Abstract Resonance scattering techniques are very useful for high-resolution atomic spectroscopy. The applicability of these techniques has been much extended, particularly through the rapid development of tunable-laser technology. The use of a narrow-band tunable laser, acting on a collimated atomic beam, gives a direct method enabling, for example, hyperfine structure and isotope shift studies. The intensity of lasers allows stepwise excitations to be performed, and with the two-photon absorption technique, Doppler-free measurements on thermal gases are also possible. By using pulsed lasers, time-resolved measurements yielding radiative life-times and structural information can be performed. The basic resonance scattering methods can be combined with radiofrequency and coherence techniques to yield a resolution, limited only by the uncertainty relation. Optical double resonance and level-crossing techniques, not requiring a narrow-band light source, have been extensively used. Several examples of the application of resonance scattering methods are given.
Abstract Resonance scattering techniques are very useful for high-resolution atomic spectroscopy. The applicability of these techniques has been much extended, particularly through the rapid development of tunable-laser technology. The use of a narrow-band tunable laser, acting on a collimated atomic beam, gives a direct method enabling, for example, hyperfine structure and isotope shift studies. The intensity of lasers allows stepwise excitations to be performed, and with the two-photon absorption technique, Doppler-free measurements on thermal gases are also possible. By using pulsed lasers, time-resolved measurements yielding radiative life-times and structural information can be performed. The basic resonance scattering methods can be combined with radiofrequency and coherence techniques to yield a resolution, limited only by the uncertainty relation. Optical double resonance and level-crossing techniques, not requiring a narrow-band light source, have been extensively used. Several examples of the application of resonance scattering methods are given.
Abstract : The goal of our work has been to investigate a few well-chosen effects in laser spectroscopy under clean experimental conditions which facilitate a sharp and meaningful contact with theory. The initially-defined task was to study large pulse-area effects in single upward transitions from metastable atoms in a fast, monovelocity Ne* beam. It proved possible as well to investigate multiple-pulse transitions on a cw basis. Ramsey fringe resonance signatures were clearly observed and for the first time in the optical domain, using three pulse excitation. Basically the first two zones of light provide initially a coherence and secondly an atomic population in the excited state. The counter-running fields in the second zone and third zones convert excited state population into a coherence again and finally into a nonlinear (with intensity) change in the excited and ground state populations. In view of the time gap tau in the preparation phase, one could anticipate and did observe narrow Ramsey fringes which vary as cos (delta, omega, tau) in the middle of the single zone excitation linewidth function ( Rabbi pedestal ). The neon beam employed was rather fast (v/c approx. .001) and, being produced by charge transfer had an exceptionally an narrow velocity distribution, delta, approx .0001. These characteristics permitted unambiguous measurements of the fringe shapes and facilitated useful contact with theory. A second extremely successful experiment was the combination of laser excitation of two-photon Doppler-free transitions in the 5S yields nS series in Rubidium with precise Lambdameter interferometer techniques to accurately measure the transition wavelength.
Abstract The paper surveys the techniques of Doppler-free spectroscopy based on the creation and detection of Hertzian coherence in atomic and molecular systems. The preparation of individual atoms in a coherent superposition of states with the use of broadband optical excitation is discussed, with particular reference to excitation by pulsed tunable dye lasers. Time-resolved observations of the fluorescent light emitted by these atoms reveal the interference phenomenon known as quantum beats and enable Landé g-factors, fine and hyperfine splittings of excited levels to be determined. An account of progress in recent experiments with probe-beam monitoring and pulse trains from mode-locked dye lasers completes this review.
Up to now, Doppler-free nonlinear spectroscopy has been applied to atoms inside a gas medium (volume spectroscopy). We have extended these methods to atoms in the vicinity of a surface. The basic principle consists of monitoring reflectivity changes produced when a laser beam, incident on a glass–vapor interface, is brought into resonance with an atomic transition. For Doppler-free spectroscopy, two counterpropagating beams are used to operate velocity selection. If these two beams are under normal incidence in the glass—velocity selection perpendicular to the surface—one observes saturated dispersion (selective reflection sensitive to the real index). For incidence angles in the glass (prism) larger than the critical angle (total internal reflection), a standing evanescent wave is produced in the gas (velocity selection along the surface), and saturated absorption is detected. Experimental demonstration was performed on the Na resonance line; high sensitivity (10−4 relative reflectivity change) and spectral resolution as good as 20 MHz were obtained. The main limitation to better resolution comes from the short atomic transit time in the evanescent wave (typical extension ~λ). Relevant applications of these techniques should also concern the diagnostics of optically thick media, as analysis of interaction between gas-phase atoms and the surface, notably atom–wall collisions, and modification of the spontaneous emission characteristics.
Resonance ionization spectroscopy, RIS, is a multistep photon absorption process in which the final state is the ionization continuum of an atom. The RIS process can be saturated with available pulsed lasers, so that one electron can be removed from each atom of the selected type. This method was first applied to the determination of the absolute number of He(21S) excited states produced when pulsed beams of protons interacted with helium gas. Laser schemes for RIS are classified into five basic types; with these, nearly all of the elements can be detected with commercially available lasers. A periodic table is included showing schemes applicable to all of the elements except He, Ne, F, and Ar. A compact theory of the RIS process is presented which delineates the conditions under which rate equations apply. Questions on the effects of collisional line broadening, laser coherence time, and nonresonant multiphoton ionization processes are discussed. The initial demonstration of one-atom detection of Cs is described. By using laser beams to saturate the RIS process and by using proportional counters as single-electron detectors, one-atom detection is made possible. With RIS, one-atom detection is highly selective, has the ultimate in sensitivity, and has excellent space and time resolution. Furthermore, a modification of the technique in which single electrons (or single ions) are detected with a channel electron multiplier permits single-atom detection in a vacuum. Resonance ionization spectroscopy has application to classical phenomena such as the diffusion of free atoms, the chemical reaction of free atoms with a gas, the measurement of concentration fluctuations in a dilute vapor, and a variety of other atomic fluctuation phenomena. The authors describe how RIS can be used for photophysics measurements such as far wing collisional line broadening, measurements of photoionization cross sections for excited states, and collisional redistribution among excited states. Modern applications include the detection of single atoms in individual ionization tracks, such as those created by the binary fission of a parent atom, and the extension of this technique to the detection of stable or unstable daughter atoms in time coincidence with the decay of a parent atom. These methods are beig developed for use in low-level counting to determine, for example, the flux of solar neutrinos on the earth.
A new spectral technique for measuring the hyperfine structure of atoms is reported. A divergent atomic beam and a divergent laser beam are crossed. Because of the Doppler effect, the hyperfine structure of atomic levels will be directly displayed in the interaction region in the form of spatially resolved fluorescence arc hands. By measuring the spatial-fluorescence intensity distribution, it is possible to obtain the hyperfine splittings of atomic levels. Basic principles and experimental results are given.
In this work radiative properties of neutral elements with one or two electrons outside closed subshells have been investigated. Using laser techniques in connection with atomic beams selective excitation of Rydberg states was performed. Most of the studied states were populated with two-step excitation. Some states were reached directly from the ground state or from a metastable state and occasionally two-photon absorption was used. The excitation sometimes involved the use of frequency-doubling and Raman- shifting techniques. By time-resolved detection of the decay light from an excited state, primarily information on the radiative lifetime is obtained. With two different experimental arrangements radiative lifetimes in several Rydberg states have been determined. Using the quantum-beat technique time-resolved detection also provides information on energy splittings. This technique was used to measure hyperfine-structure splittings.To obtain information about hyperfine-structure constants and isotope shifts high- resolution spectroscopy on a collimated atomic beam was also employed. The behaviour of highly excited alkali atoms is mostly hydrogen- like and well predicted by theory. Group III A elements have one electron outside a closed subshell and are expected to behave like alkali atoms. The situation is however complicated by the presence of doubly excited states. Configuration interaction can then cause a partial mixing between singly and doubly excited states. In the alkaline-earth atoms (group II A elements), having two electrons outside closed shells, the situation is similar. In a Rydberg series of one excited electron the admixture of doubly excited states can cause large deviations from hydrogenic behaviour. Another complication in the alkaline-earth atoms is the mixture of singlet- and triplet states. - 4 - The presented results from measurements made on Na, Mg, Ca, Sr, Ba, Al, Ga and In will primarily serve as a basis for tests of modern atomic-physics models. Some of the lifetime values are also of astrophysical interest. Keywords: Laser spectroscopy, Rydberg states, time resolved, high resolution, two-step excitation, metastable state, two-photon absorption, frequency doubling, Raman shifting, radiative lifetime, quantum beat, hyperfine structure, isotope shift, Stark shift, alkali atoms, group III A elements, alkaline-earth atoms, configuration interaction, singlet-triplet mixing.