies of (a) the collisional perturbation and (b) magnetic perturbation of such atoms.
(a) Time-resolved laser spectroscopy of highly excited 'Rydberg' alkali metal vapour atoms enabled collisional cross-sections (for depopulation and disalignment) to be determined and interpreted in terms of quasi-molecule formation (2. "Collisional Perturbation of ..."). Understanding the functioning of the sensitive thermionic diode and optogalvanic detectors we used for the Rydberg atom observation required the study of collisional ionisation processes (13. "Optogalvanic studies of a neon...").
(b) Superconducting magnets may be used to apply fields to Rydberg atoms such that the magnetic and electrostatic interaction energies are of comparable magnitude (studied for Cs Rydberg states with n = 100 at the Ecole Normale Superieure in Paris (1978 - 79)).
Developments in pure laser spectroscopy have led also to technological progress. About the same time (1983) as the international definition of the SI METRE was changed, I initiated a project at CTH, aimed at replacing the Swedish national standard of length (a former prototype Pt-Ir bar, from the last century). The project was later transferred to the National Measurement Laboratory for Weights & Measures, National Testing Institute (SP), Borås, Sweden, where I have been head of research since 1985.
Since 1989, the Swedish metre is maintained with an iodine-stabilised He-Ne laser built by myself (9. "Intercomparison of optical frequencies..."). I have developed a calibration & research laboratory for laser frequency and wavelength at the SP. I continue to develop optical frequency standards (I was on the steering committee of the 5th Symposium on Frequency Standards & Metrology, USA), including recent work on frequency stabilised grating-cavity semiconductor lasers as optical frequency standards at a variety of wavelengths (633 nm, 830 nm, 1,5 mm, ...) (48. "Laser spectroscopy of molecular ...") in collaboration with other national laboratories, including the Bureau International des Poids et Mesures in Paris. Also of interest are new clocks, such as based on laser-cooled atoms, such as Ca (collaboration with Dr Hollberg at NIST) where the aim is to improve accuracy beyond the 1014 level. I supervise at present a graduate student (Mr Åman) in this work.
Atomic physics has also proved relevant to fundamental standards of mass and amount of substance (the SI kilogram and mole). Optical interferometric measurements of the refractive index of gases (21. "A compressible Fabry-Perot...") I have applied to (a) Avogadro constant determination and (b) precision kilogram weighing.
(a) Precise measurements of refractive index of 'simple' gases of atoms enable the determination of accurate and absolute number densities. I have investigated in particular He gas, where accurate ab initio calculations of the atomic polarisability may be used in the Lorentz-Lorentz formula to deduce a value of the Boltzmann constant, k ( 41. "Microscopic and macroscopic properties of a gas...").
(b) air buoyancy corrections in weighings of Pt-Ir prototype kilograms (23. "Density of moist air...") are a primary source of uncertainties in primary mass metrology and I have developed a laser refractometer for this purpose.
I am also responsible (since 1985) for research in connection with the national standard of mass, at present a prototype kilogram, K 40, in Pt-Ir, from 1889.I am present EUROMET MASS Rapporteur, responsible for primary mass metrology amongst the Western European National Measurement Laboratories.
I am a referee for the following international journals: Journal of the Optical Society of America (Optical Physics); Journal of Physics B: Atomic, Molecular and Optical Physics; Measurement Science & Technology, Metrologia and Physica Scripta.
I have held a number of appointments in the teaching of physics at university level. I was a physics course assistant at the Open University summer schools in the late 1970's, supervising students from all walks of life in physics experiments. At Oxford University (1980) I held the post of departmental demonstrator, having responsibility for organising and developing the undergraduate teaching laboratories at the Clarendon Laboratory. I also tutored at Balliol College, Oxford. Prior to leaving Oxford, I was offered a position as research lecturer at Christ Church College.
I continue to supervise M.Sc students in final year project work (examensarbete) by students from various Swedish Universities (see enclosed list), both at the Chalmers University of Technology (CTH) and at the National Testing Institute (SP), Borås. The work of the students has in several cases led to publication in international journals. I supervise at present a graduate student (Mr Åman) at CTH.
I have taught a number of courses for students at CTH, including the final undergraduate year (F4)/ postgraduate course in 'Atomic and Molecular Spectroscopy'. I was appointed docent at Göteborg University in April 1986, and recieved professor competence in connection with a post application at Linköpings University in November 1989 and Lund University in 1990.
At the National Testing Institute, I have been responsible for the development of teaching and consultancy in metrology and quality assurance within the Department of Weights & Measures. At present I am involved in the development of a new B. Eng degree course ("Measurement and Quality Engineering") at the Borås University (see paper 40. "A review of education...). Lectures on measurement systems and data analysis are given by me both at Borås as well as at CTH (electrical measurement and physics courses). Measurement uncertainty is a special interest and I am a member of a national standardisation committee for measurement technology.