Collimated atomic beam

To resolve the problem applying methods of collimated atom beams, equilibrium vapour as well as radioactive isotopes, the Hall effect and measurement of conductivity in thin layers of semiconductor-adsorbents using adsorption of atoms of silver and sodium as an example the relationship between the number of Ag-atoms adsorbed on a film of zinc oxide and the increase in concentration of current carriers in the film caused by a partial ionization of atoms in adsorbed layer were examined. 

The measurement of isotope shifts and hyperfine structure (hfs) is possible in multistep laser excitation and ionization if one of the excitation lasers in the excitation schemes shown in Fig. 2 is a narrow band laser and if a collimated atomic beam is used as the source of absorbing atoms. The rest of the aparatus can remain as used for other studies. The narrow band laser(s) may be a pressure tuned pulsed dye laser ( 100 MHz, 0.003 cm l) or a CW dye laser (30 MHz to 30 KHz, 10- to 10 6 cm-- -). The atomic beam should be collimated to reduce "Doppler" broading to the level required to attain the resolution needed for investigating the structure and to fully utilize the narrow band width of the laser. A band width of 10cm-- - is usually adequate for most investigations of lanthanides and actinides. A portion of the scan laser beam is directed to an etalon and detector (interferometer) to provide relative frequency calibration. 

Atoms in a collimated atomic beam can therefore be slowed down by a laser beam propagating anticollinearly to the atomic beam [1120]. This can be expressed by the cooling force ... 

Fig. 9.11 Deflection of atoms in a collimated atomic beam using a multiple-path geometry. The molecular beam travels into the z-direction (a) view into the z-direction (b) view into the y-direction. On the dashed return paths the laser beam does not intersect the atomic beam...

Instead of a gated switch in the fluorescence detector for pulsed excitation, one may also use excitation by a cw laser that is phase-modulated with a modulation amplitude of tt (Fig. 9.81). The fluorescence generated under sub-Doppler excitation in a collimated atomic beam is observed during a short time interval A, which is shifted by the variable delay T against the time to of the phase jump. If the fluorescence intensity T) is monitored as a function of the laser frequency cu,... 

If a collimated atom beam expands into vacuum, the velocity component of the atoms in the beam direction is much greater than the thermal velocity component perpendicular to the beams axis, in accord with the low divergence of the beam. Consequently, the Doppler width of atom transitions, as seen by an intersecting laser field perpendicular to the axis of the atom beam, is reduced significantly. Isotopes, which have been excited selectively by the tunable laser, can then be detected by LIES, by ionization techniques, such as RIS and FILS, or by RIMS after photoionization. LEI spectroscopy cannot be applied since collisional ionization does not occur in the atom beam. 

The photon recoil can be used not only for the deceleration of collimated atomic beams but also for the deflection of the atoms, if the laser beam... 

Very well collimated atomic beams with such a high brightness can be used for the investigation of scattering, chemical reactions at very low relative velocities and for surface scattering experiments. 

With laser beams, the effect can be observed in absorption. This is the basis for collinear fast-beam laser spectroscopy. Among the Doppler-free techniques (described in Part A, Chapter 15 by W. Demtroder) it is the only one using linear absorption without velocity selection as in collimated atomic beams. 

As is well known, the first-order Doppler effect can be eliminated by irradiating a well-collimated atomic beam perpendicular to a laser beam. Since tunable, narrow-band cw dye laser radiation of sufficiently short wavelength is not yet available, in most cases the excitation of atomic Rydberg states by a one-photon transition from the ground state is not feasible. The population of Rydberg states, however, might proceed from excited, metastable or even short-lived states which are continuously pumped by an additional laser beam. The latter approach was chosen by... 

We will first describe spectroscopy on collimated atomic beams and on kinematically compressed ion beams. Two groups of nonlinear spectroscopic techniques will be discussed saturation techniques and two-photon absorp-... 

As we have already noted (Sect.6.1.1), a well-collimated atomic beam displays a very small absorption width perpendicular to the atomic beam. As shown in Fig.9.35, the collimation ratio C for an atomic beam is defined as... 

Fig.9.36. Laser spectroscopy on a collimated atomic beam. Three different detection methods are illustrated...

Fig.9.38. Recording of a D - F caesium transition obtained in a collimated atomic beam experiment using stepwise excitations [9.134]... 

We will first describe spectroscopy on collimated atomic beams and on kinematically compressed ion beams. Two groups of nonlinear spectroscopic tecliniques will be discussed saturation techniques and two-photon absorption techniques. We will also deal with the optical analogy to the Ramsey fringe technique (Sect. 7.1.2). In a subsequent section (Sect. 9.8) laser cooling and atom- and ion-trap techniques will be discussed. Here, the particles are basically brought to rest, ehminating the Doppler as well as the transit broadening effects. 

An example of laser spectrometers for Zeeman and Stark spectroscopy using a collimated atomic beam is shown schematically in Figure 2. It consists of a continuous-wave (CW) tunable dye-laser system, a frequency calibration system, a vacuum chamber with a fluorescence detector, and a data-acquisition system. The interaction point of the atomic beam with the laser is inside the vacuum chamber. 

The advent of lasers in spectroscopy has made possible highly precise measurements of spectroscopic as well as of fundamental interest, Particular emphasis has been put onto the elimination of the Doppler effect, which was one of the main obstacles in classical spectroscopy. This can be achieved using well collimated atomic beams or non-linear field/atom interactions, which, combined with quantum interference methods, are capable of yielding a resolution beyond the natural linewidth. In historical perspective, these methods were developed because of the problems associated with the Doppler effect, the possibilities offered by the high intensity and narrow spectral band width of lasers and, most important, an ever persistent wish to obtain very high optical resolution. 

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