Spectroscopy atomic beam laser, experiments

A considerable extension of the ABMR measurements in the alkali elements, discussed above, was obtained by the introduction of the atomic-beam laser experiments at ISOLDE. With this method the nuclear quadrupole moments could be reached by studying the hfs of the excited state, as well as the IS in the isotopic sequences studied. A number of nuclear spins and magnetic dipole moments was also added. Of particular importance was the discovery of the Dj optical line in francium which opened the way to hfs and IS measurements in this element. The atomic-beam laser spectroscopy works at ISOLDE on the alkali elements 3,Rb, 55CS and Fr have been presented in Refs. [20-25]. 

The first hfs measurements in francium were made with the ABMR method, giving nuclear spin values for the sequence of isotopes - 5.22o-222pj. 2], These experiments were followed by atomic-beam laser experiments [23] which, after the identification of the Dj qitical line, gave results on the hypeifine structure constants in the 7s ground state and the 7p excited state as well as isotope shifts in 208-2i3Fr. Fuller measurements in francium include the nuclear spin of Fr, the nuclear g-factor of Fr and the electronic g-factor of francium by the ABMR method [13], the identification of the D, optical transition by atomic-beam laser spectroscopy [24], and the 7s —> 8p and 7s -> 8p Pj transitions... 

Although most suitable for use with lasers, Thermionic diodes have also been successfully applied to synchrotron radiation studies by using wiggler magnets to enhance the intensity of the beam [390]. Last but not least, one should mention the important category of atomic beam experiments, complemented by the techniques of photoelectron and photoion spectroscopy. All these techniques are suitable for the experimental study of interacting resonances. We turn now to their theoretical description, which will be illustrated by experimental examples. 

Obviously, at that time Ingvar was doing experimental physics and designing new instruments for his experiments. And he has continued to work as an experimentalist and supervise experimental work in atomic beam resonance spectroscopy, laser spectroscopy and environmentally oriented applications, but theoretical work has become an increasingly large part of his scientific activity. Indeed, so much so that in a selective list of his publications that I have obtained, only theoretical publications are mentioned Also, the nuclear physics has to a large extent given way to atomic physics in his research. 

While the early optical measurements suffered from limited resolution, the development of atomic beam methods provided a useful tool in the study of atomic and nuclear magnetic moments [ 12,13] (for a review see [ 14]) and it became possible to measure the nuclear magnetic moments (and nuclear spins) in a direct way for both stable and radioactive isotopes, by using a variety of methods ] 15]. The study of optical IS was, however, limited to Doppler-limited optical spectroscopy until the invention of the laser and the development of suitable high-resolution optical methods (a review can be found in [16]). It is also possible to obtain information on the nuclear charge distribution by electron scattering experiments and from muonic X-ray transitions and electron K X-ray IS [17], perhaps even with a higher accuracy than with optical spectroscopy. 

Millimeter wave spectroscopy with a free space cell such as a Broida oven is more sensitive than lower frequency microwave spectroscopy. However, the higher J transitions monitored by millimeter wave spectroscopy often do not show the effects of hyperfine structure. In the case of CaOH and SrOH, the proton hyperfine structure was measured in beautiful pump-probe microwave optical double resonance experiments in the Steimle group [24,68], They adapted the classic atomic beam magnetic resonance experiments to work with a pulsed laser vaporization source and replaced the microwave fields in the A and C regions by optical fields (Fig. 15). These sensitive, high-precision measurements yielded a very small value for the proton Fermi contact parameter (bF), consistent with ionic bonding and a... 

In this section I hope to show how the sensitivity of laser spectroscopy is exploited to obtain data on very low concentrations of atoms. In particular I will start off by considering a few laser atomic beam studies aimed at measuring optical isotope shifts and show how short-lived nuclei can be studied in this way. I shall also mention how it is possible to beat the natural linewidth and obtain supernatural spectra . The discussion of laser studies at low atomic concentrations then leads me onto consider experiments on laser cooling and trapping of atoms and ions. In this context I will also mention some experiments using the shelved electron idea to detect very weak transitions. Finally, I will say something about Rydberg atoms and the effects of atoms near metallic surfaces. 

An example where nonlinear phenomena in connection with laser-rf spectroscopy have been used in atomic beams, is the recent work on calcium isotopes carried out in our laboratory. The goal of these experiments was to determine nuclear electric quadrupole moments from precise hyperfine structure data of the atomic spectrum. This is of some importance in the case of calcium, since Ca as well as Ca are so-called double-magic nuclei, i.e., with closed proton and neutron shells. Radioactive Ca (t = 1.03 X 10 yr) and the stable isotope Ca have been investigated by laser-rf spectroscopy. The measurements allow to study the influence of a single neutron and three neutrons, respectively, on the double-magic °Ca core. 

The development of fast ion beam laser spectroscopy techniques (for short FIBLAS) is not so unusual a case of simultaneous but independent technical evolution both in atomic and molecular physics. Although the concepts involved in both cases were quite similar, the apparatus used in the pioneering experiments were widely different, ranging from the table top mass spectrometer for the early molecular physics work to the largest tandem Van de Graaff accelerators for some of the atomic physics experiments. ... 

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