The linewidth in level-crossing experiments as normally carried out is the sum of the natural widths of the levels concerned. We have reduced the linewidth by taking the fluorescent light, not from all atoms in the assembly, but from a sample biased in favour of those which have survived as excited atoms for times longer than the average. This was achieved by pulse techniques. Improved resolution was obtained of the components on the wing of the zero-field level-crossing curve for the level 3 2P3/2 in 23Na. The values obtained for the hyperfine-coupling constants are a = 185 ± 040 MHz, b = 30 ± 06 MHz, in agreement with values found in double-resonance experiments. The present values do not represent the limit of the method, since the experiment was designed to investigate the technique, not to make precision measurements. A theoretical analysis of the method reveals that level-crossing curves obtained by this technique may, in certain circumstances, have undesirable satellites. It is shown how the line profile may be controlled and improved without too great a sacrifice in statistical accuracy.
Abstract The level-crossing-method has been used for an investigation of the hyperfine structure of the first excited 3 2P3/2-state of sodium applying an additional electric field parallel to the usual mag. netic field. By means of a detailed analysis of the measured change in intensity of the scattered fluorescence light due to the electric field the constant β of the quadratic Stark-effect of the 3 2P3/2-state of sodium was deduced to be β= (10.8± 1.2) kc/s·(kV/cm)2. The experimental result will be discussed with respect to a determination of upper and lower limits for oscillator strengths of transitions between the 3 2P3/2-state and S-states in the sodium spectrum.
Aligned atomic Rydberg states of sodium can be prepared using two-step excitation from the ground state by linearly polarized pulsed lasers. Information that is normally inaccessible, e.g., sublevel partial cross sections in charge-transfer experiments, can be obtained when aligned targets are used. The calculations of orbital alignment must carefully allow for fine and hyperfine structure, laser linewidths, pulse widths and delays, sublevel coherences, and other factors. In this paper we derive the orbital alignments and time-averaged d-state sublevel populations for 3
2S1/2\ensuremath{\rightarrow}3
2PJ1\ensuremath{\rightarrow}n
2D excitations in Na using angular-momentum and density-matrix methods. We consider both quadrupole alignment
A(2) and hexadecapole alignment
A(4), with excitation through either
J1=1/2 or 3/2 intermediate states considered on the same footing. We show sublevel populations for \ensuremath{\Vert}
ML\ensuremath{\Vert}=0, 1, and 2 analytically and graphically. Finally, we formulate the experimental design problem quantitatively in order to ascertain how to optimize the choice of polarizer angles for extraction of sublevel partial cross sections. Although perhaps the commonest instance, two-step excitation of Na(nd) is but one of a large number of interesting cases, and this study is further intended to illustrate and guide the application of these methods to other light atoms.
We demonstrate a technique for precisely measuring hyperfine intervals in alkali atoms. The atoms form a three-level Λ system in the presence of a strong control laser and a weak probe laser. The dressed states created by the control laser show significant linewidth reduction. We have developed a technique for Doppler-free spectroscopy that enables the separation between the dressed states to be measured with high accuracy even in room temperature atoms. The states go through an avoided crossing as the detuning of the control laser is changed from positive to negative. By studying the separation as a function of detuning, the center of the level-crossing diagram is determined with high precision, which yields the hyperfine interval. Using room temperature Rb vapor, we obtain a precision of 44 kHz. This is a significant improvement over the current precision of ∼ 1 MHz.
The subject of this thesis is the construction of a
stabilized cw dye laser and its use with a sodium atomic beam to
gain information about the range of validity of certain atomic
radiation theories. By lengthening the
laser cavity, cooling the dye solution and adding many other
refinements the bandwidth of a single mode cw dye laser was reduced
to 3 MHz over a period of ten seconds. The laser was designed so
that by the insertion of three uncoated glass etalons single mode
tunable operation was achieved. The purpose of stabilizing the dye
laser was to be able to perform experiments on the hyperfine
structure of sodium at high enough resolution and intensity to see
any possible differences in the theoretical predictions of Quantum
Electrodynamics, the optical Bloch equations, and Neoclassical
Radiation Theory.
The traditional method of
eliminating Doppler shifting was used, that is a well-collimated
thermal atomic beam of sodium was constructed. By crossing the
atomic and laser beams at right angles the natural linewidth of 10
MHz was observable with only one or two MHz residual broadening.
Two types of experiments were carried out:
those studying the absorption spectrum, and those studying the
emission spectrum. In the first experiments Lorentzian lineshapes
were observed for all applied field strengths. This proved that if
the Lamb shift of Neoclassical Theory exists at all it is
small compared with 10 MHz for the sodium D lines. Further, the
sharply peaked spectrum predicted by Neoclassical Theory for a
certain field strength was not observed. The width of the
absorption at high field strengths was not in good agreement with
either theory. In the second type of experiment the observed
emission spectra were in qualitative, but not good quantitative,
agreement with Quantum Electrodynamics when the effects of nearby
levels were included. The results are in disagreement with a
two-level neoclassical treatment, and we have been unable thus far
to obtain better agreement in more sophisticated treatments.
Undoubtedly a better multi-level calculation is required in all
theories since our system is not really two-level. In addition, we
have found that a factor of 2 increase in the critical intensity
calibration would bring QED into reasonable agreement with most of
the experiments. However, we have been unable to establish the
origin of such a factor.
While these
results were not sufficient to finally and absolutely settle the
controversy regarding Quantum Electrodynamics and Neoclassical
Theory they did provide a great deal of new information. For the
first
time the dynamic Stark effect was observed near resonance in
the optical region with data that could be compared to theory.
Also, the measurements of the absorption spectrum were the most
complete and among the highest resolution measurements yet obtained
by direct optical techniques. And finally, a number of of optical
pumping phenomena were observed.
We have used the theory presented by us in a recent paper to analyze a 1967 level-crossing experiment on the 2
3P state of
3He performed at the University of Michigan. Until now a consistent analysis of the experiment had not been possible because of inadequate development of the theory. The present analysis gives excellent agreement with the results of an atomic beam magnetic resonance experiment performed recently by us at Yale University. In fact we have used the combined data to give slightly improved results for four of the 11 relevant parameters. These four are the spin-antisymmetric contact hyperfine interaction constant [C'=-4327(69) MHz)], the 2
3P dipole hyperfine interaction constant [D=-28.145(21) MHz], the 2
3P tensor hyperfine interaction constant [E=-7.1353(38) MHz], and the orbital g factor [
gL=0.999 828 6(20)]. .AE