First printed in 1934, this book gives a critical survey of the principles and limitations of methods for studying resonance radiation that is the re-emission of absorbed radiation without change of wavelength and of the theoretical interpretation of the phenomenon. At the time of first publication, physicists had come to the limit of the then existing techniques in the field and the book was more useful to astronomers who were interested in line shapes existing in the spectra of stars. In past years other fields and techniques have developed for which the information in this book is of interest. These fields are: (1) those having to do with the determination of spins, magnetic moments and hyperfine structure separations by the methods of 'optical pumping' and 'optical double resonance': (2) optical MASERS; and (3) nuclear resonance absorption of gamma rays.
First printed in 1934, this book gives a critical survey of the principles and limitations of methods for studying resonance radiation that is the re-emission of absorbed radiation without change of wavelength and of the theoretical interpretation of the phenomenon. At the time of first publication, physicists had come to the limit of the then existing techniques in the field and the book was more useful to astronomers who were interested in line shapes existing in the spectra of stars. In past years other fields and techniques have developed for which the information in this book is of interest. These fields are: (1) those having to do with the determination of spins, magnetic moments and hyperfine structure separations by the methods of 'optical pumping' and 'optical double resonance': (2) optical MASERS; and (3) nuclear resonance absorption of gamma rays.
1. Introduction 2. Review of Classical Electrodynamics 3. Review of Quantum Mechanics 4. The Spontaneous Emission of Radiation 5. Selection Rules for Electric Dipole Transitions 6. Measurement of Radiative Lifetimes of Atoms and Molecules 7. Forbidden Transitions and Metastable Atoms 8. The Width and Shape of Spectral Lines 9. The Absorption and Stimulated Emission of Radiation 10. Radiative Transfer and the Formation of Spectral Lines 11. Population Inversion Mechanisms in Gas Lasers 12. Resonant Modes of Optical Cavities 13. Saturation Characteristics and the Single-Frequency Operation of Gas Lasers 14. Turnable Dye Lasers and Atomic Spectroscopy 15. The Hanle Effect and the Theory of Resonance Flourescence Experiments 16. Optical Double Resonance Experiments 17. Optical Pumping Experiments 18. The Hyperfine Structure of Atoms and its Investigation by Magnetic Resonance Methods Appendix
Abstract Radiation from spectral lines can be absorbed and re- emitted many times in atomic vapours before it reaches the boundaries of the container encasing the vapour. This effect is known as radiation trapping. It plays an important role practically everywhere where atomic vapours occur, e.g. in spectroscopy, in gas lasers, in atomic line filters, in the determination of atomic lifetimes, in measurements of atomic interaction potentials, and in electric discharge lamps. This book for the first time assembles all the information necessary for a treatment of practical problems, emphasizing both physical insights and mathematical methods. After an introduction that reviews resonance radiation and collisional processes in atomic vapours, physical effects and mathematical methods for various types of problems (e.g. with or without saturation, particle diffusion, reflecting cell walls, etc.) are explained in detail. The last part of the book describes the applications of these methods to a variety of practical problems like cross-section measurements or the design of discharge lamps.Atoms can both absorb and emit electromagnetic radiation like visible light In an assembly of many atoms, e.g., in a vapour or in a gas, radiation emitted by one atom may be reabsorbed by one of its neighbours, just to be reemitted a little later. The game can go on for quite some time—until the photon manages somehow to escape from this prison. At first glance, quite easy to understand. On the other hand, there must be some reason for this voluminous book full of sums, integrals and matrices. Our interest in this subject originally stemmed from investigations on atomic line filters we did for the European Space Agency, ESA. We believed that radiation trapping would have some influence on the performance of these filters and were looking for a simple means to take it into account We started out the same way as probably anyone new to the field would have done when faced with the problem of trapping. We read the classical paper of Holstein, and thought that was all there was to it. We soon had to realize, however, that the assumptions made by Holstein were not fulfilled in our problem, and decided to give the whole matter a closer look. That ‘closer look’ obtained a momentum of its own, and trapping became the centre of our own research in the following years. As our overview of the subject increased. we found that trapping plays a role in a staggering variety of situations. Trapping appears to be important in most experimental setups and in most engineering applications where atomic vapours are involved.
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.
The re-emission of gamma -quanta in the forward direction by an ensemble of excited nuclei after abruptly changing the energy of the nuclear excitation is studied. A sublevel of the 14.4 keV excited state with a definite spin projection of 57 Fe nuclei in a magnetic 57 FeBO 3 crystal is selectively populated. The abrupt change of the energy of the excited nuclear state is achieved by fast (<or=5 ns) reversal of the hyperfine (HF) magnetic field direction at the nuclei. The nuclear target was a black absorber prior to HF field reversal. A short (about 10 ns) intense flash followed by beats of gamma -radiation intensity is detected with some delay after reversal. The delay of the flash and the beat period depend on the HF nuclear transition excited. The duration of the flash depends on the effective thickness of the nuclear target. The theory developed interprets the time evolution of the re-emission as a result of the interference of two main spectral components of gamma -radiation. The first one has the original frequency, which represents the primary radiation. The second one has a shifted frequency, which represents radiation coherently re-emitted in the forward direction from the nuclear sublevel with energy changed by the HF field reversal. The observations reveal the feasibility of inelastic coherent gamma -resonance scattering and demonstrate the enhancement of the radiative channel in the coherent re-emission of gamma -radiation in the forward direction.
A theoretical study on double-resonance optical pumping for the transitions $5{S}_{1/2}\text{\ensuremath{-}}5{P}_{3/2}\text{\ensuremath{-}}4{D}_{3/2,5/2}$ of 87Rb atoms is presented. The full-density-matrix equations in the presence the probe and the coupling laser beams for all relevant magnetic sublevels of the hyperfine levels were solved numerically, and the absorption of a probe beam was calculated as a function of the detuning of the coupling beam. The calculated results were compared with experimental data, and they showed an excellent agreement. The results were also compared with the approximate results calculated when the coherence between the ground and the highest excited levels was neglected. We found that the dominant operating mechanism for double-resonance signals was the optical pumping rather than the two-photon coherence, although the latter affected the signals significantly.
Optical magnetometry plays a critical role in low-energy precision measurements and numerous other applications. In particular, permanent electric dipole moment (EDM) searches impose strict requirements on magnetic field sensitivity of the underlying atomic or molecular species. Other magnetometer properties -- such as chemical reactivity, dielectric strength, and interaction cross-sections with other species -- also impose limitations on experimental conditions. Here, we explore a novel approach to optical magnetometry, using multiphoton transitions of diamagnetic atoms to detect Larmor precession of polarized nuclei. Resonant probes are possible at moderate ultraviolet wavelengths, and hyperfine structure couples spin precession to fluorescence transitions with negligible backgrounds; paramagnetic rotation due to intensity-dependent dispersion may also be detectable. Nuclear spins and nonlinear optical excitation introduce new degrees of freedom, and evade limitations arising from rapid electronic decoherence. This dissertation reports progress towards two-photon optical magnetometry using ytterbium, rubidium, and xenon. We characterize the influence of probe polarization and magnetic fields on fluorescence spectra, for one- and two-photon continuous-wave (cw) excitation of ytterbium. Resolved hyperfine and isotope structure allow us to use spin-zero isotopes for diagnostics and normalization, and we develop analysis for overlapping two-photon resonances. We also report measurements of two-photon excitation in ytterbium and rubidium using picosecond laser pulses, and in xenon using a cw laser. Although hyperfine structure is unresolved, the rubidium measurements are sensitive to probe field polarization. Fluorescence spectra from two-photon excitation of ytterbium with femtosecond pulses show modulation when the repetition rate changes. Although techniques for polarizing noble gas nuclei are mature, existing cell designs are incompatible with two-photon magnetometry. We describe development of silicate-assisted hydroxide-catalysis bonding for both aluminosilicate EDM cells with silicon electrodes, and sapphire-windowed cells that transmit ultraviolet excitation light. Progress in measuring the 129Xe nuclear EDM is discussed. Absolute referencing of the picosecond laser to potassium transitions is proposed for two-photon spectroscopy of ytterbium and xenon, and a compatible frequency-tripling method is outlined to produce excitation light for xenon. Novel possibilities including spatial resolution and multiphoton optical pumping of nuclear spins are considered.