The modified stimulated photon echo is proposed as a method for the investigation of elastic collisions of excited atoms with non-excited foreign gas atoms, which induce the redistribution of the excited atoms in Zeeman sublevels. Such collisions cause the difference in the population, orientation and alignment relaxation times of a resonant level. It is shown that the proper choice of mutual orientation of the exciting-light polarisation vectors makes it possible to determine the relaxation times for the population, orientation and alignment of a resonant level. It is found that the formulae, derived in the limit of exciting-pulse small areas, are the most attractive for spectroscopic purposes, as in this case the polarisation properties of the modified stimulated photon echo do not depend on the exciting-pulse shapes, nor on their areas. A detailed discussion of the experimental results of Hartmann and collaborators (1979) and of Keller and Le Gouet (1984), mainly concerned with the investigation of the modified stimulated photon echoes in gases, is carried out.
Polarization stimulated photon echo technique is applied to measure the difference between relaxation rates of alignment and orientation of the level 3P1 (6s6p) of 174Yb. At the transition 1S0 (6s2) - 3P1 (6s6p) 174Yb (of type 0 ↔ 1) a collision induced echo is revealed, which is generated by two pulses of linear and mutually orthogonal polarizations. Photon echo arises exclusively due to collisions between atoms of ytterbium and buffer gases; its power depends non-monotonously on the buffer pressure, and the echo polarizations coincides with the polarization of the first exciting pulse of radiation.
We explore the sensitivity of the photon echo technique for achieving precise measurements of atomic lifetimes. Using short-pulse excitation of atomic rubidium vapor, we report the most statistically precise measurement of ($26.11\ifmmode\pm\else\textpm\fi{}0.03$) ns for the
52P3/2 lifetime. This statistical uncertainty of 0.11% was achieved in a total data acquisition time of 4 h over several weeks and rivals the most precise measurements in this atomic system. The experiment primarily relies on heterodyne detection and exploits the signal-to-noise ratio of the coherent release of energy along the direction of excitation, which is an exponential decay as a function of pulse separation
T, as well as large repetition rates that are feasible in a gently heated vapor cell. We have developed an understanding of the technical limitations responsible for lifetime measurement instabilities on the basis of a simple model, which also enables us to propose a feedback scheme to limit these effects. Studies of the fractional uncertainty of the lifetime suggest that the statistical precision of this technique can be extended to the level of 0.03% in 10 min of data acquisition if the technical limitations are addressed. This level of precision has so far been exceeded by only one other lifetime measurement. Under these conditions, a rigorous investigation of systematic effects could potentially allow the echo technique to achieve the most accurate measurement of atomic lifetimes.