OPTICAL PUMPING EXPERIMENTS

Figure 23. Temperature dependence of rate constant for excitation transfer in 3He (23S) + 3He, calculated from potentials of Fig. 17 and Table IV. Data are derived from analysis of optical pumping experiments.

Stock, M. and Weber, H.G. (1974). An optical pumping-experiment of ortho- and para-states of Ne2-molecules, Phys. Lett. A, 50, 343-350. 

Optical pumping experiments were first used to achieve lasing m GaN-based structures. Stimulated emission from GaN was observed as early as 1971 [17]. More recently, there have been a large number of reports on stimulated emission [18,19], without an intentionally formed cavity. This may partly be due to the well known difficulty of cleaving mirrors in the wurtzite nitrides grown on sapphire, due to the 30° tilt of the GaN unit cell with respect to the sapphire. 

The possibility of using light to drive electronic spin populations out of thermal equilibrium was first demonstrated by the optical pumping experiments of Kastler, who also considered the possibility of transferring this spin polarization to nuclei. This prediction was soon realized in the gas phase in heavy metal (e.g., Hg and Cd) vapors and noble gases.Later work demonstrated optical polarization of nuclei in solid-... 

A careful reexamination of surface coatings used in optical pumping experi-ments ° has shown that the water content used during the coating procedure is important for extending the xenon Ti. Unexpectedly, replacement of the surface protons with deuterium in the coatings had only a very small effect on the xenon... 

In a conventional optical pumping experiment in solids, an intense pumping beam perturbs the net populations of various atomic or molecular energy levels in a sample, which are then monitored to provide information about the relaxation processes that cause the system to return to its equilibrium state. While this technique is sensitive to the net level populations of the atoms, it is relatively insensitive to processes which preserve net populations while redistributing them spatially through the sample volume, for example by mutual spin flip interactions or reabsorption... 

The lo- error includes uncertainties due to magnetic field extrapolations (0.40) and to the second-order Doppler shift (0.40), and could be diminished by better shielding of the magnetic field and by optical sideband cooling. The result of a classical optical pumping experiment was... 

Since extremely narrow resonance lines can be obtained in optical pumping experiments, frequency standards of comparatively simple design can be achieved. The hyperfine transitions used in the atomic-beam clock are also used in the optically pumped frequency standards. However, the resonance frequency is comparatively strongly dependent on the pressure of the buffer gas [7.18]. It is also dependent on the intensity of the pumping light ("light shifts") [7.16]. Thus, it would seem that an absolute frequency standard of maximal precision cannot be achieved. On the other hand, optically pumped systems have proven to be very suitable for relative measurements and as secondary standards. By observing sharp AF = 0, AMp = 1... 

R 457 P.-J. Nacher, Laboratory Optical Pumping Experiments in Atomic... 

From optical pumping experiments using free atoms or ions, relatively accurate magnetic moments also are available (see data given in Ref. Mg 1, Sr 1, Ba 1). Now it is possible to give shielding constants for some of the Ila elements, which are referred to the free atom by eq. 1. This yields a more general... 

For optical pumping experiments, the GaN-AlGaN-based laser structures have also been grown by PAM BE on the nonpolar GaN quasi- wafers. Fivefold GaN-AlGaN MQWs with quantum well thicknesses of 5 and 2 nm surrounded by 12% AlGaN barriers were prepared. Then the substrates with the laser structures were cleaved along (1010) planes to get lasers of 700-, 500-, and 300-gm cavity lengths. 

Figure 3.16 presents the results of the optical pumping experiments at room temperature. 

There is a small number of studies concerning optical pumping experiments of GaN/AlGaN polar quantum structures. The record threshold power density reported for the polar structures was equal to 105 kW cm at room temperature [25]. 

In fluorescence spectroscopy and optical pumping experiments, the high intensity of lasers allows an appreciable population in selectively excited states to be achieved which may be comparable to that of the absorbing ground states. The small laser linewidth favors the selectivity of optical excitation and results in favorable cases in the exclusive population of single molecular levels. These advantageous conditions allow one to perform absorp-... 

While for most experiments in Doppler-limited spectroscopy-discussed in Chaps.8 and 9-wultimode lasers can be used (e.g., for optical pumping experiments, laser-induced fluorescence of atoms and simple molecules, or for Doppler-limited absorption spectroscopy) only some of the sub-Doppler methods, treated in this chapter, may be performed with pulsed or cw multimode lasers. Most of these techniques demand narrow-band tunable single ode lasers with a bandwidth which should be smaller than the desired spectral resolution. If the natural linewidth 6v has to be resolved, the laser frequency jitter should be smaller than 6v. This demands frequency stabilization techniques (see Sect.6.5) and there are many examples in this branch of high-resolution laser spectroscopy where the achieved resolution is- indeed limited by the stability of the laser. 

Measurement of atomic densities by optical absorption A knowledge of the densities of atoms in the ground and metastable levels is often essential for the interpretation of data in atomic collision experiments. This is particularly true for the alkali metals where optical pumping experiments are frequently used to determine collision cross-sections. Since data obtained from vapour pressure tables are unreliable, the required densities are often obtained by measuring the absorption of the gas or vapour when illuminated by light of the resonance or other suitable lines. 

In an optical pumping experiment, Fig.17.2, the light from a rubidium lamp is usually passed through a simple... 

Fig.17.. Schematic diagram of the apparatus for a rubidium optical pumping experiment.

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