This chapter starts with the spectrum of alkali atoms, which have a very similar electronic structure to hydrogen. It describes the hyperfine structure of alkali atoms in the context of the development of microwave atomic clocks that currently provide the definition of the SI second. The simple and accessible electronic transitions of alkali atoms were used for the first demonstration of laser cooling, the revolutionary approach to atomic physics developed in the '80s, which the chapter discusses with a review of its most important configurations (optical molasses, magneto-optical traps, sub-Doppler cooling). The application of laser cooling to the development of very precise atomic clocks and to the field of atom interferometry is also covered.
This chapter starts with the spectrum of alkali atoms, which have a very similar electronic structure to hydrogen. It describes the hyperfine structure of alkali atoms in the context of the development of microwave atomic clocks that currently provide the definition of the SI second. The simple and accessible electronic transitions of alkali atoms were used for the first demonstration of laser cooling, the revolutionary approach to atomic physics developed in the '80s, which the chapter discusses with a review of its most important configurations (optical molasses, magneto-optical traps, sub-Doppler cooling). The application of laser cooling to the development of very precise atomic clocks and to the field of atom interferometry is also covered.
Abstract In previous chapters we have seen how laser spectroscopy gives Doppler free spectra and also how other older techniques of radio-frequency and microwave spectroscopy can resolve small splittings, e.g. hyperfine structure. These methods just observe the atoms as they go past, but this chapter describes the experimental techniques that use the force exerted by laser light to slow the atomic motion and manipulate atoms. These techniques have become extremely important in atomic physics and have many applications, e.g. they have greatly improved the stability of the caesium atomic clocks that are used as primary standards of time around the world.
The ability to cool, manipulate, and trap atoms using laser light has allowed a new, fast developing field to emerge.The term "laser cooling" describes a variety of methods that use one or more laser light fields to interact with atoms and molecules to cool them down to almost absolute zero.The review paper explores the advancements in laser cooling and magnetic trapping methods, focusing on their applications in achieving ultra-cold temperatures for atoms.It discussed various techniques such as Doppler cooling, optical molasses and evaporative cooling, highlighting their roles in advancing atomic clock accuracy and quantum degeneracy research..The paper emphasizes the importance of these methods in achieving temperatures in the nano-kelvin range without cryogenic methods, marking a significant leap in atomic manipulation and study.
Over the past several decades, the field of atomic physics has seen outstanding developments, which have had an important impact on the development of atomic frequency standards. This is mainly due to improvements in laser technology, which has had a direct effect on the technique of optical pumping and made possible the cooling and trapping of ensembles of atoms to sub-Kelvin (sub-K) temperatures. The laser as such was developed in the 1960s. In early stages of its development, however, the use of the laser in the study of interactions between electromagnetic radiation and atoms was limited by the very restricted number of wavelengths available with the existing lasers and the rather narrow tunability of the instruments developed. The so-called dye laser extended the range of possible studies, but such an instrument is rather cumbersome and its size and complexity restricted its use to limited laboratory applications. The advent of room temperature solid-state diode lasers, which could be fabricated to emit wavelengths in resonance with many transitions in alkali atoms such as Cs and Rb, for example, as well as in ions such as Sr + and Yb + , among many others, changed the whole picture. The power emitted by such lasers may be several tens of milliwatts. The spectrum of the radiation emitted is relatively narrow and the frequency can be adjusted over a relatively broad range by means of doping the substrate with selected elements at the time of fabrication. Fine frequency tuning of the device can also be done by means of the temperature of the substrate and its driving current. This property allows the exciting of transitions in selected atoms from one single ground-state hyperfine level to an excited state. This makes possible nearly complete inversion of population in ground states through optical pumping. Furthermore, as will be seen below, the exchange of momentum between a photon and an atom makes possible alteration of atomic velocities leading to so-called laser cooling of atoms. These two possibilities by themselves have totally altered the landscape of research in the field of atomic frequency standards leading to new realizations in both the microwave and the optical ranges. We will review selected subjects and recent advances in atomic physics that have had a specific impact on the development of atomic frequency standards. For a broader overview of such advances in atomic physics, the reader is referred to the excellent review on the subject by Cohen-Tannoudji and Guéry-Odelin (2011) .
Over the past several decades, the field of atomic physics has seen outstanding developments, which have had an important impact on the development of atomic frequency standards. This is mainly due to improvements in laser technology, which has had a direct effect on the technique of optical pumping and made possible the cooling and trapping of ensembles of atoms to sub-Kelvin (sub-K) temperatures. The laser as such was developed in the 1960s. In early stages of its development, however, the use of the laser in the study of interactions between electromagnetic radiation and atoms was limited by the very restricted number of wavelengths available with the existing lasers and the rather narrow tunability of the instruments developed. The so-called dye laser extended the range of possible studies, but such an instrument is rather cumbersome and its size and complexity restricted its use to limited laboratory applications. The advent of room temperature solid-state diode lasers, which could be fabricated to emit wavelengths in resonance with many transitions in alkali atoms such as Cs and Rb, for example, as well as in ions such as Sr+ and Yb+, among many others, changed the whole picture. The power emitted by such lasers may be several tens of milliwatts. The spectrum of the radiation emitted is relatively narrow and the frequency can be adjusted over a relatively broad range by means of doping the substrate with selected elements at the time of fabrication. Fine frequency tuning of the device can also be done by means of the temperature of the substrate and its driving current. This property allows the exciting of transitions in selected atoms from one single ground-state hyperfine level to an excited state. This makes possible nearly complete inversion of population in ground states through optical pumping. Furthermore, as will be seen below, the exchange of momentum between a photon and an atom makes possible alteration of atomic velocities leading to so-called laser cooling of atoms. These two possibilities by themselves have totally altered the landscape of research in the field of atomic frequency standards leading to new realizations in both the microwave and the optical ranges. We will review selected subjects and recent advances in atomic physics that have had a specific impact on the development of atomic frequency standards. For a broader overview of such advances in atomic physics, the reader is referred to the excellent review on the subject by Cohen-Tannoudji and Guéry-Odelin (2011).
The final chapter of this book considers some applications of ultracold atoms in addition to the study of Bose–Einstein condensates. These applications focus largely on the use of ultracold atoms for the purpose of constructing a highly accurate atomic clock. These clocks include atomic fountain clocks, which are presently used for the definition of the second. These clocks operate at microwave frequencies by observing the transitions between hyperfine split atomic ground states. More recent developments in atomic clocks utilize optical transitions between the ground state and an excited atomic state and typically utilize atoms trapped in an optical lattice.
Alkali metals have played an important role in optical and atomic physics from the very beginning. This thesis deals with three aspects and applications of alkali-metal atoms, in particular rubidium (Rb). Optical pumping changes both the amplitudes and the center positions of the absorption profiles in the Doppler-broadened D-line spectra of the alkali-metal atoms. This effect has been studied by reducing the multilevel system to an effective three-level system and by treating the finite interaction time and collisions with the vapor-cell walls in two different ways: as ground-state relaxation and by averaging the time-dependent absorption over the distribution of interaction times. The former is a computationally efficient way to compare theoretical spectra to experimental results, and the latter reveals lineshape details that are due to the coupling between the Doppler shift and the interaction times through the longitudinal velocity of the atoms. Using coherent population trapping (CPT) in 85Rb, an all-optical atomic clock has been realized. The good noise properties of the diode laser, an optimized buffer gas, and a very low light intensity allow detection of ultranarrow CPT resonances < 20 Hz, apparently the narrowest optically induced hyperfine CPT resonance ever measured. The Q value of this resonance, 1.5 × 108, is comparable to Q values in cesium clocks and the stability of the CPT clock is sufficient for many high-precision applications. Trapping of Rb atoms in microscopic magneto-optical traps (MOTs) a few hundred micrometers from the surface of an optically transparent ferrite-garnet permanent-magnet atom chip has been demonstrated. The required magnetic fields are created by magnetic patterns magneto-optically written into the ferrite-garnet film and the transparency of the chip allows using a conventional MOT geometry. The magnetic patterns can be erased and re-written in situ, even during the experiments. Magnetic traps with a trap depth up to 1 mK could be realized using this type of atom chip.